DOI: 10.1016/j.earscirev.2020.103443
论文题名: Redox changes in the outer Yangtze Sea (South China) through the Hirnantian Glaciation and their implications for the end-Ordovician biocrisis
作者: Li N. ; Li C. ; Algeo T.J. ; Cheng M. ; Jin C. ; Zhu G. ; Fan J. ; Sun Z.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2021
卷: 212 语种: 英语
中文关键词: Chemical weathering
; Euxinia
; Graptolite
; Late Ordovician
; Mass extinction
; Sulfur isotopes
英文关键词: chemical weathering
; chemostratigraphy
; euxinic environment
; graptolite
; Hirnantian
; mass extinction
; Ordovician
; paleoceanography
; paleoclimate
; redox conditions
; sulfur isotope
; China
英文摘要: Two pulses of faunal mortality occurred during the Late Ordovician mass extinction (ca. 445 Ma). This biocrisis is recorded in Hirnantian strata of South China as a stepwise extinction of graptolites in both the hydrologically semi-restricted inner and open outer Yangtze Sea. Although expanded marine euxinia is widely regarded as the main cause of the biocrisis, the spatial-temporal pattern and driving mechanisms behind redox changes, as well as the extent to which they influenced marine faunas, remain unclear. Here, we present a study of mid-shelf and outer-shelf sections of the less-studied outer Yangtze Sea, based on an integrated suite of geochemical proxies [i.e., iron speciation, pyrite δ34S (δ34Spy), and major- and trace-element data] to provide insight into changes in marine redox conditions, chemical weathering rates, and primary productivity across the Hirnantian Glaciation. Iron speciation ratios and trace-element enrichment factors show that euxinia appeared in mid-shelf settings during the late Katian, subsequently expanded into deeper waters, and then diminished during the Hirnantian Glaciation and expanded again thereafter. Expansions of euxinia across the outer Yangtze Sea prior to and after the Hirnantian Glaciation may have been the result of both elevated primary productivity, as indicated by elevated organic carbon accumulation rates (OCAR), and increased sulfate weathering inputs due to preglacial and postglacial enhanced fresh-rock exposure on land. However, we propose that the local development of euxinia was controlled mainly by sulfate availability, which depended on continental weathering intensity—a hypothesis supported by strong covariant relationships between the chemical index of alteration (CIA, a weathering proxy), redox proxies, and δ34Spy values. The contraction of oceanic euxinia during the main glacial interval was caused by a reduction in continental weathering intensity; contemporaneously weaker euxinia, as well as higher δ34Spy values, in outer-shelf relative to mid-shelf areas may have been due to limited terrestrial sulfate supply in deeper sites and small sulfate reservoir in the open ocean during the glaciation. Persistence of euxinia in the outer Yangtze Sea after the termination of the main glacial interval is evidence of a growing sulfate reservoir in early Silurian oceans, probably due to increased continental weathering. Furthermore, the comparision of the redox and fossil records indicates that elevated extinctions among mesopelagic graptolites coincided with enhanced euxinia in the outer Yangtze Sea, supporting the hypothesis that redox changes were the main stressor of both benthic fauna and some zooplankton. Our results highlight the interrelated influences of climate, continental weathering, and riverine sulfate fluxes on marine redox variations and the biotic crisis of the Late Ordovician. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166444
Appears in Collections: 气候变化与战略
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作者单位: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, 430074, China; State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China; Department of Geology, University of Cincinnati, Cincinnati, OH 45221, United States; Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming, 650091, China; Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, 100083, China; School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China; State Key Laboratory of oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, 610059, China; Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, 610059, China
Recommended Citation:
Li N.,Li C.,Algeo T.J.,et al. Redox changes in the outer Yangtze Sea (South China) through the Hirnantian Glaciation and their implications for the end-Ordovician biocrisis[J]. Earth Science Reviews,2021-01-01,212