秭归盆地峡口剖面中侏罗统千佛崖组古气候演化的地球化学记录  

Palaeoclimate Change of the Middle Jurassic Qianfoya Formation Revealed by Geochemical Records of Xiakou Section in Zigui Basin

作　　者：戴贤铎 杜远生[1,2] 马千里 郭华[1,2] Dai Xianduo;Du Yuansheng;Ma Qianli;Guo Hua(State Key Laboratory of Biogeology and Environmental Geology;Faculty of Earth Sciences, China University of Geosciences（Wuhan）, Wuhan 430074, China)

机构地区：[1]中国地质大学(武汉)生物地质与环境地质国家重点实验室,武汉430074 [2]中国地质大学(武汉)地球科学学院,武汉430074

出　　处：《地质科技情报》2018年第2期50-58,共9页Geological Science and Technology Information

基　　金：国家自然科学基金项目(41672106)

摘　　要：通过对秭归盆地峡口剖面千佛崖组细碎屑岩样品的元素地球化学分析,恢复了区域内中侏罗世早期古气候的演化历程。结果显示:样品的化学风化指数(CIA)校正值的变化可分为2个阶段,在千佛崖组底部和中上部其平均值分别为82和64,微量元素风化指标Rb/Sr和古气候指标Sr/Cu(2.3,7.9)和C值(1.13,0.52)也有相同的反映,这指示了沉积物源区发生过由古气候转变导致的化学风化强度的减弱。利用P元素含量与Fe/Mn的变化特征,重建了区域古温度和古湿度的演化趋势。多元地球化学指标综合指示了研究区在中侏罗世早期为温暖、潮湿气候类型,而在中侏罗世中晚期区域内的干热化事件,使得气候转变为温暖、干旱的半潮湿气候类型,随着干热化趋势的不断加剧,最终气候过渡为干旱、炎热的半干旱气候类型,这与前人基于古植物研究得出的古气候变化过程相吻合,为盆地内中侏罗世早期古气候演化的进一步研究提供了地球化学方面的证据和参考。Geochemical characteristics of sedimentary rock in continental basin is useful in rebuilding the palaeocli- mate. Based on the geochemical analysis of fine-grained clasolite from the Qianfoya Formation of the Xiakou section in the Zigui Basin,this paper rebuilds the process of palaeoclimate evolution of the early Middle Jurassic. The re- sults reveal that：average values of corrected CIA（Chemical weathering index） from bottom Qianfoya Formation to its upper part decrease from 82 to 64. Similar decrease trend is found for the change of Rb/Sr ratio and average palaeoelimate index Sr/Cu（2. 3,7. 9） and C values（1.13,0.52）. This implies the degree of chemical weathering is weaken by the palaeoclimate transformation taking place in provenance. The trend of paleotemperature and ancient moisture in the region can also be reconstructed based on Fe/Mn ratio and phosphorus contents curve. Comprehen- sive geochemical indices suggest that in early Middle Jurassic, the palaeoclimate was warm and humid. The hot-arid climate event happened during the middle-late Middle Jurassic and palaeoclimate transformed into warm and semi- arid palaeoclimate. With the last effect of hot-arid climate event, the palaeoclimate became hot and arid. The geo chemical analysis of palaeoclimate evolution matches with the results revealed by the study of palaeobotany. This investigation will provide geochemical statistical evidence for study of early Middle Jurassic palaeoclimate change in the Zigui Basin.

关 键 词：古气候 早中侏罗世 地球化学 秭归盆地 

分 类 号：P534.52[天文地球—古生物学与地层学]