山东青州地区黄土的粒度组成及成因分析

在鲁中山地北侧的山间谷地及山麓地带广泛发育厚度不一的黄土堆积。对该区青州傅家庄黄土剖面进行了系统的粒度分析, 并与黄土高原的第四纪黄土-古土壤、北京现代降尘、剖面附近的河流相样品进行了对比。结果表明, 青州黄土的粒度分布特征与北京现代降尘、黄土高原黄土非常相似, 与河流相样品则有很大的不同; 在整个序列中, 青州黄土粒度变化与黄土高原典型的风成黄土、古土壤一致, 黄土层颗粒粗, 古土壤层颗粒细。上述结果从沉积学的角度为青州黄土风成成因提供了证据。青州黄土的粒度组成特征及前人的研究表明, 青州黄土主要来源于沉积区以北的黄泛平原和莱州弯等地出露的海相地层, 其次是高空气流携带的西北内陆的远缘粉尘。

GRAIN-SIZE DISTRIBUTION AND GENESIS OF LOESS IN THE QINGZHOU AREA, SHANDONG

Loess deposits with varying thicknesses are widely distributed on intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous region.A systematic grain-size analysis was performed along the Fujiazhuang loess section of the Qingzhou area.The analytic results of the samples were correlated with those of the samples taken from Quaternary loess-paleosol of the Loess Plateau,modern dust fallouts in Beijing and fluvial deposits.The results show that the grain-size distribution of the Qingzhou loess is very similar to that of modern dust fallouts in Beijing and loess of the Loess Plateau but notably different from that of the fluvial samples.In the whole loess-paleosol sequence,the grain-size variation of the Qingzhou loess is consistent with the typical eolian loess and paleosol of the Loess Plateau.The loess is coarse in size,while the paleosol is fine in size.The above-mentioned results provide evidence for the eolian origin of the Qingzhou loess in the sedimentological context.The grain-size distribution of the Qingzhou loess combined with the previous studies indicates that the main provenances of the Qingzhou loess are the marine strata exposed in the flood plain of the Yellow River and Laizhou Bay north of the sedimentary region and less commonly distal silt and dust carried by highlayer circulation from northwest inland.