GeoZogicaZ Survey of Wes tern A u s t r a Z i a
Record 1 9 8 i / 8
EXPLANATORY NOTES
Of4 THE
SHARK BAY - EDEL 1:250 000 GEOLOGICAL SHEET
WESTERN AUSTRALIA
BY
BnPn BUTCHER, WnJaEn VAN D E GRAAFFj AND RaMe HOCKING
PERTH 1381
Map r e f e r e n e e S G 4 9 - 8 S G 4 9 - 1 2
N a t i o n a l L i b r a r y of A u s t r a l i a card number and ISBN
0 7 2 4 4 8 1 9 0 7
(ii I
CONTENTS
In t roduct ion .. .. * . .. Previous work . * .. ..
Physiography I. .. .. .. Climate .. .. .. .. Tides and s a l i n i t y g r a d i e n t s .. Geomorphology I. .. ..
Edel Province .. .. Peron Province .. .. Gascoyne-Wooramel Province
S t r a t i g r aphy .. .. .. Palaeozoic .. .. ..
Tumblagooda Sandstone Dirk Hartog Formation
Cretaceous .. . * .. Winning Group .. Toolonga C a l c i l u t i t e
Cainozoic .. T e r t i a r y
P le i s tocene Holocene S u p e r f i c i a l
S t r u c t u r e * . .. Geological h i s t o r y Economic geology
Petroleum * .
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.. Evaporite Minerals Water Supplies .. Construct ion m a t e r i a l s
Selected re ferences * .
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ILLUSTRATIONS
.. .. .. 5 F igure 1 Physiographic s k e t c h map 2 S t r u c t u r e contour maps showing d e p t h
t o magnetic basement and contours .. 3 S t r u c t u r e contours and i sopachs , Dirk
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.. 1. .. 2 4 Hartog I s l a n d .. ..
Shark Bay-Edel 1:250 0 0 0 g e o l o g i c a l series * . .. .. .. .. .. (pocket )
TAB LE
.. .. .. 10 Table 1 S t r a t i g r a p h i c summary ..
EXPLANATORY IWTES ON THE
SHARK BAY - EDEL 1:250 000 GEOLOGICAL SHEET WESTERN AUSTRALIA
BY
BBP, BUTCHER) W , J , E , VAN DE GRAAFFJ AND RmM, HOCKING
INTRODUCTION
The SHARK BAY-EDEL 1:250 000 Shee t (SG/59-8,12) i s
bounded by l a t i t u d e s 25OS and 27OS and long i tudes 112°50'E
and 1 1 4 O E , and covers p a r t of t h e sou th -cen t r a l Carnarvon Basin. The only s e t t l e m e n t s i n t h e area are t h e f i s h i n g
p o r t of Denham, t h e s m a l l township of Useless Loop, a caravan park and t o u r i s t r e s o r t a t Nanga, and t h e s t a t i o n homesteads
of Carrarang, Dirk Hartog, Nanga, Peron and T a m a l a .
A c c e s s i s by p a r t l y s e a l e d road t o Denham, by unsealed
s h i r e road t o Useless Loop, and by s t a t i o n t r a c k s elsewhere.
A c c e s s t o t h e northwestern p a r t of Edel Land i s very d i f f i - c u l t because of s teep-s ided sand dunes.
I n t h e p r e s e n t survey, a i r photographs a t a scale of
1:84 000 (1968) and 1 : 4 0 0 0 0 (1964-65) w e r e used, t oge the r w i th 1:lOO 000 topographic maps which w e r e used as base maps,
PREVIOUS WORK
Ea r ly g e o l o g i c a l work by Forman (1937), Clarke and
T e i c h e r t (1948, p . 4 4 ) , and Conrad and Maynard (1948) w a s ............................................................ * Sheet names are p r i n t e d i n upper case le t ters t o avoid
confusion wi th l i k e p l a c e names.
1
summarized by Johnstone and Playford ( 1 9 5 5 ) , who mapped the area for West Australian Petroleum Pty Ltd (Wapet).
Konecki and others ( 1 9 5 8 ) reported on a regional study of the area conducted by the Bureau of Mineral Resources, and also incorporated the work of Johnstone and Playford ( 1 9 5 5 ) .
Logan ( 1 9 5 9 ; 1 9 6 1 ) described Holocene sediments within Shark Bay, including the occurrence of modern algal stroma- tolites in Hamelin Pool. Detailed studies of the stromato- lites, related algal mats, and the Quaternary sediments of the region were reported by Logan and others ( 1 9 7 0 ; 1 9 7 4 ) ,
who incorporated the results of unpublished theses by Collins ( 1 9 6 7 ) and Tuppin ( 1 9 6 9 ) . Playford and Cockbain ( 1 9 7 6 ) , and Playford ( 1 9 8 0 ) , also described the stromatolites in Hamelin Pool.
A geological reconnaissance of Dirk Hartog Island by Playford and Chase ( 1 9 5 5 ) resulted in Wapet undertaking a programme of scout drilling to locate an anticlinal feature in the Tertiary limestones, the culmination of which was drilled by Dirk Hartog 17B. This well (total depth 1 5 2 3 . 3
m) penetrated the first recognized Silurian strata in Western Australia (Glenister and Glenister, 1 9 5 7 ) .
Tamala 1 (Kempin and Fujioka, 1 9 7 3 ) drilled by Oceania Petroleum Pty Ltd to 1 2 2 5 . 2 m, is the only other petroleum exploration well in the sheet area.
A BMR seismic survey of the southern Carnarvon Basin in 1 9 6 3 was reported by Bow and Turpie ( 1 9 6 4 ) . Other geophysi- cal surveys conducted by petroleum exploration companies are listed in the bibliography.
Megallaa's ( 1 9 8 0 ) review and synthesis of previous geophysical work in the southern Carnarvon Basin was the main source of subsurface data for these notes.
2
PHYSIOGRAPHY
CLIMATE
SHARK BAY-EDEL has a semi-arid climate, with annual rainfall averaging between 200 and 222 mm and annual evapor- ation between 2 000 and 2 200 mm: runoff into the embayment from the surrounding low-lying, sandy terrain is therefore negligible.
Prevailing winds are southerly and are consistently strong for much of the year, especially in the summer months. Temperatures are highest in January, with an average maximum of 36.7 C, and lowest in June, with an average minimum of 9.9OC (temperature data taken at Hamelin Pool; from Royal Australian Air Force, 1943).
0
TIDES AND SALINITY GRADIENTS
Tidal influx into Shark Bay is restricted by the Edel Land peninsula and by the Dirk Hartog-Bernier-Dorre Island chain. The normal diurnal tidal oscillation is 1.6 m, but this decreases towards the southern end of the embayment due to numerous promontories and seagrass-covered banks, the most important of which is the Faure Sill.
The reduced tidal influx and arid climate of Shark Bay have resulted in increased salinities in the southern parts of the embayment. The high salinities in Hamelin Pool and Lharidon Bight have drastically reduced the fauna1 and floral diversity, with an accompanying increase in numbers of individual salt-tolerant forms, such as Fragum erugatum and blue-green algae. The high salinity also allows the growth of algal stromatolites in these basins by restricting the number of grazing organisms, Algae occurs both as widespread
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algal mats and as discrete columnar stromatolites.
GEOMORPHOLOGY
Shark Bay was formed by a Holocene marine transgression over a terrain of Pleistocene dunes, localized by Tertiary anticlines. It is a shallow embayment, approximately 8 000 km in area, which is subdivided into a number of gulfs, inlets, and broad basins by ridges of mainly north-trending dune fields (Fig. 1). Average water depth within the embay- ment is about 10 m, although much of the area is occupied by shoals only about 1 m deep. The body of water previously named Freyci.net Estuary is now officially Henri Freycinet Harbour.
2
Logan, Read and Davies (1970, p.42) recognize three geomorphological subdivisions on SHARK BAY -EDEL:
Edel Province: comprising Edel Land, Dirk Hartog Island, Bernier Island and Dorre Island - a landscape of calcareous dunes which formed over lithologically similar, but indurated, eolianite with fairly well preserved dune shapes.
Peron Province: consisting of Peron Peninsula, Nanga Peninsula and Faure Island - an area of red sand dunes.
Gascoyne -Wooramel Province: the coastal strip along the northeastern margin of Shark Bay - an alluvial coastal plain with river floodplain deposits. This area now receives little additional sediment from the almost defunct Wooramel River system and the Boodalia Channel of the Gascoyne River delta.
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OCEAN
Figure 1
E SHARK BAY-EDEL
SHEETS SG49-8 and 12
0 10 20 30km - R E F E R E N C E
Tidal and supratidal f l a t s with
Pleistocene beach ridge, tidal flats and
associated beach ridges
supratidal flat remnants Mobile and fixed calcareous dunes
Numerous gypsiferous pans (birridas) and sandplain
in interdune depressions - Transverse and longitudinal dunes and
Numerous gypsiferous pans (birridas)
Coastal cliffs
sandplain, composed of red quartz sand
in interdune depressions
Boodalia Delta, alluvium
Brown Delta, alluvium with associated I beach ridges and dunes
Quartzose sandplain, dunes and wash, derived from ancient alluvium of Gascoyne River
3 --- Sand, shell and seagrass banks
__-_ _- * or low sand ridge
Tidal channel in seagrass bank
I+ Palaeodrainage, marked by channel
@ Station homestead, settlement
'HYSIOGRAPHIC PROVINCES
1 Edel Province
Peron Province
3 Gascoyne-Wooramel Province
s -% Boundary of physiographic province
GSWA 19393
5
EdeZ Province
E d e l Province sepa ra t e s Shark Bay from t h e Indian Ocean. I t i s bounded along i t s western edge by t h e Zuytdorp C l i f f s , one of t he most s t r i k i n g f e a t u r e s of t h e Western Aus t r a l i an coas t . These c l i f f s may be f a u l t con t ro l l ed because they form a s t r a i g h t , almost unbroken l i n e f r o m Steep P o i n t t o j u s t no r th of t h e Murchison River , a distance of 2 2 5 km.
They a t t a i n a maximum he igh t of nea r ly 300 m above sea l e v e l a t Womerangee H i l l on Tamala S t a t i o n . Marine e ros ion has produced c o a s t a l platforms and- "paddy-f i e l d " terraces a t t h e
f o o t of t h e c l i f f s , and blowholes have been formed a t s e v e r a l loca l i t i es due t o undercut t ing.
The eastern c o a s t l i n e of Edel Land i s p ro tec t ed from t h e
open oceanic wind and wave a c t i o n t o which t h e western c o a s t is exposed. Consequently, t h e dieeply embayed e a s t e r n coas t - l i n e i s of f a i r l y low relief and t h e southern ends of i n l e t s a r e occupied by broad, i n t e r t i d a l and s u p r a t i d a l f l a t s . Prominent e leva ted p la t forms , formed during e a r l i e r high sea l e v e l s t ands , r i m most i n l e t s a t about 2 m above t h e present - day shore platforms.
Algal m a t s , which t r a p and bind sediments, grow i n t h e
i n t e r t i d a l zones and inc rease i n importance towards t h e
southern end of t h e province. Seagrass growths on t h e sub- l i t t o r a l platforms s i m i l a r l y t r a p and bind sediments.
Numerous evapor i t e pans, known l o c a l l y a s " b i r r i d a s " , occur i n t h e area. These range from s m a l l , c i r c u l a r o r ova l depressions about 1 0 0 m i n diameter , t o e longate o r i r r e g u l a r interdune depress ions s e v e r a l ki lometres i n length . Some are connected t o t h e sea by remnant, e v a p o r i t e - f i l l e d channels and may r ece ive an i n f l u x of seawater during storms, b u t most a r e i s o l a t e d .
B i r r i d a s commonly c o n s i s t of a c e n t r a l , r a i s e d platform r inged by a moat-like depression. I t i s bel ieved t h a t the
c e n t r a l s e c t i o n corresponds t o t h e l e v e l of t h e water t a b l e
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during the Late Pleistocene Bibra marine phase. The "moat" is formed by seepage of fresh groundwater from surrounding dunes which dissolves gypsum from the periphery of the central platform. Birridas will usually retain water for several months after heavy rain.
Peron Province
Underlying most of the Peron Province are relict Pleistocene dunes of red and yellow, quartz sandstone ("Peron" dunes). These occur as sets of large, transverse dunes (reminiscent of coastal, parabolic dune sets), the shape of which has been preserved by development of calcrete in the core of the original dunes (i.e. at the original water table). Following the development of the calcrete, minor eolian reworking of the overlying (unconsolidated) sand produced broad, undulate red sand dunes ("Nilemah" dunes), which have been partly fixed by scrubby vegetation and are superimposed on the relict "Peron" dunes.
Although many relict dunes are quite high, up to about 50 m above sea level, the floors of the interdune depressions are rarely more than a few metres above present sea level, and commonly contain birridas. Marine lagoons occupy some interdune depressions adjacent to the coast.
Indurated and unconsolidated calcareous coastal ("Tamala") dunes, ubiquitous in Edel Province, are confined to a narrow strip bordering the western margin of the province and overlie the older "Peron" dunes (.
A generally well-lithified beach ridge coquina containing an open-marine fauna and having its crest about 4.4 m above present high-water mark, is preserved along the shore of Lharidon Bight. A prominent bench has been incised into the ridge at about 2.6 m below its crest, and this is covered by littoral sediments which are only slightly calcreted. Calcreted beach ridges, with similar benches cut into them,
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are preserved a t s e v e r a l l o c a l i t i e s i n Shark Bay. I t i s
thought t h a t t he o l d e r , w e l l - l i t h i f i e d beach r i d g e s formed during t h e Dampier Marine Phase of Logan, Read and Davies ( 1 9 7 0 ) , w h i l e t h e less-calcreted benches and/or s e p a r a t e beach r i d g e s formed during t h e Bibra Marine Phase (Logan, Read and Davies, 1 9 7 0 ) . The Dampier Marine Phase probably formed during t h e high sea- leve l s tand of t h e penul t imate P le i s tocene i n t e r g l a c i a l per iod , w h i l e t h e Bibra Marine Phase belongs t o t h e f i n a l (Riss-Wurm) i n t e r g l a c i a l .
The Holocene (Flandrian) marine t r ansg res s ion flooded Shark Bay during t h e l a s t 1 0 000 years . The proximity of t h e p re sen t high-water mark t o t h e s t r a n d l i n e implied by t h e Dampier-age beach r idges and t h e Bibra age benches and beach r idges indicates t h a t sea l e v e l i n t h i s area during t h e P le i s tocene t r ansg res s ions was only a f e w metres higher than a t p resent .
Thus, records of t h r e e Quaternary t r ansg res s ions a r e preserved onshore i n Peron and E d e l Provinces. The repeated f looding of t he Shark Bay embayment was p r imar i ly due t o e u s t a t i c sea l e v e l rises during i n t e r g l a c i a l pe r iods , although g e n t l e , l o c a l t ec ton i sm probably a f f e c t e d t h e e x t e n t of t h e
e u s t a t i c t r ansg res s ions .
Gaseoyne - Wooramei! Provinee
T h e no r theas t e rn corner of t h e a rea c o n s i s t s of spa r se ly vegetated, red, e o l i a n sand dunes, ex tens ive areas of co l lu- vium, and occasional claypans. P a r t of t h i s province i s occupied by sediments of t he Brown and Boodalia d e l t a s (Johnson, 1 9 7 4 ) of t h e a n c e s t r a l Gascoyne River. O l d e r
palaeodrainage l i n e s t o t h e south w e r e a l s o a n c e s t r a l Gascoyne River courses bu t they have been t runca ted by c o a s t a l e ros ion and no de l ta shapes are preserved. The
palaeodrainage channels preda te t h e development of t h e
long i tud ina l dunes t h a t - c o v e r much of t h i s area and ad jacen t WOORAMEL. Sand has been trapped by t h e moisture
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and/or vege ta t ion along, o r beside, these palaeodrainage l i n e s , forming sand r idges which c u t a c r o s s t h e long i tud ina l dunes and are p a r a l l e l t o t h e palaeodrainages.
A c a l c r e t e p r o f i l e unde r l i e s the c o l l u v i a l s o i l a t depths of about a metre o r less. I t i s l o c a l l y exposed i n a low c o a s t a l c l i f f t h a t borders t h e s u p r a t i d a l f l a t s on southwest Brickhouse S ta t ion .
I n t h i s region t h e c o a s t l i n e t r ends about 330" and i s
intersected by a series of beach s p i t s , formed by northward, long-shore d r i f t .
I n t e r t i d a l and s u p r a t i d a l f l a t s , u p t o about a ki lometre wide, have developed behind t h e s p i t s , and there are exten- s i v e growths of a l g a l m a t s and mangroves. Where both man- groves and a l g a l mats occur toge the r , t h e mangroves are on the seaward side of an i n t e r t i d a l - s u p r a t i d a l f l a t , which i s p a r t l y covered, by a l g a l m a t s . Towards t h e south, where t i d a l i n f l u x i s restricted by t h e Wooramel seagrass bank, t h e h igher s a l i n i t i e s prevent mangrove growth, and a l g a l m a t s occupy t h e whole i n t e r t i d a l f l a t .
ST RAT I G RAPHY
Although only Quaternary sediments a r e exposed on SHARK
BAY -EDEL, S i l u r i a n , Cretaceous, and T e r t i a r y sediments a r e known from t h e Tamala and D i r k Hartog 1 7 B bores . Table 1
summarizes t h e s t r a t i g r a p h y of t h e area.
PALAEOZOIC
TumbZagooda Sandstone
The Tumblagooda Sandstone i s a t h i c k sequence of va r i ab ly
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STRATIGRAPHY OF THE SHARK BAY-EDEL SHEET
Rock unit
Coastal dunes, beach
Hamelin Coquina
Supratidal flat deposits
Tidal flat deposits
Colluvium
Claypan and salt lake deposits
Evaporite-pan ("birrida") deposits
Claypan and dune terrain
TABLE 1.
Thickness (m)
10
10
0 .5
1
?5
?20
?8
? 10
Li thology
Unconsolidated to weakly lithified quartz-carbonatc (skeletal fragment) sand; locally shelly and rich in gastropods and fora- minif era
Calcirudite coquina con- sisting predominantly of small shells of Fragum erugatwn Shelly calcisiltite, cal- carenite, calcirudite; some evaporites
Shelly calcisiltite, cal- carenite, and calcirudite algal-laminated sediments
Poorly sorted clay, silt, sand and gravel
Clay, silt, sand, minor gravel; authigenic gyp- sum and salt
Clay, silt, sand layers alternating with gypsum layers
Clay, silt, sand, minor gravel, authigenic gyp- sum (+ calcrete)
Stratigraphic relationships
Unconformably overlies older units; grades lat- erally into Qu, Qm, Qsh
Unconformably overlies older units; grades lat- erally into Qs, Qu, Qm
Unconformably overlies older units; grades lat- erally into Qs, Qm, Qsh
Unconformably overlies older units; grades lat- erally into Qs, Qsh, Qu and subaqueous sediments
Grades into Ql, Qlg, Qle
Grades into Qc, Qlg, Qle Qe, Qlb
Qe, Qlb
Grades into Qc, Qg, Qle, Qe, Q1
Grades into Qc, Ql, Qlb, Qlgi Qe
Remarks
Separated from Qt and Atm on the basis of mor-
Forms predominantly dur- ing storms - beach ridge deposits
Minor authigenic evapor- ites at surface
Extensive algal mats, and columnar stromatolites extending into subtidal zone; mangroves in northern part
Deposited by sheet floods and soil creep
Substantial thicknesses expected only in major palaeodrainage valleys
Central raised platform often surrounded by moat- like ring
Table 1 - continued 2.
U H
0
i - 1 N
0 i-1
z H
4 U
Rock unit
Gypsiferous dune deposits
Sandplain and dune deposits
Older supratidal flat deposits
Alluvial deposits
Bibra Limestone
Depuch Formation
Dampier Limestone
?50
10
1
10
Lit hology
Silt, sand, gypsum
Red to yellow quartz sand
Shelly calcisiltite, calcarenite calcarenites poorly consolidated, some authigenic evaporites
Poorly sorted sand, silt, gravel, clay; partly calcre ted
Shelly calcarenite to cal. ciruditic coquina; poorly calcreted
Calcarenite and cal- cirudi te
Shelly calcarenite to calcirudite
Strati gr ap h i c relationships
Grades into Qc, Ql, Qlb, Qle, Qe Grades into Qc, Ql, Qlb, Qle
Grades into Qle, Qlb. May be associated with Qbi Qd
Grades into Qe, Qc; un- conformably overlies older units
Unconformably overlies Depuch Formation, Dampier Limestone, Tamala Limestone or Peron Sandstone
Unconformably overlies Dampier Limestone or Tamala Limestone
Unconformably overlies Tamala Limestone
Remarks
Formed by deflation from birradas
Mostly derived from wea- thering profile on under- lying sandy bedrock; "Nilemah Sands" formed by reworking of Peron Sands tone
Developed along southern coastline of Henri Freycinet Harbour
Deposits of Boodalia Channel; Pleistocene delta with veneer of Holocene alluvium due to regular flooding
Shallow marine to beach ridge deposit. Qbr - coral reef of Bibra age. Qbd - Bibra Limestone/ Dampier Limestone (in- distinguishable)
Formed by erosion and working of older Pleis- tocene units
Shallow marine to beach ridge deposits
Table 1 - continued 3 .
Rock unit
Tamala Limestone
Peron Sandstone
Alluvial deposits
Giralia calcarenite
Cardabia Group
Toolonga Calcilutite
Thi ckne s s (m)
300+
? 2 0
?50
1 2 5
Li thology
Calcarenite, unconsolida- ted to strongly lithified skeletal - fragments locally quartzose; large- scale eolian cross- bedding
Red, quartz sand with numerous soil structures
Poorly sorted sand, silt, gravel, clay; partly calcreted
Calcarenite, sparsely glauconitic, greenish, f ossi liferous
Mudstone or calcilutite, soft, calcareous, glauco- nitic, fossiliferous
Calcilutite to marl, sparse-fossiliferous, greenish-grey or white
S t ra t igrap hi c relationships
Unconformably overlies Cretaceous or Tertiary rocks; or Peron Sandstone
Unconformably overlies Toolonga Calcilutite or Tertiary rocks
Grades into Q1, Qc, Qle
Unconformably overlies Toolonga Calcilutite or Cardabia Group
Unconformably overlies Toolonga Calcilutite
Unconformably overlies Winning Group
Remarks
Eolian dune deposit; cal- creted in exposed parts; cemented by calcite and minor dolomite where lithified. May be partly same age as Peron Sand- stone
Eolian deposit
Deposits of Brown Channel; Pleistocene delta with veneer of Holocene allu- vium due to regular flooding. Age uncertain - older than Boodalia Delta ... "early" Pleisto- cene
Pelagic, open-marine, shelf deposit
Table 1 - continued 4.
Fhicknes s (4
Stratigraphic relationships
Lateral (northerly) equivalent of Alinga Formation
Conformably overlies Windalia Radiolarite
Rock unit Li thology Remarks
Gearle Siltstone (b) ?50
50
Dark grey siltstone and clays tone
Open-marine, shelf deposit
Alinga Formation Glauconitic siltstone and sandstone grading to greensand
Possibly condensed, open- marine, shelf deposit
Windalia Radio- larite
20
46
67
Dark, radiolarian silt- stone, chert and inter- bedded claystone; radiolarian siltstone has very low specific gravity (specific gravity of chert is 2.64)
Claystone, siltstone, minor greensand
Conformably overlies Muderong Shale or Birdrong Sandstone
Pelagic, open-marine, shelf
Forms upper par of marine transgressive, fining-upwards sequence
Basal sandstone of transgressive sequence; excellent artesian aquifer
Conformably overlies Birdrong Sandstone
Muderong Shale
Birdrong Sandstonf Unconformably overlies Palaeozoic
Glauconitic, poorly con- solidated, -fine to very coarse-grained sandstone
Fine to medium-grained grey to orange or red quartz. Sandstone with calcareous cement; thin shale beds
Conformably at top of Dirk Hartog Formation
Age uncertain; correlated with "Unit B" of Unknown Formation in Yaringa 1 (YARINGA )
27 "Unknown Formation"
Dirk Hartog Formatioi
~
Limestone, shale, silt- stone, anhydrite, halite
Conformably overlies Tumblagooda Sandstone
Evaporitic marine to coas- tal environment. Contains Yaringa Evaporite Member Fluviatile to shallow marine environment
1380
(b) ?3000 Tumblagooda Sandstoni
(d) I Red, yellow, white quartz feldspathic sandstone
?Rests unconformably on Precambrian
I
(a) Approximate (b) Estimated (c) Not shown at 1:250 000 (d) Not exposed
red-mottled sandstone which was deposited in fluviatile to shallow-marine environments (Hocking, 1979). It probably underlies the whole of SHARK BAY-EDEL, and is of probable Silurian age, being conformable with the overlying Dirk Hartog Formation.
D i r k H a r t o g F o r m a t i o n
The Dirk Hartog Formation conformably overlies the Tumblagooda Sandstone, and consists of interbedded mudstone, dolomite, anhydrite, limestone, halite and sandstone. Glenister and Glenister (1957) obtained a Middle Silurian age for the unit, based on conodonts and brachiopods from the type section in Dirk Hartog 17B. However, later work on conodonts by Philip (1969) dated the unit as Late Silurian.
The Yaringa Evaporite Member (Playford and others, 1975) is a halite-and-anhydrite-bearing sequence within the unit which is probably present in the east of SHARK BAY-EDEL.
A mature sandstone near the top of the unit in Tamala 1, Yaringa 1, and Hamelin Pool 1 and 2 represents a return to Tumblagooda Sandstone-type deposition, and could be Devonian in age (Henderson and Shannon 1966). No younger Palaeozoic rocks are known from the area.
CRETACEOUS
Winning Croup
A marine transgression covered most of the Carnarvon Basin from Late Neocomian to Turonian. The Winning Group was deposited during this time and consists in ascending order of the Birdrong Sandstone, Muderong Shale, Windalia Radiolarite and Alinga Formation. From south to north across the area, the Alinga Formation undergoes a facies
14
change, grad ing i n t o t h e Gearle S i l t s t o n e , and t h e Muderong
Sha le a l so becomes a t h i c k e r and more d i s t i n c t u n i t nor th-
wards.
B i r d r o n g S a n d s b o n e : The Birdrong Sandstone i s a u n i t of weakly l i t h i f i e d , medium- t o coarse-gra ined , q u a r t z sands tone , commonly g l a u c o n i t i c , w i t h minor s i l t s t o n e and q u a r t z wacke. The u n i t i s a widespread b a s a l sands tone , and forms a major a r t e s i a n a q u i f e r throughout m o s t of t h e wes tern Carnarvon Basin. I t has been da ted as l a t e Neocomian t o e a r l y Apt ian
(Cookson and Eisenack, 1958) and unconformably overl ies t h e Dirk Hartog Formation i n t h e area mapped.
Muderong ShaZe: The Muderong Shale conformably overl ies t h e Birdrong Sandstone and c o n s i s t s of f r i a b l e , porous s h a l e , w i t h c l ays tone , s i l t s t o n e and greensand. I n Dirk Hartog 1 7 B ,
t h e u n i t i s only 2 . 6 m t h i c k , as i n d i c a t e d by e lec t r ic l o g s . I t has been da ted as Apt ian (Cookson and Eisenack, 1958) .
WindaZia R a d i o l a r i t e : Conformably ove r ly ing t h e Muderong
Shale i s t h e Windalia R a d i o l a r i t e , of Aptian t o Albian age.
T h i s i s a u n i t of l i g h t t o dark-grey, r a d i o l a r i a n c l a y s t o n e
and r a d i o l a r i t e , o c c a s i o n a l l y g l a u c o n i t i c , w i th minor l i m e - s t o n e and c h e r t . The h igh c o n t e n t of p e l a g i c microfossi ls i n d i c a t e s t h a t t h i s u n i t w a s d e p o s i t e d i n q u i e t w a t e r s w i t h
l i t t l e t e r r i g e n o u s i n f l u x , b u t i t s s t r a t i g r a p h i c s e t t i n g i n d i c a t e s a marine-shelf r a t h e r t han a deep-sea d e p o s i t . I t
i s be l i eved t h a t t h e h igh sea-level s t and i n t h e Cretaceous
must have l i m i t e d t e r r i g e n o u s i n f l u x , f i r s t l y by reducing t h e area of land a v a i l a b l e as a s o u r c e and, secondly, by lowering t h e sediment-carrying c a p a c i t y of t h e streams on t h e a l r e a d y
peneplaned s u r f a c e . The reduced c las t ic i n p u t i n t u r n , l e d t o t h e accumulation of p e l a g i c sediments over wide areas of
c o n t i n e n t a l s h e l f .
15
A Z i n g a F o r m a t i o n : The Alinga Formation conformably overlies the Windalia Radiolarite in Tamala 1. It consists typically of soft, dark-grey, glauconitic shale and siltstone, containing belemnite guards, and has been dated as Albian to Turonian.
G e a r l e S i Z t s t o n e : Disconformably overlying the Windalia Radiolarite in Dirk Hartog 17B is the upper Gearle Siltstone, of lower Turonian age. Although lithologically similar to the overlying Toolonga Calcilutite, this unit is harder, more compact and has a higher resistivity. It is probably equi- valent to the upper part of the Alinga Formation.
Too l o n g a Ca Zci Z u t i t e
The Toolonga Calcilutite disconformably overlies the Winning Group and was dated as Santonian to Maastrichtian in age by McWhae and others (1958). It consists of greenish- grey to white-weathering, coccolith-rich, argillaceous calcilutite, grading to siltstone, and is characterized by abundant fragments of the larger bivalve I n o c e r a r n u s . The unit outcrops on adjoining YARINGA.
The upward change in lithology of the pelagic deposits, from the siliceous Windalia Radiolarite to the calcareous Toolonga Calcilutite, may reflect a change from cool to warm oceanic conditions. This may, in turn, be due to a marked change in oceanic circulation patterns, perhaps as a result of the rapid opening of the Indian Ocean in the Late Cretaceous,
CAINOZOIC
Cainozoic marine sediments have been deposited in four main cycles in the Carnarvon Basin (Quilty, 1977):
1 6
(1) Late Paleocene t o Early Eocene ( 2 ) Middle t o L a t e Eocene ( 3 ) L a t e Oligocene t o Middle Miocene ( 4 ) L a t e Miocene t o Holocene.
Qui l ty suggested t h a t these cyc les r e f l e c t l a r g e sea- l e v e l changes of a world-wide, e u s t a t i c na tu re , r a t h e r than l o c a l events .
T e r t i a r y
Cardabia Group: Cycle 1 sedimentation i s represented on SHARK BAY-EDEL by t h e Paleocene Cardabia Group, which i n Tamala 1 c o n s i s t s of c a l c a r e n i t e and l i gh t -g rey , s o f t , very ca lcareous , and g l a u c o n i t i c mudstone o r c a l c i l u t i t e , w i t h
abundant f o s s i l s .
GiraZ ia C a l c a r e n i t e : The Middle t o Late Eocene G i r a l i a Ca lca ren i t e (Cycle 2 ) i s a u n i t of hard, bryozoal c a l c a r e n i t e and g l a u c o n i t i c l imestone, disconformably overlying t h e Cardabia Group i n t h e nor thern p a r t of t h e area. I t was recognized i n D i r k Hartog 1 7 B , b u t was n o t encountered i n Tamala 1, and is considered t o have been completely eroded from t h e southern p a r t of t h e a r e a p r i o r t o t h e depos i t i on of t h e T a m a l a Limestone.
Cape Range Group: Sediments of t h e Late Oligocene t o Middle Miocene Cape Range Group ( C y c l e 3 ) have no t been recognized on SHARK BAY-EDEL, b u t a r e known from adjo in ing YARINGA.
The fou r th cyc le of marine Cainozoic depos i t i on i s
represented by var ious P le i s tocene and Holocene u n i t s .
P Z e i s t o c e n e
I n t e r f i n g e r i n g of marine and c o n t i n e n t a l sediments on SHARK BAY-EDEL makes t h i s one of t h e best l o c a l i t i e s on t h e Western Aus t ra l ian c o a s t f o r s tudying Quaternary e u s t a t i c
1 7
sea-level changes. Logan and others ( 1 9 7 0 , 1 9 7 4 ) have reported extensively on the Quaternary marine sediments of the area and their environmental significance.
Many of the units described below were mapped more on a morphological than a lithological basis because of the juxta- position of lithologically similar units of different ages and the reworking of older sediments caused by repeated flooding of the embayment.
Peron Sands tone : The Peron Sandstone ( Q p ) is the oldest Pleistocene unit in the area, having formed as a series of large dunes unconformably overlying Cretaceous and Tertiary rocks. It consists of red, yellow or red-brown, medium- grained, poorly consolidated quartz sandstone. The unit is probably at least 250 000 years old (i.e. Middle Pleistocene) as it underlies the Dampier Limestone, which formed during an interglacial high-sea-level stand.
A calcrete zone at the top of the Peron Sandstone has preserved the approximate shape of the original dune landscape. The preserved dune shapes, the lack of marine fossils; and the presence of fossil soil profiles containing pupal cases and, rarely, land snails attest to an eolian origin for the unit.
TarnaZa L i m e s t o n e : To the west, the Peron Sandstone is onlapped by the Tamala Limestone ( Q t ) (formerly "Tamala Eolianite" , amended by Playford and others, 1 9 7 6 ) which consists of medium to coarse-grained strongly consolidated to unconsolidated, skeletal-fragment, locally quartzose calcarenite. Where lithified, the cement is predominantly calcite and subordinate dolomite. Lithification is most intense in calcreted, exposed parts of older dunes. Fossil soil profiles and large-scale, eolian cross-bedding are common and attest to the eolian origin of the unit. The type section, at Womerangee Hill on Tamala Station, is approximately 285 m thick
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Damgisr Limestone: The Dampier Limestone (Qd) ( formerly "Dampier Formation", amended by van de Graaff and o t h e r s , 1 9 8 0 ) i s a shallow-marine t o s u p r a t i d a l u n i t of bivalve- and foramini fe r - r ich coqu in i t e , which i s ex tens ive ly c a l c r e t e d on upper sur faces . I t was depos i ted a s beach r i d g e s and shallow-marine depos i t s i n t h e in te rdune depress ions of t h e
Peron Sandstone o r t h e Tamala Limestone landscape, which w a s p a r t l y flooded during t h e "middle" P le i s tocene , Dampier marine phase (Logan, Read and Davies, 1 9 7 0 , p .67) , n o t less than about 240 000 years ago. P rese rva t ion i s b e s t around t h e
margins of s h e l t e r e d headlands, where a maximum th i ckness of about 4 . 5 m was measured for t h e u n i t .
Depuch Formation: T h e Depuch Formation (Logan, Read and Davies, 1 9 7 0 ) i s a t h i n u n i t of wel l - indurated, red-brown c a l c a r e n i t e and c a l c i r u d i t e , formed by eros ion and c o l l u v i a l reworking of o lde r P le i s tocene u n i t s . I t i s confined t o narrow s t r i p s around t h e margins of promontories on Edel
Land and could n o t be mapped a t 1 :250 000 scale.
Bibra Limestone: Following t h e Dampier marine phase and the regress ion during which t h e Depuch Formation formed, t h e
Shark Bay embayment w a s aga in flooded. T h i s occurred dur ing t h e l a s t P le i s tocene i n t e r g l a c i a l high sea- leve l s t and , approximately 1 2 0 000 - 1 3 0 000 yea r s ago, and i s referred t o as the Bibra m a r i n e phase. During t h i s t r ansg res s ion , t h e
Bibra Limestone (Qb) (formerly "Bibra Formation" , amended by van de Graaff and o t h e r s , 1980) was formed. I t c o n s i s t s of beach r idges and shallow-marine depos i t s of b iva lve coqu in i t e , s k e l e t a l c a l c i r u d i t e o r c a l c a r e n i t e and minor c o r a l biostromal l imestone, and i s widely exposed i n t h e i n t e r t i d a l and supra- t i d a l zones around Shark Bay, A f o s s i l c o r a l reef, i n t e r - f i n g e r i n g w i t h a c a l c a r e n i t e beach d e p o s i t , is p resen t i n t h e u n i t a t Crayfish Bay.
Where outcrops of t h e Dampier and Bibra Limestones occur toge the r , t h e former may be d i s t ingu i shed by i t s more advanced
19
induration. However, this distinction is often difficult to make in isolated outcrops, and the symbol ( Q b d ) is used; it is also used where separate mapping of small, adjoining areas of the two units is impracticable at 1:250 000 scale.
The fossil faunas in both the Bibra and Dampier Limestones, in particular the corals, indicate that near-oceanic salinities prevailed during the Pleistocene.
Dune and sand-pZain d e p o s i t s : Dune and sand-plain deposits ( Q e ) , consisting of medium to coarse-grained, red or red-brown, unconsolidated quartz sand, cover much of Peron Province and the Gascoyne -Wooramel Province. Logan and others (1970) use the name "Nilemah Sands" for this unit in the Shark Bay area. The dunes are thought to have formed at the height of the last glacial, i.e. about 25 000-15 000 years ago, by reworking of the unconsolidated sand overlying the calcrete cores of the Peron dunes.
Brown and BoodaZia D e l t a s : The alluvial sediments of the Brown Delta ( Q a b ) and Boodalia Delta ( Q a B ) are of Pleistocene age because they predate the present Gascoyne Delta, which is believed to have been active during the entire Holocene. Physiographic evidence indicates that the Brown Delta is older than the Boodalia Delta (Johnson, 1974). Beach ridge and eolian deposits from the Brown Range ( Q e b ) are associated with the Brown Delta.
Duricrust calcrete has formed on and in many of the Pleistocene units,
HoZocene
Marine sedimentation in Shark Bay resumed following the Holocene (Flandrian) Transgression of the last 10 000 years. During this time sea level within the embayment has returned to within a few metres of the Pleistocene sea-level stands. In Hamelin Pool and Lharidon Bight, sedimentation is largely
2 0
controlled by the hypersalinity of the waters, which in turn is largely due to the development in the last 4 000 years of a sea-grass bank on the Faure Sill. Of particular importance is the occurrence of modern columnar stromatol- ites in Hamelin Pool (Logan, 1961; Davies, 1970a,b; Playford and Cockbain, 1976; Playford, 1 9 8 0 ) , which flourish because hypersalinity restricts grazing organisms that would other- wise destroy the stromatolites and associated algal mats.
HameZin Coquina: The Hamelin Coquina ( Q s h ) occurs as beach ridges, composed of shells of the small bivalve Fragum erugatum. Individual ridges are up to 3 m thick, about a kilometre wide, and are several tens of kilometres long. Hypersalinity has limited the size of individuals of Fragum erugatum to about one third of their size in normal oceanic salinity, while permitting a "population explosion" for the species by restricting competing organisms.
Ooids are generated on the sublittoral platforms and swept up on to beaches during storms (Logan, 1974). Preci- pitation of carbonate as ooids is promoted by hypersalinity, high evaporation rates and wave agitation.
E v a p o r a t i c [ " b i r r i d a ") d e p o s i t s
The gypsiferous pans (QZb), or birridas, discussed pre- viously, are easily recognizable on air photos as circular or elliptical depressions, occurring either singly or in clusters. Most consist of a central, raised platform sur- rounded by a 'moat', which is commonly dry. The surface of the central platform and (dry) moat is covered with powdery and crystalline gypsum, which may be removed by deflation to form gypsiferous dunes (QZg)
S u p e r f i c i a l D e p o s i t s
The northeastern corner of SHARK BAY-EDEL forms part of the Gascoyne-Wooramel Province and is covered by extensive areas
21
of colluvium (&c) o r c o l l u v i a l - t y p e d e p o s i t s . The o l d e r a l l u v i a l d e p o s i t s of t h e Brown and Boodalia D e l t a s are d i s - t i n g u i s h e d from r e c e n t a l l u v i a l d e p o s i t s (&a), occurr ing
elsewhere on t h e s h e e t , on t h e b a s i s of morphology. Large
c l a y pans (&Z) w e r e mapped i n d i v i d u a l l y , b u t where pans a s s o c i a t e d wi th dune f i e l d s are t o o s m a l l t o be sepa ra t ed a t map scale, they have been mapped as mixed dune and c lay-
pan d e p o s i t s ( Q Z e ) .
STRUCTURE
SHARK BAY-EDEL covers p a r t of t h e Gascoyne Sub-basin
of t h e Carnarvon Basin. The Gascoyne Sub-basin i s c l e a r l y d e l i n e a t e d on both g r a v i t y and aeromagnetic d a t a , and i s
bounded t o t h e east by a basement h igh , t h e Ajana-Wandagee Ridge. Megal laa 's (1980) s y n t h e s i s of t h e g r a v i t y and mag-
n e t i c work i n t h e area has shown t h a t SHARK BAY-EDEL over- l i es a basement dep res s ion con ta in ing more than 6 0 0 0 m of
sediments a t i t s deepes t p o i n t , nea r t h e southern t i p of
Dirk Hartog I s l a n d (F ig . 2 ) .
A s d i scussed p rev ious ly , a major f a u l t i s p o s t u l a t e d t o
e x p l a i n t h e Zuytdorp C l i f f s , and hydrogeologica l evidence
tends t o suppor t t h i s hypothes is (see: W a t e r s u p p Z i e s ) .
A WAPET d r i l l i n g programme on Dirk Hartog I s l a n d i n 1955-56, showed t h a t t h e T a m a l a Limestone forming t h e i s l a n d had accumulated on a ve ry g e n t l e a n t i c l i n e w i t h i n T e r t i a r y
and L a t e Cretaceous rocks (F ig . 3 ) , w i th i t s a x i s p a r a l l e l t o t h e i s l a n d and i t s cu lmina t ion i n t h e c e n t r e (Playford and Cockbain, 1 9 7 6 ) . P layford and Cockbain be l i eved t h a t t h e
major pen insu la s i n Shark Bay may a l s o o v e r l i e g e n t l e a n t i -
c l i n e s , whi le Hamelin Pool , Lharidon Bight , Henri F r e y c i n e t
Harbour, and t h e F r e y c i n e t Reach may ref lect g e n t l e s y n c l i n a l warping. The work of Megallaa (1980) suppor ts t h i s i n t e r p r e t a t i o n .
22
Hamelin Pool I
N w
REFERENCE -.-300.,,- Structure contours, top of Birdrong Sandstone,
definite and inferred. From bore data (mbsl) -550- Structure contours, top of Birdrong Sandstone,
definite and inferred. From seismic data (mbsl)
Fault, from seismic data ~+ Anticlinal axis, Cretaceous and Tertiary
(Contours derived from Megallaa, 1979)
REFERENCE Fault,from gravity and aeromagnetic data
-3000- Depth to basement, from gravity and magnetic data
(Contours derived from Megallaa, 1979)
0 50 km I
Figure 2 : Structure contour maps, showing depth to magnetic basement and contours on top of Birdrong Sandstone GSWA 19394
D Structure contours on top of Giralia Calcarenite
Figure 3
STRUCTURE CONT AND ISOPACHS DIRK MAR SLAND
0 5 10 15 20krn L f I I 1
REFERENCE F,
0
Deep well drilled by WAPET (abandoned, dry hole)
Shallow borehole drilled by WAPET
Isopachs, "D" Horizon to top of Giralia Calcarenite
GSWA 19395
It is possible that the mild folding continued into the Quaternary, as is the case in coastal anticlines further north in the Carnarvon Basin (van de Graaff and others, 1976; Denman and van de Graaff, 1 9 7 7 ) . The probable minor regression in the area during the last 4 000 years could be attributed to continuing local uplift associated with the folding .
Seismic work though poor in coverage and data quality, has demonstrated a slight northwesterly regional dip for the Tertiary -Cretaceous sequence under the flat lying Quaternary cover (Fig. 2) .)
GEOLOG I CAL H I STORY
The earliest recorded event on SHARK BAY-EDEL is the deposition, during the Silurian, of the fluviatile and shallow-marine Tumblagooda Sandstone and the overlying, evaporitic, red-bed sequence, the Dirk Hartog Formation. Carboniferous and Permian sediments, which are thought to have been present in this part of the basin, were completely removed by pre-Cretaceous erosion.
During the Triassic and Jurassic, a major phase of block-faulting, due to rifting associated with the break-up of Gondwanaland, affected the Carnarvon Basin. The Gascoyne Sub-basin was formed as a clearly separate entity at this time (Thomas and Smith, 1 9 7 6 ) .
Deposition of the Winning Group followed the Neocomian transgression, and the Toolonga Calcilutite was deposited during the Late Cretaceous in response to continued down- warping. The Windalia Radiolarite (which forms part of the Winning Group) and the Toolonga Calcilutite are both pelagic deposits which formed in fairly shallow waters, during high sea-level stands of the Cretaceous.
25
During the Paleocene and Eocene, the area was again covered by the sea, but it was exposed during most of the remainder of the Tertiary.
The area remained above sea level during the "early" Pleistocene, when a dune landscape was formed prior to 240 000 years ago. Initially, dunes of red quartzose sand accumulated in the Peron and Gascoyne -Wooramel Provinces. Persistent onshore winds then built up calcareous dunes from material generated on the sea floor, and along coastal belts in the south and west of SHARK BAY-EDEL. The most active periods of calcareous dune-building would have been during the final phases of glacial periods, when extensive areas of the shelf were exposed.
The major interdune depressions have since been flooded during three i n t e r g l a c i a l , e u s t a t i c , h i g h sea-level stands. In order of decreasing age, the Quaternary transgressions in the Shark Bay region are called the Dampier, Bibra and Holocene marine phases. Maximum sea level during the two earlier transgressive phases was only a few metres above present sea level.
Probable post-Miocene reverse movement along pre-existing normal faults gave rise to gentle anticlinal structures which control the morphology of the major coastal landforms in the Shark Bay area. Continued folding in the Holocene may account for the minor regression of about 1-2 metres that has occurred in the area during the last 4 000 years.
The development of a sea-grass bank on the Faure Sill over the past 4 000 years has restricted tidal influx into Hamelin Pool and Lharidon Bight. The waters within these basins have become hypersaline, allowing a uniquely diverse assemblage of modern stromatolites to develop.
26
ECONOPIIC GEOLOGY
PETROLEUM
Exploration for petroleum in the area has been unsuc- cessful to date. Geological, geophysical, and drilling operations have been conducted by West Australian Petroleum Pty Ltd, Continental Oil Company of Australia, and Oceania Petroleum Ltd I
Although suitable reservoir rocks were encountered, the petroleum prospects of the region have been significantly downgraded by the failure to delineate suitable structures and the apparent absence of adequate source rocks or levels of maturation. dolomites and limestones, as well as evaporites which could provide seals to any oil accumulation, but the oxidized nature of the whole Silurian sequence detracts from its source pot- ential. Similarly, the thin Cretaceous sequence is unpros- pective as it has not been buried deeply enough for oil generation, and the only reservoir (the Birdrong Sandstone) is being flushed by meteoric waters.
The Dirk Hartog Formation contains porous
E v a p o r i t e M i n e r a l s
The halite and anhydrite-bearing Yaringa Evaporite Member of the Dirk Hartog Formation is probably present in the east of the sheet area. As drilling has shown the potash resources of that sequence to be uneconomic on YARINGA, it is doubtful whether the Dirk Hartog Formation elsewhere may be prospective for the more soluble salts.
With annual evaporation about 10 times as great as annual precipitation, the area is suitable for "salt farming". At Useless Loop, the shallow, northern end of a coastal inlet has been cut off from the ocean by an artificial barrier of consolidated Tamala Limestone, which is used extensively as breakwater material in the area. The closed inlet has been divided into numerous square ponds which are allowed to fill
27
wi th seawater a t high t i d e . Only t h e f i n a l evapora t ing ponds
from which t h e s a l t i s harves ted are s e a l e d , w i th poly thene .
Seve ra l " b i r r i d a s " i n t h e v i c i n i t y of Useless Loop have
been mined f o r gypsum.
I n t h e 1977-78 f i n a n c i a l y e a r , 335 k t of s a l t and 6 6 k t
o f gypsum w e r e shipped from Useless Loop by t h e Shark Bay S a l t Company.
F u r t h e r b a r r i e r s have r e c e n t l y been cons t ruc t ed across t h e c e n t r a l and southern p a r t s of Useless I n l e t t o provide more areas f o r evapora t ion ponds.
Water Supplies
I n a few p l a c e s on Edel Land, soaks occur between dunes
of unconsol idated T a m a l a Limestone. Other , h igh ly s a l i n e
s u p p l i e s of s u r f a c e w a t e r are r e s t r i c t e d t o b i r r i d a s o r
c o a s t a l i n l e t s .
Brackish a r t e s i a n w a t e r i s a v a i l a b l e from t h e b a s a l Cretaceous Birdrong Sandstone and, on Peron Pen insu la , from t h e over ly ing Windalia R a d i o l a r i t e . High product ion rates are observed (e .g- 2 050 m /day from Peron 2 ) , b u t t h e w a t e r i s only s u i t a b l e f o r s t o c k o r a b l u t i o n purposes. Water from t h e Birdrong Sandstone i s c h a r a c t e r i z e d by a s t r o n g , sulphur-
ous odour, probably from t h e o x i d a t i o n of p y r i t e .
3
S a l i n i t y i n c r e a s e s towards t h e w e s t from about 4 000
mg/L a t Useless Loop t o 1 0 0 0 0 mg/L on Dirk Hartog I s l a n d .
A s t h e po ten t iome t r i c contours i n d i c a t e t h a t f low w i t h i n t h e Birdrong/Windalia a q u i f e r s i s t o t h e northwest , t h e high
s a l i n i t i e s on Dirk Hartog I s l a n d may re f lec t a hydrau l i c b a r r i e r r e l a t e d t o t h e i n f e r r e d Zuytdorp F a u l t .
Borehead temperatures of a r t e s i a n w a t e r g e n e r a l l y i n c r e a s e westwards as t h e dep th of t h e a q u i f e r i n c r e a s e s ,
from 38OC a t Nanga 3 (producing from Windalia R a d i o l a r i t e a t
310 m ) t o 4OoC a t Tamala Homestead (producing from Birdrong
Sandstone, 374 m ) .
28
Rainwater is used for human consumption on the stations, and reverse-osmosis desalination plants supply fresh water to the towns of Useless Loop and Denham.
Construction Materials
Red eolian quartz sand, shelly limesand, thick calcrete, gypsum from birridas, and consolidated Tamala Limestone have been quarried for road construction. Consolidated Tamala Limestone is also used for breakwater material near Useless Loop -
Coquinite of Fragum erugatum is cut into blocks and used for building construction, though its use outside the Shark Bay region is now prohibited. Unconsolidated coquina is used for road building and decorative purposes, as well as being a source of shell grit for fowls.
SELECTED REFEWEKES
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Bow, G.W.G., and Turpie, A., 1 9 6 4 , Southern Carnarvon Basin seismic survey, Western Australia, 1 9 6 3 , traverse A, Tamala-Narryer area: Australia BMR Geophysical Progress Rept 1 9 6 4 / 6 (unpublished).
29
Butler, D,H., and Sanderlin, J., 1968, Hamelin Pool Noel Western Australia: Magellan Petroleum Pty Ltd Rept (unpublished) .
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30
Ellis, H.A., 1961, Report on lime shell deposits - Hamelin Pool, W.A.: West. Australia Geol, Survey Ann. Rept 1960, p.7-8.
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31
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32
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33
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34
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35
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3 6
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37
