滇中禄丰川街盆地中-晚侏罗世温室地球气候环境演变特征及其对生物埋藏的影响

Characteristics of the Middle-Late Jurassic Greenhouse Earth Climate Environment Evolution in Lufeng Chuanjie Basin,Central Yunnan,and Its Impact on Bioburial

滇中禄丰地区川街盆地记录了上扬子地区中—上侏罗统陆相沉积和生物演化的重要信息,为侏罗纪温室地球气候环境研究提供了良好载体。本文通过对川街盆地中—晚侏罗世陆相红层进行沉积学、碳-氧同位素、微量元素地球化学系统研究,恢复其古气候环境特征。研究认为:禄丰地区侏罗纪巴通期—卡洛夫早期湖泊为封闭性较好、盐度逐渐升高的咸水湖,该时期气候由相对湿润转为干燥,气温总体较高,从早期到晚期表现为温度逐渐降低的趋势;卡洛夫中—晚期湖泊封闭性减弱,由咸水湖转为半咸水湖,该阶段气候由干燥向相对湿润气候转变,温度回升,但气候波动剧烈,干湿交替频繁;牛津期—提塘期湖泊封闭性进一步减弱,为半咸水湖泊,气候总体趋于稳定,为湿润型气候。本次工作在禄丰地区陆相红层中识别出中—晚侏罗世过渡期寒冷事件(即MLJT事件),为中生代温室地球气候环境研究和西南地区陆相红层对比研究提供了重要参考。中侏罗世晚期急剧变化的气候使得生物快速死亡,加之暴雨期河流的搬运、沉积和快速埋藏,造成了川街盆地如今的生物埋藏特征。

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.