湖南慈利溪口震旦系陡山沱组震积岩的发现及其地质意义

Characteristics and Geological Significance of Seismites of the Doushantuo Formation in Xikou,Hunan Province

湘西慈利溪口地区震旦系陡山沱组地层中首次发现碳酸盐岩原地震积岩。笔者通过剖面实测,详细观察和描述,结合构造背景,识别出阶梯状层内断层、液化碳酸盐岩脉、液化角砾岩、负荷构造以及微褶纹理等典型的震积软沉积变形构造的地质记录;震积序列在剖面结构上显示自下而上由下伏未震动层—阶梯状层内断层—微褶皱层—液化碳酸盐岩层—液化角砾岩层—上覆未震动层的渐变过程及震积作用逐渐衰减的趋势。震积岩发育的层位在时空上显示良好的可对比性,反映陡山沱期晚期构造活动强烈,并具备多旋回、多周期的特点。构造的活跃加速了有机碳库的氧化,为该时期多细胞生物的繁盛和大规模的成磷成矿作用奠定了基础;同时保存完好的震积地层记录对推断研究区的古沉积环境也具有重要意义。

Autochthonous seismites of the Doushantuo Formation have been discovered for_the first time in Xikou, Cili County in Hunan Province. Based on the profile measurement, detailed observations and description, combined with the analysis of the tectonic background, many typical seismites soft sedimentary deformation structures have been rec- ognized, such as ： fault-graded, liquefied carbonate vein, liquefied breccias, convolute deformation Structure, water- escape structur and seismo-folds, and so on. The vertical sequence of the seimites is underlying unshocked layer, syn- sedimentary microtracture （fault-graded）, micro-corrugated layer, vibrational liquefaction layer, liquefied breccias layer, liquefied homogenization layer and overlying unshocked layer from down to up. The horizon of the seismite shows a good contradistinctive relation in time and space. It suggests that in the Doushantuo Period, strong and fre- quency seismic activity occurred in study area, the nature and activity of earthquake fault varied with different phases. Tectonic activity which accelerates the organic carbon the oxidation is beneficial to development of organisms and also helpful to the phosphate accumulation. In addition, well-kept paleoseismic records are of great significance to deduce the sedimentary environment.