博格达山前凹陷上二叠统乌拉泊组沉积相及沉积模式

Sedimentary Facies and Depositional Model of Wulabo Formation,Upper Permian Series in Bogeda Piedmont Depression, Junggar Basin

有关准噶尔盆地南缘上二叠统乌拉泊组的沉积环境 ,一直存在较大争议。作者根据沉积物中的地球化学标志、碎屑岩的粒度分布特征及泥岩中的粘土矿物组合 ,对博格达山前凹陷上二叠统乌拉泊组的沉积环境进行了分析 ,认为乌拉泊组为一套海退背景下的沉积产物 ,底部属海相沉积 ,中、上部为陆相沉积。通过对野外剖面的岩性组合、沉积物的结构、原生沉积构造及沉积韵律等特征的研究 ,在乌拉泊组中 ,从底到顶识别出四种沉积相类型 ,分别为潮坪相、滨岸水下扇相、辫状河流相和冲积扇相 。

The geologists have different opinions about the depositional environment of Wulabo Formation,Upper Permian series in the south margin of Junggar Basin.In this article,the depositional environment of Wulabo Formation,Upper Permian Series in Bogeda piedmont depression is analyzed based on the geochemical criteria in the sediments, including the content of equivalent boron,the ratio of B/Ga,Sr/Ba and the relationship among B?Rb?Ga,sandstone grain size distribution and clay mineral association of mudstone. It is considered that the Wulabo Formation was formed under marine regression background. The bottom of the strata was formed in shallow marine environment, and the middle to upper section was formed in terrestrial environment. By studies of rock types and their combination, the texture of fragmental rock, primary sedimentary structures and their evolution sequence, sedimentary rhythm, four kinds of sedimentary facies have been recognized in the strata. They are tidal flat, coastal subaqueous fan, braided stream and alluvial fan. The tidal flat and coastal subaqueous fan facies are distributed at the bottom,and braided stream facies in the middle,alluvial fan facies on the top of Wulabo Formation. The evolution of the sedimentary facies in this area was controlled by the formation and evolution of Bogeda intercontinental rift system.