束鹿凹陷碳酸盐角砾岩的成因研究

The Formation of Carbonate Breccia in Shulu Depression

碳酸盐角砾岩一般为内源或构造等成因,陆相沉积环境极难形成。研究发现束鹿凹陷古近系角砾岩为陆相成因。束鹿凹陷角砾岩分布于沙河街组三段中下部,在凹陷的东西斜坡地带呈裙状发育,是一种以碳酸盐岩碎屑为主的沉积岩。岩石类型为角砾岩及少量含砾泥灰岩,角砾岩具有以颗粒支撑为主,块状构造、粒序构造或其它层理构造不明显,角砾大小混杂,没有出现方向的优选,砾岩层单层厚度较大等特点;含砾泥灰岩为杂基支撑,具正粒序构造,并可见倒三角形状角砾。碳酸盐角砾岩中无论角砾还是填隙物都主要由棱角状及次棱角状碳酸盐碎屑颗粒构成,其母岩为盆地周围奥陶系及寒武系碳酸盐岩。研究认为束鹿凹陷沿缓坡分布的角砾岩属陆源非粘性碎屑流沉积产物。

Breccia in Shulu depression was found in the middle and low of the third segment of Shahejie Formation, it is a breccia with carbonate fragment as its main constituent, and distributes skirt shapely on slopes in the depression. Breccia and marlstone with breccia are familiar breccias in the area and the former is domestic. Grain and matrix in the breccia are mainly angular and subangular carbonate clastic particles, whose parent rock were carbonate stratum of Ordovician. Mainly grain support, massive structure, infrequent graded bedding and others bedding, unsorting of detrital grains and thicker breccia layer are important features of carbonate breccia in Shulu depression. Characteristics of component, fabric, structure and geologic background all reveal that the breccia in the study area is inviscous debris flow sediment of terrestrial formation.