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前言 ××坳陷是洞庭地洼中的次一级坳陷,呈北东延伸,属断坳或断陷盆地。盆地中地洼沉积层(包括K—Q)的厚度大于4000米。对于洞庭地洼及其邻侧的大地构造发展历史,陈国达教授等作过明确的论述,认为元古代～震旦代中期属地槽阶段,震旦代晚期～中三迭世属地台阶段;第三纪(或晚白垩世晚期)发展到地洼阶段的余动期。××坳陷地洼型碳酸盐岩主要发育在下第三系沅江组二段中亚段下部地层中,属地洼余动期的产物。上述地层中,根据岩性组合、电性特征、沉积韵律及能量指数等特点,从下而上可以分出在盆地较大范围
Foreword ×× Depression is a sub-level depression in the depression of Dongtingdian, extending to the north east, belonging to a fault depression or fault basin. The thickness of sediments (including K-Q) in the middle dike of the basin is greater than 4,000 meters. For Dongtingdiwa and its neighboring tectonic evolution history, Professor Chen Guoda and other made a clear statement that the Proterozoic to mid Sinian geosyncline belonged to the stage, the late Sinian to Middle Triassic is a platform stage; the third Ji (or late Late Cretaceous) developed to the depression phase of the waving period. The depression depression type carbonate rocks mainly develop in the lower part of the middle member of the second member of the Yuanjiang Formation in the lower Tertiary, which belongs to the product of the active period of the subsurface depression. According to the characteristics of lithology, electrical characteristics, depositional rhythm and energy index, the above strata can be divided into a large range