江西信江盆地罗塘凹陷膏盐微量元素地球化学特征

摘要

江西信江盆地罗塘凹陷发育一套晚白垩世周田组暗色泥岩与膏盐岩互层沉积，为了解膏盐岩成因，综合利用钻井资料和地球化学分析手段进行研究。结果表明，研究区膏盐岩主要发育在周田组二、三、四段，岩性为含钙石膏泥岩和泥质石膏岩，其次为（硬）石膏岩。稀土和微量元素地球化学特征揭示了膏盐岩与围岩的物源均来自陆源，而非深部卤水。膏盐岩具有早期高水位浅水区和晚期低水位深水区两种沉积模式。早期高水位浅水区沉积模式主要分布在盆地边缘，沉积了紫红色含钙质结核泥岩夹膏盐岩；晚期低水位深水区沉积模式主要分布在盆地中心，发育了膏盐岩与暗色泥岩互层沉积，并组成多个盐韵律。平面上由盆地边缘到中心依次沉积了碳酸盐岩、膏盐岩类的典型蒸发岩序列。%Dark red mudstone interbedded gypsum of late Cretaceous was developed in the Luotang depression in Xinjiang Basin, Jiangxi. Gypsum trace element geochemical characteristics provide ways to decipher the depositional environment, together with well log data. This study shows that:(1) Gypsum was mainly developed in the second, third, and fourth section in Zhoutian Formation, which consists of gypsum-bearing calcium mudstone and muddy gypsum rock and a small amount of (hard) gypsum rocks; (2) Trace normalized patterns show that gypsum and wall rocks were terrigenous rather than deep brine sources;(3) Gypsum was developed in shallow water and deep water in early and late stage, respectively. It was probably located at the edge of basin in early stage, intercalated with purple calcareous mudstone tuberculosis gypsolith. It was mainly distributed in the central basin with gypsum rock and dark mudstone deposition in the late stage,forming rhythmic salt layers. From the edge to the center of the basin, it was deposited as typical evaporite sequence from carbonate rocks to gypsolith.