| The biological extinction, which was occurred near the Permian-Triassic boundary (PTB), was the largest crisis in the Paleozoic earth history (-600 Ma). It is still under much debate about the causes of this catastrophe, although large number of works had been focused on that during the past few decades. Large amount of evidences linked the disaster to the volcanisms, but the geobiological processes of the volcanic effects to the oceanic environments and organisms are still unclear. During the Permian-Triassic transition, volcanic ash layers were widespread in the South China craton. Previous works were focused on the distribution and special minerals of the volcanic ash layers together with the dating of the volcanic eruptions. The linkage between volcanisms and the changes of oceanic environments and organisms at the Latest Permian mass extinction (LPME) and the Early Triassic recovery were still scarce.In this thesis, four intermediate-to deep-water sections, which had nice volcanic ash record, were sampled. We try to explore volcanic effects to the changes of oceanic environments (e.g., oceanic productivity, redox condition, and oceanic carbon cycle) and marine biotas by integrations of paleontology, sedimentology, stratigraphy, and geochemistry data. Additionally, fourteen section (widespread globally) were integrated to review the changes of oceanic productivity in long term (-20 Ma, from the Middle Permian to the Early Triassic), and then link that to the protracted recovery in the Early Triassic.Numerous volcanic ash layers were preserved in deep water sections of South China. In this study, we focused on the volcanic events in three deep-water sections (Dongpan, Xinmin, and Xiakou section). The volcanic ash layers have obvious characters in the field outcrop:gray or green in color, the mineral main consist of clay mineral (especially illite), yielding very few calcite and quartz. Ferruginous and paramagnetic mineral were also enriched in these layers (with high MS values). Besides, high-temperature quartz and zircon were found in these ash layers. The volcanic ash layers were enriched in Al, Fe, Th, and Zr, but show negative Eu anomalies and depletions of LREE and MREE. High CIA values, abundant pyrite and positive Ce anomalies were record in these volcanic layers. This show the chemical weathering rates become more intensity on land and more reducing condition in the water column during volcanic eruptions. This may result from the input the volcanic gases (e.g., HC1, SO2) to the atmosphere, and then form acid rain when they react with water. Acrid rain can strengthen the chemical weathering of the land, and then increase nutrients to the ocean. Producers will be bloom for the abundance nutrients from the land. High productivity in the surface ocean resulted in more organic matter settling to water column. More reducing condition will be devoleped by respirations of organic matter in water column.It’s clear about the volcanic effects to the Earth surface system for the direct measuring and record of eruptions nowadays. But, it is rare about the volcanic effects to contemporaneous oceanic environments especially organisms in earth history. It is still unclear about the geobiological processes of volcanic effects to oceanic organisms, although numerous works were linked the cause of the end-Permian crisis to volcanisms. This work was the first time to examine the relationship of two components of the microplankton community (acritarchs and radiolarians) to volcanic ash deposits in two deep-water sections from South China (Shangsi and Xinmin). Short time scale and high precise sample were taken and analyzed. The strata were straddled the Permian-Triassic boundary from the Clarkina yini Zone to the Hindeodus parvus Zone, about 0.5 Ma interval. Base on the quantitative analysis of the microplankton community (acritarchs and radiolarians). The fossil record were various in different part of the "Sandwich structure", which was consisted by volcanic ash layers, black mudstone and background siliceous and/or calcareous deposits in ascending order. Very rare fossil were record in the volcanic ash layers; abundance producers (e.g., acritarchs), but few consumers (e.g., radiolarians) were record in the black shale. Both producers and consumers were record in the background deposits. Oceanic productivity increased abruptly in the black shale by input of nutrients, which were brought by volcanic ashes and terrigenous materials. However, volcanic ashes also bring other materials (e.g., Pb, Cd, HC1), which would induce oceanic toxic, acidic, and turbid. These oceanic variations may have negative effects to zooplankton (e.g., radiolarian). Few fossils were recovered from volcanic ash layers. Producers enriched in the black shale for the increase of productivity by addition of nutrients from volcanic ashes and terrigenous inputs. Background sediments, which record both producers and consumers, were deposited when oceanic systems recoverd after volcanic eruption.Both inorganic and organic carbon isotope negative excursions were record near the Permian-Triassic boundary globally. It’s still under much debate about the relationship between volcanic eruptions and carbon isotope excursions, although amount of works linked the excursions to volcanisms. In this chapter, carbon isotope excursions (both inorganic carbon and organic carbon isotopes) were associated with the volcanic ash layers in two deep water sections (Xiakou section and Xinmin from Northern and Southern marginal of South China craton respectively). Carbon isotope negative excursions were record in each volcanic ash layers, and the thicknesses of volcanic ash layer relative to the sizes of carbon isotope excursions. The sizes of organic carbon isotope excursion (△δ13 Corg) from Xinmin section were larger than inorganic carbon isotope excursions (△δ13 Ccarb) from Xiakou section (△δ13 Corg=～6%o, △δ13 Ccarb=～2%o). These relationships document the direct influence of volcanisms on marine carbon cycle during the PTB crisis. They may result from the input of light C (enriched in 12C) to the atmosphere and oceanic system by volcanic gases and/or heating the organic matter as magna move up. The 12C enriched CO2, CH4 add to the atmosphere and then affect to the producer first in the surface ocean, this can result in negative excursions of organic carbon. Then the lighter C adds to the oceanic system, this can induce inorganic carbon isotope excursions. Positive correlations between volcanisms and carbon isotope excursions show significant effects to the oceanic carbon cycle by volcanisms. However, it is still unclear about the scale (regional or globally) of the effects? Besides, more works should be taken about the source of the volcanic ash deposits in South China.It is also under much debate about the changes of oceanic environment (e.g., productivity and redox condition) during the Permian-Triassic transition. Base on the record of four sections, which represent different water-depth deposits, we concluded:1) Oceanic productivity decrease from pre-LPME to the post-LPME in the records of four sections. This show the producers were also collapsed in the biggest crisis. The decrease of producers may contribute to the decrease and/or miniaturization of other organisms.2) The records from the three sections (Xiakou, Xinmin, and Dongpan section, represent from shallow to deep settings) show, near the LPME, bottom water were oxic condition, suboxic condition and anoxic condition, in Dongpan, Xinmin and Xiakou sections respectively. Intense reducing condition was record in Xiakou section, which was located in the intermediate water environment (it may represent the depth of oxygen minimum zone) show the oxygen concentration in water was not depletion in the deep ocean, but in the mid-depth areas (such as OMZ). The conditions become more oxic from the intermediate toward up and down (from Xiakou section to the deeper water section, such as Xinmin and Dongpan section). This show the widespread redox condition near the Permian-Triassic transition may result from the expanding of the OMZ, but not the whole deep water. This was also evidenced by the step decrease of the different radiolarian orders:deep-water order (e.g., Albaillellaria) decrease earlier than shallow water order (e.g., Spumellaria).Research on the Permian-Triassic events was the "hot topic" during the past decades. This is because not only the Latest Permian mass extinction was the largest crisis, but also the recovery in the Early Triassic was the slowest one in earth history. Complete biotic recovery, characterized by a return to pre-extinction diversity levels, took an extraordinarily long time (-5 Ma). It is still unclear about the control factors of the events, although numerous hypotheses had been proposed to explain the cause of the protracted recovery and unstable oceanic environment in the Early Triassic. Large numbers of geochemical data were integrated from fourteen sections globally to explore the changes of oceanic environment in long term (from the Middle Permian to the Early Triassic,～20Ma). We concluded:1) Line sedimentary rates (LSR) increased from the Late Permian to the Early Triassic, this may result from the intense of the physical and chemical weathering of the continent for the volcanisms in the Early Triassic.2) Oceanic productivity increase in most of the world, but decrease in South China area from Changhsingian to Griesbachian. More works are required to resolve the various changes of productivity among different areas. This may result from the actual record of the decrease trend of productivity in South China area, or the change of the phytoplankton community (from algae in the Late Permian to short-spine acritarchs and cyanobacteria in the Early Triassic), which would control the amount of export productivity from the euphotic zone to the deep water.3) Similar to the volcanic effects to oceanic environments and organisms from the Late Permian to the Earliest Triassic. The volcanisms in the Early Triassic may contribute to the carbon negative excursions, high continental weathering, high temperature, high oceanic productivity and more reducing condition in the water column. The intensity of volcanisms in the Greiesbachian and Smithian associated with the abruptly changes of them. The associations show the volcanic eruptions could bring 12C enriched carbon to the atmosphere and ocean. This can lead to the global warming and then increase the temperature of the surface earth. Productivity were increase for additions of nutrients from volcanic eruptions. Larger number of organic matter formed in the surface ocean and settled to the deep ocean, this will lead more reducing condition in water column. We assumed volcanisms may be a cause for the delaied recovery in the Early Triassic. |
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