鄂尔多斯盆地苏里格地区奥陶系马家沟组白云石化

Dolomitization of Ordovician Majiagou Formation in Sulige region, Ordos Basin

付金华 王宝清 孙六一 包洪平 徐波

Fu Jinhua Wang Baoqing Sun Liuyi Bao Hongping Xu Bo

中国石油长庆油田公司勘探开发研究院, 西安710018 2. 西安石油大学, 西安710065

Research Institute of Petroleum Exploration and Development, Changqing Oil Field, PetroChina, Xi'an, Shaanxi 710018, China 2. Xi'an Shiyou University, Xi'an, Shaanxi 710065, China

苏里格地区马家沟组为一套碳酸盐岩为主,夹蒸发岩的地层,沉积于超盐度的局限陆表海环境。白云石分为以泥晶结构为主的,以细—中晶结构为主和充填于孔、缝中3类。白云石Na含量(0~2099)×10-6,Sr含量(0~70)×10-6,Mn含量(0~112)×10-6,Fe含量(39~86746)×10-6,以变化较大的Na含量、低的Sr和Mn含量、高的Fe含量为特征。白云石δ18O值在-16.00‰~-5.73‰之间,δ13C值在-11.46‰~1.90‰之间,说明碳酸盐岩经历了淋滤作用和埋藏作用。大多数孔、缝充填白云石较围岩组分有较低的δ18O和δ13C值,说明孔缝充填的白云石形成较晚。白云石以低的有序度,非理想配比的CaCO3和MgCO3含量为特征。白云石的87Sr/86Sr值为0.707977±0.000070至0.711791±0.000064,绝大部分高于全球中、上奥陶统分界线对应的87Sr/86Sr值。微生物白云石化是形成白云石的机理。

The Ordovician Majiagou Formation in Sulige region of the Ordos Basin was deposited in hypersaline restricted epicontinental environment.It is mainly composed of carbonate rocks with thin evaporate interbeds.The dolomites are classified into 3 kinds:micrite,fine-medium crystal dolomite,and dolomite filled in pores and fractures.The Na concentrations range from 0 to 2 099×10-6,the Sr concentrations range from 0 to 70×10-6,the Mn concentrations range from 0 to 112×10-6,and the Fe concentrations range from 39 to 86 746×10-6 in dolomites.The dolomites are characterized with varied Na,low Sr and Mn,and high Fe concentrations.The 18O values for dolomites range from-16.00‰ to-5.73‰,and the 13C values range from -11.46‰ to 1.90‰(PDB).It indicates that carbonate rocks have experienced leaching and burial diagenesis.Most filled dolomites have lower 18O and 13C values than surrounding components,indicating that the former was formed later.The dolomites are characterized with low degrees of order and less stoichiometry.The 87Sr/86Sr values of dolomites range from 0.707 977±0.000 070 to 0.711 791±0.000 064,most of which are higher than that corresponding to global boundary between middle and upper ordovician.Microbial dolomitization is the reason for dolomite genesis.

国家科技重大专项(2008ZX05004-003)资助

https://doi.org/10.11781/sysydz201103266