广西合山地区上二叠统的沉积间断和旋回特征

DISCONTINUITIES AND CYCLIC CHARACTERISTICS OF UPPER PERMIAN IN HESHAN, GUANGXI

广西中部合山一带上二叠统存在有三个沉积间断面,其一是上二叠统之底界面,其二是合山组上下段的分界面,其三是合山组上段二煤层底板铝土质泥岩之底界面,它们都是海平面下降期间沉积基底暴露出水面而形成的古风化面,有些还发育典型的古岩溶地貌特征。由这三个沉积间断面分隔,上二叠统可分为三个旋回层序,其一是合山组底界古风化面到合山组上下段分界,是一个较大的海侵海退旋回,其二是合山组上段底界到二煤层底板铝土质泥岩之底界面,其中又包括多个海侵、海退小旋回,其三是从合山组上段二煤层底板铝土质泥岩之底界一直到上二叠统大隆组顶部界面,是一个连续的海侵旋回层序。

There are three discontinuous surfaces in the Upper Permian sequence of Heshan,Guangxi.They are:the bottom boundary of Upper Permian, the boundary between the upper member and lower member of Heshan Formation and bottom of the aluminous mudstone beneath the No.2 coal seam in Heshan Formation. They are palaeo-weathered surfaces resulted from exposure in sea level descending period and typical palaeo-karsts geomorphic characteristics were found in some places.The Upper Permian is separated by these discontinuities into three cyclic sequences:the first one consists of lower member of Heshan Formation which was a large transgressive-regressive cycle,the second is from the bottom of No.4 coal seam to the bottom of No,2 coal seam,which includes a series of small transgressive -regressive cycles,and the third is from the bottom of aluminous mudstone floor of No.2 coal seam to the top boundary of Dalong Member of the Upper Permian, which is a continuous transgressive cycle.