地质科学2011，Vol.46Issue(1)：27-41,15.
湘西地区前寒武纪-寒武纪转折期碳酸盐-硅泥质沉积体系的截然转换:地层-沉积样式,形成机理及意义
Sharp transition from carbonates to cherts across the platform margin in western Hunan,south China during Precambrian-Cambrian transition:Stratal-depositional patterns, mechanisms and implications
摘要
Abstract
The Precambrian-Cambrian transition is a key period for the understanding of one of the most important intervals in Earth's history, as it records the advent, extinction and accelerated diversification of metazoans coeval with sharp shifts in ocean geochemistry,a prolonged global oceanic anoxia. In order to investigate the trigging mechanism for these co-occurring processes,detailed crossing-platform-strike facies tracing from the transitional zone of platform-basin in western Hunan, were carried out to unravel different sedimentary facies and their spatial variation across this critical interval. A sharp transition from carbonates to cherts across the platform margin in western Hunan was identified in the earliest Cambrian, indicating syndepositional extensional faulting could have occurred along the transitional zone of platformbasin. Mounded chert,funnelized brecciated chert and vein chert which characterized by unique mineral compositions and internal structures in this transition zone, were formed by submarine hydrothermal venting on the fault-controlled terraces along the margin-to-slope of Yangtze carbonate platform where syndepositional fault/fracture zone could have acted as conduits channeling the hydrothermal fluids heated up by the deep-seated thermal source updip to the seafloor. The bedded chert, mainly distributed in the localities farther basinwards, implies enhanced influences of seawater away the vent fields during deposition. Considering widespread chert along the transitional zone of platform-basin in Yangtze area, intense hydrothermal venting might have occurred along the platform margin such that vast amounts of greenhouse gases,anoxic fluids rich in metal and nonmetal elements would have been released to the ocean/atmosphere, leading to climate warming, oceanic anoxia and oceanic eutrophication. As the hydrothermal activity waned, sea level would rise due to basin subsidence induced by crust cooling, abundant nutrient materials in the deep ocean were then brought to the ocean surface by upwelling currents,which could have increased primary productivity,and facilitated organic accumulation and preservation in the anoxic waters already during the Niutitang interval.关键词
前寒武纪-寒武纪转折期/碳酸盐岩/硅质岩/同生断层/热液活动Key words
Precambrian-Cambrian transition/ Carbonate rock/ Chert/ Syndepositional fault Hydrothermal activity分类
天文与地球科学引用本文复制引用
汪建国,陈代钊,严德天,韦恒叶,遇昊..湘西地区前寒武纪-寒武纪转折期碳酸盐-硅泥质沉积体系的截然转换:地层-沉积样式,形成机理及意义[J].地质科学,2011,46(1):27-41,15.基金项目
国家重点基础研究发展计划"973"项目(编号:2005CB422101)和国家自然科学基金项目(编号:4J0839907)资助. （编号:2005CB422101）
