鄂尔多斯西南缘水泉岭组碳酸盐岩地球化学特征

Geochemical Characteristics of the Shuiquanling Formation Carbonates in the Southwestern Margin of Ordos Basin

对采自鄂尔多斯盆地西南缘中奥陶统水泉岭组的碳酸盐岩进行详细的元素地球化学分析,探讨各特征元素对古环境、古气候的指示意义。研究认为,研究区所测样品中典型陆源特征元素(如Al,Th,Zr等)的含量均较低,Y/Ho比值平均为41.27,均反映出研究区碳酸盐岩较少受陆源成分影响的特征;δEu和δCe对ΣREE未呈现出良好的相关性,也不具备明显的Eu正异常,这说明其受成岩作用和热液作用的影响也较为有限,所采样品能够较好地反映原始沉积环境。此外,结合MgO/CaO,V/(V+Ni),Th/U,Sr/Ba,V/Ni和m值等特征元素分析,研究区中奥陶统水泉岭组碳酸盐岩早期发育在高温潮湿且盐度较大的还原环境之中,而晚期则表现出盐度相对降低的弱氧化还原环境。

This study analyses the major elements,trace elements and rare earth elements of limestone from Shuiquanling Formation in the Middle Ordovician to discuss the paleo-environment and paleo-climate of the southwestern margin of Ordos Basin during the period. The results show low contents of typical continental elements,such as Al,Th,and Zr. Combine with the value of Y/Ho（41. 27）,limited terrestrial input is suggested to the samples of the study area. Additionally,the δEu and δCe do not display good correlation withΣREE and no obviously positive Eu anomaly is shown in the REE distribution patterns. It indicates that the diagenesis and hydrothermal process have little impact on the sediments,making it possible to interpret paleoenvironment during the Middle Ordovician. The depositional condition of the samples was reducing paleoenvironment,which is supported by the sensitive redox indicators of Th/U,V/（V ＋ Ni） and δCe ratios. Based on the Sr/Ba,V/Ni,Mg O/Cao and m values,the suggestion is given that the Ordovician carbonitite in early stage of the Shuiquanling Formation was a warm and humid,and high salinity marine environment,and the late stage was a warm humid anoxic environment with high salinity,while those in the late stage were developed in slightly oxicanoxic environment with relatively lower salinity.