Depositional environments of the Carboniferous-Permian Taiyuan Formation (southern North China Block) as deduced from trace elements and from carbon and oxygen isotopes

Abstract

Limestone layers are extensively developed in the continental/ocean transitional Taiyuan Formation. This formation accumulated on the southern North China Block. The precise environmental conditions of the Taiyuan Formation are still controversial. More information about these topics is presented here on the basis of the analysis of trace elements (Mo, V, Cd, Cr, U, Th), which can be used to determine characteristics of the depositional environment, and of carbon and oxygen isotopes (δ 13 C and δ 18 O) in limestone samples from the Huainan Coal Basin. Samples were taken for the purpose from cores of all 13 limestone levels, obtained from a coal-exploration borehole (code P2) in the Huainan Coal Basin. It was found that the δ 18 O values show a decreasing trend, suggesting a gradual rise of the sea level in a warm climate. Three negative shifts of δ 13 C appear in a lower, a middle and an upper limestone layer, accompanied by relative enrichment of the redox-sensitive elements (Cd, Cr, Mo and V). These three layers are thus deduced to have been deposited in a warm climate with a high sea level and with more terrigenous input than during deposition of the other limestone layers. The redox elements and elemental ratios (V/Cr, Th/U) in the limestones suggest deposition in an oxygen-rich sea with high salinity.