川东南龙王庙组埋藏及混合水白云岩化作用

通过野外调查和地球化学分析，认为四川盆地东南部土河场和南山坪剖面龙王庙组的白云岩不同于区内其他的白云岩。川东南地区龙王庙组白云岩多为回流渗透成因，土河场白云岩则为埋藏白云岩，而南山坪白云岩则为混合水成因。土河场白云岩分布在龙王庙组的下部，不具备形成回流渗透白云岩的地质条件，包体测温显示土河场白云岩的形成温度较高，均在105 ℃以上，其Mn元素和Fe元素含量较高，平均值分别为792.5×10-6和3 428.8×10-6，且具有很好的相关性，δ18O平均为-8.18‰，明显低于研究区其他剖面的白云岩，这些特征均反映了土河场剖面白云岩形成于埋藏环境的特征。南山坪剖面主体处于斜坡相中，也不具备形成回流渗透白云岩的地质条件。南山坪白云岩具有明显的低Na元素的特征，δ18O也明显偏负，显示其形成于温度相对较低的低盐度流体环境中，此外，南山坪白云岩具有明显的U元素富集的特征，指示南山坪白云岩形成与大气淡水有关，为混合水成因的白云岩。这两类白云岩具有相对较好的物性条件，对川东南地区储层发育具有重要意义。

Burial Dolomitization and Mixed Water Dolomitization in Longwangmiao Formation,Southeastern Sichuan Basin

Based on field investigation and geochemical analysis， it is believed that the dolomites of the Longwangmiao Formation in the Tuhechang and Nanshanping sections， southeast Sichuan Basin， differ from other dolomites in the area， being mainly of reflux seepage origin. Tuhechang dolomite is of burial origin， and the dolomite in Nanshanping is of mixed-water origin. The Tuhechang dolomites occur in the lower part of the Longwangmiao Formation， and did not have the geological conditions suitable for forming reflux seepage dolomites. The temperature of inclusions of the Tuhechang dolomites shows a formation temperature higher than 105 °C. Its Mn element and Fe element content are relatively high （average 792.5×10–6 and 3 428.8×10–6 respectively）， with good correlation. The average δ18O content is –8.18‰， which is significantly lower than for dolomites in other sections of the study area. These all reflect a burial environment in the Tuhechang section. The main part of the Nanshanping section lies in a slope facies zone， and did not have the geological conditions for the formation of reflux seepage dolomite. Nanshanping dolomite contains an obviously low value for Na element， and δ18O is also obviously negative， both indicating that it was formed in a low-salinity fluid environment at a relatively low temperature. In addition， Nanshanping dolomite shows obvious U element enrichment， indicating that its formation was related to atmospheric fresh water， and it is therefore a mixed-water dolomite. These two dolomite types have relatively good physical properties， which is highly significant for reservoir development in the southeastern Sichuan Basin.