A Study on mineralogical and in-situ geochemical characteristics of pyrite under different sedimentary environments in the South China Sea
ZHANG Yaru1, ZHANG Guanglu1, YANG Jun1, ZHAO Yanyan1,2, GUAN Hongxiang1,2, LIU Sheng1
1 Frontiers Science Center for Deep Ocean Multispheres and Earth System,Key Lab of Submarine Geosciences and Prospecting Techniques,MOE and College of Marine Geosciences,Ocean University of China,Shandong Qingdao 266100,China; 2 Laboratory for Marine Geology,National Laboratory for Marine Science and Technology(Qingdao), Shandong Qingdao 266237,China
Abstract Pyrite is a common mineral in sediments and sedimentary rocks,and its geochemical characteristics can clearly indicate the surrounding sedimentary environment. However,the differences in geochemical characteristics of pyrite and the controlling factors of its formation are still unclear. This study uses scanning electron microscope and laser ablation inductively coupled plasma mass spectrometry to study the morphology and in-situ geochemical characteristics of pyrite in different sedimentary environments in the South China Sea. The results show that the contents of pyrite and δ34S values at site SH-CL38 exhibit a mirror-image relationship,representing the pyrite formed in a normal marine sedimentary environment,which is controlled by organoclastic sulfate reduction;The extremely low δ13C value(-45.55‰)of authigenic carbonate particles at site F indicates methane seepage,and the formation of pyrite is related to sulfate-driven anaerobic oxidation of methane process. There are significant differences in the geochemical distribution of pyrite micro-areas between the two sites: the contents of Mn,Co,Ni,Mo,and Sb in pyrite at site SH-CL38 are higher than those at site F,which may be caused by the reducing dissolution of iron and manganese(hydrogen)oxide. In contrast,the content of Cu,V,As,and Cd in pyrite at site F is higher than that at site SH-CL38,which may be influenced by organic matter mineralization. The Ca and Mg content of pyrite particles indicate that,under methane seepage condition at the site F,authigenic calcite with low Mg and high Ca was preferentially precipitated,resulting in the later precipitated pyrite having high Mg and low Ca characteristics. The differences in morphology and trace element content of pyrite in two different sedimentary environments indicate that the mineralogical and geochemical characteristics of pyrite can be used to identify methane seepage.
Fund:Co-funded by the National Natural Science Foundation of China(No.42121005),the Fundamental Research Funds for the Central Universities(Nos. 202172002,202172003)and the Young Taishan Scholars Program(No. tsqn202211069)
Corresponding Authors:
ZHAO Yanyan,born in 1978,a professor and director of Ph.D. candidate,is mainly engaged in research on marine sedimentary chemistry. E-mail: zhaoyanyan@ouc.edu.cn.
About author: About the first author ZHANG Yaru,born in 1998,master degree candidate,is mainly engaged in research on sedimentology. E-mail: yaruzhang0929@163.com.
Cite this article:
ZHANG Yaru,ZHANG Guanglu,YANG Jun et al. A Study on mineralogical and in-situ geochemical characteristics of pyrite under different sedimentary environments in the South China Sea[J]. JOPC, 2024, 26(6): 1498-1515.
ZHANG Yaru,ZHANG Guanglu,YANG Jun et al. A Study on mineralogical and in-situ geochemical characteristics of pyrite under different sedimentary environments in the South China Sea[J]. JOPC, 2024, 26(6): 1498-1515.
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