Organic petrology and geochemistry of mudstones from the lower Shahejie Formation in the Tanggu area of eastern China : evidence for the presence of an ancient saline lake - Li, L. (Sinopec Jianghan Oilfield Companye (Wuhan, Xina)) ; Yao, G. Q. (Ministry of Education of China. Key Laboratory of Tectonics & Petroleum Resources) ; Cai, M. J. (PetroChina Dagang Oilfield Company) ; Liu, Y. H. (PetroChina Dagang Oilfield Company)