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 QiangqiPingliang 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.