PALEOCLIMATE OF THE MIDDLE EOCENE CLIMATIC OPTIMUM RECORDED IN ORGANIC-RICH SHALE IN THE JIYANG DEPRESSION
The Middle Eocene Climatic Optimum(MECO)was a global warming event that occurred at about 40.5～40.1 Ma.At present,the response characteristics of this event in the marine environment are relatively clear,while the understanding of the response and differences in the terrestrial environment before,during,and after the occurrence of this event still needs further study.The lower third Member of the Shahejie Formation(Es3L)in the Zhanhua sag of the Jiyang Depression is a set of organic-rich shale succession with continuous deposition,which is not only a key layer for shale oil exploration in this area,but also provides a detailed sedimentary record for the study of the response of the terrestrial environment to the MECO event.In this study,high-resolution gamma(GR)data from the Luo69 well in the Zhanhua sag,which spans the Es3L and has a length of about 194 m,are used to carry out the cyclostratigraphy analysis,combining the correlation coefficient method(COCO)and the evolutionary correlation coefficient method(eCOCO),to establish an astronomical time scale with the base age of the Es3L of 41.21 Ma as an anchor point.On this basis,Fe content,Ti/K ratio,V/Al ratio,and TOC content of the Luo69 well,and magnetostratigraphy of the FY1 well are integrated to determine the response time of the MECO event in the study area,and to identify the climatic and hydrological changes in the Jiyang Depression before,during,and after the MECO event and their effects on organic matter enrichment.The results show that the 20.7～27.7 m wavelengths in the GR data of Luo69 well represent 405 ka long eccentricity,and the duration of 3.34 Ma for GR data and 2.48 Ma for Es3L is obtained through tuning,which is consistent with the reported results of FY1 well.Combined with the anchor point,an astronomical time scale from 41.77 Ma to 38.43 Ma was established,and the response time of the MECO event in the Jiyang Depression was inferred to be about 40.51～40.06 Ma.Before the MECO event,the climate fluctuated from humid to arid largely in this period,causing hydrodynamics of the lake basin and redox state of the lake water to change significantly.During MECO,the climate was wetter,allowing for increased basin hydrodynamics,resulting in oxygen-enriched lake water,but TOC levels were higher overall during this period,likely related to higher primary productivity.During the MECO period,the climate was more humid,which led to an increase in the hydrodynamics of the catchment,resulting in oxygen-enriched lake water,but TOC contents were generally high during this period,likely related to high primary productivity.After the MECO event,the climate change was smaller and relatively stable,and wetter than before the event,and TOC was slightly higher than before the event,which was mainly controlled by the increased primary productivity.
warming eventstatistical tuningtime series analysispaleoclimateorganic matter enrichmentshale oil
万方数据
维普
