鲁中山地北麓黄土-古土壤粘土矿物组成及古环境意义

鲁中山地北麓的黄土沉积是我国东部平原区第四纪冰期-间冰期古环境变化的重要记录。目前，对这套沉积经历的风化成壤过程还没有开展系统的研究，限制了轨道尺度古环境变化信息的挖掘。本文采用X射线衍射分析方法，对鲁中山地北麓黑山剖面末次间冰期以来代表性的黄土L₁和古土壤S₁样品进行了粘土矿物测试分析。结果表明，黑山黄土沉积的粘土矿物组成以伊利石和蛭石（含层间羟基矿物，简称HIM）为主，二者含量在70.9%~82.2%之间，而高岭石、绿泥石和蒙脱石含量相对较少；与冰期黄土L₁相比，间冰期古土壤S₁含有较高的蛭石（+HIM）和高岭石，而伊利石、绿泥石和蒙脱石的含量相对较低，并且伊利石结晶度KI值和绿泥石风化指数（0.47/0.71 nm）显著增高。粘土矿物组合以及伊利石和绿泥石的化学风化特征表明古土壤经历了中等风化成壤作用，指示了暖温带湿润-半湿润的气候环境，夏季风显著增强。末次冰期黄土L₁中含有较多碎屑成因的蛭石（+HIM），与已有黄土高原末次冰期黄土研究结果对比分析后，排除了鲁中山地北麓黄土与黄土高原黄土一样主要来自西北内陆荒漠区的可能，这进一步支持了鲁中山地北麓黄土主要来源于近源的华北平原各类沉积物的结论。

Clay mineral composition of loess deposits and it's paleoenvironmental significance in the northern piedmont of the Central Shandong Mountainous Region

The loess deposits in the northern piedmont of the Central Shandong Mountains(CSM) region are significant records of Quaternary paleoenvironmental changes in the eastern plains of China. At present, there is no systematic research on the weathering and soil formation process experienced by this set of sediments, which limits the interpretation of paleoenvironmental information. In this paper, the Heishan(36°10.05'N, 116°20.63'E) section, a typical eolian loess section in the northern piedmont of the CSM, was investigated. Annual temperature and precipitation are typically 14.4℃ and 631.0 mm in this region, respectively. The section has a thickness of 12.3 m, with yellow plough horizon(0~0.8 m), greyish black Holocene soil(S0:0.8~2.9 m), Malan loess(L1:2.9~7.5 m) and the last interglacial palaeosol(S1:7.5~12.3 m). The Optically Stimulated Luminescence(OSL) dating results indicate that the top and bottom ages of L1 are 10.9±0.6 ka and 65.0±2.2 ka, respectively(Zhao et al., 2019, 2020). Clay minerals were measured using the X-ray diffraction(XRD) on oriented mounts of clay-sized particles(< 2 μm). In this section, 5 and 7 samples were selected from the glacial loess(L1) and the last interglacial soils(S1), respectively. All samples for clay minerals analysis were disaggregated in deionized water and treated with 10% H2O2 and 1 mol/L HAC to remove organic materials and carbonate, respectively. XRD Analysis was carried out using a PANalytical X'Pert PRO X-ray Diffractometer with CuKα radiation, operating at 40 kV, 40 mA. Identification of clay minerals was made mainly according to the position of the (001) series of basal reflections on the XRD diagrams(Moore and Reynolds, 1989). Illite crystallinity(Kübler index, KI) was obtained from the full width half maximum of the 1.0 nm peak(Δ°2θ).