华南地区二叠纪栖霞组燧石结核成因研究及其地质意义

Nodular Chert of the Permian Chihsia Formation from South China and Its Geological Implications

燧石结核是华南地区二叠纪栖霞组的重要识别特征之一,其成因具重要的古地理、古海洋意义。通过对湖北黄石、江苏南京和广西来宾三地栖霞组燧石结核的岩石矿物学研究,确定了栖霞组燧石结核的矿物组成和成岩作用序列。研究区燧石结核主要由微石英、负延性玉髓、粗晶石英组成,并含少量白云石、方解石及生物碎屑。其中,微石英、负延性玉髓、正延性玉髓、白云石形成于早期成岩作用,方解石晶粒形成于晚期成岩作用,粗晶石英的形成则具有多期性。结合栖霞组菊花状天青石和海泡石成因研究结果,本文认为组成栖霞组燧石结核的硅质来源与当时全球硅质生物的繁盛有关。燧石结核内玉髓和白云石形成环境条件及形成时间的确定,为建立更加合理的燧石结核成因模式和白云岩化模式提供了重要资料,同时也对深入探讨本区二叠纪层状硅质岩的成因具启发意义。

The Middle Permian Chihsia Formation of South China is featured by nodular chert, which is of implications in the reconstruction of coeval paleogeography and paleoceanography. This paper deals with mineralogical, petrologic characteristics and diagenesis of the nodular chert collected from Huangshi Hubei, Nanjing Jiangsu, and Laibin Guangxi. The nodular chert consists of mainly of microquartz, length-fast chalcedony and megaquartz with minor length-slow chalcedony,euhedral dolomite rhomb and sparry calcite as well as minor skeletal fragments.The source of silica derived from the thriving of the siliceous-shell organisms,combining with evidences from the formation of nodular celestite and sepiolite in the host rock.The reliable constraints on diagenetic conditions and precipitating time relative to the diagenetic spectrum of the Chihsia carbonates for the formation of the length-fast chalcedony and dolomite would be of far-reaching implication in our understanding about their origin,and even about the origin of the bedded siliceous rocks of Permian in the investigation area.