湖北黄石地区下侏罗统桐竹园组下部物源和粒度分析及其地质意义

Analysis of the Grain size and Provenance of the Tongzhu Formation of the Lower Jurassic in Huangshi Area,Hubei Privince and Its Geological Significance

黄石地区处于大别山南麓,扬子地块东北缘,其沉积物必然敏感地反映扬子地块大地构造格架的演化和周缘山体隆升等信息。本次通过岩矿鉴定,进行物源和粒度分析,系统研究了采自黄石地区下侏罗统桐竹园组下部的典型砂岩样品。研究表明,样品中碎屑成分含量相对稳定,主要为石英、长石、岩屑及副矿物,以石英为主,少量长石,极少量岩屑并以沉积岩屑为主,少见云母,偶见辉石和普通角闪石等副矿物;碎屑物的分选性和磨圆度较好,成分成熟度较高。物质组成及组构显示物源区为远源的"再旋回造山带物源"类型。粒度特征显示为稳定的曲流河沉积,沉积环境未明显受周缘山体隆升的影响。结合古流向资料,表明当时物源可能主要来自华夏板块内部,而来自附近大别山的物源贡献较小。

Huangshi area is located in the south of Dabie Mountain and northeast of Yangtze Block. The sediment must have contained some information of the evolution of geotectonic framework of Yangtze Block and the uplift of Dabie Mountain, and so on. In this study, the authors conduced a comprehensive survey of microscopic examination of thin-sections, analysed of provenance and grain size statistic for the typical sedimentary rock samples collected from different beds of the Lower Jurassic Tongzhu Formation from Huangshi area. The present study indicates that elastic constituents are relative stable and mainly consist of quartzs, feldspars, debris and accessory minerals, the quartz content is high, feldspars and the debris content is low ,with the later mainly composed of micritic/mieroerystalline carbonate debris and accessory minerals including mica, pyroxene, hornblende. The debris are characteristic by good sorting and psephicity, and high compositional maturity. All these above suggest that the source regions are far away from study area. The grain size feature manifest：this area frequency grain-size curves mainly develop as bimodal and unimodal shapes. The characteristics of Grain size show that it is a stable meandering river sedimentary and the depositional environment has not been significantly affected by the uplift of the Dabie Mountains.