Evolution of Cenozoic Lake Basins and the Formation of Saline Lakes

Abstract

Cenozoic lacustrine strata are well developed on the Qinghai—Tibet Plateau and salt beds can be traced back as far as the Eocene. At this time salt deposits were widespread cross the plateau, with gypsum salt basins developed from Gonjo (Eocene) in the southeastern part of the region northwestwards to Fenghuo Mountain (Oligocene). Eocene—Oligocene salt deposits are also found in the western part of the Qaidam Basin and in the area of the Dalangtan Playa^①. The salt forming basins retreated northwestwards throughout the Miocene and Pliocene, but the Pliocene witnessed an increase in the intensity of salt forming processes. For example, relatively thick (Ca. 1–5 m) halite beds have been found in the western Qaidam Basin and in the Kumkol Basin. The discussion that follows will be focused on the Quaternary salt forming periods and the nature of their cyclicity.

Salt beds were encountered in boreholes drilled in 1984 by the Tibet Bureau of Geology in the Gonjo Basin, Qamdo. There were different opinions on the age of the red beds in the area of Fenghuo Mountain due to the lack of fossils, but Sun Mengrong’s analyses of samples collected on the mudstone and gypsum rock yielded sporopollen assemblages which Sun assigned to the Oligence. Oligence salt beds were also encountered in boreholes drilled by the Qinghai Bureau of Petroleum Industry in the western Qaidam Basin.