Permian-Triassic Boundary In South China Research Articles

The source and tectonic setting of the Changhsingian K-bentonites in the Huaying Mountain region, South China

Numerous volcanic ash (or K-bentonite) beds are ubiquitous in the Permian-Triassic boundary (PTB) successions in South China and are conjectured to have been a critical factor in global events, such as the Permian-Triassic mass extinction. However, the precise location and tectonic setting of related volcanism remain debated. In this study, we present whole-rock geochemistry, zircon U Pb ages, trace element compositions and in situ Hf isotope analyses of K-bentonites found in the Late Permian Changxing Formation in the Huaying Mountain region, eastern Sichuan Province, northern South China. The two samples yield U Pb zircon ages of 253.7 ± 1.4 Ma (QJP-38-R-1 below) and 253.0 ± 2.0 Ma (QJP-38-R-2 above). Zircons with ages of 240–280 Ma from sample QJP-38-R-1 have negative ε Hf ( t ) values from −16.65 to −1.65 and two-stage model (T DM c ) ages from 1.38 to 2.34 Ga, whereas those from QJP-38-R-2 have mainly negative ε Hf ( t ) values from −7.28 to 0.13 and T DM c ages from 1.28 to 1.74 Ga. The low ε Hf ( t ) values and T DM c ages suggest that the original magmas mainly involved Paleoproterozoic-Mesoproterozoic crustal components and a few mafic mantle materials. Moreover, zircon trace element characteristics show that the two samples were sourced from a subduction-driven magmatic arc. The zircons from QJP-38-R-1 are primarily derived from S-type granites that formed in continental granitic rocks related to a continental arc tectonic setting, whereas the zircons from QJP-38-R-2 are mainly derived from S-type granites in oceanic granitic rocks related to an island arc tectonic setting. The K-bentonites near the PTB in South China may have originated from felsic volcanism as a result of the convergence of the Paleo-Tethys Ocean. The integration of zircon Hf isotope and trace element compositions indicates that the PTB K-bentonites in South China may have been derived from a series of volcanic eruptions occurring within a short interval at the continental margins around South China. Volcanic eruptions took place at the Ailaoshan-Sanjiang continental margins in or near southwestern South China and may be the major source of K-bentonites. Volcanic eruptions took place at the East Kunlun or West Qinling continental margins and may have provided a small number of original materials. This result indicates that these K-bentonites may have multiple sources. • Newly found PTB K-bentonites were reported weighted mean 206 Pb/ 238 U ages of 253.7 ± 1.4 Ma and 253.0 ± 2.0 Ma. • The PTB K-bentonites may be sourced from felsic volcanism as a result of the convergence of the Paleo-Tethys Ocean. • The PTB K-bentonites in South China may have multiple sources.

High-precision time-space correlation through coupled apatite and zircon tephrochronology: An example from the Permian-Triassic boundary in South China

Abstract Accurate and precise dating of individual volcanogenic beds that spread across multiple sedimentary successions is a powerful tool to untangle stratigraphic age contradictions, since these horizons are deposited synchronously. In this study, we show that combining apatite chemistry with zircon age, Th/U ratio, and Hf isotope composition leads to reliable lateral correlation of volcanic horizons across sections representing disparate biological, chemical, and physical paleoenvironments. We correlate two volcanogenic horizons across six sedimentary sections straddling the Permian-Triassic boundary (PTB) in the Nanpanjiang Basin (South China), including the last Permian bed below the unconformity in shallow-water sections of the Luolou Platform. We place the PTB in our sections at the marked lithological change in order to avoid the difficulties that arise from the diachronism of the index conodont Hindeodus parvus, the first occurrence of which defines the PTB at the Global Stratotype Section and Point at Meishan. Our new data demonstrate that these volcanogenic beds are contemporaneous and cogenetic, allowing us to pool high-precision U-Pb zircon ages from the same horizon across several sections, and dating the last Permian volcanic event in this basin at 252.048 ± 0.033 Ma. We show that the mineral chemistry of apatite and zircon of intra- and interbasin-wide volcanogenic beds provides tie points against which biozones, carbon isotopes, astronomic cycles, and geomagnetic polarity time series can be stringently tested.

Ages, trace elements and Hf-isotopic compositions of zircons from claystones around the Permian-Triassic boundary in the Zunyi Section, South China: Implications for nature and tectonic setting of the volcanism

A growing body of evidence shows that volcanism near the Permian-Triassic boundary (PTB) may be crucial in triggering the Permian–Triassic (P–Tr) mass extinction. Thus, the ash beds near the PTB in South China may carry information on this event. Three volcanic ash layers, altered to clay, outcropped in the PTB beds in Zunyi Section, Guizhou Province, Southwest China. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these three ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons are mainly magmatic in origin (241-279 Ma) except for two inherited/xenocrystic zircons (939 and 2 325 Ma). The ages of these magmatic zircons indicate three episodes of magmatism which occurred around the Middle- Late Permian boundary (~261.5 Ma, MLPB), the Wuchiapingian-Changhsingian boundary (~254.5 Ma, WCB), and the PTB (~250.5 Ma), respectively. The first two episodes of magmatism near the MLPB and WCB may be attributed to magmatic inheritance or re-deposition. All magmatic zircons share similar trace-element and Hf-isotope compositions. They have Y, Hf, Th and U contents and Nb/Ta ratios are typical of zircons from silicic calc-alkaline magmas. These zircons also exhibit enriched Hf-isotope compositions with eHf(t) values of -11.4 to +0.2, which suggests that the three magmatic episodes involved melting of the continental crust. The more enriched Hf-isotope composition (eHf(t)=-11.4- -4.8) of Bed ZY13 (~250.5 Ma) implies more input of ancient crustal material in the magma. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggest that these three episodes of magmatism may take place along the convergent continent margin in or near southwestern South China as a result of the closure of the Palaeo-Tethys Ocean.

Conodont zones and related ash beds through the Permian-Triassic Boundary in South China

Six sections from diverse paleogeographic settings in South China provide a high-resolution succession of conodont zones and associated ash beds through the Permian-Triassic boundary. Acomplete succession of eight conodont zones and eight associated ash beds is recorded in the basin-filling sequences: in ascending order, the Clarkina yini Zone with top ash bed 1, the Clarkina meishanensis Zone and ash bed 2 within it, the Clarkina taylorae Zone with ash bed 3 at its base, the H. changxingensis-C. microcuspidata Zone with ash bed 4 at its base and ash bed 5 within it, the Hindeodus parvus Zone with top ash bed 6, the Isarcisella staeschei Zone and ash bed 7 within it, the Isarcisella isarcica Zone and ash bed 8 within it, and the Neogondolella krystyni Zone. In slope settings, ash bed 3 and the C. taylorae Zone are missing; whereas in the strata of the platform interior, the C. meishanensis Zone and associated ash beds 1 and 2 are also missing. This pattern indicates an unconformity that represents increasing missing section in increasingly shallower deposits. The Global Stratotype Section and Point for the base of the Triassic, at Meishan, China, is recognized as having been formed in a slope setting, with an unconformity at the base of Bed 25. The identification of these conodont zones in Iran indicates their applicability outside of South China.

Ostracods (Crustacea) through the Permian-Triassic boundary in South China: the Meishan stratotype (Zhejiang Province)

The Global Stratotype Section and Point (GSSP) of the Permian–Triassic boundary, located in Meishan, Zhejiang Province, South China, was sampled bed-by-bed for ostracods. Ninety-eight species belonging to forty-three genera are recognized. Twenty-five new species are described and figured: Bairdia bassoni Crasquin sp. nov., B. broutini Crasquin sp. nov., B. deweveri Crasquin sp. nov., B. fangnianqiaoi Crasquin sp. nov., B. gaelleae Crasquin sp. nov., B. limatusformis Forel sp. nov., B. paussi Crasquin sp. nov., B. pierrevalentini Crasquin sp. nov., B. wushunbaoi Crasquin sp. nov., Baschkirina ballei Crasquin sp. nov., B. huzhouensis Forel sp. nov., Basslerella annesophieae Crasquin sp. nov., Hollinella martensiformis Crasquin sp. nov., Kempfina taihuensis Forel sp. nov., Knightina hongfui Crasquin sp. nov., Liuzhinia praeantalyaensis Forel sp. nov., Microcheilinella rectodorsata Forel sp. nov., M. shicheni Crasquin sp. nov., M.? multinodosa Forel sp. nov., Orthobairdia lemairei Crasquin sp. nov., Paraparchites chenshii Crasquin sp. nov., Praezabythocypris? pulchraformis Forel sp. nov., Samarella meishanella Forel sp. nov., S. victori Crasquin sp. nov., and Silenites? zhejiangensis Forel sp. nov. One new genus name is proposed: Kempfina Crasquin nom. nov. The stratigraphic distribution of all the species is given. Ostracod biodiversity variations are analyzed through the section. The main drop is recorded in bed 22, occurring a little earlier in ostracods than in foraminifers, corals and brachiopods. The decline in ostracod diversity is more progressive than in the other groups. Variations in ostracod biodiversity during the Changhsingian are related to fluctuations in palaeoenvironmental conditions.

Life crises on land across the Permian–Triassic boundary in South China

The western Guizhou and eastern Yunnan area of southwest China commands a unique and significant position globally in the study of Permian–Triassic boundary (PTB) events as it contains well and continuously exposed PTB sections of marine, non-marine and marginal-marine origin in the same area. By using a range of high-resolution stratigraphic methods including biostratigraphy, eventostratigraphy, chronostratigraphy and chemostratigraphy, not only are the non-marine PTB sections correlated with their marine counterparts in the study area with high-resolution, the non-marine PTB sections of the study area can also be aligned with the PTB Global Stratotype Section and Point (GSSP) at Meishan in eastern China. Plant megafossils (“megaplants”) in the study area indicate a major loss in abundance and diversity across the PTB, and no coal beds and/or seams have been found in the non-marine Lower Triassic although they are very common in the non-marine Upper Permian. The megaplants, however, did not disappear consistently across the whole area, with some elements of the Late Permian Cathaysian Gigantopteris flora surviving the PTB mass extinction and locally even extending up to the Lower Triassic. Palynomorphs exhibit a similar temporal pattern characterized by a protracted stepwise decrease from fern-dominated spores in the Late Permian to pteridosperm and gymnosperm-dominated pollen in the Early Triassic, which was however punctuated by an accelerated loss in both abundance and diversity across the PTB. Contemporaneous with the PTB crisis in the study area was the peculiar prevalence and dominance of some fungi and/or algae species. The temporal patterns of megaplants and palynomorphs across the PTB in the study area are consistent with the regional trends of plant changes in South China, which also show a long-term decrease in species diversity from the Late Permian Wuchiapingian through the Changhsingian to the earliest Triassic, with about 48% and 77% losses of species occurring respectively in the end-Wuchiapingian and end-Changhsingian. Such consistent patterns, at both local and regional scales, contradict the hypothesis of a regional isochronous extinction of vegetation across the PTB, and hence call into question the notion that the end-Permian mass extinction was a one-hit disaster. Instead, the data from the study area and South China appears more consistent with a scenario that invokes climate change as the main driver for the observed land vegetation changes across the PTB in South China.

Pattern of marine mass extinction near the Permian-Triassic boundary in South China.

The Meishan section across the Permian-Triassic boundary in South China is the most thoroughly investigated in the world. A statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251.4 million years ago, coincident with a dramatic depletion of delta13C(carbonate) and an increase in microspherules.

Brachiopods Near the Permian-Triassic Boundary in South China

Brachiopods Near the Permian-Triassic Boundary in South China

Conodont Survival and Low Iridium Abundances Across the Permian-Triassic Boundary in South China

The Permian-Triassic sedimentary sequence of China includes one of the most complete and fossiliferous Paleozoic-Mesozoic boundaries known. Closely spaced sampling across the boundary, which is an important extinction event for most organisms, has produced good conodont faunas that show little diversity change. A drop in conodont abundance is the only apparent response to the extinction event. A low concentration of iridium in the boundary clay (0.002 part per billion +/-20 percent), as well as in samples immediately below and above, that range from 0.004 to 0.034 part per billion do not support the proposal of an extraterrestrial impact event at this boundary in China.

On the Transitional Bed and the Permian-Triassic boundary in South China

On the Transitional Bed and the Permian-Triassic boundary in South China