【摘要】 臼齿构造是一种发育在中—上元古界中的特殊类型的沉积构造,具有特定的时限。在对徐淮地区上元古界臼齿构造碳酸盐岩旋回层序、岩石学特征和臼齿构造形成环境研究的基础上,探讨了臼齿构造碳酸盐岩的成因。采用旋回层序、海平面变化及臼齿构造碳酸盐岩事件的综合分析方法,划分了徐淮地区上元古界臼齿构造发育的地层层序。臼齿构造主要出现在泥晶灰岩中,而在粗颗粒灰岩中则很少出现,臼齿构造与基质碳酸盐岩在组分和结构上有明显不同,臼齿构造是由纯净的微亮晶方解石组成,而基质则是由含粘土和细粉砂的泥晶碳酸盐岩组成,二者呈突变接触关系。对臼齿构造在层序中相序分布关系的详细研究表明,臼齿构造具有重要的环境意义,从台地内缓坡下部、中缓坡到外缓坡上部均有分布,但在不同环境中臼齿构造的类型不同。更多还原

【Abstract】 Molar-tooth structures are intricately crumpled, microsparry calcite fissure fill,formed during the meso-Neoproterozoic. Molar-tooth structures distributed extensively from Neoproterozoic in Xuhuai area are studied on cycle sequences,the petrological characteristics and the depositional environment, and discussed on their geological meaning and formation mechanism. The cycle sequence from Neoproterozoic of this area is divided according to analysis of the cycle sequences,the sea-level variety and the affairs of molar-tooth carbonates. Formed and developed in the subtidal environment of the stable cratonic ramp,especially on the lower part of upward-shallowing cycle sequence from the lower shallow ramp to the upper deep ramp, the molar-tooth structures can be used as the environmental marking in the stable ramp. These structures appear primarily in the micritic limestone, marls, calcisiltitic micrite and micrites, but are almost absent in thick grain carbonates.The molar-tooth structure-bearing rocks consist of two parts: the matrix and the microsparry calcite,the latter clearly differing from its surrounding carbonate matrix in terms of composition, texture and mineralogy. Most of the microsparry calcite in many of macro-structures is homogenous in general, composed of uniform, equal axial and polygonal calcite with clear boundary to the matrix, locally containing siliceous debris and pyrite cubes in the molar-tooth veins, sharply contacting or dissolved edge with the matrix. The characteristics of the molar-tooth carbonates form Neoproterozoic were induced and summarized in Xuhuai area. Finally, the geology meaning and the origin of molar-tooth structures are discussed.更多还原