广西来宾栖霞组缺氧沉积环境的地球化学特征

Geochemistry of the dysaerobic sedimentary environments of the Qixia Formation in Laibing, Guangxi

地层的岩石地球化学特征是判断其形成环境氧化还原条件的重要手段之一。笔者对广西来宾铁桥剖面栖霞组中层纹状灰岩和含泥质灰岩进行岩石地球化学分析 ,结合栖霞组沉积学和古生态学特征 ,对栖霞组沉积环境进行了探讨。岩石微量元素含量、黄铁矿矿化程的DOP值、痕量元素V/Cr、Ni/Co、U/Th、V/ (V +Ni)等比值的研究结果显示 ,研究区具有缺氧沉积成因的地球化学特征 ,是由温度引起的季节性贫氧。

The geochemical signatures of sediments and/or rocks in the oxygen-deficient environments may be employed as important indicators for the interpretation of palaeoredox conditions. The analyses of twelve laminated limestones and argillaceous limestones samples collected from the Qixia Formation in the Tieqiao section, Laibing, Guangxi, integrated with sedimentological and palaeoecological data, have reflected that the carbonate successions in the study area were accumulated in a dysaerobic environment; the pyrite-bearing black shales and carbonaceous and argillaceous limestones may be formed in an anaerobic environment, and the bioclastic massive limestones should be generated in an oxygen-rich environment. Most of the geochemical indices for the interpretation of palaeoredox conditions inferred from ancient shales, for example, DOP, V/(V+Ni), Ce/La and U/Th ratios are all valid for the interpretation of carbonate rocks. The spatio-temporal distribution of the palaeoredox conditions during the Qixian is always bound up with sea-level changes as well as palaeoclimatic changes.