Rare earth element （REE） and Y concentrations, and S7Sr/S6Sr ratios were analyzed in 33 carbonate samples from the Paleogene Shahejie Formation in the Qikou depression, eastern China, with the goal of determining de...Rare earth element （REE） and Y concentrations, and S7Sr/S6Sr ratios were analyzed in 33 carbonate samples from the Paleogene Shahejie Formation in the Qikou depression, eastern China, with the goal of determining depositional environments and post-depositional conditions of carbonates in the region. The REE and Y concentrations were normalized to the post-Archean Australian shale （PAAS） standard. The La＊pAAs/Yb＊pAAS ratios of 0.35-1.52, where ＊PAAS indicates values for the PAAS standard, show fight REE enrichment and heavy REE depletion in most samples. Values of La＊PAAS （0.775-1.284） and Ce＊PAAS （0.822-L224）, coupled with a relatively flat REE distribution, indicate that the Shahejie car- bonates were deposited in lacustrine environments. Values of Y anomalies （1.009-1.527） and Y/Ho ratios （28.43-45.00） in the Shahejie Formation are greater than those of lacustrine carbonates and closer to those of marine carbonates, indicating that diagenetic fluids were probably influenced by seawater. In the car- bonates from Well Kou-42, Eu anomalies （1.171-1.604）, ^87Sr/^86Sr ratios （0.708 001-0.710 893）, and high homogenization temperatures （104-151 ℃） suggest that the carbonates were affected by hydrothermal fluids. The REEs and Sr isotope ratios show that the carbonates from the Shahejie Formation in the Qikou depression were deposited in lacustrine environments, and were influenced by seawater and hydrothermal fluids.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 41502145)the Education Department of Jilin Province (Jijiaokehezi, No. 2016-313)
文摘Rare earth element （REE） and Y concentrations, and S7Sr/S6Sr ratios were analyzed in 33 carbonate samples from the Paleogene Shahejie Formation in the Qikou depression, eastern China, with the goal of determining depositional environments and post-depositional conditions of carbonates in the region. The REE and Y concentrations were normalized to the post-Archean Australian shale （PAAS） standard. The La＊pAAs/Yb＊pAAS ratios of 0.35-1.52, where ＊PAAS indicates values for the PAAS standard, show fight REE enrichment and heavy REE depletion in most samples. Values of La＊PAAS （0.775-1.284） and Ce＊PAAS （0.822-L224）, coupled with a relatively flat REE distribution, indicate that the Shahejie car- bonates were deposited in lacustrine environments. Values of Y anomalies （1.009-1.527） and Y/Ho ratios （28.43-45.00） in the Shahejie Formation are greater than those of lacustrine carbonates and closer to those of marine carbonates, indicating that diagenetic fluids were probably influenced by seawater. In the car- bonates from Well Kou-42, Eu anomalies （1.171-1.604）, ^87Sr/^86Sr ratios （0.708 001-0.710 893）, and high homogenization temperatures （104-151 ℃） suggest that the carbonates were affected by hydrothermal fluids. The REEs and Sr isotope ratios show that the carbonates from the Shahejie Formation in the Qikou depression were deposited in lacustrine environments, and were influenced by seawater and hydrothermal fluids.
