Gehling, J.G., Jago, J.B., Paterson, J.R., García-Bellido, D.C. & Edgecombe, G.D., 2011. The...

The geological context of the Lower Cambrian (Series 2)Emu Bay Shale Lagerstatte and adjacent stratigraphicunits, Kangaroo Island, South Australia

J. G. GEHLING1,2*, J. B. JAGO3, J. R. PATERSON4, D. C. GARCIA-BELLIDO5 ANDG. D. EDGECOMBE6

1South Australian Museum, North Terrace, Adelaide, SA 5000, Australia.2School of Geosciences, Monash University, Clayton, Victoria 3800, Australia.3School of Natural and Built Environments, University of South Australia, Mawson Lakes, SA 5095, Australia.4Division of Earth Sciences, School of Environmental and Rural Science, University of New England,Armidale, NSW 2351, Australia.

5Departamento de Paleontologıa, Instituto de Geologıa Economica (CSIC-UCM), Facultad de CC.Geologicas, Jose Antonio Novais 2, Madrid 28040, Spain.

6Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK.

The lower Cambrian (Cambrian Series 2, Stage 4) Emu Bay Shale Lagerstatte, which is by far the mostimportant Burgess Shale-type (BST) deposit in Australia, occurs mainly in the bottom 10 m of the EmuBay Shale at Big Gully on the north coast of Kangaroo Island, South Australia. In this area, the exposedCambrian succession commences with the White Point Conglomerate, the bulk of which comprises acrudely cross-bedded cobble to boulder conglomerate with minor mudstone and sandstone facies.The conglomeratic horizons thin markedly to the south. The White Point Conglomerate was depositedas coalesced fan deltas derived from an uplifted tectonic margin immediately to the north of thepresent coastline. The White Point Conglomerate is overlain by the sandstone, siltstone andconglomerate beds of the Marsden Sandstone (new name), the basal 3 m of which is a distinctivefossiliferous argillaceous limestone and shale, the Rouge Mudstone Member (new name). Syndeposi-tional folding and faulting affected both the White Point Conglomerate and Marsden Sandstone priorto the deposition of the Emu Bay Shale, the base of which represents a sequence boundary. TheLagerstatte occurs within dark grey to black laminated micaceous mudstone facies, some of whichshow evidence of syndepositional disturbance, and are interpreted to have been deposited in isolatedstagnant, anoxic to oxic depressions on the sea floor, beneath a normally oxic water column, with asharp redox boundary at the sediment–water interface; below this boundary the pore water wasanoxic. Thin (up to 20 cm) structureless fine sandstone horizons within the mudstone are interpreted aseither sediment gravity flow or storm deposits. The Lagerstatte-bearing mudstone beds thin southwardsand disappear 500–600 m south of the coast. The Emu Bay Shale coarsens upwards; arthropod tracksare abundant in fine sandstone beds towards the top of the Emu Bay Shale. In coastal sections thesandstone facies of the Boxing Bay Formation rest conformably on the Emu Bay Shale; inland thecontact is channelled.

KEY WORDS: Emu Bay Shale Lagerstatte, Cambrian Series 2, White Point Conglomerate, MarsdenSandstone, Rouge Mudstone Member, syndepositional faulting and folding, Kangaroo Island, SouthAustralia.

INTRODUCTION

This paper describes the geological context and deposi-

tional environment of the rich fossil beds of the Emu

Bay Shale from the north coast of Kangaroo Island,

South Australia (Figure 1), the most important Burgess

Shale-type (BST) locality in Australia. Burgess Shale-

type biotas are Cambrian fossil assemblages in which

soft parts such as the appendages, eyes, and digestive

glands are preserved; they are named after the

famous middle Cambrian Burgess Shale biota of British

Columbia, Canada. Such fossil assemblages, in rocks of

any age, are often collectively referred to as ‘Lagerstat-

ten’—the German term that has come to be used for

fossil deposits of exceptional quality for the paleo-

biological evidence they preserve. In the last two

decades, since the demonstration of the detailed evi-

dence to be derived from the fossils of the Burgess

Shale ‘Lagerstatte’ (in reference to a single deposit) in

British Columbia, much paleontological research has

*Corresponding author: [email protected]

Australian Journal of Earth Sciences (2011) 58, (243–257)

ISSN 0812-0099 print/ISSN 1440-0952 online � 2011 Geological Society of Australia

DOI: 10.1080/08120099.2011.555487

Downloaded By: [Paterson, John] At: 23:17 23 March 2011

concentrated on the search for and elucidation of such

fossil deposits (Gould 1989; Conway Morris 1998; Bottjer

et al. 2002). Until recently (see Jago & Cooper 2011), all

fossil collections from the Big Gully area came from

outcrops along the shore platform and adjacent cliffs.

However, this project commenced in 2007 with the

excavation of a new site (Buck Quarry) within the

Emu Bay Shale about 500 m inland. Details of the Emu

Bay Shale Lagerstatte fossil assemblages, as currently

known, are given in Paterson & Jago (2006), Paterson

et al. (2008, 2010), Garcıa-Bellido et al. (2009) and the

references contained within those papers.

Paterson et al. (2008) suggested that the Lagerstatte

correlates with the lower Cambrian Pararaia janeae

trilobite Zone of South Australia, the early–mid Can-

glangpuan Stage of China and the mid-late Botoman of

Siberia. In general terms this is equivalent to undefined

Cambrian Stage 4 of undefined Cambrian Series 2. At

this time, South Australia was probably located about

15 degrees north of the equator (Brock et al. 2000).

REGIONAL GEOLOGY

Previous Work

Daily et al. (1979) considered that the fossiliferous

Cambrian succession outcropping on the north coast of

Kangaroo Island, the Kangaroo Island Group of Daily

(1956), was comprised of six formations: Mt McDonnell

Formation (base), Stokes Bay Sandstone, Smith Bay

Shale, White Point Conglomerate, Emu Bay Shale and

Boxing Bay Formation. These sediments form part of an

essentially unmetamorphosed Cambrian shelf succes-

sion, occupying the part of Kangaroo Island to the north

of the Kangaroo Island shear zone of Flottmann et al.

(1995) (Figure 2). The three lowest formations crop out

between Smith Bay and Snelling Beach (Figure 1); the

upper three formations crop out between Cape D’Esta-

ing and Point Marsden, with the only suggested link

being the Smith Bay Shale reported by Daily et al. (1980)

at the base of a measured section that continues up

through the White Point Conglomerate, the Emu Bay

Shale and the Boxing Bay Formation (see further

comments below). The area south of the Kangaroo

Island shear zone is occupied by the metamorphosed

flysch-like deposits of the Kanmantoo Group and

granitic rocks intruded as part of the Delamerian

Orogeny (see Flottmann et al. 1998; Fairclough 2008).

The detailed tectono-sedimentary setting of the Kangar-

oo Island Group north of the Kangaroo Island shear zone

is unclear (Gravestock & Gatehouse 1995; Flottmann

et al. 1998), but it is possible that the Kangaroo Island

Group was deposited in a series of sub-basins in an area

of active syndepositional tectonic activity (Nedin 1995b,

Flottmann et al. 1998). The recently published Kingscote

Special sheet (Fairclough 2008) shows what is termed

the Cassini Fault zone trending approximately east–

west and in the vicinity of Big Gully apparently just off

the coast a short distance north of the Lagerstatte

locality (Figure 2). This tectonic activity corresponds to

the Kangarooian Movements of Daily & Forbes (1969)

and may represent an aspect of the Delamerian Oro-

geny, the details and timing of which are discussed by

Foden et al. (2006). Flottmann et al. (1995) suggested that

the Kangaroo Island Group was displaced northwards

due to imbricate thrusts that merge downwards into

some form of detachment zone (see Flottmann et al. 1995,

figures 4, 5; Flottmann et al. 1998, figure 5).

There is no known top to the succession, different

aspects of which have been described by Madigan (1928),

Sprigg et al. (1954), Sprigg (1955), Daily (1956), Daily et al.

(1979, 1980), Moore (1979), Dinnick (1985), Gravestock &

Gatehouse (1995), Nedin (1995a, b, 1997), Alexander et al.

(1997), Jago et al. (2006a), Paterson & Jago (2006) and

Fairclough (2008).

Investigator 1 drill hole

The PIRSA stratigraphic hole, Investigator 1, is sited

about 1.5 km west of Big Gully, just to the south of Bald

Rock (Figure 2). A summary section was made by

Fairclough (2008), who reported the following succes-

sion: the Paleoproterozoic Donington Suite (base),

55.5 m; the Cambrian units Winulta Formation, 39 m;

Wangkonda Formation, 16 m; Parara Limestone, 55 m;

Smith Bay Shale, 45 m; White Point Conglomerate,

132 m; and the Pleistocene Bridgewater Formation,

26 m. We have logged the hole in more detail (Figure 3).

The lowest unit is a granite gneiss that Fairclough (2008)

indicated as belonging to the Paleoproterozoic Doning-

ton Suite. The basal unit in the Cambrian succession

rests nonconformably on the Donington Suite and is

what Fairclough (2008) regarded as the Winulta Forma-

tion, the basal unit of the Cambrian succession on Yorke

Peninsula (Daily 1990). It comprises about 35.5 m of

mainly red, but with some pale green, arkosic conglom-

erate, sandstone and siltstone that in places is

burrowed, particularly towards the top of the unit. The

burrow fills are calcareous.

The Winulta Formation passes gradationally up into

10 m of brecciated pale grey dolomite with some pyrite

in the interstices. This is overlain by 5 m of red siltstone

and shale with calcareous burrow fill. Above this is

Figure 1 Location map for Big Gully near Emu Bay on the

central north coast of Kangaroo Island, South Australia.

Referred localities: Sn, Snellings Beach; St, Stokes Bay; CC,

Cape Cassini; SB, Smith Bay; CD, Cape D’Estaing; PM,

Point Marsden; CR, Cape Rouge; In-1, Investigator 1; In-2,

Investigator 2.

244 J. G. Gehling et al.


about 100 m of a carbonate dominated succession, the

basal 55.5 m of which comprises a brecciated limestone

and dolomite; all clasts within this 55.5 m are angular

carbonate clasts with some pyritic intervals in the top

17 m. The top 1.3 m of this 55.5 m interval has a red

siltstone matrix and may represent a karst horizon,

possibly equivalent to the reddened horizon between the

Kulpara Formation and the Parara Limestone on Yorke

Peninsula (e.g. Daily 1990). Above the red interval there

is about 45 m of a carbonate breccia, but with an

increasing number of well-rounded carbonate clasts.

The lowest non-carbonate clast occurs about 10 m above

the base of the carbonate breccias. These clasts are well

rounded and comprise red sandstone, deeply weathered

metamorphic rocks and other basement fragments. The

clasts are not common, but increase in number and size

up section, the largest being about 15 cm across. It is

possible that the lower part of this carbonate-rich

Figure 2 Geological map of the Big Gully area, east of Emu Bay, Kangaroo Island, showing locations of Buck Quarry,

measured sections and drill hole Investigator 1.

Lower Cambrian Emu Bay Shale Lagerstatte and adjacent stratigraphic units 245


interval is equivalent to the Kulpara Formation, and the

upper part to the Parara Limestone on Yorke Peninsula.

There is a very sharp contact between the carbonate

conglomerate and the overlying 45 m of strongly

sheared dark grey shale and siltstone which appears to

be regarded as Smith Bay Shale in Fairclough (2008).

The deformation at this contact suggests that the shales

were faulted against the underlying carbonate breccia.

Fairclough (2008) placed the top part of the Cambrian

succession has been placed in the White Point Conglom-

erate. It commences with 22 m of mainly siltstone and

shale that contain an upwards increasing amount of

slightly calcareous very fine sandstone horizons. Some

of these sandstone beds show ripple cross-lamination.

The top 73.5 m of the Cambrian comprises well sorted

fine arkosic sandstone with rare pebbles, some heavy

mineral laminations and a limited amount of tabular

and low angle trough cross-bedding. This 73.5 m interval

is calcareous towards the bottom. As discussed below,

we consider that it is probable that the top 95.5 m of

section in Investigator 1 corresponds, at least in part, to

the lower part of the section described along the coast by

Daily et al. (1980).

Coastal sections to the west of Big Gully

The stratigraphic record in Investigator 1 has no

evidence of the Mt McDonnell Formation and Stokes

Bay Sandstone, which together make up the record in

Investigator 2, 22 km west along the Kangaroo Island

coastline (Figure 1). Nearby to Investigator 2, at Cape

Cassini, archaeocyaths found in the upper part of the Mt

McDonnell Formation resemble those of the Fork Tree

Limestone on Fleurieu Peninsula to the northeast of

Kangaroo Island (Gravestock & Gatehouse 1995). Since

cobbles and boulders bearing archaeocyaths of similar

age are common in the White Point Conglomerate near

Cape D’Estaing, this formation clearly post-dates the Mt

McDonnell Formation.

Moore (1979, 1983) and Daily et al. (1980) produced

stratigraphic logs of the White Point Conglomerate,

Emu Bay Shale and Boxing Bay Formation along the

coast between Bald Rock and Boxing Bay (Figure 2),

with respective thicknesses of 605, 78 and 511 m,

although the top of the Boxing Bay Formation is not

exposed. The following information is based on the

detailed information in these papers, supplemented by

our own observations.

Daily et al. (1980) commenced their measured section

immediately to the east of Bald Rock. A low angle fault

shears the base of the boulder conglomerate that

outcrops on this prominence marking the eastern end

of Emu Bay, down-faulting the conglomerate against the

basal sandstone member of the White Point Conglomer-

ate, that outcrops on both sides of Bald Rock. Daily et al.

(1980) considered that the basal 90 m of this section

belonged to the Smith Bay Shale, thus linking the

fossiliferous Cambrian succession in the Emu Bay/Big

Gully area to that in the Smith Bay to Stokes Bay area to

the west of Emu Bay. Our observations indicate that the

‘Smith Bay Shale’ as described by Daily et al. (1980) is

essentially a thinly bedded, fine micaceous sandstone

with abundant trace fossils, occurring as thickening

upwards packages. Sedimentary structures include

abundant ripple cross-lamination plus cross-bedding

that indicate a westerly flow direction. The only shale

present is in between the ripple cross-laminae. Near the

middle of the ‘Smith Bay Shale’ is a lenticular (0.2 to

1.5 m) unit of well-sorted, stylolitic calcareous sand-

stone, some levels of which are oolitic. Poorly preserved

hyoliths and tubes occur within this unit (G. Brock pers.

comm., December 2009). Rather than belonging to the

Smith Bay Shale as suggested by Daily et al. (1980), we

regard this basal 90 m unit as a fine-grained association

within the White Point Conglomerate, possibly equiva-

lent to the upper part of the section in Investigator 1. In

outcrop, this lower finer-grained succession is overlain

abruptly, but conformably, by the conglomeratic facies

of the White Point Conglomerate. Hence, in our view:

(1) the base of the White Point Conglomerate is sheared

in Investigator 1 and is nowhere exposed in outcrop;

and (2) the stratigraphic relationships between the

Cambrian successions in the Emu Bay/Big Gully and

Smith Bay/Stokes Bay areas are still unclear, and will

be the subject of a later paper.

The basal 165 m of the White Point Conglomerate as

described by Daily et al. (1980) comprises mainly trough

cross-bedded granule-rich conglomerate beds with sub-

ordinate ripple cross-laminated sandstone, contorted

sandstone and thin mudstone horizons up to 1 m thick

that are shown in Moore (1979), but not in Daily et al.

Figure 3 Stratigraphic log of Investigator 1 drilled by

Minerals and Energy Division, PIRSA, near Bald Rock, east

of Emu Bay.



(1980). The thin mudstone horizons occur mainly in the

top 70 m of this 165 m of section. The overlying 410 m

make up the bulk of the White Point Conglomerate. It

comprises mainly a crudely bedded cobble to boulder

polymict conglomerate (Figure 4) that is largely clast

supported, but some horizons are matrix supported.

Maximum clast size is 1.5 m (Daily et al. 1980). Most of

the clasts are of carbonates (limestones including

archaeocyath bearing limestones, dolomites, rare mag-

nesite); other clast types include granite, gneiss, quart-

zite, vein quartz and red sandstone. At some levels the

matrix is calcareous. A few interbedded thin red

mudstone and fine sandstone beds contain mud cracks

and trace fossils of likely trilobitomorph origin. Our

mapping indicates that, although along the coast, the

White Point Conglomerate is mainly a cobble to boulder

conglomerate, the clast size decreases rapidly to the

south. The massive conglomerate along the coast

becomes lenticular to the south (Figure 2) with discrete

lenses of polymict conglomerate occurring within an

arkose. About 700 m west of Big Gully, the conglomerate

lenses appear to have largely, if not entirely, pinched

out within 400 m of the coast; here the White Point

Conglomerate comprises a moderately well-sorted, fine

to medium grained arkose. In thin-section, the grainsize

is up to 0.5 mm, but most grains are 0.2–0.3 mm. The

clasts consist of quartz (40%), feldspars (K feldspar,

microcline, plagioclase) (35%), clays and lithic frag-

ments (20%) with minor amounts of muscovite, opaques,

zircon and tourmaline.

Above the bulk of the conglomerate, Daily et al. (1980)

described a 3 m thick bioturbated argillaceous lime-

stone that they used as a marker bed; immediately

below this limestone is a shale that contains the

emuellid trilobite Balcoracania dailyi. We found the

combination of the argillaceous limestone and fossili-

ferous shale to be a useful marker unit, herein named

the Rouge Mudstone Member (new name, see below) of

the Marsden Sandstone (new name, see below). The top

25 m of the coastal section of this Cambrian succession

comprises mainly red-brown, moderately well-sorted,

fine to medium grained feldspathic sandstone, herein

Figure 4 Sedimentary facies of the White Point Conglomerate. (a, e) Bedded polymictic conglomerate rich in basement clasts,

with red granule rich sandstone beds, from the upper part of the WPC, west of Big Gully. (b) Cobble undercut on the down-

current side reflecting a southern transport direction. (c) Reworked archaeocyath bioclast. (d) Massive polymictic

conglomerate with a large proportion of carbonate cobbles of reworked Early Cambrian formations. (f) Basal conglomerate

near Bald Rock, east of Emu Bay.



termed the Marsden Sandstone. It should be noted that

our work indicates that the White Point Conglomerate,

as indicated in stratigraphic column B of Daily et al.

(1980, figure 5) from west of Cape D’Estaing, is equiva-

lent to what is here termed the Marsden Sandstone.

Daily et al. (1979) stated that the Emu Bay Shale, on

the coast immediately east of Big Gully, is 78 m thick

and was deposited on top of the White Point Conglom-

erate, or in the terminology used herein, on top of the

Marsden Sandstone, without a sedimentary break.

Moore (1979, 1983) and Daily et al. (1980) state that the

Emu Bay Shale comprises mainly a dark grey to black

laminated mudstone, in places pyritic, with subordinate

trough cross-bedded and linsen bedded sandstone beds

and granule conglomerate beds, with at least one

coarser conglomerate horizon. The clast content of these

conglomerate beds is similar to that found in the White

Point Conglomerate. The mudstone facies contain the

Lagerstatte that was first recorded by Daily (1956). Daily

et al. (1979, 1980) suggested that the preservation of the

Lagerstatte was due to rapid burial in stagnant bottom

conditions. Conway Morris & Jenkins (1985) and Nedin

(1995a, b) came to a similar conclusion.

In the coastal section, the Boxing Bay Formation

sharply, but conformably, overlies the Emu Bay Shale,

although further inland the base of the Boxing Bay

Formation is channelled down into the top of the Emu

Bay Shale (see below). It comprises red brown felds-

pathic sandstone and arkose that Daily et al. (1980)

suggested were deposited in a subtidal environment.

There are abundant trace fossils, particularly arthropod

tracks, and large-scale soft sediment slumping suggest-

ing rapid sedimentation within a coarsening, thickening

upward succession. In the basal 50 m of the Boxing Bay

Formation, Moore (1979) noted the presence of several

mudstone horizons up to 4 m thick within the sandstone

and fine conglomerate beds that make up the bulk of the

formation at this level.

PRESENT STUDY

We have mapped the area in the vicinity of the

coastal section and our new excavation at Buck Quarry

(Figure 2). Five sections (BGS1 to 5) have been measured

across the strata containing the Emu Bay Shale

Lagerstatte (Figure 5). Section BGS1 commenced near

the top of the highest polymict conglomerate within the

main part of the White Point Conglomerate. Here the

conglomerate is well bedded with some low angle cross-

bedding. The largest clast has a diameter of about 40 cm;

clast types include limestone, quartzite and vein quartz;

Figure 5 Stratigraphic sections through the Kangaroo Island Group from the north coast of Kangaroo Island around Emu Bay

(after Daily et al. 1980), indicating stratigraphic position of panel diagram for the Marsden Sandstone (new name) and Emu

Bay Shale.



they range from angular to well rounded. The conglom-

erate is matrix- to clast-supported, with a slightly

calcareous cement.

The polymict conglomerate is overlain sharply by

about 3 m of buff coloured muddy limestone con-

taining burrows and the trilobite Balcoracania dailyi

(Figure 6f). As noted above, we used this fossiliferous

mudstone member of the Marsden Sandstone as a

marker horizon as did Daily et al. (1980) who recorded

it at Big Gully, and east and west of Cape D’Estaing. This

unit is herein termed the Rouge Mudstone Member of

the Marsden Sandstone (see Appendix 1 for definitions).

The argillaceous limestone comprises calcareous

mudstone with iron-stained, carbonate filled, burrow

galleries and nodules (Figure 6e). The presence of

Balcoracania dailyi indicates very shallow marine

conditions (Paterson et al. 2007a). It should be noted

that previous reports of Balcoracania dailyi from the

White Point Conglomerate (e.g. Pocock 1970; Paterson &

Edgecombe 2006; Jago et al. 2006b; Paterson & Brock

2007; Paterson et al. 2007a) should now be considered

occurrences within the Rouge Mudstone Member. The

Rouge Mudstone Member is overlain by about 40 m of

an essentially coarsening and upwards thickening

package that in its lower part comprises red to grey,

micaceous, feldspathic, moderately sorted, fine sand-

stone beds that are laminated in places, and bear

Cruziana trackways. In thin-section these slightly

calcareous sandstone beds comprise quartz, plagioclase,

K-feldspar and lithic fragments that are mainly sutured

together. Isolated muscovite grains are aligned parallel

to bedding; minor amounts of zircon are present. Most of

the grains are 0.2 to 0.4 mm across but range up to

0.6 mm. Almost all of the grains are angular with little

or no sign of rounding. Some of the siltstone fragments

are iron stained. Other sedimentary structures include

interference ripples, tabular cross-bedding and wet

sediment slumping. Within the lower part of the

Figure 6 Sedimentary facies of the Marsden Sandstone (new name) above the White Point Conglomerate and below the Emu

Bay Shale. (a) Upper part of the Marsden Sandstone on the east side of Big Gully, with upper sandstone beds stepped by faults

prior to deposition of the Emu Bay Shale. (b) Trough cross-stratification in coarse-grained sandstone beds in the upper part of

the Marsden Sandstone. (c) Dimpled top of micaceous, laminated to thinly bedded sandstone overlying the Rouge Mudstone

Member of the Marsden Sandstone. (d) Corresponding base of dimpled beds. (e) Carbonate filled burrows in the top of the

Rouge Mudstone Member of the basal Marsden Sandstone. (f) The small emuellid trilobite, Balcoracania dailyi in the basal

marker beds of the Rouge Mudstone Member from Big Gully.



Marsden Sandstone there are micaceous, fine to medium

grained, laminated sandstone beds with upper surfaces

of close-packed, concave hollows and corresponding to

basal surfaces with circular, convex casts, 0.5–1.0 cm in

diameter. The wrinkled, basal casts resemble Ediacaran

polypoid forms such as Nemiana (Figure 6c, d). Two

medium-grained sandstone intervals contain mudstone

rip-up clasts. The upper 40 m of the Marsden Sandstone

contains about 11 m of predominantly mudstone near

the middle. Towards the top of this interval is a horizon

of gravel conglomerate 1.5 to 2 m thick that exhibits

tabular cross-bedding. Some of the coarse-grained

sandstone beds in the coarsening and thickening

upward succession of the Marsden Sandstone exhibit

trough cross-bedding (Figure 6b).

A thin-section from near the top of the Marsden

Sandstone shows that all the grains are completely

angular, and tend to be aligned parallel to bedding.

Grainsize is up to 0.6 mm but is mainly 0.2 to 0.3 mm;

the rock is moderately well sorted. The clasts comprise

quartz (45%) and feldspar (45%), mainly plagioclase and

K-feldspar with minor microcline. There are about 5%

lithic fragments (metamorphics and iron-stained silt-

stone) plus trace amounts of zircon and tourmaline.

Muscovite (1–2%) grains are aligned parallel to bedding.

In Section BGS1, the base of the Emu Bay Shale is a

cross-bedded conglomerate, 0.1 to 2 m thick that con-

tains angular green shale clasts up to 5 cm across

(Figure 7d); subrounded clasts of vein quartz are also

present. This conglomerate is quite variable. On the

coast in Section BGS 5 it is about 30 cm thick with

angular green siltstone clasts up to 10 cm across, with

some granite clasts up to 8 cm across. Dinnick (1985)

also considered that this conglomerate represented the

base of the Emu Bay Shale and noted the presence of

clasts of the underlying sandstone. On the coast, the

conglomerate is overlain by a 20 cm thick ferruginous

coarse sandstone horizon that passes up into green

sandstone and then into a very dark mudstone char-

acteristic of the lower part of the Emu Bay Shale at this

locality.

The base of this conglomerate, where it rests on the

Marsden Sandstone, is interpreted as a sequence

boundary at the base of the Emu Bay Shale. The

conglomerate appears to be thickest where syndeposi-

tional faults have created steps in the Marsden Sand-

stone (Figure 6a) prior to the deposition of the Emu Bay

Shale. Above the basal conglomerate in Section BGS1,

the outcrop of the Emu Bay Shale is poor with sporadic

outcrops of fine sandstone and mudstone. Between

sections BGS1 and BGS2, the first specimens of the

trilobite Estaingia bilobata appear within the lowest

3 m of shale above the basal conglomerate and below a

50 cm thick sandstone bed.

Sections BGS2 and BGS3 together (Figure 5) encom-

pass the Emu Bay Shale which here is about 61 m thick.

Above the basal conglomerate, the bottom half of the

formation consists of a highly fossiliferous, dark grey to

black, laminated, micaceous mudstone that contains the

Lagerstatte. Some of these slightly calcareous mudstone

beds show evidence of deformed lamination and small-

scale fluidisation, suggesting syndepositional distur-

bance; there is evidence of small-scale syndepositional

faulting (Figure 7f). Within the mudstone beds are thin

(*1 to 5 cm) siltstone and very fine calcareous sand-

stone horizons, some of which show grading and are

loaded into the underlying mudstone beds resulting in

flame structures. Mudstone beds grade up into struc-

tureless, silty sandstone in cycles that increase in bed

thickness and proportion up section. Within the mud-

stone are thin, structureless, fine sandstone beds up to

20 cm thick. Although no sole markings are known, we

interpret these as sediment gravity flow deposits or

possibly as storm deposits. The Lagerstatte, as currently

known, is largely confined to the basal 10 m of the Emu

Bay Shale, although linguliformean brachiopods and

hyoliths are known from 24.6 m above the base in

section 2; specimens of Estaingia bilobata and Redlichia

takooensis have also been found near this level. In places

secondary fibrous calcite is preserved on specimens of

Estaingia bilobata and Redlichia takooensis; when fresh,

the fossiliferous part of the Emu Bay Shale would have

been quite calcareous. In Section BGS2 (Figure 5), about

15–17 m above the base of the Emu Bay Shale, is a 1.5 m

interval of coarse sandstone that includes a lens of

matrix-supported gravel containing clasts up to 2 cm

across. About 350 m along strike, in the coastal expo-

sure, the coarse sandstone shows strongly contorted

bedding due to wet sediment slumping. Ball and pillow

structures are evident in sharp-based sandstone beds

9 m and 14 m above the base of the Emu Bay Shale. The

vergence of slump-roll bedding near the top of the Emu

Bay Shale indicates an approximate south to north

depositional slope (Figure 7a, c). However, in Section

BGS3, above Buck Quarry, slumps show south vergence

(Figure 7g). Without three-dimensional exposure, the

interpretation of slumping orientation is equivocal.

Evidence of syndepositional faulting, detachment of

lenses of sandstone, and inclined flame structures in

silty mudstone suggests a significant depositional gra-

dient.

In sections BGS2 and BGS3, about 30 m above the

base of the Emu Bay Shale, is a 1.5 m thick polymict

conglomerate, with angular to rounded clasts up to

40 cm across. In places the conglomerate is matrix

supported; in others it is clast supported. Clast types

include carbonates, gneiss, vein quartz, granite, quartz

siltstone, quartz sandstone and a red sandstone. The

matrix is largely a poorly sorted coarse sandstone to fine

conglomerate. The polymict conglomerate is lenticular

and thins to the south; it lenses out completely about

150 m south of Buck Quarry. The Lagerstatte-bearing

mudstone also thins southwards and seems to disappear

150–200 m south of Buck Quarry (Figure 2).

In thin-section, a 2 m thick sandstone, a little below

the polymict conglomerate, is moderately well sorted

with an iron stained calcareous cement comprising

about 60% of the rock. Almost all the clasts are

completely angular. They comprise mainly quartz and

K-feldspar with minor microcline and plagioclase with

traces of zircon and muscovite. Most of the clasts are

0.1–0.3 mm across with a few up to 0.4 mm.

In the coastal section, the base of this polymict

conglomerate is loaded down into the underlying

sediment with the development of prominent flame

structures (Figure 7a, b). Here the Emu Bay Shale, in



the 5 to 10 m below this polymict conglomerate,

comprises interbedded, lenticular micaceous sandstone

and siltstone, with beds of sandstone between 2 and

30 cm thick. Some of the sandstone horizons are

burrowed. In at least two places, isolated pebbles up to

6 cm across occur 40 cm below the base of the polymict

conglomerate. These are interpreted as pebbles that

have slid downslope in front of a fan delta.

Figure 7 Sedimentary facies of the Emu Bay Shale. (a–d) Coarsening, thickening upward section in the upper Emu Bay Shale,

below the sandstone beds of Boxing Bay Formation in the coastal cliffs, east of Big Gully, 1 km east of Emu Bay, Kangaroo

Island. (a) Fossiliferous, whitish (salt coated), laminated mudstone, fawn coloured siltstone and bold, medium to coarse

grained, gritty and pebbly sandstone beds of the upper Emu Bay Shale. (b) Pebbly and conglomeratic sandstone loads into

underlying siltstone and mudstone beds. (c) Detail of north verging slumps in sandstone beds in (a). (d) Basal breccia with

green shale clasts, vein-quartz and granite clasts. (e) Dark grey, fawn weathering mudstone and discontinuous silty

lamination in the lower part of the Emu Bay Shale on the wave-eroded platform near Big Gully. (f) Grey, laminated,

fossiliferous mudstone and thinly bedded, fawn coloured siltstone, 10.7–11.1 m above the base of the Emu Bay Shale in Buck

Quarry, with ESE–WNW-oriented normal syndepositional faulting antithetic to large-scale listric faults that stepped the top

of the underlying Marsden Sandstone. (g) South verging slumps in siltstone beds at 18.7 m above the base of the Emu Bay

Shale near Buck Quarry. Hammer, 28 cm long.



The maximum flooding surface in this broadly

coarsening and thickening-upward sequence is repre-

sented by a dark grey mudstone overlying the basal

polymict conglomerate in the freshest exposure of the

Emu Bay Shale, on the coastal platform east of the

mouth of Big Gully. The top 30 m of the Emu Bay Shale,

in the vicinity of Buck Quarry, outcrops poorly but

appears to consist of largely interbedded mudstone

facies (which contain Redlichia takooensis and Estaingia

bilobata about 4 m above the polymict conglomerate)

and very fine to fine thin-bedded red brown micaceous,

sandstone beds that exhibit flaser bedding and ripple

cross-laminations in the top 12 m of the Emu Bay Shale.

In thin-section, the sandstone beds are moderately well

sorted, and comprise mainly angular grains (although a

very few grains are rounded) 0.1 to 0.2 mm across. The

grains, particularly the 3 to 5% muscovite, show a

marked alignment parallel to bedding. Most of the clasts

are quartz (60%), with 25% lithic fragments (mainly

metamorphics) plus altered feldspar, 10% clay matrix

and minor plagioclase (1 to 2%), zircons and opaques.

Abundant large arthropod tracks, including Cruzi-

ana and Monomorphichnus, occur in the fine sandstone

beds towards the top of the Emu Bay Shale. Cruziana

trackways appear to be grouped into two size classes,

one being 5–15 mm and the other 30–80 mm wide,

possibly formed by the two common trilobite species,

Estaingia bilobata and Redlichia takooensis, respec-

tively, although no body fossils are found at this level.

The base of the Boxing Bay Formation appears to be

channelled into the top of the Emu Bay Shale, possibly

due to mass-flow and gravity sliding. The basal 3 m of

the Boxing Bay Formation comprises fine to medium

grained, well-sorted sandstone that is massive at the

base and more laminated towards the top. Some

horizons are micaceous.

INTERPRETATION

The geology of the area is shown in Figure 2; Figure 8

shows our interpreted, schematic north–south cross-

section through the immediate area of Big Gully and

Buck Quarry. Daily et al. (1980) suggested that the White

Point Conglomerate was produced as the result of the

rapid erosion of an area of Proterozoic–Lower Cambrian

rocks, similar to those on Yorke Peninsula, where

Proterozoic Gawler Craton rocks are overlain by lower

Cambrian rocks of the Stansbury Basin. Daily et al.

(1980) suggested that the uplifted area was near the

present north coast of Kangaroo Island and was the

result of the early Cambrian Kangarooian Movements of

Daily & Forbes (1969). Our observations, both at Big

Gully and Cape D’Estaing, support this hypothesis; we

interpret the White Point Conglomerate as being formed

as coalesced fan deltas on the margin of an uplifted fault

block. South of the coastal outcrops to the west of Big

Gully, there is a marked southwards thinning and

Figure 8 Schematic N–S cross-section through the top of the White Point Conglomerate, Marsden Sandstone (new name), Emu

Bay Shale and Boxing Bay Formation with inferred listric faults cutting the Marsden Sandstone and base of the Emu Bay

Shale, but not penetrating to the Boxing Bay Formation. Relative position of five measured stratigraphic sections shown in

Figure 3. The Rouge Mudstone Member of the Marsden Sandstone is characterised by the emuellid trilobite, Balcoracania

dailyi in Big Gully as well as on the western side of Emu Bay near Smith Bay on Kangaroo Island. Fossils of the Emu Bay

Shale biota are concentrated in the laminated mudstone facies, with lesser numbers in upper silty beds of the Emu Bay Shale.



lensing out of the conglomerate horizons within the

main part of the White Point Conglomerate (Figure 2).

No conglomerate beds were found in an inspection of

outcrop about 1 km to the south of the coastal outcrops

of White Point Conglomerate; this supports the concept

of the White Point Conglomerate being derived from

an uplifted tectonic margin immediately north of the

present coastline.

The Rouge Mudstone Member at the base of the

Marsden Sandstone contains very shallow marine

sediments deposited at a time of relative sea-level rise,

perhaps combined with a lowering of the source area

due to faulting and/or erosion and/or a time when the

area of deposition of the fan deltas switched. The basal

nodular limestone represents a likely transgressive

flooding event, with maximum flooding represented by

a partly exposed mudstone, followed by progradation of

the overlying poorly sorted, cross-bedded, feldspathic

sandstone facies and fine conglomerate beds of the

remainder of the Marsden Sandstone. This indicates

a rapid progradation into a deeper marine basin than

was present during deposition of the White Point

Conglomerate.

Our mapping shows that the dark mudstone facies

that contain the Lagerstatte extend from the north coast

some 500 m due south where it lenses out against a

faulted base. Numerous small faults clearly visible at

the contact between the Marsden Sandstone and the

Emu Bay Shale (Figure 6a) appear to be north-dipping

listric faults that coalesce into the top of the White Point

Conglomerate (Figure 8). The contact between the Emu

Bay Shale and the Boxing Bay Formation shows little

evidence of the numerous faults seen at the base of the

Emu Bay Shale, although there are some regional faults

(not shown on the cross-section) that cut across all units.

This suggests that syndepositional faulting occurred

during and immediately after the deposition of the

Marsden Sandstone. In addition, mapping in the area to

the south and southwest of Buck Quarry shows a fold

pattern within the Marsden Sandstone and the top part

of the White Point Conglomerate that is not reflected

within the overlying Emu Bay Shale (Figures 2, 8). We

interpret this as evidence of large-scale syndepositional

sedimentary slumping occurring on an unstable slope

near an active tectonic margin during, or shortly after,

the deposition of the White Point Conglomerate and

Marsden Sandstone, and before the deposition of the

Emu Bay Shale. Evidence of some continued instability

is provided by the presence of small-scale syndeposi-

tional faults within the Emu Bay Shale (Figure 7f).

The juxtaposition of the Lagerstatte in shale, in close

geographic and stratigraphic proximity to an active

tectonic edge, as recorded in the White Point Conglom-

erate below the Marsden Sandstone, and conglomerate

facies at the base and within the Emu Bay Shale,

suggests a genetic relationship between the basin

tectonics and the occurrence of accumulations of soft-

bodied and mineralised invertebrates. We suggest that

syndepositional faulting south of an active faulted

margin, proximal to the current Kangaroo Island north

coast, led to the development of isolated stagnant, anoxic

to oxic areas on the sea floor that allowed the in situ

preservation of the Lagerstatte. This is evident from the

dominance of complete specimens of the two common

trilobite species Estaingia bilobata and Redlichia

takooensis, associated with a relatively small percentage

(510%) of moult ensembles. The preponderance of

dorsum-down specimens (475% within three sampled

horizons at Buck Quarry) may suggest that the buoying

effect of decay gases overturned whole specimens. Since

there is no evidence that these trilobite species were

pelagic, it is unlikely that the preferred ventral-up

orientation was due to settling out of bodies after death

in the absence of wave or current agitation. There is no

sign of arthropod trackways or bioturbation, thus

supporting the idea of McKirdy et al. (2011) that

conditions below the sediment/water interface were

anoxic. On the other hand, the fauna is extremely rich,

including the presence of several benthic animals such

as paleoscolecid worms, hyoliths, leptomitid demos-

ponges and other (non-trilobite) lamellipedian arthro-

pods, thus suggesting that for most of the time the water

above the sediment/water interface contained sufficient

oxygen levels (either exaerobic or dysaerobic (sensu

Gaines & Droser 2005) to support a rich fauna. This is in

accord with the geochemical work reported by McKirdy

et al. (2011) that indicates that the sediments containing

the Lagerstatte were deposited beneath an oxic water

column, with a sharp redox boundary at the sediment–

water interface; below this boundary the pore water was

anoxic. The paucity of benthic fixosessile taxa (e.g.

brachiopods) in terms of diversity and abundance

suggests that the environmental conditions were per-

haps too extreme for some organisms.

The very high proportion of complete trilobites,

representing living or recently dead animals rather

than moults, plus the exceptional preservation of other

organisms, suggests the absence of scavengers, which is

typical of anoxic–dysoxic environments. The lack of

evidence of hiatal surfaces, oscillatory or tractional

currents at the many fossil-rich horizons, that might

have winnowed the sediment and aggregated the bodies,

suggests that both mineralised and unmineralised

organisms with benthic and nektic life modes were

mass-kill victims of abrupt anoxic events. The absence

of horizons with disarticulated moult accumulations is

indicative of a very high sedimentation rate in the Big

Gully sections, since moults of both common trilobite

species are abundant in the Emu Bay Shale on the

western side of Emu Bay (Pocock 1964). A more detailed

account of the taphonomy and synecology of the Emu

Bay Shale Lagerstatte is in preparation. While there is

no evidence at this time, as to the overall extent of the

Emu Bay Shale, outcrop ceases at the north coast of the

island, and no Lagerstatte is evident in the Emu Bay

Shale near Cape D’Estaing, 10 km to the west of Big

Gully. Thus, it appears that the Emu Bay Shale

Lagerstatte is restricted to Big Gully.

Comparison with other Cambrian Lagerstatten

Cambrian BST deposits seem to share a common mode

of fossil preservation (Gaines et al. 2008). However,

specific paleoenvironments and geological settings ap-

pear to vary greatly between localities, as reflected in

the lithostratigraphy, sedimentology and tectonic set-



ting of these sites. The Emu Bay Shale at Big Gully is

dominated by siliciclastic sediments deposited in a

relatively nearshore environment adjacent to an active

tectonic margin that generated continual syndeposi-

tional faulting and slumping. The laminated mudstone

facies that preserve the Lagerstatte, in addition to the

interbedded siltstone and sandstone beds resulting from

sediment gravity flows and/or storm events, were likely

deposited in a localised, deeper water mini-basin on the

inner shelf with isolated depressions that experienced

fluctuating anoxic-oxic conditions. This appears to

represent a unique paleogeographic setting for a BST

deposit. In contrast, many Cambrian BST deposits in

North America (e.g. Burgess Shale, Spence Shale,

Kinzers, Wheeler and Marjum Formations; Butterfield

1995; Skinner 2005; Briggs et al. 2008; Brett et al. 2009;

Collom et al. 2009; Caron & Rudkin 2009 and references

therein), China (e.g. Maotianshan Shale at Chenjiang

and the Kaili Formation; Zhu et al. 2001; Hu 2005; Zhang

et al. 2008), Greenland (Buen Formation at Sirius Passet;

Conway Morris et al. 1987; Babcock & Peel 2007) and

Siberia (Sinsk Formation; Ivantsov et al. 2005) were

formed in outer shelf to slope-basin environments and,

in the case of the North American and Greenland sites,

adjacent to carbonate platforms. However, Caron et al.

(2010) reported a new BST site from the ‘thin’ Stephen

Formation near Stanley Glacier in Kootenay National

Park, British Columbia, which was deposited in a distal

ramp setting with no evidence of a carbonate escarp-

ment. The Lagerstatte of the Wheeler and Marjum

Formations are found within black shales deposited in

a topographic low (House Range Embayment) with

dysoxic and anoxic conditions, during a High Stand

(Brett et al. 2009). There is no evidence of an associated

tectonic edge.

Regional Correlation

The Cambrian succession represented on the central

north coast of Kangaroo Island shows little resemblance

to early Cambrian successions on Yorke Peninsula to

the north and on Fleurieu Peninsula to the ENE.

Judging from the changing composition of cobbles and

boulders up section in the White Point Conglomerate,

and the presence of Balcoracania dailyi, Redlichia

takooensis and Estaingia bilobata in the overlying

Marsden Sandstone and Emu Bay Shale, these forma-

tions must post-date the time of early Cambrian shallow

carbonate platform growth to the north and east.

However, there is little available evidence to correlate

these formations to mainland South Australia. Sheared

black shale beneath the White Point Conglomerate in

Investigator 1 (Figure 3) may represent deeper water

sedimentary environments coeval with the Heatherdale

Shale on Fleurieu Peninsula and the Parara Limestone

on Yorke Peninsula (Figure 9). Clearly the Cambrian

succession on the north coast of Kangaroo Island was a

product of local tectonic movements that may reflect the

Kangarooian Movements as documented by the onset of

sedimentation in the Kanmantoo Trough on the main-

land of South Australia (Daily & Forbes 1969).

Figure 9 Stratigraphic correlation of Cambrian formations in South Australia.



Although Paterson et al. (2008) correlated the Emu

Bay Shale Lagerstatte with the lower Cambrian Para-

raia janeae trilobite Zone of mainland South Australia,

it is noteworthy that the trilobite fauna of the Emu Bay

Shale, with the exception of Estaingia bilobata, lacks

key taxa from this zone, such as the eponym, Atops

rupertensis or Serrodiscus gravestocki. However, the co-

occurrence of taxa such as Redlichia takooensis, Estain-

gia bilobata and Balcoracania dailyi suggests a late

Botoman age (Bengtson et al. 1990; Paterson & Jago 2006;

Paterson & Brock 2007) and thus represents a younger

assemblage than that preserved in the Parara Limestone

(including the Koolywurtie Limestone Member) on

Yorke Peninsula (Bengtson et al. 1990; Paterson et al.

2007b). Deposition of the Emu Bay Shale after the onset

of the Kangarooian Movements that resulted in sedi-

mentation in the Kanmantoo Trough, coupled with the

fact that no fossils of Toyonian age have been found in

the Emu Bay Shale, further supports deposition of the

Lagerstatte during the late Botoman (Figure 9).

ACKNOWLEDGEMENTS

This project was funded by an Australian Research

Council Linkage grant (LP0774959) to the University of

Adelaide with extra financial support from Beach

Energy Ltd and the South Australian Museum. We

sincerely thank the Buck family for access to the field

area. Generous logistic support was provided by

SeaLink. We thank our collaborator, Mike Lee, for

support and advice. Natalie Schroeder provided

valuable organisational support and assistance in the

field. Other field assistance was provided by Mike

Gemmell, Ronda Atkinson, Glenn Brock, John Laurie,

Dennis Rice, Aaron Camens, and Trevor and Jenny

Worthy. Stephen Hore (PIRSA) and Chris Bentley

assisted with the provision of aerial photographs of

the area. David Keith (University of New England)

prepared the thin-sections. Glenn Brock (Macquarie

University) provided advice on small shelly fossils.

Pierre Kruse and Wolfgang Preiss are thanked for their

constructive comments on the paper.

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Received 5 November 2010; accepted 1 January 2011

APPENDIX 1: STRATIGRAPHIC NOMENCLATURE

The definitions of the two new stratigraphic units

erected in this paper are given below.

Marsden Sandstone (new name)

Derivation of name: From Mt Marsden, located

about 1.2 km SSE of the mouth of Big Gully (Figure

1).

Type section: In and on the western side of Big

Gully, about 200 m upstream from the mouth of Big

Gully at about lat. 3483401900S, long. 13783403100E.

Thickness: About 43 m in the type section.

Lithology: The basal 3 m is a buff-coloured calcareous

mudstone, the Rouge Member (see definition below).

The top 40 m of the Marsden Sandstone comprises an

overall coarsening upwards package with slightly

calcareous feldspathic sandstone at the base, overlain

by an interval of mudstone and subordinate sandstone

that passes up into medium to coarse sandstone and

gravel conglomerate towards the top.

Depositional environment: The Marsden Sand-

stone was deposited in shallow subtidal to shoreface

conditions.

Relationships and boundary criteria: The Rouge

Mudstone Member of the Marsden Sandstone

conformably overlies the White Point Conglomerate.

The base is taken as the level where the calcareous



mudstone beds of the Rouge Mudstone Member

directly overlie the White Point Conglomerate. The

upper boundary is unconformable with the Emu Bay

Shale and represents a sequence boundary.

Age: Early Cambrian (Cambrian Series 2, Stage 4).

Rouge Mudstone Member of the MarsdenSandstone (new name).

Derivation of name: From nearby Cape Rouge.

Type section: In and on the western side of Big

Gully, about 100 m upstream from the mouth of Big

Gully at about lat. 3483401600S, long. 13783402900E.

Thickness: About 3 m in the type section.

Lithology: A buff-coloured calcareous mudstone

with iron stained, carbonate filled burrows. The

emuellid trilobite Balcoracania dailyi occurs on some

bedding planes.

Depositional environment: Low energy, very shal-

low marine conditions.

Relationships and boundary criteria: The Rouge

Mudstone Member occurs at the base of the Marsden

Sandstone; it conformably overlies the White Point

Conglomerate; it is overlain conformably by the

remainder of the Marsden Sandstone.

Age: Early Cambrian (Cambrian Series 2, Stage 4).



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Gehling, J.G., Jago, J.B., Paterson, J.R., García-Bellido, D.C. & Edgecombe, G.D., 2011. The...

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