RELATIONSHIP BETWEEN THE ORDOS BASIN AND SEA AREA FROM LATE PERMIAN TO MID-JURASSIC

The marine sediments of the Upper Shihezi and Sunjiagou Formations have been found in these years on the eastern, southern and western margins and in the northwestern part of the Ordos Basin. It is inferred, from the relations between the salinity and palaeoclimate as well as the fossils of cartilaginous fishes,that the sediments from the Yanchang Group, even the Yan’an Group were once subjected to transgression, and that the Ordos Basin was either a nearshore plain influenced by transgression at times, or a lake associated with seas rather than a so-called "interior" from Late Permian to Mid-Jurassic.