Geochemical characteristics and geological significance of shale in the lower member of Wufeng-Gaojiabian Formation of Well Gudi 1 in Chaohu area, Lower Yangtze region

Well Gudi 1 reveals the strata of the WF2-3 member of Wufeng Formation (Upper Ordovician) and the LM2 and LM5-6 members of lower member of Gaojiabian Formation (Lower Silurian). The element geochemistry characteristics of shale samples from the studied strata has been analyzed, and its sedimentary tectonic background, provenance background, paleoclimate, paleoproductivity, seawater depth and salinity, redox conditions are thus studied subsequently. The results show that the vertical distribution of major elements, trace elements and rare earth elements in the shale of the lower member of Wufeng Formation-Gaojiabian Formation of well Gudi 1 is uneven, and the LM2 member is obviously abnormal compared with WF2-3 member and LM5-6 member. The tectonic environment during the sedimentary period is mainly the active continental margin environment, which also has the characteristics of continental island arc. The provenance is characterized by a mixture of felsic provenance and mature continental quartz provenance. WF2-3 and LM5-6 are in shallow water environment, with high oxygen content in bottom seawater, warm and humid climate, low paleoproductivity, shallow seawater and low salinity; LM2 member is a deep-water environment with high seawater salinity and weak retention. The bottom seawater is anoxic, dry and hot climate and strong paleontological productivity.