Carbonate oxygen isotope paleoaltimetry: evaluating the effect of diagenesis on paleoelevation estimates for the Tibetan plateau
Carbonate oxygen isotope paleoaltimetry: evaluating the effect of diagenesis on paleoelevation estimates for the Tibetan plateau
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DOI：
10.1016/s0031-0182(04)00307-4
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发表时间：
2004-09
期刊：
影响因子：
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通讯作者：
C. Garzione;C. Garzione;D. Dettman;D. Dettman;B. Horton
中科院分区：
文献类型：
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作者：
C. Garzione;C. Garzione;D. Dettman;D. Dettman;B. Horton
碳酸盐氧同位素古测高是基于对地表水沉积碳酸盐的δ 18 O值的分析。解读成岩历史对于确定特定碳酸盐是否是反映古海拔的古地表沃茨的精确记录者是重要的。本研究提供了西藏南部、中东部和东北部湖相泥晶岩和成土碳酸盐岩成岩历史评价方法的实例。避免与成岩叠印有关的错误解释的最理想的技术是分析已知为原生的碳酸盐，如文石壳材料。在不含壳材料的岩石中，我们比较了湖相泥晶和成壤碳酸盐与成岩碳酸盐相，以确定成岩作用对原生碳酸盐同位素组成的影响。在成岩作用的潜在影响是微妙的或模棱两可的，我们已经评估了保真度的碳酸盐记录从系统的C和O同位素的趋势，同意与其他解释的古环境，如高频率的C和O的协方差，对应于碳酸盐镁浓度的变化。利用这些策略，我们确定成岩作用并未影响西藏南部晚中新世-上新世塔克拉地堑和西藏东北部渐新世-上新世临夏盆地碳酸盐的同位素组成。然而，就西藏中东部古近纪盆地而言，数据的模糊性阻碍了成岩作用的确定。
Carbonate oxygen isotope paleoaltimetry is based on analysis of the δ18O value of carbonate precipitated from surface water. Deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters, which reflect paleoelevation. This study provides examples from southern, east–central, and northeastern Tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates. The most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary, such as aragonitic shell material. In rocks that do not contain shell material, we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates. Where the potential effects of diagenesis are subtle or ambiguous, we have evaluated the fidelity of the carbonate record from systematic trends in C and O isotopes that agree with other interpretations of paleoenvironment, such as high frequency covariance in C and O that corresponds with changes in the Mg concentration of carbonates. Using these strategies, we have determined that diagenesis has not affected the isotopic composition of carbonates in the Late Miocene–Pliocene Thakkhola graben in southern Tibet and the Oligocene to Pliocene Linxia basin in northeastern Tibet. In the case of Paleogene basins in east–central Tibet, however, ambiguity in data precludes the determination of diagenetic effects.