Hongfu Yin

Two pulses of extinction during the Permian–Triassic crisis

Over 90% of marine species were lost during the end-Permian extinction. Fossil data show that the crisis in China was marked by two distinct phases of marine extinction separated by a 180,000-year recovery period. The Permian–Triassic mass extinction is the most severe biotic crisis identified in Earth history. Over 90% of marine species were eliminated1,2, causing the destruction of the marine ecosystem structure3. This biotic crisis is generally interpreted as a single extinction event around 252.3 million years ago2,4,5,6, and has been variously attributed to the eruption of the Siberian Traps or possibly a bolide impact7,8,9,10. Here we demonstrate that the marine extinction consisted of two pulses, separated by a 180,000-year recovery phase. We evaluated the range of 537 species representing 17 marine groups in seven Chinese sections from a 450,000-year interval spanning the Permian–Triassic boundary. The first stage of extinction occurred during the latest Permian, and was marked by the extinction of 57% of species, namely all plankton and some benthic groups, including algae, rugose corals, and fusulinids. The second phase occurred in the earliest Triassic, and resulted in the extinction of 71% of the remaining species. This second extinction phase fundamentally altered the marine ecosystem structure that had existed for the previous 200 million years. Because the two pulses showed different extinction selectivity, we conclude that they may have had different environmental causes.

Multidisciplinary high-resolution correlation of the Permian–Triassic boundary

Abstract Biostratigraphic correlation of the ten most important Permian–Triassic boundary sections throughout Tethys enables establishment of four conodont and ammonoid subdivisions within a stratigraphic interval, one to a few metres thick, representing less than 1 Ma. In ascending order, they are conodonts (Clarkina changxingensis–C. deflecta Zone; Hindeodus typicalis Interval; Isarcicella parva Zone and I. isarcica Zone) and ammonoids (Pseudotirolites–Pleuronodoceras Zone, lower Otoceras Zone, upper Otoceras Zone and Ophiceras Zone). Most of them can be traced to North America and the Arctic region. Carbon isotope investigations of 24 sections along Tethys and in Greenland and Spitzbergen confirm the consistency of δ13C negative excursions at the Permian–Triassic boundary, together with an inconsistent Ir anomaly. Eight sections show that in most cases there is a succession of: Ir anomaly (denoting the end-Permian catastrophic environment); δ13C excursion (biomass loss, extinction); P/T boundary (origination of newcomers; potentially capable of intercontinental correlation within that short time interval). There is an intercontinental sequence boundary at the top of the Permian, and a transgressive surface at the P/T boundary followed shortly by a maximum flooding surface. An intercontinental anoxia event accompanied the transgression. Three delineations of the mass extinction phases and three population explosions have been recognized and can be more or less correlated in South China and the Southern Alps. Radiometric dating of the volcanogenic boundary clays of Meishan, Shangsi and the main-stage Siberian Tunguss Traps give an almost identical age of 250 Ma, thus implying a synchronous interregional volcanic event. There are a few palaeomagnetic transforms within the PTB strata. Thus, multidisciplinary research of the P/T boundary strata allows subdivision of this short interval into more than ten intercontinentally correlatable parts. Each subdivision averages less than 100 ka in duration. This may be the highest resolution obtained so far in pre-Cretaceous rocks. High-frequency, Milankovitch-type cyclic deposits within the P/T boundary beds enable correlation of even higher resolution in the Lower Yangtze area. This high resolution is made possible because the P/T transition is a time of saltation and catastrophy in geological history. Causality of the aggregation of events merits further investigation.

Conodont Biostratigraphy and Evolution across Permian-Triassic Boundary at Yangou Section, Leping, Jiangxi Province, South China

Series of large conodont samples with 20 species and 3 similar species in 3 genera were collected from the Permian-Triassic (P-T) boundary sequence in a shallow carbonate facies at Yangou (沿沟), Leping (乐平) County, Jiangxi (江西) Province, South China. On the basis of the distributions of the identified species, seven conodont zones have been recognized in ascending order as follows, Neogondolella changxingensis zone, Neogondolella yini zone, Hindeodus changxingensis zone, Neogondolella taylorae zone, Hindeodus parvus zone, Isarcicella staeschei zone, and Isarcicella isarcica zone. The successive occurrences of Hindeodus changxingensis, Neogondolella taylorae and Hindeodus parvus serve as proxies for defining the P-T biostratigraphy boundary at the base of Sub-bed 21-4 of Bed 21 in the Yangou Section. Correlations with the Meishan Section are also discussed in terms of conodont biostratigraphy. Three successive conodont faunal assemblages are grouped through the P-T transitional interval to examine the evolution of conodonts across the great transitional event.

Application of radiolarians and other fossils in non-Smith strata — — Exemplified by the A’nyêmaqên melange belt in East Kunlun Mts.

The main character of melange strata in an orogenic belt is the integration of mixed materials due to the superposition, displacement or loss of various tectonic slices (blocks) of different origins and environments, different scales, different grades of deformation and metamorphism, and different stages of tectonic evolution. The approach to non-Smith strata in an orogenic belt is to focus on the understanding of the age, facies, tectonic setting of the original formation and the process of deformation-metamorphism of each tectonic slice, reconstruct the history of dispersal and integration of these tectonic slices in time and space, i.e. 4-dimensional. This paper studies the age and facies of the original formation of tectonic slices in the A’nyêmaqên melange belt based on new data of radiolarians, sporo-pollen and trace fossils, and cast new lights on the research of the evolution process of that belt.