202 / 2019-06-17 20:14:07

Characteristics of High-frequency lake-level fluctuation of saline lacustrine basin and Geological Significance:A case study from the Upper Member of Paleogene Lower Ganchaigou Formation in the Yingxi

Yingxi area,Qaidam Basin,Lake-level fluctuation,Saline lacustrine basin,Lower Ganchaigou Formation,Palaeogeomorphology

Abstract: The sedimentary structure of the mixed saline lacustrine basin is diverse and complex, which is an important response to lake-level fluctuation and paleogeographic evolution.Based on analysis of cores, thin sections, scanning electron microscope, well-logging, X-ray diffraction and physical properties of the Upper Member of the Paleogene Lower Ganchaigou Formation (E32) in the Yingxi area of Qaidam Basin, study on the characteristics of the sedimentary cycle interface, the structure of the cyclic and the spatial contrast of the high frequencu lake-level fluctuation was carried out to illustrate the evolution of the sedimentary environment and ancient geomorphology of the lake basin.The results show that the E32 in the Yingxi region is a mixed sedimentation of lakes in the arid and salinized background, but the internal rock components and structural occurrences change frequently, indicating the periodic vertical superimposed sedimentary cycle of the lake.The cyclical interface is characterized by a lithologic transition surface at the top, such as layered rock salt, patch gypsiferous phyre and massive sandstone,or by a locally exposed exposed erosion surface.The single sedimentary cycle is dominated by shallowing-upwards salinization sequence during the short-term lake invasion—continuous lake retreat, forming a thin layer massive phyre—a patch gypsiferous phyre, a thin layer massive phyre—a patch gypsiferous phyre—a layered rock salt, and a thin layer massive phyre—massive sandstone.The superposition of different sedimentary cycles in space is jointly controlled by the hydrodynamic energy of the lake basin, the salinity of the lake water and the frequent fluctuations of the paleoclimate.Through the cycle comparison, the difference in the thickness among wells is adopted to approximately reflect the relative paleo-geomorphic fluctuation. It is suggested that The palaeogeographic pattern of the study area is characterized by high west and low east.The difference in thickness and geomorphology gradually decreases, reflecting the evolution of the filling and leveling up of the lake basin and gradually shrinkage and salinization of the lakes