The Late Cenozoic basins in the Weihe-Shanxi Graben, North China Craton are delineated by northeast-striking faults. The faults have, since a long time, been related to the progressive uplift and northeastward expansion of the Tibetan Plateau. To show the relation between the basins and faults, two Pliocene-Pleistocene stratigraphic sections （Chengqiang and Hongyanangou） in the southern part of the Nihewan Basin at the northernmost parts of the graben are studied herein. Based on the sedimentary sequences and facies, the sections are divided into three evolutionary stages, such as alluvial fan-eolian red clay, fan delta, and fluvial, with boundaries at -2.8 and -1.8 Ma. Paleocurrent indicators, the composition of coarse clastics, heavy minerals, and the geochemistry of moderate-fine clastics are used to establish the temporal and spatial variations in the source areas. Based on features from the middle- northern basin, we infer that the Nihewan Basin comprises an old NE-SW elongate geotectogene and a young NW-SE elongate subgeotectogene. The main geotectogene in the mid-north is a half-graben bounded by northeast-striking and northwest-dipping normal faults （e.g., Liulengshan Fault）. This group of faults was mainly affected by the Pliocene （before -2.8-2.6 Ma） NW-SE extension and controlled the deposition of sediments. In contrast, the subgeotectogene in the south was affected by northwest-striking normal faults （e.g., Huliuhe Fault） that were controlled by the subsequent weak NE- SW extension in the Pleistocene. The remarkable change in the sedimentary facies and provenance since -1.8 Ma is possibly a signal of either weak or strong NE-SW extension. This result implies that the main tectonic transition ages of -2.8-2.6 Ma and -1.8 Ma in the Weihe-Shanxi Graben are affected by the Tibetan Plateau in Pliocene-Pleistocene.
LIU JinCHEN XingqiangCHI ZhenqingWANG YongMIN LongruiLI Tingdong
