Australian Gondwana Research Articles

A new Cretaceous fossil mammal locality from the Bass Coast of southeastern Australia

Mesozoic mammals from the polar regions of Australian Gondwana are exceptionally rare. The recovery of a partial jaw attributable to the australosphenid Ausktribosphenos nyktos from a new locality along the Bass Coast of Victoria is, therefore, significant because it comes from an uppermost Barremian to lowermost Aptian grit with abundant plant material that differs lithologically from other previously productive laminated sandstone deposits. We interpret this as evidence for a floodplain habitat that was distant from local water bodies. The identification of a new Cretaceous mammal locality in Australia highlights the exciting prospects for future fossil discoveries. Thomas H. Rich [trich@museum.vic.gov.au] Museums Victoria, Melbourne, Victoria, 3001, PO Box 666,Australia Melissa L. Lowery [melissalouiselowery@gmail.com] 82 Williams Street, Inverloch, Victoria, 3996, Australia Michael Hall [mike.hall@monash.edu] School of Earth, Atmosphere and Environment, Monash University, Victoria, 3800, Australia Lesley Kool [koollesley@gmail.com] Museums Victoria, Melbourne, Victoria, 3001, Australia PO Box 666; School of Earth, Atmosphere and Environment, Monash University, Victoria, 3800, Australia Joseph Bevitt [joseph.bevitt@ansto.gov.au] Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, Nsw, 2234, Australia Matt White [fossilised@hotmail.com] University of New England, Armidale, Nsw, 2350, Australia Patricia Vickers-Rich [pat.rich@monash.edu, prich@swin.edu.au] School of Earth, Atmosphere and Environment, Monash University, Victoria, 3800, Australia; Department of Chemistry and Biotechnology, Swinburne University of Science and Technology, Hawthorn, Victoria, 3122, Australia.

Late Ordovician (Katian) linguliform microbrachiopods from north‐eastern Yunnan, South China

AbstractLinguliform brachiopods are a minor but distinctive component of the Palaeozoic Evolutionary Fauna. However, there is no formal research on Katian (Late Ordovician) linguliform microbrachiopods in South China. Fossils from the ‘Pagoda’, ‘Linhsiang’ and Daduhe formations, Wanhe section of Yunnan Province, South China, provide a unique opportunity to bridge the gap. Here, we report and systematically describe, for the first time, a deep‐water Katian linguliform microbrachiopod association, including 13 species assigned to nine genera, namely Paterula cf. numerosa Popov, Hisingerella tenuis Holmer, Scaphelasma sp., Torynelasma? sp., Biernatia holmi Holmer, ?Biernatia maruiaensis Percival et al., Biernatia pseudoplana Percival et al., Biernatia wrighti Percival et al., Opsiconidion praecursor Popov et al., Opsiconidion sp., Eoconulus puteus Percival et al., Acanthambonia sp. and Nushbiella lillianae Holmer. To explore the composition and distribution model of global deep‐water micromorphic linguliforms in the Katian, a dataset of occurrence of 40 genera from five superfamilies and 10 localities in Baltica, Avalonia, Australian Gondwana, Boshchekul Island Arc and South China is established. Compared with those of other localities, the Chinese association is dominated by Acrotretoidea with no taxon of Discinoidea or Paterinoidea. The global dataset is analysed using non‐metric multidimensional scaling. The results indicate an endemic biogeographical pattern for the Katian linguliform microbrachiopods, which can be explained by oceanic circulation or environmental differences.

Late Paleozoic Woniusi basaltic province from Sibumasu terrane: Implications for the breakup of eastern Gondwana’s northern margin

Research Article| September 01, 2015 Late Paleozoic Woniusi basaltic province from Sibumasu terrane: Implications for the breakup of eastern Gondwana’s northern margin Shi-Yong Liao; Shi-Yong Liao † 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China2Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China †E-mail: liaosy@hotmail.com or syliao@pmo.ac.cn. Search for other works by this author on: GSW Google Scholar Dong-Bing Wang; Dong-Bing Wang 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar Yuan Tang; Yuan Tang 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar Fu-Guang Yin; Fu-Guang Yin 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar Shu-Nan Cao; Shu-Nan Cao 3Department of Earth Sciences, University of Hong Kong, Hong Kong, China Search for other works by this author on: GSW Google Scholar Li-Quan Wang; Li-Quan Wang 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar Bao-Di Wang; Bao-Di Wang 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar Zhi-Ming Sun Zhi-Ming Sun 1Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2015) 127 (9-10): 1313–1330. https://doi.org/10.1130/B31210.1 Article history received: 20 Sep 2014 rev-recd: 30 Jan 2015 accepted: 02 Mar 2015 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Shi-Yong Liao, Dong-Bing Wang, Yuan Tang, Fu-Guang Yin, Shu-Nan Cao, Li-Quan Wang, Bao-Di Wang, Zhi-Ming Sun; Late Paleozoic Woniusi basaltic province from Sibumasu terrane: Implications for the breakup of eastern Gondwana’s northern margin. GSA Bulletin 2015;; 127 (9-10): 1313–1330. doi: https://doi.org/10.1130/B31210.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The tectonic mechanism responsible for detachment of the Sibumasu terrane in the eastern Cimmerian continent from the Australian Gondwana margin remains poorly understood and debated. Our study on the late Paleozoic Woniusi basaltic province in the northern Sibumasu terrane may provide a new perspective on this problem, and further, on the rifting dynamics of eastern Gondwana’s northern margin. In this study, we revealed that the Woniusi basaltic province is spread over an area of ∼12,000 km2 with a thickness of ∼300–500 m for the eruptive phase. Direct zircon U-Pb dating of mafic dikes indicates that the Woniusi basaltic province was emplaced between the latest Carboniferous and late Early Permian (301 Ma to 282 Ma), synchronous with basaltic rocks from the Panjal Traps, Tethyan Himalaya (Bhote Kosi, Selong, Abor), Lhasa, and southern Qiangtang. Geochemically, the Woniusi basaltic rocks show subalkaline tholeiitic affinity and relatively homogeneous features of enriched light rare earth elements (LREEs) and large ion lithophile elements (LILEs) but depleted Nb and Ta patterns. They were most likely derived from an enriched subcontinental lithospheric mantle source and triggered by the mantle plume–induced rifting process. The Woniusi basaltic province, together with other coeval basaltic provinces from the Panjal Traps, Tethyan Himalaya, Lhasa, and southern Qiangtang, belongs to a fragmented large igneous province that may have had an original area of over 2 × 106 km2, which is comparable to that of the Ontong-Java, Deccan, or Siberian Traps. These Tethyan basaltic provinces share a common mantle plume centered in northern Greater India. It was this mantle plume that may have triggered the initial rifting of the eastern Cimmerian terranes (e.g., Sibumasu, southern Qiangtang) from both the northern Indian and Australian Gondwana margins, as well as the opening of Meso-Tethys Ocean. This study, moreover, sheds light on the paleopositions of the Lhasa and Tengchong terranes before their breakups. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

High-precision U-Pb CA-TIMS calibration of Middle Permian to Lower Triassic sequences, mass extinction and extreme climate-change in eastern Australian Gondwana

Twenty-eight new high-precision Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry U-Pb zircon dates for tuffs in the Sydney and Bowen Basins are reported. Based on these new dates, the Guadalupian-Lopingian/Capitanian-Wuchiapingian boundary is tentatively placed at the level of the Thirroul Sandstone in the lower part of the Illawarra Coal Measures in the Sydney Basin. The Wuchiapingian-Changhsingian boundary is at or close to the Kembla Sandstone horizon in the Illawarra Coal Measures, southern Sydney Basin, in the middle part of the Newcastle Coal Measures in the northern Sydney Basin, and in the middle of the Black Alley Shale in the southern Bowen Basin. The end-Permian mass extinction is recognised at the base of the Coal Cliff Sandstone in the southern Sydney Basin, at the top of the Newcastle Coal Measures in the northern Sydney Basin, and close to the base of the Rewan Group in the Bowen Basin and is dated at c. 252.2 Ma. The end-Permian mass extinction is interpreted to be synchronous globally in both marine and terrestrial environments, and in high and low latitudes (resolution <0.5 my). The GSSP-defined Permian-Triassic boundary is interpreted to be approximately at the level of the Scarborough Sandstone in the lower Narrabeen Group, Sydney Basin, and in the lower Rewan Group, Bowen Basin. New dates presented here suggest that the P3 and P4 glacial episodes in the Permian of eastern Australia are early Roadian to early Capitanian, and late Capitanian to mid Wuchiapingian in age respectively. The greenhouse crisis in the uppermost Pebbly Beach and Rowan Formations of the Sydney Basin is interpreted as early mid Roadian, a mid-Capitanian age for the crisis at the base of the Illawarra/Whittingham Coal Measures is confirmed. Greenhouse crises in the upper Illawarra/Newcastle Coal Measures and lower Narrabeen Group of the Sydney Basin are dated as upper Changhsingian-Induan, and in the upper Narrabeen Group/lower Hawksbury Sandstone as upper Olenekian.

Actinocerid Cephalopods from the Ordovician of Myanmar, and their Paleobiogeographic Implications for Northern Gondwana

This paper describes a new actinocerid cephalopod fauna from the western part of the Shan Plateau in Myanmar (Sibumasu Block), and discusses its significance. The cephalopod fossils are preserved in shallow marine limestones of the Wunbye Formation (Pindaya Group) and its equivalent strata. The fauna consists of Ordosoceras theini sp. nov. (Floian or Dapingian, late Early or early Middle Ordovician age), Armenoceras myanmarense sp. nov. (Darriwilian, late Middle Ordovician), Paratunkuskoceras sp. (Darriwilian), and Wuti- noceras moeseini (Floian, late Early Ordovician). The presence of Ordosoceras, which was previously known only in the North China Block, and specific characters in the actinocerid fauna of Sibumasu indicate a strong linkage with that of North China during Early-Middle Ordovician time; in contrast, Sibumasu's affinity to the coeval Australian fauna is less definable. It is possible that an actinocerid faunal exchange took place between North China and Sibumasu over the shelf sea environment open to the Prototethys Ocean but this did not hap- pen to the inland seas of Australian Gondwana during the period.

Stratigraphy and palaeoenvironmental evolution of the mid- to upper Palaeozoic succession in Northwest Peninsular Malaysia

The stratigraphy of the Devonian to Permian succession in Northwest Peninsular Malaysia is revised. The Timah Tasoh Formation consists of black mudstone containing graptolites and tentaculitids indicating a Pragian or earliest Emsian age. The Sanai Limestone overlies the Timah Tasoh Formation at Sanai Hill B and contains conodonts indicating a Late Devonian (Frasnian to possibly early Famennian) age. In other places, Late Tournaisian chert of the Telaga Jatoh Formation overlies the Timah Tasoh Formation. The overlying Kubang Pasu Formation is predominantly composed of mudstone and sandstone, and can be divided into 3 subunits, from oldest to youngest: (1) Chepor Member; (2) Undifferentiated Kubang Pasu Formation; (3) Uppermost Kubang Pasu Formation. The ammonoid Praedaraelites tuntungensis sp. nov. is reported and described from the Chepor Member of Bukit Tuntung, Pauh. The genus indicates a Late Viséan age for part of the subunit. Dropstones and diamictites from the Chepor Member indicate a glacial marine depositional environment. The Carbo-Permian, undifferentiated Kubang Pasu Formation consists of similar interbedded mudstone and sandstone. The uppermost Kubang Pasu Formation of Kungurian age consists of coarsening upward cycles of clastics, representing a shallow marine, wave- and storm-influenced shoreline. The Permian Chuping Limestone also represents shallow marine, wave- and storm-influenced deposits. A Mid-Palaeozoic Unconformity separating Early–Late Devonian rocks from overlying Late Devonian–Carboniferous deposits probably marks initiation of rifting on Sibumasu, which eventually led to the separation of Sibumasu from Australian Gondwana during the late Sakmarian (Early Permian).

Late Tournaisian conodonts from the Taungnyo Group near Loi Kaw, Myanmar (Burma): Implications for Shan Plateau stratigraphy and evolution of the Gondwana-derived Sibumasu Terrane

Carboniferous conodonts are reported for the first time from Myanmar (Burma). Conodont faunas representative of the Scaliognathus anchoralis and Gnathodus typicus–Protognathodus cordiformis conodont zones date the sampled Taungnyo Group south of Loi Kaw, Kayah State as late Tournaisian confirming a Mississippian (Lower Carboniferous) age for the sampled part of this stratigraphic unit. The dated strata are stratigraphically just below the Tournaisian–Visean (T-V) boundary. Tournaisian strata are thus for the first time unequivocally demonstrated in the Shan Plateau region of Myanmar. Similar conodont faunas from the T-V boundary interval in SE Asia indicate a complete stratigraphic sequence at this level in shallow-marine sequences on intra-Tethyan Cathaysian tectonic blocks (South China) and in deep-marine Palaeo-Tethyan sediments (cherts of the Inthanon suture zone, Thailand). However, in shallow-marine sequences on the Sibumasu Block, located on the NE margin of Gondwana in the Carboniferous, they demonstrate a non-sequence or unconformity at this level, also seen elsewhere in Gondwana. Biogeographic links between upper Tournaisian and early Visean conodonts on the Sibumasu Terrane and Laurentia and Eastern Australian Gondwana support a NW Australian Gondwana margin position for Sibumasu in the Late Palaeozoic.

Early Triassic (Induan–Olenekian) conodont biostratigraphy, global anoxia, carbon isotope excursions and environmental perturbations: New data from Western Australian Gondwana

The Early Triassic Induan–Olenekian Stage boundary (Dienerian–Smithian sub-stage boundary) has been identified at a depth of 2719.25m in the petroleum exploration well Senecio-1 located in the northern Perth Basin, Western Australia. Conodont faunas represent three conodont zones in ascending order, the Neospathodus dieneri Zone, the Neospathodus waageni eowaageni Zone and the Neospathodus waageni waageni Zone. The Induan–Olenekian (Dienerian–Smithian) boundary is placed at the base of the Neospathodus waageni eowaageni Zone equivalent to the first appearance of Neospathodus ex. gr. waageni utilised elsewhere and adopted by the IUGS ICS Triassic Subcommission to define the base of the Olenekian. Bulk kerogen δ13C carbon isotopes define a positive peak of c. 4 per mille that essentially coincides with the Induan–Olenekian boundary as seen in proposed Global Stratotype Sections and Points (GSSPs) in South China and Spiti, India demonstrating the global utility of this level for correlation. An anoxic zone is recognised in the lower part of the Senecio-1 core and the upper limit of this zone is dated as late Induan (late Dienerian). Temporal and spatial mapping of marine anoxia and dysoxia globally demonstrates that pulses of dysoxia/anoxia affected shallow-marine zones at different times in different locations. Dysoxia/anoxia in the shallow-marine environment appeared in the latest Permian at the extinction level, later than in the deep-marine environment, and appears to be largely restricted to the Induan (Griesbachian and Dienerian) and early Olenekian (Smithian). Temporally and geographically restricted upwelling of an oxygen minimum zone into the ocean surface layer due to environmental perturbations including extreme global warming, increased terrestrial chemical weathering intensity and continental erosion, sea level rise, and changes in marine nutrient inventories and productivity rates, is interpreted as a likely cause of observed variation in shallow-marine dysoxia/anoxia in the Early Triassic.

The origin and pre-Cenozoic evolution of the Tibetan Plateau

Different hypotheses have been proposed for the origin and pre-Cenozoic evolution of the Tibetan Plateau as a result of several collision events between a series of Gondwana-derived terranes (e.g., Qiangtang, Lhasa and India) and Asian continent since the early Paleozoic. This paper reviews and reevaluates these hypotheses in light of new data from Tibet including (1) the distribution of major tectonic boundaries and suture zones, (2) basement rocks and their sedimentary covers, (3) magmatic suites, and (4) detrital zircon constraints from Paleozoic metasedimentary rocks. The Western Qiangtang, Amdo, and Tethyan Himalaya terranes have the Indian Gondwana origin, whereas the Lhasa Terrane shows an Australian Gondwana affinity. The Cambrian magmatic record in the Lhasa Terrane resulted from the subduction of the proto-Tethyan Ocean lithosphere beneath the Australian Gondwana. The newly identified late Devonian granitoids in the southern margin of the Lhasa Terrane may represent an extensional magmatic event associated with its rifting, which ultimately resulted in the opening of the Songdo Tethyan Ocean. The Lhasa−northern Australia collision at ~263Ma was likely responsible for the initiation of a southward-dipping subduction of the Bangong-Nujiang Tethyan Oceanic lithosphere. The Yarlung-Zangbo Tethyan Ocean opened as a back-arc basin in the late Triassic, leading to the separation of the Lhasa Terrane from northern Australia. The subsequent northward subduction of the Yarlung-Zangbo Tethyan Ocean lithosphere beneath the Lhasa Terrane may have been triggered by the Qiangtang–Lhasa collision in the earliest Cretaceous. The mafic dike swarms (ca. 284Ma) in the Western Qiangtang originated from the Panjal plume activity that resulted in continental rifting and its separation from the northern Indian continent. The subsequent collision of the Western Qiangtang with the Eastern Qiangtang in the middle Triassic was followed by slab breakoff that led to the exhumation of the Qiangtang metamorphic rocks. This collision may have caused the northward subduction initiation of the Bangong-Nujiang Ocean lithosphere beneath the Western Qiangtang. Collision-related coeval igneous rocks occurring on both sides of the suture zone and the within-plate basalt affinity of associated mafic lithologies suggest slab breakoff-induced magmatism in a continent−continent collision zone. This zone may be the site of net continental crust growth, as exemplified by the Tibetan Plateau.

A new Permian species of Mooreoceras (Cephalopoda: Orthocerida) from northwestern Peninsular Malaysia

A new orthocerid cephalopod species, Mooreoceras sibumasuense sp. nov., is described from the lowest part of the Chuping Formation in Bukit Tungku Lembu of the Perlis State, northwestern Peninsular Malaysia. The holotype of the species occurs in argillaceous limestone that is most likely late Kungurian (late Early Permian) in age and was deposited under cool-temperate water conditions on the Sibumasu Terrane of the eastern Cimmerian Continent. Most Permian species of Mooreoceras appear to be palaeobiogeographically confined to cool to cool-temperate palaeoclimate zones of the Australian Gondwana to Sibumasu region. Mooreoceras sibumasuense sp. nov. belongs to a group that probably survived due to isolation from high predatory stress in tropical to temperate seas. (Communicated by Tatsuro MATSUMOTO, M.J.A.)

Land movements and animal distributions in east Wallacea (eastern Indonesia, Papua New Guinea and Melanesia)

Four generalized tracks are identified in eastern Indonesia-Papua New Guinea-Melanesia on the basis of animal distribution patterns. Two of these tracks are linked to a Melanesian rift system that developed to the north and east of Australian Gondwana during the late Cretaceous and early Tertiary. The other two tracks are related to Cretaceous rift systems formed off the west/northwest coast of Australian Gondwana. The histories of these rift systems are discussed, their present positions are tentatively located in terms of modern geography, and animal distributional patterns related to their formation and subsequent histories. Wallace's Line is reinterpreted in terms of a boundary between Asian and Australian derived terranes and microcontinents. Distributional patterns that reflect this discontinuity show incongruity with the geological pattern in Sulawesi and the Banda arcs because of the merging of Asian and Australian faunas as a direct result of Australia's collision with Asia. Indo-Australian distributions are interpreted in terms of the distribution of ancestral populations prior to the mid-Mesozoic breakup of the relevant sectors of Gondwana.

Late palaeozoic and mesozoic palaeogeography of Southeast Asia

Southeast Asia comprises a complex assemblage of allochthonous terranes derived directly or indirectly from Gondwana Land and assembled between the Late Palaeozoic and Cenozoic. The continental “core” of the region is made up of four principal continental blocks, South China, Indochina, Sibumasu and East Malaya. South China, Indochina and East Malaya were rifted from northeast Gondwanaland during the Silurian or Devonian and amalgamated to each other during the early Carboniferous. Sibumasu remained attached to northwest Australian Gondwana land until the late early Permian when it rifted away as part of the elongate Cimmerian continent. Collision between Sibumasu and Indochina-East Malaya probably occurred in the early Triassic forming the continental core of Southeast Asia. Other small terranes including Mount Victoria Land, Sikuleh, Natal, Semitau and southwest Borneo were accreted to this core during the Jurassic and Cretaceous to form “Sundaland”. A series of palaeogeographic maps are presented showing interpreted palaeopositions of the various Southeast Asian terranes in the Late Palaeozoic and Mesozoic which are consistent with the current geological and geophysical constraints.

A tectonic model of the Antarctic Gondwana margin with implications for southeastern Australia: isotopic and geochemical evidence

Abstract Geochemical studies of Paleozoic granites in northern Victoria Land (NVL) and the central Transantarctic Mountains (CTM) are integrated with structural and lithologie studies into a model for the tectonic development of the Antarctic-south-east Australian Gondwana margin in late Precambrian-middle Paleozoic time. Isotopic data (Nd, Sr, O) are used to define crustal basement age boundaries and subduction polarity and thus help identify suspect terranes. In the CTM, three basement age-blocks are recognized: The outboard two provinces are inferred to be allochthonous, with accretion to the Gondwana margin occurring between ≈ 750 and ≈ 500 Ma. This tectonic scenario is inferred to apply also to NVL and southeastern Australia (SEA). In the CTM and NVL, chemical and isotopic polarity of ca. 500 Ma granitoids indicate a cratonward-dipping subduction zone. In NVL, terranes outboard of the belt of ca. 500 Ma granites contain Devonian (ca. 400 Ma) I-type granites with chemical and isotopic polarity opposed to that of the ca. 500 Ma granites. In the furthest outboard position, S-type granites emplaced at ca. 600 and 525 Ma occur with ca. 400 Ma granites and indicate the presence of early Proterozoic basement. This NVL terrane collage is allochthonous; it was assembled, intruded by Devonian granites, and then tectonically accreted to the Gondwana margin between latest Devonian and Permian time. Terrane correlations with SEA imply that much of the latter was accreted to the Gondwana margin after Devonian time. Other fragments of this allochthonous continental collage are probably in Marie Byrd Land (West Antarctica) and New Zealand (including the Campbell Plateau).

Evolution of the southern margin of Tethys (North Australian region) from early Permian to late Cretaceous

Abstract A mid-Permian rifting episode appears to have removed continental blocks (now forming parts of Asia) from Australian Gondwana, but the present continental margin of Northern Australia-central New Guinea was formed by a later episode of rifting during the Jurassic. With the exception of the north-west Australian offshore region west of the Scott Plateau, this rifted continental margin has been greatly modified during the Cainozoic by collisions with arc-trench systems. Collision resulted in fold and thrust mountains, locally with ophiolite emplacements, that now characterize most of northern New Guinea and the Banda Arc. The identification of the Australia-New Guinea rifted continental margin in what is now the fold and thrust mountain belt of New Guinea, islands of the Outer Banda Arc, East Sulawesi, and Buton, rests largely on stratigraphic correlation and the recognition of the pre-rift sequence, breakup unconformity, and the post-breakup marine transgression and prolonged subsidence in these now highly deformed rocks. One implication of the Jurassic continental rifting is that the pre-rift rocks of the region accumulated in an intracratonic basin of eastern Gondwana. Another important implication is that the continental blocks rifted from the Northern Australia-central New Guinea margin must have drifted northwards towards Asia as the Mesozoic Tethys ocean spread across the tropics and equatorial region. These continental fragments of Gondwana collided with parts of south-east Asia that had been derived from Gondwana in an earlier phase of rifting.

Early Paleozoic Trilobites, Sedimentary Facies, Lithospheric Plates, and Ocean Currents: ABSTRACT

In examining the known occurrence of Cambrian and particularly Ordovician trilobites it has been found that: 1. Faunas of continents and platforms that have remained in a single latitudinal zone, particularly in a warm climate, show most strongly the effects of local environment. Concentric geographic changes in faunal composition and diversity result, as in North America. 2. Faunas of continents that passed rapidly through inclement climatic zones bear the print of climatic rather than local environmental variants. Faunas may be arranged in broad latitudinal bands and apparent standing diversities may change stratigraphically within each continental shelf area, as in western Gondwana (Andean area). 3. Inferred patterns of warm oceanic currents relative to changing continental obstructions are compatible with distribution of pelagic trilobites. 4. Tethyan trilobite distribution during the Ordovician shows reversals in migration related to (a) movement of Moroccan and Algerian Gondwana into warmer climate, (b) removal of Antarctic and Australian Gondwana from its obstructing position across the equatorial current, (c) westward movement of Baltoscandia, and (d) eastward movement of North America. Most oil reserves are in areas that have been in warm climates (horse latitudes) at some time in their geologic history. Lands that have spent the longest geologic time in such zones may have the greatest potential for petroleum production, provided that there is adequate stratigraphic cover and satisfactory geologic structure to retain the oil. End_Page 917------------------------------ Paleobiogeography, here exemplified by trilobite distribution, may make an important contribution to delimiting potential areas for profitable exploration. End_of_Article - Last_Page 918------------