摘要
作为优质储层的四川盆地东北部三叠系飞仙关组的结晶白云岩是通过埋藏成岩过程的封闭条件下的白云石化作用形成的。岩石所具有的高孔隙度与封闭体系中的白云石化反应:2CaCO_3+Mg^(2+):CaMg(CO_3)_2+Ca^(2+)有关。埋藏成岩体系中的高锶流体是该封闭条件下白云石化作用的产物,深埋藏条件下的热化学硫酸盐还原作用是锶进一步富集的原因,因而三叠系的大型和超大型天青石矿床的成因与这些因素有关。结晶白云岩极低的锰含量、与同期海水类似的δ^(13)C值表明白云石化流体具有强烈的海源色彩,同时也说明白云石化过程没有与大气水交换;相对较低的δ^(18)O值表明白云石化发生在较晚的埋藏成岩阶段。大多数已有的白云石化机制都是基于近地表成岩条件建立的,系统具有良好的开放性,但开放体系中的白云石化(或白云石沉淀)作用对油气储集空间和与成岩过程元素迁移有关的沉积层控矿床的形成没有多少实际意义。在四川盆地东北部三叠系飞仙关组地层中,作为非储层的微晶或泥晶白云岩以及原始结构保存的粒屑白云岩的白云石化作用主要是在有大气水介入的开放体系中发生的。
Dolomitization and origin of dolomite are still controversial in carbonate sedimentology. Dolomitization can enhance porosity and permeability of tight limestone and dolomites are the most important host rocks for base metal mineral deposits. Therefore, dolomitization and origin of dolomite are paid more attention by petroleum and economic geologists. Crystalline dolomite acts as the good reservoir in Feixianguan Formation of Triassic, NE Sichuan Basin of China, which formed by the dolomitization in a closed system through the burial diagenesis. The high porosity in the rock is related to the dolomitization reaction in the closed - system: 2CaCO(3) + Mg2+ = CaMg(CO3)(2) + Ca-2 +, which produced the pore fluid with very high Sr concentrations. The thermochemical sulphate reduction occurred in deep buried diagenesis is responsible for the further enrichment of Sr. The origin of the large scale or super - large scale celestite deposits in Triassic is also related to the closed - system dolomitization and TSR. Very low Mn concentrations ( average 20 ppm, approximately) and the delta C-13 values similar to coeval seawater in crystalline dolomite show that major source for dolomitization fluid must be marine fluid, and there is no meteoric water intervention during dolomitization. Relatively lower delta O-18 values indicate that dolomitization could occur during the time of later burial diagenesis. Most of dolomitization models are based on the subaerial diagenesis of carbonate, which should be dominated by an open environment. The dolomitization (or dolomite precipitation) in an open - system may take place by the reaction: CaCO3 + CO32- + Mg2+ = CaMg ( CO3)(2) , which can not enhance porosity and permeability of limestone, and is not benefit for the stratabound deposits. The dolomitization for micrite dolomite and grainy dolomite ( with original texture) in Feixianguan Formation of Triassic, NE Sichuan Basin of China could be controlled by an open - system dolomitization with the influence of meteoric water.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第11期2955-2962,共8页
Acta Petrologica Sinica
基金
国家自然科学基金(编号:40672072
40472068)
教育部博士点基金(编号:20050616005)资助项目
关键词
四川盆地东北部
三叠系飞仙关组
封闭系统
白云石化
富锶成岩流体
NE sichuan basin
feixianguan formation of triassic
dolomite reservoir
closed-system
dolomitization
high strontium concentration diagenetic fluid
