Dizhi lixue xuebao (Feb 2023)
Evolution and changes of the ancient Luanhe fluvial fan since the Quaternary in Tangshan, Hebei Province
Abstract
The study of the ancient Luanhe alluvial fan has focused more on the Holocene, and no systematic study has been conducted on its Pleistocene evolution and variation. We studied the magnetic stratigraphy, chronostratigraphy, sedimentology, logging sedimentology, and core color of the boreholes PZK10 and PZK20 in the ancient Luanshe alluvial fan. Based on that, we carried out a comprehensive study of the Quaternary three-dimensional geological structure, the scale of the alluvial fan body, and the migration pattern of the ancient Luanshe alluvial plain. The borehole PZK10 recorded Brunches, Matuyama, and Gauss polarity chrons; the boundaries between them are 77.42 m and 71.50 m, respectively. The borehole PZK10 also revealed a set of diluvial “mud-gravel” layers deposited in the Pliocene, with two alluvial fan-lake phase cycles in the Early Pleistocene, braided river deposits in the Middle Pleistocene, and lake, alluvial fan and braided river facies in the late Pleistocene. A set of highly thick “mud-gravel” layers was deposited in the Pliocene of the borehole PZK20. The early Pleistocene is the fan-front–plain-braided river facies deposition, the middle Pleistocene is the braided river–alluvial fan facies deposition, and the late Pleistocene is the braided river deposition. Early Pleistocene, the ancient Luanhe River out of the mountain formed a large-scale alluvial fan in Shaliuhe town, which is the first stage of the ancient Luanhe alluvial fan. In the middle of the early Pleistocene, the ancient Luanhe River diverged in the current Qiuzhuang reservoir, and the alluvial fan formed in the Fengrun area, namely the second stage alluvial fan. In the middle Pleistocene, the first alluvial fan began to shrink, while the second alluvial fan continued to develop, forming a vast thick gravel layer. Late Pleistocene, the ancient Luanhe river was captured north of Qianxi county. It flowed eastwards and migrated out of the research area into the Qian’an basin in Xixiakou village, forming the alluvial fan with Xixiakou village as its apex.
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