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Shiming Peng, School of Life Science (China)
Yuanyuan Wang, Chengdong College (China)
Yinxi* Wang, Center of Modern Analysis (China)
Huiming Li, Center of Modern Analysis (China)
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This paper makes an analysis of rare earth elements(REE) contained in 16 fossil samples (9 brachiopods and 7 pelecypods) and other trace elements from Devonian/Carboniferous Boundary at the Nanbiancun section in Guilin, China. The purposes are to research ancient life science of fossils and its pale environment significance and to quantitatively determine the paleoredox environment using the Ce anomaly. The brachiopods and pelecypods were picked out from limestones. All fossil materials were cleaned in ultra pure water. The procedure was carried out in an ultra clean laboratory. The instrument used throughout is ICAP-AES. To determine the REE distribution patterns of sediments and palaeoredox condition in ancient ocean, the brachiopods (fossil carbonates) were collected from the section. From the upper Devonian to the lower Carboniferous the REE concentertration tends to increase. Fossil distribution pattern curves are essentially consistent with obvious negative Eu and negative Ce abnormal, indicating the stability and continuity of the sedimentation without any interruption. The Ce abnormal range for 9 brachiopods, 7 pelecypods and 24 matrix samples is -0.49 to -1.7, indicating an oxidized environment of carbonate sedimentation. The REE of brachiopod and pelecypods fossil and matrix in Nanbiancun section are poor. However, the REE in matrix of Bed 62 reaches the greatest enrichment. The concentrated REE bed occurs 23cm above the boundary.
Beside the higher REE concentertration, the Bed 62 has the highest Ce abnormal value(-0.5). These characteristics may indicate a possible chemical or biological event and can be used as the geochemical criterion of Nanbiancun section. The consistency of REE patterns for matrix (diluted HCl-soluble) reflects the homogeneity and continuity of carbonate deposition. The distribution patterns of fossil brachiopods from Beds 54,55,56 and 57 are consistent with the REE patterns of the matrix (diluted HCL-soluble). This indicates that the buried brachiopods near the boundary is in situ, but not all ochthonous.
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*Wang Yinxi : Corresponding author
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