大庸市四都坪震旦系南沱组岩石特征及成因探讨

PETROLOGICAL FEATURE OF NANTUO FORMATION OF SINIAN IN SIDUPING,DAYONG CITY ANDDISCUSSION ABOUT ITS ORIGIN

文中提出以砾、砂、泥作三端员成分进行陆源沉积岩结构分类的三角图解方案,并用于四都坪南沱组岩石的划分,将其划分为杂屑岩、角砾岩、杂砂岩、粉砂质泥岩等。杂屑岩在南沱组剖面中占82％,其中的砾石成分复杂,有砂岩、板岩、大理岩、花岗岩等,大砾石表面有冰川擦痕和磨光面。角砾岩中角砾成分单一,无大漂砾,具颗粒支撑,并见夹有塑性变形的含锰灰岩。杂砾岩中发育砂纹层理及冲刷构造。因此,认为南沱组在成因上与冰川活动有关,在冰浅海环境中堆积,同沉积断裂的存在提供斜坡条件,冰川重力及埋藏冰消融等引发重力流,使冰川沉积不时受颗粒流、碎屑流干扰,而在冰期末又遭冰水及海水的改造。

A triangular diagram with the contents of gravel, sand, and mud as the three end members for textural classification of terrigenous sedimentary rocks is put forward and is applied to the classification of the rocks of Nantuo Formation in Siduping, which is classified as 'diamictite,' breccia, graywacke, silty mudstone erc. The diamictite occupays 82％ of the rocks in the profile of Nantuo For- mation, of which the gravel composition is complicated, including sandstone, slate, marble, granite etc. Glacial striae and polished surfaces can be found in the large gravels. The fragmental composition of the, breccla is unitary, without large erratic boulders, and the breccia is grain-supported, intercalated with plasticly deformed manganiferous limestone. Sand-laminated bedding and scouring stru cture are developed in the graywacke. Therefore, it is considered that the Nantuo Formation is genetically related to the glacial activities, and is accumulated in the shallow glaciomarine environment, the synsedimentary fault provided a slope, the gravity and the melting of the burried ice caused to form gravity-flow, hence, the glacial deposition is frequently interfered by the grain-flow and debris-flow, and is reformed the glacial water and sea water in the end of the glacial epoch.