Geochemical characteristics of carbonate rocks in a salinized lacustrine basin: a case study from Oligocene formation in the Qaidam Basin, northwestern China

Based on petrology, mineralogy, carbon and oxygen isotope composition, trace element composition, geochemical characteristics of carbonate rocks are systematically analyzed in the saline lacustrine basin environment in the Qaidam Basin, northwestern China. The results show that: (1) The carbon and oxygen isotopic compositions show carbonate rocks were deposited between open lake and closed lake environment; (2) the Sr/Ba ratio is greater than 1 with an average of 2.01; the Sr/Cu ratio is greater than 5 with an average of 109.04; the U/Th average value ratio is less than 1 with an average of 0.62. These data indicated the carbonate rocks deposited in an salinization, drought, and reducing lacustrine environments; (3) ΣREE values range from 39.41 to 162.67 ppm with an average of 87.67 ppm, and negative anomaly of Eu occurs in REE distribution patterns; and (4) lithologies of carbonate rocks are mainly composed of dark gray or black carbonates, commonly associated with salts deposition due to different lacustrine facies.