粘土矿物的提取、鉴定及其古气候意义——以柴达木盆地怀头他拉剖面为例

沉积物中粘土矿物类型主要有自生粘土矿物和碎屑粘土矿物。其中,自生粘土矿物含量较少,是在沉积环境中形成,可能是沉积再循环或成岩作用的产物,可作为沉积环境某方面的指示标志;而碎屑粘土矿物是母岩风化的产物,受沉积环境影响较小,能够有效示踪物源区化学风化过程,进而反映古气候变化。近年来利用碎屑粘土矿物特征来重建物源区古气候的方法得到了广泛的应用。然而,由于粘土矿物主要存在于<2 μm硅酸盐粘粒中,粘土矿物的提取、鉴定比较困难,且自生粘土矿物易受沉积环境等的影响。因此,在利用粘土矿物重建古气候变化时,需慎重选择粘土矿物的提取方法,并考虑物源和沉积环境变化以及成岩作用等对粘土矿物解释的影响。本文以柴达木盆地东北缘怀头他拉剖面硅酸盐粘土矿物的提取、鉴定及其古环境指示意义为例,介绍粘土矿物的提取及应用,为后期粘土矿物研究提供参考。

Extraction,identification and paleoclimatic significance of clay minerals:A case of the Huaitoutala section in Qaidam Basin

Clay minerals in sedimentary rocks are authigenic and detrital clay minerals. The authigenic clay minerals with small content are generated in a sedimentary environment as the product of sedimentary recycling or diagenesis and can be used as an indicator of some aspects of the sedimentary environment, whereas the detrital clay minerals are generated from weathering of source rocks and are less affected by the sedimentary environment. Thus, the detrital clay minerals can represent the chemical weathering of the source area and reflect the paleoenvironment change. Recently, these clay minerals have been used to reconstruct the paleoenvironmental changes of the source area. The extraction and identification of clay minerals are deemed difficult. Moreover, they can be affected by the grain sizes of sediments, depositional environment change, and diagenetic metasomatism. Therefore, we should carefully select the extraction method of clay minerals and consider the effect of origin and sedimentary environment changes, as well as the diagenesis process when using them to reconstruct paleoclimate changes. In this study, we present the extraction and identification process of silicate clay minerals and discuss its implications in reconstructing the paleoenvironment, in which we use the Huaitoutala profile in the northeastern Qaidam Basin of the northeast margin of the Tibetan Plateau in China, as an example, to provide a reference for further studies of clay minerals.