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Massive carbon dioxide (CO2) emissions are widely assumed to be the driver of the end-Permian mass extinction (EPME). However, the rate of and total CO2 released, and whether the source changes with time, remain poorly understood, leaving a key question surrounding the trigger for the EPME unanswered. Here, we assimilate reconstructions of atmospheric Pco2 and carbonate δ13C in an Earth system model to unravel the history of carbon emissions and sources across the EPME. We infer a transition from a CO2 source with a thermogenic carbon isotopic signature associated with a slower emission rate to a heavier, more mantle-dominated volcanic source with an increased rate of emissions. This implies that the CO2 degassing style changed as the Siberian Traps emplacement evolved, which is consistent with geochemical proxy records. Carbon cycle feedbacks from terrestrial ecosystem disturbances may have further amplified the warming and the severity of marine extinctions.

Analysis of the four cases of the sequence boundary (SB)-transgressive surface (TS) relation in nature shows that applying transgressive surfaces as sequence boundaries has the following merits: it improves the methodology of stratigraphic subdivision; the position of transgressive surface in a sea level curve is relatively fixed; the transgressive surface is a transforming surface of the stratal structure; in platforms or ramps, the transgressive surface is the only choice for determining the sequence boundary; the transgressive surface is a readily recognized physical surface reflected by seismic records in seismostratigraphy. The paper reaches a conclusion that to delineate a SB in terms of the TS is theoretically and practically better than to delineate it between highstand and lowstand sediments as has been done traditionally.

Three third–order sequences and about one hundred high–frequency cycles or Milankovitch cycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in the Meishan Section of Changxing, Zhejiang Province, southern China, the candidate stratotype section of the global Permo–Triassic boundary, based on a detailed study of the biological, ecological and high—resolution allochthonous cyclic events, microfacies and depositional systems. Furthermore, the stacking pattern of the depositional systems across various Changxingian and Griesbachian sedimentary facies of the Lower Yangtze and the sequence stratigraphic framework are outlined with the Meishan section as the principal section. In this paper the habitat types of fossil biota are applied to semiquantitative palaeobathymetry and the study of relative sea level changes.

The Lower Triassic in Chaohu area, Anhui Province, China, is well developed and its sequence is typical in South China. After a brief introduction of the Induan-Olenekian boundary of Chaohu, this article presents some new data on conodonts. More than ten times of conodont samplings and investigations have recovered thousands of conodont specimens, which are especially rich in the Induan-Olenekian boundary strata at the West Pingdingshan Section in Chaohu City, Anhui Province. The most distinctive forms are the conodonts of the Neospathodus dieneri group and N. waageni group. The first occurrence of N. waageni eowaageni , which is regarded as the indicator of the Induan-Olenekian boundary, is situated at 40.49 m above the base of Yinkeng Formation. Some key conodonts and seven new specimens are introduced.

The Early Triassic paleogeographical setting of the Chaohu section in China was in a deep part of the Yangtze platform and this has resulted in a rather complete Lower Triassic sequence with rich ammonoid and conodont successions. Three Lower Triassic sections, West Pingdingshan, North Pingdingshan and South Majiashan, have been sampled in detail for a systematic conodont study. Eight conodont zones are recognized; in ascending order these are the zones of Hindeodus typicalis , Neogondolella krystyni , Neospathodus kummeli , Neospathodus dieneri , Neospathodus waageni , Neospathodus pingdingshanensis , Neospathodus homeri , and Neospathodus anhuinensis. These are correlated with the sequences in North America and other areas of the world. The succession provides a good basis for the definition of the global stratotype of the Induan–Olenekian boundary (GSSP), which has been proposed at the base of the Neospathodus waageni Zone in West Pingdingshan. Seven new species are introduced: Neospathodus chaohuensis , N. chii , N. concavus , N. eotriangularis , N. pingdingshanensis , N. posterolongatus , N. tongi , a new subspecies N. waageni eowaageni , and three morphotypes of N. dieneri .

The Lower Triassic strata developed in Chaohu, Anhui Province of east central China, including the Yinkeng, Helongshan and Nanlinghu formations is about 268 m thick and consists of carbonate rocks such as micrite limestone and nodular limestone as well as shale and argillaceous mudstone. The deficiency of sedimentary structures and bioclastic particles and presence of pyrite and high ratios of V/(V + Ni) suggest that the Lower Triassic strata formed in a quiet, open-marine basin environment bordering carbonate slope and lower slope. Within the Lower Triassic, the cyclic deposits include two orders of thickening- and coarsening-upward successions, respectively called basic unit (BU) and basic sequence (BS), which represent shallowing-upward cycles. Five basic units are recognized and they are mostly composed of shale, argillaceous mudstone, calcareous mudstone and nodular limestone and overlying nodular limestone and micrite limestone, about 0.25–1.4 m thick. The shale and mudstone mainly formed in a deep water basin, and the nodular limestone and micrite limestone formed on the rise of basin margin or the base of slope. Thus, the basic units are interpreted to reflect cyclic sedimentation from the deep water basin to the rise of basin margin or from the rise to base of slope. The basic units are combined with medium- to thick-bedded micrite limestones and thus form four types of basic sequences, average 6.5–14.62 m thick. Likewise, they are interpreted to be shallowing-upward cycles with long period, for example from the deep water of basin, through the rise of basin margin, to the base of slope, farther, reaching to lower slope. The various orders of cycle in the Lower Triassic are laterally very extensive, regionally, which suggests that the fluctuation of sea level was likely a control on the origin of the cycles. These small-scale transgressive–regressive cycles possibly reflect Milankovitch cyclicity. The associations of basic sequences constitute two transgressive–regressive cycles which comprise strata of Yinkeng–Helongshan and Nanlinghu stages, respectively, which is similar to the carbon isotope cycles of the Lower Triassic. Tectonic activities can control the origin of the cycles. The collision of South China Block and North China Block in the Lower Middle Triassic may have resulted in the development of the two cycles, and caused the shallowing-upward sequence of the Lower Triassic from deep water basin to slope.

Early Triassic carbon isotopes are measured based on 1422 carbonate bulk samples from 10 Lower Triassic sections in different palaeogeographic settings in South China. Early Triassic fluctuation of d 13 C is used as a proxy for environmental change to discuss the devastation and restoration of marine ecosystems following the biggest Phanerozoic mass extinction at the end of the Permian. Early Triassic d 13 C profiles derived from various depositional settings in South China yield comparable excursion patterns. A dramatic negative shift of d 13 C across the Permian/Triassic boundary is followed by a moderate increase in d 13 C values throughout the Induan. A positive d 13 C anomaly occurs near the Induan/Olenekian boundary, followed by a Smithian interval of lower d 13 C values. A distinct positive shift in d 13 C coincides with the Smithian/Spathian boundary, and is followed by a high Spathian plateau of d 13 C values. Thus the distinct d 13 C anomalies coincide well with key stratigraphic boundaries. Early Triassic intervals of low d 13 C values correspond to a decline in benthic generic diversity in South China and intervals of high d 13 C values are coupled with an increase in biodiversity. The Early Triassic fluctuations of d 13 C profiles are good proxies for perturbations of ecologic environments, indicating multiple phases of devastation–restoration of marine ecosystems punctuated by several unexpected extraneous events such as volcanic activity. The initial restoration of marine ecosystems may have occurred earlier in the Induan and the ecosystems were subsequently destroyed during the Smithian. Biotic and environmental recoveries occurred at the Spathian, while the ecosystems eventually returned to normal levels in the early Middle Triassic. Copyright # 2007 John Wiley & Sons, Ltd.

Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ13C background values are intensively controlled by palaeogeographic environment. In general, δ13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan-Olenekian boundary and the Lower Triassic-Middle Triassic boundary.

This paper provides a synthetic review of researches on Meishan Section D, the Global Stratotype Section and Point of the Permian-Triassic Boundary (PTB). The history of research, geographic and geological setting of the section are briefly introduced. Changhsingian to “Griesbachian” conodont and ammonoid zonations, the most perfect Permo-Triassic zonations over the world, are presented, with a short discussion on the age of Otoceras. The Changhsingian to “Griesbachian” strata are subdivided into three 3rd order sequences, and the sedimentary structure of each sequence is indicated. The paper presents a correlation of the Changhsingian to “Griesbachian” magnetostratigraphy of the Meishan section with the general scale, and informed the negation of a short magnetic reversal at the PTB suggested by Zhu and Liu (1999). Recent developments of chemostratigraphy of δ13C and δ34S are introduced, especially the discovery of more than one negative δ13C excursions across the PTB. Two important molecular researches reveal the profound changes at the base of eco-system, the microbial catastrophy, and the euxinic conditions in the photic zone during the Permian-Triassic superanoxic event. The paper reports the changes in dating the age of PTB since 2001. According to recent achievements, the age of volcanogenic claybed 25, 14 cm below the PTB, is now set at 252.4±0.3 Ma. A discussion on the eventostratigraphy concludes that, although there is a major event episode at beds 25–26, the events across the PTB at Meishan are multi-episodic and commenced prior to the Event Beds 25–26, thus the possibility that the mass extinction was mainly induced by an exterrestrial impact is largely excluded.

The West Pingdingshan Section in Chaohu, Southeast China’s Anhui Province is one of the potential GSSP candidates for the Induan-Olenekian boundary. Extensive study has been done on the Induan-Olenekian boundary strata at the section to meet the requirements of defining the GSSP precisely. This paper focuses on the boundary strata at the section to present a review of the main results achieved in recent years. The Induan-Olenekian boundary strata here cover an interval of about four meters at the West Pingdingshan Section, in which the key indices of defining the boundary and the chief transitional processes of some parameters at the boundary are included. The relationship between the boundaries defined by ammonoids and by conodonts is well clarified at the section. The magnetic polarity analysis shows that the boundary interval belongs to a normal polarity zone. Both the carbonate and organic carbon isotopes compositions experienced a significant conversion in the boundary interval.

Based on detailed field observation and multidisciplinary studies of integrated stratigraphy, the marine Lower and Middle Triassic of Lower Yangtze region is divided into five third-order sequences, the general approach of the outcrop sequence stratigraphical study of carbonate ramp is proposed, the pattern in the development of the Early and Middle Triassic sequence under the major regression is summarized, and the sequence stratigraphical and chronostratigraphical frameworks across various paleogeographical facies zones on the marginal platform are established.