河北省唐山地区古滦河冲积扇第四纪以来演化与变迁

古滦河冲积扇研究的关注点更多在全新世，对其更新世的演化与变迁一直没有进行过系统研究。根据古滦河冲积扇上PZK10、PZK20钻孔的磁性地层学、年代地层学、沉积学、测井沉积学、岩芯色度分析等，对古滦河冲积平原的第四纪三维地质结构、冲积扇体的规模以及迁移规律进行综合研究，结果表明：PZK10孔揭露了上新世时沉积的巨厚洪积成因“泥包砾”地层，早更新世时发育两个冲积扇-湖相旋回，中更新世时发育辫状河沉积，晚更新世发育湖相、冲积扇相、辫状河相沉积。PZK20孔上新世沉积了一套巨厚“泥包砾”层，早更新世为扇前平原-辫状河相沉积，中更新世为辫状河-冲积扇相沉积，晚更新世为辫状河沉积。古滦河发育两期冲积扇，第一期为早更新世早期，在沙流河镇一带出山口形成的规模较大的冲积扇；第二期为早更新世中期，古滦河在现今丘庄水库一带发生分流，在丰润区一带出山口形成的冲积扇。中更新世，第一期冲积扇开始萎缩，第二期冲积扇继续发育，形成巨厚砾石层；晚更新世，古滦河在迁西县城以北发生袭夺，东流迁移出研究区，在西峡口进入迁安盆地，形成以西峡口为顶点的冲积扇。

Evolution and changes of the ancient Luanhe fluvial fan since the Quaternary in Tangshan,Hebei Province

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.