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《Geochimica》 2018-02
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Implications of fluid source and sedimentary environment from the sedimentary geochemistry of Late Cretaceous cold seep carbonates from Gamba,Tibet

ZHANG Wen-jin;WANG Qin-xian;CHEN Duo-fu;CAS Key Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences;University of Chinese Academy of Sciences;Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University;  
Hydrocarbon-seep carbonates are a good geological archive of past fluid venting. We present field observations, petrographic and mineralogical analyses, stable carbon and oxygen isotope data, and rare earth element(REE) compositions to trace the fluid source and sedimentary environment of seep carbonates found within the Late Cretaceous marine mudstone in the Gamba area of Tibet. The carbonates occur as lenticular nodules within shales in outcrops. Petrographically, the carbonate minerals are predominantly composed of calcite. Moderately negative δ13 CV-PDB values, ranging from-17.0‰ to-7.2‰, suggest that the seep carbonates were possibly deposited from methane-seep fluids. Furthermore, the original REE+Y patterns of the carbonate minerals exhibit middle REE enrichment, with no Ce anomalies after La anomaly corrections, indicating a weakly reduced environment. The discovery and geochemical characteristics of carbonate nodules in the Gamba area of Tibet provide strong evidence of methane leakage from the Late Cretaceous cold seeps in this region. The discussion on the source and sedimentary environment of cold seeps will provide important clues to reconstruct ancient cold seep activities.
【Fund】: 国家自然科学基金(41502113)
【CateGory Index】: P588.245;P744
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