Geochemical Characteristics of Calcite and Dolomite in Sandstone of Dongying Sinking, Shandong Province, China

This paper investigates the reasons why the REE content of ferroan calcite and ankerite in oil reservoirs is higher than that of ordinary calcite and dolomite, and why LHEE content is even higher. REE contents, fractionation characteristics, and carbon and oxygen isotopes indicate that calcite forms in fresh water, mainly forming in oxic environments, whereas dolomite originates from a mixture of water, mainly forming in reducing environments. The metallogenic temperature of both is high. The Sr/Ba ratio varies greatly but presents high values, proving the sources of lake basins are diverse. The variation, to some degree, also relates to geological events like crustal uplift and mantle-sourced magmatic activities. Only in part of ankerite the BaN/LaN ratio is high and belongs to biological sediment domains, reflecting a time-space relation with an oil and gas source.