蠕虫状灰岩特征和成因新探

下扬子地区下三叠统中广泛分布着一种外貌独特的灰岩——蠕虫状灰岩,这种灰岩出现在该区深水和浅水的多种环境中,具有灰泥结构和粒泥(或泥粒)结构;斜层理、生物扰动构造和压扁透镜状构造。蠕虫状灰岩是多成因的,各成因之间有着一定的联系,其中,先期形成的可被后期形成的叠加和改造。沉积作用、沉积分异作用是形成蠕虫状灰岩的一个重要前提,而生物扰动作用、水流作用和压实、压溶作用则是形成各种蠕虫状灰岩的关键。

THE NEW APPROACH ON THE CHARACTERTSTICS AND ORIGIN FOR VERMICULAR LIMESTONE

A special rock type vermicular limestone of Lower Triassic occurrs widely in the Lower Yangtze area, southern China. This kind of limestone won this name because of containing a large amount of Vermes-like texture. Here the vermicular limestone might occur not only in deep-water (slope to basin) environment, but also in shallow water (beach,lagoon,intertidal zone) environment,with two interal textures-mud texture and wacking (or packing) texture and three structures-biotubated structure, cross-bedding and flattened lenticular structure. Origin of vermicular limestone was very complicated, it was not a single but manifold. There was certain relationship among all kinds of origins, vermicular limestone formed in early time might be superimposed and reformed later. Sedimentation and sedimentary differentiation are a important premise of formation of vermicular limestone,and biotubation,wate-flow action and compaction,pressure-solution are a key of formation of all sorts of vermicular limestone.