摘要
本文通过对黔中石炭系九架炉组含铝岩系的沉积层序、结构、构造以及元素地球化学特征分析研究,认为铁质岩与铝质岩的分异过程主要发生在沉积期。九架炉组含铝岩系的地层层序从下往上分为铁质岩—黏土岩—铝土矿—黏土岩。其中铁质岩所具有的条带状、碎屑状和鲕状结构,说明铁质岩是单独沉积形成,而不是在整个九架炉组沉积后由铁质迁移从初始物质中分化形成。铁质岩和铝土矿中明显不同的元素组成,也应该是沉积期物源差异和沉积环境变化引起的。靠近物源区的铝土矿层中含大量铁矿物,并因此表现出高铁特征,远离物源区的铝土矿则相反,说明此时形成的铝土矿在物源上已经历了铁质的消耗,而正是这一阶段的消耗导致在溶洼中形成铁质岩。石炭系九架炉组含铝岩系中的铁铝分异过程与全球古气温、降雨及海平面变化密切相关,早石炭世维宪期正处于晚古生代冰期事件中的一个主要成冰期过渡期,此时华南板块所在的中低纬度地区由于降雨量突变与海平面升降变化,风化壳中铁质被淋滤,以胶体形式搬运至湖泊和潟湖沉淀,形成铁质岩;而残余的富铝风化壳在随后强烈降雨引起的洪泛事件中以碎屑流形式搬运到湖泊或潟湖沉积,形成碎屑状铝土矿。
Based on an analysis of the sedimentary sequence,structure,texture,and elemental geochemical characteristics of the aluminum-bearing rock series in the Carboniferous Jiujialu Formation in central Guizhou,this study proposes that the differentiation between iron-rich and aluminum-rich rocks primarily occurred during the sedimentary period.The stratigraphic sequence of the aluminum-bearing rock series in the Jiujialu Formation,from bottom to top,consists of iron-rich rocks,clay rocks,bauxite,and clay rocks.The presence of banded,clastic,and oolitic textures in the iron-rich rocks suggests deposition under distinct conditions rather than post-depositional iron migration and differentiation from precursor material.The distinct elemental compositions of the iron-rich rocks and bauxite are also attributed to differences in provenance and variations in the sedimentary environment during deposition.Proximal bauxite layers near the source area contain abundant iron minerals and exhibit high iron content,whereas distal deposits show the opposite trend.This suggests that the bauxite formed during this period had already undergone iron depletion at the source.It was precisely this depletion stage that led to the formation of iron-rich rocks in dissolution depressions.The iron-aluminum differentiation process in the aluminum-bearing rock series of the Carboniferous Jiujialu Formation is closely linked to global paleotemperature,rainfall,and sea-level changes.The Visean Age of the Early Carboniferous coincided with a major glacial transition period during the Late Paleozoic Ice Age.At this time,the mid-to-low latitude region of the South China Block experienced abrupt changes in rainfall and sea-level fluctuations.These conditions led to the leaching of iron from the weathering crust,which was then transported as colloids into lakes and lagoons,where it precipitated to form iron-rich rocks.Meanwhile,the residual aluminum-enriched weathering crust was transported by debris flows triggered by subsequent intense rainfall and flooding events,depositing in lakes or lagoons to form clastic bauxite.
作者
杨瑞东
莫洪成
罗朝坤
高军波
倪莘然
彭柔
高川黔
陈军
陈吉艳
YANG Ruidong;MO Hongcheng;LUO Chaokun;GAO Junbo;NI Xinran;PENG Rou;GAO Chuanqian;CHEN Jun;CHEN Jiyan(College of Resources and Environmental Engineering,Guizhou University,Guiyang,Guizhou 550025,China;Key laboratory of Karst Georesources and Environment,Ministry of Education,Guizhou University,Guiyang,Guizhou 550025,China)
出处
《地质学报》
北大核心
2025年第8期2711-2723,共13页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号U23A202379)
贵州省地质勘查资金项目(编号2024-2)联合资助的成果。
关键词
铁铝分异
地球化学
沉积结构
铝土矿
iron-aluminum differentiation
geochemical
sedimentary structures
bauxite
作者简介
杨瑞东,男,1963年生。教授,博士生导师,主要从事矿床学及地球化学研究。E-mail:rdyang@gzu.edu.cn。
