鄂尔多斯盆地中东部奥陶系马五_5亚段白云岩地球化学特征及成因模式  

Geochemical Characteristics and Genetic Model of Dolomite in Majiagou Submember-5_5 of Ordovician in East-Central Ordos Basin

作　　者：于洲 丁振纯[1,2] 吴东旭 魏柳斌 魏源[3] Yu zhou;Ding Zhenchun;Wu Dongxu;Wei Liubin;Wei Yuan

机构地区：[1]中国石油杭州地质研究院 [2]中国石油天然气集团公司碳酸盐岩储层重点实验室 [3]中国石油长庆油田公司勘探开发研究院

出　　处：《海相油气地质》2017年第4期85-93,共9页Marine Origin Petroleum Geology

基　　金：国家科技重大专项"大型油气田及煤层气开发"(编号:2011ZX05004-002);中国石油天然气股份有限公司重大科技专项"深层油气勘探开发关键技术研究"(编号:2014E-32)联合资助

摘　　要：依据岩心、薄片以及实验分析资料,表明鄂尔多斯盆地中东部奥陶系马五_5亚段白云岩碳同位素分布区间与泥晶灰岩的分布区间类似,均介于-1.40‰~0.14‰,分布在同期海水值区间内;氧同位素组成介于-7.51‰^-5.98‰,较泥晶灰岩的偏正,但整体均较同期海水值偏负;稀土元素的配分模式与泥晶灰岩的相似,具有轻稀土元素富集、重稀土元素亏损的特征;锶同位素也和泥晶灰岩的分布范围大致相当,且具有少数正常、多数偏正的特征。综合古气候、古沉积格局和海平面升降变化的特征,认为:(1)马五_5亚段白云岩主要由渗透回流白云石化作用形成,部分由蒸发泵白云石化作用形成;(2)白云岩空间分布受海平面升降变化与沉积古地貌背景的共同控制,古地貌较高的中央古隆起—靖西台坪和靖东隆起带这两个区域上白云岩在相对海退期更为发育;(3)白云石的岩石结构组分之间的差异性与其形成的沉积背景有关,粉晶白云岩在中央古隆起—靖西台坪和靖东隆起带上均广泛发育,颗粒白云岩和含硬石膏结核粉晶白云岩仅零星分布在中央古隆起—靖西台坪带上,而白云石化不彻底的灰质粉晶白云岩和白云质泥晶灰岩主要分布在洼地中心和边缘地带。Based on the cores,thin sections and experimental data of dolomite in Majiagou Submember-55of Ordovician in east-central Ordos Basin,it is shown that the value of carbon isotope of dolomite is the same as micritic limestone,ranging from-1.40‰to0.14‰,within the distribution of Ordovician sea water.The value of oxygen isotope of dolomite ranges from-7.51‰to-5.98‰which is heavier than that of micritic limestone,but lighter than that of Ordovician sea water.The REE distribution pattern of dolomite is the same as that of micritic limestone which is characteristic of LREE enrichment and HREE depletion.Combined with the ancient climate,sedimentary patterns and sea level changes,the results are obtained as follows:①The dolomite is mainly formed by the seepage reflux dolomitization and partly by the evaporation pump dolomitization;②Dolomite developed widely in the higher terrain such as Central Uplift-Jingxi Flat and Jingdong Uplift during the regressive period,which is controlled by the sea-level eustacy and palaeogeomorphology;③The dolomite fabrics is related with its depositional settings.Micrite dolomite widely developed in Central Uplift-Jingxi Flat and Jingdong Uplift,grain dolomite and micrite dolomite with gypsum scattered in the Central Uplift-Jingxi Flat,and calcite micrite dolomite and dolomite micrite are mainly distributed in the central depression and edge zones.

关 键 词：鄂尔多斯盆地 奥陶系 地球化学特征 沉积古地貌 海平面变化 白云岩 

分 类 号：TE122.23[石油与天然气工程—油气勘探]