贵州东北部下-中志留统层序地层研究

贵州东北部下、中志留统（Ｌｌａｎｄｏｖｅｒｙ－Ｗｅｎｌｏｃｋ统下部，４３９～４２７Ｍａ）划分为６个三级层序（ＯＳ１—ＯＳ６），其平均延限约为２Ｍａ．ＯＳ１由龙马溪组和香树园组构成．雷家屯组包括两个三级层序．ＯＳ４由马脚冲组和溶溪组构成．秀山组和回星哨组构成ＯＳ５和ＯＳ６层序．ＯＳ１为Ｉ型层序，其余为Ⅱ型层序．三级层序均发育ＴＳＴ和ＨＳＴ，而缺乏ＬＳＴ和ＳＭＳＴ．层序的发育与全球海平面变化有密切关系．加里东运动造成的扬子地台持续上升对二级层序的组成具有明显影响．

LOWER AND MIDDLE SILURIAN SEQUENCE STRATIGRAPHY OF NORTHEASTERN GUIZHOU, CHINA

The northeastern Guizhou is located on upper Yangtze platform. The present study on six sections in the region establishes six 3rd-order sequences from the Lower Llandoverian (439Ma) to the Lower Wenlockian (427Ma), with an average duration of 2Ma. The six 3rd-order sequences have constituted a well-defined 2nd-order sequence. The first sequence consists of Longmaxi Fm and Xiangshuyuan Fm, extending chronologically from Rhuddanian to Early Telychian, with a distinct type-I sequence boundary at the bottom. Basinward, the bottom boundary shows a continuity at Tongzi, while landward to the Mid-Guizhou old land it becomes an overlap disconformity. Two 3rd-order sequences have been recognized in the Leijiatun Fm. The Majiaochong Fm (TST) and Rongxi Fm (HST) make up the fourth sequence. The fifth and the sixth sequences are represented by the Xiushan Fm and Huixingshao Fm respectively. Their sequence boundary, however, is not coincident with the boundary of the formations, but in the upper part of the Xiushan Fm. The second to fifth sequences are within the Telychian, and the sixth sequence is Early Sheinwoodian in age.