沙市组层序地层与沉积体系分析

应用层序地层学原理对江陵凹陷古近系沙市组进行地层等时划分及对比，建立了等时地层格架。认为沙市组是形成于半干旱气候条件下的浅湖陆源碎屑岩和盐湖沉积。主要的沉积体系包括河流一三角洲体系、滨浅湖一半深湖砂、泥质沉积和盐湖沉积等。低位体系域以发育低水位的下切河道、三角洲及干旱盐湖沉积为特征；高位体系域发育三角洲、滨浅湖沉积。高位、湖侵及低位体系域的演化表现为河流一三角洲体系的进退和干旱盐湖的交替发育。层序Sq3和Sq4高位域发育较厚的储集砂体，具有进积式的层序结构特点。储集砂体主要分布于高位域，其中层序sq1的高位域发育的河口坝和分流河道砂体为最重要的储集地层单元。图4参12

Depositional system and sequence stratigraphy of the Shashi Formation in Jiangling depression in Jianghan basin, South China

Based on the concept of sequence stratigraphic methodologies, the cyclic sequence of Shashi Formation in age of Paleogene the in Jiangling Depression is classified and correlated in detail, and the strata contrast frameworks of cyclic sequence is defined and established. It shows that Shashi Formation composite of shallow lacustrine and continent source clastic rock and salt deposits that sedimented and developed in the half draught climate. The major deposit system is composed mainly of (1) fluvial delta deposit system; (2) shore to shallow lacustrine deposit; (3) half deep lacustrine sand deposit; (4) mudstone deposits and salt deposits. Lowstand systems tract is characteristiced by alternately developed incised valley, delta and draught salt lacustrine deposits, etc. High stand systems tract is characteristiced by delta deposits, shallow lacustrine deposits. The evolution of those three systems tracts suggests the changing of transgressive and regressive of fluvial delta system and draught salt lake during the depositing. The sequences Sq3 and Sq4 formed the thicker reservoir sand beds, and they have the character of transgressive sequence structure. The reservoir sand mainly distribute in the high stand systems tract. Among these reservoir layers, the water lain mouth bar and subaqueous channel deposits, which is developed in high stand systems tract of Sq1, are of the most important stratigraphical units of the reservoir.