Late Paleozoic Troubridge Basin sediments on ...

New geology

Late Paleozoic Troubridge Basin sediments on Kangaroo Island, South Australia Neville F Alley1,2, Robert P Bourman3 and Anthony R Milnes1 1 Department of Geology and Geophysics, University of Adelaide 3 School of Earth & Environmental Sciences, University of Wollongong.

2 Marmota Energy Limited

Peer reviewed (DMITRE and externally)

Introduction

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ulf

The Troubridge Basin in South Australia is a late Paleozoic sedimentary basin, extending from the Coorong area across Fleurieu Peninsula and Kangaroo Island to Yorke Peninsula (Alley and Bourman 1995; Fig. 1). The basin contains the Cape Jervis Formation, which crops out extensively in these areas. The formation is also widely distributed in the subsurface below Yorke and Fleurieu peninsulas, Gulf St Vincent, Investigator Strait, Backstairs Passage, the Coorong area, Kangaroo Island and on the continental shelf to the east of Kangaroo Island (Alley and Bourman 1995). In some areas the formation forms a blanket of sediment and, in others, significant thicknesses are preserved in glacially eroded troughs or local tectonic depressions.

Sp

en

ce

Gulf St Vincent 138°0'E

139°0'E

Vincent

137°0'E

35°0'S

ADELAIDE

Gu

lf

St

) "

ator

IE U UR A FLE NSUL I PEN

Strait Ba c

Kingscote

) "

ks

ta i

rs

KANGAROO ISLAND

Pa

ss

ag

Th

e

e o Co

36°0'S

Investig

50

100 km

Kingston ") 37°0'S

0

ng ro

Troubridge Basin

Projection: Lamberts 204410-021

Robe

) "

Figure 1 Location of the Late Paleozoic Troubridge Basin. (Source DMITRE 2013a)

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MESA Journal 70 Issue 3 – 2013

The Cape Jervis Formation and the associated glacial erosional features have been studied since the 1800s and a summary of these researches is given in Bourman (1987) and Alley and Bourman (1995). At the type section of the Cape Jervis Formation, Alley and Bourman (1984) established five broad units, within which there may be considerable lithological variability, and a model for their deposition (Fig. 2; Table 1). It is believed that the sediments were deposited during the passage and decay of a continental ice-mass and that this model can be applied elsewhere in the Troubridge Basin (Alley and Bourman 1984, 1995; Bourman and Alley 1999). It is highly likely that the units at Cape Jervis are part of a condensed succession plastered onto a bedrock slope, since much greater thicknesses of the formation are disclosed in drillholes in other parts of the basin. Periglacial conditions appear to have existed prior to the main glaciation, producing frost-shattered bedrock (Alley and Bourman 1984, 1995). These gelifracts are overlain by a few metres of proglacial sand and clay containing thin diamictite and striated pebbles, which are believed to have been deposited in front of advancing ice. This ice moved northwestwards across the Troubridge Basin area during the Late Carboniferous and earliest Permian, depositing lodgement till which, like such Quaternary tills, was only patchily distributed across the landscape (Bourman 1987; Bourman and Alley 1999; Alley and Bourman 1995). Decay of the ice-mass accompanied by concurrent development of extensive shallow lakes and outwash plains and marine transgression into glacioisostatically depressed lowlands during Asselian to Sakmarian time led to deposition of glaciofluvial, glaciolacustrine, ice-contact and glaciomarine sediments (Bourman and Alley 1990; Alley and

Troubridge Basin sediments

Calcrete Point Ellen Formation

Bourman 1995). Glacial influence appears to have ceased by the end of the Sakmarian (Ludbrook 1967, 1969; Foster 1974; Foster and Waterhouse 1988; Fig. 3).

60

Obscured section

55

Arenaceous foraminifera

50

5

45 Cape Jervis Formation

N

W

E

S

40 4

35

N

W

E

30

S N

25

2

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3 20

1

15

2

10 Kanmantoo Group metasediments

4

6

10 8

s ble

b

Pe

E

S

n = 50

N

E

W

S

5

Silt Clay

Sand

Pebbles

Diamicton

0 Metres

204410-022

Limestone

Cross-bedding

Clay

Gelifracts

Silt Sand Diamicton Conglomerate

Fossils

5 Unit number (refers to the facies described in Table 1)

Drop stones

Figure 2 Stratigraphy and sedimentology of the Cape Jervis Formation at the type section. (After Alley and Bourman 1995)

Table 1 Facies recognised by Alley and Bourman (1984) at the type section of the Cape Jervis Formation Unit

Lithology

Environment of deposition

5

Fine silt and clay containing dropstones and thin grit lenses; restricted arenaceous marine foraminiferal assemblages Sakmarian in age.

Glaciomarine.

4

Beds and lenses of pebbly diamicton with a sandy matrix, intercalated with sand and minor silt and clay; large granite erratics; high concentration of coarser exotic clasts; diamictons possess chaotic larger clast fabric.

Proglacial: flowtills shed as supraglacial moraine from stagnating ice into an adjacent aqueous basin.

3

Interstratified sand, silt and clay containing gravel lenses and striated dropstones. Graded bedding, intraformational slumping and cyclopels in the finer fraction.

Proglacial: fan deposited subaqueously against a stagnating ice-mass.

2

Clayey lodgement till with clasts dominated by local lithologies; low frequencies of gneiss and Encounter Bay Granite; rare porphyritic volcanic clasts.

Glacial deposition.

1

Cross-bedded medium sand and finely bedded clay containing thin lenses of diamicton and striated dropstones.

Fluvioglacial outwash.

For a number of years the authors have been systematically studying the details of the Cape Jervis Formation on Kangaroo Island, in particular, excellent exposures near Kingscote and in the Gap Hills (Fig. 4). This paper: • reports on the stratigraphic and sedimentological results of these studies • attempts to correlate the sediments with the type section at Cape Jervis • constructs a model for the deposition of the glacigene sediments.

Kangaroo Island Cape Jervis Formation: sedimentology and stratigraphy Based on the distribution of exposed glacigene sediments, occurrences in boreholes, erratics and glaciated rock surfaces, our investigations and those of the Geological Survey of South Australia (Belperio 1995; Belperio and Flint 1992; Fairclough 2007, 2008) show that the sediments occur across a large part of eastern Kangaroo Island. These investigations demonstrate that the movement of ice was generally northwestwards, paralleling that elsewhere in the Troubridge Basin. The highest known elevation of erratics is 120 m above sea level (asl) west of Cape D’Estaing (Bauer 1959). However, given the widespread occurrence of glacigene sediments preserved across much of the Australian continent, probably all of the Kangaroo Island area was covered by late Paleozoic ice at some stage. The distribution of the Cape Jervis Formation on Kangaroo Island and the sites investigated are shown in Figure 4. On Kangaroo Island the Cape Jervis Formation is just over 335 m thick in a water bore (here referred to as Kingscote Bore) on the foreshore at the town of Kingscote (Howchin 1929; Ludbrook 1967; Alley and Bourman 1995; DMITRE 2013b), which lies in close proximity to our measured Section 3 at Kingscote. Aeromagnetic and seismic surveys indicate that ~400 m of the formation may be present in a glacially scoured, N–S-trending trough along the western part of Dudley Peninsula (Fig. 5, Line 2A). Offshore drilling nearby in this latter area, however, intersected only 47.85 m of boulder-free blue clay interpreted to be Cape Jervis Formation (American Beach Oil 1 drillhole, DMITRE 2013c). It is possible that the drillhole was sited on the eastern margin of the N–S trending trough and only intersected the relatively thin part of the onlap succession along the margins of the trough. The geophysical interpretations suggest the presence of a prominent elongate late Paleozoic valley in this area. MESA Journal 70 Issue 3 – 2013

25

New geology

137°30'E

138°0'E

TATARIAN

Troubridge Basin

C

KAZANIAN

Cygnet River

American River

35°45'S

Penneshaw

?

A

0 204410-024

? STEPHANIAN 204410-023

Figure 3 Geological timescale showing approximate age of the Cape Jervis Formation. (Modified from Alley 1995a)

5

10 km

Projection: Lamberts

Sites Drillhole Cross-section (see Fig. 11) Wisanger Basalt Cape Jervis Formation

36°0'S

CAPE JERVIS FORMATION

PERMIAN

Brownlow

ARTINSKIAN

ASSELIAN

CARBONIFEROUS

Cape Jervis

A

AMERICAN BEACH OIL 1

SAKMARIAN

Figure 4 Sites investigated: A Kingscote, B Bluff Quarry area and C Turner Quarry, Gap Hills. Red line shows the stratigraphic section and correlation between sites shown in Figure 11. The outline of the Troubridge Basin has been interpreted from the presence of Cape Jervis Formation in outcrop, subcrop and drillhole occurrences and the distribution of erratics. (Source DMITRE 2013a)

Another trough north of the Cygnet Fault and south of the Gap Hills is interpreted to contain up to several hundred metres of Permian sediments (Fig. 5, Line 3A). In both of these instances of interpreted troughs there does not appear to be any geophysical evidence for the existence of faults (Fig. 5) and thus the troughs are probably glacially eroded features, as inferred by van der Stelt, Belperio and Flint (1992). The geophysical interpretations thus indicate that the Cape Jervis Formation in some areas lies in deeply eroded valleys rather than being preserved in down-faulted troughs.

Measured sections – Kingscote

The Cape Jervis Formation is overlain by Cenozoic sediments or the Jurassic Wisanger Basalt and overlies Cambrian and Neoproterozoic rocks.

At Section 1 the exposed Cape Jervis Formation is ~7 m thick and is overlain by several metres of Tertiary Kingscote Limestone (Fig. 7). The bulk of the glacigene formation is interbedded coarse sand and clay. The upper 1.4 m is massive, sandy clay, disturbed by intraformational slumping. Although the sediments are broadly flat-lying, minor cross-bedding occurs just above the 1.0 m level. Occasional small rounded pebbles occur at the 3–4 m level, whereas clay rip-up clasts occur just above this level.

A number of sections were investigated in detail along the coastal cliff at Kingscote, in and around the Bluff Quarry and in the Gap Hills (Figs 4, 6). Many other sites where the formation is poorly exposed were investigated and all available drillhole data was evaluated. We have previously reported on glacigene sediments and glacial erosional features at Christmas Cove, Boxing Bay and Smith Bay (Bourman and Alley 1999) and these will not be detailed here. To help with our understanding of the lithologies of the sediments we undertook pebble lithological and heavy mineral analyses at a number of sites. Heavy mineral analysis was undertaken by Mason Geoscience Pty Ltd (Mason 2002) and the results are summarised in the Appendix.

26

B

Kingscote

KUNGURIAN

B

Emu Bay


Cape Jervis Formation sand, silt and clay crop out along the coastal cliff north of Kingscote jetty where it is overlain by Jurassic Wisanger Basalt or the Tertiary Kingscote Limestone (Figs 6, 7). The sediments are extensively disrupted by modern landslides and intraformational slumping. We measured four detailed sections. However, as the sediments are strongly slumped, the stratigraphic relationships between the sections are not clear. Kingscote Bore lies in close proximity to Section 3 (Fig. 6) and thus we have continued our litholog of that bore with this section (Fig. 7).

The measured section at Section 2 is 12 m thick. The basal 3 m here is composed of intraformationally slumped medium and coarse sand and minor beds of sandy clay. Above this is about 1.5 m of sandy clay interbedded with thin beds of sand. From this point upwards to 10 m from the base of the section is a series of interbedded sands and clays,

The Red Ban


Line 2A West

0

East

Metres

Quaternary Tertiary

–250

Jurassic Basalt

Folding schematic –500

Permian Glacigene

Scale V = 10 H

–750

Cambrian Kanmantoo Group Kangaroo Island Group Emu Bay Shale White Point Conglomerate

Line 3A

Stokes Bay Sandstone

South

Smith Bay Shale

North

Metres

0

Boxing Bay Formation Mount McDonnell Formation Proterozoic

–250

Granulite Fault

–500

Survey line

Folding schematic Scale V = 20 H

–750

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6070000 mN

INVESTIGATOR

Line 210 606

605

Line 210

Snelli ng

STRAIT

Cape Cassini

Line 9141

Line 9140

680000 mE

Approximate position of Permian troughs

I

I

Pt Marsden

Bald Rock

Cape D’Estaing

Hummocky Point

Line 176/171

Kingscote Nepean Bay

Fault

American Beach Oil 1

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I I I

I

I

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e 2A

I

Lin

Pelican Lagoon

I

Dudley Peninsula

I

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Line 9122

I American River

I

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Parndana

603

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F au l t

Penneshaw

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Cy g n e t

604

I

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15

20

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I

Line 3A

I

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Pennington Bay

204410-025

Kilometres

Figure 5 Geophysical interpretation of potential Permian troughs on Kangaroo Island. (Modified from van der Stelt, Belperio and Flint 1992)


27

New geology

736000

738000

740000

7 Bluff Quarry

THE BLUFF

742000 Qhck8

Qhck8

6053000

!

6 Qhck8 Qhcks ! BEATRICE POINT

5 642600593

Qhck8

642600556

642600169

642600168

642600557

642600167

642600191

CP-j1

KINGSCOTE SCHOOL 1 and 2 KINGSCOTE SILO KWS 2 KINGSCOTE SILO KWS 1

642600657 CP-j

6051000

Teok

Qhck8 1,000 m

Projection: Zone 53

Teok Teok

Qha

642600579

) "

642600577

1 KINGSCOTE JETTY BLAST HOLE A and B

Qhck8

KINGSCOTE JETTY BLAST HOLE 1–9

Qhck8

Drillholes HOLOCENE Qha Present day alluvium Qhcks SEMAPHORE SAND MEMBER Shelly/quartz muddy sand of Qhck8 intertidal flats PLEISTOCENE Qpcb BRIDGEWATER FORMATION EOCENE-PLIOCENE Tep1 Quartz sand, grit EOCENE-OLIGOCENE Teok KINGSCOTE LIMESTONE JURASSIC J-i WISANGER BASALT

SPRING

CP-j

500

2

KINGSCOTE 3

SB1/MW1, SB2/MW2, SB3/MW3, Qhck8 SB4/MW4

MW 1,8,9,12,13,18 Qha MW 5-7

Kingscote

0

3 and Kingscote Bore

KINGSCOTE 2 KINGSCOTE 1

Tep1

204410-026

4

CP-j

J-i

Qpcb

6052000

QhcksKINGSCOTE JETTY 1–3

642600354

CP-j1

Qhck8

CARBONIFEROUS-PERMIAN CP-j CAPE JERVIS FORMATION Sand, gritty, kaolinised, CP-j1 cross-bedded, fluviatile

Figure 6 Surface geology of the Kingscote – Bluff Quarry area showing location of sections measured and boreholes investigated. (Base map from DMITRE 2013c)

which, because of the upward fining characteristics, we interpret to be turbidites. The sand beds are lenticular, some with eroded bases, upper surfaces are rippled and a few pebbles are present. The top of the section is capped by 2 m of medium sand, the base of which is a minor disconformity, either from erosion or slumping. Following an inspection of the Kingscote Bore samples, we have been able to extend Section 3 down to a depth of 335.5 m (Fig. 7). However, in view of the fact that the drill samples are cuttings we were unable to get a great appreciation of the original textural or bedding characteristics. The brief log kept at the time the drilling ceased in January 1910 suggests that the drilling terminated

Pebbly coarse sand occurs from 200 to 194 m followed by sandy clay containing a small striated and facetted quartzite pebble between 194 to 166 m. Medium sand dominates from 166 to 17.4 m (top of cuttings available). Within the sand unit are: • slightly sandy clay (143 to 125 m) containing the bimodal population of quartz grains and low frequencies of pink garnet grains

in hard slate (DMITRE 2013b), but we were unable

• a pink quartzite pebble at 90 m

to confirm this from the drill cuttings. The base of

• friable medium to coarse sand with very angular grains from 72 to 68 m

the glacigene section at 335.5 m commences with about 26 m of sandy clay containing small, facetted, polished and striated (some crossing striae) pebbles of limestone, quartzite, granodiorite, granite and sandstone. Grains of garnet and small clasts of igneous rocks are common. The shape and size of quartz grains are typical of the glacigene sediments reported elsewhere in the Troubridge Basin, with two distinct populations of large rounded and polished grains and smaller more angular grains (Bourman and Alley 1990). Thin layers of sandy diamicton, fine gravelly sand and white clean sand with bedding preserved are present. We interpret the characteristics of this lower part of the drillhole as a glacial diamicton, possibly a lodgement till.

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Overlying the basal pebbly, sandy clay is about 102 m of dense clay and rare thin quartz sand beds containing garnet grains, a small, polished and facetted quartzite pebble and a pebble of possible Mount Monster Porphyry (from the Padthaway Ridge). In the upper 20 m of this part of the section, more frequent pebbles of quartzite and gneiss occur, some with striated, polished and facetted surfaces.


• coarse sand containing abundant rounded and angular quartz pebbles from 24 to 14.7 m. No samples are available between 14.7 m and the current land surface. Our detailed measurements of the exposed 10 m of section (the Old Government Quarry) show that the remainder of the sediments at Section 3 are strongly planar and trough cross-bedded and levelbedded medium and coarse sand containing and interbedded with very coarse to fine gravel layers. A pebbly sandy diamicton, coarser in the lower part, occurs at the 3.7–4.2 m level. The exposure is capped by almost 2 m of Jurassic Wisanger Basalt, of which the basal surface displays a local relief of a metre or so.


Section 2 –12 –11 Section 3 –10 Section 1

–9

V V V V V V V

–9

–10 Wisanger Basalt

Section 4 –9

Kingscote Bore (subsurface; note change

–9

in vertical scale)

–8

–8

–7

–7

–7

–6

–6

–6

–5

–5

–4

–4

–4

–3

–3

–3

–2

–2

–2

–1 K1

–1

–1

0 Metres

0 Metres

K3

K8

K10

–200 –3 –250

K5

Quaternary beach

–2

–300

–1

K9

0 Metres

–350 Peb Di Sa Si C

Peb Di Sa Si C

Peb Di Sa Si C

Pebbles Diamicton Sand Silt Clay

–5

204410-027

Trough cross-bedding

Sand

Horizontal bedding

Diamicton

Intraformational slumping

Conglomerate

Boulder

Basalt

Ripple

Bedrock

Pebbles K2

Figure 7

–6

Planar cross-bedding

Clay

V

–7

–4

K7 K6

0 Metres

Limestone

V

–50

–150

K2

V

–8

–100

–5

K4

0

Peb Di Sa Si C

Kingscote –8 Limestone

Heavy mineral and petrographic analysis sample

Lithologs for sections measured in the Kingscote area.

The cross-bedding in the sands at Section 3 indicates deposition from a northerly direction. Harris (1971) also examined the cross-bedding in the sand at the Old Government Quarry section and concluded that deposition was from north to northwest, which is in agreement with our own observations. The basal 1.6 m of sediment at Section 4 is strongly disrupted by slumping but appears to commence with interbedded pebbly sand and clay, followed by very clean coarse sand with rounded grains and clay rip-up clasts (Fig. 7). The sand continues for almost another 1.4 m and displays horizontal bedding. Inset into this sand unit is a Quaternary bouldery beach deposit containing shells. Overlying the sand is ~6 m of level bedded clay, interbedded with

lenses and beds of sand in the lower half. A large boulder occurs in a sand bed at about 6 m from the base of the section. To help correlation between sections and determine the provenance of the sediments, ten samples were collected from the measured sections for heavy mineral and petrographic analysis (Fig. 7; App.). Ilmenite is common in all samples from the cliff sections and to a lesser extent tourmaline, zircon, rutile and staurolite. Garnet is largely low to absent except for a significant amount in sample K10 in Section 4. Elevated levels of sillimanite occur in samples from the cross-bedded sand units underlying the Wisanger Basalt in Section 3. MESA Journal 70 Issue 3 – 2013

29

New geology

While the grain shape of samples examined along the Kingscote Cliff is variable, a significant proportion is subrounded to rounded and some contain populations that vary from angular to rounded. These characteristics are typical of what we observe of the Cape Jervis Formation elsewhere in the Troubridge Basin.

Measured sections – Bluff Quarry area Cape Jervis Formation is exposed along the northfacing coastal slope in a deep gully (Section 5), then westwards another 0.76 km to near the pier (Section 6) and a further 0.7 km along the coast to the excellent section at Bluff Quarry (Section 7; Figs 6, 8, 9). At sections 5 and 7 the sediments are overlain by Wisanger Basalt.

Site 5 From the base of the section at 3 m asl is 5–6 m of interbedded fine sand and clay with strongly distorted clay in the basal part. Rip-up clasts of clay are common. A sample for heavy mineral analysis was taken of the sand at the 6 m level (BS2 in Fig. 9). The sand unit is overlain by 13 m of indistinctly level-bedded white medium to fine sand, dominated by angular grains with a minor population of well-rounded grains and biotite flakes. Overlying the sand is 9 m of cross-bedded mediumgrained quartz sand containing biotite flakes; again the grains are dominantly angular. The sand unit coarsens upwards and is capped by 1 m of calcareous sand and gravel breccia. Overlying the sands is an unknown thickness of Wisanger Basalt. The thick cross-bedded sand unit is patchily exposed over 100 m or so near this site and its upper undulating surface has a relief of 6–7 m. These sands are very similar to those we measured in the Kingscote sections and in the Gap Hills.

Pier site (Section 6) This section is a road cutting just west of the pier and boat harbour. At the base (2–3 m asl) is almost 2 m of level-bedded medium sand containing a 10 cm bed of finely bedded clay with thin, slightly bioturbated interbeds of fine sand. Overlying this is 2 m of laminated clay and thin beds of sand, then upward fining sand containing a few beds of silt and clay in the upper part. A sample was taken from a bed of sand at the 5.5 m level for heavy mineral analysis (BS1 in Fig. 9). Generally the sediments dip at 10–25° to the NNE.

Bluff Quarry (Section 7) A continuous section (base ~1.5 asl) was measured along the track cutting diagonally across the slope in the quarry (A–B in Fig. 10). The lower 16 m of

30


this measured section consists of intraformationally slumped and interbedded silty clay and sand. The sands thicken towards the top of this part of the section and clay rip-up clasts become more common (Fig. 9). Zones of bioturbation occur in the clay beds of the lowermost 7 m, but whether this occurred in marine or non-marine conditions is not certain. However, we have noted glaciomarine conditions in the Cape Jervis section (Table 1) and it is possible that marine influence also occurred on Kangaroo Island. Proximity to glacial ice is indicated by thin diamictite layers at 2–3 m, 10.45–11.35 m and 15.7–16 m from the base of section. A large ice-rafted boulder of granodiorite, 1.2 m in diameter, occurs at 5–6 m (Fig. 8b), below which the clay beds are strongly deformed, typical of ice-rafted boulders. Further evidence for the proximity of ice is the presence of rounded to angular granules of quartz within the clay beds. From 16 to 23 m are three units of sand. The lowermost unit is very coarse, almost to granule size, with well-rounded large grains and angular smaller grains. Bedding in this unit is badly slumped, but appears to be cross-bedded. The middle unit is strongly contorted friable, medium sand and the top unit is an eastward-dipping medium-fine sand, containing occasional thin beds of clay. At the top of Section 7 is just over 4 m of levelbedded and cross-bedded gravelly coarse sand containing thin beds of gravel overlain by Wisanger Basalt. The gravelly sand unit appears to sit conformably on the underlying sand and although minor scour surfaces are locally present they do not represent a significant disconformity. The basal gravel of the gravelly sand unit is dominated by rounded to subrounded quartz pebbles and boulders with a minor component of clasts derived from the local Kanmantoo Group bedrock. Mica flakes are common in other parts of the sand–gravel unit, along with occasional pebbles of igneous rocks. Some of the clasts in the finer gravels are quite angular, suggesting that the clasts have not travelled very far or were deposited from ice. The orientation of foreset beds we measured indicates deposition by flow from the northeast, although Harris (1971) interpreted flow from north to northwesterly directions. Taken together these orientations generally indicate deposition by water flowing from the north, which is similar to that for the sand unit underlying basalt at Kingscote (Section 3). Overall the sand and gravel are comparable to the sand unit directly underlying the Wisanger Basalt near Kingscote and are here correlated with it (Fig 11).


8 (a) Exposures of Cape Jervis Formation along the southern coast of Bay of Shoals. Section 5 in cliff above car, Section 6 inland of thin headland of pier area and Section 7 is Bluff Quarry (main forested point). (Photo 412885)

8 (b) Large weathered granodiorite ice-rafted erratic at 5–6 m level, Bluff Quarry section. (Photo 412886)

8 (c) Clay rip-up clasts to right of black pen in lower sands at ~10 m level, Bluff Quarry section. (Photo 412887)

8 (d) Intraformationally slumped sand unit at 16–23 m level, Bluff Quarry section. (Photo 412888)

8 (e) Cross-bedded sands underlying the dark coloured Wisanger Basalt at 25–27 m level, Bluff Quarry section. North is to right. (Photo 412889)

8 (f) Details of cross-bedding in sands underlying the Wisanger Basalt, Bluff Quarry section. Spade for scale mid picture; north is to right. (Photo 412890)

Figure 8

Exposures of Cape Jervis Formation.


31

New geology

Section 5 V V

V V V

Wisanger Basalt

Section 7 Clay

V

V V V V V V V V V

27

26

Sand

Wisanger Basalt

BQ1

Diamicton 27

Gravel breccia Conglomerate

25

26

24

25

V VV

Basalt Rip–up clasts Deformed bedding Planar cross–bedding

BQ2 23

Trough cross–bedding

12

24 BQ3

22

Horizontal bedding Intraformational slumping

11

23

Bioturbations

BQ4 22

10

20

21

9

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20

8

19

18

BQ7

Section 6 BS2

Boulder BS2 Heavy mineral and petropraphic analysis sample Very fine diamicton interbeds

21

7

BQ8 6

18

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5

17

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4

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0 Metres

12 Metres

0 Metres

6 BS1

BQ5

BQ9 BQ10

4

Figure 9

204410-028

Lithologs for sections measured in the Bluff Quarry area.

Sands similar to those immediately underlying the Wisanger Basalt in the Bluff Quarry and Kingscote areas also occur in the Gap Hills (see below). Ten samples were taken at the Bluff Quarry (Section 7) and one at each of sections 5 and 6 for heavy mineral and petrographic analysis (Fig. 9; App.). The sediments at the Bluff Quarry are dominated by ilmenite, zircon, tourmaline and rutile, similar to the sediments at Kingscote. Samples from the lower part of the section, below 13 m, contain significant amounts of garnet as the samples do

32

Peb Di Sa Si C

Peb Di Sa Si C

Pebbles Diamicton Sand Silt Clay

Peb Di Sa Si C

BQ6


at sites 5 and 6. We find the presence of garnet often to be associated with the sediments deposited from ice nearby, commonly as flowtills and thin diamictites or as sediment rain from icebergs. One sample of the lodgement till at Smith Bay (see below) contains high levels of garnet. This is consistent with the evidence we presented above for the proximity of ice. It is also interesting to note that, like at Kingscote, sillimanite is present in the crossbedded sand and gravel underlying the Wisanger Basalt, which further strengthens correlation of these sediments between the sites.


Gap Hills A number of sites were investigated in the Gap Hills area but the best exposure is in a quarry on George Turner’s farm (Fig. 12) where about 8 m of sediment is exposed. Bourman and Alley (1999) described a coastal section at Smith Bay (SB in Fig. 12) where the Cape Jervis Formation is about 18 m thick and consists almost entirely of lodgement till, the basal part of the formation. The latter site lies ~100 m below the Turner Quarry site. Limited borehole data on the slope from the quarry to the Smith Bay site indicates that the formation is about 15 m thick and overlies Cambrian Stokes Bay Sandstone (Rock unit ‘Eat’ in Fig. 12). Since the Cape Jervis Formation is generally undeformed and flat lying in this area, it appears that it was deposited as an onlap sequence on a northerly facing bedrock slope and thus locally may not reach any great thickness.

N

B

A

Ocean

Figure 10 Location of Section 7 (A–B) in the Bluff Quarry. Google Earth image, February 2012. West

East

Metres 150 Turner Quarry V

125

V

V

100 Cape Jervis ?

75 Smith Bay

Bluff Quarry

50

V

V

25

V

Bay of Shoals V

V

Old Government Quarry

V

V

V

V

Sea level ?

?

? 14.7

?

Glacigene outwash Lodgement till Glaciolacustrine/glaciomarine V

V

0

2 km

Kingscote Bore

Carbonaceous claystone

V Wisanger Basalt

Bedrock

335.5 Metres 204410-035

Figure 11 Stratigraphic correlation chart for the Cape Jervis Formation between the sites investigated on Kangaroo Island and with the type section at Cape Jervis. Line of section is located in Figure 4.


33

New geology

725000

6060000

720000

CAPE D'ESTAING

Eaw

Eaw

Smith Bay

TpQr1

Qha

Eas Qpcb

SB

Eas1

Tp\fe SMITH CREEK

DAM SC 1–4

SMITH CREEK DAM PDH 1–3

Eas 6055000 6050000

Qhck6 Qa

SPRING

FLORENCE, L.K. SPRING FLORENCE, L.K.

Qpcb Tep1

Tep1 Qhl4

CY 5A,5B J-i

Qa

CP-j1

Tep1

TpQr1

CY 3A,3B

Eam

Tep1

Ty1

Tep1

MIO SPRING

Qpah

Tep1

DEPT OF MINES DUCK LAGOON

Qpah Eat

BELL Qpah

Qpah

Cygnet River

) "

DEPT OF MINES WR 32

ANGLE POLE ROAD Qhck6

KI 31 Qpah

BOETTCHER, W.A.

BA 1

204410-029

Drillholes EOCENE-PLIOCENE

HOLOCENE

Qhck6

Carbonate/terrigenous mud of samphire-algal marsh

Qhcks

SEMAPHORE SAND MEMBER

Qhl4

Lacustrine sediment

!!! ! ! !! ! ! ! ! !! ! !! !! !! ! ! ! ! ! ! ! ! ! ! !! ! ! ! !!

Qhl5

Lacustrine beach lunette

PLEISTOCENE-HOLOCENE Undifferentiated alluvial/fluvial Qa sediments PLEISTOCENE ! ! !

!

!

!

Qpah !

!

!

!

!

!

Qpcb !

!

!

!

!

!

!

!

!

!

!

!

Qpcg

!

!

Qpl5

!!! !

!

!

!! ! ! ! !

! !! ! ! !! !

!

Tep1

Present day alluvium

Qha

! ! !

!! ! ! !!

! ! !! ! ! !!! ! !! !

HINDMARSH CLAY

Quartz sand, grit

EOCENE-OLIGOCENE Teok

KINGSCOTE LIMESTONE

JURASSIC J-i

WISANGER BASALT

CARBONIFEROUS-PERMIAN CP-j

CAPE JERVIS FORMATION

CP-j1

Sand, gritty, kaolinised, cross-bedded, fluviatile

CAMBRIAN Eam

MOUNT McDONNELL FORMATION

BRIDGEWATER FORMATION

Eas

SMITH BAY SHALE

GLANVILLE FORMATION

Eat

STOKES BAY SANDSTONE

Lacustrine beach lunette

Eaw

WHITE POINT CONGLOMERATE

PLIOCENE-PLEISTOCENE Gravelly clay, clay, sand, local TpQr1 ferruginous nodules

Eas1 ! ! !

Lower shale-siltstone facies

!

!

!

!

!

!

!

!

!

Eas2

Upper sandstone facies

PLIOCENE ! !

Tp\fe !

!

!

!

!

!

From the base of the section at Turner Quarry is 2.5 m of trough cross-bedded pebbly to gravelly medium- to coarse-grained arkosic sandstone containing a thin layer of level-bedded, mediumgrained sandstone (Fig. 13). Overlying the gravelly sand is 2 m of planar cross-bedded mediumgrained arkosic sandstone in which silty clay rip-up clasts are common (Fig. 14a). The orientation of the bedding indicates deposition from a northerly direction. The sands contain a mixture of angular and well-rounded grains. A further 1 m or so of medium sand containing thin gravel lenses and thin beds of clay rip-up clasts sharply overlies the crossbedded sands. We correlate the sand and gravels with similar sediments underlying Wisanger Basalt at Kingscote and the Bluff Quarry. The heavy mineral fraction of the lower part of the sand unit is dominated by ilmenite, rutile and sillimanite with lesser amounts of tourmaline and zircon, but garnet is absent from the samples examined, except in the weathered, carbonaceous silty claystone unit (App.). The presence of significant sillimanite strengthens our correlation with the sand and gravel at Kingscote and the Bluff Quarry. Conformably overlying the sands is at least 3 m of weathered carbonaceous silty claystone containing leaf impressions (Figs 14b, d). The thickness of the clay unit varies across the quarry and may be significantly thicker than 3 m, but the upper part of the quarry exposure is obscured by a thick slope deposit. Thin lenses of cross-bedded sandstone are present in the clay unit (Fig. 14c). While there is a hint of bioturbation in the lower part of the silty clay there is no clear evidence that it is a marine deposit. Wisanger Basalt caps the section.

Undifferentiated ferricrete

OLIGOCENE-MIOCENE Ty1

Measured section – Turner Quarry

Qha

DEPT OF MINES TCWQ 45

CYGNET PARK

Eas

Teok

DEPT OF MINES MULBERRY (BOXER) WELL

BOETTCHER, W.A. GARDEN WELL

TpQr1 6045000

Qhl4

J-i CP-j1

CP-j

Ty1

C

Qhl4

GH1

CROWS NEST CREEK ONE TREE HILL CREEK BELL MANOR CREEK CY 4A,4B

Qpcg Qpl5

Qhl4

J-i

GARNET BELL

Ty1

Qhl4

GH2,3

J-i Qha Eat

Qpl5 Qhl4

Qha

Qpl5

CP-j1

Tp\fe

KI 30

Qpcb

CP-j1

J-i

Qhcks

Qha

GT

TpQr1

WHITWORTH, W.E.

Emu Bay

Qpcb

Eas2

SMITHS CREEK

Emu Bay

SV 124

Eas1 Qpcb" )

Eat

Elsewhere in the Gap Hills area drillhole data is sparse and drillholes rarely penetrate the base of the Cape Jervis Formation, but generally the formation appears thin and may reach a thickness of at least 28 m in an unnamed water drillhole (circled in red in Fig. 12). However, our investigations at a few sites in the hills indicate that at least 40 m of the formation occurs below the Wisanger Basalt (GH1 and GH2 below).

730000

Undifferentiated Pata Formation 0

1

2

3

4

5 km

We interpret the claystone to have been deposited in shallow fluviolacustrine conditions and that vegetation grew around the site of deposition.

Projection: Zone 53

Figure 12 Geology and drillholes for the western Gap Hills area (base map from DMITRE 2013a). Location of sites referred to in text: GT (George Turner’s farm and quarries); SB (Smith Bay site of Bourman and Alley 1999); GH sample sites; and red circle is unnamed water well.

34


Mineralogical examination of the silty clay indicates that the grains are largely subangular, although the zircons tend to be subrounded. The heavy mineral fraction is dominated by garnet, which suggests that the deposit contains particles recycled from older parts of the glacigene succession, some parts of which can contain significant amounts of garnet.


V

V

V V V V V

The carbonaceous unit was closely examined for recoverable macro- and micro-plant remains but none was found. Samples were taken for plant cuticle analysis to determine the age of the clay, but the results were ambiguous (A Rowett, Primary Industries and Resources South Australia, pers. comm., 2003). Leaf remains were recovered by Sprigg, Campana and King (1954) in the Gap Hills, presumably from the clay, but the collection site is unknown and no age was determined.

Wisanger Basalt

Land slump – section obscured

8

7 GT2

Based on the stratigraphic continuity of the claystone with the underlying sand and its heavy mineral lithology we include the claystone in the Cape Jervis Formation. However, we recommend further testing of floral evidence to clarify its age as mining continues to expose more claystone at the site.

6

5

Other sites in the Gap Hills Very thin exposures of probable glacigene sediments and erratics are relatively common in the Gap Hills area. We report here on a few exposures where some stratigraphy is obvious.

4

Sandy, bouldery diamictite with indistinct horizontal stratification that includes gravel and sand beds is exposed in a shallow dam site west of Rettie Bluff, about 40 m below the Wisanger Basalt (GH1 in Fig. 12). The greatest proportion of larger clasts is well rounded but a small number of angular clasts are also present. Erratics including igneous lithologies and quartzite occur, some of which are polished, striated and facetted, indicating a glacial origin. Although there are no other exposures in the local area with which we can correlate, we interpret the sediments to be proximal ice-contact in origin.

3

GT5

2

1

GT4 GT3

V

V

V

Silt

Clay

Sand

Diamicton

Pebbles

0 Metres

Clay

Plant-bearing beds

Sand

Planar cross-bedding

Basalt

Trough cross-bedding

Rip up clasts

Horizontal bedding

Gravel lens

Intraformational slumping

Pebbles

Bioturbation

GT Heavy mineral and petrographic analysis sample

204410-036

Figure 13 Litholog for section measured at Turner Quarry, Gap Hills.

In a valley west of the above site (enter through ‘Thereabouts Cottage’) two exposures (GH2 and GH3, positions approximate) were investigated. On the eastern flank of the valley ~4 m of cross-bedded coarse, micaceous sand and fine gravel are exposed (GH2) about 40 m below the base of the Wisanger Basalt that caps the hill above. The sandstone grains are dominantly angular although a low frequency of very well rounded grains is also present. The high levels of the heavy minerals tourmaline and zircon in GH1 and GH2 (App.) suggest that they are correlative. Down and across the valley, but at a higher elevation than GH2, are some 4 m of more massive silt (GH3) with intraclasts of clay. The silt is characterised by numerous small perforations, which formed from the decay of plant matter within the sediment. It is possible that the sediment correlates with the carbonaceous unit at Turner Quarry, a correlation supported by the high levels of rutile in the units at both sites. MESA Journal 70 Issue 3 – 2013

35

New geology

14 (a) Lower cross-bedded sand overlain by sand containing abundant clay rip-up clasts, Turner Quarry. (Courtesy of Andrew Burtt; photo 412891)

14 (b) Cross-bedded sands overlain by weathered grey silty clay unit, Turner Quarry. (Courtesy of Andrew Burtt; photo 412892)

14 (c) Sand lens (buff coloured unit below hammer head) within silty clay unit, Turner Quarry. (Courtesy of Andrew Burtt; photo 412893)

14 (d) Plant matter in silty clay unit, Turner Quarry. (Courtesy of Andrew Burtt; photo 412894)

14 (e) Glaciated bedrock surface overlain by lodgement till, Smith Bay site. (Photo 412895)

14 (f) Glaciated bedrock surface overlain by lodgement till (upper part of photo), Boxing Bay. Till squeezed into irregularities in the bedrock surface, in part highlighting striae. (Photo 412896)

Figure 14 Cape Jervis Formation exposures.

36



The topographic position of sites GH1 and GH2, some 40 m below the Wisanger Basalt, indicates that the Cape Jervis Formation is at least 40 m thick in the Gap Hills.

Correlation and environment of deposition Some, but not all, of the facies recognised at the type section of the Cape Jervis Formation are present on Kangaroo Island. Those that are present are much thicker. We recognise two new, younger units of the formation on the island although there is still some question about the age of the younger of these. We discuss the possible mode of formation of the Cape Jervis Formation on Kangaroo Island in the conclusion.

Lodgement till This basal diamictite is present at sites we have previously described (Christmas Cove, Boxing Bay and Smith Bay) and, based on its stratigraphic position in the local succession, its lithology and its strong clast fabric, is correlated with the basal lodgement till at the type section (Fig. 11; Bourman and Alley 1999). At Christmas Cove the till is very thin, as it may well be at Boxing Bay, although here the full thickness is not known since the area is partly obscured by landslide material. Overlying a glacially striated rock surface at Smith Bay is at least 18 m of lodgement till, which is the thickest exposed till we have yet encountered on Kangaroo Island. Since we reported on the above sites where the lodgement till is present (Bourman and Alley 1999) we have undertaken pebble lithology and heavy mineral analyses at those localities. As we expected from a lodgement till, the pebble lithologies are dominated by local bedrock types. At Smith Bay metasandstone and sandstone make up the greatest proportion of pebbles, which we interpret to have been derived from local bedrock, the Cambrian Stokes Bay Sandstone. Lower frequencies of pebbles of gneiss, schist, quartzite and granodiorite occur, the last named lithology probably reflecting longer distance transport from the Padthaway Ridge or western Victoria areas. Boxing Bay lithologies are similar and are dominated by sandstone, most likely from the local Cambrian bedrock, the Boxing Bay Formation.

sandy clay containing small, facetted, polished and striated pebbles occurs. However, as we note above in our descriptions of Section 3 at Kingscote, we cannot be certain of this designation because only cuttings are available for examination in this drillhole. For the time being, we tentatively ascribe these sediments to the lodgement till of the Cape Jervis Formation.

Proglacial sediments Overlying the possible lodgement till in Kingscote Bore to the top of the measured cliff sections is about 340 m of what we interpret to be glaciolacustrine sediments, in the absence of any direct evidence of marine influence. We cannot discount the latter since there is some suggestion of bioturbation in the lower part of the succession at the Bluff Quarry and in the exposure at Turner Quarry. As shown in our lithological descriptions above, there is good evidence that the sediments were derived from melting ice, some from icebergs. In the exposed sections at Kingscote the occurrence of turbidites suggests some parts of the proglacial sediments were deposited on the distal part of a subaqueous fan, as has been reported elsewhere in the Troubridge Basin (Alley and Bourman 1984, 1995; Bourman and Alley 1990, 1999). The sediments in Kingscote Bore were examined by Bauer (1959) and he concluded that the succession below 101 m bears little resemblance to glacial deposits and that the sandstone in the top 30 m of the bore was aeolianite. However, the glacial aspect of the sediments throughout the bore and in the overlying exposed section is conclusive evidence that they are glacigene in origin. Underlying the Wisanger Basalt at Kingscote, the Bluff Quarry and coastal sections to the east of here and in the Gap Hills, the proglacial sediments coarsen into tabular and trough cross-bedded sand interbedded with gravel in some places. Our investigations show that the gravel–sand part of the succession is stratigraphically continuous with the underlying sediments. We have not recognised the sand and gravel facies elsewhere in the basin.

Heavy minerals at the above sites and Christmas Cove show a preponderance of garnet, which we have observed elsewhere in the Troubridge Basin for this unit.

We interpret the sand and gravel to be outwash deposited along the margins of stagnating ice as water in the glaciolacustrine–marine basin shallowed. Based on the orientation of the foreset beds, deposition appears to have been from melting remnant ice lying out in the current Investigator Strait area to the north.

Our current study shows that the only other occurrence of possible lodgement till is in the basal section of Kingscote Bore where at least 26 m of

The age of the sand and gravel facies immediately underlying the Wisanger Basalt has been discussed by a number of authors, but it clearly predates the MESA Journal 70 Issue 3 – 2013

37

New geology

38


10

Temperature (°C)

δ180, pH adj. (CO2[Geocarb] +CA++) δ180, pH adj. (CO2[proxies] +CA++) Cold periods Glaciations

8

6

4

2

Cretaceous

Jurassic

Permian

-2

Triassic

0

Carboniferous

Bird and Chivas (1993) produced a similar pre-late Mesozoic age from weathered basement underlying an outlier of the Jurassic Algebuckina Sandstone of the Mesozoic Eromanga Basin, on the southern margin of Leigh Creek coalfield. From their study of kaolinite within the Algebuckina Sandstone, Bird and Chivas further concluded that the weathering within the sandstone is much younger than that in the underlying basement. The age of the Algebuckina Sandstone in the outlier is regarded as Early Jurassic (Sinemurian Stage; fig 9.8, Kwitko 1995). The Sinemurian Stage is in the early part of the Early Jurassic and thus the age of the weathering found in the bedrock below the outlier by Bird and Chivas (1993) predates this, which has relevance to the discussion below.

This claystone has only been found in Turner Quarry in the Gap Hills and we have not observed it elsewhere in the Troubridge Basin, other than a possible equivalent in a shallow exposure in the central Gap Hills (site GH3 in Fig. 12). As noted

Devonian

A paleomagnetic study of the kaolinised material in the weathered sediments by Schmidt, Currey and Ollier (1976) produced a Late Cainozoic age, which was supported by K–Ar analyses of alunite from the profile (Bird, Chivas and McDougall 1990). However, subsequent oxygen-isotope studies of the weathering (Bird and Chivas 1993) concluded that it is pre-late Mesozoic in age and that there had been significant remobilisation of iron and sulfate in the late Cainozoic, thus accounting for the younger age proposed by Schmidt, Currey and Ollier (1976).

Carbonaceous silty claystone

Silurian

Milnes, Cooper and Cooper (1982) and Milnes, Bourman and Northgate (1985) pointed out that the sands and gravels beneath the Wisanger Basalt were ‘highly leached and kaolinised’ and, together with Twidale (1983), argued that the weathering predates the extrusion of the basalt, which is essentially unweathered.

Bird and Chivas (1993) concluded that the pre-late Mesozoic weathering profiles formed under cool to cold average temperatures, probably