陕南西乡寒武纪梅树村期微古生物群产出层位的地球化学特征及古环境和古气候条件研究

陕南西乡微体化石对于研究寒武纪大爆发具有非常重要的意义,前人研究大都局限于微体古生物的研究,而化石的成岩背景以及古环境研究尚属空白。因此本文通过测试主微量稀土元素及氧同位素来分析研究区的古沉积环境,在一定程度上填补了这一区域的空白。研究手段虽然在地化领域比较常见,但具有重要的参考价值。本文通过对富含小壳化石的“宽川铺段”及其上、下地层的微量元素Sr/Ba、Ni/Co、Sr/Cu、Rb/Sr、Mn/Fe等比值及主量元素、稀土元素含量、氧同位素特征的综合研究发现,研究区灯影组顶部环境为缺氧状态到宽川铺段弱氧化状态再到郭家坝组底部缺氧状态的海相沉积环境;水动力条件较弱,水体先上升后下降;上白云岩段、宽川铺段是较为温暖的气候,且比郭家坝组底部气候干旱。这对于研究该区寒武纪梅树村期的古环境和古气候变化具有重要的理论意义。

Geochemical characteristics and palaeo-environment and palaeoclimate conditions of Early Cambrian Meishucun micropalaeontological strata in Xixiang,southern Shaanxi

Objectives:The research aims to study the geochemical characteristics of the Xixiang micropaleontological biota area and analyze the element characteristics of rock samples to restruct the sedimentary environment.Methods:The research takes integrated stratigraphic theory as the core,uses lithostratigraphy,sedimentology,geochemistry and other methods and combines with field exploration to further improve the geochemcial characteristics and sedimentary environment of the Xixiang micropaleontological biota area;based on the analysis of the major elements,trace elements,rare elements and oxygen isotope,the elements which are sensitive to the sedimentary environment were selected in this study.The relationship between the content with its ratios of trace elements and sedimentary medium environment was analyzed.Furthermore,it discusses the palaeoclimate and palaeo-environmental characteristics of the Xixiang micropaleobiota area,such as climate,redox conditions,and water depth.Results and Conclusions:Through a comprehensive study of the characteristics of oxygen isotope,the ratio of trace elements Sr/Ba Ni/Co Sr/Cu Rb/Sr Mn/Fe and the content characteristics of major elements and rare earth elements in the strata and the upper and lower strata,it is found that the overall environment of the study area has gradually varied from anoxic state to weak oxidation state and finally became anoxic state.The depth of water changed from deep to shallow,and the climate changed from relatively dry to relatively humid.