湘北九溪下奥陶统盘家咀组岩石类型及沉积环境

Rock Type and Depositional Environment of the Lower Ordovician Panjiazui Formation at Jiuxi Area,North of Hunan Province

在野外剖面详细描述及测量的基础之上,湘北九溪下奥陶统盘家咀组主要发育有灰色-深灰色泥屑(晶)灰岩、粉屑灰岩、生物屑灰岩,以及少量的砾屑灰岩、砂屑灰岩、灰质云岩、含灰云岩。通过对岩性特征、沉积构造、生物遗迹、垂向组合等综合分析,认为盘家咀组沉积环境主要为大陆斜坡—深水盆地。大陆斜坡相可以进一步划分为上斜坡和下斜坡两个亚相,包含等深流沉积、重力流沉积、原地深水沉积3个微相;深水盆地相以盆地边缘亚相为主,包含等深流沉积和原地深水沉积两个微相。其中等深流沉积发育砂屑等深岩、粉屑等深岩、泥屑等深岩、生物屑等深岩4种等深岩,在垂向上发育单一岩性的、不完整的、完整的3种等深岩层序。剖面相分析表明,盘家咀组为一个低海平面-海平面上升-高海平面的海进过程。

Based on the detailed outcrop descriptions and measurements,the Lower Ordovician Panjiazui Formation in Jiuxi Area,north of Hunan province mainly developed gray- dark gray calcilutite（ micritic） limestone,calcisiltite,bioclastic,and small amounts of calcirudite,calcarenite,calcitic dolomite,limestone bearing dolomite. By a comprehensive analysis of lithology,sedimentary structures,biohermal trail,vertical combination,it is believed that the sedimentary environment of Panjiazui Formation is mainly continental slope-deepwater basins,continental slope facies can be further divided into upper and lower ramps,including three deep-water microfacies： contour current,gravity current,in-situ deep water deposition. The deep-water basin facies is mainly the basin edge subfacies,other subfacies including contour current and in-situ deposition. In this succession,contour current deposition can be classified into caleilutitie eontourite,calearenitie contourite,calcilutite eontourite and bioclastic contourite. The vertical section includs 3 kinds of contour current sequence： pure lithology,incomplete and complete.Sectional phase analysis shows that the Panjiazui Formation went through a low sea level-rising sea levels-high sea level transgression process.