迁安山叶口常州沟组一段岩石学特征

Petrological characteristics of the first member of Changzhougou formation in Shanyekou,Qian'an

在沉积盆地分析中,对特定地质历史时期沉积的地层进行岩石学特征研究,是反映盆地演化特征和恢复古沉积环境的必要步骤。研究了迁安山叶口地区常州沟组一段的岩石学特征,对岩石沉积结构和构造进行了分析,对古水流方向进行了统计与分析,并探讨了该套地层形成时的古沉积环境。结果表明:本区常州沟组一段岩性为一套巨砾岩、砂岩,砂岩岩性以成分成熟度低的长石砂岩为主,巨砾岩砾石成分主要为成分成熟度较高的石英砂岩、石英岩和硅质岩。砾岩层序总体上表现为一个向上变细的正旋回,代表了水体向上逐渐变深的特征,3种典型的韵律特征形式。古水流优势方向为南东向,主要物源区可能位于今秦皇岛一带,沉积环境为干旱炎热气候下山间盆地中水流湍急的不成熟直流河,由于构造活动等因素逐渐向成熟的河流演变。

In the sedimentary basin analysis,it is necessary to study the petrological characteristics of the strata deposited in a specific geological history period in order to reflect the evolution pattern of the basin and restore the sedimentary environment.In this paper,the petrological characteristics of the first member of the Changzhougou formation in the Shanyekou area of Qian'an are studied;the sedimentary structure of the rocks are analyzed;the paleocurrent direction is measured and analyzed;and the palaeosedimentary environment during the formation of this set of strata is also discussed.The result shows that the lithology of the first member of Changzhougou formation is a strata of boulder conglomerate and sandstone,lithology of the sandstone is mainly composed of feldspar sandstone with low compositional maturity.Gravels of the boulder conglomerate is mainly composed of quartz sandstone,quartzite and siliceous rock with high compositional maturity.In general,the conglomerate demonstrates a fining-upwards sequence,which means that the water body gradually deepens upward,and three typical rhythmic patterns can be extracted.The dominant direction of paleocurrent is toward southeast,which reveals that the main provenance may be located in the present Qinhuangdao area.The sedimentary environment of the area in the early Changzhougou stage is an immature direct river with rapid currents in the inter-mountain basin under dry and hot climate,which gradually evolve to become a mature river due to tectonic activities and other factors.