Petrographic Characterization and Rare Earth Elements as Geochemical Tracers for Redox Condition of Seep Carbonates from Northwestern Black Sea

Abstract

Abstract:

Seep carbonate crusts described here were collected on the Romanian (RO)shelf(120 m water depth)and Ukrainian(UKR)slope(190 m water depth)of the Black Sea. X-ray diffraction investigations show that high-Mg-calcite and aragonite are the dominant minerals. Peloids and botryoidal aragonite in the carbonate crust suggest a genesis induced by bacterial metabolism at the seep sites. The content of rare earth elements(REE)of the 5% HNO_³treated solution of the carbonates are very low(0.068×10-6 to 2.817×10-6).The shale-normalized REE patterns of RO carbonate show significantly negative Ce anomalies, while that of UKR carbonate shows no Ce anomalies, indicating that RO and UKR seep carbonates were deposited in oxic and anoxic environments, respectively. The contents of REE and trace elements(e.g.V, Cd and U)are highest in microcrystalline, lowest in sparite, and intermediate in microspar, suggesting that the elements concentration of seep carbonate is a function of diagenesis. 

Key words: seep carbonate, biogenic fabrics, rare earth element, geochemical tracer, redox condition, Black Sea, X-ray diffraction

CLC Number:

P74
P588.2

FENG Dong, CHEN Duo-fu. Petrographic Characterization and Rare Earth Elements as Geochemical Tracers for Redox Condition of Seep Carbonates from Northwestern Black Sea[J]. Geoscience, 2008, 22(3): 390-396.

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