The phanerozoic sedimentary basins of Australia and their tectonic implications

The phanerozoic sedimentary basins of Australia and their tectonic implications

Tectonophysics, 48 (1978) 365-388 0 Elsevier Scientific Publishing Company, 365 Amsterdam - Printed in The Netherlands THE PHANEROZOIC SEDIMENTARY...

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Tectonophysics, 48 (1978) 365-388 0 Elsevier Scientific Publishing Company,

365 Amsterdam

- Printed

in The Netherlands

THE PHANEROZOIC SEDIMENTARY BASINS OF AUSTRALIA THEIR TECTONIC IMPLICATIONS *

H.F. DOUTCH

and E. NICHOLAS

Bureau of Mineral Resources, (Received

AND

for publication

Canberra, A.C.T.

January

(Australia)

5, 1978)

ABSTRACT Doutch, H.F. and Nicholas, E., 1978. the Phanerozoic sedimentary basins of Australia and their tectonic implications. In: E. Scheibner (Editor), The Phanerozoic Structure of Australia and Variations in Tectonic Style. Tectonophysics, 48: 365-388. The stratigraphy, structure and tectonics of Australia’s Phanerozoic sedimentary basins are described briefly in terms of three settings: younger internal basins, older internal basins and peripheral basins. The younger internal basins developed successively following part by part cratonization of the Palaeozoic Tasman Fold Belt System. Most of the older internal basins probably had late Proterozoic beginnings and all have Precambrian cratonic basements. The peripheral basins occur around the present continental margins and in New Guinea; the oIdest of them may be Devonian. The peripheral basins are the simplest to explain in terms of plate tectonics: some can be related to Australia breaking away from Gondwanaland, others to plate convergence in the east and in New Guinea. An attempt is made to fit the internal basins into a platetectonic geological history.

INTRODUCTION

A comprehensive introduction to Australia’s sedimentary basins is given in the BMR “Record” Series (BMR, 1974) and their geology and petroleum prospects are described in a recent monograph (Leslie et al., 1976). Most Phanerozoic sedimentary basins in Australia (Fig. 1) are in a tectonic sense platform cover. On the 1 : 5,000,OOO scale Tectonic Map of Australia and New Guinea (GSA, 1971) they are depicted as either “Trans-Australian Platform Cover” and transitional predecessors, or as the younger part of the “Central Australian Platform Cover”. When organized as Platform Covers the basins provide a first step towards identifying and formally naming the cratons they succeeded to, and to recognizing the tectonic ~f~iations of some * Published with and Geophysics.

the permission

of the Director,

Bureau

of Mineral

Resources,

GeologJ

366

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SOUTHERN OCEAN 36’

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* TASMAN FOLD BELT SYSTEM

0L .._..-.L 200 .2~_2%A_d

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140.

ix?*

Fig. 1. F’hanerozoic sedimentary basins of Australia (after BMR, 1974).

of the structures controlling. basin development. Explanations of these and associated concepts is provided in the map key (GSA, 1971). In this paper we examine the Australian Phanerozoic basins in three assemblages (Fig. 2): younger internal ~~tr~ratoni~) basins, older internal (intracratonic) basins, and peripheral basins (cf. Cameron, 1967). New stratigraphic charts by Mayne (1976) are of considerable background value for this discussion. The younger internal basins are discussed first because they provide a model for examining the development and nomenclature of the older internal basins. The younger basins mostly overlie the East Australian Erogenic

I

Fig. 2. Subdivision

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BASINS

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i 8

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: FOLD BELT

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of Yhanerozoic seciimeniary La&s uLC AU&~-ak.

Central Australian Platform Cover

Trans-Austraiian Platform Cover

PER!PHERAt

YOUNGER

INTERNAL

INTERNAL

BASINS

OLDER

SYY I tM

368

Province * (the Tasman Fold Belt System ** and its components of Scheibner (1973), whose terminology for the Province is used in this paper), or the “Tasman Geosyncline” * of many previous authors; however, some overlap westwards over Precambrian cratons (Fig. 2). With one exception mentioned below the oldest of these basins began to develop early in Devonian time; they came into existence during and after the latest episodes of erogenic activity of the Fold Belt System. The older internal basins do not extend beyond the Precambrian cratons. Some of them originated in late Proterozoic times and contain Adelaidean System rocks. Some of their Phanerozoic episodes of sedimentation and deformation seem to be related to broadly synchronous sedimentation and deformation in the adjacent Tasman Fold Belt System. The peripheral basins around the Australian continent had their origins in the west in the Permian (or earlier), in the south in the Jurassic. They are pericratonic and have resulted from the splitting up of Gondwanaland (cf., Veevers and Evans, 1975; Branson, this Symposium). Most cut across previous structural trends (cf., Wellman, 1976; BMR, 1976); in particular around northwestern Australia they are imposed athwart older internal basins. By using plate tectonics to interpret Australia’s peripheral basins we raise the problem of the consistent application of plate-tectonic theories to the origins of its internal basins. This we attempt with debatable success, but with perhaps a more liberal attitude than that held by fixists (e.g., Meyerhoff and Meyerhoff, 1972), undeniable though some of their points may be. YOUNGER

INTERNAL

BASINS

The development of most of Australia’s younger internal basins (Fig. 2) began early in Devonian times and is still in progress. The sequence of development seems to be closely related to the progressive cratonization from west to east of the Kanmantoo, Thomson, Lachlan and New England Fold Belts of the Tasman Fold Belt System (Fig. 3). Each basin owes something not only to the behaviour of the new craton it modified but also to contemporaneous pre-cratonic tectonism in adjacent parts of the Fold Belt System to the east. The pattern of development is one which appears to apply in some respects to the older internal basins, and to the evolution of platform cover in many parts of the world; Figs. 3 and 4 show those younger internal basins which best illustrate this pattern of development. Four sets of younger internal basins are recognized. The first set is represented by the Devonian-Carboniferous basins which form platform cover that succeeded the Tasman Fold Belt System. These are the Adavale, Darling and Drummond Basins. The Adavale and Darling Basins started to develop early in Devonian times, the Drummond in latest Devonian. Basin histories

* Stratotectonic

term; ** structural or tectogenic term. (Editor.)

369

370

In

w

371

reflect both the final stages of stabilization - i.e., cratonization - of the Lachlan Fold Belt thereabouts and contemporaneous tectonic activity on the site of the New England Fold Belt (cf., Scheibner, 1976). The Adavale, Darling and Drummond Basins are grouped together tectonically because they can be considered as representing both the beginnings of platform cover on the Tasman Fold Belt System and the end of “erogenic” transformation of these parts of the belt into a craton. They are therefore classified as “transitional” basins (GSA, 1971; Doutch, 1972; Scheibner, 1976), specifically with respect to cratonization of the Lachlan Fold Belt. In the Adavale Basin acid continental volcanics, and minor sediments of presumed Early Devonian age occur at the base of the succession, conformably overlain by a Middle Devonian marine sequence of labile sandstone, limestone and shale which grades to fluviatile sandstone at the top. An unconformity separates these rocks from a Middle Devonian sequence containing rock salt, dolomite, varicoloured sandstone, shale and siltstone deposited in evaporitic, marine, and terrestrial environments. Late Devonian continental and shallow marine redbeds complete the sequence. In terms of basinwide distribution the marine sediments are mainly confined to the eastern parts of the basin, the sedimentary sequence in the central and western area being mainly non-marine and detrital. Similarly in the Darling Basin the sandstone and shale which comprise the Early Devonian sequence is marine in the east and non-marine in the west, and is overlain unconformably or disconformably by some Middle, but mostly Late Devonian to Early Carboniferous “red beds” and fluviatile clastics (Evans, 1977). The discontinuity in the Devonian in the Adavale and Darling Basins probably reflects the mid-Devonian Tabberabberan Orogeny in adjacent parts of the Tasman Fold Belt System. In the Drummond Basin, deposition was mainly in the Early Carboniferous, but began in Late Devonian times after elevation of the adjacent Anakie High (Fig. 3) (by the mid-Devonian Tabberabberan Orogeny?). The sequence consists of predominantly fluviatile and lacustrine conglomerate, sandstone, shale and minor limestone; acid tuffs provide marker beds and are thicker to the east, suggesting that the volcanoes were perhaps on the flanking Anakie High. In the Drummond Basin mild syndepositional warping and folding occurred, with concomitant faulting, but the main deformation of the basin took place during the Kanimblan Orogeny, an event which included the Late Carboniferous volcanism and granite intrusion that occurred marginal to some parts of the basin after folding (GSA, 1971). The Kanimblan Orogeny also resulted in block faulting of the Adavale Basin (Fig. 4), associated with a northeast-trending series of anticlines and horsts and small salt diapirs, and in faulting and broad folding of the Darling Basin. Internally, then, these three transitional basins have much in common. Continental influence predominated in their sediments; the Tabberabberan Orogeny appears to have set the stage for similar conformable successions;

372

culmination of the only deformation of all three was during the Kanimblan Orogeny; the structures in the three basins could as well be due to vertical as to compressional tectonics; the basins themselves do not seem to have been the sites of igneous activity, but volcanism was marginal to them; none of them have been regionally metamorphosed. These characteristics should not be regarded as being definitive for all transitional basins; rather, some or all of them may well be associated with the beginnings of any platform cover succeeding geosynclines like the Tasman. Older transitional “basins” in Australia occupy the same position in the cratonization sequence, but some differ markedly in content from those of the Palaeozoic. The Darling and Drummond Basins are very similar: sediments are molasse-like; folds are parallel, up to two kilometres in amplitude and wavelength, commonly ten kilometres long, and the rocks tend to brittle fracture; contemporaneous igneous activity was mainly marginal, and more vigorous to the east towards the developing New England Fold Belt. There was limited subsequent deformation of the Lachlan Fold Belt and its transitional basins. Other transitional “basins” of Devono-Carboniferous age are the Burdekin Basin and part of the Broken River Embayment in Queensland, the Mount Howitt Province in Victoria, and the Bancannia Trough in New South Wales. The Bancannia Trough (Fig. 3) also contains Ordovician rocks which can be said to be transitional from the Kanmantoo Fold Belt, the oldest part of the Tasman Fold Belt System (Scheibner, 1976). The second set of younger internal basins to develop were the Permian Pedirka and Arckaringa Basins, the Permo-Triassic Cooper and Galilee Basins, and the Permo-Triassic Bowen and Sydney Basins. The Pedirka, Arckaringa, Cooper and Galilee Basins are intracratonic. The Pedirka and Arckaringa Basins and the southwestern part of the Cooper Basin overlie the Precambrian Craton and part of its platform cover, namely the older internal Warburton and Amadeus Basins (Figs. 1 and 4). The Cooper and Galilee Basins partly overlie the Lachlan Fold Belt Devonian-Carboniferous transitional basins (Fig. 3). While these intracratonic basins were developing, the Bowen and Sydney Basins formed as foredeeps on the western flanks of the New England Fold Belt (GSA, 1971; Scheibner, 1976). The Cooper, Galilee, Bowen and Sydney Basins still form one large composite basin continuous with parts of the New England Fold Belt, for example the Yarrol Basin (Fig. 3). Permian sediments in the Arckaringa and Pedirka Basins, and PermoTriassic successions in the Cooper and Galilee Basins, are mainly non-marine elastics, including coal, which were deposited in fluviatile, lacustrine and flood-plain environments. Glacigene sediments occur at the base of the successions in each basin. In the Galilee Basin some tuffaceous material is also present. In the Cooper and Galilee Basins folds and faults developed during sedimentation. Perhaps because of their location on the Precambrian craton, the Pedirka and Arckaringa Basins are less deformed than the Cooper and Galilee Basins.

373

Deformation of the Cooper and Galilee Basins reflects phases of the PermoTriassic Hunter-Bowen Orogeny that affected the adjacent Bowen Basin and the New England Fold Belt. Day et al. (1974) discuss this in detail. In the Bowen and Sydney foredeep basins, glacigene sediments also occur at the base of the Early Permian sequences, which include shallow marine, coastal and deltaic sediments. Thick coal measures characterize t,he Late Permian. Volcanogenic detritus is common throughout. In the Triassic, nonmarine redbeds and lithic and quartzose sandstone were laid down, in sequences which were thicker in the Bowen Basin than in the Sydney Basin. The HunterBowen Orogeny of the adjacent New England Fold Belt deformed parts of the Bowen and Sydney Basins (Day et al., 1974). Uplift, folding and faulting occurred along the northeastern margin of the Sydney Basin in Late Permian and Early Triassic times. In the Late Triassic parts of the Bowen Basin were gently to isoclinally folded, and strata along its eastern margin were overturned; decollement may have accompanied the folding. Permian platform cover sediments are also preserved in poorly known structures beneath the Murray and Eucla Basins (Figs. 1 and 3); in the Murray Basin they include coal of Late Permian age. Permo-Triassic sediments including coal also occur in the Tasmania Basin. Thin Permo-Triassic veneers are present over many older internal basins. Gas and oil in the Cooper Basin and coal in the Bowen, Sydney, and Galilee Basins are major economic resources. The third set of younger internal basins consists mainly of the broad, shallow, Jurassic-Cretaceous intra~ratonic downwarp complex of the Carpentaria, Eromanga and Surat Basins *. They conceal most of the DevonoCarboniferous and Permo-Triassic basins of the first two sets, and overlap on to the Precambrian cratons and their covers to the west; in particular the Eromanga Basin overlaps the platform cover of the older internal Arrowie, Warburton, Amadeus and Georgina Basins. To the north the Carpentaria Basin lies on Precambrian basement and is continuous with the Morehead Basin in New Guinea, which apparently adjoined a “geosyncline”. To the east this basin complex is joined to the small Laura and Clarence-Moreton Basins. Sedimentation in most of these basins was dominantly continental during the Jurassic, with local development of coal swamps. In early Cretaceous times an eustatic rise in sea level produced a widespread marine transgression and resulted in the deposition of shallow marine elastics and minor limestone. The seas had almost completely retreated by mid-Cretaceous times. The Eromanga and Surat Basins are very gently folded; faults are relatively few, and displacements on them a few hundred metres or less. Some folding is due to compaction over older structures, some to structural growth during deposition, and some to movements of Late Cretaceous or Tertiary age. Further east the isolated peripheral (?) Jurassic-Cretaceous Maryborough Basin, * To these basins Basin”. (Editor.)

is often

referred

as the

“Great

Australian

Basin”

or “Great

Artesian

374

a successor to the Triassic transitional Esk Rift (Figs. 1 and 3), was more intensely folded during what has been discussed by some authors as a Late Cretaceous “Maryborough Orogeny”. The Lord Howe Rise and Dampier Ridge to the east of the Australian continent may yield a better picture of this tectonic episode in due course; the Maryborough Basin may have been a foredeep basin. In the Carpentaria, Eromanga and Surat Basins coal, oil, gas, manganese and artesian water are all commercially exploited, and reserves of oil shale have been established. A fourth set of younger internal basins of Cainozoic age are shown on Fig. 5, together with major faults of all ages, present-day seismicity, and Cainozoic basalts. Thin Cainozoic continental sediments accumulated in the

I MURRAY

0

-*e

Fig. 5. Cainozoic deposits of Australia (by courtesy of the Map Compilation Section of the Geological Branch, and Observatories and Regional Section of the Geophysical Branch, Bureau of Mineral Resources).

375

Karumba Basin overlying the Carpentaria Basin (Doutch, 1976b), and in small basins and synclines superimposed on the Eromanga Basin (GSA, 1971). To the south some Tertiary marine carbonates were laid down in the Murray and Eucla Basins. Control of growth of most Cainozoic basins has yet to be investigated; those basins created by deformation of the Eromanga Basin were controlled by structures that originated during Cooper Basin development. Most, if not all, Cainozoic sediments are unconformable on older rocks. Rate of growth of the basins is to some extent indicated by the thickness of Cainozoic deposits. It may also be suggested by the level of present-day seismicity, which indicates that the margins only of four or five basins are currently active (Fig. 5). Overall, the rate of growth of Cainozoic platform cover appears to have been much slower than that of almost any older covers. In plate-tectonic terms Cainozoic intracratonic structural developments took place during the drift of Australia away from Antarctica. Features in New Guinea interpreted as the results of plate-margin collisions support this concept of northerly drift as does the nature of sediments and structures on the southern margins of the Australian continent (Cainozoic development of the Otway Basin, treated below as a type peripheral “break-up” basin, is part of this story), and the distribLItion of ages of the basalts shown on Fig. 5 (Wellman and McDougall, 1974a), which are generally older in the north. Basalt extrusions were penecontemporaneous with uplifts, possibly over “hot-spots”, which set basin limits, and with the opening of the Tasman Sea, a Late Cretaceous--Cainozoic marine basin (see Branson, this Symposium). These points constitute a basis for classifying Australia’s Cainozoic platform cover as a distinctive tectonic stage (Doutch, 1974, 1976h), and for separating it from the Trans-Australian Platform Cover of GSA (1971). This proposal raises the possibility of recognizing stages of platform cover and sedimentary basin development which reflect drift and/or plate collision episodes. Concepts such as ‘Sequence” (Johnson, 1971; Sloss and Speed, 1974) and “Synthem” (Chang, 1975) are also relevant to the case. The evolution of the pre-Cainozoic younger internal basins has also been interpreted in terms of plate-tectonic theory. Scheibner (1976) has suggested a relationship between the Lachlan Fold Belt transitio~~al basins and subduction to the east in the region of the New England Fold Belt. The general trend of transitional basin structures in the south is in harmony both with this proposition and with the controlling north to northwest structural grain of the underlying Lachlan Fold Belt; in the north the Drummond and Adavale Basins and their fold axes also trend northerly, but are apparently at an angle to the northeast trend of the underlying Thomson Fold Belt (Murray and Kirkegaard, this Symposium), a time equivalent in Queensland of the Lachlan Fold Belt in new South Wales. A similar relationship can be proposed between the New England Fold

376

Belt, the Permo-Triassic basins, and a further episode of plate interaction that began at the eastern plate margin after the Kanimblan Orogeny (cf., Scheibner, 1973). The gross northwest and northeast trends of the Pedirka, Arckaringa, Cooper and Galilee 3asins could be said to be conjugate with respect to the plate margin of the times. The two trends could also be inherited from the Thomson Fold Belt. However, the underlying Devono-Carboniferous transitional basins were predominantly north--south, and therefore these four Permo-Triassic basins may also be reactions to stress on and strain within the contemporary non-homogeneous crust of Australia related to inception of the oceanic Wharton Basin to the northwest, and consequent drift of the continent (cf., Branson, this Symposium). The position of the plate Mann east of Australia during the development of the Jurassic-Cretaceous basins is difficult to place, although off western Australia both the opening of the Wharton Basin and movement on the Wallaby-Perth transform (see below) suggest that the Australian-Antarctic plate was drifting towards the east until the Palaeocene, when Austraiia split from Antarctica. Jurassic--Cretaceous basins have no characteristic structural trends of their own. Internal structures associated with basin sagging appear to be inherited from basement or older basins. OLDER INTERNAL

BASINS

The older Phanerozoic internal basins of Australia (Figs. 1 and 2) can be divided into two groups: one lying centrally in the continent, the other consisting of basins cut across by the western coastline of Australia. The central group commonly contains late Proterozoic Adelaidean System rocks, which in the south were preceded by acid volcanism and plutonism attributed to a transitional “basin” event (GSA, 1971; Doutch, 1972; Plumb, this Symposium *). This transitional tectonism was related to the cratonization of the Central Australian Orogenic Province; the succeeding Central Australian Platform Cover which overlies this Province, and which consists of all the older internal basins, overlaps the early Proterozoic North Australian Orogenic Province, and in places its mid-Proterozoic platform cover (GSA, 1971). The central group of older internal basins contains Proterozoic and Palaeozoic successions which are separated by an unconfo~ity in some places but by no means everywhere. The southern basins of the group are deeper than the northern (Fig. 6), perhaps reflecting the younger less stable cratonic basement in the south belonging to the Central Australian Orogenic Province. The southern basins of the central group include the Amadeus, Ngalia, Warburton, Arrowie and Officer Basins. Early Cambrian basalts occur in the Officer Basin, but in general the Cambrian sequence in these basins changes from elastics in the southwest to carbonates in the northeast, and the Ordo* Not in this issue; submitted to Tectonophysics.

377 North OFFICER

AMADEUS

NGAilA

ARUNTA

Before Rodmgon Movement in Si/ur,bn

(450

m.y

/

OROGENIC

PROVINCE

/

Fig. 6. Evolution of central group of older internal basins (diagrammatic only). tions are vertically exaggerated, but the dip of faults was purposely not corrected

The secfor this.

vician is characterized by interbedded sandstone, siltstone and shale; rocks of both ages are mainly marine. There is a hiatus in the Silurian. Devonian to Carboniferous rocks are syntectonic continental sandstone and rudites. In the Amadeus Basin, Wells et al. (1970) postulate a marine influence from the west in the Early Devonian (cf., Early Devonian sequences of the transitional basins of the “Younger Internal Basins”). Resources of gas and oil have been proved in the Cambro-Ordovician sequences of the Amadeus Basin. The northern basins of the group consist of the Georgina, Wiso and Daly River Basins, and also the little known Arafura Basin further north. In contrast to the southern group, Adelaidean rocks are patchily distributed, and Palaeozoic basin history began with thin plateau basalts (but a large volume, cf., Veevers, 1976) extruded in early Cambrian times in the northern part of’ the area. The early mid-Cambrian sequences of the northern basins are dominated by shallow-water marine carbonates; in the Georgina Basin these include most of Australia’s resources of phosphate rock. In later mid-Cambrian times the sea retreated to the north and south where shalIow-water conditions persisted until the middle of the Ordovician, with a gradual change from carbonate to sandstone and siltstone. Silurian rocks are knowr. only from the Arafura Basin, and Devonian rocks are present only in the south of the Georgina Basin. The Early Cambrian basalts imply that the tectonic regime in the Officer

378

Basin and in the northern basins in Early Cambrian times was probably extensional. More importantly, this regime differed markedly from that of the region between them, in the centre of the continent, where movements of the already intensely deformed Musgrave Block (Fig. 6), which were penecontemporaneous with the volcanism include overthrusting to the north along the southern margins of the Amadeus Basin about 600 million years ago (Petermann Ranges Orogeny; Forman and Shaw, 1973). Associated uplifts led to consequent local molasse-like sedimentation in the flanking basins. In Silurian times the centre of the continent was again disturbed, this time by broad upwarps, e.g., the Rodingan Movement of the Amadeus Basin. In the Carboniferous, the Alice Springs Orogeny, which seems to have been a time-equivalent of the Kanimblan Orogeny, brought about the major fold deformation of the central group of basins. Folding of this age is pronounced in the centre of the continent; to the north it is weak and restricted to the southern margin of the Georgina Basin, and to the south, along the northern edge of the Officer Basin, it is poorly known. In general, Late DevonianCarboniferous syntectonic sedimentation was very like the sedimentation which took place during the interval between the Tabberabberan and Kanimblan Orogenies in the transitional basins of the “Younger Internal Basins”, and the style of Carboniferous deformation was also similar. Important differences were the southerly over-thrusting and nappes along the northern margins of the Amadeus and Ngalia Basins, and in the transitional younger internal contrasting fold trends - northerly basins and westerly and northwesterly in the older internal basins. The older, more stable parts of the continent were unlikely to react to a Carboniferous tectonic event in the same way as the younger, less stable, Tasman Fold Belt region and in the areas affected contrasting gravity features (which were probably much the same at the end of the Carboniferous as they are now) no doubt reflect this. The Officer, Amadeus and Ngalia Basins and the southern part of the Wiso Basin are associated with Australia’s greatest negative Bouguer anomalies (BMR, 1976). These anomalies, and also the development of the basins, have been explained in terms of compressive buckling leading to granite anatexis in downwarps (Anfiloff and Shaw, 1973), and by postulating intracratonic plate movements (Forman and Shaw, 1973). However, the anomalies are unlikely to reflect the results of only a single event, and may even indicate mantle involvement. The Alice Springs Orogeny was, on the face of it, essentially a Carboniferous uplift which most affected the southern basins and their underlying craton, and resulted in the rise and eventual exposure of the Arunta Block, the separation of the Amadeus, Ngalia and northern basins from each other (cf., Plumb, this Symposium), and the virtual cessation of deposition in them. Folding in the basins was a consequence of the uplift. Although plate movements to account for the Petermann Ranges Orogeny

379

could be related to the beginnings of the Tasman Fold Belt System in the east and to a possible “geosyncline” north of the Arafura Basin (cf., Visser and Hermes, 1962; GSA, 1971), and the Alice Springs Orogeny can be associated with the Kanimblan Orogeny and the plate-margin events of the Fold Belt System, it is difficult at first to reconcile the north--south compressions implied by the orogenies for the Precambrian cratons with contemporaneous east-west compressions in the Fold Belt System. This point is discussed further below. From the end of the Precambrian until the ~arboniferous, the Amadeus, Ngalia and northern basins may have been one large basin (Fig. 6). In its early stages this composite basin was probably continuous with the “‘geosyncline” to the north, and connected with Tasman Fold Belt System depressions at all times except during the Silurian, In this way the older internal basins are reminiscent of the Permo-Triassic younger internal basins, and might simply represent part of an earlier cycle of a repetitive process. However, most of the younger internal basins were immediately preceded by relevant transitional basins (Fig. 3), whereas late Proterozoic (Adelaidean System) deposition intervened between the Phanerozoic older internal basins and preceding transitional basins related to the Central Australian Orogenic Province (GSA, 1971). The sequence and pattern of development of the central set of older internal basins is therefore one in which stability was essentially achieved in late Proterozoic times after transitional beginnings, with the Petermann Ranges and Alice Springs Orogenies being almost accidentaily superimposed on the area. The late Proterozoic stability of the whole of the Australian continent resulted in something of a tabula rasa setting for its Phanerozoic development, and the principle of actualism perhaps could be applied since the Cambrian? The western group of older internal basins consists of the Bonaparte Gulf, Canning, Carnarvon and Perth Basins. They are not so obviously associated with late Proterozoic forerunners as are the central group, and their relationships with basement are more conjectural than is the case for many other basins. Their pre-Permian stratigraphy (pre-Late Carboniferous in most places) reflects two marine transgressive and regressive cycles. The first transgression began in the north in mid-Cambrian times, and extended into the Canning Basin in the Ordovician and the Carnarvon Basin in the Silurian; it apparently did not reach as far south as the Perth Basin, in which probable Silurian continental red sandstones are the only known pre-Permian sediments. The first cycle was probably associated with relatively slow basin sagging and is notable for Late Silurian to Early Devonian evaporites and red beds; the second is characterized by Late Devonian and Early Carboniferous reef complexes and deeper water equiv~ents associated with the development of two northwesttrending rifts, the Petrel Graben in the Bonaparte Gulf Basin (Fig. 7) and the Fitzroy Graben in the northern Canning Basin. The grabens lie at the north-

380

E

Y

w”

N

W

W

381

ern end of a northwest-trending “central corridor” of TabberabberanKanimblan deformation (Fig. 10) which includes features resulting from the Alice Springs Orogeny. The Late Carboniferous to Early Cretaceous rocks that are generally regarded as belonging to these four basins reflect to varying degrees development in an extensional tectonic regime, which has been interpreted as the rifting phase that led up to the separation of the “Indian” and Australian parts of Gondwanaland (Veevers and Evans, 1975). Separation began in the north in the Jurassic, and in the south during the Cretaceous. The basins that were initiated with the rifting phase of this episode and which are still developing along the western margin of the continent more properly belong to the peripheral basins very briefly discussed below rather than to the western group of older internal basins (Figs. 7 and 9). PERIPHERAL

BASINS

As the peripheral basins are the subject of Branson’s paper in this Symposium, we confine our discussions to a generalized outline of their tectonic history. Development of basins along the northwestern, western and southern margins of the continent can be explained in terms of Falvey’s concepts of offshore basin development for basins facing ocean-floor spreading centres (Falvey, 1974). Figure 8 shows our generalized version of these concepts as applied to the Otway Basin by Boeuf and Doust (1975). The oldest of these basins (e.g., Browse Basin), lie off northwestern Australia and are a consequence of the development of the adjacent oceanic Wharton Basin. Figure 9 shows our application of the Otway Basin model to the peripheral basin - in part the Petrel Graben (Fig. 7) -that modified the Bonaparte Gulf Basin. The Fitzroy Graben is similarly associated with a peripheral modification of the Canning Basin, and both grabens could be aulacogens related to sea-floor spreading. Farther south the development of the Permian to Holocene sequences in the Carnarvon and Perth Basins has been related to the break-up of Gondwanaland and the westerly drift of “India” away from the present southwest margin of the Australian continent along the Wallaby-Perth Transform (Johnstone et al., 1973). The paucity of peripheral basins off eastern Australia seems due to platemargin complexities related to eastwards migration of subduction zones and the opening of the Tasman Sea. It is obviously necessary to distinguish between peripheral basins formed where continents break up, such as those to the south and west of the continent, and those formed near subducting plate margins, the local example of which lies in New Guinea (Fig. 2). The latter become incorporated in fold belts, while the former could apparently be terminated only by epeirogenic uplift, new transforms or subduction zones. Terms for various types of subduction margin basins already exist; we

382

0

V_ -_ H 5 Generalized

Cainozoic

dter

I

Corbonoh

r-l II.

Deighton et. al.(l976),B~uf

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383

term those around Australia facing ocean-floor spreading centres “break-up basins”. Australia’s greatest oil and gas resources occur in the Carnarvon and Gippsland Basins, which are break-up basins. In any revision of the concept of the Trans-Australian Platform Cover, in particular involving ideas about its genesis, the inclusion or exclusion of peripheral basins will be fundamental. They are probably best treated as at least two separate structural classes, and, further, as unique tectonic entities developing contemporaneously with platform covers and erogenic provinces. A BASINS-BIASED

PHANEROZOIC

PLATE-TECTONIC

HISTORY

OF AUSTRALIA

The Australian continent has been shaped in the Phanerozoic by tectonism in three major domains, those of the peripheral basins, the “Tasman Fold Belt System” (here amended to include New Guinea) and its succeeding platform cover basins, and the northwesterly trending central corridor of basins and uplifts. Much of this tectonism has already been interpreted in plate-tectonic terms, but a little further speculation is warranted to interrelate some of it. Phanerozoic tectonism had to work on and possibly derive from a foundation of Precambrian domains. In late Proterozoic times this part of Gondwanaland was tectonically quiet: in a structural setting somewhat reminiscent of contemporary Africa, sags along junctions between cratonized erogenic provinces collected Adelaidean System sediments, and there was little igneous activity, deformation or metamorphism (Plumb, this Symposium). The central corridor sag was located above the junction between the cratons of the North and Central Australian Orogenic Provinces (Fig. 10); this junction had had a prior history of compression, with reworking of both provinces where they met. But overall, Australia in the late Proterozoic seems to have been free of subduction. The central corridor “sag” was probably a composite feature (Fig. 6), and gravity features in it have been interpreted to support an origin in compressive downwarping, as already mentioned. But there is also the possible analogy of the “failed” rift (aulacogen) of a triple diverging plate junction. In this sense basins in the central corridor may well have been aulacogens during late Proterozoic times, and Veevers (1976) and others have applied this term to them, the other rift arms had perhaps been replaced by the beginning of the Cambrian with new oceanic crust from a rift-born slowacting ocean-floor spreading centre to the east of the continent - that is to say, to the east of Gondwanaland (or, better still, of Pangea?). The history, nature and location of the Adelaide “Geosyncline”, (Fig. 10; Scheibner, 1976; Thomson, this Symposium) support this sea-floor spreading idea, and the western boundary of the Tasman Fold Belt System has a convenient re-entrant into the central corridor which simulates a triple point. The spatial and structural relationships of the central corridor and the re-en-

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BASINS YOUNGER OLDER INTERNAL iNTERNAL

deformations.

385

trant bear something of a family resemblance to the Gulf of Guinea and its associated “failed arm”. At the beginning of the Cambrian this passive continental margin developed a subduction zone (Scheibner, 1976) just to its east - and possibly to the north. This was perhaps an inevitable mechanical break once the oceanfloor spreading centre had retreated to a critical distance from continental crust. The gentle hinterland of epeirogenic basins was compressed at about the same time within the central corridor in the Petermann Ranges Orogeny, and stretched in adjacent areas to such an extent that basalts were extruded. The collision of the cratons in the central corridor could be put down to jostling subduction, but the contemporaneous stretching tempts the invocation of asthenospheric flow to explain the simultaneous compression and tension. It was a curiously short-lived burst of tectonism within the cratons (considering the vigour of Tasman Fold Belt System development during Cambrian and Ordovician times), and on-again, off-again asthenospheric flow presents problems. However, if a late Proterozoic flow beneath the continent was brought to an end when subduction began, an adjustment of flows to new equilibria would have had to be made. In the Silurian, interpretation in some areas of the widespread hiatus in deposition as being due to uplifts can be generalized as doming within the limits indicated on Fig. 10. Lithostratigraphy (e.g., Mayne, 1976) suggests doming began in the Ordovician; it appears to have culminated in the central corridor, where the Silurian hiatus has resulted in the concept of the Rodingan Movement in the Amadeus Basin. The hiatus is not dated accurately enough to correlate it with tectonic events in the developing fold belt systems to the east and north (GSA, 1971). As with the preceding tectonism doming may have been either a compressional response to subduction or more directly related to asthenospheric upwelling contemporaneous with the subduction, perhaps both; at any rate, there was no intracratonic Silurian igneous activity. In the west and south the periphery of the dome appears to have been in the vicinity of subsequent Gondwanaland splits. The dome offered an appropriate setting for major penecontemporaneous tensional rifting of the Fitzroy and Petrel Grabens, and further compressional closure of the Adelaidean System sags during the Alice Springs Orogeny. All this activity took place during the Devonian and Carboniferous Tabberabberan-Kanimblan interval, the type events of which in the Tasman Fold Belt System are interpreted by Scheibner (1976) in terms of phases of subduction and eastward movement of the Australian continent. That these contrasting phenomena should be confined to the central corridor suggests overall control by the boundary between the cratons of the North and Central Orogenic Provinces (Fig. 10). That the phenomena should contrast suggests a domain junction along a geological discontinuity, possibly en-echelon structures, joining the Halls Creek Mobile Zone and the Fraser and Bremer Faults (Fig. 10, and cf. GSA, 1971). The opening of the grabens could indicate an early episode of sea-floor spreading to the west - a possi-

386

bility that might find favour with those requiring an arm of Tethys to be present west of Australia in the late Palaeozoic. The north-south compressions of the Alice Springs Orogeny and the westerly subductions attributable to the Tabberabberan and Kanimblan Orogenies repeat in a general way the early Cambrian episode; in this instance the change in the asthenospheric flow regime to account for the Alice Springs Orogeny is associated with completion of cratonization of the Lachlan Fold Belt and the rigid welding to it of the two older cratons. Thereafter Australian tectonics becomes a more straightforward matter of Gondwanaland break-up with sea-floor spreading on one side and complementary subduction on the other; internal basins developed from the end of the ~~boniferous onwards as a consequence of drift towards the subduction zones. Some deeper, narrower basins such as the Bowen and Sydney foredeeps seem to be a compressional response to drift and flow, whereas broader and shallower depressions such as the Eromanga Basin, with its normal faults and thinning of drape folds, appear to be tensional in origin. However, the distribution of deposition and erosion indicated by Mayne’s (1976) charts suggests that, superimposed on this somewhat simplistic picture, there were Middle and Late Permian uplifts south of the central corridor which were followed by continent-wide Triassic uphft and subsequent Jurassic to Holocene collapses reminiscent of Silurian, Devonian and Early Carboniferous events. As the continent drifted one might also expect that its sides, as distinct from its leading and trailing edges, should undergo changes. Features such as the Exmouth and Queensland Plateaux (Figs. 1 and 2; Branson, this Symposium) may have Cainozoic components so generated. Similar pre-Cainozoic features may be recognizable in New Guinea. ACKNOWLEDGEMENTS

The authors are grateful to many colleagues for information and comment, and to the Bureau of Mineral Resources Drawing Office for the figures. We thank especialIy Dr. G.E. Wilford for valuable discussion and advice. Critical comments offered by Drs. P.R. Evans, M.J. Rickard and E. Scheibner are also gratefully acknowl~ged. REFERENCES Anfiloff, W. and Shaw, R.D., 1973. blocks in separate Australian shield itors), Proceedings of Symposium in position. Univ. N.S.W., Sydney. BMR (Bureau of Mineral Resources), of Australia and adjacent regions, (unpublished). BMR (Bureau of Mineral Resources), berra.

The gravity effects of three large uplifted granulite areas. In: R.S. Mathur and P.V. Angus-Leppan (Edon Earth’s gravitational field and secular variations 1974. Summary of Phanerozoic sedimentary basins 1974. Rec. Bur. Miner. Resour. Aust., 1974/178 1976. Gravity Map of Australia,

1 : 5 000 000. Can-

381 Boeuf, M.G. and Doust, H., 1975. Structure and development of the southern margin of Australia. APEA J., 15(l): 33-43. Burke, K.C. and Wilson, J.T., 1976. Hot spots on the Earth’s surface. Sci. Am., 235 (2): 46-57. Cameron, J.C., 1967. Australia’s oil and gas potential -a review of the main sedimentary basins. Proceedings of the Seventh World Petroleum Conference, Mexico, 1967. Elsevier (London), 2: 151-160. Chang, K.H., 1975. Unconformity-bounded stratigraphic units. Geol. SOC. Am. Bull., 86: 1544-1552. Day, R.W., Cranfield, L.C. and Schwarzbock, H., 1974. Stratigraphy and structural setting of Mesozoic basins in southeastern Queensland and northeastern New South Wales. In: A.K. Denmead, G.W. Tweedale and A.F. Wilson (Editors), The Tasman Geosyncline - A Symposium. Geol. Sot. Aust. Queensl. Div., Brisbane, pp. 319-362. Deighton, I., Falvey, D.A. and Taylor, D.J., 1976. Depositional environments and geotectonic framework: southern Australian continental margin. APEA J., 16( 1): 25-36. Devine, S.B. and Youngs, B.C., 1975. Review of the Palaeozoic stratigraphy and petroleum potential of northern South Australia. APEA J., 15(l): 45-54. Dickins, J.M. and Malone, E.J., 1973. Geology of the Bowen Basin, Queensland. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 130. Doutch, H.F., 1972. The concept of transitional tectonism in Australia. Abstracts, Geol. Sot. Aust. Joint Specialists Groups Meetings, Canberra, Feb. 1972. Symposium E. Doutch, H.F., 1974. Legend recommendations, Tectonic Map of Asia and the Far East. Bull. Comm. Geol. Map World, 15: 20-49. Doutch, H.F., 1976a. Formal lithostratigraphy for sedimentary rocks: a code based on some underdeveloped principles. J. Geol. Sot. Aust., 23(l): 67-72. Doutch, H.F., 1976b. The Karumba Basin, northeastern Australia and southern New Guinea. Bur. Miner. Resour. J. Aust. Geol. Geophys., l(2): 131-140. Edgerly, D.W. and Crist, R.P., 1974. Salt and diapiric anomalies in the Southeast Bonaparte Gulf Basin. APEA J., 14(2): 95-106. Evans, P.R., 1977. Petroleum geology of western New South Wales. APEA J., 17(l): 4249. Falvey, D.A., 1974. The development of continental margins in plate tectonic theory. APEA J., 14(l): 95-106. Forman, D.J. and Shaw, R.D., 1973. Deformation of the crust and mantle in Central Australia. Bull. Bur. Miner. Resour. Geol. Geophys. Aust. Bull., 144. G.S.A. (Geological Society of Australia), 1971. Tectonic Map of Australia and New Guinea, 1 : 5 000 000. Sydney. Jensen, A.R., 1975. Permo-Triassic stratigraphy and sedimentation in the Bowen Basin, Queensland. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 154. 1971. Timing and co-ordination of erogenic, epeirogenic and eustatic Johnson, J.G., events. Geol. Sot. Am. Bull., 82: 3263-3298. Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of southwestern Australia - a review. J. R. Sot. West Aust., 56 (1,2): 5-15. Laws, R.A. and Kraus, G.P., 1974. The regional geology of the Bonaparte Gulf-Timor Sea area. APEA J., 14(l): 77-84. Leslie, R.B., Evans, H.D. and Knight, C.L. (Editors), 1976. Petroleum. Monograph NO. 7. In: Economic Geology of Australia and Papua New Guinea. Australas. Inst. Min. Metall., Proc. Mayne, S.J., 1976. Australian Phanerozoic correlation charts - Adelaidean to Recent. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 183. Meyerhoff, A.A. and Meyerhoff, H.A., 1972. “The New Global Tectonics”: Major Inconsistencies. Bull. Am. Assoc. Pet. Geol., 56(2): 269-336. Olgers, F., 1972. The geology of the Drummond Basin, Queensland. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 132.

388 Playford, P.E., Cope, R.N., Cockbain, G.H., Low, G.H. and Lowry, D.C., 1975, Phanerozoic. In: Geology of Western Australia. Geol. Surv. West Au&., Mem., 2: 223-432. Powell, D.E., 1976. The geological evolution and hydrocarbon potential of the continental margin off northwest Australia. APEA J., 16(l): 13-23. Scheibner, E., 19’73. A plate tectonic model of the Palaeozoic tectonic history of New South Wales. J. Geol, Sot. Au&, 20{4): 405-426. Scheibner, E., 1976. Explanatory Notes on the Tect.onic Map of New South Wales, Geol. Surv. N.S.W., Sydney, 283 pp. Sloss, L.L. and Speed, R.C., 1974. Relationships of cratonic and continental margin tectonic episodes. Spec. Publ. Sot. Econ. Paleontol. Miner. Tulsa, 22: 98-119. Smith, K.G., 1972. Stratigraphy of the Georgina Basin. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 111. Tanner, J.J., 1966. Distribution of Palaeozoic rocks beneath the Great Artesian Basin, Queensland. APEA J., 6: 116-120. Veevers, J.J., 1976. Early Phanerozoic events on and alongside the Austral~ian-Antarctic Platform. J. Geol. Sot. Aust., 23(2): 183-206. Veevers, J.J. and Evans, P.R., 1975. Late Palaeozoic and Mesozoic history of Australia. In: K.S.W. Campbell (Editor), Gondwana Geology. Third Gondwanaland Symposium, Canberra, 1973, pp. 579-607. Visser, W.A. and Hermes, J.J., 1962. Geological Results on the Exploration for Oil in Netherlands New Guinea. Staatsdrukkerij en Uitgeverijbedrijf, The Hague. Wellman, P., 1976. Gravity trends and the growth of Australia: a tentative correlation. J. Geol. Soe. Aust., 23(l): 11-14. Wellman, P. and McDougall, I., 1974a. Cainozoic igneous activity in eastern Australia. Tectonophysics, 23: 49-65. Wellman, P. and McDougall, I., 1974b. Potassium-argon ages on the Cainozoic volcanic rocks of New South Wales. J. Geol. Sot. N.S.W., X(3): 247-272. Wells, A.T. and Richter-Bernberg, G., 1976. Evaporites in Australia. Bur. Miner. Resour. Aust. Rec., 1973/170 ~unpublished). Wells, A.T., Forman, D.J., Ranford, L.C. and Cook, P.J., 1970. Geology of the Amadeus Basin, Central Australia. Bull. Bur. Miner. Resour. Geol. Geophys. Au&., 100.