Sedimentary history of the western Bohai coastal plain since the late Pliocene: Implications on tectonic, climatic and sea-level changes

Thick Cenozoic deposits from the western Bohai coastal plain, a tectonic-subsiding region, provide the potential to study the relations between sedimentary environments and tectonic, climatic and sea-level changes. However, sedimentary history of this region extending to the whole Quaternary, as well as their links to tectonic, climatic and sea-level changes are still poorly understood, mainly because of the lack of long-term records with well-constrained chronology. In this study, we present an integrated record based on sedimentology and proxies (grain-size and color reflectance) of a 203.6 m core recovered from the western Bohai coastal plain near Tianjin. The core was chronologically well constrained using paleomagnetic and optically stimulated luminescence dating methods. The results show that from the late Pliocene (similar to 3.3 Ma) to the late Pleistocene (similar to 0.10 Ma), the study region was mainly dominated by fluvial setting, and the extensive incursion of sea water into this region began during the last interglacial period (similar to 0.10 Ma). The sedimentology and the color index suggest that tectonic subsidence of the Bohai Basin during the Plio-Quaternary must have played a significant role in controlling the sedimentary environments in this region. The changes in base-level because of sea-level fluctuations during the Quaternary influenced the fluvial development greatly and led to the alternations of coarse crevasse splay/channel and finer floodplain deposits in the core sequence. In addition, climatic changes since the late Pliocene also have had significant effects on the sedimentary settings in the Bohai coastal plain by influencing the fluvial process with a series of mechanisms.