鄂尔多斯盆地中侏罗世直罗—安定期沉积构造特征

中侏罗世直罗—安定期伴随大华北盆地分化瓦解,直罗—安定组除在鄂尔多斯盆地呈整体分布外,在其周邻地区亦有大量零星分布的同期可对比地层。在现今盆地内,直罗组主要为河流相沉积;安定组以干旱气候条件下的河流、湖泊相沉积为主。直罗—安定组的湖相沉积主要位于盆地东南部的古沉积中心部位,其堆积中心位于盆地西部的乌海—鄂托克前旗—平凉一线,堆积中心与沉积中心偏离。直罗组沉积前古构造格局为南高北低、东高西低。直罗—安定期的古地质面貌呈西北高东南低特点,南、北分异表现甚微。结合周邻同期地层岩性、岩相和现今构造单元形成时限等综合分析,认为直罗—安定期原始盆地的边界大致为:西在贺兰山之西,东达吕梁山之东、太行山以西,北抵大青山,南至秦岭。

Sedimentary tectonic features of Ordos basin in Middle Jurassic Zhiluo-Anding stages

Along with the breakup of Grand North China basin in Middle Jurassic Zhiluo-Anding ages, the Zhiluo-Anding Fms were relatively completely preserved in Ordos basin, with many scattered and contemporaneously correlated strata occurring in adjacent areas. In present Ordos basin, the Zhiluo Formation is dominated by fluvial deposits, while the Anding Formation is dominated by fluvial and lacustrine sediments deposited in arid climate. The lacustrine sediments in Zhiluo-Anding Fms were mainly deposited in the palaeo-depocenter in the southeastern part of the basin, while its accumulation center was located along Wuhai-Otog Qiangqi-Pingliang in the western part of the basin, deviating from the depocenter. The palaeotectonic framework prior to deposition of Zhiluo Fm was characterized by being high in the south and low in the north, as well as high in the east and low in the west. The palaeogeologic features in Zhiluo-Anding ages were characterized by being high in the northwest and low in the southeast, with very slight south-north differentiation. Based on comprehensive analyses of the lithology and lithofacies of equivalent layers and the timing of present tectonic units in the adjacent areas, it is believed that the primary basin in Zhiluo-Anding ages extended to the west of Helan mountain in the west, reached somewhere between east of Luliang mountain and west of Taihang mountain in the east, and was bounded by Daqing mountain in the north and Qinling mountain in the south.