松辽盆地嫩江组白云岩形成机理——以松科1井南孔为例

The Forming Mechanism of Dolostone of Nengjiang Formation in Songliao Basin——Example from CCSD-SKⅡ

松科1井是中国大陆第一口以白垩系地层为主的全取心科学探井,由松科1井南孔和松科1井北孔两个钻孔组成。在松科1井南孔岩心精细描述的过程中发现嫩江组地层中发育层状白云岩和椭球状白云岩,共62层。白云岩结核垂向截面的透镜形状、结核内部上凸下凹两端收敛的层理特点以及在显微镜下观察到的白云石的雾心亮边结构和泥灰岩被局部交代产生的"豹斑状"白云石聚集均显示嫩江组白云岩是湖相泥灰岩在准同生期被交代的产物。白云岩的形成机制是在晚白垩世松辽盆地海侵背景下Mg2+在准同生期交代由浊积事件、介形虫灭绝事件所带来的泥灰岩沉积而成。

The CCSD-SK is the first scientific drilling well of whole core Cretaceous rocks in the continent of China, which is composed of two drilling wells： CCSD-SK Ⅰ in the north and CCSD-SK Ⅱ in the south. Totally, 62 layers Of bedded and ellipsoidal dolostone were identified in the Nenjiang Formation during the description of CCSD-SK Ⅱ. Dolostone nodular occurs as lens in the vertical section, and interior of the nodular is characterized by foliation which converges at both lateral edges. Under microscopic observation, dolostone is grey in the core and bright at the rim, and marl has been replaced, locally forming ＂leopard spot＂ dolomite. All these features indicate that dolomite of the Nengjiang Formation was the product of lacustrine facies limestone during penecontemporaneous replacement. The forming mechanism of dolostone of the Nenjiang Formation was that under the setting of the marine transgression of Late Cretaceous in the Songliao Basin, marls brought by turbidity flow and extinction of ostracoda began to deposit during the replacement, thus forming the dolostone.