Abstract:

The Chuanjie basin in the Lufeng area of central Yunnan has recorded important information on the continental sedimentation and biological evolution of the Middle-Upper Jurassic in the Upper Yangtze region, providing a good carrier for the study of the Jurassic greenhouse earth climate environment. In this paper, the sedimentary, carbon-oxygen isotope and trace element geochemical systems of the Middle-Late Jurassic continental red beds in Chuanjie basin were studied to restore their paleoclimatic and environmental characteristics. Research suggests that the Jurassic Batonian to Early Kalo lakes in the Lufeng region were saline lakes with good sealing and gradually increasing salinity. During this period, the climate changed from relatively humid to dry, and the temperature was generally higher, showing a trend of gradually decreasing temperature from the early to late stages. The closure of the lake in the middle to late stages of the Kalo period weakened, making it a semi saline lake. During this stage, the climate changed from dry to relatively humid, and the temperature rose. However, the climate fluctuated violently, with frequent dry-wet alternations. During the Oxford Titang period, the lake’s closure further weakened and became a semi saline lake, with a generally stable humid climate. This work identified the Middle-Late Jurassic transition cold event (MLJT event) in the terrestrial red beds of the Lufeng area, providing an important reference for the study of the Mesozoic greenhouse earth climate environment and the comparative study of the terrestrial red beds in Southwestern China. The rapid change of climate in the late Middle Jurassic led to the rapid death of organisms, coupled with the transportation, sedimentation and rapid burial of rivers during the rainstorm period, resulting in the present biological burial characteristics of the Chuanjie basin.

Key words: Lufeng area, Middle-Late Jurassic, terrestrial red layer, greenhouse earth, paleoclimate, palaeoenvironment, Chuanjie Basin