豫西登封地区寒武系第二统朱砂洞组古气候演变记录*

河南登封地区发育完整的早寒武世朱砂洞组地层,记录了该地区气候演变的重要信息。本文通过岩石学、元素地球化学、沉积学和古生物学综合方法对关口剖面早寒武世朱砂洞组碳酸盐岩古气候和沉积特征进行了详细分析。研究表明,研究区朱砂洞组可分为下部的纹层状白云岩段、上部的豹斑灰岩段和顶部的纹层状白云岩段3个岩性段。纹层状白云岩中的顺层溶孔、燧石团块和石膏矿物,豹斑灰岩中的强烈生物扰动构造以及Mn含量、Sr/Cu值、Rb/Sr值、MgO/CaO值均反映出研究区朱砂洞组古气候从下部纹层状白云岩段的炎热干旱,到上部豹斑灰岩段的温暖潮湿,再到顶部纹层状白云岩段的炎热干旱,具有明显的阶段性变化。华北地区同期沉积物也显示出与研究区朱砂洞组具有相似的古气候变化特征。

Paleoclimate evolution recorded in the Cambrian Epoch 2 Zhushadong Formation from Dengfeng area,western Henan Province

The complete early Cambrian Zhushadong Formation is developed in Dengfeng area,Henan Province,which record important information of paleoclimate variation. The lithology,element geochemistry,sedimentology and palaeontology are investigated to have a closer insight into the paleoclimate and environmental variations during deposition of the early Cambrian Zhushadong Formation of the western Henan. The results show that the Zhushadong Formation can be divided into three lithological members: Lower laminated dolomite Member,the upper leopard limestone Member and the top laminated dolomite Member. The paleoclimate variations are reflected by stratified dissolved pores,chert and gypsum in the laminated dolomites,intensive bioturbation in leopard limestones and multiple geochemical parameters,including Mn concentration,and the ratios of Sr/Cu,Rb/Sr and MgO/CaO. It displays a clear change from hot and arid climate of the lower laminated dolomite Member,to warm and humid climate of the upper leopard limestone Member,and back to hot and arid climate of the top laminated dolomite Member. The contemporaneous sediments in North China show the similar paleoclimate variations to the Zhushadong Formation in western Henan Province.