晚泥盆世大陆风化作用增强及其海洋环境效应:来自华南碳酸盐岩锶同位素的制约  

Enhanced continental weathering and its marine environmental effects in the late Devonian:Constraints from strontium isotopes of carbonate rocks in South China

作　　者：邓发亮[1,2] 刘希军[1,2] 余红霞 杨锋[1,2] 袁永海[1,2] Deng Faliang;Liu Xijun;Yu Hongxia;Yang Feng;Yuan Yonghai(School of Earth Sciences,Guilin University of Technology,Guilin Guangxi 541006,China;Guangxi Key Laboratory of Exploration for Hidden Metallic Ore Deposits,Guilin University of Technology,Guilin Guangxi 541006,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541006 [2]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541006

出　　处：《地质科技通报》2022年第4期207-214,共8页Bulletin of Geological Science and Technology

基　　金：广西自然科学基金杰出青年科学基金项目(2018GXNSFFA281009);广西八桂学者项目(2018,有色金属成矿理论与勘查技术)。

摘　　要：上泥盆统弗拉斯阶和法门阶界线附近发生了大规模的生物灭绝,其起因被认为是植物登陆导致的陆地化学风化作用加强及其引起的海洋水体缺氧所致,但其直接证据还比较缺乏。运用广西地区广泛发育的浅海碳酸盐岩中锶元素(Sr)和同位素(^(87)Sr/^(86)Sr)、铀钍比值(U/Th)记录,探究了从中泥盆统到下石炭统的陆地化学风化速率及海水氧化还原条件的变化。研究结果表明,在晚泥盆世(法门阶早期)陆地化学风化作用加强,导致海水中Sr浓度升高,及更富集重的Sr同位素组分;低的U/Th比值也显示该时期水体缺氧严重,海水中U元素被还原到沉积物中,导致海水中的U浓度降低。陆地表面化学风化的加强对晚泥盆世海洋水体氧化还原条件的波动以及海洋生物的灭绝有重要影响。The Frasnian-Famennian extinction in the late Devonian was one of the largest mass extinction during Earth′s history,which was believed to be caused by the plant landing-indued intensification of terrestrial chemical weathering and the consequent hypoxia of marine water.However,direct evidence remains limited.Here,we apply strontium(Sr)concentrations and isotopes(^(87)Sr/^(86)Sr)as well as uranium-thorium ratios(U/Th)of shallow marine carbonate rocks that are widely developed in the Guangxi area to explore the rate of continental chemical weathering and the redox condition of seawater from the middle devonian to lower Carboniferous.The results show that,the intensification of terrestrial chemical weathering in the late Devonian(early Famennian)caused the increase of Sr concentration and the enrichment of heavy Sr isotopes in seawater.The low U/Th ratio in carbonate also suggests that the water was highly hypoxia during this period.Uranium in seawater was reduced and deposited in sediments,resulting in the decrease of U concentration in seawater.The intensification of chemical weathering on land surface has a significant influence on the fluctuation of redox conditions and the extinction of marine organisms in the late Devonian.

关 键 词：风化速率 水体缺氧 植物登陆 生物大灭绝 碳酸盐岩 锶同位素 

分 类 号：P597[天文地球—地球化学] P534.44[天文地球—地质学]