吉辽地区新元古代臼齿碳酸盐岩岩相的若干岩石学特征研究

Sedimentary Lithofacies and Petrological Features of Neoproterozoic MT Structures-Bearing Carbonates in Jilin-Liaoning Area

通过研究吉辽地区新元古代地层中一种特殊的沉积构造———臼齿 (简称MT)构造 ,揭示了它的时空分布范围、分类和含该沉积构造岩石的宏观和微观特征 ,并对该种构造的形成环境进行了简要讨论。吉林辽宁地区的臼齿构造主要发育在新元古代地层中 ,按其成因可分为原地和异地两类。其中原地MT主要分布在泥晶灰岩、粉屑泥晶灰岩、泥灰岩或泥岩中 ,按其形态可分为丝状 ,条带状和瘤状 3个亚类 ,13种微相类型。异地MT主要发育在砂屑灰岩、钙质粉砂岩或粉砂质泥岩中。臼齿碳酸盐岩的岩石学特征指示其形成并发育于稳定克拉通浅海潮下环境 ,特别是中 深缓坡上部向上变浅旋回的底部。

Molar Tooth Structure( called Mtfor short) is a special sedimentary structure developed in Jilin-Liaoning area. The macro- and micro- features and the environment for its formation are discussed in this paper. MT of this area mainly occurrs in Proterozoic strata and can be classified into two types: one remains in situ and the other has been transported. The in situ type, which can be subdivided into filament-shaped, ribbon-like and tumorous subtype and 13 microfacies mostly occurs in arenaceous limestones, calcareous siltstone and silty mudstone, while the micro-crystal allochthonous MT carbonates are distributed in arenaceous limestones, calcareous siltstones or silt mudstones. MT structures in Jilin-Liaoning area are closely related to storms. Hummocky cross bedding and graded bedding, for example,are developed commonly at the surface of rocks. MTS-bearing rocks contist of two parts: the matrix and the micro-sparry carbonates. Petrographic statistic show that terrigenous debris in the matrix is less than 30%, pyrite and hematite account for about 0～3%, and the matrix is dominated by Ca, Mg, Al, Si, K and Fe. MT micro-sparry carbonates clearly differ from their carbonate matrix in terms of composition, texture and mineralogy. The material comprises merely peaks of Si and Ca. MT microsparite in macro-structures are mostly homogenous and composed of uniform, isometric or polygonal calcite aggregates,which are about 0.01 mm on average and have clear boundary with the matrix. MT carbonates were formed and developed in the subtidal environment of the stable cratonic ramp, especially in the lower part of the upward-shallowing cycle within the middle-upper deep ramp.