中扬子地区早三叠世嘉陵江期岩相古地理研究

在中扬子地区下三叠统嘉陵江组中,岩石类型丰富多样,碳酸盐岩、碎屑岩和蒸发岩均有。用单因素分析综合作图法,做出了单因素基础图件5幅及岩相古地理图1幅。在早三叠世嘉陵江期,整个中扬子海域具“四分”特征,即自北而南依次为北缘碳酸盐开阔台地、北部蒸发盐-碳酸盐台地、中央碳酸盐局限台地、南部三角洲。在该时期内,从早到晚,沉积水体曾经历了两次大的海侵、海退,且交替进行。

ON THE STUDY OF LITHOFACIES PALEOGEOGRAPHY OF LOWER TRIASSIC JIALINGJIANG FORMATION IN MIDDLE YANGTZE REGION

The study area mainly covers Hubei province and also parts of Sichuan, Guizhou, Hunan and Jiangxi provinces. Rocks of Lower Triassic Jialingjiang Formation are widely distributed in the area and especially well outcropped in the east of Sichuan and west and east of Hubei.The greatest thickness of Jialingjiang Formation attains 996.8 meters. There exist various sedimentary rocks with promising potentials for oil and gas. According to the study of previous workers, Jialingjiang Formation can be divided into five members from bottom to top. There are three kinds of sedimentary rock in the Jialingjiang Formation, i.e. carbonate rock, clastic rock and evaporite.Carbonate rocks including limestone and dolostone are most widely distributed in the area. The limestone can be divided into two types: grain limestone and limemud limestone. The dolostone can be classified into penecontemporaneous and postpenecontemporaneous dolostones. The clastic rocks are dominated by sandstone, siltstone, mudstone and shale. Together with cooperating units, we have measured 9 main sections and 6 auxiliary sections in total in this study area. Moreover, we collected the data of some sections measured by previous workers and other geological data. On the basis of above conditions and using "the single factor analysis and comprehensive mapping method”, lithofacies paleogeography of Jialingjiang age of Early Triassic in Middle Yangtze region was studied. In this paper, the following single factors were selected: thickness, terrigenous materials content, gypsum rocks contents, shallow-water grains content and penecontemporaneous dolostone contents. At the same time, five fundamental maps of each single factor were drawn.. On the basis of the five fundamental single factor maps, combined with other quantitative and qualitative information and other regional geological information, one piece of lithofacies paleogeographic map of Jialingjiang age of Early Triassic in middle Yangtze region was drawn.According to this map the whole area of the middle Yangtze Sea with fourfold pattern was displayed. From north to south, there were the North Marginal Open Platform, the North Evaporite-Carbonate Platform, the Central Carbonate Restricted Platform and the South Delta,respectively. There were two big cycles of transgression and regression from early to late time through Jialingjiang age of Lower Triassic in the study region.