贵州关岭动物群产出地层的地球化学特征及对物源和沉积环境的指示意义

Geochemistry characteristics and implications on provenance and sedimentary environments of Guanling Fauna bearing strata,Guizhou Province

对贵州关岭上三叠统法郎组瓦窑段底部的毛凹剖面系统地采集了10 5个岩石样品,测定了样品中的36种化学元素含量。对它们进行元素富集因子(EF)分析、R型聚类分析、R型因子分析、元素和氧化物的含量与Al2 O3 的含量比值以及δCe在剖面中垂向变化的分析,讨论了元素含量变化的制约因素、沉积物的来源、古海洋氧化还原条件的变化、关岭动物群的埋藏环境。结果表明:研究的5 2～17 7m段剖面地层以陆源碎屑和生物碎屑混合沉积为主,沉积物来源于陆壳,而不是火山和热液的来源,其沉积的氧化还原条件多次反复变化;元素的含量变化主要受陆源物质、氧化还原条件、生物碎屑以及成岩作用控制;从元素地层学角度将所研究的剖面段从下到上划分为4层,层1至层4元素对比值曲线呈现出平缓波动→频繁波动→平缓波动的周期性变化特征;该段的偏还原环境对海百合及海生爬行动物化石的保存和埋藏起了良好的作用。

Altogether 105 rock samples are collected from the M aowa section,the bottom part of the Wayao Member of Falang Formation of Upper Triassic in Guanli ng County,Guizhou Province,and the contents of 36 elements of the rock samples a re m easured by ICP (Inductively Coupled Plasma Emission Spectroscopy). Based on the measured data,the authors analyze the enrichment factors (EF ),R type cluster analysis and R type factors of the elements,and chronolo gical changes of the ratio of elements to Al 2O 3,the ratio of oxides to Al 2O 3 and the value of δCe,then discuss the factors controlling the changes of element contents,and present an interpretation about the sediment ary provenance,paleoredox condition and burial environment of Guanling Fauna.As a conclusion,the sediments within the studied interval in 5.2 ～17.7 m in the Maowa section are mainly composed of terrigenous and biogenic substances,which are derived from continent crust rather than volcanic material or thermal water .During this course,paleo-oceanic redox conditions changed repeatedly.The cha ng es of element contents are controlled by terrigenous material,redox conditions,b iogenic material and diagenesis.The 5.2 ～17.7 m interval of the section can be divided into four beds in terms of elementary stratigraphy.The ratio of elem ents and oxides to Al 2O 3 changes frequently from the first bed (bott om part of the interval) to the fourth bed (top part of the interval),showing a periodicity from slight to strong fluctuation.By correlating the paleoredox con ditions with the occurrences of fossils,the authors suggest the formation and pr eservation of the crinoids and marine reptiles fossils benefit from anoxic condi tions.