Diagenetic Environment and Implication of Seep Carbona-te Precipitations from theSouthwestern Dongsha Area，South China Sea

Abstract

Abstract:

Cold fluids and authigenic carbonate precipitations at the seafloor are closely associated with gas hydrate dissociation, thus the identification and study on authigenic carbonates at cold fluids can be a key in the investigation for gas hydrates and seep communities. In this paper a comprehensive comparison has been performed on the lithology, chemical composition, isotope geochemistry and evaluation of seep carbonate precipitations collected from the Dongsha Islands area, Shenhu area and deepsea core of Site 1146, ODP Leg 184, South China Sea. Those seep precipitations are different in lithology, stable isotopes of carbon and oxygen, possibly reflecting their different diagenetic environments. Chemical compositions of TFe, AlAl₂O₃、TiO₂、K₂O、Na₂O、MnO and P₂O₅ are different in seep precipitations from the Dongsha Islands area and Shenhu area, implying they were influenced possibly by clay minerals and was micro Fe-, Mn-nodules or crusts, respectively. Cold fluid activity occurred once at the Shenhu area which was formed in early and later stages of seep precipitations. At least three times of cold fluid activities and several stages of carbonate precipitations were identified at the Dongsha Islands area, reflecting the difference in carbon sources and tectonics systems in two areas. It is concluded that gas hydrates could exist in the area of southern Dongsha Island, which were associated with thermogenic methane from deep sediments, and seep communities could also occur at that seafloor. This is a new access to investigate for gas hydrates and seep communities at the Southwestern Dongsha area.

Key words: carbonate precipitation, cold fluid, gas hydrate, seep community, Southwestern Dongsha area

CLC Number:

CHEN Zhong，YANG Hua-ping，HUANG Chi-yue，YAN Wen, LU Jun. Diagenetic Environment and Implication of Seep Carbona-te Precipitations from theSouthwestern Dongsha Area，South China Sea[J]. Geoscience, 2008, 22(3): 382-389.

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