山东淄博地区太原组菱铁质结核成因及古环境意义

Genesis and palaeoenvironmental significance of siderite nodules in the Taiyuan Formation,Zibo area of Shandong Province,China

华北地区晚古生代海陆过渡相地层中广泛发育菱铁质结核层,同沉积阶段形成的菱铁质结核中蕴含了丰富的沉积期古环境信息。以华北东部山东淄博地区石炭—二叠系太原组菱铁质结核层为例,通过岩石学、沉积学、地球化学等方面的测试与分析,开展菱铁质结核的成因条件、成岩阶段、古环境等研究,主要获得以下认识:(1)淄博地区菱铁质结核是在同沉积阶段形成的,菱铁质结核内部的化学成分及特征可以有效地反映沉积期的古环境特征;(2)淄博地区菱铁质结核形成于海陆过渡相的半咸水、弱还原—还原、弱碱性—碱性环境;(3)淄博地区菱铁质结核形成于早二叠世Asselian-Sakmarian过渡期(295.6±1.1—296.7±1.1 Ma),对应早二叠世不连续的冰期P1末期;(4)淄博地区菱铁质结核形成期,陆地风化程度较高,气候整体温暖湿润;陆表海的底层海水温度介于9.3~19.6℃之间,平均为13℃。

Siderite nodules are widely developed in the Late Paleozoic marine-continental transitional facies strata in North China.The siderite nodules formed in the syndepositional stage contain rich sedimentary paleoenvironmental information.This study focuses on the siderite nodule layer within the Taiyuan Formation in the Zibo area of eastern North China.By conducting petrological,sedimentological,and geochemical analyses,we explored the formation conditions,diagenetic stage,and paleoenvironmental context of the siderite nodules.The main conclusions are as follows:1)The siderite nodules in Zibo area were formed in the syndepositional stage.The chemical composition and characteristics of siderite nodules can effectively reflect the palaeoenvironmental characteristics of the sedimentary period;2)Siderite nodules were formed in brackish water,weak reduction-reduction,weak alkaline-alkaline environment of marine-continental transitional facies;3)The siderite nodules were formed in the Early Permian Asselian-Sakmarian transition period(295.6±1.1~296.7±1.1 Ma),correlating with the terminal phase of the Early Permian’s discontinuous glacial P1;4)During their formation,the region experienced significant terrestrial weathering,with a generally warm and humid climate.The bottom seawater temperature of the epicontinental sea was between 9.3℃and 19.6℃,with an average of 13℃.