泥河湾盆地马圈沟剖面早更新世矿物变化特征及其古环境意义

Mineral Variation of Majuangou Profile in the Nihewan Basin During the Early Pleistocene and Its Paleoenvironmental Significance

在野外考察采样的基础上,对泥河湾盆地马圈沟剖面更新世河湖相沉积序列进行了XRD矿物组分和磁性矿物分析。研究发现,剖面沉积矿物主要由碎屑矿物和碳酸盐矿物组成,碎屑矿物主要为石英、钠长石、白云母和斜绿泥石,其平均含量分别为38.77%、17.16%、29.63%和4.11%,是剖面沉积矿物组成主体,且各矿物之间基本没有相关性;相对于碎屑矿物,碳酸盐矿物在整个剖面中含量较低,主要为方解石和白云石,其平均含量分别为4.72%、3.59%,文石在剖面中零星出现。对剖面典型样品进行热磁分析,确定了沉积物中磁性矿物的种类以及加热过程中的变化和产物,并对其来源进行了探讨。同时发现,含绿泥石较高的灰绿色粉砂样品加热后磁化率的升幅比灰黄色样品高,而绿泥石的相对含量与该地区化学风化密切相关,进一步说明κ-T曲线的变化特征可以用来反应盆地化学风化作用强度的变化,具有重要的古环境意义。

Based on the field investigation and systemic samples collected at Majuangou profile,67 selected samples with equal intervals of 1 m,the anthors analysed the mineral assemblages by XRD,and established the relationship between characteristic of minerals and paleoenvironment of Nihewan basin in the early Pleistocene.The results show that the sedimentary minerals have major component of detrital minerals and carbonate minerals.Detrital minerals are dominating in the profile and cornposed of quartz,sodium feldspar,dolomite and plagioclase,with the mean values of 38.77%,17.16%,29.63%,and 4.11%.Each of the detrital minerals has hardly the correlation.The carbonate minerals have low content in the profile and mainly include the calcite and dolomite,with the content of 4.72%and 3.59%.It has a few of aragonite in the profile.Coupled with thermomagnetic analysis,the grayish-green silt samples generally have higher contents of chlorite and more enhanced magnetic susceptibility after heating than the grayish-brown silts samples.In addition,the contents of chlorite have a positive correlation with the chemical weathering in the study areas,suggesting that the thermomagnetic analysis(especiallyκ-T curve)can be used to reflect the intensity variation of chemical weathering in the Nihewan Basin.It is important for paleoenvironmental studies.