The eastern Taiergou section is located in the east of Eastern Nihewan Basin in North China.The main strata of this section belong to Pleistocene and Pliocene.Pleistocene Haojiatai and Nihewan formations underlie the Malan loess and palaeosol strata,which exposed on the top of the eastern Taiergou section with 9.4 m in thickness,and overlie the Pliocene Yuxian Formation.Both sedimentary textures and lithofacies simultaneously suggest that the Haojiatai and Nihewan formations should be dominated by the delta plain and delta front subfacies deposits,with minor prodelta deposits.The delta plain subfacies consists of clistributary channel,bifurcated river bend,natural levee,marsh and freshwater lake microfacies.They are characterized by lenticular coarse-grained sand and gravel deposits with large tabular cross-bedding and basal erosion scouring structure,yellowish-brown medium-fined sandy lenticles with calcareous concretions,and dark clay with abundant carbon clasts.The delta front deposits,which consist of branch channel,channel bay,river mouth sand bars,and end bar of branching channel microfacies,are characterized by basal erosion scouring structure,lenticularly medium-fined sand deposits with gravels,fine-grained sand deposits with small tabular cross-beddings,and well-sorted fine-grained quartz sands.The prodelta is less developed relatively,which mainly consists of light-gray clay,green and gray clay with calcareous concretion.The Yuxian Formation contains shore and shallow-lake subfacies deposits.The shore-lake deposits contain clay,silty sand and minor sand-gravel deposits with various colors;they are characterized by mud crack and slumping structure.The shallow-lake deposits,however,consist of silty sand and clay deposits,with lenticular sand and mud interlayers locally.Paleocurrent data indicate that the source of the Pliocene Yuxian Formation should be located in the NE of the Nihewan Basin,and the Pleistocene Nihewan Formation and Haojiatai Formation should be derived from the NE-NW of the Nihewan Basin.The bottom 15 m sediments of the Nihewan Formation is not only derived from the NE source area,but also some sediments should be derived from the SSW source.It indicates that the paleogeography of the Nihewan Basin and its peripheral areas was southward-inclined,i.e.,high in the north and low to the south during the Pliocene and Pleistocene time.%泥河湾盆地东部郝家台地区的台儿沟东剖面主要出露地层为更新统和上新统,剖面顶部为厚9.4m的马兰黄土和古土壤,剖面中部由更新统郝家台组和泥河湾组构成,剖面下部为上新统蔚县组。郝家台组和泥河湾组为三角洲平原、三角洲前缘和少量前三角洲亚相沉积组合,其中三角洲平原亚相可分为分支河道、分支间湾、天然堤、沼泽和淡水湖泊5个微相,由发育大型板状斜层理和底冲刷面构造的粗砂夹砾石透镜体,含钙质结核的透镜状黄褐色中-细砂以及富含炭屑的深色粘土等共同构成;三角洲前缘亚相则由水下分支河道、支流间湾、河口砂坝和末端砂坝构成,以发育底冲刷面构造并夹有细砾石透镜体的细-中粒砂、小型板状斜层理细砂以及分选好且质纯的细砂等组合为特征;前三角洲亚相相对不发育,主要由浅灰色粘土以及灰绿色、灰黑色粘土夹钙质结核构成。蔚县组主要由滨湖亚相和浅湖亚相构成,其中前者为多种颜色的并发育泥裂和滑塌构造的粘土、粉砂组合,局部夹有透镜状砂砾层,底冲刷面发育;后者主要由粉砂、粘土组合构成,局部可见由砂泥交互构成的透镜状层理。古水流分析结果表明,上新统蔚县组沉积物源区位于泥河湾盆地NE侧,更新统泥河湾组和郝家台组碎屑沉积物主要来自于NE和NW方向,而泥河湾组底部约15m厚沉积物除了来自NE方向外,还有部分沉积物来自SSW方向物源区。表明自上新世以来,泥河湾盆地周边具有北高南低古地理格局,从而为盆地提供丰富的碎屑沉积物。
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