Characteristics of Sr Isotopes and Rare Earth Elements of Cap Carbonates in Doushantuo Formation in the Three Gorges Area

Abstract

Abstract:

Rare earth elements and strontium isotopes of cap carbonates in the Three Gorges area have been studied. The results are used to examine the geochemical feature of water from which these carbonates precipitated in the Snowball Earth aftermath. The REE patterns of cap carbonates from the Jiulongwan section are characterized by LREE and HREE depleted REE distribution patterns, positive Y anomalies and high Y/Ho values, without significant La anomaly. These indicate that the cap carbonates are unlike those typicality of the normal marine carbonates, but similar to those carbonates that are deposited in the environment dominated by freshwater influx from rivers. High 87Sr/86Sr values of cap carbonates display that the source of Sr from terrestrial weathering make the seawater 87Sr/86Sr value increase after the Neoproterozoic Snowball Earth events. Furthermore, Ce negative anomalies show that sedimentary environment of cap carbonates was weak oxidation. REE and Sr isotope characteristics indicate the ambient water is the seawater that mixed the freshwater with a large number of terrestrial weathering in the Snowball Earth aftermath

Key words: rare earth elements, strontium isotope, cap carbonate, Neoproterozoic, Three Gorges area

CLC Number:

P597

YAN Bin, ZHU Xiang-Kun, TANG Suo-Han, QI Liang. Characteristics of Sr Isotopes and Rare Earth Elements of Cap Carbonates in Doushantuo Formation in the Three Gorges Area[J]. Geoscience, 2010, 24(5): 832-839.

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