楚雄盆地白垩纪晚期盐湖风成砂微观组构特征研究

    Study on the microstructure characteristics of Late Cretaceous aeolian sand in the playa from Chuxiong Basin

    • 摘要: 白垩纪是地球历史上一个持续时间较长的典型温室气候期,受区域古地形叠加影响,在东亚地区促成了广泛的干旱气候带,并伴有大面积出露的古沙漠和蒸发岩沉积,而楚雄盆地上白垩统江底河组即为该时期形成的一套干盐湖相红色碎屑岩夹膏盐沉积。通过光学显微镜和扫描电镜(SEM)及能谱(EDS)分析,对江底河组砂岩石英颗粒结构形态及表面微形貌特征进行研究。结果显示,楚雄盆地江底河组砂岩的石英颗粒具有高磨圆度和分选性、碟形撞击坑、“沙漠漆”以及强化学作用溶蚀孔(洞)群等现象,展现出风成砂的典型特征。同时基于石英颗粒表面机械作用、化学(溶蚀、沉淀)作用及其组合特征,系统总结了石英颗粒在不同沉积阶段和环境背景下,其表面微形貌特征的演化规律。这项研究有助于对盐湖环境中风成砂的特征以及风成沉积和水成沉积相互作用机制的认识。

       

      Abstract: Cretaceous greenhouse, a long-lasting typical warminginterval in the history of the earth, and the regional paleotopography effect triggered a wide spread arid-climate belt in East Asia accompanying with extensive paleo-desert outcrops and evaporite deposits. The Upper Cretaceous Jiangdihe Formation in the Chuxiong Basin is characterized by a set of red clastic rocks interbedded with gypsum, being atypical playa environment. Through multiple approaches including optical microscopy, Scanning Electron Microscopy (SEM) and Energy Spectrum (EDS) analysis, the structural morphology and surface micro-morphology characteristics of quartz grains from the Jiangdihe Fm. sandstones from the Chuxiong basin have been studied. The results show that the quartz grains of the Jiangdihe Fm. sandstone has high roundness and wellsorting, dish-shaped impact scars, "desert varnish", and groups of intense chemical corrosion pores (caves), all of which show the typical characteristics of aeolian sand. In addition, the evolution rule of micro-morphology on the quartz grains under different sedimentary environment has been systematically summarized, based on physical interaction, chemical (dissolution, precipitation) interaction, and their combination characteristics of the quartz grains surface. This study will contribute to the further understanding for the characteristics of aeolian sand deposited in the playa environment and the mechanism of the interacting aeolian-aqueous deposition.

       

    /

    返回文章
    返回