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. Newdates 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.

The Early Triassic Induan-Olenekian Stage boundary (Dienerian-Smithian sub-stage boundary) has been identified at a depth of 2719.25 m 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 Late Paleozoic Ice Age involved several pulses of glaciation from the early Carboniferous through mid-Permian in southern Gondwana. In eastern Australia, biostratigraphy suggested the final pulse to be c. 265 Ma. New U-Pb zircon ages from volcanic layers revise the age of latest glacigenic deposits to c. 255 Ma, making the late stage of the LPIA broadly synchronous with emplacement of the Emeishan large igneous province (ELIP) of China. Recent zircon U-Pb ages indicate rapid emplacement of the intrusive phase of the ELIP, from 260-257 Ma. New zircon U-Pb ages from volcanics overlying the youngest basalts indicate a short-lived effusive component, ending by 258 Ma. Emeishan volcanism has been linked with the end-Mid-Permian mass extinction, though radioisotopic ages from sedimentary units that record the extinction are limited. The ELIP is smaller than other magmatic provinces that have been associated with mass extinctions, though in terms of devolatilization reactions that can affect climate, volume is less significant than eruption rate and composition of the host rock. An important test of the impact of the ELIP on climate is the stable isotopic record of ocean sediments. Initial stable Ca isotope data from marine carbonates indicate the change in ocean chemistry in the Mid- to Late Permian was smaller than that associated with the end-Permian extinction, but suggest ocean anoxia. Efforts are ongoing to establish a robust chronology for the end-Mid-Permian extinction.

Hainan Island is a key component of the South China Sea region and provides insights on regional geological evolution since the Paleozoic. Ten newLA-ICPMS zircon U-Pb ages from granites of Hainan Island include Late Permian (254±3Ma; 252±3 Ma), Middle-Late Triassic (243±2Ma; 242±3Ma; 240±2Ma; 228±2 Ma) and late Early to early Late Cretaceous (105±1Ma; 101±1Ma; 96±2Ma; 95±3 Ma) ages. All samples in the present study, including late Permian, Middle-Late Triassic, and late Early to early Late Cretaceous granitic rocks show geochemical characteristics similar to those of calc-alkaline to high-K calc-alkaline I-type granites. Major and trace element geochemical variations show that during petrogenesis, these granites experienced fractional crystallization of minerals (e.g., Ti oxides and apatite). Compared to the late Permian and Middle-Late Triassic granitic rocks, middle to late Cretaceous granites generally have lower initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70594 to 0.70886, lower TDM2 ages of 1314 to 1382 Ma, and higher εNd(t) of -4.94 to -5.96, implying that the magmatic source for Cretaceous granites received more significant contribution from juvenile material relative to that for Permo-Triassic granites. These new data, combined with data from literature for Hainan Island and the South China Sea (SCS) region underpin a conceptual model for late Paleozoic to Mesozoic tectonic evolution for Hainan Island and the general SCS region as follows, (a) Late Permian (272-252 Ma), the initiation and development of continental arc related to the subduction of Palaeo-Tethys ocean; (b) Triassic (249-228 Ma), continued arc magmatism, the gradual cessation of Palaeo-Tethys subduction and subsequent development of an extensional setting; (c) Early Jurassic to early Cretaceous (190-130Ma), the development of an Andean-type continental arc, and regional tectonic regime switch to the westward subduction of the Palaeo-Pacific plate; (d) Middle to late Cretaceous (128-70Ma), the continuation of the Andean-type arc, the development of an extensional setting due to slab rollback, and the cessation (~70 Ma) of Palaeo-Pacific plate subduction.

Ocean anoxia was widespread in the latest Permian and continued episodically into the Early Triassic. These episodes of anoxia have been interpreted to be due to the upward rise(s) of the chemocline, oceanic overturn(s) and/or major climatic perturbations. A significant anoxic event is recorded in the Kockatea Shale of the lower part of the Senecio-1 borehole core from the northern Perth Basin, Australia. We here present new biostratigraphic and chemostratigraphic data constraining the age of this anoxic event. The Early Triassic Induan-Olenkian Stage boundary (Dienerian-Smithian Sub-Stage boundary) has been identified in the Senecio-1 Well. This is the first international Triassic stage boundary to be unequivocally placed in Australia. Relatively abundant conodont faunas (1,000+ elements) represent three conodont zones in ascending order, the 'Clarkina carinata' - 'Neospathodus dieneri' Zone, the 'Neospathodus waageni eowaageni' Zone and the 'Neospathodus waageni waageni' Zone. In addition, a 'Neospathodus waageni' subsp. nov. subzone is recognised in the upper part of the 'Neospathodus waageni waageni' Zone.

Measured lithostratigraphic sections of the classic Permian–Triassic non-marine transitional sequences covering the upper Quanzijie, Wutonggou, Guodikeng and lower Jiucaiyuan Formations at Dalongkou and Lucaogou, Xinjiang Province, China are presented. These measured sections form the framework and reference sections for a range of multi-disciplinary studies of the P–T transition in this large ancient lake basin, including palynostratigraphy, vertebrate biostratigraphy, chemostratigraphy and magnetostratigraphy. The 121 m thick Wutonggou Formation at Dalongkou includes 12 sandstone units ranging in thickness from 0.5 to 10.5 m that represent cyclical coarse terrigenous input to the lake basin during the Late Permian. The rhythmically-bedded, mudstone-dominated Guodikeng Formation is 197 m and 209 m thick on the north and south limbs of the Dalongkou anticline, respectively, and 129 m thick at Lucaogou. Based on limited palynological data, the Permian–Triassic boundary was previously placed approximately 50 m below the top of this formation at Dalongkou. This boundary does not coincide with any mappable lithologic unit, such as the basal sandstones of the overlying Jiucaiyuan Formation, assigned to the Early Triassic. The presence of multiple organic δ¹³C-isotope excursions, mutant pollen, and multiple algal and conchostracan blooms in this formation, together with Late Permian palynomorphs, suggests that the Guodikeng Formation records multiple climatic perturbation signals representing environmental stress during the late Permian mass extinction interval. The overlap between the vertebrates Dicynodon and Lystrosaurus in the upper part of this formation, and the occurrence of late Permian spores and the latest Permian to earliest Triassic megaspore Otynisporites eotriassicus is consistent with a latest Permian age for at least part of the Guodikeng Formation. Palynostratigrahic placement of the Permian–Triassic boundary in the Junggar Basin remains problematic because key miospore taxa, such as Aratrisporites spp. are not present. Palynomorphs from the Guodikeng are assigned to two assemblages; the youngest, from the upper 100 m of the formation (and the overlying Jiucaiyuan Formation), contains both typical Permian elements and distinctive taxa that elsewhere are known from the Early Triassic of Canada, Greenland, Norway, and Russia. The latter include spores assigned to Pechorosporites disertus, Lundbladispora foveota, Naumovaspora striata, Decussatisporites mulstrigatus and Leptolepidites jonkerii. While the presence of Devonian and Carboniferous spores and Early Permian pollen demonstrate reworking is occurring in the Guodikeng assemblages, the sometimes common occurrence of Scutasporites sp. cf. Scutasporites unicus, and other pollen, suggests that the Late Permian elements are in place, and that the upper assemblage derives from a genuine transitional flora of Early Triassic aspect. In the Junggar Basin, biostratigraphic data and magnetostratigraphic data indicate that the Permian–Triassic boundary (GSSP Level) is in the middle to upper Guodikeng Formation and perhaps as high as the formational contact with the overlying Jiucaiyuan Formation.

Accurate and precise calibration of the geological timescale is a fundamental aspect of geoscience. The advent of the 'chemical abrasion' technique (e.g., Mattinson, 2005) for zircon preparation prior to thermal ionisation mass spectrometry (CA-TIMS) has significantly improved concordance and coherence of single-zircon analyses across a range of rock types, enhancing the geological accuracy of the interpreted crystallisation ages. This development affords an excellent opportunity to revisit and re-evaluate the accuracy of SHRIMP 206Pb/238U dating of natural zircon, and particularly the hypothesis that carefully targeting the 'best' areas of the 'best' grains with the ion beam should yield crystallisation ages closely comparable to those determined via CA-TIMS (cf. Kryza et al., 2012). This study examines a series of 10 samples, largely assumed to be airfall ash beds, within the coal-rich Middle to Late Permian successions of the Sydney and Bowen basins of eastern Australia. Recent work focussed on understanding mass extinctions and climate change across the critical Late Permian-Early Triassic boundary in eastern Australia has been hampered by the endemic nature of the local faunal assemblages, which has precluded reliable high-resolution biostratigraphic correlations to global stratotypes in China and elsewhere.

The Middle Permian-Early Triassic (MP-ET) of Eastern Australia hosts extensive black coal reserves of major economic importance but contains predominantly endemic biota precluding precise international correlation. MP-ET stage boundaries, and end-Guadalupian and end Permian mass extinction levels are poorly constrained. Attempts to calibrate the MP-ET of Australia using SHRIMP resulted in controversial radioisotopic ages with percent-level uncertainty and compromised accuracy. We here report more than 40 new high-precision (most at the ±0.05 myr level) using U-Pb CA-IDTIMS single zircon techniques for tuffs in the Sydney, Gunnedah and Bowen basins. These dates provide vital international timescale tie points and allow us to correlate individual tuff beds at the intra and inter basin levels. The youngest dates from the Garie Fm Sydney Basin (c. 247.7 Ma, c. 248.0 Ma) give a late Early Triassic (late Spathian) age. An age of c. 252.2 Ma from the top Bandanna Formation, Bowen Basin equates with the Permian-Triassic boundary. The oldest dates obtained are c. 263.4 Ma from the Broughton Fm and c. 271.4 Ma for the Rowan Fm, Sydney Basin, older than the Guadalupian-Lopingian boundary of c. 260 Ma. Implications of these ages for calibration of stratigraphy, local and regional correlations, placement of mass extinction levels, sedimentation rates, dating of environmental and climate change (including glaciation) and as a chronological framework for energy resources are presented.

The Late Permian - Early Triassic interval of Australia contains a predominantly endemic biota. A paucity of international marine index fossils, in particular conodonts and ammonoids, has previously precluded precise correlation with standard northern hemisphere marine sequences and internationally established System and Stage Global Stratotype Sections and Points (GSSPs). The Permian-Triassic boundary and other Late Permian and Early Triassic stage boundary levels, and the major end-Guadalupian and latest Changhsingian (end-Permian) mass extinction levels in Australia remain poorly constrained. Attempts to calibrate the Late Permian - Early Triassic of Australia using U-Pb analyses on of zircons from volcanic products using micro-beam Sensitive High Resolution Ion Microprobe (SHRIMP) techniques have resulted in controversial radio-isotopic ages with per cent-level uncertainty and accuracy that may be compromised due to the use of a standard which is now deemed unsuitable. We will present new high-precision biostratigraphic, isoptopic geochronologic (U-Pb IDTIMS ages on chemically abraded individual zircons with permil-level resolution) and chemostratigraphic data that provide important international timescale calibration points in the Late Permian - Early Triassic of Australia. We expect that through integration of U-Pb and 40Ar/39Ar geochronology with chemo- and biostratigraphy, that the time scale of the Late Permian - Early Triassic of Australia will be greatly improved and will lead to more realistic evaluation of high-latitude end-Guadalupian and end-Permian biotic crises and their aftermaths and greater understanding of climate change in Australia and globally during this economically important time period.

Intraplate volcanism initiated shortly after the cessation of Cenozoic seafloor spreading in the South China Sea (SCS) region, but the full extent of its influence on the Indochina block has not been well constrained. Here we present major and trace element data and Sr-Nd-Pb-Hf isotope ratios of late Cenozoic basaltic lavas from the Khorat plateau and some volcanic centers in the Paleozoic Sukhothai arc terrane in Thailand. These volcanic rocks are mainly trachybasalts and basaltic trachyandesites. Trace element patterns and Sr-Nd-Pb-Hf isotopic compositions show that these alkaline volcanic lavas exhibit oceanic island basalt (OIB)-like characteristics with enrichments in both large-ion lithophile elements (LILE) and high field strength elements (HFSEs). Their mantle source is a mixture between a depleted Indian MORB-type mantle and an enriched mantle type 2 (EMII). We suggest that the post-spreading intraplate volcanism in the SCS region was induced by a Hainan mantle plume which spread westwards to the Paleozoic Sukhothai arc terrane.