深水型条带状灰岩的特征和形成机理

CHARACTERISTICS AND FORMATION MECHANISM OF DEEP-WATER TYPE BANDED LIMESTONE

寒武纪时,在我国东南部,一种常见的岩石类型——条带状灰岩普遍地发育在扬子台地南北边缘的深水斜坡相中。这种灰岩因风化外貌呈黑白条带相间而得名,笔者通过对条带状灰岩中条带的颜色、成分、厚度、横向变化以及各种层理构造的讨论,指出这种外貌单调而简单的灰岩形成机理非常复杂,至少有下述5种作用参与:高密度-低密度浊流沉积、等深流沉积、颗粒流沉积、碎屑流沉积和半远洋-远洋沉积。各种作用所形成的条带状灰岩内在特征各不相同。

A common rock type——banded limestone——was widely developed in thedeep-water slope facies on the north and south edges of the Yangtze platform in southeastern China during the Cambrian. This type of limestone won its name because of its weathering appearance of alternately black and white bands. According to the colours, composition, thickness and lateral variation of the bands and all kinds of bedding structures, the authors point out that the formation mechanism of this type banded limestone is very complicated, and at least, there occurred five kinds of sedimentation: high-to low-density turbidity current, contour current, grain-flow, debris flow and hemipelagic to pelagic sedimentation. Banded limestones formed by the abovementioned kinds sedimentation have different sedimentary characteristics.