江汉盆地下第三系泥岩粘土矿物组合特征和沉积环境的探讨

DISCUSSION ON THE ASSEMBLAGE CHARACTERISTICS OF CLAY MINERALS IN THE JIANGHAN BASIN AND THEIR SEDIMENTARY ENVIRONMENT

江汉盆地是白垩纪时形成的陆相断陷盆地。从白垩纪到早第三纪末,整个盆地逐步收缩,各沉积层系分布面积逐渐缩小。新沟咀组分布范围为24100km^2,潜江组时为10460km^2。这两组地层是本区的主要生油层和勘探目的层。 在这两组地层中,发育着一套独特的泥岩粘土矿物组合,它们都以伊利石为主(90—100％),含少量绿泥石(大部分小于7.7％),矿种单调、稳定,不受层位、深度控制,不随温度、压力的变化而变化,控制这套特殊泥岩粘土矿物组合的主要因素是盆地水体性质。 本文据实际资料,论证了当时江汉盆地为一海侵及海漫所控制的湖盆,并通过扫描电镜,鉴定了砂岩中石英颗粒表面特征、绘出了潜江凹陷潜江组4~3—4~2砂层沉称时海侵水体的边界。

Jianghan Basin is a non-marine faulted-down basin developed during Cretaceous time. During the period from Cretaceous to the end of Tertiary, the whole basin gradually contracted and the distributive areas of individual sedimentary sequences reduced from the area of the Xinjingzhui Formation over 24100km2, to that of the Qianjiang Formation over 10460km2. Both of the two are of major source beds and exploratory targets. A set of unique characteristic clay minerals in these two formations are dominated by illites ( 90 - 900% ) with a little chlorites ( usually less than 7.7% ) , the unitary and stable mineral species would not be controlled by horizon and depth,neither would change with temperatures and pressures.What the principle factor on such an assemblage characteristics is the water body of the basin. Based on available data, it is proved that the Jianghan Basin had been a lacustrine basin controlled by transgression and regression. In addition, with the application of SEM,the determination of surface characteristics of quartz particles,and the mappings of the transgressive water body boundaries during the sedimentation of 43-42 sand bed in the Qianjiang Formation of the Qianjiang Depression are also made in the paper.