THE MINERALOGY, GEOCHEMISTRY
AND ORIGIN OF
LOWER TERTIARY SMECTITE-MUDSTONES
EAST COAST DEFORMED BELT
NEW ZEALAND
A thesis
submitted in partial fulfilment
of the requirements for the Degree
of
Master of Science in Geology
in the
University of Canterbury
by
L.J. Fergusson :~:.
University of Canterbury
1985
CONTENTS
CHAPTER
ABSTRACT
ONE INTRODUCTION 1.1 Scope 1.2 Previous Work 1.3 The 'Bentonite' Problem
TWO FIELD GEOLOGY 2.1 Introduction 2.2 Marlborough 2.3 Wairarapa 2.4 Hawkes Bay 2.5 Synthesis
THREE LABORATORY METHODS 3.1 Sample Preparation 3.2 Analytical Techniques
FOUR MINERALOGY 4.1 Introduction 4.2 Clay Fraction Mineralogy 4.3 Smectite Mineralogy 4.4 Sand Fraction Mineralogy
FIVE GEOCHEMISTRY 5.1 Introduction 5.2 Major Element Geochemistry 5.3 Trace Element Geochemistry
SIX ORIGIN OF THE SMECTITE-MUDSTONES 6.1 Introduction 6.2 Sedimentology 6.3 Mineralogy 6.4 Geochemistry 6.5 Summary and Conclusions
ACKNOWLEDGEMENTS
REFERENCES
APPENDICES
PAGE
1
3 3 4 5
8 8 11 35 43 54
58 58 61
69 69 69 91 ll5
123 123 123 136
143 143 144 149 156 161
164
166
170
TABLE
2.1
4.1 4.2
4.3 4.4
4.5
4.6 4.7 4.8
5.1 5.2
5.3
5.4
5.5
5.6
LIST OF TABLES
Marlborough sample localities
XRD standard mixture compositions Results of quantitative XRD analysis of smectitemudstone clay fractions Classification of smectites Results of Li+-saturation test for smectite in mudstone clay fractions Results of K+-saturation tests for smectite in mudstone clay fractions DTA results for smectite-mudstone clay fractions Characteristics of montmorillonite subspecies Heavy mineral suites of selected smectite-mudstones
Example of a structural formula calculation Accuracy of XRF major element analyses of bentonite standards Average structural formulas of smectite + illite in smecti te-mudstone· clay fractions Exchangeable cations in smectite-mudstone samples and duplicates Trace element analyses of smectite-mudstone whole-rock samples Trace element analyses of other lithologies associated with the smectite-mudstones
5.7 Correlation coefficient matrix for trace elements in smectite-mudstones
6.1 Trace element abundances in shale and carbonate and
PAGE
13
81
86 91
96
102 108 112 116
125
127
132
135
137
138
140
mean shale-carbonate values 157
FIGURE
1.1
1.2
LIST OF FIGURES
Eroded and slumped smectite-mudstone, Seymour Stream Shrinkage cracks in smectite-mudstone, Porangahau Quarry
2.1 The East Coast Deformed Belt and the present
2.2 2.3
2.4
2.5
2.6
2.7
2.8 2.9
2.10 2.11 2.12 2.13
2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22
2.23 2.24 2.25
2.26
2.27
2.28, 2.29
2.30 2.31
2.32 2.33
2.34
2.35 2.36
day plate·boundary system Generalised geology of Marlborough Summary stratigraphic columns of the Arouri Limestone in Marlborough Surnmary stratigraphic columns of the Marl units of the Arouri Limestone in Marlborough Interbedded smectite-mudstone and limestone, Seymour Stream Interbedded smectite-mudstone and limestone, Mead Stream gorge Typical internal stratigraphy of the Marls. Lower Marl, Chalk Range The geology of Woodside Creek Alternating marl-limestone, Lower Marl, Woodside Creek The geology of the upper Ure River View of part of the Chalk Range The Lower Marl, Chalk Range Detailed stratigraphic column of the Lower Marl, Chalk Range Highly sheared Upper Marl, Chalk Range Whales Back ridge The geology of Mead Stream gorge Lower Marl, Mead Stream gorge Marl unit, Bluff Stream The geology of the Lower Seymour outlier Massive marl lithology, Seymour Stream Marl unit, Fells Basin Detailed stratigraphic column of the Arouri Limestone, Fells Basin The geology of the Limestone Hill outlier The geology of the Tora area Summary stratigraphic column of the Kandahar Formation, Pukemuri Stream Interbedded sandstone, limestone and smectitemudstone, Kandahar Formation, Pukemuri Stream Alternating marl-limestone, Kandahar Formation, Awheaiti Stream Marl interbeds in the Mungaroa Limestone, Mungaroa Point Generalised geology of southern Hawkes Bay Summary stratigraphic columns of the Wanstead Formation, Waimarama Beach and Waewae Stream The geology of Waimarama Beach Interbedded sandstone and smectite-mudstone, Wanstead Formation, Waimarama Beach Sedimentologic cycle, Wanstead Formation, Waimarama Beach Melange zone, Waimarama Beach The geology of Waewae Stream
PAGE
6
6
9 12
15
16
18
18
20 21
20 23 25 25
26 27 27 28 29 29 31 32 32
33 34 36
37
40
40
42 44
46 47
49
50 49 51
FIGURE PAGE
2.37 The geology of the coastal slope near Red Island 53
2.38 Lower Tertiary stratigraphic columns for Marlborough, Wairarapa and Hawkes Bay 55
3.1 Preliminary sample preparation methods 59 3.2 Cation exchange leaching procedure 66
4.1 Layer structure of smectite clay minerals 71 4.2 X-ray diffractograms of basal peaks of untreated
smecti tes 7 2 4.3 X-ray diffractograms of the basal peak of untreated
and glycerol treated smectite 74 4.4 X-ray diffractograms of the basal peak of heat
treated smectite 74 4.5 X-ray diffractogram of the clay fraction of a
smectite-mudstone 76 4.6 X-ray diffractogram of a sample from the Kandahar
Formation 78 4.7 X-ray diffractograms of three standard mixtures 82 4.8 Calibration curves for determination of% quartz
4.9
4.10 4.11
4.12
4.13
4.14
4.15,4.16
4.17
4.18
4.19
4.20 4.21
4.22 4.23 4.24 4.25 4.26
4.27
5.1
5.2
6.1
6.2
from XRD Calibration curve for determination of% smectite and% illite from XRD X-ray diffractograms of three size fractions Scanning electron micrograph of mudstone from Marlborough Scanning electron micrograph of mudstone from Wairarapa Scanning electron micrograph of mudstone from Hawkes Bay Scanning electron micrograph of mudstone from the melange, Waimarama Beach Scanning electron micrographs of clay particles in two mudstone clay fractions X-ray diffractograms of smectite basal peaks after the Li+-saturation test X-ray diffractograms of smectite basal peaks after K+-saturation X-ray diffractograms of smectite basal peaks after K+/300°C/E.G. treatment DTA curves of four smectite-mudstone clay fractions Representative DTA, TGA and DTGA curves of smectitemudstone clay fractions Micrograph of sample C7 heavy sand fraction Micrograph of sample Ll4 heavy sand fraction Micrograph of sample S2 heavy sand fraction Micrograph of sample SB heavy sand fraction Micrograph of Paoanui red smectite-mudstone heavy sand fraction Micrograph of sample SB light sand fraction
Scatter plots of %K20 against other variables in smectite-mudstone clay fractions Scatter plot of ppm Sr vs %Caco 3 in smectitemudstones
Trace element abundances in smectite-mudstones normalised against the mean shale-carbonate abundances Scatter plots of trace element concentrations in smectite-mudstones and associated lithologies
83
83 85
88
88
89
89
90
98
104
105 109
114 118 118 120 120
122 122
130
140
158
160
l
ABSTRACT
Marine smectite-mudstones of Lower Tertiary age (Teurian to Runangan)
occur throughout the East Coast Deformed Belt of New Zealand. In
Marlborough, Marl lithofacies of the Amuri Limestone comprise calcareous,
siliceous smectite-mudstone alternating with biomicrite. In Wairarapa,
the Kandahar Formation consists of calcareous smectite-mudstone, micritic
limestone beds and mass-flow greensand beds; Calcareous smectite-mudstone
is also a minor interbedded lithology in the Mungaroa Limestone of
Wairarapa. The Wanstead Formation in Hawkes Bay comprises uncemented
smectite-mudstone with interbedded mass-flow greensands. Lower Tertiary
sequences throughout the East Coast Deformed Belt are typically
disrupted by thrust faults and associated shear/melange zones which have
developed in the weak smectite-mudstone lithology.
Insoluble clay fractions of the smectite-mudstones are composed of well
crystallised sme.ctite + illite ±_ quartz (chert). Both the smectite and
illite clays are discrete phases with no interstratification suggestive
of post-sedimentary transformation of smectite to illite. From detailed
phase analysis, the smectite clay overall is a montmorillonitic species,
but with varying interstratification of other dioctahedral smectite
species and varying layer charge. No distinct stratigraphic trends in
clay fraction mineralogy or smectite mineralogy are apparent. Sand
fractions of the mudstones are dominated by authigenic or non-volcanic
detrital minerals.
Average smectite + illite structural formulas calculated from chemical
ana~yses are commonly non-ideal, with deficiencies in aluminium
particularly apparent. The dominant exchangeable cations are calcium in
Marlborough mudstones and sodium in Hawkes Bay mudstones. Trace
element geochemistry of the smectite-mudstones is similar to that of
typical shale and carbonate rocks. Variations in trace element
abundances· reflect the lithological character of the mudstones and do
not appear to be a useful tool for regional stratigraphic correlation.
Combined sedimentological, mineralogical and geochemical features of the
smectite-mudstones indicate a non-volcanic origin. They did not form
by in-situ alteration of ash-falls and are unlikely to have formed from
transported/reworked ash. Previous use of the term 'bentonite' for the
sme~tite-mudstones implies such a mode of genesis and should be
discontinued. Hemipelagic sedimentation and/or mass-flow redeposition
of detrital or neoformed clay in an open oceanic, relatively deep water
environment is proposed as the origin of the smectite-mudstones.
2
1.1 SCOPE
CHAPTER ONE
INTRODUCTION
Marine mudstones, in which smectite (swelling) clay minerals are a
major component, are a feature of Lower Tertiary stratigraphy in
the East Coast regions of Marlborough, Wairarapa and Hawkes Bay.
This study is a detailed investigation into three main aspects of
the mudstones:
( 1) sedimentology and local stratigraphy,
( 2) mineralogy,
and (3) geochemistry.
The aims of the study are to:
(1) describe and characterise the mudstones,
I particularly their clay mineralogy,
(2) evaluate the use of geochemical parameters
for regional stratigraphic correlations,
and ( 3) determine the origin of the mudstones.
3
1.2 PREVIOUS WORK
Previous investigations of the mudstones have been carried out
with respect to their economic potential. However the research
dates back to the 1950's and earlier - before important advances
in techniques of studying clay mineralogy were made.
Fyfe (1934) gave an account of the mudstones from the Gisborne
area, including some chemical analyses. The geology of the
mudstones in southern Hawkes Bay was described by MacPherson and
Coventry (1941), and MacPherson (1952) described the mudstones in
the Kekerengu area of Marlborough. The commercial properties of
the Porangahau mudstone in Hawkes Bay were investigated by Dunn
and Wilkinson (1941) · and Miller (1948) . Gordon et al. ( 1955) made
the only detailed study of clay mineralogy and chemistry on
mudstones from Porangahau and Mangatu (Gisborne). Ritchie (1962)
reviewed the earlier work and contributed further mineralogical
and chemical data.
General mapping work involving the mudstones has been carried out
in Marlborough by Hall (1964), Prebble (1976) and Reay (1980); in
Wairarapa by Waterhouse (1955), Waterhouse and Bradley (1957),
van den Heuvel (19 60) , Eade ( 1966) , Kingma ( 19 6 7) and Johnston
(1980) ; and in Hawkes Bay by Lillie ( 1953) , Kingma ( 1971) and
Pettinga (1980).
4
5
1.3 THE 'BENTONITE' PROBLEM
The Lower Tertiary mudstones have been referred to as 'bentonites'
by all previous workers. There are a number of reasons for this
terminology:
(1) Bentonite is a convenient field term for a
mudstone lithology susceptible to mass
movement when wet due to high moisture
absorption (Fig. 1.1) and exhibiting
shrinkage when dry (Fig. 1.2).
(2) Bentonite is a commercial term for mud with
suitable properties for a variety of
industrial uses, such as drilling mud,
bonding foundry sands and decolourisation
of oils.'
(3) Bentonite is a lithological term for deposits
composed dominantly of smectite (swelling)
clay minerals. Unfortunately, bentonite is
sometimes also used as a mineral name
synonymous with smectite.
(4) Bentonite is a genetic term for clay
deposits whid;i have formed as the alteration
product of glassy volcanic material, usually ash.
The first three usages of'bentonite'all require that smectite clay
minerals are a dominant component of the material,in accord with
the AGI definitions. The fourth genetic interpretation, in
contrast, has resulted in use of the term bentonite for any
altered volcanic ash, whether smectite clay minerals are present
Figure 1.1: Eroded and slumped calcareous smectite-mudstone, east bank of Seymour Stream, Middle Clarence Valley.
Figure .1.2: Shrinkage cracks in smectite-mudstone, Porangahau Quarry, Southern Hawkes Bay.
6
or not (e.g. Schultz, 1963). Despite efforts to redefine
bentonite on a mineralogical basis only (e.g. Wright, 1968;
Roen and Hosterman, 1982), the 'bentonite = volcanic origin'
concept is firmly entrenched in the geological literature.
In New Zealand, a volcanic origin for the mudstones has often
been assumed when the term bentonite has been used, although
most authors in practice based their usage on either the field,
commercial or mineralogical descriptions of bentonite. Only
Fyfe (1934) and Ritchie (1962) discuss the evidence of
a volcanic origin (see Chapter 6). The currently accepted view
on the origin of the mudstones is summarised by Grim and Guven
(l978) p.115:
"In view of the abundant volcanic activity in
New Zealand, it is not surprising that bentonites
have been reported in many areas".
In this study, the term 'smectite-mudstone' is used to avoid the
genetic connotations of 'bentonit§'.
7
2.1 INTRODUCTION
CHAPTER TWO
FIELD GEOLOGY
Lower Tertiary smectite-mudstones occur in the structural/tectonic
zone known as the East Coast Deformed Belt (Sporli, 1980) which
extends from Marlborough to East Cape. The belt and its main
features are shown in Fig. 2.1.
The mudstones are part of a widespread east coast marine sequence
of Upper Cretaceous to Oligocene age, which is characterised by
fine grain-size and siliceous and carbonate lithologies. The
sequence reaches a maximum thickness of not more than 1500 metres
in Marlborough (Prebble, 1980). This condensed sedimentary
succession represents a quiescent period of marine transgression
in Upper Cretaceous and Lower Tertiary time. Relief on land is
inferred to have been subdued (Suggate et al., 1978;
8
Pettinga, 1982), with the supply of terrigenous detritus to the
marine environment being much reduced in both volume and grain-size.
As a result, broad patterns of chemical/biogenic marine
sedimentation predominated, particularly in Marlborough where the
Arouri Limestone is a widespread unit. Coarser grained sandstone
lithologies in the sequence contain glauconite and are considered
AUSTRALIAN PLATE
arlborough ,..--
PACIFIC PLATE
O 100km .. -=
N
t
Figure 2.1: The East Coast Deformed Belt and major elements of the present-day plate boundary system (after Suggate et al, 1978; Walcott, 1978) .
9
to have been remobilised within the marine environment (Waterhouse
and Bradley, 1957; Pettinga, 1980).
10
The present day distribution of the smecti te.-mudstones is largely
controlled by the structural features of the East Coast Deformed
Be.l t which reflect late Cenozoic plate-margin tectonics (Fig. 2 .1) .
Subduction under the North Island has resulted in a dominance of
thrust faults in Wairarapa and Hawkes Bay. Many of the thrusts
have developed in the weak smectite-mudstone lithology (Pettinga,
1980, 1982). The subduction complex in the north changes to a
transform boundary in the. South Island. North-east trending
dextral shear faults are the main structural feature in
Marlborough and Cretaceous-Tertiary rocks are preserved in narrow
fault-bounded zones which are internally thrust-faulted and folded
(Prebble, 1980).
Fieldwork was carried out primarily in Marlborough, and later
extended to the North Island areas of Wairarapa and Hawkes Bay.
Fieldwork involved stratigraphic description and detailed
sampling at various localities. Fresh samples were excavated
where possible. General field mapping was not attempted and
geological maps made by previous workers are utilised to show
sample localities. Representative samples are held by the
Geology Department, University of Canterbury and their University
of Canterbury numbers are listed in Appendix I. The field
numbers of samples are used within the thesis. The geology of the
smectite-mudstones in Marlborough, Wairarapa and Hawkes Bay is
discussed in the following sections.
11
2.2 MARLBOROUGH
2.2.1 General Geology
The geology of Marlborough comprises basement rocks of Jurassic
and Lower Cretaceous age overlain by Upper Cretaceous and Tertiary
cover strata which include the smectite-mudstones (Prebble, 1980)
The general distribution of basement and cover rocks is shown in
Fig. 2. 2.
Upper Cretaceous and Tertiary sequences are preserved on the
downthrown side of each of the major dextral shear faults
(Awatere, Clarence, Kekerengu and Hope faults) in the region.
Two major areas of Lower Tertiary outcrop occur (Fig. 2.2):
(l) the prominent Benmore Anticline structure,
where a thick thrust-faulted and folded
cover sequence is wrapped around a basement
core (Prebble, 1976, 1980).
(2) an extensive fault-bounded northeast-south
west trending block in the Clarence Valley.
Fieldwork was carried out in the Kekerengu, Coverham and Middle
Clarence Valley areas. General sample localities are shown in
Fig. 2.2 and listed in Table 2.1.
The Kekerengu area has been mapped by Prebble (1976) and the
geology of the adjoining Coverham area to the west was described
by Hall (1964). Further southwest in the Middle Clarence Valley,
Cretaceous and Tertiary outliers were mapped by Reay (1980).
N
t
O==:JX)km
D
l<ekerengu River
Middle Clareixe Volley
Seymour Stream
Figure 2.2: Generalised geology of Marlborough (after Lensen, 1962).
~ ~
LEGEND
Undifferentiated Upper Tertiary and Quaternary
Lower Tertiary Amuri Limestone
Mesozoic
0 5 10 15 20km -----===== .... --...i::::==~
N
r
13
Table 2.1: Marlborough Sample Localities
Area Locality
(1) Woodside Creek, lower and upper
Kekerengu gorges
(2) Upper Ure River
( 3) N.E. end of Chalk Range Cover ham
( 4) Mead Stream gorge
( 5) Bluff Stream
Middle (6) Seymour Stream
Clarence Valley ( 7) E. edge Fells Basin
( 8) Limestone Hill
The smectite-mudstones in Marlborough are stratigraphically
included by previous workers in the Amuri Limestone, which was
first described by Hutton (1874) from Haumuri Bluff where the
lithology is thinly-bedded micritic limestone. The Amuri
Limestone name has since been applied to similar fine-grained
calcareous lithologies which are widespread throughout
Marlborough (Fig. 2.2) and form a major part of the Tertiary
column, spanning the Dannevirke and Arnold Series. The
nomenclature and status of the Amuri Limestone have not been
formalised and are currently under review by the N.Z. Geological
Survey.
This thesis follows the informal stratigraphic subdivision of the
Amuri Limestone into seven units by Hall (1964) and Prebble (1976)
for the Coverham and Kekerengu areas respectively and the
14
stratigraphic description of Reay (l980) for the Middle Clarence
Valley. The member terminology used by these workers is not used
here however, due.to pending formalisation of the nomenclature.
Summary stratigraphic columns for the Arouri Limestone in Kekerengu/
Coverham and the Middle Clarence Valley are presented in Fig. 2.3
and columns for sample localities are given in Fig. 2.4.
Smectite-mudstones form two units in the Arouri Limestone in the
Kekerengu and Coverham areas, known as the Lower Bentonite and the
Upper Bentonite (Hall, 1964; Prebble, 1976). In this thesis, the
names Lower Marl and Upper Marl are used, which more closely reflect
their calcareous mudstone lithology. The Marls are on the order of
50-100 metres thick and have conformable gradational contacts with
the Lower Limestone, Middle Limestone and Fells Greensand units of
the Arouri Limestone (Fig. 2.3).
Microfossil dating of the Marls gave age ranges of Waipawan to
Heretaungan for the Lower Marl and Porangan to Runangan for the
Upper Marl (see Appendix II and sample locality maps). These ages
are in general agreement with previous respective determinations
of Mangaorapan to Heretaungan and Porangan to Runangan (Prebble,
19761. However, a condensed sequence in lower Woodside Creek
yielded older ages of Teurian to Waipawan for the Lower Marl and
Mangaorapan to Heretaungan for the Upper Marl (Prebble, 1976).
The Marls are a relatively weak lithology in the Upper Cretaceous
Tertiary succession and are cormnonly disrupted by major thrust
faults. Consequently the Marls are characteristically highly
sheared with complex internal faulting and folding.
AMURI LIMESTONE, COASTAL MARLBOROUGH
Lw Wai ma Siltstone
--
Lwh-Lw Whales Back Limestone
Ar-Lwh Fells Greensand
Op-Ar Upper Marl
Oh-Ab Middle Limestone
Amuri Limestone
~-
Ow-Oh Lower Marl ~--
Ow Lower Limestone
Mh-Dt Flint Beds
--------------------
Mh Whangai Shale
1:0 J
AMUR! LIMESTONE, PART OF
THE MIDDLE CLARENCE VALLEY
lwh -------Op- Ab Grass Seed Volcanics
Marl
I0t-Dw Baso.l Limestone ------------
Ow
Cookson Volcanics
Amuri Limestone
Dip Basin Green sand
Figure 2.3: Schematic summary stratigraphic columns of the Arnuri Limestone in coastal Marlborough (after Prebble, 1976) ~ and in part of the middle Clarence Valley (after Reay, 1980). ~
LEGEND
~ ~
~
~ ~t&ftfH!tj
~
Whales Back Limestone Fells Greensand IJpper Marl Middle Limestone Lower Harl
Lower Limestone
Southwest
SEYMOUR STREAM FELLS BASIN
After Reay ( 1980)
=--,-,-,1 Cookson lVvcvvv Volcanics
f{GSVv~
W.?:FfM6j h1~(~
Grass Seed Volcanics
Marl
Undifferentiated Amuri Limestone
g;:013c;·~·;I Dip Basin Greensand
LIMESTONE HILL
VV(yVVV v v v v v v v v
v v v v v v v v v
vvvGSVv/ v v v v
v v v v v v v v v v v v v v v v v v
After Reay (1980)
MEAD STREAM GORGE
CHALK RANGE
After Hall 11964)
After Prebble (1976)
UPPER URE RIVER
After
Northeast
F
metres
Prebble (1976)
Figure 2.4: Schematic summary stratigraphic columns of the Marl units of the Arouri Limestone in Marlborough. See Appendix II for dated samples.
In the Middle Clarence Valley, only one Marl unit is mapped
(Figs 2.3, 2.4) which occurs in the Seymour Stream outlier and
ranges in age from ?Teurian to at least Porangan (Appendix II)
An upper age of Bortonian is given by Reay (1980). The Marl
constitutes almost the entire thickness of the Arouri Limestone
of approximately 100 metres and has a gradational lower contact
with a 10 metre thick basal limestone unit. The upper contact of
the Marl with overlying Cookson Volcanics of Whaingaroan age is a
sharp disconformity (Reay, 1980).
The Arouri Limestone in the Middle Clarence Valley also contains a
localised unit known as the Grass Seed Volcanics (Reay, 1980)
17
which occurs in the Limestone Hill outlier. The Grass Seed
Volcanics is Arnold Series in age (Reay, 1980) and does not occur
together in stratigraphic sequence with the Marl unit with which it
is partly time-equivalent.
2.2.2 Local Stratigraphy and Sedimentology
The Marls of the Arouri Limestone have very similar lithology and
internal stratigraphy throughout the Marlborough region and a
description is given below which applies to the sample localities
discussed in the following sections unless otherwise stated.
The typical lithology of the Marls is alternating green, soft to
moderately indurated, calcareous smectite-mudstone (marl) and
white-green, well indurated biomicrite (Figs 2.5 and 2.6).
Recognition of alternating marl-limestone sequences in the field
requires that carbonate and mud contents oscillate around the
transition line between marl and limestone at approximately 70%
carbonate and 30% mud (Einsele, 1982). Carbonate contents
determined for marl beds range from 30% to 67% (Appendix III) and
Figure 2.5: Interbedded calcareous smectite-mudstone and micritic limestone, west bank of Seymour Stream, Middle Clarence Valley.
Figure 2.6: Interbedded calcareous smectite-mudstone and micritic limestone, south bank of Mead Stream gorge.
18
the limestone beds (>67% caco 3 ) yielded acid-insoluble mud
residues. The only cormnon sedimentary structure in the Marls
is burrows, including zoophycos trace fossils. The contacts
between marl and limestone beds are gradational, although sharp
contacts are common where the marl beds are highly sheared as a
result of bedding-plane slip. The less cemented marl beds
(CaC0 3 <50%) invariably show some degree of development of a
fissile shear fabric approximately parallel to bedding.
In more highly calcareous marl beds, a platy fracturing may be a
result of both sedimentary/diagentic processes and shear
deformation. Very intense deformation along major faults trans
forms the marl into soft plastic clay, such as at Blue Slip on
the Kekerengu coast.
The Marls have a characteristic internal three-part stratigraphy
(Fig. 2.7). The basal and top sections of the Marls consist of
regularly alternating marl and limestone beds 10-30 cm thick, with
an overall increase in the thickness of the marl beds towards the
centre of the unit. The middle interval consists of more massive
marl in bands up to several metres thick with intermittent
interbedded limestones.
(1) Woodside Creek. Sequences through the Marls occur in both
the lower and upper gorges of Woodside Creek and are separated by
a major thrust fault (Fig. 2.8).
A typical section through the Marls is exposed in the upper gorge
and the geology and sample locations are shown in Fig. 2.8. The
Lower Marl is approximately 80 metres thick and is relatively
undeformed. The typical regularly alternating marl-limestone
lithology near the basal contact of the Lower Marl with the Lower
19
Figure 2.7: Typical internal stratigraphy of the Marls. Lower Marl, northeastern end of Chalk Range, looking north.
Figure 2.9: Alternating marllimestone at the base of the Lower Marl, south bank of Woodside Creek upper gorge.
20
LEGEND
jWaiS I Waima Siltstone
j WBL J Whales Back limestone
~ Fells Greensand
• Upper Marl
~ Middle Limestone
Lower Marl
~ Lower Limestone
~ Flint Beds
~-Whangai Shale
~ Woodside Formation
___-, Formation Boundary
,,,.,.- Fault
~~ Coastline
? River stream
~ Road
W1 • Sample localities
O 250 500 750 1000 m
Figure 2.8: The geology of Woodside Creek, (from Prebble, 1976) and sample localities.
21
Limestone is shown in Fig. 2.9. The thickness of the Upper Marl
is uncertain due to thrust-fault repetition and complex internal
deformation. The Upper Marl in the upper gorge of Woodside
Creek is exceptionally calcareous with Caco3 contents greater
than 60% (WlO, Wl3, W14).
The sequence through the Marls in the lower gorge of Woodside
Creek is considerably thinner and older than at other localities
in the Kekerengu and Coverham areas and structural complexities
are apparent. Approximate thicknesses are 20 metres for the
Lower Marl and 40 metres for the Upper Marl. The Marls are
separated by the Middle Limestone which at this locality is red
purple in colour. The Upper Marl is overlain by the Waipawan to
Heretaungan Woodside Formation (Prebble, 1976) consisting of
alternating graded glauconitic sandstones and dark mudstones.
The contact appears to be gradational with some sandy glauconitic
limestone beds occurring towards the top of the Upper Marl. A
similar interbedded sequence of glauconitic calcareous sandstone,
micritic limestone and marl occurs at the head of Te Rapa Stream.
22
(2) Upper Ure River. As in upper Woodside Creek, the Ure River
section consists of a complete relatively undeformed sequence
through the Lower Marl (70 metres) and a fault-disrupted Upper
Marl sequence (Fig. 2.10). Approximately 15 metres of deformed
Upper Marl is present beneath a sharp thrust fault contact with
Middle Limestone. At the base of the Upper Marl, a graded 1 metre
thick bed was observed, comprising silty limestone with parallel
lamination and rare cross lamination defined by concentrations of
darker coloured mud, which grades up with increasing mud component
into marl (U7, US). Similar graded beds were described by
Prebble (1976) from the Upper Marl.
~ I/ !wsL I
~
@]
U9
N
vvvvvvvtv vvvvvvvvv
vvvvvvvvv vvvvvvvvv vvvvvvvv
v Blue Mountain v v Station v v v v
v • v v v
~iz,i,~~,u~·~~,~~~~·~
LEG ENO 0 250 500 750 1000m
Cookson Volcanics
Whales_ Bad~ limestone
Upper Marl ~ Formation Boundary
Middle Limestone _,,,,,.,. Fault
Lower Marl ·~ River, stream
Lower Limestone U1 • Sample localities
Figure 2.10: The geology of the upper Ure River (from Prebble, 1976) and sample localities.
23
(3) Northeastern end of Chalk Range. The basal four units of
the Arouri Limestone form a prominent strike ridge in the Coverham
area known as the.Chalk Range (Fig. 2.11). The Lower Marl is
exposed in the steep scarp slope of the Chalk Range just below
24
the summit and crosses over the summit at the northeastern end of
the range (Fig. 2.12). A detailed section through the well-exposed
Lower Marl at this locality is given in Fig. 2.13. The Upper
Marl {Cll-Cl9} occurs on the dip-slope side of the Chalk Range.
Occasional exposures indicate a high degree of deformation in the
Upper Marl (Fig. 2.14). The Upper Marl is overlain by Fells
Greensand and Whales Back Limestone - the latter forming Whales
Back ridge immediately north of the Chalk Range. The gradational
contact of the Upper Marl with the Fells Greensand is exposed in
the scarp slope of Whales Back ridge (Fig. 2.15) and consists of
5-10 cm thick beds of laminated glauconitic calcareous sandstone
(Cl2) which grade up into marl beds less than 5 cm thick.
(4) Mead Stream Gorge. A well exposed complete section through
the Arouri Limestone occurs in the gorge of Mead Stream (Fig. 2.16)
Relatively undeformed sequences through both the Lower and Upper
Marls are present, although the contact of the Upper Marl with
overlying glauconitic sandy limestone (Fells Greensand/Whales Back
Limestone?) is uncharacteristically sharp and is probably a
bedding plane fault. Approximate thicknesses are 60 metres for
the Lower Marl and 80 metres for the Upper Marl. The typical
lithology and internal stratigraphy of the Marls are illustrated
in Fig . 2 .17 .
(.5) Bluff Streai.-n. A syncline of Upper Cretaceous-Lower Tertiary
rocks is exposed in lower Bluff Stream. Approximately the basal
50 metres of the Arouri Limestone forms the core of the syncline
Figure 2.11: View of part of the Chalk Range in the middle distance, looking northwest. The Lower Limestone, Lower Marl and Middle Limestone are exposed.
Figure 2.l2: The Lower Marl (60 metres thick) exposed at the northeastern end of the Chalk Range, looking northeast.
25
NZ FR F Sample Stage no. no. m
(9110 60
so
:z < I..::> 40 z :::)
< I-u..l a: w 30 C,8 ::i::
C,7
:z <(
20 3 < a.
C,6 < 3 C4,5
10 P29/ C1, 2 n,a
C3
LOWER MARL CHALK RANGE
P29 /850204
u.J :z
i.uO ...JI-
20-30cm bedded Cl l/l ClUJ
lime stone _z: Z:::J
20·50cm bedded limestone with some 5·30cm marl interbeds
20-50 cm bedded alternating marl limestone
_, er: <( z:
a: w 3
Massive-marl 0 ..J with occasional 10 cm limesrone interbeds
20-30 cm bedded alternating_ marl-limestone
20-30 bedded limestone 1..1.1
with occasional z 10 cm marl interbeds ;=
l.-:z:iz:;zzb;zclz:z;:::::;,::::±:::::;::::::~=±=;l O::Vl ji;i -----------i u..l u.J
1-L.--.--1-.--i.....-..i....,.--'--,--.._,._._.,......... 2 0 -3 0 c m 3 ~ 0-
bedded limestore..J....J
I.U
z 0
I-
l/l
,. l.u
~
..J
Cl!
:::)
z: <(
Figure 2.13: Schematic detailed stratigraphic column of the Lower Marl at the i:i,ortheastern end of the Chalk Range.
26
Figure 2.14: An exposure of highly sheared Upper Marl on the dip-slope side of the Chalk Range, looking west.
Figure 2.15: Whales Back ridge capped by Whales Back Limestone and underlain by Fells Greensand and Upper Marl, looking north.
27
LEGEND
I GMC I Great Marlborough Conglomerate
I Wais r Waima Siltstaie
I 1HBL I Whales Back Limestone
@] Fells Greensand
Upper Marl
~ Middle Limestone
- Lower Mar\
~ Lower Limestone
QJ Flint Beds
/ Formation Boundary
~ River, stream
M1 • Sample localities
':OOm •
Figure 2.16: The geology of Mead Stream gorge and sample localities. Plotted from aerial photo 1770/62, N.Z. Aerial Mapping, 1952.
28
Figure 2.17: Lower Marl comprising alternating marl-limestone and a middle interval of massive marl, north bank of Mead Stream gorge.
Figure 2.18: Folded and faulted Marl unit, west bank of Bluff Stream.
29
--
and comprises flinty micritic limestone (Bl) of Haumurian age
overlain with conformable and gradational contact by a (Lower?)
Marl unit (B4) shown in Fig. 2.18. Tight internal folding
characterises the Amuri Limestone at this locality.
(6) Seymour Stream. A section through the folded Upper
Cretaceous-Tertiary sequence of the Lower Seymour outlier is
exposed in Seymour Stream. Fig. 2.19 shows the detailed geology
and sample localities for both Seymour Stream and the Fells Basin
(see below). The Arouri Limestone is represented by one Marl unit
exposed on the eastern bank of Seymour Stream. The Marl consists
of basal alternating marl-limestone beds which are overlain by a
thick massive interval of moderately soft smectite-mudstone with
Caco 3 contents around 40% (Sl, 82) and which is eroded into
pinnacles (Fig. 2.20). The massive marl is truncated by a sharp
disconforrnable contact with overlying Cookson Volcanics.
(7) Eastern edge Fells Basin. Further exposure through the
Lower Seymour outlier sequence occurs to the west of Seymour
Stream in the Fells Basin (Fig. 2.19). A 100 metre section
through the Marl very similar to the section in Seymour Stream,
is well exposed on the steep eastern slope of the Fells Basin
(Fig. 2.21). A detailed stratigraphic column for the Marl is
given in Fig. 2.22.
30
(8) Limestone Hill. The P..muri Limestone in the Limestone Hill
outlier contains the Grass Seed Volcanics. The geology of the
Limestone Hill outlier is shown in Fig. 2.23. The Grass Seed
Volcanics unit CL3, L5) re-aches a maximum thickness of 160 metres
(Reay, 1980) in the vicinity of Grass Seed Stream and consists of
fine-grained basaltic tuff containing clasts of basalt up to
0 500 1000 m LE GENO
G2] Upper Tertiary --- Formation Boundary
~ Lower Tertiary ~ Fault Amuri limestone ;;;;--
[Q Cretaceous ~ Thrust Fault
+ .A.nticline Fold Axis ~ River stream
• S1 Sample Loe aliti es ~ Syncline Fold Axis
Figure 2.19: The geology of the Lower Seymour outlier (from Reay, 1980) and sample localities.
31
Figure 2.20: Massive marl lithology, east bank of Seymour Stream.
Figure 2.21: Marl unit (-100 metres thick) comprising basal interbedded marl-limestone and massive marl, eastern edge Fells Basin, looking north.
32
.. '
A MURI LIMESTONE FELLS BASIN 031 / 417 844
NZ FRF Sample Stage No. No.
1--~~--1-~~--1~~--.m
z <( I.!)
z <(
0::: 0 a. I
z <(
0::: :::) UJ I-c-,..
031 / t 145
031 / f 146
S 13
90
30
vvvvvvv vvvvvvv
vvvvvvv Tuff
Massive marl with occasional S-20cm limestone interbeds
...J a:: < l:
Dem bedded /...J 1-'-.,...._ ......... ...,_,_......,_~c..,......-,-J'--,--'-,-....._. l i m esto n e ~ t:i ~.L..,-J'-,-1-,-1..,....J...,.....l-,....L.,....L.,_.!...-,-1..-.-1 <...J 1-'--r-'-,--'-,--'-T-....,..;.-,-J-.,....c-,........_-,-J-...,.......~ cQ
Greensand
v, _u =-oz v, <( :::.::u O....J oo u>
UJ
z 0
f-
v,
1.1.J
l:
.....
...J
a::
Figure 2.22: Schematic detailed stratigraphic column of the Arouri Limestone on the eastern edge of Fells Basin.
33
34
N
t
1000m
,. _. ...... - Formation Boundary
LEGEND .-,,,.--- Fault
@iJ Up per Tertiary -\- Anticline Axis
jv/v\vl Grass Seed } Lower Tertiary x Syncline Axis Volcanics
~ Limestone Amuri
~ River, stream lime stone
IT] Cretaceous • L 1 Sa.mpl e Localities
Figure 2.23: The geology of the Limestone Hill outlier (from Reay, 1980) and sample localities.
boulder size and occasional lenses of marly micritic limestone
(L4). The Grass Seed Volcanics is underlain by marly micritic
limestone (Ll) but a well developed Marl unit was not observed
at the Grass Seed Stream locality.
2.3 WAIRARAPA
2.3.1 General Geology
35
Smectite-mudstones in Wairarapa occur in faulted Upper Cretaceous
Lower Tertiary sequences along the eastern coast of the region.
The Tora area was mapped by Waterhouse (1955) and the geology
summarised by Waterhouse and Bradley (1957). To the north, the
· Mt Adams, Flat Point and Tinui-Awatoitoi areas have been mapped by
Eade (1966), van den Heuvel (1960) and Johnston (1980) respectively.
ThBre are no reported complete stratigraphic sections through the
smectite-mudstones as a result of faulting and poor exposure. The
best stratigraphic sections occur in the Tora area (J.R. Pettinga,
pers. comm.) where fieldwork for this study was carried out.
A geological map for the Tora area is given in Fig. 2.24. A
sequence of Upper Cretaceous-Lower Tertiary rocks occurs on the
western limb of an anticline trending approximately parallel to
the coast. The sequence is exposed in the stream sections cutting
across the structure. The localities visited were: Awheaiti
Stream, Pukemuri Stream, Oroi Stream and Mungaroa (Te Kau Kau)
Point. A summary stratigraphic column for the Pukemuri Stream
locality is given in Fig. 2.25.
Smectite-mudstones form the youngest unit in the area named the
Kandahar Formation (Waterhouse, 1955; Waterhouse and Bradley, 1957).
HUNGAROA POlt-H
LEGEND
1111 Kandahar Formation
I'·\(} I Pul<e muri Siltstone
~ Mungaroa Limestone
D S st I M st lithologies
~ Whangai Formation
... --~
WAt•
-r --=-,......_~ ..,... __ :::::
Formation Boundaries
Rives stream
Sample Localities
Thrust Fault
Anticline Axis
Shear Zone
Figure 2.24: The geology of the Tora area, southeast Wairarapa (from Waterhouse and Bradley, 1957) and sample localities.
36
PUKE MURI
Om-Oh
metres
0
so
100
STREAM
Large blocks of interbedded
greensand, marly limestone
and smectite - muds tone in
a matrix of soft highly
sheared smectite - mudstone.
Thinly bedded greensands
and marly limestones
interbedded with calcareous
smectite-mudstone
? Slump unit of clasts of light green sm ectite -mudstone in a dark brown siltstone matrix
Laminated dark brown
z 0
lo-< ::z: a:: 0 u.
a:: < J: <(
a :z <(
~
siltstone containing exotic clasts,
Figure 2.25: Schematic summary stratigraphic column of the Kandahar Formation in Pukemuri Stream. See Appendix II for dated sample.
37
An age range of Heretaungan to Bortonian is given by Waterhouse
and Bradley (.195 7) for the Kandahar Formation. Microfossil
dating in this study gave a similar range from Mangaorapan
Heret.aungan to Bortonian (Appendix II). However, stratigraphic
control on the samples was poor as the Kandahar Formation is
extremely complexly deformed. The formation has an upper west
ward-dipping thrust fault contact with Lower Cretaceous rocks and
much of what has been previously mapped as the Kandahar Formation
is essentially a major shear zone in which occasional blocks of
coherent bedded lithology are preserved. The Kandahar Formation
is underlain by the Pukermuri Siltstone. The contact between the
two formations is obscure, but probably sedimentary.
Waterhouse and Bradley, 1957).
(See also
38
A lithological correlative of the Arouri Limestone named the
Mungaroa Limestone (Waterhouse and Bradley, 1957) occurs as part
of the Upper Cretaceous-Lower Tertiary sequence in the Tora area.
Smectite-mudstones are a minor component of the Mungaroa Limestone
and occur as thin partings·between limestone beds. A sample of
the smectite-mudstones from Mungaroa Point yielded a Teurian age
(Appendix II). Waterhouse and Bradley (1957) described a
foraminiferal assemblage containing Cretaceo-Tertiary elements
from Mungaroa Point but considered the assemblage to be
redeposited. Subsequent revisional and additional work however
does not support redeposition (Browne, in prep). The Mungaroa
Limestone thins rapidly northwest from a maximum thickness of
approximately 100 metres at Mungaroa Point and passes laterally
into Lower Tertiary alternating sandstone and mudstone lithologies
(Waterhouse and Bradley, 1957).
2.3.2 Local Stratigraphy and Sedimentology
(1) Pukemuri Stream. Pukemuri Stream provides the best exposure
through the Kandahar Formation. The inferred stratigraphic
thickness is of the order of several hundred metres but the upper
contact is faulted and the internal stratigraphy is highly
disrupted by shear deformation. The contact between the
Kandahar Formation and the underlying Pukemuri Siltstone appears
39
to coincide with an olistostrome or slump unit in which light green
clasts of the Kandahar Formation, up to several metres in size,
occur within a matrix of dark brown Pukemuri Siltstone. Further
detailed mapping would be required to establish with certainty the
relationship between the two formations. The Pukemuri Siltstone
is also characterised by the occurrence of exotic pebbles and
boulders from underlying formations and large bedded blocks of
sandstone, indicating substantial redeposition. (See also
Waterhouse and Bradley, 1957).
The dominant lithology of the Kandahar Formation is a highly
sheared soft green smectite-mudstone which forms a matrix to large
floater blocks in which the sedimentary features of the Kandahar
Formation are preserved. Glauconitic sandstone is a common
lithology interbedded with calcareous smectite-mudstone (Fig. 2.26)
The sandstone beds are often channelised with a coarse granular
base composed largely of glauconite and rip-up clasts of mudstone.
Parallel and cross lamination structures occur in the upper
portions of the sandstone beds and gradation up into dark brown
grey smectite-mudstone is typical. The dark mudstone then passes
gradationally up into light green calcareous smectite-mudstone.
The sandstone beds are generally less than 10 cm thick and the
smectite-mudstone beds are up to 50 cm thick. The carbonate
Figure 2.26: Interbedded glauconitic sandstone, marly limestone and smectite-mudstone in the Kandahar Formation, Pukemuri Stream.
Figure 2.27: Alternating marllimestone lithology of the basal Kandahar Formation, west bank of Awheaiti Stream.
40
41
content of the mudstones is variable, reflecting a range of
lithologies from soft plastic mudstone to well cemented marl.
Moderately cemented marls range from 30-40% Caco 3 (WPl, WP2, WP3).
(2) Awheaiti Stream. The Kandahar Formation in Awheaiti Stream
shows several additional features to those described from Pukemuri
Stream.
Red coloured smectite-mudstone occurs near the base of the
formation, mixed with green smectite-mudstone and both are highly
sheared. The red colouration appears to be a secondary alteration
feature (see also Waterhouse, 1955). The basal part of the
Kandahar Formation in Awheaiti Stream also includes thinly-bedded
packets of alternating green marl and chalky white limestone
(Fig. 2 .27). The Caco 3 content determined for one marl bed (WA3)
is 56.5%. Occasional exotic angular pebbles of a fine-grained
carbonate lithology (cf Mungaroa Limestone) occur in both sandstone
and smectite-mudstone beds of the Kandahar Formation.
(3) Mungaroa Point. The Mungaroa Limestone is well exposed in
the shore platform at Mungaroa Point and consists of interbedded
micritic limestone, marl and laminated calcareous glauconitic
sandstone. Non-calcareous glauconitic sandstone diapirs also
occur. The Marl is present as thin interbeds less than 5 cm
thick between limestone and sandstone beds up to 30 cm thick
(Figs 2.28, 2.29).
Figures 2.28, 2.29: Thin sheared marl interbeds in the Mungaroa Limestone, Mungaroa Point shore platform.
42
2.4 HAWKES BAY
2.4.1 General Geology
The smectite-mudstones of southern Hawkes Bay occur in three
structural highs comprising Cretaceous and Paleogene rocks, as
shown in the generalised geological map in Fig. 2.30. Sampling
of the mudstones was mainly restricted to the Coastal High with
the best exposure. The main sample localities are: Waimarama
Beach, Waewae Stream, the coastal slope near Red Island, and the
bentonite quarry near Porangahau.
43
Detailed geological mapping in southern Hawkes Bay has been carried
out by Lillie (1953), Kingma (1971) and Pettinga (1980). The
smectite-mudstones are stratigraphically included in the Wanstead
Formation - a name applied by Lillie (1953, p.36) to "soft beds
of clay-like character overlying the Whangai beds" and ranging in
age from Teurian to Bortonian. Later workers in Wairarapa, who
encountered a greater variety of Lower Tertiary lithologies,
adopted a Wanstead Group status (Waterhouse and Bradley, 1957;
van den Heuvel, 1960; Eade, 1966; Johnston, 1980). Pettinga (1980)
renamed the smectite-mudstones in southern Hawkes Bay as the
Mackintosh and Raratu Formations without reference to a Wanstead
Group. In view of the need for clarification of the stratigraphic
nomenclature (which at the time of writing is in progress), the
Wanstead Formation name of Lillie (1953) is retained in this study.
The distribution of the Wanstead Formation smectite-mudstones in
coastal southern Hawkes Bay is closely related to the complex
structure dominated by thrust faults. No complete unfaulted
sections through the Wanstead Formation occur and only the basal
part of the formation exposed at Waimarama Beach and Waewae
WAE WAE STREAM
0 4
LEGEND
D Ptio -Pleistocene ----- Geological BoundCll'y
. CR] Neogene x Syncline Axis
Cretaceous - ® Coastal High Paleogene
® E lsthorpe Anticline
© Inland High
Figure 2.30: Generalised geology of southern Hawkes Bay (from Pettinga, 1982).
S km
44
N
t
Stream is stratigraphically coherent. Summary stratigraphic
columns for these two localities are presented in Fig. 2.31.
Microfossil dating of the base of the Wanstead Formation gave
ages of Teurian and Waipawan-Heretaungan at the Waimarama Beach
and Waewae Stream localities respectively (Appendix II). These
ages indicate a conformable contact with the underlying Whangai
Formation of Haumurian-Teurian age (Lillie, 1953).
A characteristic mode of occurrence of the Wanstead Formation is
as a component of melange zones, which are tectonic mixtures of
different lithologies associated with thrust faults (Pettinga,
1980}. Sampling of unrecognised melange zones, particularly at
Porangahau, is a shortcoming of some previous mineralogical
studies (Gordon et al, 1955; Ritchie, 1962).
2.4.2 Local Stratigraphy and Sedimentology
45
(1) Southern End of Waimarama Beach. A stratigraphic section
through approximately 30 metres of the basal Wanstead Formation is
present at Waimarama Beach. The detailed geology is shown in
Fig. 2.32.
The contact of the Wanstead Formation with the underlying Whangai
Formation mudstone appears to be conformable and is distinguished
on the appearance of soft, relatively pure smectite-mudstone.
Clay mineralogical analysis of the top of the Whangai Formation
(HBlBl showed a major smectite component, but the Whangai
mudstone is well cemented by caco 3 (35%) and silica and is
lithologically distinct from the uncemented Wanstead mudstone.
metres 0
20
40
WAIMARAMA BEACH
W22 I 524451
Melange Zone
Thick and thinly bedded greensands alternating with thin sheared smectite- mudstones
Alternating greensond and dork mudstone
FAULT ____ _, <Cw l!J _.
Thinly bedded light z 4: and dork induroted ~ti mud stones 3
FAULT ____ __._ _ ___,
WAEWAE STREAM
V22/425308
FAULT
Shear zone
Thick and thinly bedded green sands alternating with sheared smectitemudstones and occasional marls
Thinly bedded Ii ght induroted mudstones
Figure 2.31: Schematic surmnary stratigraphic columns of the Wanstead Formation at the southern end of Waimarama Beach and in Waewae Stream (after Pettinga, 1980). See Appendix II for dated samples.
• D ' .
LEG ENO
w'anstead Formation
Whangai Formation
Und iff erenti ated Upper Cretaceous Formations
N
T
Bluff
0 100 200m
Formation Boundary
Thrust Fault
Melange Zone
•HB 11 Sample locality
Figure 2.32: The geology of the southern end of Waimarama Beach (from Pettinga, 1980) and sample localities.
47
The smectite-mudstones at the base of the Wanstead Formation
occur in beds up to 10 cm thick which alternate with
glauconitic sandstones in beds up to 1 m thick (Fig. 2.33). A
typical sedimentological cycle is shown diagrarrunatically in
Fig. 2.34. The internal features of the sandstone beds are
medium to very-fine size grading and parallel, cross and
convolute types of lamination which are defined by thin layers
48
of mud. Rip-up clasts of mudstone are occasionally present. The
sandstones have sharp basal contacts and gradatiqnal tops into
dark brown-grey smectite-mudstone. The dark mudstone in turn
grades up into light green smectite-mudstone. The mudstones, when
unsheared, show mottling resulting from bioturbation. Carbonate
analysis of the dark (HB15) and light (HB14) mudstones gave
contents of 7.6% and 2.3% respectively.
The basal Wanstead sequence at Waimarama Beach is cut by a
melange zone shown in Fig. 2.35, in which highly sheared smectite
mudstone forms a matrix to large exotic clasts. The melange has
a well-developed lozenge shear fabric and shear surfaces in the
mudstone matrix are highly polished and striated.
(2) Waewae Stream. A similar succession through the Wanstead
Formation to that at Waimarama Beach, is exposed in Waewae Stream.
The detailed geology is shown in Fig. 2.36.
The Wanstead Formation conformably overlies the Whangai Formation
and the basal 50 metres present comprises interbedded sheared
smectite-mudstone and glauconitic sandstone. The lithology and
sedimentology are very similar to that described at Waimarama
Beach, except the mudstone carbonate content is higher
(HB9 = 21% caco 3) and occasional cemented marl bands occur
Figure 2.33: Interbedded glauconitic sandstone and sheared smectitemudstone at the base of the Wanstead Formation, southern Waimarama Beach.
Figure 2.35: Melange zone with a sheared smectite-mudstone matrix, southern Waimarama Beach.
49
50
40
30
20
10
0 cm
SEOIMENTOLOGIC CYCLE BASAL WANSTEAO FORMATION WAIMARAMA BEACH
light green srnectite -mudstone
Dark brown-grey silty smectite-mudstone
Convolute laminated fine to very fine scrndstone
Cross laminated fine sandstone
Parallel laminated fine sandstone
Massive medium to fine graded glou con iti c sands tone
containing mudstone clasts
Figure 2.34: Schematic diagram of a typical sedimentologic cycle at the base of the Wanstead Formation at the southern end of Waimararna Beach.
(J]
0
N
t 0
0 200 400m
LEGEND
Wanstead Formation
Whangai Formation
Undifferentiated Upper Cretaceous Formations
--- Formation Boundary
U__..-0 . ..........--n Normal Fault
.>,>-- Thrust Fault
..;.-_:=,. ---~:::-- Shear Zone - -:::=-c:_ River, stream
•HB 8 Sample locality
Figure 2.36: The geology of Waewae Stream (from Pettinga, 1980) and sample locality.
51
within the soft mudstones. The bedded Wanstead sequence passes
up into a sh.ear zone associated with an upper thrust fault
boundary.
C3) Coastal Slope near Red Island. A small exposure in the
hillslope above Red Island was the highest inferred stratigraphic
position sampled in the Wanstead Formation. The location and
geology are shown in Fig. 2.37.
Microfossil dating gave an age of Teurian-Waipawan (Appendix II).
The lithology is alternating glauconitic sandstone and smectite
mudstone. The sandstone beds are graded from medium to very-fine
sand, are parallel and cross laminated, and are very fissile.
The interbedded smectite-mudstones are light green in colour,
sheared, and one Caco3 analysis (HB21) gave a value of 9.2%. In
comparison with the base of the Wanstead Formation, this sequence
has thinner sandstone and thicker smectite-mudstone beds.
Pettinga (1980) suggested an overall fining-upward trend for the
Wanstead Formation.
(4) Porangahau Quarry. The Wanstead Formation exposed in the
quarry at Porangahau appears to be part of a melange zone. The
melange comprises highly sheared smectite-mudstone (HB3),
interbedded glauconitic sandstones and exotic clasts.
(5) Red Smectite-Mudstones. Samples of smectite-mudstones in
Hawkes Bay which appear to have a primary red colouration were
supplied by P.R. Moore (NZ Geological Survey) from Paoanui
(V23/41251865) and Mangamauku Stream (214/812739) and by
J.R. Pettinga (Geology Department, University of Canterbury)
from Gilray Bay (W22/514427). The author also collected a
52
RED ISLAND
0 100
LEGEND
Wanstead Formation ,... .... -- Formo.tion Boundary
Whangai Formation ~ Thrust Fault
Undifferentiated Upper Cretaceous Formations
~- Melange Zone ,.,
Red !sland Volcanics •H B 21 Sample Locality
Figure 2.37: The geology of the coastal slope near Red Island (from Pettinga, 1980) and sample locality.
53
N
t
200m
sample (HB6) of mottled red-green mudstone from near Paoanui.
An additional red smectite-mudstone sample from East Cape was
supplied by P.R. Moore.
2.5 SYNTHESIS
Marine smectite-mudstones form distinctive lithostratigraphic
units of Dannevirke to Arnold Series age in the East Coast
Deformed Be.lt. Broad stratigraphic correlations between
Marlborough, Wairarapa and Hawkes Bay are depicted in Fig. 2.38.
The lack of complete stratigraphic sequences in Wairarapa and
Hawkes Bay means that the. thicknesses and age ranges of the
Kandahar and Wanstead Formations are uncertain and definite
correlations are consequently not possible.
54
The smectite-mudstone unit in southwest Marlborough (Marl,
Clarence Valley) constitutes most of a condensed Lower Tertiary
sequence approximately .100 metres thick. Sedimentation of the
Marl probably began in Teurian time and continue.d into the Middle
Late Eocene,
In northeast Marlborough, carbonate sediments dominate the Lower
Tertiary sequence and smectite-mudstone units are part of an
Amuri Limestone succession up to 1000 metres thick. Sedimentation
of smectite-mudstone occurred in two phases represented by the
Lower and Upper Marls of Early Eocene and Middle-Late Eocene age
respectively. The Lower Marl is partly equivalent to the Marl in
the Clarence Valley, as are the Flint, Lower Limestone and Middle
Limestone units of the Amuri Limestone in northeast Marlborough.
The Upper Marl may have been deposited largely after the time of
deposition of the Clarence Valley Marl, however possible Late
LEGEND
Smectite -Muds fone
M icritic Limestone
Sandstone I Siltstone
Flint beds and lenses
Volcanics
Sheared lithology
vertical scale 100
50
0 metres
Op-Ab
South NORTHEAST MARLBORO UGH
Ar
WAIRARAPA
\ c\ 0
:;:: \ d·
E \
\ \
North
\\ HAWKES BAY
c .!2 -+-0 E '-0
LL
:: -0
d (\)
+VJ c d
_T_e_rt_i_ar~~~~~~~~-7_._D_t:~~];;;L-~~~~~,t;;;;;;:;;;;;:;;;;~~~~~_.'.::'...'__J:~~~-k::=-~~~--='D~tl~l ... ~~!3
Cretuceous Dip Basin Whangai Whangai Greensand Shale Shale
After Reay I 1980 l After Prebble I 1976) After Waterhouse &- After Pettinga (1980) Bradley I 19571
lJl lJl
Eocene erosion may have removed the top part of the latter unit
(Reay, 1980) .
56
The Lower Tertiary sequence in Wairarapa is at least 400-500 metres
thick and is characterised by a diversity of lithofacies and marked
facies changes. The Mungaroa Limestone containing minor
interbedded smectite-mudstone was deposited during Teurian time.
The limestone represents 'Arouri-type' carbonate sedimentation and
passes laterally into sandstone-mudstone lithofacies and is
overlain by the Pukemuri Siltstone (Waterhouse and Bradley, l957).
The timing of major deposition of smectite-mudstone (Kandahar
Formation) is uncertain due to poor stratigraphic control, but
possibly commenced later than in other regions during
Mangaorapan-Heretaungan time and continued into the Middle-Late
Eocene. The Kandahar Formation may correlate largely with the
Middle Limestone unit of the Arouri Limestone, but is also
probably equivalent to parts of the Lower and Upper Marls and
much of the Clarence Valley Marl.
In Hawkes Bay, the Lower Tertiary column resembles that of south
west Marlborough, in that it consists of a srnectite-mudstone
unit (Wanstead Formation) which is probably on the order of
several hundre.d metres thick (Pettinga, 1980) . Sedimentation
began in the Teurian and probably continued into the Middle-Late
Eocene, similar to the Clarence Valley Marl.
A regional variation in the lithological character of the
smectite-mudstone units is evident. In Marlborough the smectite
mudstones are highly calcareous and contain interbedded limestones,
whereas in Hawkes Bay the Wanstead Formation has low carbonate
contents and interbedded glauconitic sandstones. In the
intervening Wairarapa region, moderate carbonate contents and
both limestone and glauconi tic sandstone. interbedded
lithologies are characteristic. Further discussion on th.e
sedimentology of the. smecti te-mudstones is presented in
Chapter 6.
57
CHAPTER THREE LABORATORY
METHODS
3.1 SAMPLE PREPARATION
Initial sample preparation procedures modified from the methods
of Jackson (1956) and Wells and Smidt (1978) are summarised in
Fig. 3.1 and detailed below. Further preparations specific
58
to certain analytical techniques are given in the next Section 3.2.
3.1.1 Disaggregation
Samples were initially disaggregated using a rock crusher.
Further disaggregation was carried out by:
(1) wet hand grinding of 15 gram subsamples
using a porcelain pestle and mortar, with
continual removal of fine suspended particles,
or (2) dry grinding of 50 gram subsamples in a
tungsten carbide ringmill.
3.1.2 caco 3 Dissolution
Caco3 cement was removed by treatment of disaggregated samples
with a solution of lM sodium acetate and glacial acetic acid
buffered at pH 4, over a water bath for up to an hour.
Hand grind
NaOAc/HAC, pH4
' centrifugi washing
dispersion
' <2µm se aration
cation saturation I
(l)centrifuging
freeze dry
~ ~
Figure 3.1: Preliminary Sample Preparation Methods
Whole Rock
Crush
(2) shaking
• freeze dry
~ ~
wet sieve <63µm
oven dry 4l Cation Exchange
AA
Ringmill
(1)3 min. (2)5 sec.
' NaOAc/HAC, pH4
J wet sieve
63-250µm
J oven dry
40°c
' Optical Microscopy
3.l.3 Centrifuge Washing
Samples were washed after acid treatment by centrifuging at
l500 r.p.m. for several minutes, decanting the clear supernatant
liquid and re-suspending in distilled water. This procedure was
repeated 3 times or until the sample dispersed.
3.l.4 Chemical Dispersion
Many samples remained flocculated after repeated washing and
were dispersed by the addition of 0.5 g/£ of sodium hexameta
phosphate (calgon) .
3.l.5 Clay Size Separation
60
Clay-sized particles are defined as having an equivalent spherical
diameter of <2µm. Equivalent spherical diameter refers to the
diameter of a sphere of specific gravity 2.65 which has the same
settling velocity as a particle under the same conditions.
Size separation was carried out on 100 mt dispersed sample
suspensions using a six-head Multex MSE centrifuge. For the
sedimentation of 2µm-sized particles, the centrifuging time at
various speeds was calculated from Stokes Law. After
centrifuging, the supernatant liquid containing the <2µm fraction
was decanted off. Further repeated separations to achieve a
complete clay size fractionation were not done routinely, since
a grain-size analysis was not the purpose of the separation and
x-ray diffraction results were not significantly altered.
3.1.6 Cation Saturation
The <2µm fractions of the samples were saturated with various
cations - Mg2+, ca2+, K+, Na+ or Li+, generally using lM
solutions of the chloride salts. Two methods were used:
(1) samples were saturated by centrifuging
twice with the cation solution.
(2) samples were saturated by reciprocal
shaking three times in the cation solution
for 5 minutes followed by centrifuging.
The second more rigorous method ensured complete cation exchange
and saturation. After saturation, samples were then washed by
centrifuging until dispersion occurred.
3.2 ANALYTICAL TECHNIQUES
3.2.1 X-Ray Diffraction
61
X-ray diffraction was the primary method used for phase analysis
of the mudstones. Broad mineral types and particular clay mineral
species were identified using various sample pretreatments in
conjunction with XRD analysis.
The majority of the XRD analyses were made on the <2µm fractions of
the mudstones, since the main purpose was to study the smectite
clay minerals in detail (cf. Towe, 1974). Further separation of
some samples into the size fractions <0.5µm, 0.5-1.0µm, 1.0-2.0µm,
2.0-4.0µm and 4.0-8.0µm, were made to determine mineralogy-size
relationships.
To aid mineral identification, all sample <2µm fractions were
saturated with Mg2+, K+ and Li+ and particular samples were also
boiled in lM HCl for 10 minutes.
62
XRD analyses were generally carried out on oriented mounts, where
the natural preferred orientation of platy crystals enhances the
reflections from basal 00,Q, planes. The clay fraction suspensions
were dropped onto glass slides and dried under a heat lamp.
The drying time of approximately 15 minutes minimised differential
size settling and the development of mineralogical layering
(Gibbs, l965). Some unoriented mounts to check for non-basal
reflections were made by packing an aluminium holder with clay
powder.
Following slide preparation, two further treatments of the samples
were necessary for positive mineral identification:
(1) Saturation with an organic liquid - either
glycerol or ethylene glycol. For glycerol
saturation, a solution of 10% glycerol in
water was sprayed onto the prepared slides
using an atomiser. In the case of ethylene
glycol saturation, the slides were left
overnight in a closed container over the
liquid.
(2) Heating - slides were placed in a muffle
furnace preheated to the required temperature.
For the purposes of quantitative XRD analysis, <2µm suspensions
comprising varying weight proportions of mineral standards were
prepared to approximate the compositions of the samples. Oriented
glycerol-saturated slides of the standard mixtures were then made
and x-rayed.
63
Analysis was done on a Philips PW 1050 x-ray diffractometer
using nickel-filtered Cu Ka radiation. The tube was run at
34 kV and 34 mA with the divergence slit set at 1°, the receiving
slit at 0.2 mm and the anti-scatter slit at 1°. An oriented
<2µm glycerol-saturated slide for each sample was scanned from
2° 2 6 to 40° 2 e at a speed of 1 ° 2 6/minute. Other pretreated
slides were scanned at the same speed over angles corresponding
to the peaks of interest.
3.2.2 Differential Thermal and Gravimetric Analysis
Differential thermal analysis (DTA) and thermal gravimetric
analysis (TGA) provided supplementary clay mineralogical
information to that obtained from XRD.
2+ + Samples for DTA and TGA consisted of Mg or Na -saturated
<2µm powders. Approximately 80 milligrams of sample was packed
into one of a pair of platinum crucibles. The other crucible
contained calcinated kaolinite as an inert reference material.
The thermal and gravimetric analyses were done simultaneously on
a Stanton Redcroft STA 780 machine. Samples were heated from
20°c to 1200°c at a rate of 10°/minute, in a nitrogen atmosphere.
3.2.3 Scanning Electron Microscopy
The morphology of clay mineral particles and the fabric of selected
mudstones were examined with a Cambridge 250 Stereoscan MK.2
scanning electron microscope (operated by Mrs K. Card, Botany
Department, University of Canterbury).
64
Two types of sample were prepared:
(1) dilute suspensions were dropped onto glass cover
slips mounted on stubs with double-sided sellotape.
(2) chips of mudstone were mounted on stubs using
copper print.
Before examination, the dried sample stubs were coated with SOµm
of gold in a Polaron diode splutterer.
3.2.4 Optical Microscopy
The mineralogy of 63-250µm sand fractions separated from the
mudstones was determined by optical microscopy using refractive
index oils.
The heavy and light minerals in each sand sample were separated in
tetrabromoethane liquid (S.G. ::= 2.89). A 10 gram subsample was
stirred thoroughly several times in TBE contained in a separating
funnel. After 10 minutes separation time, the heavy mineral
fraction was separated off and then the light fraction allowed to
drain through. Each. fraction was collected in filter paper,
washed with acetone and dried prior to optical examination.
3.2.5 X-Ray Fluorescence
Most of the chemical analyses of the mudstones were done by x-ray
fluorescence on a Philips PW 1400 automatic spectrometer, using
calibrations erected by Mr A. Alloway, Geology Department.
2+ Major element analyses were done on Ca -saturated <2µm samples
made into fusion beads according to the methods of Norrish and
Hutton (1969). Fusion beads of similarly pretreated API standard
clay minerals and some untreated samples were also prepared.
Analyses were carried out with a Cr tube operating at 50 kV and
50 mA. Iterative mass absorption corrections were performed
using an online HP9835B computer following the methods of Norrish
and Hutton (19691.
For the analysis of trace elements, whole-rock powder samples
were mixed with a few drops of polyvinylalcohol binder (Mowiol)
and pressed into 52 mm pellets. The elements Rb, Sr, Y, Pb, Th,
Ga were determined using a Mo tube operating at 95 kV and 25 mA
and Zr and Nb were determined using an Au tube operating at 75 kV
and 40 mA. Corrections for mass absorption variations were
applied for all trace element determinations.
3.2.6 Cation Exchange and Atomic Absorption
Exchangeable cations and exchange capacities of the mudstones
65
were determined with a leaching procedure followed by atomic
absorption analysis of the leachates. The procedure is summarised
in Fig. 3.2 and detailed below.
Cation exchange was carried out on 1 gram samples of chemically
untreated <63µm fractions. The samples were mixed with 20 grams
of acid-washed silica sand to facilitate leaching. The calcareous
nature of the mudstones precluded the usual method of leaching
first with lM ammonium acetate, since caco 3 in quantities >1% is
not extracted quantitatively (Blakemore et al, 1977). Complete
dissolution of caco 3 was achieved using an initial leaching
solution of 0.5M HCl. The sample/sand mixes were reacted with the
HCl in flasks before transferring to leaching columns, so that air
locks did not form in the columns. A 230 mi volume of HCl was then
passed through each column. A second leaching to saturate the
samples with Na+ was carried out with 230 mi volumes of lM sodium
lg sample + 20g silica sand
1st leaching O.SM HCl
'' H+ saturated
carbonate-free sample
i 2nd leaching lM NaOAc pH7
3rd leaching ethanol
1'
Na+ saturated sample
i 4th leaching lM NH40Ac pH7
Figure 3.2:
Collect leachate Analyse for exchangeable cations + ca2+ from caco
3
Collect leachate Analyse for further ca2+
Collect leachate Analyse for total exchangeable Na+
Cation Exchange Leaching Procedure for Calcareous Mudstones
66
acetate pH 7. The remaining sodium acetate in the columns was
removed by passing through 200 mt of ethanol. The samples were
finally leached with 230 mi of ammonium acetate pH 7, to extract
the Na+. All leachate solutions except ethanol were collected in
250 mt flasks and made up to volume.
Atomic absorption analysis of the leachates was done on a Varian-
Techtron Model AA l475 using series of standard solutions for
calibration. The HCl leachates containing exchangeable cations
and ca2+ from caco3 were analysed for the elements listed below
at the stated wavelengths:
Element Wavelength (nm)
Na 589.0
K 766.5
Mg 285.2
Ca 422.7
Fe 248.3
Mn 279.5
Zn 213.9
Ni 232.0
Cu 324.7
Co 240.7
Pb 217.0
Cr 357.9
v 318.5
An air/acetylene flame was used in all cases except for the
analysis of Cr and V which required a nitrous oxide/acetylene
flame. For the analysis of Mg2+ and ca2+, 2 mg/ml of sr2+ was
67
added to the sample and standard solutions to suppress ionisation.
2+ The sodium acetate leachates were checked for any further Ca ,
but concentrations were found to be negligible. The ammonium
+ acetate leachates were analysed for total exchangeable Na at a
wavelength of 589.0 nm.
68
3.2.7 Carbonate Analysis
Sample Caco3 contents were determined using a back titration
method. Approximately 1 gram milled samples were boiled in 25 mi
of lM HCl for several minutes. The excess acid was then titrated
with lM NaOH using phenolphthalein as an indicator of the endpoint.
4.1 INTRODUCTION
CHAPTER FOUR
MINERALOGY
The mineralogy of the smectite-mudstones was studied in two
parts:
Cl) Analysis of clay fraction (<2µm) mineralogy,
with emphasis on smectite clay mineral
species.
(2) Analysis of fine-very fine sand fraction
(250-63 µm) mineralogy, with emphasis on
heavy mineral suites.
4.2 CLAY FRACTION MINERALOGY
69
The mineralogy of <2µm insoluble residues of smectite-mudstone
samples was analysed both qualitatively and quantitatively by
x-ray diffraction. Bulk samples and clay fractions were also
studied by scanning electron microscopy. The clay fraction phases
identified are described in the following sections.
4.2.l Smectite
Smectite is a group name for clay minerals characterised by the
following properties:
(1) A 2:l unit layer structure comprising
a sheet of Al04 (0H) 2 octahedra between two
sheets of Si04 tetrahedra (.Fig. 4.1).
(2) Weak interlayer bonding allowing for
interlayer swelling or contraction. The
spacing from the base of one layer to the
next is variable from 1oi to 20R depending
on the interlayer species present (Fig. 4.1)
Inorganic cations such as Na+, ca2+, Mg2+ and
sheets of water are normally present in the
interlayer position of untreated smectites.
(31 Interparticle swelling from 40~ upwards and
dispersion in liquid which is typically
exhibited by smectites with interlayer Na+.
The second property of variable basal spacing is the basis for
the identification of smectites in XRD analysis.
In the untreated mudstone samples, the smectite basal spacing is
between 12i and 16~. The smectite in the Marlborough mudstones
typically has a sharp basal (001) peak at -ls.Si and the
Wairarapa mudstones exhibit smectite basal peaks between 14R and
15.sR. The Hawkes Bay smectites commonly have a basal spacing of
l2.5-13R or a broad basal peak which ranges over an interval of
12-lSR. Representative.x-ray diffractograms showing these
features are given in Fig. 4.2
70
Interlayer a<
0 S"' 0 ..-c:r, J .5
Si o4 Tetrahedra u r:! 0. v,
} d Alo4
(OH)2
Octnhedra V1
~
} Si O Tetrahedra 4
LEGEND
• Si 4+ 0 N + a, Ci} Mg 2 +
0 Al 3+ ® H2 0
0 o2-
® OH-
Figure 4.l: Layer structure of smectite clay minerals (from Dixon and Weed, 1977).
71
Untreated S mectite 001
0 12·S -15·2A
( il HAWKES BAY MUDS TONE
( HB 14)
( ii) WAJRARAPA MUD STONE ( WO 1)
(iii l MARLBOROUGH MUD STONE ( W9)
10
Illite 001a 10 A
6
DEGREES 2 g..,
14.7 A
4 2
Figure 4.2: X-ray diffractograms showing the basal peaks of smectites in three untreated mudstone samples.
72
The basal spacings of the untreated smectites indicate the nature
of the interlayer cations and their degree of hydration. At
normal humidities, a spacing of -12.si corresponds to interlayer
Na+ with a single-sheet hydration complex and a spacing of -ls.si
indicates interlayer ca2+ and/or Mg2+ with a double-sheet
73
hydration complex (.e.g. Brindley and Brown, 1980). The Marlborough
mudstones therefore contain dominantly ca2+/Mg2+-smectite, as
expected from their calcareous nature and association with lime-
stone. The Wairarapa smectites also have interlayer ca2+ and/or
Mg2+ with possibly small amounts of Na+ and the Hawkes Bay
smectites contain significant interlayer Na+. Quantitative
analyses of exchangeable cations are presented in Chapter 5.
Treatment of clay samples with organic liquids is the most
commonly used XRD identification technique for smectites and
results in expansion of the basal spacing as large organic
molecules enter the interlayer space. In all samples, the
smectite basal peak expanded to 1si with glycerol treatment
(~ig. 4.3}. Distinction between smectite and swelling
vermiculite - which has an untreated basal spacing of -14~ and
also expands with glycerol treatment - was carried out by
2+ saturating one sample in four with Mg prior to glycerol
treatment. Whereas Mg-vermiculite is rendered non-swelling
(.e.g. Brindley and Brown, 1980), the Mg-smectite in the samples
expanded fully to lBi with glycerol treatment.
A second diagnostic property of smectites is collapse of the
layers with heat treatment as interlayer water is volatilised.
Heat treatment at 5So0 c for 1 hour caused irreversible complete
collapse of the smectite basal peak to 1oi in all samples (Fig.4.4)
Glycerol treated Smectite 001
Untreated Smectite 001
e 6
10 l
4
DEGREES 2 tr
2
Figure 4.3: X-ray diffractograms showing expansion of smectite basal peak with glycerol treatment.
Heat treated (550°( tor 1 hr)
Smectite 001 10 A
Heat treated ( 300°( for Ji hrl
Smectite 001
12 10 8 6
DEGREES 2 (}
4 2
Figure 4.4: X-ray diffractograms showing collapse of smectite basal peak with heat treatment.
This result ruled out the possibility of swelling chlorite being
present, as this clay maintains a basal spacing of -14i with
heat treatment.Ce.g. Brindley and Brown, 1980). Heating at Joo0 c
for~ hour also caused collapse of the smectite basal peak to
75
10R, but rehydration occurred rapidly on cooling, producing a
distinctly asymmetric basal peak (Fig. 4.4). Complete collapse of
the smectites at 300°c indicates that interlayer Mg2+ or Al3+
are not present in appreciable amounts. Both these cations form
relatively stable hydroxyl-water complexes which are not
volatilised at 30o0
c and inhibit collapse of the layers
(Schultz, 1969) .
The smectite clay in all the x-rayed mudstone samples appears
well-crystallised. The expanded 18g basal peak is
characteristically sharp and the crystallinity index of Biscaye
(1965), which is the ratio of the depth of the low angle valley
and the peak height, is typically high. The higher order OOt
peaks are also commonly well developed. An x-ray diffractogram
showing these features is given in Fig. 4.5.
4.2.2 Illite
Illite is present in all the mudstone samples analysed by XRD.
The term illite has a confused usage in the literature, but was
originally defined as a general term for the clay mineral
constituents of argillaceous sediments belonging to the mica
group (Grim et al., 1937) . This definition is followed here
and the illite in the mudstones has a basal peak at 10R which is
broad in comparison to a 10~ peak of a well-crystallised mica
(see Fig. 4.5). Illite has the same 2:1 unit layer structure as
smectites but does not show interlayer swelling/collapse behaviour,
as non-hydrated K+ cations are "fixed" in the interlayer position.
0 0 3·6 A
3 A Smectite Smectite 005 006
32 30 28 26 24 22
0 4 ·5 A Smectite 5 ~ 004 lllite
002
20 16
Crystallini ty Index
valley depth "',_,1
.0
peak height
0 6 A Smectite 003
16 14 12
DEGREES 2 g,
0 9 A
0
18 A Smee tite 001
Smectite 002 0
10 A llite 001
10 8 6
Figure 4.5: X-ray diffractogram of the glycerol treated clay fraction of a srnectite-rnudstone showing the high crystallinity of the smectite clay.
4 2
77
The basal lO~ peak of illite in the mudstone sa.~ples diagnostically
remains unaffected by cation saturations, glycerol treatment and
heat treatments.
The presence of illite in addition to smectite was noted by
Gordon et al. (.1955) and Ritchie (1962) in samples from the
Porangahau quarry. Gordon et al. (1955) suggested that there is
considerable interstratification between smectite and illite due
to "broad bands about l0~11
(p. 138}. From this study however, it
is evident that the smectite and illite in all of the mudstone
samples are discrete phases with no detectable interstratification,
either random or regular, between them. Both smectite and illite
behave as pure species with_,glycerol and heat treatments and
rational series of basal reflections are shown by both minerals,
unlike randomly interstratified clays. The smectite plus illite
peaks do not form a rational series consistent with regular
interstratification and superorder peaks are lacking.
4.2.3 Kaolinite and Chlorite
A number of samples contain a clay mineral with a peak at 7~.
This clay is a very minor component in the majority of samples,
but is present in significant amounts (Fig. 4.6) in five of the
Wairarapa samples (WAS, W02, WPl, WP6, WP7). One sample (W02)
is from the Pukemuri Siltstone and of the remaining four
Kandahar Formation samples, three were collected near the contact
with the Pukemuri Siltstone (WAS, WP6, WP7).
A 7~ clay peak can be attributed to the 001 reflection of
kaolinite and/or the 002 reflection of chlorite. Commonly the
0 001 chlorite peak at l4A is very low in intensity and can also be
masked by other clay peaks. Two treatments were used to positively
identify the 7~ clay (e.g. Thorez, 1976):
16
Kaolinite- 001 0
7 A
_) 14 12
flt ite 001 o'
10 A
10 8
DEGREES 2 9-
6
Glycerol treated Smectite 001
0 1S A
4
Figure 4.6: X-ray diffractogram of the glycerol treated clay fraction of a sample from the Kandahar Formation, showing a major kaolinite component.
78
2
(1) Boiling th.e sample in l0% HCl for 5-10
minutes, which generally breaks down the
structure of chlorite but not kaolinite.
(2) Heating the sample at sso0 c for 1 hour,
which generally breaks down the structure
of kaolinite but not chlorite.
79
The 7R peak in the x-ray diffractograms of the Wairarapa mudstones
resisted acid treatment but was destroyed with heating, indicating
that kaolinite is the clay present. Apart from the Wairarapa
samples, one other sample from Marlborough (U4) was found to
contain a 7~ peak large enough to show the effects of the
treatments. The peak was destroyed by acid treatment but
resisted heat treatment, indicating the presence of chlorite.
4.2.4 Non-Clay Minerals
Common non-clay minerals in the clay fraction of the mudstones are
calcite and quartz. Calcite was analysed chemically in bulk
samples (Appendix IIl) and removed from th·e samples by acid
dissolution before clay size separation and XRD analysis.
Quartz is present in the majority of samples and readily
identifiable by sharp peaks at 4.26i and 3.34i. No other forms
of silica such as opal or cristobalite are evident in the x-ray
diffractograms.
Three samples from the Middle Clarence Valley (SS, L4, L14)
contain a minor amount of a mineral with a sharp 9.oR peak, which
is probably a zeolite.
4.2.5 Quantitative XRD Results
The majority of the clay fractions of the mudstones are three
component mixtures of smectite, illite and quartz. This simple
mineralogy allowed for quantitative XRD analysis by preparation
80
of a set of smectite-illite-quartz mixtures as external standards
(Table 4.l). This method is useful in making quick but reasonably
reliable estimates of the proportions of major components in clay
materials (Brindley and Brown, 1980). Due to the chemical and
structural variability of clay minerals, the major problem in any
quantitative XRD analysis of clays is the choice of suitable
standards. In this study, API No. 26 Clay Spur Bentonite and
No. 35 Illite (Kerr and Hamilton, 1949) were used as smectite and
illite standards after thorough determination of their purity and
properites by XRD analysis. The standard mixtures were prepared by
mixing in suspension various weight proportions of <2µm fractions
of smectite, illite and quartz. Two oriented gylcerol-treated
mounts were made to check reproducibility and the x-ray diffracto
grams compared with those of oriented glycerol-treated mounts of
<2µm fractions of the mudstones. Fig. 4.7 shows representative
x-ray diffractograms of standard mixtures.
For the determination of quartz, the area of the 3.34i peak in the
standard mixtures was measured and plotted against weight% quartz
3 to give straight-line calibration curves for XRD scales of 4 x 10
and 1 x 104 (Fig. 4.8). The 3.34i peak was chosen, even though
there is some interference with the illite 003 peak at 3.35i, since
the other main quartz peak at 4.26~ is commonly too small to
measure accurately in the x-ray diffractograms of the mudstones.
The choice of parameters to measure for the calibrations of
smectite and illite proved more difficult. The expanded basal
peak of the smectite in the standard mixtures was found to be too
81
variable in intensity and area to provide a useful calibration
curve. Accurate measurement of the smectite basal peak area is
hindered by the difficulty of estimating the background intensity
at low 2 8 angles.
Table 4.1: XRD Standard Mixture Compositions
Mixture Weight% Weight% Weight% Smectite Illite Quartz
1 80 10 10
2 65 35 0
3 60 40 0
4* 60 35 5
5 60 25 15
6 55 40 5
7 55 35 10
8 55 30 15
9* 50 40 10
10 50 30 20
11 50 20 30
12 45 45 10
13 40 45 15
14* 35 50 15
*X-ray diffractogram given in Fig. 4.7
The area of the illite basal peak was also difficult to measure
accurately due to broadness and was not found to be a sensitive
indicator of illite quantity.
The best calibration parameter for smectite and illite was
determined to be the ratio of the illite 001 peak intensity to the
srnectite 002 peak intensity. This ratio was plotted against the
ratio of weight% illite to weight% srnectite in the standard
mixtures, giving a straight-line calibration curve (Fig. 4.9).
STANDARD 4
STANDARD 9
STANDARD 14
Quartz 10'T
0
3·3 A
_A_/
I
I 28 26/
Glycerol treated Smectite 001 10 A
Smectite 002
10
DEGREES
a 6
2 9--
4 2
Figure 4.7: X-ray diffractograms of three prepared smectite-illitequartz mixtures for use as external standards.
82
240
220
200
~ 180 e :: 160 d
~ 140 o< ~ 120 "' N 100 .... ... c::I
6, 80
a f 60 <
40
20
0
/• v
J
I/ v v
'
~ V•
<::i
·~ ~
'JI.~
( I/ • )/
·v ~ ~ I ~ ' /
.v ,,.v ~ J v v I /
lj, v :,
o 246amn~~~~n~~~~~ % Quartz
Figure 4.8: Calibration curves for determination of% quartz from XRD analysis.
1·6
_ 1·4 N
81-2
~ 0·4 :.::: .... ....
0·2
v /
l7 /
L7 y
/ v I I
/ v '
_/ v.
I/ v
0 0·2 0·4 0·6 0·8 1-0 1·2 1 ·4 1·6
% Illite I% Smectite
Figure 4.9: Calibration curve for determination of% smectite and% illite from XRD analysis.
83
For the mudstone samples, proportions of smectite and illite were
calculated using determined values for% quartz and the ratio (R)
of% illite/% smectite:
100- % Quartz % Smectite = R + 1
R (100- % Quartz) % Illite = R + 1
Quantitative analysis was carried out only on the clay fractions
of the mudstones, as the clay mineralogy was of primary interest.
Selected samples however were separated into size fractions of
<0.5 µm, 0.5-1.0 µm, 1.0-2.0 µm, 2.0-4.0 µm and 4.0-8.0 µm and
the x-ray diffractograrns compared. All samples showed a trend of
relative decrease in smectite component with increasing size
(.Fig. 4.10), indicating the small size of smectite particles.
The proportions of other non-smectite components increase with
increasing size and the presence of mica is indicated in >2 µm
size fractions from the sharpness of the 1oi peak (Fig. 4.10).
84
The quantitative results for the mudstone clay fractions are given
in Table 4.2. Minerals other than smectite, illite and quartz are
present in some samples in very minor amounts and are listed.
Quantitative analysis was not attempted for those samples which
contain appreciable amounts of other minerals, such as the
kaolinite-bearing samples from Wairarapa (see Section 4.2.3)
The clay fractions of the mudstones are remarkably uniform in
composition. Smectite proportions range from 33% to 66% with an
average of 51% and only four samples have a smectite content of
<40%. Illite proportions range from 28% to 57% with an average
of 41% and quartz proportions range from 0% to 19% with an average
of 8 2, 0. No distinct correlations of clay fraction composition with
stratigraphy are apparent.
S mectite 001
0·5.4tm -1·0 ,'(. m FRACTION
Illite OOi
<2-"m FRACTION
2 M-m - 4,,c,t. m FRACTION
10 8 6 4 2
DEGREES 2 8--1
Figure 4.10.: X-ray diffractograms showing the relationship between size fraction and clay mineralogy in the smectite-mudstones.
85
Table 4.2: Results of Quantitative XRD Analysis of Smectite-Mudstone Clay Fractions
Unit
'
Stratigraphic Sample
% % % Other
I Position Smectite Illite Quartz
I i W3 39 42 19
Base W4 46 42 12
C3 54 38 8
Ul6 33 57 10
Lower Marl, W6 43 41 16 ?Chlorite
Amuri Middle W7 46 40 14 Limestone
C7 59 30 ll
W8 44 40 16
Top W9 50 44 6
C9 61 28 11
Ull 51 37 12 ?Chlorite
WlO 51 39 10
Base U4 47 43 10 Chlorite
Upper Marl, us 35 53 12
Amuri Middle Wl3 53 34 13
Limestone U9 48 48 4
Top Wl4 47 35 18
Cll 58 34 8
Ll4 56 40 4 Zeolite
Marl Base SS
(Clarence 51 49 0 Zeolite
Valley), 812 63 37 0 Amuri Limestone Middle S2 64 36 0
SB 66 34 0
Kandahar Base WOl 47 48 5 Kaolinite
Formation Top ( ?) WAl 41 45 14 Kaolinite
Mungaroa (?) W04 48 43 9
Limestone
HB6 35 51 14
Base HB14 58 39 3
Wanstead HB15 57 40 3
Formation ( ?) HBl 60 37 3
I Middle (?) HB3 54 41 5
(?) HB17 60 40 0
HB21 61 39 0
86
On a regional basis however, the Marl unit in the Clarence
Valley and the Wanstead Formation in Hawkes Bay are characterised
by an absence or low proportion of clay-sized quartz and often a
high proportion (>60%) of smectite.
4.2.6 Scanning Electron Microscopy
The morphology of clay particles and the fabric of selected mud
stone samples were studied by scanning electron microscopy.
The fracture surfaces of three mudstone chip samples from
Marlborough, Wairarapa and Hawkes Bay are shown in Figs 4.11, 4.12
and 4.13 respectively. The calcite-cemented mudstones from
Marlborough exhibit an interlocking texture of calcite plates
87
(Fig. 4.11). The Wairarapa mudstones are generally less calcareous
and consist largely of thin aggregate sheets of clay particles
(Fig. 4.l2l. The uncemented and sheared mudstones from Hawkes Bay
characteristically show development of a fissile fabric composed
of thin crumpled sheets of clay flakes (Fig. 4.13). A sample from
the melange at Waimarama Beach, Hawkes Bay with a striated shear
surface of sheets of oriented clay flakes is shown in Fig. 4.14.
Dried dilute suspensions of clay fractions of two mudstone samples
are shown in Figs 4.15 and 4.16. The smectite clay particles
are characteristically small thin flakes with irregular
outlines and curled edges which have dried in aggregates. Larger
single particles in the samples, such as that in the centre of
Fig. 4.16, are possibly flakes of illite.
Figure 4.11: Scanning electron micrograph of a fracture surface of mudstone from Marlborough (Upper Marl). A coccolith can be seen at right of centre.
Figure 4.12: Scanning electron micrograph of a fracture surface of mudstone from Wairarapa (Kandahar Formation).
88
Figure 4.13: Scanning electron micrograph of a fracture surface of mudstone from Hawkes Bay (Wanstead Formation).
Figure 4.14: Scanning electron micrograph of a striated shear surface of mudstone from the matrix of the melange at Waimarama Beach.
89
Figures 4.15, 4.16: Scanning electron rnicrographs of clay particles dried from dilute suspensions of two mudstone clay fractions.
90
91
4.3 SMECTITE MINERALOGY
The smectite group of clays is subdivided into dioctahedral and
trioctahedral subgroups according to the ideal number of
octahedrally co-ordinated cations per half unit cell.
Dioctahedral smectites have two out of three of octahedral sites
filled with dominantly trivalent cations and trioctahedral
smectites have all octahedral sites filled with dominantly divalent
cations. Individual species within these subgroups are defined
chemically. Table 4.3 lists the most important smectite species
and their formulas.
The distinction between dioctahedral and trioctahedral smectites
is often uncertain using phase analysis techniques only. In this
study two XRD techniques were used and the results verified by
chemical analysis (_Chapter 5) .
Table 4.3: Classification of Smectites (after Brindley and Brown, 1980)
Subgroup Species Ideal Formula
DI OCTAHEDRAL Beidellite
Nontronite
Saponite o,/ nH 0) (Mg3
(Al,Fe) ) (Si4
Al )o10
(0H)2 x-y 2 -y y -x x TRI OCTAHEDRAL
Hectorite (M+ nH20) (Mg3 Li )Si4o10
(0H) 2 y -y y
The first method of distinguishing the smectite subgroups
utilises the 06/33 hk diffraction band which has ad-spacing of
-l.50~ for dioctahedral smectites and l.52-l.53R for
trioctahedral smectites (e.g. Brindley and Brown, 1980). Random
powder mounts of selected mudstone samples were made and the peak
scanned at slow speed. The peak was found to be at 1.soR,
indicating a dioctahedral smectite type. The second method uses
the resistance of dioctahedral smectites to treatment with
92
inorganic acids relative to trioctahedral smectites which generally
break down leaving a residue of amorphous silica (Brindley and
Brown, 1980). Selected samples were boiled in 10% HCl for 10
minutes and x-rayed. The smectite basal peak in all samples did
not show any significant structural breakdown, suggesting again a
dioctahedral type of smectite.
As outlined in Table 4.3, there are three important dioctahedral
smectite species. The formulas given are for ideal end-member
compositions, but intermediate compositions are common.
Montmorillonite is the most widely occurring species and is
2+ 3+ characterised by substitution of Mg for Al in the octahedral
sheet. This substitution creates a net negative layer charge
which is balanced by exchangeable interlayer cations. Beidellite
is an aluminous smectite in which the negative charge arises in
the tetrahedral sheet due to substitution of Al3+ for si4+
Nontronite is the third important dioctahedral species and has
substitution of Fe 3+ for Al3+ in the octahedral sheet. This
substitution does not create a charge imbalance and the negative
charge of nontronite originates in the tetrahedral sheet due to
Al3+ substitution of Si4+, as for beidellite.
Further to the classification of dioctahedral smectites into
species, numerous sub-species, particularly of montmorillonite,
have been recognised (e.g. Schultz, 1969).
93
Determination of smectite species and sub-species can be achieved
by phase analysis techniques as well as by chemical analysis. Two
XRD techniques and DTA/TGA were used to characterise the detailed
smectite mineralogy of the mudstones. The methods and results
are described in the following sections.
4.3.1 Li+-saturation (Greene-Kelly) Test
A technique of sample treatments and XRD analysis was developed by
Greene-Kelly (19531 to distinguish montmorillonite from the other
dioctahedral smectites beidellite and nontronite. The technique
involves saturation with Li+ (using 3M LiCl), followed by heating
at 250°c overnight and then saturation with glycerol. The
treatment was carried out on acid-insoluble clay fractions of the
mudstones. After saturation with Li+, the samples were mounted on
silica glass slides as anomalous results may be obtained with
ordinary glass slides (Brindley and Brown, 1980). XRD analysis
was carried out both after heat treatment and after glycerol
treatment.
The Li+-saturation test is based on the difference in site of
the layer charge in montmorillonite and beidellite/nontronite.
Heating of a Li+-smectite volatilises the interlayer water causing
collapse of the basal spacing to 10~. The interlayer Li+ ions,
unlike other cations, are then small enough to enter the smectite
structure and do so in the octahedral sheet where there are vacant
sites in dioctahedral smectites. If the smectite is a
rnontmorillonite with the layer charge originating in the
94
octahedral sheet, the charge will be neutralised by the
Li+ ions. The uncharged layers are then rendered non-expanding
and remain at a collapsed 1oi thickness when treated with
glycerol. If however the smectite is a beidellite or a nontronite,
the Li+ in the octahedral sheet will not neutralise the layer
charge, which for these two smectites originates in the
tetrahedral sheet. Treatment with glycerol th~n re-expands the
collapsed layers of a beidellite or nontronite to 1si.
The smectite-mudstone samples on which the Li+-saturation test
was carried out gave a range of results. A common result was the
presence of both a collapsed 1oi peak and an expanded 1si peak
after glycerol treatment, indicating smectite species which are
intermediate between pure montmorillonite and pure beidellite/
nontronite. The smectites however are not compositionally
homogeneous Call layers the same) because the Li+-saturation test
would result in partial expansion of all layers to give one peak
intermediate between 10~ and 1si. Rather, the presence of two
0 0 peaks at lOA and l8A reflects a compositional inhomogeneity in
the smectites, with some layers being non-expanding
(montmorillonite) and some being expanding (beidellite/nontronite)
The proportions of non-expanding and expanding layers can be
estimated by comparing x-ray diffractograms of a sample after heat
treatment and after glycerol treatment. Normally, the shift in
position of higher order 00£ reflections is used to determine the
proportions of expanding and non-expanding layers (Greene-Kelly,
1953; Schultz, 1969, 1978). However, reflections from significant
quantities of illite in the mudstone samples interfered with the
higher order smectite peaks. The method used in this study is
based on the smectite 001 peak and is detailed by Schultz (1969)
95
Although the results are semi-quantitative, impure clay samples
can be studied.
If the smectite is close to a pure montmorillonite in
composition, there is no change in the collapsed 001 peak at 10R
with glycerol treatment. As the proportion of expandable layers
increases from 0% to -35%, the 001 peak of the glycerol treated
smectite remains at 1oi but broadens and decreases in intensity.
The baseline may also rise in the 1si - 20R region. At about
40-50% content of expandable layers, a broad peak develops at
-18~. With further increasing proportions of expandable layers,
the 18~ peak increases in intensity and pure beidellite or
nontronite show 100% expansion to a sharp 1si peak similar in
intensity to that in a normal diffractogram of glycerol treated
smectite.
The results of the Li+-saturation test for the smectites in the
mudstones are given in Table 4.4. The proportions are probably
accurate to 10% (Schultz, 1969) and ranges are quoted for some
samples. The test was repeated for six samples with comparable
results obtained except for sample W9. The cause of this
discrepancy is uncertain, but may reflect inhomogeneity within the
bulk mudstone sample. Representative x-ray diffractograms
illustrating the features described in the above paragraph are
presented in Fig. 4.17.
The proportions of expanding layers in the smectites range from
0-10% to 50-60%. Those smectites estimated to have 0-10%
0 expanding layers due to little change in the collapsed lOA peak
are classified as montmorillonites. The remainder of the
smectites are interstratified montmorillonite-beidellite/nontronite
Table 4.4: Results of Li+-Saturation Test for Smectite in Mudstone Clay Fractions
Stratigraphic Sample
% Expanding Unit Position Layers
W3 10
W4 10-20
Base C3 0-10
Ul6 20-30
Lower Marl, W6 45, 40
Arouri Limestone Middle W7 40
C7 0-10
W8 40
W9 10, 40 Top * C9 0-10
Ull 40
WlO 0-10
U4 35-40 Base * us 20-30
Upper Marl,
Arouri Limestone Wl3 35
Middle (?) ClS 20-30
* U9 40
Top Wl4 50-60
Cll 20-30
Ll4 40
SS 20-30 Base
Sl2 10-20
Marl (Clarence Valley), Bl 50-60
Arouri Limestone (?) Ll 40
Middle (?) L4 40
S2 0-10
SS 35, 30-40
(Continued overleaf)
96
'
Table 4.4 Results of Li+-saturation Test for Smectite in .Mud~tone 'clay Fractions (Continued)
Unit Stratigraphic
Sample % Expanding
Position Layers
Base WOl 50
WAS 35-40
Kandahar Formation Middle (?) WPl 10-20
Top (?) WAl 40
Mungaroa Limestone (?) *wo4 50
HB6 20-30,10-20
Base HB9 0-10 Wanstead Formation
HB14 0-10, 0-10
HB15 0-10
(?) HBl 0-10
Middle (?) HB3 35 I 40
( ?) HB17 0-10
HB21 0-10
Top HB18 10-20 Whangai Formation
HB20 10-20
East Cape 20-30
Paoanui 20-30
Red Mangamauku 45 Smectite-Mudstones Stream
Gilray 50 Bay
(?) Uncertain stratigraphic position
* X-ray diffractograms given in Fig. 4.17
97
I
(ii) u+; 250°(/GL
SAMPLE C9 0·10% EXPANDING LAYERS
0
10 A
No Change
12t==i==1ot:::=t:=s:t==:t==6:r.::=::t:=4==:c=2 DEGREES 2 8"
!il u+; 2so 0 c
12 10 s
SAMPLE US 20-30% EXPANDING LAYERS
6 4
DEGREES 2 6'
Figure 4.17: X-ray diffractograms showing the range in smectite basal peaks after the Li+-saturation test.
2
\..0 OJ
12 10 8
SAMPLE U9 ""40 °/o EXPANDING LAYERS
6 4
DEGREES 2 fr
Figure 4.17: continued
2
Ii l u+; 250° c
12 10 8
SAMPLE W04 rJ 50% EXPANDING LAYERS
0
16 A
6 4
DEGREES 28-"
2
100
species which show intermediate behaviour. The majority of these
smectites contain a dominant component of non-expanding
montmorillonite layers.
The variability in the smectite mineralogy of the mudstones does
not appear to correlate well with stratigraphy, although the
Lower Marl and particularly the Wanstead Formation are
characterised by mbntmorillonite. The red smectite-mudstones from
Hawkes Bay and East Cape typically contain interstratified smectite
in contrast to the green mudstones of the Wanstead Formation.
4.3.2 K+-Saturation Tests
Treatment of smectite clays with K+ is a technique which commonly
shows up structural variability in dioctahedral smectites. In a
large number of studies in the literature, a range of basal
spacings for K+-smectites has been reported and is generally
believed to be a result of variability in layer charge (Machajdik
and Cicel, 1981). There is some contention however as to whether
the controlling factor is the site of the layer charge
Ce.g. Weaver, 1958) or the total amount of layer charge
(B.g. Schultz, 1969).
Weaver (l958) suggested that smectites with their layer charge
originating dominantly in the tetrahedral sheet near the interlayer
cations will fix interlayer K+ ions and develop a mica-like
structure. The result of K+-fixation is collapse of the smectite
b l . l O asa spacing to OA. Conversely those smectites with their
layer charge in the octahedral sheet away from the interlayer
cations will not collapse when K+-saturated. Interstratified
smectites should show both types of behaviour.
Differences in the site of smectite layer charge was also
the basis for the Li+-saturation test described in the
previous section and the results of K+-saturation should
corroborate those of Li+-saturation.
Schultz (1969)_ studied the re-expandability of K+-smectites
after heating and treatment with ethylene glycol. It was found
that smecti tes with. low overall layer charge remained fully
expandable whereas high-charge smectites did not re-expand fully.
The K+-saturation test method used in this study is given by
Schultz (_1969) and involved saturation of acid-insoluble clay
fraction samples with K+ (using lM KCl), followed by heat treat-
ment at 300°c for~ hour, then saturation with ethylene glycol
and XRD analysis. Weaver (1958) treated samples with lM KOH for
15 hours followed by XRD analysis. This method was incorporated
into the test since it was found from a preliminary study of
K+-saturation of the mudstones that 15 hours soaking in lM KOH
produced the same results as centrifuging with lM KCl.
Table 4.5 lists the basal spacings for the smectites in the mud
stone samples after K+-saturation and K+/300°c/ethylene glycol
treatment. Representative x-ray diffractograms are shown in
Figs 4.18 and 4.19.
The basal spacings of all the K+-smectites lie in the range
ll.5~ - 12.si, indicating no significant K+-fixation. The
0 presence of the 001 illite peak at lOA makes it difficult to
determine if any smectite layers have collapsed and the intensity
of the lO~ peak is also affected by it's position on the shoulder
101
of the uncollapsed basal smectite peak (Fig. 4.18). If any of the
Table 4.5: Results of K+-s.aturation Tests for Smectite in-Mudstone Clay Fractions
Unit Stratigraphic Sample
K+ K+/300°C/E.G. Position 001~ 001~
W3 12.5 17 ( +)
Base * W4 11.5 17 (-)
C3 12.l 17 (+)
Ul6 12.5 14.5
Lower Marl, W6 12.5 15 Arouri Limestone Middle W7 12.4 17 (+)
C7 12.1 17 ( +)
ws 12.5 17 (-)
Top W9 11.6 16
C9 12.2 17 ( +)
Ull 12.5 15
WlO 12.0 17 ( +)
Base * U4 12.5 l6
us 12.5 16
Upper Marl, Wl3 12.5 17(-)
Arouri Limestone Middle (?) Cl5 12.5 17 (+)
09 12.5 15
Top *Wl4 12.3 17 (-)
Cll 12.5 16.5
Ll4 12.5 16.5
Base SS 12.3 17(+)
Marl (Clarence Sl2 12.l 17 (+)
Valley), Arouri Bl 12.5 14
Limestone ( ?) Ll 12.4 17 (-)
Middle (?) L4 12.3 16.5
S2 12.l 17 (+)
SS 12.1 17(+)
(Continued overleaf)
102
Table 4.5: Results of K+-saturation Tests for Smectite in Mudstone Clay Fractions (Continued)
Unit Stratigraphic
Sample K+ K+/300°C/E.G.
Position 001i 001~.
Base WOl 12.3 17 (+)
* WAS 12.5 15
Kandahar Formation
Middle (?) WPl 12.0 16
Top (_?} WAl 12.1 17 (-)
Mungaroa Limestone ( ?) W04 12.3 14.5
HB6 12.3 16.5
HB9 11.8 17 ( +) Wanstead Formation Base
HB14 11.8 17 (+)
HB15 12.0 17 (+)
(?) HBl 12.0 17 ( +)
Middle (?) HB3 12.0 17 ( +)
(?) *HBl 7 11.5 17 (+)
HB21 11.8 17 ( +)
Whangai Formation Top HB18 11.6 17(-)
HB20 12.0 17 (+)
East Cape 11.6 17 (-)
Paoanui 12.5 17(-)
Red Mangamauku 12.l 14.5 Smectite-Mudstones Stream
Gilray 12.4 16 Bay
(?) Uncertain stratigraphic position
* X-ray diffractogram given in Figs 4.18 or 4.19
103
r
S mectite 001
SAMPLE U4 K•- Treated
lllite 001
SAMPLE W4 K+- Treated
10 e
0 12·5 A
6 4 2
DEGREES 2 &-
Figure 4.18: X-ray diffractograms showing the range in smectite basal peaks after K+-saturation.
104
0 17 (+ l A SAMPLE HB17
K+ I 30a°C I EG
Smectite 002
0 17 (-) A
. SAMPLE W14 K+/300°C/ EG
0 < 17 A SAMPLE WAS ~I 300°C/ EG
12
Smectite 001
10 8 6
Sharp 17 i
4 2 ==========================~ DEGREES 2 IS-
Figure 4.19: X-ray diffractograms showing the range in smectite basal peaks after K+/3oo0 c/ethylene glycol treatment.
105
106
K+ -smecti.tes contain interstratified collapsed layers though,
th.eir proportion is: very small. The interpretation of the
K+-saturation results according to Weaver (.1958) is that the
smectites in all the mudstone samples are characterised by a
layer charge which originates primarily in the octahedral sheet.
This interpretation is not in agreement with the results of the
Li+-saturation test and suggests that the alternative explanation
in terms of total amount of layer charge may be more accurate.
The results of re-expansion of the heated K+-smectites using
ethylene glycol, which gives a basal spacing of 17i, are
variable and can be grouped into three categories (after Schultz,
1969)_:
(.1) 17(.+)i, characterised by a sharp 17i 001
peak and a rational series of higher order
reflections.
(.2) 17(-)i, characterised by a broad 17i 001
peak and an irrational, poorly developed
series of higher order reflections.
CJ) <l7i, characterised by a broad 001 peak
, d O O situate between 14A and 16.SA.
Schultz (1969) showed that the degree of re-expansion can be
correlated with total layer charge. Full expansion as in category
(_l) above, indicates no fixation of K+ and a relatively low layer
charge. Smectites in category (2) have a slightly higher charge
and do not quite expand fully. Incomplete expansion to basal
spacings less than 17i, as in category (3), is a result of
K+-fixation due to high total layer charge.
107
The majority of the smectites in the mudstones are relatively
low-charge types, although an appreciable number did not re-expand
to l7~ and. can be considered as high-charge. (Note that the
results are not comparable with those of K+-saturation only, due
to the difference in treatments).
Comparison with the results of the Li+-saturation test (Table 4.4)
shows that all the montmorillonite species are low-charge
(l7(+)i), but the interstratified species are either low or high-
charge. The low-charge nature of the montmorillonites is typical
of the 'Wyoming' subspecies of montmorillonite (Schultz, 1969) and
this is further discussed in the next section.
4.3.3 Differential Thermal and Gravimetric Analysis
Differential Thermal Analysis (DTA) is a phase analysis technique
which was used to supplement XRD analysis and to further
characterise the smectites in the mudstones. DTA measures the
difference in temperature (6T) between a sample and an inert
reference material as they are heated and a DTA curve is a plot of
6T against temperature (Mackenzie, 1957). Reactions in the sample
produce thermal effects which appear as deviations from the baseline
of zero 6T of the DTA curve. Exothermic reactions in the sample
give rise to peaks which project above the baseline and
endothermic reaction peaks project below the baseline.
+ 2+ DTA results for the acid-insoluble Na or Mg -saturated clay
fractions of l2 smectite-mudstones are given in Table 4.6 and
representative graphs are shown in Fig. 4.20.
Table 4.6: DTA Results for Smectite-Mudstone Clay Fractions
Unit Sample Interlayer Dehydration
Cation Endotherm, oc
W6* Na
Lower Marl, W8 Na
Amuri Limestone W9* Na
Ull* Mg
WlO Mg Upper Marl,
Arnuri Limestone Cll Mg
Marl Ll4 Mg
(Clarence Valley) Arnuri Limestone SS Na
HB3 Mg
HB6 Mg Wanstead Formation
HB14 Mg
HB.21* Mg
VB, B, S, VS denote Very Broad, Broad, Sharp, Very Sharp * DTA curve given in Fig. 4.20
180
185
180
195~. 275
170, 275
200, 290
200, 280
180
175, 270
190, 275
170, ?230
180, 250
Dehydroxylation Endotherrns, oc
-550 VB 665 s
570 VB 685 s
555-675
550 B 605 VB 665 B
-530 VB 665 s
560 B 670 s
560 B 670 B
430-485 665 s
555 s -650 B
545 B -645 VB
545 s 675 s 550 s 675 s
Decomposition 0 Endotherrn, C
850 B
855 B
860 B
840-920
810 s
895 s
850 B
Exotherms, 0 c
935 vs llOO B
950 vs 1125 s
965 vs ll40 s
970 s 1090 vs 890 vs 1180 s 950 vs 1140 B 980 s 1115 vs
1--' 0 (X)
SAMPLE W 6
SAMPLE W9
SAMPLE U 11
(6)
SAMPLE HB21
(1 l Dehydration Endotherm
( 2} ( 3) Dehydroxylation Endotharms
( 4) Decomposition Endotherm
( S l ( 6) Phase Change Exotherms
(1)
200 400 600 800 1000
TEMPERATURE ° C
Figure 4.20: Differential Thermal Analysis curves of the clay fractions of four smectite-mudstones.
109
1200
110
Selected samples were heated up to 1200°c to determine the nature
of the high temperature reactions and the remainder were heated
to 75o0 c.
All of the DTA curves are characterised by a large endothermic
0 0 peak situated in the temperature range of l70 -300 c. The peak,
particularly its size, is diagnostic of smectite and is caused by
the volatilisation of interlayer water. Illite generally also
shows a low temperature endothermic peak which is much smaller
than the smectite peak and in the samples would be masked by the
latter. The shape of the smectite dehydration endotherm is
controlled by the interlayer cations present and their degree of
hydration (Mackenzie, 1957). Samples that were pre-saturated with
+ Na, which has a single-sheet hydration complex, show a single
dehydration peak at l80-190°c (Fig. 4.20, samples W6, W9).
Pre-saturation with Mg2+ which has a double-sheet hydration
complex gave rise to a double-peak endotherm with a second higher
0 temperature peak at 250-300 C. (Fig. 4.20, samples Ull, HB21).
0 0 At temperatures between 450 C and 700 C, the DTA curves of the
mudstone samples consist of a number of smaller endothermic peaks.
These endotherms are a result of dehydroxylation reactions
involving loss of hydroxyl groups from clay mineral structures.
The temperature of dehydroxylation has been shown from many
studies in the literature to be dependent at least indirectly on
mineralogy (Mackenzie, 1957). The dioctahedral smectites can
generally be distinguished on their dehydroxylation endotherm
temperatures. Montmorillonites usually give one endotherm
between 600° and 700°c whereas beidellites and nontronites usually
have their major endotherm at 500-55o0c. This difference is
111
believed to result from beidellite and nontronite having
weaker bonds due to considerable amounts of tetrahedral Al 3+ in
their structures. The interpretation of smectite species in the
mudstones based on dehydroxylation temperatures however, is
inhibited by the presence of considerable amounts of illite in
all samples. The dehydroxylation endotherm of illite normally
0 occurs at -550 C, similar to beidellite and nontronite.
All the DTA curves of the mudstone samples show a dehydroxylation
endotherm at 640° - 685°c (Fig. 4.20). This peak can be assigned
to smectite with a composition close to montmorillonite, which is
in agreement with the overall result of the Li+-saturation test.
A lower temperature endotherm occurring at 530° - 575°c (except
in sample 88) is also a constant feature of the DTA curves and
is likely to be largely due to the dehydroxylation of illite.
DTA curves given by Gordon et al. (1955) for two samples of
smectite-mudstone from Porangahau show smectite and illite
dehydroxylation endotherrns similar to those in this study.
In some samples, one or both of the dehydroxylation endotherms
are very broad and additional endothermic effects are
occasionally evident in between 550° and 6So0 c (Fig. 4.20,
samples W9, U.ll). These features may be a result of smectite
interstratification but there is no simple correlation with the
k
estimates of interstratification made from the Li'-saturation
test. Other possible factors which may affect the nature of
dehydroxylation endotherms include: sample grainsize, packing
density, interlayer cations and structural irregularities.
112
The DTA curves for those samples heated up to 1200°c show a
high-temperature endothermic peak between 800° and 900°c
(Fig. 4.20, samples Ull, HB21). This endotherm corresponds to
breakdown of the structures of smectite and illite. Further
heating beyond the temperature of structural breakdown produces
bonding rearrangements and phase changes for smectite and some-
times illite. These reactions are represented by high-temperature
exothermic peaks (Fig. 4.20, Samples Ull, HB21).
Smectite DTA curve endings (.>800°c) are not generally definitive
for differentiation between the dioctahedral species, but have
been used to define subspecies of montmorillonite, given that
dehydroxylation characteristics indicate montmorillonite
(.e.g. Grim and Kulbicki, 1961; Schultz, 1969). The subspecies
nomenclature is not standardised and that used by Schultz (1969)
is referred to here. Table 4.7 summarises the DTA characteristics
and also the results of K+-saturation for montmorillonite
subspecies.
Table 4.7: Characteristics of Montmorillonite Subspecies (after Schultz, 1969)
Montmorillonite Dehydroxylation Decomposition First Exotherm K+-Saturation Subspecies 0 c 0 c 0 c Result
Wyoming 700-725 900+10 -950 Low-Charge
Otay 650-690 840+20 1000-1100 High-Charge
Tatatilla 710-730 Variable Variable High-Charge
Chambers 660-690 850+20 -900 High-Charge
113
The smectites in the mudstones do not match any subspecies very
well, as they generally have relatively low dehydroxylation and
decomposition temperatures but moderately high exotherm
temperatures. The Wyoming and Chambers montmorillonites however
appear to most closely resemble the smectites in the mudstones
and chemical analyses presented in Chapter 5 support this
interpretation.
Thermal gravimetric analysis CTGA) was run simultaneously with
DTA and measures the sample weight during heating. Differential
TGA was also carried out, showing the change in sample weight with
temperature. Representative TGA and DTGA curves are shown together
with a DTA curve in Fig. 4.21. The TGA curve for all the mudstone
samples consist of four segments:
(l) A steep slope up to -200°c corresponding
to rapid loss of interlayer water;
C2l 0 0 A gradual slope up to 450 - 500 C;
Ll) A steep slope up to -7oo0 c corresponding to
loss of structural hydroxyls;
(Al 0 A gradual slope up to -900 C after which no
further weight loss occurs.
The gradual slopes of segments (2) and (4) indicate that
dehydration and dehydroxylation reactions continue above their
main reaction temperatures. The DTGA curve closely resembles the
DTA curve up to -7oo0 c in all samples, showing that the marked
changes in weight correspond to dehydration and dehydroxylation.
Reactions above -7oo0 c are not accompanied by significant weight
changes.
0 OTGA
1
2
3 ( 1 }
4
~5 0 ....J
I- 6 ::r ':2 LU
-:,: 7 I-z LU
~a LU a.
9
10
11
12 200 400 600 800 1000 1200
TEMPERATURE oc
Figure 4.21: Representative Differential Thermal and Gravimetric Analysis curves (see text for explanation of TGA curve) of smectitemudstone clay fractions.
114
115
4.4 SAND FRACTION MINERALOGY
Sand-sized material is a very minor component in the bulk
smectite-mudstone samples, although samples of the Marl in the
Clarence Valley are relatively sandy in comparison to the other
units sampled. The mineralogy of 63-250µm fractions separated
from selected mudstones and further separated into heavy and light
fractions was determined by optical microscopy.
The mineralogy of the heavy fractions is summarised in Table 4.8
using a semiquantitative system developed by Dr D. Smale, N.Z.
Geological Survey. The samples analysed show a wide variation in
heavy mineral suites.
Samples from both the Lower and Upper Marls of the Arouri Limestone
are characterised by abundant semi-opaque material which is not
rnineralogically identifiable. Heavy fractions from the Upper Marl
also contain abundant pyrite. Non-opaque minerals which are
present in proportions >2% in heavy mineral suites from the Lower
and Upper Marls are: baryte, clinozoisite/epidote (Fig. 4.22),
chlorite and muscovite. Siliceous microfossils, dominantly
spumellarian radiolaria (D. Mackinnon, pers. comm.), which are
infilled with pyrite or semi-opaque material are common in the
heavy fractions of some samples (Fig. 4.22).
Heavy mineral suites from the Marl in the Clarence Valley are more
distinctive than those from the Lower and Upper Marls. Samples Ll4
and B4 yielded virtually monomineralic suites comprising baryte
(Fig. 4.23) and pyrite respectively. The suite of sample S6 is
also dominated by pyrite. Samples S2 and SS, both taken from the
massive mudstone interval of the Marl, contain significant amounts
Table 4.8: Heavy Mineral Suites of Selected Smectite-Mudstones
LOWER MARL UPPER MARL
HEAVY MINERALS Wl C4 C7 Wll U6
Opaques - Pyrite
} } } I VA I I A I Magnetite 0 0 ~ tr
Other
Semi-Opaques I VA ;io I I VA* I I VA* I I A I I VA I Zircon ~ tr ~ tr
Tourmaline
Hornblende Or ? ~ tr ~ tr
Pyroxene ? ~ tr
Sphene Il tr
Garnet ? ~tr ~ tr ? Or Epidote Or
Clinozoisite 0 Baryte @] ~ ~ Biotite
Chlorite [TI Muscovite [J Volcanic Glass
Key: VA* - Flood >64%; VA -·very abundant 32-64%; A - Abundant 16-32%; C - Common 8-16%
S - Sparse 4-8%; R - Rare 2-4%; r - Very rare 1-2%; tr - Trace <1%
MARL (CLARENCE VALLEY)
Ll4 S2 S6
} I A I I VA* I
Dr IT] [I]
I A I [CJ [I]
0 ~ tr
m ~ tr
? ~ tr ? ~ tr
[] ~ tr
I VA* I [J
IT] [] []
Table 4.8: Heavy Mineral Suites of Selected Smectite-Mudstones (Continued}
MARL (CLARENCE VALLEY} WANSTEAD FORMATION RED SMECTITE-MUDSTONES
HEAVY MINERALS SB 84 HB3 HB21 Paoanui Mangamauk~ Gilray Bay Stream
Opaques - Pyrite I VA I I VA * I I A I I VA I I VA I Magnetite
Other I A I [I] [D Semi-Opaques 0 I VA I Zircon ~ ~ tr ~ tr
Tourmaline 0 Hornblende @ ~tr
Pyroxene ? ~ tr [ tr
Sphene II] Garnet [tr [ tr [ tr H tr
Epidote ~ tr
Clinozoisi te
Baryte ~ 0 I VA I I VA I Biotite I VA ;)ff I [I] 0 Chlorite m ~ tr [] [I] Muscovite CD fl tr 0 [I] [TI Volcanic Glass
7 ~ tr 7 ~tr
Key: VA* - Flood >64%; VA - Very abundant 32-64%; A - Abundant 16-32%; C - Common 8-16%
s - Sparse 4-8%; R - Rare 2-4%; r - Very rare 1-2%; tr - trace <1%
Figure 4.22: Clinozoisite/epidote and infilled siliceous microfossils in the heavy fraction of sample C7. Plane-polarised light, 40x magnification.
Figure 4.23: Baryte in the heavy fraction of sample Ll4. Crossedpolarised light, 40x magnification.
118
.
·• ..
of zircon, tourmaline, hornblende, sphene, biotite, chlorite
and muscovite (Figs 4.24, 4.25). The grains of zircon and
tourmaline are commonly euhedral in shape.
119
Two samples of the green smectite-mudstone of the Wanstead
Formation yielded heavy mineral suites consisting largely of
pyrite and baryte. In contrast, suites from the red smectite
mudstones of Hawkes Bay contain abundant phyllosilicates - biotite,
muscovite and chlorite - in addition to opaques. The sample from
Paoanui cliffs in particular is very rich in biotite (Fig. 4.26).
Two of the red smectite-mudstone suites also contain trace amounts
of isotropic material which may be volcanic glass.
The mineralogy of the light fractions of all the smectite-mudstone
samples was found to consist of chert-clay fragments±. quartz+
feldspar±. muscovite±. glauconite. The fragments composed of
chert and clay are very abundant and the other minerals, if
present, are minor components in all light fractions except those
of samples S2 and SS. The light mineral suites of S2 and SS
contain abundant quartz and feldspar. Both minerals occur as
subangular, anhedral grains and no euhedral shapes were observed.
Two types of feldspar are present in both samples - sodic
plagioclase and microcline with distinctive cross-hatched twinning
(.Fig. 4. 27) .
Previous studies of the sand fraction mineralogy of samples from
Porangahau quarry have been reported in the literature
(Gordon et al., 1955; Ritchie, 1962). In addition to the
mineralogy determined in this study for sample HB3 from
Porangahau, Gordon et al. (1955) noted the presence of volcanic
glass. The mineralogical analysis given by Ritchie (1962)
Figure 4.24: Euhedral zircons, sphene, green tourmaline and pyrite (opaque} in the heavy fraction of sample 82. Planepolarised light, 40x magnification.
Figure 4.25: Brown/green tqurmaline, chlorite and pyrite (opaque) in the heavy fraction of sample S8. Planepolarised light, 40x magnification.
120
•
•
'
includes biotite, apatite, volcanic glass and volcanic
fragments, but no haryte which is the dominant heavy mineral
in sample HB3.
121
Figure 4.26: Biotite in the heavy fraction of red smectite-mudstone from Paoanui. Plane-polarised light, 40x magnification.
Figure 4.27: Microcline showing crosshatched twinning, quartz and glauconite in the light fraction of sample 88. Crossedpolarised light, 63x magnification.
l22
5.1 INTRODUCTION
CHAPTER FIVE
GEOCHEMISTRY
123
The geochemistry of the smectite-mudstones was studied in two parts:
Cl) Major element geochemistry of clay fractions
involving analysis of structural elements
and exchangeable cations to determine clay
mineral chemistry.
(2) Trace element geochemistry involving analysis
of whole rocks and exchangeable cations with
emphasis on stratigraphic trends.
5.2 MAJOR ELEMENT GEOCHEMISTRY
A study of the major element geochemistry of smectite-mudstone
clay fractions was carried out to determine the chemistry and
structural formulas of the smectite clay and to supplement the
phase analysis techniques in distinguishing smectite species.
Structural elements were analysed by x-ray fluorescence and
exchangeable cations in leachate solutions from the leaching
procedure were analysed by atomic absorption.
5,2.l Method of Structural Formula Calculation
The calculation of clay mineral structural formulas from chemical
data involves locating each element in a structural position
based on a general ideal structural formula. For dioctahedral
smectites, the following ideal structure is generally accepted
(Ross and Hendricks, 1945):
(Al FebMg ) a-y c
octahedral sheet
(.Si4
Al ) -y y
tetrahedral sheet
anions hydrated exchangeable
cations
The ideal structural formulas for the three end-member species of
dioctahedral smectite are:
Montmorillonite
Beidellite
Nontronite
Isomorphous substitution series between the three end-members
do not appear to be continuous (Brigatti and Poppi, 1981;
Nemecz, 1981). The validity of the Greene-Kelly Li+-test in
distinguishing montmorillonite from beidellite and nontronite
suggests that there is a miscibility gap between montmorillonite
and the other two dioctahedral species. A miscibility gap is
3+ also evident between nontronite and the other species, as Fe
constitutes >75% of the octahedral cations in nontronite and
usually <30% in montmorillonite and beidellite. The dioctahedral
smectite species can therefore usually be readily differentiated
by chemical analysis.
124
The method of calculating structural formulas of dioctahedral
smectites is given by Ross and Hendricks (1945) and is described
below with a worked example.
(1) Given a chemical analysis expressed in weight% of oxides
(.Table 5.1, column 2), atomic proportions of the elements
are calculated (column 3):
At. Prop.= wt% (.no. cations in oxide) M.W. oxide
Table 5.1: Example of a Structural Formula Calculation (Chemical analysis of API no. 24 bentonite from Schultz (1969) t
Element wt% Atomic Proportions Structural Formula oxide
Si 63 .Cl4 l.049 = z 3.98
J Tetrahedral cations
0.362 A/ 0..006=Y 0.02
Al 18.44 = '- 0.356=A-Y l.35
] 0.06 Octahedral
Fe 1.20 0.015 =.B cations
Mg 7.30 0 .J.8J. = c 0.69
Ca 0.08 a.ao] Na 3.40 O..llQ = x 0.42
Exchangeable cations
K 0..02
(2) The atomic proportions are multiplied by a factor K to
give the structural formula (column 4). K is
calculated from the equation:
22 K = 3A + 3B + 2C + 4Z + X
This equation expresses the condition that the sum of
the cation valences equals the sum of anion valences -
which for an ideal structure is 22.
125
For the example in Table 5.1:
22 K = 3(0.362) + 3(0.015) + 2(0.181) + 4(1.049) + 0.111
= 3. 793
(3) The amount of Al in the tetrahedral sheet (Y) is calculated
by:
y = 4 K
- Z, which expresses the condition that the sum
of tetrahedral cations in an ideal structure is 4. For
the example in Table 5.1:
4 Y 3.793 - 1.049
0.006
(4) The full structural formula for the dioctahedral smectite
example is:
5.2.2 Limitations of Formula Calculations
The accuracy of clay mineral structural formulas calculated from
126
chemical analyses may be affected by several factors (e.g. Schultz,
1969) .
Firstly, the accuracy of the chemical analysis is important. The
XRF analyses of the smectite-mudstones were checked by analysing
five API bentonite standards (Appendix IV) which were pretreated
and prepared in the same way as the samples. Table 5.2 gives the
results obtained for the standards in this study and the analyses
given in the literature (Schultz, 1969), with both sets of data
recalculated to exclude minor elements and loss on ignition. Note
that the values for Cao, Na2
o and K2
0 are not comparable as the
2+ standards were saturated with Ca prior to analysis in this study.
Table 5.2: Accuracy of XRF Major Element Analyses of Bentonite Standards
Burns (W) Chambers (W) Otay (E) Clay Spur (W) Cameron (W)
Newly Collected Newly Collected Original Newly Collected Newly Collected API No. 2l API No. 23 API No. 24 API No. 26 API No. 31
A B A B A B A B A .B
Si0 2 66.52 66.48 66.21 65.91 66.96 67.44 70.57 70.06 59 .99 63.70
Al2o3 20.58 21.17 21.40 22. 72 19.48 19.73 19 .89 21.00 24.19 20.84
MgO 5.04 5.73 4.86 4.56 7.20 7.81 2.35 3.40 2.14 1.41
Fe203
4.29 3.16 3.66 3.21 2.20 1. 28 3.86 3.41 7.69 8.68
cao 3.53 2.75 3.81 3.05 4.04 0.09 3.06 0.12 2.44 2.14
Na20 - 0.22 - 0.19 - 3.64 0.18 1.66 - 0.31
K20 0.04 0.49 0.06 0.37 0.13 0.02 0 .10 0.36 3.56 2.92
2+ A= XRF analyses in this study of Ca -saturated insoluble residues
B = XRF analyses from the literature (Schultz, 1969)
A second factor which must be assessed in the calculation of
structural formulas is sample purity. Components which are
present in addition to the one for which the formula is being
calculated may be able to be removed, or if not, have to be
accurately corrected for.
128
The smectite-mudstones were partially purified by treatment with
dilute acetic acid to dissolve caco3 . Carroll and Starkey (1971)
reported that only minor amounts of structural silica and alumina
are dissolved from montmorillonite and illite with prolonged
acetic acid treatment. The mild treatment used in this study
should therefore not have significantly altered the clay chemistry
and some analyses of untreated non-calcareous standards were
found to be comparable to the analyses after treatment (Appendix IV).
The acid-insoluble clay fractions of the majority of smectite
mudstones contain illite and quartz in addition to smectite
(Chapter 4, Section 4.2). Quartz impurities were corrected for by
subtracting the% quartz figure obtained by quantitative XRD
analysis from the weight% Si02 in the chemical analysis. A
similar correction for the illite component in the samples could
not be applied however. The chemistry of illite is variable
(Weaver and Pollard, 1973) and use of an average illite formula
may have induced considerable error in the correction of the
chemical analyses. It was more meaningful therefore to include
illite in the structural formula calculations and obtain overall
smectite + illite formulas, as is done in the case of interlayered
smectite-illite clays (e.g. Schultz, 1978). The method of formula
calculation for dioctahedral smectites is applicable to illite as
the two clays have the same structure. The chemistry of illite
differs from that of smectites in a higher degree of substitution
of Al3+ for tetrahedral Si4+. The resulting high layer charge of
illite is balanced by interlayer K+ cations which are generally
non-exchangeable.
A third major problem in structural formula calculations is the
validity of the assumption of an ideal structure and the
assumptions involved in assigning elements to certain structural
positions. The ideal structure for dioctahedral smectites, upon
which formula calculations are based, appears to be validated by
the numerous calculated formulas in the literature (e.g. Weaver
and Pollard, 1973) which are close to ideal. Schultz (1969)
however has shown that the amount of structural water may not
always be ideal. Errors in structural formulas may also arise if
it is not recognised that some elements occur in more than one
structural position, such as Al 3+ (octahedral, tetrahedral or
interlayer) and Mg2+ (octahedral or interlayer). The
exchangeable cations in the smectite-mudstone clay fractions were
replaced with ca2+ prior to analysis to alleviate this problem.
XRD analysis (Chapter 4, Section 4.2.1) also indicated that
· 3+ 2+ significant interlayer Al or Mg are not present.
5.2,3 Structural Formula Results
The XRF analyses of smectite-mudstone clay fractions are given in
129
Appendix V. All the samples chemically analysed were also analysed
by quantitative XRD and consist essentially of smectite + illite
+ quartz. The samples were pre-saturated with ca2+ by reciprocal
shaking to replace the interlayer cations except non-exchangeable
+ . 'll't K in i i e. The weight% K20 correlates with% illite determined
from quantitative XRD as shown in Fig. 5.1. K20 also shows a
positive correlation with Al 2o3 and a negative correlation with
Si0 2 corrected for quartz (Fig. 5.1), indicating the more
aluminous nature of illite relative to smectites.
2·87 r .. 0·529
%K2o
• •
1 ·'28 ~
30
• • %K
2o
1·~ 49·21
2·S7 r .::.0·692
•
1 ·28 11·32
•
•
• •
• • • • •
• • • •
• • • • • % Illite 51
• r--0· 541
• • .c
•• • •
• • • • • •
%Si0z - O/o Quartz 69·31
if
• • • • • • • • •
• • e • •
• • 0/o At 2 o3
19·11
Figure 5.1: Scatter plots and correlation coefficients (r) of %K20 vs %Illite, %K20 vs %Si0 2-%Quartz and %K20 vs %Al2o3 in smectite-mudstone clay fractions.
130
131
Average s.mectite + illite structural formulas calculated from
the chemical analyses of smectite-mudstone clay fractions are
given in Table 5.3. Octahedral Al3+ ranges from 0.99 to 1.49 with
an average of 1.31, Mg2+ ranges from 0.16 to 0.33 with an average
of 0.25 and Fe3+ ranges from 0.21 to 0.37 with an average of 0.27.
The amount of tetrahedral Al3+ ranges from 0.00 to 0.15, but
approximately two-thirds of the samples have no tetrahedral Al3+.
Total interlayer cations range from 0.23 to 0.43 with an average
of 0.34. Detailed analyses of exchangeable cations are presented
in the following Section 5.2.4.
The low amount of tetrahedral substitution in the structural
formulas is consistent with the overall result of the Li+-saturation
test that the smectite species in the mudstones are closest to
end-member montmorillonite. The Mg and Fe proportions in the
formulas are respectively low and high relative to the averages of
0.35 and 0.19 for montmorillonites (Weaver and Pollard, 1973).
Assuming the illite in the samples has average Mg and Fe contents,
this chemistry is similar to the Wyoming and Chambers subspecies of
montmorillonite (Shultz, 1969) as discussed in Chapter 4,
Section 4.3.3.
The most striking aspect of the calculated average smectite +
illite structural formulas is that many formulas are non-ideal
with octahedral cation totals that are considerably less than the
ideal total of 2.00 per o10 (0H) 2 . This deficiency appears to be
largely a result of low amounts of Al3+. Only four samples (WS,
W9, U4, U9) have formulas with significant Al3+ substitution in the
tetrahedral sheet even though illite typically contains on the
~+ order of 0.5 tetrahedral Al~ (Weaver and Pollard, l973). The
Li+-saturation test also indicated that the smectites in some
samples are tetrahedrally substituted, but there is no good
Table 5.3: Average Structural Formulas of Smectite + Illite in Smectite-Mudstone Clay Fractions
Sample Octahedral Tetrahedral
Unit Al3+ Mg2+ 3+ Si4+ Al3+ Fe Total
Marl, W8 1.41 0.33 0.29 2.03 3.85 0.15
Lower W9 1.40 0.28 0.32 2.00 3.88 0 .12
Amuri Limestone C3 1.44 0.32 0.23 1.99 3 .94 0.06 C7 1.43 0.25 0.29 1.97 3.95 0.05 Ull 1.33 0.26 0.27 1.86 4.08 0.00
WlO 1.38 0.22 0.29 1.89 4.05 0.00 Wl3 1.19 0.20 0.22 1.61 4.27 0.00
Upper Marl, Wl3* 1.19 0.20 0.22 1.61 4.28 0.00 Wl4 1.28 0.20 0.22 1. 70 4 .19 0.00
Arouri Limestone Cll l.26 0.24 0.21 1. 71 4.19 0.00 U4 l. 38 0.33 0.33 2.04 3.88 0 .12 U4* 1.37 0.32 0.33 2.02 3.87 0.13 U9 l.42 0.29 0.29 2.00 3.87 0.13
Marl Ll4 1.37 0.27 0.22 1.86 4.09 0.00 (Clarence Valley), S2 1.25 0.29 0.27 1.81 4.14 0.00 Arouri Limestone SS 1.24 0.32 0.29 1.85 4.10 0.00
SS 1.17 0.29 0.27 1. 73 4.21 0.00
Mungaroa Limestone W04 1.34 0.25 0.21 1.80 4.13 0.00
HB3 1.49 0.17 0.30 1.96 3.94 0.06
Wanstead Formation HB6 0.99 0 .16 0.37 l.52 4.33 0.00 HB14 l.26 0.21 0.25 1. 72 4.18 0.00 HB21 l.08 0.16 0.22 1.46 4.38 0.00
* Duplicate sample
Interlayer
x
0.40 0.40 0.39 0.38 0.39
0.33 0.28 0.27 0.32 0.31 0.36 0.37 0.43
0.34 0.31 0.35 0.26
0.33
0.35 0.30 0.32 0.23
I-' w tv
133
correlation between those results and the chemical analyses on an
individual sample basis.
The non-ideal structural formulas are not a result of analytical
error, as demonstrated by the analyses of standard bentonites in
Table 5.2. The low Al3+ values are accompanied by values for
h d 1 ,4+ h'. . tetra era Si w ich are in excess of the ideal 4.00 per
o10 (0H) 2 and it is possible that free silica in the clay fractions
of the samples was underestimated in the quantitative XRD analysis.
However, the chemical analysis of sample HB21 for example, would
have to be corrected for 22% free silica to obtain an ideal formula
(with no tetrahedral substitution), but no quartz or other forms
of silica were detected in the clay fraction by XRD analysis and
no volcanic glass was found in the sand fraction. It is unlikely
therefore that error in the corrections for free silica can account
for the large deviations from ideality in the structural formulas.
It appears then that either one or both of the smectite and illite
clays in the smectite-mudstones are commonly characterised by major
structural irregularities, in terms of an ideal structure. A
deficiency in the octahedral cation total suggests that some
octahedral sites are vacant, whereas the tetrahedral sheet contains
greater than ideal amounts of si4+. The effect of these
irregularities on the outcome of the phase analysis techniques
described in Chapter 4 is uncertain. There is no indication of
non-ideal structures from XRD analysis and the smectite clay
appears well crystallised.
Some chemical analyses of smectite-mudstones from Hawkes Bay are
given by Gordon et al. (1955), Ritchie (1962) and Pettinga (1980)
134
Comparison of the analyses with those in this study is not
possible however due to unknown amounts of impurities such as
Caco 3 and Si02 in the literature samples. The results in this
study contrast markedly with the numerous structural formulas
which are invariably close to ideal, given in general studies of
smectite chemistry (e.g. Schultz, 1969; Weaver and Pollard, 1973)
5.2.4 Exchangeable Cations
· 2+ + 2+ K+ Analyses of the maJor exchangeable cations Ca , Na, Mg and
for selected smectite-mudstone samples and duplicates are given in
Appendix VI. Table 5.4 gives the results expressed in
milliequivalents % (meq%) which.is defined as:
mmol charge on ion per lOOg oven dry sample.
These cations were determined in HCl leachate solutions and as
most of the samples are calcareous, the analyses of ca2+ were
corrected by subtracting the amount of ca2+ produced by the
dissolution of Caco3 .
As qualitatively indicated by XRD analysis (Chapter 4, Section
4.2.1), the dominant exchangeable cation in the Marlborough
· d · 2+ k d smectite-mu stones is Ca whereas the Haw es Bay mu stones are
typically Na+-saturated. Exchangeable Mg2+ and K+ are present in
all samples in minor amounts, although most interlayer K+ is fixed
in the structure of illite.
The total exchangeable cations in the smectite-mudstones range
from 8.4 to 66.0 meq%. Cation exchange capacities were also
determined by leaching the samples with sodium acetate followed by
ammonium acetate and analysing the Na+ extracted in the final
leachate solutions. The results however were variable and generally
lower than the exchangeable cation totals. This discrepancy may be
Table 5.4: Exchangeable Cations in Smectite-Mudstone Samples and Duplicates
I 2+* Na+ 2+ K+ Ca Mg
Unit Sample meq % meq % meq % meq %
W6 39.9 1.1 3.2 0.7 W6 31.2 0.9 4.7 2.6
Lower Marl, I
Arouri Limestone I C7 52.0 0.7 2.0 0.4
I C7 37.7 0.5 2.0 0.4
I Ull 45.0 1. 2 4.5 0.7 I Ull 55.8 0.6 6.3 1.8 I I
Wl4 61.6 0.6 1.6 1.1 Upper Marl, Wl4 61.5 1.1 2.0 1.4
Arouri Limestone
Cll 52.3 0.6 1.8 0.8 Cll 55.5 0.5 1. 7 0.9
82 40.8 15.3 3.1 2.1
Marl 82 16.9 13.l 2.3 2.9
(Clarence Valley),
Arouri Limestone SS 46.3 1.2 1. 7 1.5 SS 21.6 1.0 1. 7 1.6
I HB3 18.4 20.1 3.6 3.8
I HB3 21.0 21.2 3.7 3.9
HB6 - 2.8 4.2 2.6 HB6 - 2.4 3.5 2.5
Wanstead
I Formation
I HB14 - 30.3 4.2 3.8
I HB14 - 28.8 3.5 3.5
HB17 - 23.4 2.2 3.0 HB17 - 23.2 2.3 3.2
* Corrected for ca2+ derived from caco 3
Negligible
135
Total I meq % !
)
44.9 39.4
55.1 40.6
51.4 64.5
64.9 66.0
55.5 58.6
61.3 35.2
50.7 25.9
45.9 49.8
9.6 8.4
38.3 35.8
28.6 28.7
due to the presence of soluble salts which would increase the
exchangeable cation totals (e.g. Blakemore et al., 1977). It is
also possible that the later stages of the leaching procedure may
not have resulted in complete cation exchange. The cation
exchange capacity of smectites is generally in the range 70-130
meq% and that of illite is 10-15 meq% (Weaver and Pollard, 1973).
The smectite-mudstones contain both clay minerals and their
intermediate total exchangeable cation values reflect this
mineralogy.
5.3 TRACE ELEMENT GEOCHEMISTRY
The trace elements Sr, Rb, Zr, Y, Nb, Pb, Th and Ga in whole-rock
samples of smectite-mudstones were analysed by x-ray fluorescence
and other lithologies associated with the smectite-mudstones were
similarly analysed. This study was carried out to determine any
consistent variations, particularly stratigraphic trends,in trace
element geochemistry. Trace metal elements in HCl leachates from
the cation exchange leaching procedure were also analysed by
atomic absorption.
5.3.1 Whole-Rock Trace Elements
The whole-rock element analyses of smectite-mudstones are given
in Appendix VII and the results according to area and
stratigraphic position are presented in Table 5.5. Analyses
of samples of other lithologies are given in Table 5.6. The
accuracy of the analyses is demonstrated in Appendix VIII.
Strontium values in the smectite-mudstones range from 123 ppm to
1222 ppm and are relatively high in the Marlborough samples but
low in the Wanstead Formation of Hawkes Bay. The limestones
136
Table 5.5: Trace Element Analyses of Smectite-Mudstone Whole-Rock Samples (Averaged concentration values are given)
Unit Stratigraphic
Samples Sr Rb Zr y Nb Pb Th Ga
Position ppm ppm ppm ppm ppm ppm ppm ppm
W3, C3, 500 36 36 15 6 7 5 4 Base
Ul6
Lower Marl, i W6, C7, 441 50 47 12 7 8 5 7 Amuri Limestone
j Middle Ul3
i
I W8, C9, 528 46 45 10 6 8 5 7 '
Top Ull
Base WlO, U4 734 37 48 11 6 8 5 5
Marl, Middle Wl3, U9, 752 29 42 10 6 6 3 4
Upper M3
Amuri Limestone Wl4, Cll, 639 34 42 10 5 7 4 5
Top Cl3, M2
Base S5, Sl2 531 28 59 15 3 7 4 5
Marl Bl (Clarence Valley)
Amuri Limestone Middle Sl, SB 744 46 107 9 7 9 6 7 SlO I B4
Kandahar Base WOl, WAS 518 66 86 12 7 9 7 11 Formation
Top? WAl 506 67 73 10 8 9 6 12
Mungaroa Limestone ? W04 232 69 74 34 6 13 9 14
HB6, HB9, 187 91 127 25 9 12 9 15 Base HB14 Wanstead Formation
Middle HB3, HB21 355 87 94 13 10 11 8 14
I-' w -..J
Table 5.6: Trace Element Analyses of Other Lithologies Associated with the Smectite-Mudstones
Unit/Lithology Sample Geology Dept ·Sr Rb Zr y Nb File No. ppm ppm ppm ppm ppm
W5 11378 524 5 11 11 5
Ul8 11395 618 8 13 13 1
Limestone Cl4 11394 560 2 7 7 3
Interbedded with L4 11387 643 13 25 8 4
Marls
S9 11396 632 14 42 8 3
Sll 11383 623 17 51 9 3
L3 11405 427 12 149 17 29 Grass Seed
Volcanics i
LS 11406 203 11 _157 22 32
Whangai I Formation
HB20 11385 133 62 110 8 6
Red Paoanui 11401 89 134 112 15 12
Smectite-Mudstones Gilray 11402 223 131 264 30 17 Bay
Pb Th ppm ppm
4 3
4 1
3 2
5 3
5 3
6 3
5 3
5 3
14 7
11 13
16 14
Ga ppm
0
0
0
3
2
3
15
11
9
20
19
I ! f i
I
I-' w m
interbedded with the Marlborough smectite-mudstones also contain
high concentrations of Sr and it is probable that Sr occurs
dominantly as a.substituent for Ca in Caco3 . The concentration
of Sr in the smectite-mudstones therefore shows a positive
correlation with carbonate content as shown in Fig. 5.2.
139
Rubidium concentrations range from 19 ppm to 109 ppm with an areal
trend of relatively low levels in Marlborough smectite-mudstones
and higher concentrations in Wairarapa and Hawkes Bay smectite
mudstones. Gallium ranges from 2 ppm to 18 ppm and shows a similar
areal trend. These variations may also be controlled by the
carbonate content of the smecti'te-mudstones as the limestones
analysed have very low Rb and Ga concentrations. The red smectite
mudstones from Hawkes Bay are characterised by the highest Rb and
Ga contents. Rb may substitute for Kin illite and Ga may
substitute for Al in clays. Both elements are also likely to
occur in mineral grains.
Zirconium concentrations range from 30 ppm to 148 ppm and are
highest in smectite-mudstone samples from the middle of the Marl
in the Clarence Valley and the Wanstead Formation. It is likely
that Zr occurs dominantly in zircon grains and heavy mineral
suites from the middle of the Marl in particular contain
significant amounts of zircon. Concentrations of Zr are also
relatively high in the Grass Seed Volcanics, Whangai Formation
and red smectite-mudstones.
Yttrium in the smectite-mudstones ranges from 8 ppm to 34 ppm and
appears to show a stratigraphic trend of increasing concentration
with increasing age. The highest Y values occur at the base of
the Lower Marl, at the base of the Marl in the Clarence Valley, in
the Mungaroa Limestone and at the base of the Wanstead Formation.
Figure 5.2: Scatter plot and correlation coefficient (.r) of ppm Sr vs %CaC03 in smectite-mudstones.
790 • r = 0·768 • •
•
• •
pi:m Sr • • • • •
• •
• •
•
•
• •
• •
•
•
123 ~·~~~~~~~~~~~~~~~~~~~~~~~~~--..
1. 3 66·5
Table 5.7: Correlation Coefficient Matrix for Trace Elements in Smectite-Mudstones.
Ro Zr y Nb Pb Th Ga
-Q.449 -0.442 -0.536 -0.358 -0.364 -0.469 -0.526
Q.572 0.534 0.228 0.895 0 .967 0.882
O.Sl3 0.615 0.589 0.621 0.695
0.378 0.6l7 0.602 0.637
0.180 0.244 0.580
0.910 0.815
0.876
140
Sr
Rb
Zr
y
Nb
Pb
Th
However, one sample of the Whangai Formation underlying the
Wanstead Formation at Waimarama Beach has a relatively low y
concentration (8 ppm) and more detailed work is necessary to
establish a certain correlation with stratigraphy. The
concentration of Y may also be controlled by lithology, as
relatively high Y levels characterise the Grass Seed Volcanics
and red smectite-mudstones.
The elements niobium, lead and thorium in the smectite-mudstones
do not show any distinct trends except that concentrations are
marginally higher in the Wanstead Formation in comparison to the
other units. The levels of Nb, Pb and Th are also relatively
high in the red smectite-mudstones and distinctly high Nb
concentrations occur in the samples of the Grass Seed Volcanics.
A correlation coefficient matrix for the trace elements analysed
in all samples is given in Table 5.7. The elements Rb, Th, Pb
141
and Ga show strong positive correlations with each other,
indicating that they are closely associated. Correlations between
Zr, Nb and Y and with the above four elements are also positive
but weaker. Sr is distinctly different to the other trace
elements in that its correlations are all negative. This
difference is probably a result of Sr occurring largely in the
carbonate component of the samples, whereas the other trace
elements are present dominantly in the non-carbonate components.
5.3.2 Exchangeable Trace Elements
The elements V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb were analysed
in solutions collected from the leaching of smectite-mudstone
samples with HCl. The results for Fe and Mn are given in
Appendix VI. The concentrations of Fe range from 4.75 ppm to
25.6 ppm and small quantities of Mn up to 2.1 ppm were found for
most samples. The Fe and Mn may occur as exchangeable cations
and/or as oxide coatings on clay particles which were dissolved
by the HCl leaching. Of the other elements analysed, minor
amounts of Zn (up to 0.5 ppm) and Ni (up to 0.1 ppm) were found
in the leachate solutions of all samples and the remaining
elements were not detected.
142
6.1 INTRODUCTION
CHAPTER SIX
ORIGIN OF THE
SMECTITE-MU DST ONES
Marine deposits composed dominantly of smectite clay can be
classified into three genetic groups (after Weaver, 1963;
Jeans et al., 1982):
(1) Primary bentonites formeo. by the in-situ
alteration of volcanic ash-fall beds.
(2)_ Secondary bentonites formed from volcanic
ash which has been transported and/or
reworked by sedimentary processes before
or after alteration.
(3) Other smeatite-riah deposits formed by
detrital sedimentation or neoformation with
no direct volcanic precursor.
The Lower Tertiary marine smectite-mudstones in the East Coast
Deformed Belt have previously been called 'bentonites' (see
143
Chapter 1), with the implication that they originated by the
alteration of volcanic ash (either in-situ ash-falls or transported
ash). The evidence obtained in this study for the origin of the
smectite-mudstones is discussed in the following sections.
6.2 SEDIMENTOLOGY
The three genetic categories of smectite-rich deposits defined in
Section 6.1 are characterised by the following sedimentological
criteria (after Jeans et al., 1982):
(1) Primary bentonites occur as beds on the
order of millimetres or centimetres thick
which are laterally extensive up to
hundreds of kilometres. Relict graded
bedding may be evident in primary bentonites.
(2) Secondary bentonites are variable in
thickness up to several metres, are
commonly lenticular in form and limited in
lateral extent to some hundreds of metres.
Sedimentary structures such as graded
bedding and cross-bedding are commonly
preserved in secondary bentonites where the
ash has been transported/reworked before
alteration.
(3) Other smectite-rich deposits generally form
well defined facies which are relatively
thick (tens of metres) and extend over
kilometres. They are well-sorted, fine
grained deposits and lack the sedimentary
structures indicative of a sand-grade ash
parent.
144
6.2.l Volcanic Origin
The smectite-mudstones in the East Coast Deformed Belt are well
described by the sedimentological summary of non-volcanogenic
smectite-rich deposits given in the preceding section. The
mudstones are a distinct lithofacies in the Upper Cretaceous
Lower Tertiary sequence of the east coast. They are on the
145
order of tens of metres thick and are regionally extensive. In
Marlborough, where the .stratigraphy is less disrupted by faulting,
the Lower and Upper Marls can be traced for at least twenty
kilometres from the Ure River into the Clarence Valley.
Within the smectite-mudstone units, the mudstone beds range from
millimetres to metres in thickness, are homogeneously fine-grained
and lack sedimentary structures except bioturbation. Structures
such as graded bedding and cross-bedding occur only in the
greensands and rarely in the limestones interbedded with the
mudstones. Grim and Guven (1978), in their summary of New Zealand
bentonites, report (p.117) relict ash structures in the smectite
mudstone at Porangahau, but the mudstone at this locality appears
highly tectonised with no preservation of original sedimentary
structures (see also Pettinga, 1980, p.101).
The sedimentological features of the smectite-mudstones are
therefore not indicative of a wholly or dominantly volcanic
origin. A further problem with advancing a volcanic origin is the
lack of evidence of a contemporaneous volcanic source(s) for
considerable quantities of ash, particularly in the North Island
(see also Pettinga, 1980, p. 335). In Marlborough, the Grass Seed
Volcanics unit is proof of volcanic activity but is localised in
the middle Clarence Valley and is contemporaneous only with
smectite-mudstones of Arnold Series age. Basaltic pillow lavas
146
and tuffs are reported to be interbedded in the Arouri Limestone
in Woodside Creek and the Kekerengu River. (Lensen, 1962;
Prebble, 1976). However exposures are poor (Prebble, 1976) and
in the lower gorge of Woodside Creek the contacts of a thin
igneous body appear to be structural in nature. MacPherson (1952)
also reported basalt flows and high-level intrusives associated
with smectite-mudstones in the Kekerengu area, but was uncertain
of their stratigraphic relationship due to structural
complexities. Kingma (1967) proposed that smectite-mudstones in
the North Island formed by the alteration of Upper Cretaceous
acid volcanics during the Lower Tertiary, but there is no evidence
of volcanism contemporaneous with the smectite-mudstones.
6.2.2 Sedimentary Origin
(1) Alternating Marl-Limestone. The Marls in the Arouri Limestone
and the Mungaroa Limestone are composed of clay-rich beds which
alternate with micritic limestone beds. Similar alternating marl
limestone sequences occur worldwide since Paleozoic time and there
is considerable literature on their origin (e.g. Duff et al., 1967;
Millot, 1970; Einsele, 1982). In a review of the subject,
Einsele (1982) concludes that the alternating beds are most likely
to be a result of fluctuations in hemipelagic sedimentation of
detrital clay against a background of continuous carbonate
sedimentation. In deep water depositional environments, cyclic
dissolution of carbonate due to fluctuations in the carbonate
compensation depth or changing bottom currents may also be an
important factor. The time period of marl-limestone cycles is
generally on the order of tens of thousands of years and the
ultimate cause of the cyclic sedimentation is likely to be climatic
variations possibly accompanied by eustatic fluctuations
(Einsele, 1982) .
147
In the Arouri Limestone and Mungaroa Limestone however, another
possible origin of the marl-limestone cycles is mass-flow
deposition. Occasional silty-sandy limestone beds with
sedimentary structures indicative of mass-flow deposition have
been observed (this study; Prebble, 1976; G.J. van der Lingen,
l9.84, pers. comm.). Waterhouse and Bradley (l957) considered the
limestone beds in the Mungaroa Limestone to be redeposited.
Although their evidence of soft-sediment folding and reworked
fauna appears to be invalid (Browne, in prep.), the possibility
is not ruled out, particularly as mass-flow greensand beds occur
in the Mungaroa Limestone. Such mass-flow events could potentially
redeposit large amounts of clay as well as carbonate.
In addition to the causes of marl-limestone cycles discussed
above, diagenesis may significantly enhance the lithological
variations. Stylolitisation is one mechanism by which diagenetic
'unmixing' can occur and is probably very commonly developed
throughout the Arouri Limestone (G.J. van der Lingen, 1984, pers.
comm.).
(2) Alternating Greensand-Mudstone. Both the Kandahar Formation
and Wanstead Formation comprise interbedded glauconitic sandstones
and smectite-mudstones. Structures in the greensands are
indicative of deposition by mass-flow processes. The sandstone
beds grade up into dark brown-grey carbonaceous siltstones/
mudstones which are interpreted as deposits of waning mass-flow
currents. These siltstones/mudstones in turn grade up into light
green mudstones which are strongly bioturbated and interpreted to
represent background hemipelagic sedimentation (see also Pettinga,
1980 I 1982) •
6.2.3 Regional Sedimentation Patterns
The smectite-mudstones are a regionally extensive and
stratigraphically important Lower Tertiary lithofacies in the
148
East Coast Deformed Belt. Their present day geographic
distribution is controlled by the Late Cenozoic transcurrent
dextral shear zone which traverses the New Zealand continental
block from East Cape in the north to Fiordland in the south
(Walcott, 1978; Sporli, 1980). Schematic paleogeographic
reconstructions of the east coast region during the Lower Tertiary
are presented by Kamp (in prep.) and show that the Hawkes Bay and
Wairarapa regions were more closely associated and contiguous
with Marlborough. Sedimentation is inferred to have occurred on
a passive continental margin with gross sedimentation patterns
controlled by extensional tectonics (Sporli, 1980; Kamp, in prep.)
The depositional environment of the smectite-mudstones is
envisaged as a regionally uniform, open oceanic environment
receiving a limited supply of elastic sediment and characterised
by slow average sedimentation rates. Paleontological evidence
suggests a deeper water outer shelf/slope environment
(C.P. Strong, 1983, pers. comm.) but does not rule out a
continental plateau setting where water depths may be in excess of
1000 metres, possibly similar to the present day Campbell Plateau.
Alternatively, a shallower water middle shelf setting may be more
appropriate, however further such considerations are beyond the
scope of this study.
Areally within the depositional environment, sedimentation of
hemipelagic clay and carbonate occurred concurrently. Fluctuations
in the input of detrital clay is favoured to account for the
internal cyclic sedimentology of the Marl units. Depths of
149
deposition were probably not great enough for cyclic dissolution
of carbonate to be an important factor. Local remobilisation of
carbonate and clay sediments however may have also been
significant. The Lower and Upper Marls overall represent a
major long-term pattern of alternating clay-carbonate
sedimentation during Lower Tertiary time, whereas the Clarence
Valley Marl represents essentially uninterrupted clay
sedimentation. These facies variations may reflect different
local conditions of deposition such as proximity to the source
of clay, seafloor relief and current activity, with carbonate
sedimentation also controlled by biogenic carbonate produc·tivity
factors.
In other areas of the regional depositional environment,
background hemipelagic sedimentation of clay was periodically
interrupted by mass-flow events which redeposited coarser
sediments interpreted as being derived from shallower water
environments. Large-scale slumping is indicated in one area
(Pukemuri Siltstone, Wairarapa) and facies changes are marked,
with implications of significant seafloor relief and instability
resulting from extensional tectonics.
6.3 MINERALOGY
The three types of smectite-rich deposits (Section 6.1) are
characterised by the following mineralogical features:
(1) Primary bentonites occur as horizons
with a distinctly different mineralogy
to that of the enclosing sediments.
They are composed of smectite (or
interstratified smectite-illite, see
Section 6.3.1) which is commonly
accompanied by authigenic silica and
zeolite minerals. Other clay mineral
components are very minor or lacking.
Non-authigenic heavy and light minerals
in primary bentonites form restricted
volcanic suites.
(2) Secondary bentonites have a mineralogy
dominated by smectite clay (or smectite
illite) .and volcanic heavy and light
minerals, similar to primary bentonites.
Non-volcanogenic components are also
likely to be present however, as a
result of mixing during transportation or
reworking.
(3) Other smectite-rich deposits are not
generally as mineralogically well defined
as primary and secondary bentonites and
typically show gradation into enclosing
lithologies. In addition to smectite,
other clays are commonly a major
component of the deposits and heavy and
light mineral suites are not dominated by
volcanic minerals.
150
6.3.l Volcanic Origin
The lithological aspect of the smectite-mudstones in the East
Coast Deformed Belt does not resemble that of primary bentonites
produced by the in-situ alteration of ash-fall beds. In
Marlborough, where stratigraphic and sedimentary relationships
are evident, the Marls have gradational contacts with underlying
and overlying limestone units. The smectite-mudstone beds within
the Marls are calcareous and the insoluble residues from the
interbedded limestones have the same mineralogy as the mudstones.
151
The dominant component of the clay fraction of the smectite
mudstones is generally a montmorillonitic clay. The type of
smectite does not appear to be definitive of a particular origin -
either volcanic or otherwise. Weaver and Pollard (l973} suggest
that the montmorillonite species is most likely to form from the
alteration of volcanic material, however their data base is
strongly biased towards volcanogenic bentonites. In recent
sediments, particularly in the South Pacific Ocean (Griffin et al.,
1968) basaltic volcanic material has altered to smectite and the
most common species appear to be trioctahedral saponite and
dioctahedral nontronite (Cole and Shaw, 1983). Weaver (1958)
suggested that smectites derived from volcanic material should not
collapse with K+-saturation in contrast to smectites which have
inherited a high tetrahedral charge from micaceous precursors.
However as discussed in Chapter 4, Section 4.3.2, K+-fixation
more probably reflects total layer charge and cannot'be simply
related back to a particular source.
It seems probable that uniformity in smectite mineralogy, rather
than a type of smectite, is more indicative of genesis by
alteration of a particular ash deposit in the marine environment.
152
The 'classic' bentonites of Cretaceous age in Wyoming, Montana
and South Dakota for example. have. a very similar smectite
mineralogy (Weaver and Pollard, l973). The detailed XRD analysis
of the smectites in the mudstones of this study showed up
significant variations in mineralogy and layer charge,
particularly within the Marl units. The lack of consistent
stratigraphic trends suggests the variability cannot be attributed
to changing volcanic ash composition.
Illite is a major component in the clay fraction of the smectite
mudstones and sometimes exceeds the amount of smectite. As
discussed in Chapter 4, Section 4.2.2, the illite and smectite
clays are discrete phases with no evidence of interstratification.
Interstratified smectite-illite clays are characteristic of
K-bentonite (or meta-bentonite) deposits which are well
documented in the literature (e.g. Weaver, 1953). These bentonites
are generally believed to be the result of burial diagenesis of
deposits that were originally composed of smectite only. Intense
deformation accompanied by localised elevated temperatures might
also be expected to convert some smectite into interstratified
smectite-illite given a sufficient period of time. However
illite in the highly tectonised units such as the Kandahar and
Wanstead Formations is a discrete phase like that in the less
deformed Marls and is therefore an original sedimentary constituent
of the mudstones. The abundance of illite suggests that the
smectite-mudstones are extensively transported/reworked secondary
bentonites or are not volcanic in origin.
Kaolinite is abundant in the Kandahar Formation, particularly
near the base where large-scale redeposition and mixing with the
Pukemuri Siltstone is apparent. The presence of kaolinite in the
Kandahar Formation is a likely result of this mixing.
The sand fraction mineralogy of bentonites is commonly used as
evidence of a volcanic origin. In a review of heavy mineral
suites in bentonites, Weaver (1963) found that primary bentonites
are characterised by restricted suites containing biotite,
euhedral zircon, apatite and sometimes titanite, hornblende and
pyroxene. In the light mineral suites of primary bentonites,
feldspar is generally dominant.
The heavy and light mineral suites in the majority of smectite
mudstones studied are characterised by a lack or only trace
amounts of minerals which are of possible volcanic origin.
Authigenic minerals such as pyrite and baryte dominate in the
heavy fractions. The light fractions are made up largely of
153
chert fragments, indicating a secondary origin for the quartz
component in the smectite-mudstones. Thin sections of two
greensand beds (HBlO, HB12) in the Wanstead Formation were also
studied. The sandstones are rich in quartz and contain only minor
amounts of possible volcanic feldspar. There is also no evidence
that the glauconite is derived from volcanic material.
The presence of volcanic minerals including glass shards in
smectite-mudstones from Porangahau and the Gisborne area is
reported by Fyfe (1934), Gordon et al. (1955) and Ritchie
(1962) and appears to be the only basis for previous use of
the term bentonite. No such volcanic suite was found in the
Porangahau mudstone in this study however and the occurrence of
a melange zone at Porangahau invalidates any genetic
interpretations from mineralogy (see also Pettinga, 1980, p.101).
Two groups of smectite-mudstones in this study differ from the
rest in their sand fraction mineralogy. Firstly, mineral suites
from two samples of the massive interval of the Marl in the
Clarence Valley contain biotite, euhedral zircon, hornblende and
plagioclase which may be volcanic. The laterally equivalent
Grass Seed Volcanics in the Clarence Valley is a likely source of
these minerals. Other non-volcanic minerals such as tourmaline,
chlorite, muscovite, quartz and microcline feldspar dominate the
mineral suites from the Marl however. Some of these minerals may
be authigenic in origin but it seems more probable that they are
detrital and represent a significant non-volcanic input into the
depositional environment of the Marl. The second group of
samples with distinctive sand fraction mineralogy is the red
smectite-mudstones from Hawkes Bay. Their heavy mineral suites
appear to be the closest examples of restricted volcanic suites.
Biotite is prominent and traces of volcanic glass are possibly
present in two samples. Some non-volcanic contamination however
is evident from the presence of muscovite+ chlorite and all the
red smectite-mudstone samples come from melange zones (P.R. Moore,
J.R. Pettinga, 1984, pers. comm.) ,making interpretation of heavy
mineral suites difficult. Red smectite-mudstones also occur in
East Cape (P.R. Moore, 1983, pers. comm.) and further
investigation of stratigraphically in-situ beds is needed. The
154
red colouration can be secondary (as observed in Wairarapa) as well
as a primary feature which may be indicative of a volcanic origin.
6.3.2 Sedimentary Origin
The mine'ralogical features of the smecti te-mudstones, with the
exception of the heavy mineral suites of red smectite-mudstones
from Hawkes Bay, do not indicate a wholly or dominantly direct
volcanic origin. Sedimentological features, as discussed in
155
Section 6.2.2 indicate that clay-rich beds represent
hemipelagic sedimentation and/or redeposition by mass-flow• events.
In the cas·e of hemipelagic deposits, the clay is likely to be
terrigenous detritus. Redeposited clays however may be originally
either detrital or neoformed (precipitated from solution in
sediments on the seafloor (Millot, 1970)).
The abundant illite in the smectite-mudstones is very probably
detrital and a similar origin is possible for the smectite clay.
Detrital illite and smectite may be derived from older sediments
and/or from soils. During the Lower Tertiary, the New Zealand
landmass is considered to have been low in relief and weathered
under a subtropical to tropical climate (Suggate et al., 1978,
p. 438-439, 718). The formation of smectite in modern soils is
favoured under warm climates in neutral poorly-drained
environments (Dixon and Weed, 1977) and it is likely that such
conditions existed on the low-lying landmass. A more extensive
study is necessary to further consider the possibility of the
smectite clay being derived from soils and to identify possible
smectite-bearing source rocks, as large quantities of smectite
clay have to be accounted for. There are also two other problems
evident in this study with advancing a detrital origin for the
smectite in the mudstones. Firstly, the smectite appears well
crystallised which is not typical of detrital clays, particularly
those formed in soils. Secondly, there is an absence of
interstratified clays (involving two different clay mineral types)
in the mudstones, whereas detrital clays are commonly
interstratified due to transformations during weathering,
transportation and deposition.
A neoformation origin is possible for the redeposited smectite
clay in the mudstones and is consistent with the high degree of
crystallinity and lack of interstratification of the clays.
Neoformation has been suggested as the origin of smectite clay
in the Upper Cretaceous European Chalk (Jeans, 1968; Millot,
J.970) and in Oligocene limestones in the North Island of
156
New Zealand (Hume, 1978). With chemical weathering on land, large
amounts of dissolved constituents such as Si, Ca and Mg are
supplied to the marine environment and chemical sedimentation
prevails (Millot, 1970). Such a situation during Lower Tertiary
time is indicated by the dominance of carbonate, chert and
glauconite in the Lower Tertiary sequences throughout the
East Coast Deformed Belt and a neoformation origin for smectite
clay appears likely.
6.4 GEOCHEMISTRY
The geochemical distinction between primary bentonites, secondary
bentonites and other smectite-rich deposits is not as well
documented as the sedimentological and mineralogical distinctions.
Two generalisations appear justified however from data presented
in the literature. Firstly, volcanogenic bentonites are composed
of smectite minerals with ideal structural formulas. Weaver and
Pollard (1973) collated nearly a hundred analyses of volcanically
derived montmorillonites-beidellites and all have structural
formulas which are close to ideal. Secondly, the trace element
geochemistry of primary and secondary bentonites reflects their
volcanic origin. Smith (1967), Jeans et al. (1982) and
Pacey (1984) have shown that bentonites have a distinctly different
trace element chemistry to that of surrounding sediments, which
can be related back to an original volcanic composition.
6.4.1 Volcanic or Sedimentary Origin
The smectite-mudstones for which structural formulas were
calculated in this study commonly contain smectite and illite
clays which appear from the formulas to be non-ideal. This result
suggests that the clays in the .mudstones have a different origin
to the structurally ideal smectites characteristic of bentonites.
Clays with structural irregularities are likely to be detrital
rather than neoformed. However, the paradox of structurally
irregular but well crystallised smectites requires further
investigation.
The concentrations of trace elements in the smectite-mudstones can
be compared with those in an average mudstone given by Turekian
and Wedepohl (1961). Since the majority of the smectite-mudstones
analysed are calcareous, the mean values of the trace element
concentrations in an average shale and an average carbonate were
used as a basis for comparison (Table 6.1). The trace element
concentrations in the smectite-mudstones were normalised against
the mean shale-carbonate concentrations and the resulting plot
showing the field of trace element compositions of the smectite-
mudstones is given in Fig. 6.1.
Table 6.1: Trace Element Abundances (ppm) in Shale and Carbonate (from Turekian and Wedepohl, 1961) and Mean ShaleCarbonate Values
Shale Carbonate Mean Shale-Carbonate
Sr 300 610 455 Rb 140 3 71.5 Zr 160 19 89.5 y 26 30 28 Nb 11 0.3 5.7 Pb 20 9 14.5 Th 12 1.7 6.9
Ga 19 4 11.5
157
10 9 8 7
6 QI ....
5 d c: 0
..c a 4 ....,
~ c:
.3 d QI
d -'= VI -0 2 c: d OJ E
' (11
0.. E d VI
1 c: := 0·9
OJ 0·8 ...., § 0·7 ~
§ 0·6 ..c <(
.... O·S c: OJ E ~ 0·4 L..i
OJ ...., 2 0-3 ~
0·2
Sr Rb Zr y Nb Pb ih Ga
Compositional field of Smectite Mud stones
Figure 6.1: Trace element abundances in smectite-mudstones normalised against the mean of the abundances in a typical shale and carbonate.
158
The compositional field of the smectite-mudstones encompasses
the mean shale-carbonate composition, with all elements varying
both above and below the mean concentration levels. In contrast,
Pacey (1984) found that bentonites in the Chalk of England had a
strongly differentiated trace element pattern enriched in some
elements and depleted in others relative to an average shale,
which could only be explained by inheritance from a volcanic
precursor. The concentrations of elements such as Zr, Nb and Th
in particular remain unchanged during alteration of volcanic ash
to smectite. The trace element pattern of the smectite-mudstones
in this study, which is undifferentiated with respect to an
average shale-carbonate, indicates a sedimentary rather than
volcanic origin.
The trace element geochemistry of two samples from the Grass Seed
Volcanics further suggests that the smectite-mudstones are not
volcanogenic. The Grass Seed Volcanics are characterised by high
concentrations of Zr, Nb and Ga and low concentrations of Rb, Pb
and Th relative to the smectite-mudstones. These differences
show up well in some scatter plots, for example Rb vs Nb and Ga
vs Th (Fig. 6.2). The Marl in the Clarence Valley at least would
be expected to have a similar trace element geochemistry to the
Grass Seed Volcanics, but this does not appear to be the case.
159
The red smectite-mudstones from Hawkes Bay differ from the other
smectite-mudstones and also the Grass Seed Volcanics in containing
relatively high levels of all the trace elements except Sr. This
geochemistry may be a result of their non-calcareous nature, but
could also reflect a volcanic parent with a different composition
to the Grass Seed Volcanics.
133·5
ppm Rb
• 1·6
20·4
ppm Ga
• 0 • •
H
Figure 6.2: and Ga VS Th showing the samples.
•
I • • • • • •
I
• • • •
•
• • • • ' •
• • • • • • • • • •
• • • •
I
• •
ppm Nb
Grass Seed Volcanics
Ii •
• • • • • • ..
• • • •• • ...
• • • • • • .o t
' • • • • •
ppm Th
Grass Seed Volcanics
/\ 32
• • • •
• • • •
14·2
Trace element concentration scatter plots of Rb vs Nb in smectite-mudstones and associated lithologies,
distinctive geochemistr_y of the Grass Seed Volcanics
160
161
Trace elements have been used successfully for regional
stratigraphic correlation purposes in the case of primary
bentonites, which are geochemically distinct from associated
lithologies and may show stratigraphic trends in composition
corresponding to volcanic differentiation trends (e.g. Huff, 1983).
In contrast, the trace element geochemistry of the smectite
mudstones in this study does not appear to be a useful means of
correlation.
6.5 SUMMARY AND CONCLUSIONS
(1) Lower Tertiary smectite-mudstones in the East Coast Deformed
Belt are considered to be non-volcanic in origin.
(2) Genesis by in-situ alteration of ash-falls is untenable as
the smectite-mudstones are not localised in thin
mineralogically/geochemically distinct horizons and are not
free of non-volcanic detritus. Discounting the possibility
that the. smectite-mudstones are secondary bentonites is more
difficult and depends on evidence of relative contributions
from possible volcanic and non-volcanic sources.
(3) The smectite-mudstones are laterally extensive over
kilometres and are on the order of tens of metres thick,
in contrast to secondary bentonites formed during phases
of volcanogenic sedimentation. There is no evidence of major
volcanic activity contemporaneous with the mudstones.
(4) The clay mineralogy of the mudstones consists of smectite
and illite. The smectite clay is montmorillonitic but
often contains interstratified layers of other dioctahedral
smectites and has variable layer charge. The smectite is
typically well crystallised although commonly appears from
structural formulas to have a non-ideal structure with a
deficiency in aluminium. These features, with the
exception of high crystallinity, are not characteristic of
volcanogenic smectites with uniform mineralogy and ideal
structures. Illite is a major sedimentary constituent of
162
the mudstones, indicating a significant non-volcanic detrital
input. No stratigraphic trends in clay mineralogy are
evident.
(5) The paucity of minerals of possible volcanic origin in the
sand fractions of the smectite-mudstones would not be
expected in volcanogenic deposits. Red smectite-mudstones
are possibly an exception and require further investigation.
(6) The smectite-mudstones have a typical sedimentary trace
element geochemistry, unlike that of associated localised
volcanics. Variations in trace element abundances do not
show distinct stratigraphic trends and the lack of success
in using geochemistry for regional stratigraphic correlations
further points to a non-volcanic origin for the smectite
mudstones.
(7) The lithology of the smectite-mudstone units varies
regionally from alternating marl-limestone to interbedded
mass-flow greensands and mudstones. The mudstone beds are
considered to represent hemipelagic sedimentation of
detrital clays and/or mass-flow redeposition of detrital
or neoformed clays.
163
(8) An open oceanic, relatively deep water environment of
deposition of the smectite-mudstones is envisaged. The
smectite-mudstone units pass laterally into other carbonate
and elastic lithofacies, reflecting local variations in
depositional conditions which were probably partly controlled
by offshore extensional tectonic activity.
ACK...l'iOWLEDGEMENTS
I wish to thank Dr J.R. Pettinga and Dr S.D. Weaver of the Geology
Department, University of Canterbury for supervision of this thesis.
I am indebted to Dr Pettinga who suggested the thesis topic and
contributed much time in the field and in discussion of many aspects
of the project. Dr Weaver provided valuable assistance in the area of
geochemistry. Financial support for the thesis was provided by DSIR
Research Contract (C-40) and this is gratefully acknowledged.
Fieldwork on several occasions was assisted by D.X. Lauw and
A.E. Alloway (Geology Dept, u. of C.) and W.M. Prebble (Geology Dept,
164
U. of Auckland). Much useful information and guidance was obtained from
discussions with Dr D.W. Lewis and Dr J.D. Bradshaw (Geology Dept,
U. of C.) and M.B. Reay, Dr M.G. Laird, P.R. Moore, G.H. Browne and
Dr G.J. van der Lingen (N.Z. Geological Survey). Mr and Mrs D. Parsons
of Woodside Creek provided acconunodation and hospitality for several
fieldtrips.
Paleontological age determinations were done by Dr C.P. Strong and
H.E.G. Morgans (N.Z.G.S.) and A.A. Cameron (Geology Dept, U. of C.)
Optical microscopy was assisted by Dr D. Shelley (Geology Dept, U. of C.)
and Dr D. Smale (N.Z.G.S.). Dr A.S. Campbell, Dr R. Harrison and F. Fox
of the Soil Science Department, Lincoln College advised and assisted
with DTA and cation exchange methods. Dr J.E. Fergusson (Chemistry
Dept, U. of C.) helped with AA analysis and computing work on chemical
data. Various technical assistance was provided by A.E. Alloway,
K.M. Swanson, A. Downing and D.J. MacDonald (Geology Dept, U. of C.);
J.B. Smith (N.Z.G.S.); Dr J.P.L. Walker and K.A. Card (Botany Dept,
U. of C.).
Typing was done by H.E. Licence and draughting by M.A. Perera both of
KRTA Ltd and the support of other staff at KRTA in the final stages of
the project is appreciated.
I wish to thank my parents and friends for their support and
encouragement throughout.
165
166
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169
A;i?J?ENDIX I - UNIVERSITY OF CANTERBURY
ROCK CATALOGUE NUMBERS
Representative samples of smectite-mudstones and associated lithologies
Thesis Number
W6
Wl3
C7
ell
us Ul3
M2
Sl
SlO
B4
HB3
HBl4
HB.17
WPl
W04
WAl
Cl2 Greens and
U7 Limestone
U8 Limestone
LS Grass. Se.ed
HBlO Greens-and
HB12 Greens and
University of Canterbury Number
Smectite-Mudstones
10371
10372
10373
10374
10375
10376
10377
10379
10380
10381
10382
10383
10384
10385
10386
10387
Associated Lithologies
10390
10388
10389
Volcanics 10378
10391
10392
170
APPENDIX II - MICROFOSSIL AGE DETERMINATIONS
-·
FRF No. LOCALITY GRID REF. STRATIGRAPHIC POSITION SAMPLE NO. PALEONTOLOGIST AGE
P30/fl75 Woodside Creek, 945189 Base Lower Marl W4 C.P. Strong NZGS Dw
Upper Gorge
P30/fl76 Woodside Creek, 947188 Top Lower Marl W8 C.P. Strong NZGS Dm-Dh
Upper Gorge
P30/£177 Woodside Creek 954191 Base Upper Marl WlO C.P. Strong NZGS Ab
Upper Gorge
P29/f218 Chalk Range 850204 Base Lower Marl Cl A.A. Cameron D u. of C.
P29/f207 Chalk Range 844207 Top ,Upper Marl? Cl3 C.P. Strong NZGS • Dw
P30/fl81 Chalk Range 824196 Top Upper Marl Cl8 A.A. Cameron D-A u. of c.
I P30/£182 Mead Stream Gorge 756162 Base Upper Marl M3 A.A. Cameron I Ab
u. of c. I
P30/fl83 Mead Stream Gorge 755163 Top Upper Marl M2 A.A. Cameron j I Dp-Ar I
U. of c. ' I I
031/£146 Fells Basin 416844 Base Marl Sl2 C.P. Strong NZGS I ?Dt-?Dm i I
031/fl45 Fells Basin 417844 Massive Interval of Marl 88 C.P. Strong NZGS i Dp I
i
030/f44 Bluff Stream 585977 Base Amuri Limestone Bl A.A. Cameron I Mh I
u. of c. I !
i i
(Appendix II Cantin.)
APPENDIX II - Continued
FRF NO. LOCALITY GRID REF. STRATIGRAPHIC POSITION SAMPLE NO. PALEONTOLOGIST AGE
S28/fl24 Mungaroa Point 124569 Mungaroa Limestone W04 H.E.G. Morgans Dt NZGS
S28/fl25 Awheaiti Stream 183642 Base Kandahar Formation WAS H.E.G. Morgans Ab NZGS
S28/fl26 Pukemuri Stream 165626 Kandahar Formation WPl H.E.G. Morgans Dm-Dh NZGS
S28/fl27 Awheaiti Stream 172643 Kandahar Formation WAl H.E.G. Morgans Ab NZGS
S28/fl28 Oroi Stream 145601 Top Pukemuri Siltstone W02 H.E.G. Morgans N.F. NZGS
V22/f284 Waewae Stream 425308 Base Wanstead Formation HB8 C.P. Strong NZGS ?Dw-?Dh
W22/f77 Waimarama Beach 524451 Base Wan stead Formation HB13 C.P. Strong NZGS D?
W22/f80 Waimarama Beach 524451 Base Wanstead Formation HB13 A.A. Cameron Dt recolln. u. of C.
W22/f79 Waimarama Beach 524451 Base Wanstead Formation HB12 A.A. Cameron N.F. u. of C.
W22/f78 Coast, above Red Is. 422507 Wanstead Formation ' HB21 A.A. Cameron Dt-Dw u. of c.
173
APPENDIX III - MUDSTONE CARBONATE CONTENTS
MUDSTONE UNIT SAMPLE NO. % Caco3
W3 63.3
W4 54.0
Lower Marl, W6 37.9
Amuri Limestone W7 58.7
W8 45.5
W9 36.6
C3 65.7
C7 46.6
C9 42.5
ClO 30.3
Ull 52.3
WlO 63.5
Upper Marl, Wl3 66.3
Amuri Limestone Wl4 61. 7
Cll 50.2
U4 54.1
us 67.0
U9 66.5
Sl 41.2
Marl (Clarence Valley), 82 45.1
Arouri Limestone SS 65.6
88 43.4
SlO 60.0
WAl 25.5
WA3 56.5
Kandahar Formation WOl 35.8
WPl 29. 7
WP2 39.8
WP3 33.0
HB3 19 .1
HB6 1. 3
Wanstead Formation HB9 21.0
HB14 2.3
HB15 7.6
HB17 4.7
HB21 9.2
Whangai Formation HB18 34.8
Untreated No. 21
Si02 60.80
Al2o3 18.70
MgO 4.78
Fe2o3
3.80
K20 0.08
CaO 2.56
Na2o -
Ti02 0.23
MnO 0.03
P205 0.04
L.O.I. 9.43
Total 100 .45
* Duplicate sample
APPENDIX IV - MAJOR ELEMENT XRF ANALYSES OF A.P.I. BENTONITE STANDARDS
Samples are ca2+-saturated insoluble residues or are untreated
Untreated No.21 No.23 No.24 No.24* No. 26 No.26
60.44 59. 82 59.53 60.30 66.34 64.08
18. 70 19.33 l7.32 17.42 19.09 18.05
4.58 4.39 6.40 6.38 2.29 2.13
3.90 3.30 1.96 1.96 3.39 3.50
0.04 0.06 0.12 0.12 0.37 0.09
3.2l 3.44 ?.59 3.62 0.61 2. 77
- - - - 2.46 0.16
0.23 0.33 0.31 0.32 0.15 0.14
0.01 0.02 0.02 0.01 - -
0.04 0.02 0.04 0.03 0.04 0.04
9.63 9.79 11.37 10.10 5.63 8.00
100.78 100. 50 100.66 100.26 100.37 98.96
No.26* No.31
66.03 54.61
18.37 22.02
2.14 1.94
3.50 7.00
0.09 3.24
2.75 2. ;22
- -
0.14 0.58
- 0.01
0.03 0 .04.
7.00 9.53
100.05 101.19
W8
Si02 65.l2
Al2o
3 l6.86
MgO 2.83
Fe2o3
4.87
K20 2.27
CaO 2.02
Na2o -
Ti02
0.59
MnO 0.02
P205 0.09
L.O.I. 6.33
Total 101.00
*Duplicate sample
APPENDIX V - MAJOR ELEMENT XRF ANALYSES OF SMECTITE-MUDSTONE CLAY FRACTIONS
All samples are ca2+-saturated insoluble residues
W9 WlO Wl3 Wl3* Wl4 C3 C7 C7* Cll
60.60 65.68 7l. 33 71.48 71.54 62.94 64.57 64.95 67.73
18.81 16 .08 13.76 13. 79 13.92 17. 71 17.07 16.92 15.26
2.69 2.06 1.80 l.83 1.89 3.03 2.43 2.46 2.46
6.03 5.34 3 .98 4.03 3.76 4.34 5.20 5.27 4.03
2.65 1.88 1.33 l.34 1.44 2.29 l.82 l.80 1.66
1.87 l.82 l.80 1.81 1.66 2.32 2.24 2.23 1.89
0.12 0.09 O.l2 - 0.17 - O.l3 0.17 0.06
0.59 0.62 0.47 0.47 0.48 0.60 0.54 0.55 0.62
0.01 - - - 0.02 O.Ol 0.02 0.01 0.02
0.10 0.12 0.24 0.25 0.16 0.20 0 .14 0.13 0.09
5 .93 4.97 5.30 5.23 4.17 6.43 6.13 5.13 6.17
99.40 98.66 100.13 100.23 99.21 99.87 100.29 99.62 99.99
U4 U4*
62.84 62;97
17.28 17.46
2 .98 2.93
5 .89 5.99
2.27 2.29
1.83 1.87
- 0.05
0.57 0.58
0.02 0.01
0.12 0.11
5.67 5.97
99.47 100.23
(Appendix V Cantin.)
APPENDIX V - Continued
U9 Ull S2 SS SS Ll4 W04 HB3 HB6 HB14 HB21
Si02 60.21 67 .ll 63.73 62.20 65.34 64.04 66.52 61.94 72.28 67.35 69. 31
Al2o
3 19.ll 15.20 16.27 16.00 15.39 17 .11 15.81 18.96 ll.32 16 .41 14.54
MgO 2.79 2.75 3.16 3.27 3.16 2.69 2.33 1.97 l. 78 2.49 l. 71
Fe203
5.57 4.88 5.54 5.74 5.62 4.21 3 .91 5.83 6.56 5.19 4.63
K2
0 2.87 1.85 1.49 2.11 1.28 1. 74 2.05 1.89 1.56 1.57 1.46
CaO 2.08 1.83 2.23 2.26 2 .13 2.33 1.83 1.81 1.39 1.90 l. 72
Na2o 0.18 0.19 0.06 0.12 - 0.17 - 0.11 0.07 0.24 -
Ti02
0.69 0.48 0.61 0.69 0.56 0.58 0.48 0.73 0.46 0.59 0.55
MnO 0.01 - 0.02 0.01 - 0.02 - 0.01 0.03 - 0.02
P205 0.15 0 .10 0.15 0.33 0.15 0.17 0.12 0.08 0.08 0.10 0.04
L.O.I. 5.97 6.43 6.70 6.73 6.87 6.93 7.70 7.57 5.23 5.73 5.40
Total 99.63 100.82 99.96 99.46 100.50 99.99 100.75 100.90 100.76 101.57 99.38
APPENDIX VI: ATOMIC ABSORPTION ANALYSIS OF CATIONS IN HCL LEACHATES
Sample
W6
W6
Wl4
Wl4
C7
C7
en
Cll
Ull
Ull
82
82
SB
SB
HB3
HB3
HB.6.
HB6.
HB14
HBJ.4
HBJ.7
HB17
Samples and duplicates are untreated <63µm fractions
Ca ppm
700
673
ll56
ll56
869
825
935
945
950
983
838
763
BJ.5
738
355
363
.13 .8
14.1
33.l
33.3
62.5
60.0
Na ppm
0.95
0.78
0.58
0.95
0.60
0.42
0.51
0.47
1.10
0.55
13.8
J.l. 8
1.09
0.85
18.0
-19.0
2.47
2.13
26.8
25.5
21.0
20.8
Mg ppm
5.95
8.75
3.00
3.75
3.75
3.63
3.44
3.25
8.38
.11.9
5.94
4.38
3.13
3.13
6.75
7.00
7.94
6.63
7.88
6.50
4.19
4.38
K ppm
1.05
3.95
1.80
2 .J.5
0.63
0.65
1.33
1.43
1.20
2.80
3.23
4.60
2.35
2.48
5.78
6.05
4.05
3.82
5.73
5.30
4.58
4.87
Fe ppm
12.3
20.6
14.8
17.6
8.85
7.85
14.9
13.7
12.0
21.8
13 .1
9.80
19 .8
22.2
25.0
25.6
14.8
8.07
14.5
9.42
4.75
5.28
Mn ppm
0.89
0 .89
0.27
0.36
1.52
1.37
0.17
0.15
0.99
0.95
0 .19
0.19
0.13
0.11
2 .10
2.08
0.25
0.17
0.00
0.00
0.09
0.00
177
APPENDIX VII - TRACE ELEMENT XRF ANALYSES OF SMECTITE-MUDSTONE WHOLE-ROCK SAMPLES
Geology Dept Sr Rb Zr y Nb Pb Th Ga Sample File No. ppm ppm ppm ppm ppm ppm ppm ppm
W3 11363 507 30 33 19 5 8 5 3
W6 11365 431 52 47 12 8 9 6 7
W8 11366 439 53 51 9 5 8 5 7
WlO 11388 677 31 41 9 5 7 4 4
Wl3 11389 613 20 31 10 5 5 2 2
Wl4 11364 710 23 30 9 4 5 2 3
C3 11367 434 30 32 14 6 6 4 4
C7 11368 456 42 44 14 8 9 6 6
C9 11369 395 49 51 10 6 9 6 8
Cll 11370 699 34 50 12 5 7 3 4
Cl3 11380 420 52 58 12 7 10 5 8
U4 11371 790 43 55 12 7 8 5 6
U9 .1.1372 785 34 41 10 6 7 4 4
Ull ll381 75.1 35 34 .1.1 7 7 4 5
Ul3 1.1397 435 54 49 11 5 7 5 6 Ul6 11379 559 49 43 12 7 8
I-' 5 5 --.]
co (Appendix VII Cantin.)
Sample
M2
M3
Sl
SS
SB
SlO
Sl2
Bl
B4
WAl
WAS
WOl
W04
HB3
HB6
HB9
HBl4
HB21
Geology Dept File No.
11398
ll399
11374
11382
11393
11390
11384
11386
11373
11473
11474
11475
ll476
11376
_ll375
11377
11392
11391
Sr ppm
726
858
584
603
501
671
604
385
1222
506
438
598
232
390
l23
153
285
320
APPENDIX VII Continued
Rb ppm
28
32
43
22
38
23
19
44
82
67
69
62
69
91
109
59
l05
83
Zr ppm
31
53
136
58
148
70
59
60
72
73
89
82
74
106
l41
107
134
81
y
ppm
8
10
9
14
11
9
10
21
9
10
11
12
34
14
20
21
33
11
Nb ppm
5
6
7
3
6
4
3
4
9
8
6
8
6
10
11
8
9
9
Pb ppm
6
7
8
7
8
7
5
9
14
9
10
9
13
11
11
10
16
10
Th ppm
4
4
6
4
4
4
4
5
8
6
8
6
9
9
9
8
11
8
Ga ppm
4
5
6
4
6
3
3
7
13
12
12
11
14
14
16
10
18
14 I-' -.J I..O
AGV-1
A B
Sr 660 662
Rb 68 67
Zr 221 220
y 20 21
Nb 12 15
Pb 38 36
Th 6.3 6.5
Ga 20 20
APPENDIX VIII - ACCURACY OF XRF ANALYSES OF TRACE
ELEMENTS IN INTERNATIONAL STANDARDS
GA SY-2
A B A
305 310 261
173 175 222
135 150 N.A.
21 21 124
13 10 N.A.
32 30 81
20 17 373
15 16 27
NIM-N
B A B
270 255 260
220 4 5
270 N.A. 22
130 7 7
25 N.A. 2
80 5 6
380 2 0.4
28 16 16
A XRF analyses in this study of trace elements in international standards, Dept. of Geology, University of Canterbury
B Recommended results in the literature for trace elements in international standards
N.A. = Not Analysed f-' ()) 0
