Australian Jurassic sedimentary and fossil successions: current work and future prospects for marine and non-marine correlation

Abstract

Strata of Jurassic age occur extensively across onshore Australia, but they are predominantly of non-marine origin. Marine Jurassic strata have only limited onshore exposure in northwestern and central-western Australia, with thick marine sequences lying offshore on the North West Shelf. The richest petroleum province in Australia is located at the shelf's southern end, where the Dingo Claystone represents an important source rock for oil and gas. By and large, non-marine deposits, including economic coals, are distributed in the eastern states. Jurassic stage boundaries, in the main, are poorly constrained with respect to the Australian sedimentary succession. New work on microfossils, plants, fish, and zircon dating is providing a basis for improved correlation across Australian basins, with overseas successions, and recent international IUGS geologic timescales.

Keywords:

• Jurassic
• eastern Gondwana
• plants
• palynology
• vertebrates
• environmental settings

Introduction

Jurassic deposits are extensive in several Australian basins (Figs. 1, 2). In the west, they are located in the onshore Bonaparte, Canning, Carnarvon, and Perth basins and in the offshore Westralian Superbasin, which comprises the Northern Bonaparte, Browse, Roebuck, and Northern Carnarvon basins. In eastern and central-eastern Australia, they are embraced by the Laura, Carpentaria, Eromanga, Surat, Mulgildie, Clarence-Moreton, and Nambour basins. In South Australia, they are represented in the Polda and Bight basins, and the isolated deposits of the Rhaeto-Liassic Leigh Creek Coal Measures. In southeastern Australia, the oldest deposits of the Otway and Gippsland basins are probably of latest Jurassic age (Burger & Shafik 1996). These successions were mostly deposited in fluvial sedimentary systems.

Fig. 1 Onshore and offshore Australian basins containing Jurassic sediments (prepared by Geological Survey of Queensland, courtesy of the Information Development and Analysis Services Group, Geoscience Australia).

Fig. 2 Contd.

Sedimentation was not entirely continuous through the period, as widespread hiatuses occurred at its beginning (largely during the Hettangian) and during the latest Middle–early Late Jurassic. In eastern Australia, the earlier unconformity is present in the western Clarence-Moreton basin and in basins further to the west, but in the eastern Clarence-Moreton basin, a complete section across the system-period boundary appears to be present (McKellar in press). The geographic and stratigraphic extent of these hiatuses is presently not well defined. In places (e.g. in the Surat and Eromanga basins), the uppermost Jurassic is also represented by a hiatus. Moreover, in some basinal areas on or near the eastern continental margin (Nambour, northern Clarence-Moreton basins), Upper Jurassic strata are missing entirely. The hiatus extends earlier to the mid- to late Middle Jurassic in the northern Clarence-Moreton and northern Nambour basins and to the late Early Jurassic in the southern Nambour basin (e.g. McKellar in press).

Forest mires that developed into coal deposits were established in several basins during the Early to Middle Jurassic (Fig. 2). The Walloon Coal Measures, which were deposited during the latter epoch in the Clarence-Moreton and Surat basins, are an important source of thermal coal, and also (in the Surat basin) coal seam gas, commercially exploited since January 2006. Contrastingly, in the northern Nambour basin, the Lower-Middle Jurassic Tiaro Coal Measures, which are extensively intruded and vary considerably in rank, have been considered uneconomic, although they have been mined previously for graphite and are being explored presently for economic coal. The uppermost Triassic–Middle Jurassic succession preserved in this northern area of the Nambour Basin was previously included in the Maryborough Basin (now restricted to Lower Cretaceous strata). For summaries of the distribution and properties of Australia's Jurassic coals, see Goscombe & Coxhead (1995) and Sappal & Suwarna (1997).

From 1984 to 1996, the Bureau of Mineral Resources (renamed the Australian Geological Survey Organisation, AGSO, in 1992; now named Geoscience Australia, GA) compiled and produced a series of palaeogeographic atlases of Australia for the Phanerozoic Eon, as a succession of time-slice maps for most periods. The first volumes were published in 1988, with the Jurassic assessment by Bradshaw & Yeung (1990, 1992) coming later. More recently, the entire set was published on CD-ROM (Geoscience Australia 2002) and, presently, the Palaeo Atlas is freely available online at http://www.ga.gov.au/multimedia/palaeo/html/palaeo.html

The first Australian Jurassic fossils were found in the early nineteenth century by the pioneer explorers and scientists, Thomas Mitchell (in 1838) and J.W. Gregory (in 1849), but the fossils' ages were not clarified until much later (Burger & Shafik 1996; Grant-Mackie et al. 2000). Fossil plants and fish have been important from the earliest investigations, but attempts to understand the hydrogeology and hydrocarbon potential of Australia's Jurassic basins did not begin in earnest until the 1950s and 1960s, with ongoing exploration for, and development of, petroleum and coal/coal seam gas giving impetus to continuing palynostratigraphic studies (e.g. McKellar in press) and PhD project work [e.g. by Daniel Mantle at the Department of Earth Sciences, University of Queensland, on the palynology, sequence stratigraphy and palaeoenvironments of Middle to Upper Jurassic strata in the Bayu-Undan (gas condensate) Field, Timor Sea region (see below); and Natalie Sinclair, Department of Earth and Marine Sciences, Australian National University, Canberra, on the sequence stratigraphy and palynostratigraphy of the Late Jurassic in the Jansz Gas Field on the North West Shelf].

The Jurassic is now taken to cover a time range of some 54 million years, from 199.6–145.5 Ma, based on the international geologic timescale of Gradstein et al. [2004; abbreviated here to GTS (2004), updated by Ogg et al. 2008, abbreviated to GTS (2008); Fig. 2]. The period incorporated a broad interval of marine transgression in most parts of the world (Haq et al. 1987; Hallam 1996; Haq & Al-Qahtani 2005), but eastern Australia predominantly remained above sea level (Bradshaw & Yeung 1990, 1992; Burger & Shafik 1996). Eastern Australian basins contain many hundreds of metres of continental strata, which thus lack the appropriate marine microplankton and invertebrate indices to enable ready correlation with marine rocks in Western Australia and overseas, and with international chronostratigraphic stages. Hill & Maxwell (1967, p. 55) noted thin ferruginous-oolite and associated beds rich in acritarchs in Lower Jurassic (Toarcian) strata of eastern Australia (Fig. 2), but the earlier inferred marine influence for these horizons has been discounted; absence of marine fossils and sedimentologial evidence imply a lacustrine environment (Cranfield et al. 1994; Grant-Mackie et al. 2000; McKellar in press).

Grant-Mackie et al. (2000) reviewed the published data on the biota and palaeobiogeography of the Australasian Jurassic and concluded that the climate was warm, deserts were few, and there were no polar icecaps; dinosaurs were the dominant land vertebrates and, in the air, by the Late Jurassic, there were pterosaurs and early birds while conifers and pteridosperms dominated the terrestrial floras. McKellar (1996, 2004, in press) has also assessed the changes in Australian palaeogeography, climate and floras from the late Palaeozoic to the early Mesozoic, and provided largely geophysical and tectonic explanations for the sequence of events leading into the beginning of the Jurassic. Based on his interpretations, the Australian region was rotated through the Permo-Triassic to earliest Jurassic into progressively lower and warmer latitudes. At the very beginning of the Jurassic (Hettangian), the palynofloral evidence from the eastern Clarence-Moreton basin suggests that there was a transition from the mesothermal climate of the Late Triassic of southeastern Queensland to a slightly warmer and more monsoonally influenced climate in the early Sinemurian (McKellar in press). These latitudinal/climatic changes enabled thermophilic and xeromorphic cheirolepidiacean conifers to thrive there during most of the Early Jurassic, under seasonally dry, warm conditions. Before the end of the epoch, the climate had become consistently humid, and remained so for the remainder of the Jurassic, with a mesothermal (warm temperate) climate becoming well established in the Late Jurassic, in accord with relocation into somewhat higher latitudes.

A resurgence of interest in the Australian Mesozoic floras has followed the remarkable discovery of the extant Wollemi Pine in the Blue Mountains Area, west of Sydney, NSW, in 1994. This discovery has particularly prompted intense study of the 200-million-year-plus history of the once cosmopolitan, but now relictual family Araucariaceae. Furthermore, discovery of new fossil assemblages has expanded the potential biogeographic, palaeoenvironmental and phylogenetic application of Australian Jurassic plants (Clifford 1998; Pattemore 2000; Pattemore & Rigby 2005; McLoughlin & Vajda 2005; Jansson et al. 2008b; McLoughlin & Pott 2009).

In the marine Jurassic sequences of Western Australia, belemnites have been recorded from the Middle Jurassic (Bajocian), but are found far more commonly in Upper Jurassic strata; ammonites from the lower Bajocian Newmarracarra Limestone, Champion Bay Group (Perth basin), allow correlation with the European standard biozones (Burger & Shafik 1996; Grant-Mackie et al. 2000). Marine vertebrates are less well known in the Jurassic of Australia (Long 1998; Grant-Mackie et al. 2000), and most vertebrate work in recent years has been conducted on non-marine, lower vertebrates (see below).

This paper provides an update on the state of work on the Jurassic in Australia, with particular focus on palaeobotanical–palynological and palaeoichthyological studies. It also highlights the current problems and deficiencies in dating and correlating Australian Jurassic strata that need to be addressed by future research.

Geological–palaeogeographical setting of Australia

The shifting pattern of environments through the Jurassic was primarily influenced by changes in global sea level/base level, changes in palaeogeographic location, and by the new tectonic regime that became established early in the period (Bradshaw & Yeung 1990, 1992; McKellar in press). These parameters were controlled not only by the break-up of Pangaea and, within its southern region, Gondwana, but also, importantly, a change in direction of rotation of Pangaea around the beginning of the Jurassic.

Tectonism and continental rotation

Australia was thermally emergent, high-riding and relatively stable in the Early Jurassic (Bradshaw & Yeung 1990). The break-up of eastern Gondwana began during the early Late Jurassic with the Argoland rifting event (along northwestern Australia), represented by a widespread unconformity associated with thermal uplift, normal and strike-slip faulting, rift volcanism and erosion (Bradshaw & Yeung 1990; Ramsay & Exon 1994; Exon & Colwell 1994; Exon & von Rad 1994). This tectonism, according to the cited authors, resulted in the genesis of the Argo Abyssal Plain by commencement of sea-floor spreading at 155 Ma (latest Oxfordian) when the Argo Landmass began to rift away prior to drifting northwestwards. More recently, Heine & Müller (2005) have indicated that formation of the northern Gascoyne Abyssal Plain, northwest of the Exmouth Plateau and west of the Argo Abyssal Plain, was also associated with separation of this landmass, said probably to be the West Burma Block of Metcalfe (1999), with the “Argo” spreading ridge continuing around the northern margin of Greater India. Their interpretation of the magnetic anomaly record, based on Gradstein et al. (1994), shows that spreading started with M25 (154.1 Ma) as the first correlatable anomaly in both abyssal-plain areas, and with M26 (155.0 Ma) as the oldest identifiable in the southern Argo Abyssal Plain. Largely, however, the Gascoyne Abyssal Plain is related to the slightly younger Greater India–Australia break-up event (Heine & Müller 2005). Further, according to Gradstein & von Rad (1991), the Argo break up unconformity preceded the onset of sea-floor spreading by about 5–10 million years. Effects of this fragmentation were widespread. They are not only evident in all basins of the Westralian Superbasin (Fig. 1), but are also recorded in the Nepal Himalaya Thakkhola region by a “Callovian-Oxfordian” hiatus and the occurrence of a ferruginous oolite horizon, the distribution of which embraces southern Tibet and parts of the Indian subcontinent (Klootwijk 1996). During the Triassic and Jurassic, these areas (including Thakkhola) and, to the east, the Exmouth Plateau, formed part of a broad continental shelf along the south Tethyan continental margin of northeastern Gondwanan (Gradstein & von Rad 1991; Gradstein et al. 1992; Exon & von Rad 1994; Ogg & von Rad 1994). Later, further seafloor spreading in the Gascoyne and Cuvier abyssal plains commenced around 136–131.9 Ma (Early Cretaceous; Veevers 2000) as Greater India rifted to the west. Rifting continued in an anticlockwise sense around Australia until the Paleogene.

Although there are relatively few Jurassic intrusive and extrusive igneous rocks exposed in eastern Australia, it is clear that there was considerable volcanic activity near the eastern margin, based on the large volume of pyroclastic and epiclastic material accumulated in the region's sedimentary basins at that time. Much of this volcanism might have occurred from extensional/incipient-rifting activity on the Lord Howe Rise–Norfolk Ridge–New Zealand terranes, which in the Jurassic were united to Australia's eastern margin, only detaching to the east during the Cretaceous–Paleogene (Veevers 2000). Fielding (1996) and Yago & Fielding (1996), in considering the distribution of volcanic-ash beds in the Middle Jurassic Walloon Coal Measures (Clarence-Moreton basin), suggested that the volcanic sources might have been intra-basinal. The meridional depocentre in the eastern Clarence-Moreton basin coincides approximately with the zone encompassing the greatest concentration of volcanic-ash deposits and possibly coeval volcanic centres, lavas and intrusives of bimodal mafic and felsic composition, leading them to propose that this belt might represent the site of a failed rift. A former commonly held view maintained that the volcanic debris resulted from volcanism associated with a subducting-plate margin and arc to the east during the mid-Late Jurassic (Exon 1976; Veevers 1984; Hawlader 1990; He & Conaghan 1994).

Australia/eastern Gondwana was rotated clockwise into higher southern latitudes through most of the Jurassic (Klootwijk 1996). This process followed the anticlockwise rotation of the region (and Pangaea in general) during the Permo–Triassic–earliest Jurassic, which brought Australia, more or less progressively, into lower palaeolatitudes. These latest Palaeozoic–early Mesozoic changes in latitude are indicated by palaeomagnetic data and accord not only with floristic changes during the Permian to earliest Jurassic, but also the development of Rhaetian reef structures on the northwestern margin (Klootwijk 1996; McKellar 2004, in press). The change from clockwise to anticlockwise rotation is also implied by the distinct Triassic–Jurassic loop in the Indian apparent polar wander path (APWP), with an apex dated approximately as latest Triassic–earliest Jurassic (Klootwijk 1996, fig. 19). The apices of this pole-path loop and equivalent features in other Pangaean APWPs (Piper 1987, p. 304, fig. 11.2; Sichler & Perrin 1993, pp. 13, 22–25, figs. 10, 11; Gordon et al. 1984; Ekstrand & Butler 1989; Bazard & Butler 1991; Molina-Garza et al. 2003) collectively indicate a global lithospheric event and have been held to reflect a major change in the direction of true polar wander (TPW) and, therefore, in the global pattern and distribution of crustal stresses (McKellar 2004, in press). This interpretation, relating the changing direction of rotation of Pangaea to TPW events, is supported by the work of Steinberger & Torsvik (2008) and matches an interval of global plate reorganisation (e.g. Korsch & Totterdell 1996). In Greater Eastern Australia, the changes in crustal stress along the ocean-continent interface led to termination of the compressional regime that dominated the Permo-Triassic, with its associated “dextral rotational force couple” then being replaced by a sinistral system of shear (Evans & Roberts 1980, p. 325), although the latter authors dated the change as Norian. However, the timing of the change in tectonic style and contemporaneous floristic changes (with attendant climatic signatures) in eastern Australia suggests that the anticlockwise rotation and northward displacement of the region continued into the Hettangian, before being reversed in the Sinemurian (McKellar in press).

Eastern Australian Late Permian–Triassic tectonism encompassed a series of compressional pulses that emanated from the Panthalassan hemisphere and, for eastern Australia, has been referred to, with the exception of further deformations in the Norian (Late Triassic) and latest Triassic–earliest Jurassic, as the Hunter–Bowen Orogeny (e.g. McKellar in press). On a broader scale, Du Toit (1937, p. 63, 79–80, fig. 10) coined the contractional term, Samfrau Geosyncline/Orogenic Zone, to represent the “lengthy trough” that existed along the Gondwanan margin of South America–South Africa–Australia, in which strata were subjected to “several pulses” of “intermittent compression and upheaval” at this time. However, the Hunter–Bowen Orogeny, which was previously considered to have terminated about the end of the Middle Triassic (e.g. Fielding 1996; Stephens et al. 1996), continued into the beginning of the Jurassic, as similarly recognised for the Cape Orogeny (Cape Fold Belt, South Africa), which embraced a comparable series of deformational events that has been identified with the aid of ⁴⁰Ar/³⁹Ar step-heating analysis (Hälbich et al. 1983). Overall, the tectonic system that encompassed these compressional episodes has been viewed as being TPW-induced, consequent to tectonism generated by a changing geoid as rapid rotation-axis adjustments occurred during the Permian–earliest Jurassic (McKellar 2004, in press).

As compressional relaxation occurred in eastern Australia with the beginning of the clockwise rotation, the subduction zone to the east apparently retreated. The new stress regime controlled sedimentation and structure during the Early Jurassic (Evans & Roberts 1980). Moreover, the changing patterns of global lithospheric stress in the latest Triassic–earliest Jurassic might have assisted rifting of the Pangaean supercontinent. Significantly, onset of this rifting was a Pangaea-wide event, which facilitated considerable heat loss from the Pangaean thermal anomaly. The modern relic of this process is purported to be the long-wavelength African-eastern Atlantic residual geoid high (Anderson 1982, 1989). Accumulation of heat below, and thermal elevation of, the massive, mantle-insulating supercontinent created a mass anomaly in Earth's rotation, since thermal elevation places mass at a particular latitude at a greater distance from Earth's rotation axis, thus increasing the contribution to the moment of inertia at that latitude. Such a process effects a change in the location of the planet's principal axis of inertia, with which the spin axis needs to be aligned for rotational stability (Gold 1955; Anderson 1989). These were the primary influences that seemingly controlled the anti-clockwise rotation and northwards displacement of Pangaea during the latest Palaeozoic and early Mesozoic, a long-drawn-out adjustment that was completed in the earliest Jurassic, that point in time being marked by the above-cited Indian pole-path loop apex (McKellar 2004, in press). Soon after the beginning of the Jurassic, the Australian region was located in the lowest latitudes that it was to occupy for the entire duration of the latest Palaeozoic and Mesozoic, and more of Pangaea was located in low to middle latitudes than at any other time in the supercontinent's history. There would have been an equal distribution of Pangaea, with its underlying mass anomaly, its peripheral subduction zones (also representing geoid anomalies, but of intermediate scale), and other mass anomalies about the equator at this time – a requirement of the planet's physical system to minimise kinetic energy of rotation. This largely accounts for the traditional view, from a global perspective, that Jurassic climates were warm and highly equable (e.g. Barnard 1973; White 1986). No landmass occupied the rotation poles at the beginning of the period, as TPW located geoid highs (and mass excesses) about the equator and geoid lows about the geographic poles. That a major period of TPW did occur during the latest Palaeozoic–early Mesozoic has been strongly advocated by Anderson (1982, 1989, 2007) and subsequently maintained by Marcano, van der Voo, & Mac Niocaill (1999) and Steinberger & Torsvik (2008).

Basin development

Mid-Mesozoic sediment accumulation in the broad epicratonic basins of eastern Australia began, on a limited scale, in the latest Triassic (Rhaetian), but tectonism, involving the final compressional pulse of the above-cited Permo–Triassic tectonic regime, gave rise to a widespread unconformity about the beginning of the Jurassic. Along the northwestern Australian margin, the end-Triassic unconformity locally embraces the Hettangian, although sedimentation may have continued in some areas without interruption across the Triassic–Jurassic boundary (Bradshaw & Yeung 1990, 1992; Exon & Colwell 1994). The depositional break in northwestern Australia has been associated primarily with the commencement of rifting, with rift volcanics of latest Triassic–earliest Jurassic age being erupted in areas of future break-up. In eastern Australia, the Hettangian–earliest Sinemurian unconformity is present in the western Clarence-Moreton Basin and basins further west, but, in the eastern Clarence-Moreton Basin and perhaps also in the coastal Nambour Basin, there was apparently continuous sedimentation across the period boundary (McKellar in press). Deposition recommenced elsewhere in the early Sinemurian, greatly increasing throughout the Early Jurassic. It expanded in a westerly direction, with sediments ultimately accumulating in the western Clarence-Moreton, Surat, Mulgildie, and Eromanga basins (McKellar in press; Fig. 2).

Where such a hiatus is present in eastern Australia, it delimits the change from the Alisporites/Falcisporites Microflora, representative of the temperate Dicroidium Flora, to palynofloras of Jurassic aspect dominated by cheirolepidiacean pollen (Classopollis), reflecting the assumed shift to somewhat lower palaeolatitudes and warmer climates (e.g. Grant-Mackie et al. 2000). Where the hiatus is apparently absent (eastern Clarence-Moreton and probably Nambour basins), the Hettangian and earliest Sinemurian embrace a transitional palynoflora, although it is, by far, more closely allied to the Alisporites Microflora (based on data from N. de Jersey and J. McKellar).

A significant regional unconformity is also represented at the boundary between the Birkhead Formation and Adori Sandstone in the Eromanga Basin, and most likely at the corresponding Walloon Coal Measures–Springbok Sandstone boundary in the Surat Basin, based on palynostratigraphic assessment and lithostratigraphic extrapolation. This break has been taken to represent the Callovian–Oxfordian Argoland break-up unconformity at 155 Ma (latest Oxfordian) and extensional (incipient-rifting) influences in eastern Australia (discussed above; McKellar in press).

Six major cycles of sedimentation have been recognised in the Surat Basin Jurassic-Cretaceous succession, which are represented to a greater or lesser degree in adjoining basins, depending on the extent of the succession preserved (Exon 1976, 1980; Exon & Burger 1981). Each cycle commenced with sandy deposits of high-energy braided river systems and terminated with mudrock-dominated deposits of low-energy meandering rivers, lakes, and mires. Ponding in the Clarence-Moreton, Surat, and Mulgildie basins at the end of one such cycle in the Middle Jurassic led to the development of extensive forest-mire systems now represented by the Walloon Coal Measures (Fig. 2). These large-scale sedimentary cycles (some spanning >10 Ma) probably developed in response to episodic flexure along the eastern continental margin, because of thermal doming and incipient rifting; and extension/incipient-rifting within the Clarence-Moreton Basin (discussed above). In contrast, the Surat, Clarence-Moreton, and northern Nambour (“Maryborough”) basins were incorrectly interpreted by Jones and Veevers (1983, 1984) in terms of a foreland-basin system; they attributed the sedimentary cycles to periodic tectonic uplift in the orogen, and maintained that the cycles correlated with global sea-level movements to an extent that suggests global links between tectonism and eustasy. On the other hand, Exon & Burger (1981) and Burger (1986, 1989) related changing patterns of sedimentation directly to sea-level movements, using the most likely ages of associated palynofloras as a guide to correlate with the global sea-level curve of Vail et al. (1977). A slight modification of these relationships, based on other curves (Vail & Todd 1981; Haq et al. 1987), was subsequently adopted (Burger 1994a, 1994b; Burger & Shafik 1996). However, ages assigned to Jurassic formations in the Surat Basin interpreted from correlations with sea-level curves, differ from ages obtained via correlation of their attendant palynofloras with those in New Zealand that have been accurately dated by associated marine faunas (de Jersey & Raine 2002; McKellar in press). This suggests that the published “global” sea-level curves may not be fully reflected in the pattern of eastern Australian sedimentation. Nonetheless, the geographically extensive deposition of oolitic ironstone in southeastern Queensland in the Surat, Mulgildie, Clarence-Moreton, and Nambour basins (e.g. Grant-Mackie et al. 2000) does appear to correlate with the early Toarcian peak in global sea level (McKellar in press). Such deposits were apparently formed in warm humid climates and generally in association with conditions of rising base level (Hallam 1975; Frakes et al. 1992, p. 63).

Palaeogeography and palaeoclimate

A wealth of palaeontological evidence has been compiled on the Australasian Jurassic and interpreted palaeogeographically and palaeoclimatically (Bradshaw & Yeung 1990, 1992; McKellar 1996, 2004, in press; Grant-Mackie et al. 2000). However, Australia's palaeolatitudinal location during the Jurassic is still not well constrained. The Australian Mesozoic APWP has been little studied since publication of the largely conceptual pole path of Embleton (1981, Fig. 3), which was based on a few averaged poles (Klootwijk 1996). Klootwijk (1996) indicated that the Australian pole path shows the general outline of a (Late Triassic–) Early Jurassic loop, followed by a Late Jurassic–Early Cretaceous loop. The Indian APWP is considerably better established and is characterised by an extensive Triassic–Jurassic loop with an apex around the Triassic–Jurassic boundary, followed by a Jurassic–Early Cretaceous loop with an apex around the Jurassic–Cretaceous boundary. The Indian Triassic–Jurassic loop is far more extensive than the Australian loop, suggesting that the apex of the latter is presently undefined. The Indian Jurassic–Early Cretaceous loop is less extensive than the Australian loop, leading to the conclusion that the former is possibly underdetermined. These palaeomagnetic data indicate that, during the Jurassic, eastern Gondwana rebounded towards higher southern latitudes. However, the Australian and Indian pole paths are no more than broadly determined for the Jurassic and do not provide fine detail of this southward movement (Klootwijk 1996). Hence, palaeogeographic reconstructions showing Australia's location during the period can be regarded as providing only a general picture. Nonetheless, Australia's rotation to higher (and cooler) latitudes through the Middle to Late Jurassic is reflected by the palynofloristic change from the Araucariacean Phase to the Podocarpacean Phase and the attendant onset of the Microcachryidites Microflora [of Helby et al. (1987); see below].

Fig. 3 Representative Australian Jurassic plant macrofossils. A. Dictyophyllum sp. (dipteridacean fern), QMF12659. B. Sagenopteris nilssoniana (Brongniart) Ward (caytonialean gymnosperm), QMF12971. C. Pachydermophyllum sp. (“seed-fern”), GSQF13548. D. Masculostrobus sp. (conifer microsporangiate cone), AMF78330. E. Palissya ovalis Parris, Drinnan & Cantrill (palissyacean gymnosperm), UQF79695. F. Taeniopteris spatulata McClelland (pentoxylalean gymnosperm), UQF79721. G. Hausmannia sp. cf. H. deferrariisii Feruglio (dipteridacean fern), UQF79687. H. Podozamites jurassica White (araucariacean conifer), AMF59990. I. ?Rissikia talbragarensis White (?podocarpacean conifer), AMF72408. J. Rintoulia sp. (“seed-fern”), AMF127292. Specimens from Gatton Sandstone, Pliensbachian, Clarence-Moreton basin (A, B); Injune Creek Group, Bathonian–Callovian, northern Surat basin (C); Walloon Coal Measures, Bathonian–Callovian, Clarence-Moreton basin (D–G); and Talbragar fossil beds, latest Oxfordian–Tithonian, southern Surat basin (H–J). Scale bars = 5 mm.

This transition from the Araucariacean to the Podocarpacean Phase was viewed by Grant-Mackie et al. (2000), who supported the general (global) palaeoclimatic model proposed by Frakes et al. (1992), as a time of climate cooling. Based on Australian palynofloral criteria similar to those considered by Grant-Mackie et al. (2000), McKellar (1996, in press) had likewise recognised this time as a period of cooling, but only in a regional context. Grant-Mackie et al. (2000) proposed that the development of a proto-Indian Ocean, in the form of the Argo Abyssal Plain, contributed to the progressive rise in mean sea level that continued into the Early Cretaceous. This sea-level rise was said to have expanded the area of shallow epicontinental seas and hence the available extent of the maritime heat sink, transferring heat to the oceans and giving rise to generally cooler and more equable global temperatures (although the cooling was possibly ameliorated by an increase in atmospheric CO₂) during the Middle and Late Jurassic.

The Araucariacean–Podocarpacean Phase transition, reflecting the purported climatic cooling in eastern Gondwana, suggests that much of the palaeolatitudinal motion revealed by Klootwijk (1996) must have occurred quickly during the Late Jurassic, probably following commencement in the latest Oxfordian of sea-floor spreading associated with separation of the Argo Landmass on the northwestern margin (McKellar in press). In the Northern Hemisphere, there was a northwards shift of floral zones across Eurasia during the Late Jurassic, which was contrastingly interpreted by Vakhrameev (1964), Krassilov (1981), Hallam (1985) and Vajda (2001) as pointing to a general warming trend. Ziegler et al. (1993), however, considered that these motions have no direct implications for global change as they are relative only to the land area and not to palaeolatitude. They indicated that by Middle to Late Jurassic times, a clockwise southern motion of the continents had replaced a previous general northward movement, thus supporting Klootwijk's (1996) interpretation for the eastern Gondwanan sector and accounting for the differing climatic trends in opposing hemispheres during the Late Jurassic (McKellar in press).

Timescales and boundaries

AGSO published An Australian Phanerozoic Timescale (Young & Laurie 1996), in which Burger & Shafik (1996) detailed the Australian Jurassic, including biostratigraphic zonation and international correlation. However, since publication of GTS (2004), the emphasis in GA, with its Timescales and Virtual Centre of Economic Micropalaeontology and Palynology (VCEMP) Project, has been not only to maintain microfossil biozonations and develop them further, but also to define the relationship of Australian sequences with that timescale, rather than to update and maintain independent charts, nonetheless continuing to place particular emphasis on those parts of the stratigraphic column, where economic resources are important.

GTS (2004) (see also Ogg et al. 2008) defines the Middle Jurassic as spanning a considerably shorter time interval compared to previous timescales. Although GTS (2004) (see also GTS 2008) is the most researched and accurate chronostratigraphic scheme to date, the definitions of many stage boundaries remain problematical, and most remain informally defined, largely based on European usage. Hence, no stage boundary in Australia is well constrained, although current work is improving the biostratigraphic resolution of the Rhaetian–Hettangian (Triassic–Jurassic) and the Hettangian–Sinemurian boundaries in eastern Australia (work of N. de Jersey and JMcK in progress in eastern Clarence-Moreton Basin, see below). It is difficult to determine the age of biostratigraphic zones and hence lithostratigraphic units representing them in the Jurassic of Australia, at the level of stages, because the system is dominated by continental sequences. Marine invertebrate faunas and dinoflagellate assemblages that provide good biostratigraphic control via international correlation are recorded only in Western Australia. It has been largely by establishing relationships between the marine and continental biostratigraphies via analysis of spore–pollen assemblages that correlations and age determinations have been improved across the country. Dating of lithostratigraphic units in eastern Australia has also been facilitated by spore–pollen correlation with New Zealand, where palynological zones have been well dated using marine invertebrates (de Jersey & Raine 2002; McKellar in press). Generally, however, stage boundaries appear to fall within biostratigraphic zones, hence the indication above that, by and large, these chronostratigraphic units can not be well delimited.

Palaeontology

Plant macrofossils

Jurassic macrofloras (Fig. 3H–J) are widely distributed, but poorly studied in Australia. Based on the more extensive palynological record, three major modifications of Australasian floras are recognisable during the Jurassic: the first somewhat after the beginning of the period; the second in the Toarcian; and the third in the early Late Jurassic (McKellar 1996, in press, Grant-Mackie et al. 2000).

The Triassic–Jurassic transition in Australia is represented by a relatively abrupt decline of the corystosperm-dominated Dicroidium Flora, and the Jurassic is characterised by the rise of conifer and bennettite-dominated floras. However, as noted above, Hettangian strata, present in the eastern Clarence-Moreton Basin (and perhaps also in the Nambour Basin) embrace a transitional palynoflora, which displays significantly closer relationships to the Alisporites/Falcisporites Microflora (the palynofloral representation of the Dicroidium Flora) than to subsequent (Sinemurian–Pliensbachian–earliest Toarcian) palynofloras that are rich in Classopollis. The dominance of Classopollis in mid–Early Jurassic palynofloras points to significant representation of cheirolepidiacean conifers in the vegetation, but macrofossils of this group have not yet been identified with confidence from Australian deposits of this age.

The best-described Early Jurassic floras, generally associated with the later part of the epoch, derive from the Clarence-Moreton and Nambour basins (e.g. Gould 1968, 1971; Rozefelds & Sobbe 1983; Grant-Mackie et al. 2000; Pattemore & Rigby 2005; Jansson et al. 2008b). These Pliensbachian–Toarcian assemblages contain a range of lycophytes, equisetaleans, osmundaceous, dipteridaceous (Fig. 3A), dicksoniaceous and matoniaceous ferns, the pteridosperms Komlopteris and Rintoulia, caytonialeans [Sagenopteris (Fig. 3B) and Caytonia], bennettitaleans (Otozamites spp.), putative ginkgoaleans, small-leafed conifers (Plagiophyllum and Allocladus), and Palissya fructifications.

The fossil floras from Ida Bay and Lune River, in Tasmania, include a broad array of exquisitely permineralised conifers, bennettites, and especially osmundaceous and cyathealean ferns (Gould 1972; Tidwell 1987, 1992; Tidwell & Jones 1987; Tidwell et al. 1987; Tidwell et al. 1989; Tidwell et al. 1991; White 1990, 1991; Tidwell & Pigg 1993). These assemblages have traditionally been ascribed a Late Jurassic age, but radiometric dating has revealed an age of 175 ± 6.4 Ma (Toarcian–Bajocian) for basalts associated with the sediments (Hergt et al. 1989; Bromfield et al. 2007).

Australasian and Gondwanan floras generally were strongly modified over a short transitional phase through the late Early Jurassic; plant assemblage changes of this time have been used as palaeoclimatic indicators (McKellar 1996; Hallam 1996). Most notable was the decline in cheirolepidiacean conifer pollen and the rise in relative abundance of araucarian and podocarp conifers. This transition is matched in the sedimentary record of several eastern Australian basins by the occurrence of one or more beds of oolitic ironstone (e.g. Grant-Mackie et al. 2000) and suggests a significant perturbation of the terrestrial environment (Cranfield et al. 1994). Significantly, these terrestrial changes were roughly coeval with the early Toarcian peak in global sea level (see above, McKellar in press) and the early Toarcian anoxic event in the Tethys Ocean (Fig. 2).

The Walloon Coal Measures and their equivalents in the Clarence-Moreton, Surat, and Mulgildie basins have been considered to be Bajocian–Bathonian in age, based on macrofloral affinity with the Clent Hills Group flora of New Zealand (Grant-Mackie et al. 2000), or Bathonian–Callovian in age, based on palynological evidence. The latter encompasses the oldest records of Contignisporites glebulentus (Fig. 4D) in the latest Temaikan marine succession at Awakino (North Island, New Zealand; de Jersey & Raine 2002) and of Murospora florida, a species not reported from New Zealand but occurring in the late Temaikan of New Caledonia (Grant-Mackie et al. 2000). In terms of international stage divisions, these occurrences (C. glebulentus, M. florida) collectively indicate a Callovian age. However, in the Walloon Coal Measures of the Surat Basin, the two species first appear, in the order cited, part of the way through the succession, although the range of C. glebulentus might extend down to just above the base of the formation (McKellar in press). In comparison, the formation in the southeastern Queensland portion of the adjacent Clarence-Moreton Basin lacks these species and may be somewhat older (Bathonian). Further, the top of the coal measures in eastern Australia is marked by the unconformity between the Middle and Late Jurassic (discussed above).

Fig. 4 Representative Australian Jurassic palynomorphs from the Surat basin, Queensland. A. Dictyotosporites complex Cookson & Dettmann, Walloon Coal Measures, Q354. B. Retitriletes circolumenus (Cookson & Dettmann) Backhouse, Westbourne Formation, Q379. C. Staplinisporites manifestus McKellar, Hutton Sandstone, Q432. D. Contignisporites glebulentus Dettmann emend. Filatoff & Price, Westbourne Formation, Q612. E. Nevesisporites vallatus de Jersey & Paten, Walloon Coal Measures, Q572. F. Foraminisporis dailyi (Cookson & Dettmann) Dettmann, Westbourne Formation, Q583. G. R. watherooensis Backhouse, Westbourne Formation, Q381. H. Leptolepidites verrucatus Couper, Westbourne Formation, Q487. I. Classopollis sp. cf. C. chateaunovi Reyre, Walloon Coal Measures, Q763. J. Ischyosporites punctatus Cookson & Dettmann, Westbourne Formation, Q446. K. Podosporites variabilis Sukh Dev, Walloon Coal Measures, Q735. L. Murospora florida (Balme) Pocock, Westbourne Formation, Q627. M. Araucariacites fissus Reiser & Williams, Walloon Coal Measures, Q759. N. Callialasporites dampieri (Balme) Sukh Dev, Westbourne Formation, Q691. Fig. 4M × 600, all other images approximately × 500. Ages of host units indicated in Fig. 2. Numbers prefixed by “Q” refer to the palynological specimen-locality catalogue of the Geological Survey of Queensland, Department of Employment, Economic Development and Innovation.

The coal measures host a typical Middle Jurassic flora incorporating liverworts, selaginellalean lycophytes, equisetaleans, osmundaceous, marattiaceous, matoniaceous, dicksoniaceous and dipteridaceous ferns (Fig. 3G) and araucarian, podocarpacean, and palissyacean conifers [Araucarites sp., Mataia sp., Allocladus sp., Elatocladus spp., Pagiophyllum sp., Brachyphyllum crassum, Masculostrobus sp. (Fig. 3D), Palissya ovalis (Fig. 3E)], bennettitaleans (Ptilophyllum pecten, Otozamites feistmanteli, Williamsonia sp.), pentoxylaleans (Taenopteris spatulata: Fig. 3F), and some gymnosperms of unknown affinity (Pachypteris and Pachydermophyllum spp.: Fig. 3C) (Tenison-Woods 1882, 1883; Walkom 1917a, 1917b, 1919; Day 1964; Hill et al. 1966; Townrow 1967a, 1967b; Gould 1968, 1975, 1980; Grant-Mackie et al. 2000). Surprisingly, given their abundance in most parts of the middle to high latitudes in both hemispheres at this time, ginkgoaleans have not been recorded in the Middle Jurassic of Australia, the regional climate then being considered too warm for this group to proliferate in lowland settings, as they did in the Late Triassic and Early Cretaceous of the region (McKellar 1996).

The rich macroflora of the Walloon Coal Measures is encompassed by the concept of the Otozamites-Ptilophyllum Flora of Gould & Shibaoka (1980), although bennettitaleans are not abundant in all assemblages (McLoughlin & Drinnan 1995). The presence of large dipteridaceous ferns and large-leafed araucaraiacean conifers generally favours a mesothermal climate.

Permineralised gymnosperm wood is common in Middle Jurassic volcanigenic sediments of eastern Australia, but has not been extensively studied. Following recent taxonomic revision of global Jurassic–Cretaceous wood records (Bamford & Philippe 2001), such fossils may find renewed application for terrestrial biostratigraphy and palaeobiogeography (Philippe et al. 2004). Unstudied in situ stumps occur at Miles in the Surat basin and a range of permineralised osmundaceous and dicksoniaceous fern axes have been described from nearby deposits (Tidwell & Rozefelds 1990, 1991; Tidwell & Clifford 1995). Pronounced growth rings in conifer woods and the abundance of matted bennettitalean-pentoxylalean leaf horizons suggest that the climate was seasonal with some plants deciduous. However, severe winters in the late Early to Late Jurassic in the Surat and adjacent basins might have been moderated by the extensive system of swamps, lakes, and rivers, a scenario mooted by Yemane (1993), Ziegler et al. (1993) and Kutzbach & Ziegler (1993). Also, without details of the growth-ring patterns, determining likely causes of their formation is difficult, as these features can result from different environmental parameters and can be found even at low elevations at low latitudes (Fritts 1976).

Floras of the mid-Jurassic Araucariacean Phase are similar from all Australasian localities and correlate with assemblages in Argentina; comparable assemblages are known from peninsula India, Madagascar, and Antarctica (Grant-Mackie et al. 2000). Recent use of U-Pb zircon ages for calibration of Southern Hemisphere biostratigraphy has provided fresh insights into the age of plants from the non-marine Botany Bay Group, Antarctica. Hunter et al. (2005) gave an absolute age of 168.9 ± 1.3–167.1 ± 1.1 Ma (Bajocian to early Bathonian, GTS 2004) for the reference flora, which had previously been assigned to the Early Jurassic (Gee 1989; Rees 1993; Rees & Cleal 2004).

Australian Late Jurassic plant macrofossils are poorly known (Young & Laurie 1996; Hill et al. 1999). They are recorded from disparate parts of the continent, but are broadly similar to those of the Early and Middle Jurassic in their representation of conifers, bennettitaleans, pentoxylaleans, pteridosperms, ferns, and equisetaleans. The Talbragar fish beds in the southern Surat basin host a rich impression flora that has traditionally been assigned a late Early Jurassic or early Middle Jurassic age, based on palynological data (Morgan 1984; see below). Recent radiometric dating (see below) suggests a Late Jurassic (latest Oxfordian–Kimmeridgian–Tithonian) age for these beds (Bean 2006b). The flora, studied most thoroughly by Walkom (1921b) and White (1981a), includes conifers [Podozamites jurassica (Fig. 3H), ?Rissikia talbragarensis (Fig. 3I), “Brachyphylum sp.”, “?Pagiophyllum peregrinum”, Elatocladus australis, Allocladus cribbii, Allocladus milneanus, Elatocladus australis], pentoxylaleans (Taeniopteris, Carnoconites and Sahnia spp.), ?cycadophytes (Nilssonia compta), some enigmatic seed-ferns (Rintoulia sp., Fig. 3J), and fern fragments. In recent years, several media and technical reports have compared Podozamites jurassica fossils, from Talbragar, to the foliage of the extant wollemi pine (Wollemia nobilis), suggesting great antiquity for the Wollemia lineage. However, P. jurassica does not provide a close match in venation pattern, leaf shape or phyllotaxy to either Wollemia or other extant araucariacean genera (McLoughlin & Vajda 2005). Convincing evidence for Wollemia extends back only to the Late Cretaceous.

Small fossil-plant assemblages, from the Carpentaria Basin in far northern Queensland (e.g. Gould 1975), the Tarlton Range, Eromanga Basin, Northern Territory (Gould 1978), and the northern Perth Basin (e.g. Walkom 1921a; Glauert 1923; McLoughlin & Hill 1996; McLoughlin & Pott 2009 ) have also been considered to be of Late Jurassic age. These floras contain putative lycophytes, dipteridacean, ?gleicheniacean, osmundacean and ?matoniacean ferns, bennettitaleans, pentoxylaleans, and small-leafed conifers (Pagiophyllum and Elatocladus spp.). In terms of their generic composition and the typically small-leafed conifers, they show some similarities to southeastern Australian Neocomian floras (McLoughlin et al. 2002), but other features (medium-leafed bennettitales) show similarities to Middle Jurassic floras of India, Patagonia, and the Antarctic Peninsula (McLoughlin & Pott 2009). Late Jurassic to Early Cretaceous Pachypteris leaves from the Battle Camp Formation of the Laura basin, north Queensland, are notable for the presence of lepidopteran leaf mines, one of the oldest records of phytophagy in the Australian fossil record (Rozefelds 1988). As several eastern Australian basins contain a near-complete record of Jurassic continental sedimentation, great scope exists for further systematic studies of the fossil floras and their application to non-marine biostratigraphy.

Palynology

A substantial database now exists on the palynofloral succession represented in Australia's Jurassic sedimentary basins. Following early systematic studies of microplankton (I.C. Cookson and co-workers) and of spores and pollen from Western Australian marginal basins (B.E. Balme), and eastern basins (N.J. de Jersey and co-workers), work was focused on developing intra- and inter-basinal palynostratigraphic schemes, primarily in response to the needs for stratigraphic correlation in hydrocarbon exploration. In the intracratonic terrestrial sequences of eastern Australia, Evans (1966) largely pioneered Mesozoic miospore biostratigraphy when he defined a series of “palynological units” in the Triassic, Jurassic and Early Cretaceous successions of the Bowen-Surat and Eromanga basins in Queensland (also see Evans 1965). Subsequently, Burger (1968, 1976, 1984, 1989, 1994a, 1994b) and Burger & Senior (1979) modified and further qualified Evans' (1965, 1966) scheme in order to make it more amenable to practical usage, but deficiencies remained, primarily because published details of miospore-assemblage composition and species distribution in the Middle–Late Jurassic succession were wanting. Various “in-house” and unpublished versions of Evans' scheme were also developed by palynologists working for petroleum exploration companies. However, continual modification of the zonal units and varying approaches to their application in and outside of the exploration industry generated a degree of confusion; to some extent, this was unavoidable as acquisition of palynological data and evolution of the palynostratigraphy went hand-in-hand, being not only constrained by resources available, but also driven generally by the need for immediate results. The most widely used of the private-industry zonations modified from Evans' original (1966) biostratigraphy is that of Price et al. (1985). Their informal zonal nomenclature, which was devised to overcome the disorder generated by the sundry versions of Evans' palynostratigraphic units, was published in brief by Filatoff & Price (1988). The scheme was reviewed by Burger et al. (1992) and subsequently modified and documented more fully by Price (1997). That zonation bears little resemblance to Evans' (1965) original scheme, and comprises range/partial range/interval zones, unlike that of Helby et al. (1987; discussed below) and its subsequent modifications, in which most of the zones are Oppel zones.

Reiser & Williams (1969), studying the Precipice Sandstone and Evergreen Formation of the northern Surat Basin, partly formalised Evans' (1966) units by erecting their Classopollis classoides Zone (with two constituent subzones) and succeeding Tsugaepollenites segmentatus-T. dampieri “zone”; the latter was not formally instituted, as Reiser and Williams were unable to define an upper limit.

Zonation of the latest Triassic–Early Jurassic interval in the Clarence-Moreton Basin was subsequently formulated by de Jersey (1975), primarily for broad comparison with other regions of Gondwana. An ensuing, but informal scheme (de Jersey 1976) established a somewhat finer subdivision of the latest Triassic–Early Jurassic strata in the Clarence-Moreton and Nambour basins; a modification was proposed by McKellar (1981) on the basis of additional species-distribution data obtained from the latter basin.

For the latest Jurassic–Early Cretaceous succession in the Surat and Eromanga basins in Queensland, formal biostratigraphic subdivision has been undertaken by Burger (1973, 1989). However, incomplete knowledge of latest Jurassic–earliest Cretaceous palynofloras in strata succeeding the Injune Creek Group and equivalents remains a concern and considerably impedes biostratigraphic appraisal of, and correlation in, this interval. Additionally, on a global scale, the marine faunas of the latest Jurassic–earliest Cretaceous show a high degree of provinciality inhibiting a precise correlation between marine and terrestrial ecosystems (Vajda & Wigforss-Lange 2006). In the southern Eromanga Basin of South Australia, Gallagher et al. (2008), following a regional palynological review, recognised six subzones of the late Middle–Late Jurassic palynological unit APJ5 (of Price 1997). In Western Australia, Jurassic zonal schemes were established by Balme (1957, 1964), Filatoff (1975), and Backhouse (1978, and see Grant-Mackie et al. 2000); the work of Filatoff, in particular, has facilitated comparison between the Jurassic palynofloral successions in eastern and Western Australia. However, confident correlation between east and west is complicated not only by quantitative differences in the palynofloras, but also by differences in the relative ranges of certain species and the development of slight provincialism in the Early Jurassic (Truswell et al. 1999; Grant-Mackie et al. 2000).

Much of this work provided the basis for the Mesozoic, pan-Australian, palynostratigraphic zonation proposed by Helby et al. (1987). Their scheme integrated spore–pollen and microplankton biostratigraphies, and, for some intervals, is linked to the marine invertebrate record and extra-Australian dinocyst records. For the Jurassic, the Helby et al. spore–pollen zonation comprised one new zone (Callialasporites turbatus Oppel Zone) and several other zones, which represented modifications of previously established biostratigraphic units (Reiser & Williams 1969; Burger 1973; de Jersey 1975; Filatoff 1975; Backhouse 1978). However, the concept of the Dictyotosporites complex Oppel Zone, which was based by Helby et al. (1987) on the identically named biostratigraphic unit established in the Perth Basin by Filatoff (1975), is difficult to apply in eastern Australia, primarily because the nominate species (Fig. 4A) is rare and sporadically distributed in Middle–Late Jurassic strata. This also has impacted upon recognition (in eastern Australia) of the upper limit of their preceding C. turbatus Oppel Zone. The Contignisporites cooksoniae Oppel Zone (Helby et al. 1987), which succeeds the D. complex Oppel Zone, is similarly difficult to delineate in the east, because of the rare and sporadic distribution of C. cooksoniae (Balme) Dettmann (sensu Filatoff 1975; recorded under C. burgeri Filatoff, McKellar and Price by McKellar in press). Nonetheless, the M. florida and Retitriletes watherooensis Oppel zones (Helby et al. 1987) have been employed by McKellar (in press), with nomenclatural and other modifications, for subdivision of the late Middle–Late Jurassic interval in the Surat Basin. However, because of apparent differences in the relative appearances of certain miospore taxa (e.g. Fig. 4G, L), the mutual boundary between these zones in the Surat Basin was somewhat differently interpreted from the definition given by Helby et al. (1987), which was based principally on the western and northwestern Australian succession.

The zonation of Helby et al. (1987) was incorporated in the AGSO 1996 Australian Timescale (Young & Laurie 1996; discussed above) and associated Wallchart (AGSO 1996), although alternative ages were suggested for some of their Jurassic–Cretaceous dinocyst zones by Burger & Shafik (1996). Subsequently, in 2004, Helby et al., via GA's Timescales-VCEMP Project, published an updated dinocyst zonation for the Jurassic–Early Cretaceous of the North West Shelf, plotted against the AGSO 1996 timescale, also incorporating a comparison between the spore–pollen and dinocyst zones in the Early and early Middle Jurassic. More recently, the Timescales-VCEMP Project has facilitated a further update of this North-West-Shelf-dinocyst zonation, together with updates for the Jurassic–Early Cretaceous and Late Cretaceous–Cenozoic spore–pollen, dinocyst and palynological zonations for Australia and Late Cretaceous–Cenozoic palynological zonations for the Gippsland Basin (Monteil 2006, Partridge 2006a, 2006b, 2006c, 2006d), all now charted against GTS (2004).

The Jurassic spore–pollen zones are grouped into two superzones, an older Callialasporites dampieri Superzone, dated by Helby et al. (1987) as Hettangian–Kimmeridgian, and the younger Microcachryidites Superzone, dated as Tithonian–Albian, and characterised by distinctive ranges and abundances of key spore–pollen taxa (e.g. Fig. 4A–N). The base of the C. dampieri Superzone records the replacement of the corystosperm-dominated Late Triassic vegetation by a flora dominated by cheirolepidiacean conifers. The latter is embodied by the Cheirolepidiacean Phase of Grant-Mackie et al. (2000). The onset of this phase was dated by Helby et al. (1987) as early Hettangian, whereas McKellar (1996) initially favoured a late Hettangian date (in terms of significantly increased frequencies of Classopollis) and, recently, an early Sinemurian age (McKellar in press; and based on data, for eastern Australia and New Zealand, from N de Jersey and JMcK). The next major change occurred during the Toarcian with the C. dampieri Superzone being characterised by an increased representation of araucarian conifers (McKellar 1996, in press; Grant-Mackie et al. 2000), representing the Araucariacean Phase of the latter authors. The third modification was dated as late Oxfordian by McKellar (1996), (?)mid-Oxfordian by Grant-Mackie et al. (2000), and as middle Kimmeridgian by McKellar (in press). Its onset corresponds to the C. dampieri/Microcachyridites Superzone boundary, originally dated by Helby et al. (1987) as Tithonian (as inferred above). Floristic provincialism between eastern and Western Australia and a diachronous depositional hiatus across the continent may account for such a great divergence in the interpreted age of this major zonal boundary (McKellar in press). Increased frequencies of bi- and trisaccate pollen signify expansion and possibly diversification of the podocarp conifers within the vegetation at this time (Podocarpacean Phase: Grant-Mackie et al. 2000).

Major modifications to Australia's Jurassic floras are reflected by the quantitative and qualitative changes in spore–pollen assemblages across the three major events outlined above. Within each biozone, more subtle quantitative/qualitative variations in spore–pollen suites may reflect local facies influences or gradual palaeoecological (latitudinal, topographical, or climate-related) gradients across Australia.

In Queensland, Sajjadi and Playford (2002a, 2002b) have published a two-part compilation of the systematic and stratigraphic palynology of the Late Jurassic–earliest Cretaceous interval in the Eromanga Basin. Furthermore, McKellar (in press) has studied the late Early to Late Jurassic palynology, biostratigraphy, and palaeogeography of the Roma Shelf area in the northwestern Surat Basin, assessing the Australia-wide phytogeographic-palaeoclimatic implications of the Callialasporites dampieri and Microcachryidites superzone palynofloras (Jurassic–Early Cretaceous) on the basis of a revised tectonic model for the continent. A new cross-Tasman palynostratigraphic compilation has been developed (by N de Jersey and JMcK) embracing work on accurate location of the Triassic–Jurassic (Rhaetian–Hettangian) and Hettangian–Sinemurian boundaries in continental eastern Australia. The results are based on correlation with the marine, ammonite-dated succession in New Zealand, then part of Greater Eastern Australia. Another major paper, on Early and Middle Jurassic spore–pollen assemblages of New Zealand (again accurately dated by associated marine invertebrate fossils) and their biostratigraphic relationships with palynofloras from continental eastern Australia, has been largely completed (see de Jersey & Raine 2002 for preliminary biostratigraphic results). Raine et al. (2005) also provided a valuable atlas of palynomorphs for the New Zealand region (encompassing Jurassic forms), many of which also characterise Australian palynofloras.

The Jurassic palynozonation schemes developed for Australia also enable correlation to adjoining terranes of southern Gondwana. For instance, palynofloral assemblages from the MacRobertson Shelf, East Antarctica, although reworked, have demonstrated the presence of upper Lower Jurassic–Lower Cretaceous strata in that region. These palynofloras are compositionally similar to those of the Perth Basin and formerly contiguous basins in eastern India (Truswell et al. 1999). Other Indian subcontinent palynofloras have similarities to Australian suites (Upadhay et al. 2005) and Truswell et al. (1999) provided an overview of palynofloral relationships between the separate southern Gondwanan regions.

Ongoing research on Australian Jurassic palynofloras is being undertaken at several institutions/consultancies and is principally aimed at providing high-resolution age and facies controls on strata intersected by hydrocarbon exploration wells. Integration of this data with seismic and downhole petrophysical data is providing improved sequence and systems-tract definition for modelling sea-level changes and basin evolution (e.g. see Longley et al. 2002). In particular, PhD thesis work on the Upper Jurassic in the Jansz Gas Field, on the Exmouth Plateau of the offshore Northern Carnarvon basin (North West Shelf), has been concentrating on sequence stratigraphy and palynostratigraphy (Natalie Sinclair, pers. comm.).

Other doctoral research (Mantle 2006), including illustration of palynomorph diversity and abundance in assemblages that include both marine (dinocysts and acritarchs) and terrestrial (spores and pollen) components, has interpreted the palynology, sequence stratigraphy and palaeoenvironments of Middle to Late Jurassic strata of the Bayu-Undan Field, Timor Sea. The Bayu-Undan Field, located in the northern Bonaparte Basin, contains thick Mesozoic–Cenozoic sedimentary successions, with the majority of target economic petroleum reservoirs confined to the Middle–Upper Jurassic. This PhD project was developed as a response to the need for further characterisation and higher resolution biostratigraphy of the Bathonian–Oxfordian reservoir intervals within the field. The comprehensive taxonomic study was based on 230 sidewall and conventional core samples from the uppermost Plover, Elang, and lower Frigate formations. The marine palynofloras display a high degree of endemism and 14 new species of dinocyst have been described (Mantle 2006); more cosmopolitan dinocyst species allow comparisons with ammonite-dated European and Russian assemblages, and a latest Bathonian to early Oxfordian age is ascribed to the reservoir sections. However, Mantle (2006) noted that there are appreciable inter-provincial disparities between the first and last appearance datums of several dinocyst species.

Ten subzones have been recognised informally, collectively encompassing the Ternia balmei and Voodooia tabulata Interval zones (Helby et al. 2004) within the Bayu-Undan Field. The methods used to delimit some of these subzones (e.g. first and last common occurrences and acme events) are probably related to environmental parameters and are thus unlikely to prove reliable across a broader geographic region. However, the significant acme events (e.g. the widely recognised Durotrigia magna acme) correlate with regionally recognised flooding episodes (Mantle 2006).

The Elang Formation, the main lithological focus of the research, is typically divided into three third-order sequences. Detailed counts of the palynomorph assemblages allowed the recognition of various palynological markers or bioevents that correlated with most of the chronostratigraphic horizons (e.g. transgressive surfaces and maximum flooding surfaces). This enabled the lowstand, transgressive, and highstand system tracts of each sequence to be delimited. The marine-flooding episodes, in particular, are marked by distinctive compositional changes in the palynofloras (particularly acmes), an increase in stenohaline species, or an overall increase in dinoflagellate species diversity. These palynological-assemblage variations correlated extremely closely with gamma-ray log profiles traceable across the Bayu-Undan Field. Palynofacies analyses have also been used to identify depositional trends within the systems tracts and to aid in assessing the palaeoenvironments (Mantle 2006). However, the placement of conformable sequence boundaries, marking the gradational change from highstand to lowstand systems tracts, remains imprecise.

Various dinoflagellate species or groups were also considered useful palaeoenvironmental indicators: viz., Ternia balmei (shallow water, nearshore, euryhaline–stenohaline conditions); the Meiourogonyaulax group (nearshore, stenohaline); the Ctenidodinium group (the change from common occurrence of C. fuscibasilarum to abundant C. ancorum mirrors the progressive transgression through the Elang Formation); and the Rigaudella group (offshore, stenohaline).

Palaeoenvironmental inferences derived from analysis of the palynomorph assemblages concur with previous sedimentological interpretations of the Elang Formation (Mantle 2006). Thus, it is hoped that this will enable similar interpretations to be made from non-cored intervals (e.g. cuttings samples) that are based exclusively on the palynological content (Mantle 2006).

Vertebrate fauna

In terms of clarifying stage boundaries and events, the Jurassic vertebrate record is relatively uninformative, but it may have greater value for the definition of terrestrial biogeographic provinces and climates (Walliser 1996). The Australian Jurassic, with its long sequence of non-marine beds, has yielded a series of small but significant faunas (Long 1995; Vickers-Rich & Rich 1993). Molnar and Thulborn (in Grant-Mackie et al. 2000) reviewed knowledge of fossil vertebrates up to 1997. Since, then, new material from several vertebrates has become available from terrestrial and presumed non-marine sites. These discoveries, for instance, have led to work in progress on the classic Talbragar Fossil Fish bed in the southern Surat Basin (e.g. Pogson & Cameron 1999; Grant-Mackie et al. 2000; Bean 2006a, 2006b; and see below).

Early and Middle Jurassic fish faunas

There are sparse actinopterygian records in the Clarence-Moreton Basin. Of these, seven fragmentary semionotiform specimens (e.g. Fig. 5A) have been reported from the Middle Jurassic Walloon Coal Measures (Grant-Mackie et al. 2000). Further, the partial body outline of a semionotid fish, probably Lepidotes sp., has been reported from near Monto in the Mulgildie Basin (Thies & Turner 2001). It is preserved in dark, iron-rich sandstone, presumably representing the Hutton Sandstone (the unit underlying the Walloon Coal Measures), and was associated with specimens of ?Osmundacaulis, the occurrence of which supports a mid-Jurassic age.

Fig. 5 Jurassic fish: A. semionotiform fish from the Walloon Coal Measures (mid-Jurassic), Queensland [from Turner and Rozefelds (1987) reproduced with permission of MQM]. B. Cavenderichthys talbragarensis, Australian Museum specimen AMF4133. C. Cavenderichthys talbragarensis, Geological Survey of New South Wales specimen MMF13561a. D. Coccolepis sp. AMF117880. E. Aphnelepis sp., unregistered specimen, Bean collection, ANU; F. Archaeomene sp., MMF23674. B–F from the Upper Jurassic Talbragar fish beds, Talbragar, NSW. Scale bars = 10 mm.

Lepidotes Agassiz, 1832 is a genus of bony fish related to modern gars that inhabited both freshwater lakes and shallow seas. Some species exceeded 2 m in length and were covered by thick, enamelled scales. They possessed batteries of rounded, peg-like teeth, which enabled them to crush the shells of their molluscan prey. Such semionotiform fish are cosmopolitan in the Jurassic–Cretaceous (Thies 1989; Olsen & McClune 1991). Their wide geographic and aquatic distribution endows them with potential for development of a marine-to-continental-correlation scheme and a taxonomic review to this end is underway for the Jurassic (Turner 2008).

The Late Jurassic Talbragar fish fauna

Woodward's (1895) assessment of fossil fish from Talbragar, near Gulgong, led to the first recognition of Jurassic beds in New South Wales. More recent studies by Bean (2006a, 2006b) have provided new information on the faunal composition and palaeoenvironmental setting of these fossil fish beds.

“Leptolepis” talbragarensis Woodward 1895 (Fig. 5B, C) is the most common fish species recorded in the Talbragar fauna. Long (1991) considered the taxon to represent the first appearance of teleosteans in the Australian fossil record. However, doubt on generic assignment was clarified when Arratia (1997) assigned the species to a new genus, Cavenderichthys. This taxonomic reappraisal and amendment was supported by Bean (2006a) in her review of the actinopterygian taxa at Talbragar. Further, Woodward (1895) had originally referred specimens to three species, “Leptolepis” talbragarensis, “L.” gregarious, and “L.” loweii. Arratia (1997) considered all three to be synonymous and united them under C. talbragarensis, a concept that was first put forward by Wade (1941). A detailed comparison of the species by one of us (LB) with taxa presently referred to Leptolepis, and also with other Late Jurassic forms, Tharsis dubius and Leptolepides sprattiformis, indicates that C. talbragarensis is most closely related to Late Jurassic members of the Leptolepididae.

Additionally, the Talbragar fauna includes to date one palaeoniscid, Coccolepis australis (Fig. 5D), and members of the “holostean” family Archaeomenidae, e.g. Archaeomaene tenuis (Fig. 5F), Aphnelepis australis (Fig. 5E) and Aetheolepis mirabilis (Bean 2006b). The genus Madariscus, erected by Wade (1941) in the above family, is based on a series of imperfect specimens; those in the Australian Museum, Sydney, and the Natural History Museum, London, do not have enough detail to determine that they belong to a new genus, but, in general, they all seem to be very like a mature form of Archaeomene. The affinities of Uarbryichthys latus Wade 1941 are uncertain, but this taxon is no longer thought to be a macrosemiid and its affinities lie with the Macrosemiiformes (LB, work in progress). Bean (2006a) found the Talbragar fish fauna to have the strongest faunal similarities with the assemblage from the Early Cretaceous (Aptian) Koonwarra biota of Victoria (e.g. Long 1991), since these both include a species of Coccolepis, a “leptolepid”, and archaeomenids, rather than taxa represented at older sites in the Clarence-Moreton Basin (see above).

During digs in 2006–07, several specimens of a larger amiiform caturidid fish similar to Furo Gistl, 1848, known from the Upper Jurassic of Europe and Asia (see Frickhinger 1996) were discovered. This new Talbragar fish grew to >30 cm, is covered with heavily enamelled scales and has a single row of teeth on both upper and lower jaws; it will be described in detail elsewhere (by LB).

The first Australian Jurassic chondrichthyan was found recently from the Talbragar fossil lagerstätten by S. Avery (NSW); this is a hybodontiform shark based on its squamation (ST pers. obs.) and will be described in due course. This exciting find underpins the potential for discovery of further freshwater or euryhaline forms (see below) and for correlation with the rich lagerstätten in Europe and elsewhere (Thies et al. 2007; Turner 2008).

The Talbragar fossil-fish assemblage indicates a Late Jurassic age (Bean 2006a, 2006b). This contrasts with Early to Middle Jurassic dates reported by most previous workers for the Purlawaugh Formation, with which the Talbragar Fossil Fish bed has been formerly associated. For example, Hind & Helby (1969) recorded palynofloras referable to Evans' (1966) J2 Palynozone (of Pliensbachian to early Toarcian age) from close to the base of the Purlawaugh Formation at another site near Gulgong. They recorded assemblages referable to Evans' (1966) J3–J4 palynozones (of roughly mid-Toarcian to early Callovian age) from higher in the Purlawaugh Formation. No palynofloras have been recovered from the fish beds themselves but it is now apparent, based on faunal and SHRIMP (Sensitive High Resolution Ion Microprobe) dating, that these beds are somewhat younger than those parts of the Purlawaugh Formation from which the palynofloras were derived. The SHRIMP analysis of fossil fish bed samples, carried out at the ANU Research School of Earth Sciences, indicates an age for the youngest zircon population of 151.55 ± 4.27 Ma, or latest Oxfordian–Kimmeridgian–Tithonian in terms of GTS (2004). The affinities of Cavenderichthys with Kimmeridgian forms in Europe accords with the isotopic date. This provides a maximum age for the strata and, given that the zircon grains show no sign of transport abrasion, suggests that the sediments were deposited at about this time. The occurrence of euhedral zircon crystals and the strongly silicified nature of the fossil fish beds support the idea, outlined further below, that ash from a felsic volcanic eruption filled the Talbragar lake and caused a mass fish kill. The fine detail preserved in both plants and fish not only promotes this view, but also implies an anaerobic burial environment.

The Talbragar Fossil Fish bed actually consists of several beds collectively 60–100 cm thick, which are divided into an upper package of very fine layers totalling 30–40 cm, and a lower rather more massive but still fine-grained bed, all of which are heavily fossiliferous (LB pers. obs.). The outcrop extends at least 200 m along strike and is thought to represent the erosional remnant of the margin of a freshwater lake-bed deposit (Percival 1979). Evidence for the cause of the mass death of fish now points to several anoxic events, including occasional eruptions of volcanic ash (Bean 2006a). The upper layers contain a high concentration of extremely well-preserved small fish, ranging in size from 4 to 12 cm, whereas the lower layer has scattered fish throughout, indicating a more normal lacustrine environment of deposition. There is little indication of desiccation, such as mud cracks or aerially exposed surfaces, so this part of the fish bed is not a mound spring deposit. Neither are the Talbragar Fossil Fish beds a typical overbank deposit, as such successions usually include coarse-grained beds with erosive bases (crevasse splay sediments), interspersed with palaeosols that developed during periodic exposure. The uppermost beds capping the main fossiliferous bed are very fine grained and represent an interval of slow deposition in still-water conditions that suddenly became anoxic.

The composition of the rock was described by Dulhunty & Eadie (1969) as a hard, fine, limonitic cherty shale. However, recent thin-section and chemical analyses indicate that the clastic components of the sediments are largely reworked from underlying sandstones, which are interbedded with thin tuffs representing one or more very fine-grained ash falls (Bean 2006a). EDXA (Energy Dispersive X-ray Analysis) has shown no evidence of carbonate or calcium ions. The striking red-brown colour of the fossiliferous beds is post-depositional because each block has Liesegang rings associated with jointing. Manganese dioxide is commonly found infilling the fossil-fish cavities and commonly forms dendrites near block boundaries. Many of the fish and most of the plant impressions are replaced with white kaolinite and opaline quartz (Dr A. Christy pers. comm. to LB, see also White 1981b, 1986).

Recent excavations to the west of the best-known outcrop have exposed a continuation of the fish beds that has not been stained with iron oxide and is just a very fine, soft, white, and fossiliferous mudstone. This indicates that the staining of the rock and subsequent infilling of fish impressions are recent artefacts of ground-water movement (Bean, work in progress).

Fossil insects recovered from the Talbragar fossil fish beds include Cicada? lowei (Etheridge & Olliff 1890). Undescribed forms discovered recently were derived mainly from the southernmost extent of the deposit, although a few insects have been found in the most widely explored (northern) part of the outcrop. At least 50 insect specimens have been found, including a water boatman, rove beetle, stonefly larva, jumping plant louse, dragonfly naiads, lacewings, and assorted beetles, including at least one water beetle and one bark beetle. Small bivalve and gastropod molluscs have also been discovered, together with filamentous aquatic plants. All these taxa suggest a shallow-water environment at the lake margin (R. Beattie, pers. comm. to LB). Since none occur in the lower layers, where fish are more scattered, it seems most likely that the insects were trapped by the major ash fall that enveloped the body of water.

Tetrapods

Molnar and Thulborn (in Grant-Mackie et al. 2000) emphasised that Australian Jurassic dinosaur and other tetrapod body fossils are endemic. Fossil amphibians are rare. The upper jaw with alveoli of a very large, probably late Early to early Middle Jurassic “labyrinthodont” amphibian, Austropelor Longman, 1941, came from the Marburg Subgroup near Lowood, Clarence-Moreton Basin, and there is a reasonably complete skeleton of Siderops kehli from the Evergreen Formation in the Surat Basin (Grant-Mackie et al. 2000). Interestingly, these temnospondyl amphibians represent a phenomenon well known in southeastern Gondwana, namely that taxa persisted longer in this part of the world while becoming extinct elsewhere. This poses problems for inter-continental correlations based on higher-level taxa of terrestrial vertebrates. Another unusual occurrence is the association of freshwater plesiosaurs, which are typically marine elsewhere, but occur in Queensland in freshwater deposits, highlighted by Siderops in the Evergreen Formation (Surat Basin) and in the Razorback beds at Mt Morgan (e.g. Thulborn & Warren 1980; Grant-Mackie et al. 2000).

Only three dinosaur taxa have been found in the Jurassic (Bajocian) of Australia; one in the east, two in the west (Grant-Mackie et al. 2000; Rich & Vickers-Rich 2003). An incomplete skeleton of a sauropod, Rhoetosaurus brownei, was first found in the Hutton Sandstone in the 1920s, with subsequent collecting of parts of the same animal over 70 years. A single caudal centrum of a possible sauropod and a theropod, Ozraptor subotaii, have come from one site in the Bajocian Colalura Sandstone of Western Australia (Long 1998).

Traces of dinosaurs are far more common than body fossils in Australia. Footprints are more diverse and illuminating, confirming the age of the Precipice Sandstone in Queensland as Early Jurassic and suggesting a cosmopolitan distribution for ornithopod dinosaurs as early as the Early Jurassic (Beeston & Gray 1993). Many dinosaur footprints have been sporadically recorded in coal mines in the Clarence-Moreton Basin in southeastern Queensland, with a more recent dearth because of the shift from manual to automated longwall mining; those from the Walloon Coal Measures are around 168–161 Ma (Bathonian–Callovian: Grant-Mackie et al. 2000). Tracks of small to medium, agile, plant-eating dinosaurs with nails or “hooves” also occur (foot-print ichnotaxa include cf. Anomoepus, 20 cm long, Fig. 6A; ornithopods cf. Wintonopus, Fig. 6B). The latter type is widespread in the Early to Middle Jurassic worldwide (Grant-Mackie et al. 2000). Large three-toed and clawed predatory dinosaur prints (Fig. 6C; ichnotaxon Eubrontes, 54 cm long, Fig. 6D) from the Rosewood-Walloon coalfield resemble those of allosaurs and megalosaurs in the northern and western parts of Pangaea. A further major study of Jurassic dinosaur footprints at the Mt Morgan mines in central Queensland is soon to be published (Cook et al. in press).

Fig. 6 Examples of early to mid-Jurassic dinosaur footprint taxa: A. Reconstruction of possible fabrosaurid trackmaker, cf. Anomoepus from Lower Jurassic Precipice Sandstone, Carnarvon Gorge, Surat Basin. B. Large ornithopod footprint cf. Wintonopus, ca. 48 cm long, Balgowan Colliery, Dalby-Oakey coalfield, Darling Downs. C. Dinosaur footprint ca. 54 cm long, Balgowan Colliery, Dalbey-Oakey coalfield, Darling Downs. D. Large theropod footprint Eubrontes ca. 54 cm long, Oakleigh No 3 underground colliery. E. E. theropod footprint ca. 46 cm long, Lanefield Colliery, Rosewood-Walloon coalfield (Ball photo, courtesy of GSQ) B, D, from Walloon Coal Measures, Bathonian–Callovian, Clarence-Moreton basin (photos courtesy of and drawing ©T. Thulborn).

One further possibility for tetrapods in the Southern Hemisphere is the existence of a relict dicynodont population in eastern Gondwana (Thulborn & Turner 2003). All Jurassic basins, not just in Australia, will need to be examined for further evidence of a post-Triassic extension for these paramammals. Even mammalian remains might be expected.

Other Invertebrate faunas

Shelly marine faunas are restricted to the Western Australian marginal basins, and studied onshore assemblages are confined to the Middle and Late Jurassic (e.g. Playford et al. 1975; Playford et al. 1976; and see references in Grant-Mackie et al. 2000). The assemblages (particularly the ammonoids) have provided important tie points between Australian biostratigraphic zones and the international chronostratigraphic stages (Helby et al. 1987). Offshore Jurassic marine sequences are more continuous, but the limited material available from bore cores does not favour detailed macroinvertebrate studies. There is potential for work on microinvertebrates and shelly protists (e.g. Bown 1992, Grant-Mackie et al. 2000, Howe 2000), but the restricted marine conditions during deposition of some major units (e.g. the Dingo Claystone) and the general impoverishment in carbonate facies may limit scope for identifying diverse faunas of some groups. Jurassic invertebrate faunas are far better known from the neighbouring terranes of New Zealand, New Caledonia and New Guinea (Grant-Mackie et al. 2000; Haig et al. 2007; Hikuroa & Grant-Mackie 2008).

Four freshwater/estuarine bivalve species have been recorded from the eastern Australian Jurassic in a recent revision by Hocknull (2000). These isolated records have yet to reveal significant biostratigraphic or biogeographical value (see Grant-Mackie et al. 2000).

Insects (Coleoptera and Blattaria) have been recovered from at least three sites in the Early Jurassic Cattamarra Coal Measures Member (Cockleshell Gully Formation), Perth Basin, Western Australia, and there appears to be scope for additional biogeographic research on this fauna (Jell 2004; Martin 2005). The Late Jurassic Talbragar fish bed (see above) also contains an apparently diverse insect fauna (R. Beattie, pers. comm), but, because the assemblage has not yet been thoroughly studied, its stratigraphic, palaeoenvironmental, and palaeobiogeographic significance cannot be evaluated here.

There is moderate potential for investigations of other non-marine fossil groups in the Australian Jurassic. For example, the oldest Australian leech cocoons have recently been described from the probable Pliensbachian Gatton Sandstone in the Clarence-Moreton Basin, which sits well above the appearance of Classopollis cf. chateaunovi that defines the Hettangian–Sinemurian boundary (Jansson et al. 2008). The durable proteinaceous cocoons of leeches and oligochaetes have been poorly studied, but they appear to be relatively common in the fossil record world-wide (Manum et al. 1991) and offer some potential as palaeoenvironmental or palaeobiogeographic indices once more records are published and their taxonomy is better resolved. Trace-fossil associations are also proving to be of substantial value as facies-demarcation tools within deltaic and shallow-marine sequences intersected in the course of hydrocarbon exploration along the Western Australian margin (Burns et al. 2001; Burns & Taylor 2005).

Discussion

Grant-Mackie et al. (2000, pp. 344–345) concluded that “All marine faunas show clear Tethyan or eastern Tethyan affinities throughout the Jurassic along the northwestern and northern Australasian margins as far east as New Guinea and the Pahau Terrane”; and that “Whilst there is a clear and continuing Tethyan influence, there is in the Middle Jurassic a strong south Andean connection and a weaker Mexican link which continue into the Late Jurassic.” Further work is required to test whether this conclusion also applies to the terrestrial biota.

Australian Jurassic terrestrial fossil biotas are best represented in the eastern basins. Forests there were dominated successively by cheirolepidiacean, araucariacean, and podocarpacean conifers together with a range of seed-ferns. There are moderate differences between the Early Jurassic floras of Western and Eastern Australia, especially expressed in the distribution of the Exesipollenites association along the Tethyan margin (Grant-Mackie et al. 2000, Fig. 8). Later Jurassic assemblages are essentially pan-Australasian, possibly reflecting the higher latitude and more insular setting of Australia-New Zealand later in the period.

Few definitive palaeogeographic conclusions can be drawn from the sparse vertebrates, with only the possibility of a western Pacific zoogeographic province in the mid-Jurassic. In terms of the vertebrates providing useful global biostratigraphic, geochronologic, and palaeobiogeographic data, the fish of the Semionotidae were widespread in the Jurassic with several taxa already known from the Southern Hemisphere. As this group seems to have been capable of diadromy, detailed work on scales and teeth may assist in both improved zonation of continental rocks and better marine to non-marine correlation. Likewise, a good global record for non-marine sharks is emerging, with teeth of hybodonts showing potential for a refined stratigraphy (Thies et al. 2007).

Work is required to better correlate marine/non-marine sequences along the Western Australian margin. There are also shortcomings in the correlation of latest Middle to Late Jurassic units in eastern Australian basins. Marine microfossils are unavailable in these basins and palynozones for this interval are relatively long-ranging, hence more details of spore–pollen taxa and their ranges are required for better biostratigraphic resolution.

Conclusions and Future Directions of Research

The main problem for Southern-Hemisphere biostratigraphers emanates from the GTS (2004) being Euramerican in its focus. Despite this difficulty, every effort is being undertaken to relate Australian zonal and other biostratigraphic data to it. In terms of the IGCP 506 Project, correlations and interpolations of Australian Jurassic zonations, based on this timescale, are required, providing a specific task for local biostratigraphers during the life of the project and beyond. However, many deficiencies exist in the broad spectrum of Australian biostratigraphy, and not all of them will be overcome in the short-term, because there is a serious shortage of expertise in all areas of the science. This will be exacerbated, in the next few years, by the retirement of several specialists, especially in palynology.

In the Australian region, marine sedimentation, during the Jurassic, was largely restricted to the Western Australian marginal basins. Some of the deposits therein constitute important hydrocarbon source rocks. Onshore thereto, there is very limited exposure of marine Jurassic rocks, which are known mostly from the northern Perth Basin. In the onshore subsurface, they are present in parts of the Carnarvon and Canning basins. Offshore, marine Jurassic strata are very extensive and known from hundreds of oil-exploration wells from the Carnarvon Basin northwards to the Timor Sea. In this area, particularly on the North West Shelf, palynology is presently used almost exclusively in sequences older than mid-Cretaceous and, as inferred above, a great deal of economic activity depends on it. Non-marine units (also deposited in the west) are extensively developed in eastern Australia, where marine strata are not known to occur, although, in northern Queensland (northeastern Australia), in the Laura and Carpentaria basins, the latest Jurassic-Neocomian Gilbert River Formation is lagoonal to marginal marine, and the poorly understood, Middle Jurassic-Early Cretaceous Helby beds, in the western part of the latter basin, are marine (Day et al. 1975; Bain & Draper 1997).

GA, through their Timescales and VCEMP Project, is relating biozonations to GTS (2004). This national organisation has largely completed the update of the integrated spore–pollen and dinocyst zonations of Helby et al. (1987, 2004), and their conversion to the international timescale (e.g. Partridge 2006b). McKellar (in press) has similarly documented the litho- and palynostratigraphic zonation of the continental Jurassic in the Surat Basin (eastern Australia), employing, for the Early–Middle Jurassic, correlation with the spore–pollen floras of New Zealand and New Caledonia, in order to establish relationships with the international timescale at stage level. The palynofloras of these regions have been dated by associated marine invertebrates (Grant-Mackie et al. 2000; de Jersey & Raine 2002). Further, N. de Jersey and JMcK have now delimited the Triassic–Jurassic (Rhaetian–Hettangian) and Hettangian–Sinemurian boundaries in the eastern Clarence-Moreton Basin (eastern Australia), in a rather exceptional continental section that apparently embraces the period/system transition without the unconformity that generally characterises the stratigraphic record at that level, based on correlation with spore–pollen floras from accurately dated marine strata in New Zealand.

As yet, no extensive isotopic-dating or magnetostratigraphic studies have been undertaken for the Australian Jurassic. Such investigations would assist calibration of Australian biozonations and complement both intra- and international biostratigraphic correlations and contribute to the establishment of relationships with the international timescale. However, with magnetostratigraphy, its expense and the availability of suitable material are limiting factors. From a biostratigraphic perspective, the most likely ways to tie Australian sequences to the Euramerican schemes will be using a combination of dinoflagellate, spore–pollen, foraminiferal, nannoplankton, and ammonite data.

The palynological zones, mainly the dinocyst zones, are now highly sophisticated and accurate within any given basin, and provide a level of resolution that will not be matched by other biostratigraphic methods in the foreseeable future. Dinoflagellates and miospores have the advantage that they are recoverable from a wide range of strata that are substantially devoid of other fossil groups. However, there is a need for improved correlation between regional Australian zonations based on them, and between the marine (dinocyst) and continental (spore–pollen) schemes, to facilitate improved dating of the latter, but this is inhibited by the commonly low abundances of miospores in marine strata.

Further to the spore–pollen studies already undertaken on the ammonite-dated (Hettangian–Sinemurian), New Zealand sequences (cited above) and additional to the work of Helby et al. (1988) on dinoflagellate associations from the late Middle and Late Jurassic of that region (which were interpreted in terms of Australian zones), there is potential for obtaining similarly useful dinocyst data from the region's intervening Jurassic, for which ammonite data are also wanting. Ammonites in Western Australia are not likely to provide much more information than is already available, as all the known localities have been dated and only occasional finds are made in cores. However, foraminifera and nannofossil data are presently wanting.

For the Australian Jurassic, the following points are also highlighted:

•	Fish may possibly assist with marine to non-marine correlation.
•	A satisfactory definition for the J–K boundary has not yet been found, as provincialism in ammonites, caused by Late Jurassic regression in northern Europe, has fuelled debates on Tethyan vs. Boreal distributions. Also, this boundary is mostly embraced by non-marine successions in Australia, so its identification must rely on good correlation of marine and non-marine zonations.
•	The unpublished cross-Tasman compilation of de Jersey and JMcK provides accurate palynostratigraphic location of the Triassic–Jurassic (Rhaetian–Hettangian) and Hettangian–Sinemurian boundaries in continental eastern Australia, but more extensive work is required to clarify the positions of other stage boundaries. However, it is likely that they may not necessarily coincide with local biostratigraphic, or, for that matter, lithostratigraphic boundaries.
•	The integrated dinocyst and spore–pollen zonations (viz. Helby et al. 1987, 2004, Partridge 2006b) may provide resolution to sub-million year intervals, allowing recognition of high-frequency sea-level changes and enabling better characterisation of the evolution of sedimentary facies pertinent to the search for stratigraphic hydrocarbon traps.
•	There are 5–10 km of both marine and non-marine Jurassic strata evident in seismic profiles on the North West Shelf, so the challenge for the years to come under the auspices of IGCP 506 and its successors will be to prepare an integrated high-resolution biostratigraphy calibrated to the European standard.

Acknowledgements

Professor Sha Jingeng (co-leader IGCP 506, NIGPAS) provided valuable support to enable the beginnings of this paper given by ST at the 1st IGCP 506 Symposium in Nanjing; the Australian IGCP Committee Grant-in-Aid Scheme and UNESCO-IUGS IGCP 506 are thanked for support to attend the 2005 and 2008 symposia; she and MD thank the Board of the Queensland Museum for basic support. LBB would like to thank Professor KSW Campbell (ANU), Dr GC Young (ANU) and Prof. JA Long (Museum Victoria, Melbourne) for advice on fish; Dr IS Williams (Research School of Earth Sciences, ANU, Canberra) for expertise and help with the SHRIMP analysis; Dr A. Christy (ANU) for carrying out SEM/EXDA (scanning electron microscope and energy dispersive X-ray analysis) studies; Professor RJ Arculus (ANU) for help with histological work; R. Beattie for information about fossil insects. SM was supported by Australian Research Council Discovery Grant A10020305 and a Swedish Research Council grant and a Riksmusei Vänner stipendium. We thank Drs Elizabeth Truswell (ANU, Canberra) and Eric Monteil (formerly GA, Canberra) for their helpful reviews. Further, Dr John Backhouse (University of Western Australia) provided extensive comments on the Jurassic of Western Australia, especially on the North West Shelf, and the future direction of biostratigraphic and related work in the Mesozoic of Australia; many of his comments have been incorporated into the final section. We thank Natalie Sinclair (ANU, GA) for providing a resumé of her doctoral thesis work and other data on Western Australia and Dr Daniel Mantle (GA) for providing information on the palynology of the Bonaparte basin derived largely from his unpublished PhD thesis.

Notes

This is a contribution to IGCP 506: Marine/Non-marine Jurassic correlation.