Paleoceanographic conditions following the end-Permian mass extinction recorded by giant ooids (Moyang, South China)

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• 作者：Fei Li^a ; ^b ; ^{feinan.li@gmail.com} ; Jiaxin Yan^a ; ^{jxyan_cn@yahoo.com} ; Thomas Algeo^a ; ^c ; Xia Wu^b
• 关键词：Early Triassic ; South China ; anachronistic facies ; giant ooids ; carbonate fluorapatite (CFA)
• 刊名：Global and Planetary Change
• 出版年：2013
• 出版时间：June, 2013
• 年：2013
• 卷：105
• 期：Complete
• 页码：102-120
• 全文大小：5151 K

文摘

Early Triassic oceans were characterized by deposition of a number of ¡°anachronistic facies¡±, including microbialites, seafloor carbonate cement fans, and giant ooids. Giant ooids were particularly prevalent in Lower Triassic sections across South China and exhibit unusual features that may provide insights into marine environmental conditions following the end-Permian mass extinction. The section at Moyang (Guizhou Province) contains abundant giant ooids ranging in size between 2 and 6 mm (maximum 12 mm) and exhibiting various cortical structures, including regular, deformed, compound, regenerated and ¡°domed¡±. Preservation of ooid cortical structure is generally good as indicated by petrographic observations, and trace element and carbon isotope analyses suggest that diagenesis occurred in a closed diagenetic system. All ooids exhibit fine concentric laminae, frequently alternating between light-colored coarsely crystalline and dark-colored finely crystalline layers probably reflecting variation in organic content or original mineralogy. Under scanning electron microscope, biomineralized filaments or biofilms and tiny carbonate fluorapatite (CFA) crystals are commonly found in the finely crystalline layers. We infer that the precipitation of CFA was related to adsorption of P via microbial activity on the surfaces of ooids following episodic incursions of deep waters rich in CO₂, H₂S and phosphate into shallow-marine environments. Giant ooid precipitation may have been promoted in shallow ramp settings during these events by increased watermass agitation and supersaturation with respect to CaCO₃, as well as reduced carbonate removal rates through biotic skeletal formation. Spatio-temporal distribution data reveal that giant ooids were widespread in the Tethyan region during the Early Triassic, and that they were most abundant immediately after the end-Permian crisis and disappeared gradually as metazoans repopulated marine environments.