宁夏固原古近系寺口子组砂岩成因探讨*

宁夏固原寺口子组砂岩是中国古近纪内陆古环境研究的重要载体。通过岩性、沉积构造、石英颗粒表面微结构和粒度分布特征研究,对其成因进行了深入探讨。结果表明,古近系寺口子组砂岩由3个成因段构成:段Ⅰ为河流相沉积;段Ⅱ,即砂岩主体,为典型风成砂岩,沉积环境为风成沙丘和丘间地;段Ⅲ,初步推断其为湖相沉积。结合中国古近纪气候背景、研究区域地形条件及古风向,推断寺口子组砂岩主体风成沉积为行星风系控制下的沙漠沉积。

Discussion about origin of the Paleogene Sikouzi Formation sandstones in Guyuan,Ningxia

The Paleogene Sikouzi Formation sandstones in Guyuan,Ningxia provide great potential for understanding paleo-environment of the Paleogene inland in China. Based on the lithology,sedimentary structures,surface features of quartz grains and grain size distribution,the orgin of these red sandstones are intensively discussed. This study indicates that the Paleogene Sikouzi Formation sandstones are with a combination of three kinds of sedimentary members: The Member Ⅰ of Sikouzi Formation is fluvial sediments; the Member Ⅱ of Sikouzi Formation,as the main part of the sandstones,belongs to the typical eolian sandstones,and it can be inferred that the sedimentary environment is eolian sand dunes and interdunal depression;the Member Ⅲ of Sikouzi Formation is judged to be lacustrine sediments preliminarily. Combined with the palaeoclimate,orographic condition of the study area and palaeowind, the eolian deposits,as the main part of the Sikouzi Formation sandstones,can be deduced to develop in desert environment controlled by the planetary-wind system.