鄂尔多斯西缘奥陶纪海底扇沉积体系

ORDOVICIAN SUBMARINE FAN SYSTEMS IN WEST MARGIN OF ORDOS

鄂尔多斯西缘中奥陶统重力流沉积可分为：（１）低密度浊流沉积，（２）高密度浊流沉积，（３）富基质碎屑流沉积和（４）贫基质碎屑流沉积四种类型。尤以陆源碎屑重力流，沉积厚度大、分布面积广，十分发育。依据古流向、重力流沉积类型、粒度、砂泥比、厚度及物源区等特征，由北向南识别出桌子山、贺兰山和同心三个海底扇。总面积达４．３万ｋｍ２，厚度达３０００ｍ．其中，贺兰山海底扇属高效能海底扇，以发育相对稳定的中扇水道沉积组合为特征；桌子山和同心海底扇为低效能海底扇，分别发育易迁移的网状水道系统组成的中扇和以具向上变薄变细层系的中扇水道沉积为特征。它们具有良好的生储盖组合条件，是有利的油气远景区。

Various kinds of gravity flow sediments including terrigenous elastic gravity flow deposits and carbonate gravity flow deposits developed in the west margin of Ordos Basin from late Early to Middle Ordovician.The terrigenous elastic gravity flow deposits are more significant due to its great thickness and broad distribution extent.The gravity flow sediments could be classified into(1)low-density turbidity current deposit;(2)high-density turbidity current deposit;(3)matrix-rich debris flow deposit;(4)matrix-poor debris flow deposit.The first two types are well developed. Based on the study of sedimentary sequence,paleocurrent direction, distribution of turbidite in time and space, and major provenance,three submarine fans named Tongxin,Helanshan and Zhuozishan submarine fans have been identified with the total area of more than 43000km2 and the thickness approximately 3000m.Among these submarine fans, Helanshan submarine fan is a high energy one,the other two are low energy ones. The submarine fan systems mentioned above possess good hydrocarbon prospects.