浙江省长兴县煤山剖面二叠系-三叠系界线层序的沉积微相特征及层序地层划分

通过对浙江煤山剖面二叠系-三叠系界线层序新鲜露头的仔细研究后发现,长兴组顶部岩层(层22—层24)主要由3种微相构成:生物碎屑粒泥灰岩、富有机质生屑泥粒灰岩和含生屑或生屑质高有机质泥状灰岩—粒泥灰岩,其间夹有少量硅质骨针灰岩薄层或条带。殷坑组底部泥岩段(层30—层37)也主要由三种基本微相组成:灰绿色白云质泥岩、黑色白云质泥岩和灰白色瘤状白云质灰岩,其间夹有5层灰绿色火山灰层。界线附近的层25—层29的岩性及生物变化较为独特和复杂,属于以上两者的过渡部分。根据沉积微相组合特征和生物面貌纵向上的变化特征,将界线层序归为斜坡上部、斜坡下部和盆地环境3个沉积相带,并组成一个跨越界线的三级层序,层序底界位于层22中部(层22-11底面)。

SEDIMENTARY MICROFACIES AND SEQUENCE STRATIGRAPHY OF THE P-T BOUNDARY BEDS OF THE MEISHAN SECTION, CHANGXING COUNTY, ZHEJIANG

Detailed study on the P-T boundary beds of the Meishan Section, Zhejiang Province, shows that the topmost part of the Changhsing Formation (bed 22 to bed 24) mainly consists of three types of microfacies, i.e. bioclastic wackstone, organic-rich bioclastic packstone and bioclast-bearing high-organic matter-content mudstone, interbedded by a few siliceous spicularite thin beds. The base of the Yinkeng Formation (bed 30 to bed 37) is composed of three microfacies, including grayish green dolomitic mudrock, grayish black dolomitic mudrock and grayish white dolomitic nodular limestone, with five interbeds of pale green ashes. The boundary beds from bed 25 to bed 29 form a transitional sequence from the Changhsing Formation to the Yinkeng Formation. The microfacies change suggests a third-order sequence with a type-Ⅰ sequence boundary at the base of bed 22-11 and a transgression surface within bed 27.