四川盆地白垩纪沙漠石英沙颗粒表面特征

The surface features of the quartz sand grains from the Cretaceous desert in the Sichuan Basin

关键词:  四川盆地  白垩纪沙漠  石英沙颗粒表面特征

Key words:  Sichuan Basin  Cretaceous desert  surface features of quartz sand grains

摘要:

石英具有较大的硬度和较高的化学稳定性,因而其颗粒表面特征能很好地反映沉积环境。而通过扫描电镜研究石英颗粒表面微细特征是分析沉积环境行之有效的方法。虽然多数人认为四川盆地白垩纪地层存在沙漠沉积(打儿凼组和夹关组),但仍有人对沙漠沉积的存在持怀疑态度,并认为是河流或三角洲沉积。过去关于其沉积环境的判别主要是根据沉积结构和构造,并未对其石英沙颗粒表面特征进行过系统分析。笔者对采自四川盆地白垩系不同层位地层的样品进行了石英沙颗粒表面特征系统分析。结果表明,石英沙颗粒表面特征分析可以成功地将石英沙区分为风成和水成沉积。因此,本文从石英沙颗粒表面特征方面进一步肯定了四川盆地白垩纪古沙漠的存在。

Abstract:

The surface features of quartz sand grains may well be used as the indicators of their depositional environments due to larger hardness and chemical stability. The examination of surface features of quartz sand grains with the aid of scanning electron microscopy is generally viable to the approaches of sedimentary environments. Some of the workers once argued that the Cretaceous strata in the Sichuan Basin should be assigned to the fluvial or delta deposits rather than the desert deposits (Da'erdang and Jiaguan Formations). The previous examination of sedimentary environments was based on sedimentary textures and structures. In the present study, the surface features of quartz sand grains are explored on the basis of the samples from varying levels of the Cretaceous strata in the Sichuan Basin. The exploration of surface features of quartz sand grains has resulted in the recognition of eolian and aqueous deposits. These features of quartz sand grains may serve as the reliable evidences in favour of the presence of the paleodeserts in the basin.