河南济源大峪槐圪塔岭二叠—三叠系元素地球化学特征及古环境

Element Geochemistry and Palaeoenvironment of Permian-Triassic Stratum in the Huaigeda Hill of Dayu Town Jiyuan Basin,Henan Province

本文对河南济源盆地大峪槐疙瘩岭二叠系上石盒子组(P3sh)、孙家沟组(P3s)和三叠系刘家沟组(T1l)剖面岩石样品进行了元素、频率磁化率、碳酸盐以及总有机质等的分析研究,结果表明在二叠系孙家沟组(P3s)底部济源动物群化石层、以及三叠系刘家沟组(T1l)底部界线(P/T)附近,其微量和常量元素发生了较明显的变化。化石层中Ba,Cr,Hf,Nb,Th,Ti,V,Y,Tl,Zn,Cu,Ga,Pb,Ni,La,Rb,Nd,以及K2O,Al2O3,Fe2O3含量相对较高,Zr,W,Sr,Bi,Co,Ce,以及SiO2,Na2O含量较低,MgO,CaO,Mn则没有明显的变化。Ba,Hf,Nb,Th,Ti,V,Y,W,K2O,Al2O3,SiO2,Na2O,Bi,Fe2O3,Ni,Co,La,Nd,Ce,及有机碳含量在三叠系底部含量明显上升,Cu,Ga,Pb,Tl,Zn,Cr,Zr,Sr,MgO,CaO,以及岩石频率磁化率Xfd、碳酸盐含量则明显下降。该剖面不仅记录了二叠—三叠纪的生物灭绝事件,而且有明显的二叠—三叠系界线,事件及界线的形成可能与沉积环境和古气候有关,水体的变浅、炎热气候和风化作用加强可能是直接的原因。石盒子组(P3sh)主要为河流—三角洲沉积环境,古气候相对温暖湿润;孙家沟组(P3s)为三角洲平原相,前期和后期有强烈风化作用,并且炎热多雨。中期则水平面上升,水下三角洲前缘砂质沉积为主;三叠系刘家沟组(T1l)则水体进一步扩张,气温相对下降。

Rock samples collected from Permian Shangshihezhi Formation （Pash） and Sunjiagou Formation （Pa s） and Triassic Liujiagou Formation （T1 l） in the Huigeda hill of Dayu Town in the Henan Jiyuan Basin had been analyzed and studied according to the elements, frequency dependent susceptibility, carbonate and organic matter contents. It was shown that trace and macroelement in the bottom of Jiyuan Fauna fossil stratum in Permian Sunjiagou Formation （Pas） and near P-Tr boundary in the bottom of Triassic Liujiagou Formation （T1 l） had changed greatly. Elements Ba, Cr, Hf, Nb, Th, Ti, V, Y, T1, Zn, Cu, Ga, Pb, Ni, La, Rb,Nd,and K20, A12Oa ,FeeOa had high content in the fossil stratum,but elements Zr,W,Sr,Bi,Co,Ce, and SiOe ,Na20 had low content,MgO,CaO,Mn kept stable a little. Elements Ba, Hf,Nb,Th,Ti,V,Y ,W, K2 O, A12 Oa, SiO2, Na2 O, Bi, Fee Oa, Ni, Co, La, Nd, Ce and organic matter content had increased obviously from the Triassic bottom, but elements Cu, Ga, Pb, T1, Zn, Cr, Zr, St, MgO, CaO, and frequency dependent susceptibility,carbonate content decreased greatly. This P-Tr section not only recorded the end-Permian mass extinction,but also had an obvious P-Tr boundary. It is shown that event and boundary formation had a closed-correlation with deposition environments and palaeoclimate at that time. The directive reason to form event and boundary were the shallow water and warm climate and high chemical weathering. The sediment face was the river-delta environment with warm and wet during the Shangshihezhi Formation （P3 sh）. And delta plain face during Sunjiagou Formation （Pas） ,had very strong weathering and extremely hot and rainy at the early and end periods. But water level in this basin rose a little to make sandy sediments forming in the front of delta. Waterbody had continued to expend during Triassic Liujiagou Formation （T1I） with a relatively falling temperature.