Changqun Cao

Calibrating the End-Permian Mass Extinction

High-precision geochronologic dating constrains probable causes of Earths largest mass extinction. The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

The carbon isotope excursion on GSSP candidate section of Lopingian-Guadalupian boundary

An isotopic stratigraphically well-documented outcrop in Penglaitan, Guangxi Province, South China, has been proposed as a candidate GSSP for the Lopingian–Guadalupian boundary. Correlatable outcrops from the west wing (Tieqiao section) and east wing (Penglaitan section) of the Laibin Syncline exhibit synchronous excursions in carbon isotopes. The isotopic excursions (δ13C) show the best placement of the boundary may lie at the base of Bed 6k which coincides with the Clarkina postbitteri conodont zone and with eustatic change. δ13C increases during the uppermost Guadalupian (Jinogondolella granti conodont zone from the top of 3c to the base of 6i). A δ13C peak value of 5‰ is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression. A gradual depletion of carbon isotopes occurs in the C. postbitteri zone from Bed 6e to 7b, and this gradual δ13C excursion also suggests the sequences around the Guadalupian–Lopingian boundary at the candidate section are conformable. During the middle-later C. postbitteri zone a 3.5‰ dramatic δ13C depletion is recorded at the Tieqiao section, but only a 2‰ depletion at the deeper facies Penglaitan section, synchronous with conodont zones that mark eustatic changes.

Methanogenic burst in the end-Permian carbon cycle

Significance The end-Permian extinction is the most severe biotic crisis in the fossil record. Its occurrence has been attributed to increased CO2 levels deriving from massive Siberian volcanism. However, such arguments have been difficult to justify quantitatively. We propose that the disruption of the carbon cycle resulted from the emergence of a new microbial metabolic pathway that enabled efficient conversion of marine organic carbon to methane. The methanogenic expansion was catalyzed by nickel associated with the volcanic event. We support this hypothesis with an analysis of carbon isotopic changes leading up to the extinction, phylogenetic analysis of methanogenic archaea, and measurements of nickel concentrations in South China sediments. Our results highlight the sensitivity of the Earth system to microbial evolution. The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation.

An early Cambrian agglutinated tubular lophophorate with brachiopod characters

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long pedicle with coelomic space. The terminal bulb of the pedicle provided anchorage in soft sediment. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.

Late Permian magnetostratigraphy and its global correlation

A calibration among magnetic polarity sequence, biostratigraphy zonation and isotopic age reveals that the boundary between the Carboniferous-Permian reversed Polarity Superzone and Permian-Triassic Mixed Polarity Superzone occurs at the top of the Wordian Stage of the Guadalupian Series and is dated as 265 Ma. The Late Permian magnetic polarity sequence integrates four polarity zones, corresponding to the Upper Guadalupian Series, the Wuchiapingian Stage, and the Lower and the Upper Changhsingian Stage of the Lopingian Series. This reference magnetostratigraphy polarity sequence may serve as a useful guide to the chronostratigraphic correlation of Late Permian strata across major biogeographic and facies barriers.

Conodont sample-population approach to defining the base of the Changhsingian Stage, Lopingian Series, Upper Permian

Abstract Conodonts have been restudied in order to define the base of the Changhsingian Stage boundary at Meishan, Changxing County, Zhejiang Province, China. The Changhsingian represents the second and last stage of the Upper Permian, which is also known as the Lopingian Series. A sample-population based taxonomic approach has been used and described. This approach usually views the entire collection within a given sample as a population and recognizes the most consistent and stable characters within that ‘sample-population’ for identification. Three related conodont species, Clarkina longicuspidata Mei & Wardlaw in Mei et al. 1994, C. wangi (Zhang 1987) and C. subcarinata (Sweet in Teichert et al. 1973) have been redefined and redescribed using this new approach that recognizes carinal development as an apomorphic character for these taxa. A consistent change in denticulation has been observed between Clarkina longicuspidata and Clarkina wangi wherein C. longicuspidata has a prominent gap in front of the cusp, whereas C. wangi has a ‘wall’-like carina. The carinal change may have resulted from a heterochronic process involving acceleration, since juvenile descendants exhibit features of ancestral adults; the change may be related to the evolution of other biota that may represent potential food sources for the conodont animal, given the apparent importance of the conodont carina for food processing. It is suggested that the base of the Changhsingian Stage could be defined within the C. longicuspidata-C. wangi lineage, based on the newly refined taxonomy. This boundary occurs close to the flooding surface that represents at least the second parasequence within the Changxing Limestone. The proposed boundary is close to, but not identical with, the traditionally defined boundary.

LOPINGIAN (LATE PERMIAN) BRACHIOPOD FAUNAS FROM THE QUBUERGA FORMATION AT TULONG AND KUJIANLA IN THE MT. EVEREST AREA OF SOUTHERN TIBET, CHINA

Permian strata containing abundant brachiopods are well developed in the Himalaya Tethys Zone. However, relatively few has been systematically described due to the difficult working condition for collecting. In this paper, we describe the brachiopods from the Qubuerga Formation at the Tulong and Kujianla sections in southern Tibet. The brachiopod faunas consist of 15 species belonging to 11 genera. Among the identified 15 species, Retimarginfera xizangensis , Costiferina indica , Fusispirifer semiplicatus , Spiriferella sinica , Biplatyconcha grandis and Neospirifer ( Quadrospina ) tibetensis are very common in the equivalents of the Himalaya Tethys Zone including the Selong Group at the Selong Xishan and Qubu sections in southern Tibet, the Senja Formation in northwest Nepal, the Zewan Formation in Kashmir, and the upper part of the Wargal Formation and the Chhidru Formation in the Salt Range, Pakistan. They are all comparable and can be assigned to the Wuchiapingian- early Changhsingian. Since the brachiopods from the Qubuerga Formation at Tulong and Kujianla are all composed of typical Gondwanan, bipolar or cosmopolitan elements, it is conclusive that the Himalaya Tethys Zone in the northern margin of the Indian Plate was still situated at southern high-latitudes under cold palaeoclimatic conditions during most of the Lopingian. The faunal succession at Tulong also recorded a rapid warming at the very end of the Changhsingian in view of the fact that the typical cold-water Lopingian brachiopod, gastropod and bivalve faunas were dramatically replaced by extremely abundant conodonts Clarkina in the basal part of the dolostone unit of the Tulong Formation. This end-Changhsingian warming is comparable with that recorded throughout the Permian-Triassic boundary interval at Selong, Qubu in southern Tibet, the Salt Range, Pakistan and the sections in Kashmir as well as South China.

Biostratigraphy constraining strontium isotopic stratigraphy and its application on the Lopingian (Late Permian)

The Lopingian is one of the fastest rising periods of seawater strontium isotopic ratios (87Sr/86Sr) in earth history, and its mechanisms and increasing rates of the 87Sr/86Sr evolution were still disputed widely. These disputations among researchers were caused mainly by timeframe selection (sections’ thickness or data of radiometric ages), and different stratigraphic boundaries and un-upmost dated ages. This paper examined published 87Sr/86Sr data of the Lopingian, and projected them on timescales based on evolutionary and age constrained conodonts fossils. 87Sr/86Sr evolution vs fossil constraining timescales was re-established in this period. This research suggests: (1) 87Sr/86Sr excursion projects on fossil zones can truly support 87Sr/86Sr evolutionary pattern in the period; (2) 87Sr/86Sr evolution provides a new approach for stratigraphic research of marine carbonate sections in lieu of biostratigraphic data; (3) 87Sr/86Sr stratigraphy works on marine carbonate sections of different sedimentation rates even between different basins; (4) the 87Sr/86Sr data and its shift was dependent on samples materials and chemical treatment methods; (5) the increasing rate of marine water 87Sr/86Sr in the Late Permian is suggested as 5.4×10−5/Ma or slightly lower; (6) sedimentation age and its 87Sr/86Sr of the Lopingian marine carbonate suggested as: DPRO=259-(RS−0.70695)/5.4×10−5±1 Ma.