摘要
通过剖面实测、薄片鉴定、阴极发光分析和地球化学分析,对川东北地区下寒武统龙王庙组白云岩成因进行了研究。研究结果表明:研究区龙王庙组自下而上发育灰岩—过渡岩性—白云岩,以颗粒结构为主,白云石主要为泥—粉晶,呈它形—半自形晶,阴极发光呈昏暗光—暗红光。样品的MgO与CaO呈负相关,白云岩Mg^2+/Ca^2+较低,高Na含量,低Sr、Fe、Mn含量,白云石有序度较低,各岩性稀土元素配分曲线平行一致分布,δCe无异常,δEu负异常,灰岩δ^13C偏正、δ^18O处于同期海水内,白云岩δ^13C、δ^18O偏正,^87Sr/^86Sr高于同期海水值。结合区域地质背景、岩石学特征和地球化学分析结果,研究区白云石化流体为高盐度蒸发海水,研究区白云岩为渗透回流白云石化作用形成。
Based on measurement of field outcrops,microscopic thin section identification,cathodoluminescence analysis and geochemical analysis,this paper systematically studied the genesis of dolomite in the lower Cambrian Longwangmiao Formation,northeastern Sichuan Basin.It was found that limestone-transitional lithology-dolomite was developed from bottom to top in the study area,and the rocks have a predominantly grainy texture.The dolomite is mainly subhedral-xenotopic micritic to powder crystalline,and exhibits dim,dark-red luminescence.The MgO and CaO contents of the samples are negatively correlated.The Mg^2+/Ca^2+ratio,the Sr,Fe and Mn contents and the order degree of the dolomite are relatively low,but the Na content is relatively high.The distribution curves of rare earth elements(REE)in each lithology are parallel and uniform,and it showsδEu anomalies but noδCe anomalies.Theδ^18O value of the limestone is consistent with that of coeval seawater.Theδ^13C andδ^18O values of the dolomite and theδ^13C values of the limestone are slightly higher than for coeval seawater.The ^87Sr/^86Sr ratio of the dolomite is higher than for coeval seawater.Combined with the regional geological background,petrological characteristics and geochemical analysis results,it is considered that the dolomitization fluid in the study area was highly saline evaporating seawater.The dolomite in the study area was formed by seepage-reflux dolomitization.
作者
余晶洁
宋金民
刘树根
杨迪
王瀚
赵聪
邓双林
何宇
李立基
YU JingJie;SONG JinMin;LIU ShuGen;YANG Di;WANG Han;ZHAO Cong;DENG ShuangLin;HE Yu;LI LiJi(State Key Laboratory of Oil and Gas Reservoir Geology and Exploration,Chengdu University of Technology,Chengdu 610059,China;College of Energy,Chengdu University of Technology,Chengdu 610059,China)
出处
《沉积学报》
CAS
CSCD
北大核心
2020年第6期1284-1295,共12页
Acta Sedimentologica Sinica
基金
四川省科技厅重点研发项目(2018JZ0078)
国家自然科学基金项目(41872150)
国家科技重大专项(2017ZX05005003-007)。
关键词
白云岩
龙王庙组
寒武系
地球化学特征
川东北
dolomite
Longwangmiao Formation
Cambrian
geochemical characteristics
northeastern Sichuan Basin
