THE TEMPORAL AND SPATIAL DISTRIBUTION OF THE ZINIQUANZI FORMATION ON THE SOUTHERN MARGIN OF THE JUNGGAR BASIN AND THE EXPLANATION OF CONTRIBUTING FACTORS

The Ziniquanzi Formation is distributed on the southern margin of the Junggar Basin with rare fossil remains. In literatures, only few Palcogene ostracodes and charophytes were recorded from the upper part of this formation. Therefore, according to stratigraphyical succession, the Ziniquanzi Formation was assigned to the Paleocene to the lower part of the Upper Eocene (《The Regional Stratigraphic Scale of Xinjiang Uygur Autonomous Region, Northwest China》 and 《The Lithostratigraphy of Xinjiang Uygur Autonomous Region》). Since 1992, significant fossil ostracodes and charophytes have, however, been found by the authors from the Ziniquanzi Formation in both outcrops and well sections. Based on the known geological extension of these fossils in the world, the age of the Ziniquanzi Formation should be Late Cretaceous to Middle Eocene. Biostratigraphical study shows also that the Ziniquanzi Formation is poorly developed in the outcrop area, as compared with that of the covered area. Certain layers while developed in the covered area are missing in the cropped sections. It is held that the rising and dropping of lake level and river equilibrium profile resulting from the change of climate control the development of strata on the southern margin of the Basin.