福建下三叠统溪口组浊积岩的发现其意义

THE DISCOVERY AND SIGNIFICANCE OF TURBIDITES IN THE LOWER TRIASSIC XIKOU FORMATION,FUJIAN

摘要:

福建下三叠统溪口组主要出露于闽西南地区,北起将乐,南至永定,西部见于清流,东部延至长泰、德化一带,以龙岩、永定、漳平、永安、大田等地最为发育。溪口组主要是一套细碎屑沉积组合,局部地区出现碳酸盐岩夹层。最大厚度可达到1484m,可分为三个岩性段:下段以泥岩、含粉砂泥岩和粉砂质泥岩为主,局部夹薄层粉砂岩。东南部的安溪、长泰尚见有钙硅质胶结的细粒石英杂砂岩夹层。大部分地区岩石具不同程度的角岩化。

Abstract:

The present paper deals with lithology and various sedimentary structures in the lower and middle members of the Lower Triassic Xikou Formation, Fujian. The authors contend in this paper that the early Indosinian environments in southwestern Fujian should be a lower slope and base of slope environment in a deep-sea basin with the following reasons. (1) lithologically, higher porpotions of finer and thinner distal turbidites occur in the lower member of the Xikou Formation, and Locally proximal turbidites in the middle member of it; (2) The structural characteristics of some of graded units composed of sand-silt-mud admixtures are similar to those of the immature "dirty sand" or graywacke in the ancient flysch formations; (3) The sedimentary structures such as scour marks, tool marks, flute casts, groove casts, flame and load structures, convolute bedding, ripple drift microlamination show that the activity of turbidity current and fluidized flow are strong; (4) Compared with the Late Permian, there are considerable variations in the Indosinian faunas in Fujian. The lower abundance and diversity of these faunas suggest that the environments of the Xikou Formation may be a deep sea characterized by planktonic bivalves.
Tectonically,it is obvious that a deep-sea basin created by tensional deep fracture once occurred in the central part of southwestern Fujian depression, and the transgression had its largest scale, although the depth and scale of the basin is still a puzzle.