A Field Excursion Guide Te

PERMIAN STRATIGRAPHY, SEDIMENTOLOGY AND PALAEONTOLOGY OF THE SOUTHERN SYDNEYBASm, EASTERN AUSTRALIA -

A Field Excursion Guide

[Map courtesy: Ziegler et aI. 1996]

[Prepared for the Strzelecki International Symposiwn on The Permian of Eastern Tetbys: Biostratigraphy, Palaeogeography and Resources, Deakin University. Rusden Campus, Melbourne, Australia,

30 November - 3 December 1997]

School of Aquatic Science and Natural Resources Management, Deakin University

Technical Paper 1997/2

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Published by the School of Aquatic Science and Natural Resources Management, Deakin University,

Printed by the Burwood Campus Printery, Deakin University

This publicati on is available for purchase in hardcopy or disk format. Send all communications to: The Secretary, School of Aquatic Science and Natural Resources Management, Deakin University, Rusden Campus, 662 Blackburn Road, Clayton, Victoria 3168, Australia.

ISBN 0-7300-2467-5 ©Copyright 1997. G. R. Shi and Stephen McLoughlin

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Deakin University, Scbool of Aquatic Science IDd Natural Resources Management, Technical Paper 199712

PERMIAN STRATIGRAPHY, SEDIMENTOLOGY AND PALAEONTOLOGY OF THE SOUTHERN SYDNEY BASIN, EASTERN AUSTRALIA - A Field Excursion Guide

G. R. Shi School of Aquatic Science and Natural Resources Management, Deakin University, Rusden Campus, 662 Blackburn Road, Clayton, Victoria, Australia ADd

Stephen McLoughlin School of Botany, The University of Melbourne, Parkville, Victoria 3052, Australia

ii

•, I , , •II II II

•.. .. •.. .. •II

II

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TABLE OF CONTENTS

Introduction Regional setting.

3

Structural framework of the Sydney Basin

3

Stratigraphical framework.

3

Talaterang Group.

7

Shoalhaven Group.

12

Illawarra Coal Measures

17

TriassiC units overlying the IlIawarra Coal Measures

27

lntrusive rocks

28

A palaeogeographical syntbesb

28

Phase I - Back -arc extensional stage

•

29

Phase II - Passive thennal subsidence stage

29

Phase III - Flexura1loading and compression stage

31

Description of excursion stops

37

Stop 1 - Myrtle Beach (base of Wasp Head Formation) Stop 2 - Wasp Head, South DUrTas (Upper Wasp Head Formation) . Stop 3 - Pebbly Beach (Upper Pebbly Beach Formation) . Stop 4 - Merry Beach South and Snapper Point (Snapper Point Formation) Stop 5 - Merry Beach North (Termeil Essexite) . Stop 6 - Warden Head Lighthouse (Wandrawandian Siltstone) . Stop 7 - Bellarnbi Pool (pheasants Nest Formation) . Stop 8 - Collins Rock (Flat Rock), Woonona Beach (Erins Vale Formation) . Stop 9 - South Thirroul Beach (upper Erins Vale and lower Wilton Fannatians) Stop 10 - Austinmer Beach (upper Wilton Fonnation, Tongarra Coal and Austinmer Sandstone Member of Bargo Formation Stop 11 - North side of Scarborough Hotel (permian-Triassic boundary)

Stop 12 - Lawrence Hargrave Lookout (Upper Pennian-Lower Triassic units) Stop 13 - Otford Lookout (Lower Triassic units) .

37 40 42 44 46 46 48 49 49 49 50

51 51

Acknowledgments

51

References .

52

Plates and Explanations ..

57

iii

INTRODUCTION

, •, III • I

Continental Australia consists of two major tectonic units: a stable craton in the west that was consolidated by the end of the Proterozoic, and an orogen, namely the Tasman Fold Belt, that occupies the eastern margin afthe continent (Fig. I) . During the Pennian three distinct tectonic (hence depositional) settings were developed in Australia (BrakeJ and Totterdell, 1996): (i) a group of intra-cratonic basins located on the Australian Craton; (ii) a tectonic collage, known as the New England Fold Belt (a sub-orogenic system within the broader Tasman Fold Belt), on the eastern fringe of eastern Australia, and (iii) a massive north-south trending, elongate sedimentary trough, namely the Bowen-Gunnedah-Sydney Basin system, situated between the New England Fold Belt and the stable Australian Craton (Fig. 1). Presumably controlled by their unique tectonic environment, each depositional setting hosts a characteristic tectonostratigraphical sequence. Within the intracratonic basins, the Pennian system is characterised by shallow marine and nonmarine terrigenous sediments with sporadic carbonate intercalations (especially in Western Australia). In the New England Fold Belt, the Pennian sequence is dominated by acid volcaniclastics and flysch deposists typical of an ocean to magmatic arc subductiOn/accretion system. Located in between these two contrasting tectonic settings, the Penno-Triassic Bowen-GUIUledah-Sydney Basin system contains many transitional features. Firstly, the basin system's geometry is asymetrical with depocentres located close to the New England Fold Belt and their western margins progressively and subhori zont~ll y lapping on to the craton to the west. Secondly, a number of petrographic studies have demonstrated that the provenance of the Pennian-Triassic sediments accumulated within the Bowen-GWUledah-Sydney Basins is dominantly bimodal, with the craton in the west and the New England Fold Belt in the east being the primary sources (e.g., Baker et al.,1993 ; Tye et al., 1996). With the above characteristics, the BowenGUlUledah-Sydney Basin system is generally believed to be a back-arc extensional to foreland basin system (Murray, 1990; Fielding, 1990; Baker et al. , 1993; Scheibner, 1993). Palaeobiogeographically, Australia also exhibits marked provincial patterns throughout the Pennian (see Archbold, 1996 and references therein provided). A unifonn Indo-Australian faunal province has been recognised for the Asselian-Tastubian interval, which included both eastern and western Australia, New Zealand, Peninsular India, the Shan-Thai terrane of southeast Asia, the Himalaya, and the Lhasa block ofTibet (Shi and Archbold, 1993). The development of this province corresponds to the climax of the Late Palaeozoic Gondwanan glaciation. Stronger proviciality developed across Australia after the Tastubian with the Indoralian Province being devolved into two distinctive units: the Austrazean Province characterising the marine faunas of eastern Australia and New Zealand and the Westralian Province representing the marine faunas of Western Australia and Peninsular India. The two provinces persisted to the end of the Pennian. The purpose of this field trip is to allow participants to examine the stratigraphy, sedimentology, and palaeontology of the Shoalhaven Group and the Illawma Coal Measures of the southern Sydney Basin exposed along the south coast of New South Wales from Batemans Bay north to Wollongong (Figs 2 and 3). A number of key localities have been selected for inspection and are described and discussed in this guide, along with a brief description on the regional geological setting and geologicaJ history of the southern Sydney Basin.

•••• •.. .•. • • :

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TASMAN FOLD

BELT

Canning

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AUSTRALIAN ) 1

CRATON '"

2 Excursion site (Fig. 3)

PERMIAN DEPOSITIONAL AREAS

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Inlracratontc Basins

•

Bowen.ounnedah-Sydney Bilsin System (an back-arc extensional to foreland basin system)

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New England Fold Belt (encompassing small depositional areas ilnd

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basm remnants within the orogenic province.)

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Basin

1

Fig. I. Main Pennian depositional areas of Australia (Brakel and Totterdell, 1996)

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II

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REGIONAL SETIING Structural framework of the Sydney Basin Extending from the Gunnedah district south to the Batemans Bay. the Sydney Basin is the southern part of a much larger, approximately north-south trending elongate PermoTriassic sedimentary trough located between the New England Fold Belt to the east and the Lachlan Fold Belt to the west (Fig. 2). The outline of the basin is clearly defmed by a number of tectonic lineaments (Bembrick and Herbert 1980) (Fig. 2). To the northeast the Sydney Basin is bounded by a major structural lineament, the Hunter-Mooki Thrust, a structure probably fonned during the Hunter-Bowen Orogeny from the middle Permian to Middle Triassic and which has brought older rocks oftbe New England Fold Belt over the eastern edge of the Sydney Basin. To the north and northwest the Sydney Basin is divided from the Gunnedah Basin by the Mount Coricudgy Anticline. Unlike the northeastern and northwestern boundaries, the western boundary of the Sydney Basin is more erosional and characterised by an unconformity that allows the Permian-Triassic sediment of the basin to progressively lap on to the basement rock of the Lachlan Fold Belt. Probably controlled by the pre-Pennian topography of the Lachlan Fo ld, this erosional western boundary of the Sydney Basin is highly irregular, extending from Myrtle Beach, near Batemans Bay, northwards through Tallong and Kanangroo Walls to Lithgow and Portland (Fig. 2). However, outliers of the Permian-Triassic sequence of the Sydney Basin also occur to the west of this described boundary (see Fig. 3). By contrast to the boundaries outlined above, the southeastern boundary of the Sydney Basin has not been clearly defined . Based on marine seismic data Mayne et al (1974) have shown that the Sydney Basin extends offshore at least to the edge of the continental shelf. Other scenarios have also been proposed. For instance, Carey (1969) suggested that the offshore southeastern boundary was rifted during the opening of the Tasman Sea in the Late Cretaceous and that evidence of the Sydney Bas in could be found on the present Lord Howe Rise. This view seems to have been advocated by Jones et al. (1984) and Evans and Migliucci (1991). These authors have further postulated that an orogenic belt, coined the "Currarong Orogen ', supposedly similar to the New England Fold Belt, may have originally existed east and southeast of the Sydney Basin and was later rifted away during the opening of the Tasman Sea. More recently Bradley (1993), based on offshore borehole and seismic reflection data, has suggested that a currently submerged, east-dipping tilted block, which he coined the Offshore Uplift, exists east of and approximately parallel to the onshore eastern margin of the Sydney Basin (Fig. 2) . According to Bradley, the structural uplift was an emergent, vo lcanically active and eroding high from the Late Pennian to Early Triassic and, as such, probably defined the eastern margin of the Sydney Basin during this period.

Stratigraphical framework of the southern Sydney Basin The Permian System of the southern Sydney Basin comprises both marine and norunarine sedimentary sequences, as well as igneous rocks (Fig. 3). The Pennian sedimentary succession is separated from the highly defonned and metamorphosed Lachlan Fold Belt by a distinct angular unconfonnity. In general, the Pennian succession in the southern Sydney Basin is much thinner and less defonned than its counter pan in the northeastern portion of the basin (Hunter Valley region) (Fig. 4) and has gentle easterly to northeasterly dips of 2_10°. The variation ofrock thickness and defonnation style from southwest to northeast across the Sydney Basin is characteristic of a foreland basin setting and reflects 3

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GUNNEDAH

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SYDNEY

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wonongong /

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· .2. Structural outline of the Sydney Basin. F Ig

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: }.': J~Otf'''d Lookout (STOP 14)

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Bellambi Point (STOP 8)

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W ianamatta Group. Ha'ltrilesbu"y Sandstone, Narrabeen Group

lIIawarra Coat Measures Igneous Rocks

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Wandrawandian Siltstone· Formation

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Snapper Point Formation

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Pebbly Beach Formation Yadboro and Tallong Wasp Head Formation Clyde Coal Measures Palaeozoic Basement

Fig . 3. Simplified geolgical map of the southern Sydney Basin (adopted from Jones et al., 1986 and Tye at al. 1996)

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30

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SYDNEY BASIN SW·NE CROSS SECTION

SOUTHWEST

NORTHEAST HUNTER

Ulawarra

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Be"" Nowra Wandrawandlan

-MOOKI THRUST

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Snapper Point F"m.'~'.:i:;~ Tallong and Yadboro

Shoalhaven and Talalerang Groups

Newcastle Coal Measure

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Oempsey Formation Upper Tomago

Coal Measures

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Pebbly Beach

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Siltstone

Muree Sandstone

Silstone, daystone, generally marine

Branx(on Formation

Approximate 0 .... ertical scale

Sandstones, marine and non.marine

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Coal measures and conglomerate

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-y-y'" Unconformity, d lsconformily

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Carboniferous , ...-'\- LA" Volcanics

Fig. 4. Diagrammatic cross-section of the Sydney Basin Penno-Triassic sequence from southwest to northeast (adopted from Jones et aI., 1986).

6

the extent to which the Permian· Triassic Hunter·Bowen orogeny has affected the sedimentary fill of the basin: the northern Sydney Basin, being closer to the New England Fold Belt which bore the brunt of the Hunter-Bowen compressional event, was naturally more susceptible to crustal compression and loading and subsequently became the ' depocentre of the entire basin. The Permian stratigraphy of the southern Sydney Basin has been intensively studied, resulting in a varied nomenclature (see Table I). In this guide we follow the framework recently revised by Tye et al. (1996), who, contrary to Gostin and Herbert (1973) and Herbert (I 980a), have excluded the Tallong and Yadboro Conglomerates from the Talaterang Group and treated the Wasp Head Formation as the lateral and seashore equivalent of the Clyde Coal Measures (Table I). In addition, Tye et al. (1996) have also included the Pigeon House Siltstone as part of the Clyde Coal Measures. A schematic composite stratigraphic column summarising all the major stratigraphical subdivisions and corresponding depositional environments of the southern Sydney Basin is shown in F ig. 5, along with indication of the three broad tectonic stages that are considered to have influenced the deposition within the basin,

Ta/aterang Group Clyde Coal Measures The Pennian sedimentary succession of the southern Sydney Basin begins with two mutually distinctive and isolated sequences, respectively known as the Clyde Coal Measures (incorporating the Pigeon House Siltstone) and the Wasp Head Fonnation. The Clyde Coal Measures, first named by David and Stonier (1891), are mainly found in the upper Clyde VaHey in the southwestern part of the Sydney Basin (Fig. 3). Here, the coal measures unconformably overJie the Ordovician metasedimentary basement and are disconfonnably overlain by the Yadboro Conglomerate (McElroy and Rose, 1962), In areas where the Yadboro Conglomerate is absent, the Clyde Coal Measures are overlain disconformably by the Snapper Point Formation (Tye et al ., 1996). The lithostratigraphy of the Clyde Coal Measures has been examined in detail, notably by McElroy and Rose (1962), Gostin and Herbert (1973) and Tye et al. (1996). At the type section in the upper Clyde VaHey, McElroy and Rose (1962) estimated some 41 m for the coal measure sequence and observed that the sequence was dominantly silty and sandy with a basal quartz pebble conglomerate, which rests unconformably on the highly deformed Lower Ordovician metasediments. Up to 11 plies of thin coal beds were observed from the type section by McElroy and Rose (1962), mainly from the middle part of the section where they were found intimately associated with carbonaceous siltstones (Fig. 5). Fine to medium-grained cross-bedded and ripple cross-laminated sandstones occur most commonly in the lower and upper parts of the sequence. Some sandstone bodies bear low-angle bedding surfaces interpreted by Tye et al. ( 1996) as depositional surfaces fo nned by lateral accretion in a small channel. Palaeocurrent data from the crossstratified strata indicate palaeoflow towards the north for the lower part of the succession and a bimodal current in the upper 12 m (Tye et aI., 1996). Plant remains are abundant throughout the type section but mostly fragmentary. McElroy and Rose (1962) reported ?Glossopteris sp., ?Gangamopteris sp. and Noeggerathiopsis sp. from the Coal Measures, indicating a general Permian age. Microflora characteristic of the eastern Australian palynological zone Stage 3a (Sakmarian-Artinskian) (Price, 1983) have also been recorded from the coal measures (Evans et a1. , 1983). Rare Skolithos burrows have also been found in the sandstone beds, The Pigeon House Siltstone of McElroy and Rose (1962), now included in the Clyde Coal Measures by Tye et aI, (1996), is very similar to the Clyde Coal Measures described above in overall lithology and sedimentary structures. The sequence consists of interbedded sandstone and carbonaceous siltstone; however, it lacks any coal seams. At its p

7

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Table 1. Correlation of several previously proposed stratigraphical schemes for the southern Sydney Basin Archbold & Dickins 1996

McElroy and Rose, 1962; McElroy ct al. , 1969

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Gostin and Herbert, 1973; Herbert, 1980a

IIJawarra Coal

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Plate 8

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