State Key Laboratory of Petroleum Resources and Prospecting;
China University of Petroleum;
Beijing 102249;
China;
Basin and Reservoir Research Center;
China University of Petroleum;
Beijing 102249;
China;
Unconventional Natural Gas Research Institute;
China University of Petroleum;
Beijing 102249;
China;
elements; lacustrine mudstone; Pleistocene; Qigequan Formation; Qaidam Basin;