羌塘盆地那底岗日地区上侏罗统—下白垩统碳酸盐岩微量元素与古环境

Trace element in carbonate rocks and the palaeoenvironment during the Late Jurassic-Early Cretaceous in the Nadigangri area of Qiangtang Basin,China

那底岗日剖面是羌塘盆地发育最完整的上三叠统-下白垩统剖面之一。采用V/Cr、V/Sc、V/(V+Ni)、Th/U、Ni/Co和Fe2+/Fe3+的比值作为判断氧化还原环境的指标,Mn、Ti、P的富集程度推断古气候,Sr/Ba、Sr/Ca、Rb、V/Ni反映古盐度变化,结合沉积相的分析,研究那底岗日地区晚侏罗世-早白垩世的古环境变化。结果表明:上侏罗统索瓦组为开阔台地相,形成于贫氧的干旱炎热高盐度环境;下白垩统索瓦组经历了局限台地相和三角洲相沉积环境,形成于氧化-贫氧的潮湿-干旱炎热高盐度环境,且盐度高于上侏罗统。剖面中页岩产出层位与下白垩统海相油页岩的产出层位相当,均为潟湖相沉积;该时期气候温暖潮湿,有利于生物的大量繁殖,导致区域上大规模油页岩的沉积。

The Nadigangri profile is one of the most complete marine Jurassic-Early Cretaceous sections.V/Cr,V/Sc,V/（V＋Ni）,Th/U,Ni/Co and Fe2 ＋/Fe3 ＋ redox ratios are used as the environmental indicators,the contents of Mn,Ti,P are used to infer paleoclimate and Sr/Ba,Sr/Ca,Rb,V/Ni are used to reflect the changes of paleosalinity.Combined with the sedimentary facies analysis,this paper researches the paleoenvironmental changes in the Nadigangri area during the Late Jurassic-Early Cretaceous.The results show that the Late Jurassic Suowa Formation is open platform facies formed in the dry and suboxidation environment of high salinity.Early Cretaceous has undergone restricted platform facies and delta facies environment,formed in the dry and oxidation-suboxidation environment of high salinity which is higher than that of Late Jurassic.The shale layer horizon of the profile is the same as that of the Early Cretaceous marine oil shale,both being lagoon environment.This period had a warm and wet climate favorable for organism to breed abundantly,which leaded to extensive deposition of oil shale in this area.