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The Permian–Triassic boundary interval in shallow shelf seas of South China shows Upper Permian limestones overlain by lowermost Triassic microbialites. Global sea-level rose across the Permian–Triassic boundary, but an irregular top-Permian erosion surface across a 10 km north–south transect of the Great Bank of Guizhou contains evidence of sea-level fluctuation. The surface represents the ‘event horizon’ of mass extinction, below the biostratigraphic Permian–Triassic boundary defined by first appearance datum of conodont Hindeodus parvus. An Upper Permian foraminiferal grainstone beneath this surface contains geopetal sediments, etched grains, and pendent and meniscus cements interpreted here as vadose. However, these latter diagenetic processes occurred before the event horizon and were followed by erosion of the final Permian surface. This erosion cuts previous fabrics but lacks evidence of weathering or bioerosion. A few centimetres below is an earlier grainstone that was also eroded but lacks proof of sub-aerial processes. Samples therefore reveal one, or possibly two, small-scale relative sea-level changes before the Triassic transgression in this area, and these may relate to local tectonics. The final Permian surface is subject to at least four interpretations: (i) sub-aerial physical erosion and dissolution by carbon dioxide-enriched fresh water or carbon dioxide-enriched mixed water, prior to Triassic transgression; (ii) sub-aerial physical erosion overprinted by dissolution related to carbon dioxide-enriched sea water in the Early Triassic transgression; (iii) submarine dissolution affected by acidified sea water due to rapid increase in volcanically-derived carbon dioxide and oxidized methane released from marine clathrates; (iv) submarine dissolution due to acid anoxic waters rising across the continental shelf, unrelated to atmospheric carbon dioxide or oxidized methane. Field and petrographic evidence suggests that (i) is the simplest option; and it is possible that (ii) and (iii) occurred, but none are proved. Option (iv) is unlikely given the evidence and modelling of supersaturation of upwelled waters with respect to bicarbonate. [ABSTRACT FROM AUTHOR]

High–resolution clay mineralogical investigations were conducted on the Permian–Triassic (P–Tr) carbonate– and siliceous rocks from the Shangsi section, South China. The clay mineralogy is dominated by illite and illite/smectite mixed–layers (I/S) throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 (approaching the End–Permian mass extinction horizon–EPME) onwards. Positive correlations of clay fraction with mainly land–derived TiO 2 and magnetic susceptibility (MS) indicate a primary continental origin of the clay minerals. Rock–Eval pyrolysis analysis, palynomorph coloration, scanning electron microscope (SEM) and Transmission Electron Microscope (TEM) observations, all suggest that the rocks experienced thermal diagenesis which mainly promotes illitization processes of smectite clay minerals while discrete clay minerals are merely affected. Despite this diagenetic effect, clay minerals still carry valuable paleoenvironmental and paleoclimatic information in the Shangsi section. The overall illitic composition of the clay minerals and nearly absence of kaolinite suggest a general semi–arid condition during the P–Tr interval. Appearance of chlorite from bed 24 onwards suggests further aridification compared to the Late Permian. Occurrence of vermiculite from beds 24–28 in association with abundant volcanogenic materials, most negative δ 13 C carb values as well as enhanced soil–derived moretane abundance, suggests catastrophic soil erosion and likely soil acidification during the P–Tr transition in the source area(s) in relation with the active volcanism in that time. Further, decrease of chemical weathering and increase of physical weathering are indicated by increased input of primary clay minerals such as chlorite, a better illite crystallinity and increase of Al 2 O 3 /TiO 2 ratios. A climate cooling period corresponding to the Clarkina changxingensis – Clarkina deflecta conodont zone to the lower Clarkina zhangi conodont zone is indicated by higher abundance of illite, lower terrigenous TiO 2 , MS and Al 2 O 3 /TiO 2 in comparison with the overlying uppermost Permian strata. [ABSTRACT FROM AUTHOR]

Abstract: Brachiopod miniaturization is both the reduction in size of individuals of a species over time, and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time. This paper investigates this phenomenon prior to and during the end-Permian crisis in a deep water setting in South China, based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species. The process of miniaturization near the Permian–Triassic boundary in deep water environments is characterized by: (1) Larger species, including Martinia sp., Costatumulus dongpanensis, and Anidanthus mucronata, reduced in average body size and abundance over time towards the end-Permian brachiopod extinction event. (2) Small species, including Attenuatella mengi and Spinomarginifera semicircridge, showed a mixed response with either no size change, or a reduction in average body size, while these species increased in abundance over time, indicating they were less sensitive to the stressed environmental setting. (3) Both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end-Permian crisis. Regression, an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization, based on the biotic replacement and changes in sea-water chemistry. Among these factors, the fall in sea level is perhaps the primary factor, and led to a decline in productivity and an increased input of terrestrial material into the marine setting. [Copyright &y& Elsevier]

Abstract: Changes in marine primary productivity following the latest Permian mass extinction (LPME) have been debated at length, with little resolution to date owing to a paucity of quantitative data. Herein, we report total organic carbon (TOC) concentrations and organic carbon accumulation rates (OCAR) for 40 Permian–Triassic boundary (PTB) sections with a near-global distribution and consider their implications for changes in marine productivity during the boundary crisis. Many sections in South China exhibit abrupt declines in TOC and OCAR from the Changhsingian (latest Permian) to the Griesbachian (earliest Triassic), a pattern not observed for sections in other regions. This pattern cannot be explained through secular changes in sedimentation rates, sedimentary facies, or redox conditions, all of which would have favored higher (rather than lower) TOCs and OCARs during the Griesbachian. Further, back-calculation of OC fluxes demonstrate that this pattern cannot be attributed to diagenetic loss of OC in the sediment or, possibly, to OC remineralization in the water column. The most likely explanation is a collapse of marine primary productivity across the South China region concurrently with the LPME and continuing for an extended interval into the Early Triassic. The productivity crash as well as the coeval decimation of benthic marine fauna coincided with deposition of the “boundary clay” at Meishan D, suggesting that both events were related to a large explosive volcanic eruption of uncertain provenance. In other PTB sections having a wide geographic distribution, OCARs increased on average by a factor of ~4× across the LPME, largely owing to a concurrent increase in bulk accumulation rates (BARs). Radiometric dating uncertainties can account at most for only a fraction of the secular change in BARs, which are likely to reflect an increase in subaerial weathering rates and elevated fluxes of detrital material to Early Triassic marine systems. Intensification of chemical weathering relative to physical weathering may have increased the flux of nutrients to the Early Triassic ocean, enhancing marine productivity and contributing to the widespread development of marine dysoxia–anoxia. [Copyright &y& Elsevier]