Organic carbon isotope gradient and ocean stratification across the late Ediacaran-Early Cambrian Yangtze Platform  

作　　者：WANG XinQiang SHI XiaoYing JIANG GanQing TANG DongJie 

机构地区：[1]State Key Laboratory of Biogeology and Environmental Geology [2]School of Earth Sciences and Resources, China University of Geosciences [3]Department of Geoscience, University of Nevada

出　　处：《Science China Earth Sciences》2014年第5期919-929,共11页中国科学（地球科学英文版）

基　　金：supported by Ministry of Science and Technology of China(Grant No.2011CB808806);US National Science Foundation(Grant No.EAR-0745825);Doctoral Fund of Ministry of Education of China(Grant No.2012002212008)

摘　　要：Organic carbon isotope （δ-13 Corg） data from two well-preserved sections across a shallow-to-deep water transect of the late Edi- acaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ-13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24%0. In the deep-water Longbizui section, δ-13Corg values from time-equivalent strata of the Dengying Formation are mostly between -35‰ and -32‰）. These new data, in combination with δ-13Corg data reported from other sections in South China, reveal a 6‰-8‰ shallow-to-deep water δ-13Corg gradient. High δ-13Corg values （〉-30‰） occur mostly in shallow-water carbonate rocks, whereas low δ-13Corg values （〈-32‰） dominate the deep-water black shale and chert. The large temporal and spatial δ-13Corg variations imply limited buffering effect from a large dissolved organic carbon （DOC） reservoir that was inferred to have existed in Edi- acaran-Early Cambrian oceans. Instead, δ-13C-org variations between platform and basin sections are more likely caused by dif- ferential microbial biomass contribution to total organic matter. High δ-13Corg values （〉-30‰） documented from shallow-water carbonates are within the range of typical Phanerozoic δ-13Corg data and may record the isotope signature of organic matter from primary （photosynthetic） production. In contrast, low δ-13Corg values （〈-32‰） from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ-13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.Organic carbon isotope(δ13Corg) data from two well-preserved sections across a shallow-to-deep water transect of the late Ediacaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24‰. In the deep-water Longbizui section, δ13Corg values from time-equivalent strata of the Dengying Formation are mostly between –35‰ and -32‰. These new data, in combination with δ13Corg data reported from other sections in South China, reveal a 6‰–8‰ shallow-to-deep water δ13Corg gradient. High δ13Corg values(>-30‰) occur mostly in shallow-water carbonate rocks, whereas low δ13Corg values(<-32‰) dominate the deep-water black shale and chert. The large temporal and spatial δ13Corg variations imply limited buffering effect from a large dissolved organic carbon(DOC) reservoir that was inferred to have existed in Ediacaran-Early Cambrian oceans. Instead, δ13Corg variations between platform and basin sections are more likely caused by differential microbial biomass contribution to total organic matter. High δ13Corg values(>-30‰) documented from shallow-water carbonates are within the range of typical Phanerozoic δ13Corg data and may record the isotope signature of organic matter from primary(photosynthetic) production. In contrast, low δ13Corg values(<-32‰) from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.

关 键 词：late Ediacaran Early Cambrian South China organic carbon isotopes ocean stratification 

分 类 号：P736[天文地球—海洋地质]