Clay mineral assemblages of the oceanic red beds in the northern South China Sea and their responses to the Middle Miocene Climate Transition

作     者：Lei HE Zhifei LIU Xuan LYU Pengfei MA Lei HE;Zhifei LIU;Xuan LYU;Pengfei MA

作者机构：State Key Laboratory of Marine GeologyTongji UniversityShanghai 200092China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2022年第65卷第5期

页      面：899-909页

核心收录：

学科分类：0709[理学-地质学] 081803[工学-地质工程] 07[理学] 08[工学] 0818[工学-地质资源与地质工程] 0703[理学-化学] 

基　　金：supported by the National Key Research and Development Program of China (Grant No. 2018YFE0202402) the Shanghai Science and Technology Innovation Action Plan (Grant No. 20590780200) the National Natural Science Foundation of China (Grant Nos. 41530964 & 41942046) 

主　　题：Clay minerals Chemical weathering Oceanic red beds(ORB) Middle Miocene Climate Transition(MMCT) South China Sea IODP Expedition 368 Site U1502 

摘      要：The Middle Miocene Climate Transition(MMCT,~14 Ma)is the largest cooling event in the Cenozoic“Coolhouse,which significantly impacts the global chemical weathering *** this paper,the responses of the MMCT global cooling event in the deep South China Sea were studied by clay mineral assemblages analysis of the oceanic red beds(ORB)at International Ocean Discovery Program(IODP)Expedition 368 Site *** results show that the clay mineral assemblages of the ORB at Site U1502 are mainly composed of smectite(56–88%),illite(7–29%),and kaolinite(6–20%),without *** contents of these clay minerals and illite crystallinity show a four-stage variation pattern during early-middle Miocene(22.8–10.8 Ma).Smectite decreased from average 81%during 22.8–16.2 Ma and 16.2–14.4 Ma to average 67%during 13.8–10.8 Ma,with a rapid decrease of~14%during 14.4–13.8 *** the contrary,illite and kaolinite increased rapidly by~8%and~6%,respectively,during 14.4–13.8 *** crystallinity increased from average 0.18°Δ2θduring 22.8–16.2 Ma to average 0.19°Δ2θduring 16.2–14.4 Ma,and then decreased rapidly by~0.02°Δ2θduring 14.4–13.8 *** provenance analysis of clay minerals shows that illite and kaolinite mainly originated from South China landmass due to physical erosion,while smectite mainly came from the Luzon arc as the product of chemical ***,smectite/illite ratio and illite crystallinity are used as proxies of chemical weathering intensity in the early-middle *** values of the ratio and the crystallinity represent the enhanced chemical weathering,whereas low values indicate the weakened chemical weathering or the strengthened physical erosion *** smectite/illite ratio and illite crystallinity both decreased rapidly during 14.4–13.8 Ma,indicating the chemical weathering in the surrounding area of the South China Sea weakened rapidly,which we believe is the result of the MMCT event *** addition,their values increased slightly durin