# Study on Sedimentary Evolution of the Hanjiang River Delta during the Late Quaternary
###### Abstract
The main factors affecting the evolutionary history of river deltas are sea level changes, monsoon climate and human activities in the late Quaternary [6], which makes the river delta region an excellent place to judge human activities, climate change and sea level changes. Although current research exhibits substantial differences and uncertainties, it has still received extensive attention from scholars inside and outside of China [7; 8; 9]. Since the late Quaternary river delta system has certain similarities with the evolution process of the present and future delta regions, to reduce these uncertainties, we need to better understand the evolution process of modern delta regions. There are different views on the vertical variation in Quaternary sedimentary facies in the Hanjiang Delta. [PERSON] [10] believed that the Quaternary deposits in the western Shantou-Raoping fault zone can be divided into three parts: the lower part is continental sand and gravel with clay, the middle part is marine clay and sand layer, and the upper part is continental and artificial fine and medium sand accumulation. The Quaternary to the east of the fault zone is also divided into three parts, but the lower and upper parts are marine strata and the middle is continental strata; some sections under the lower marine strata have more than ten meters of continental deposits [10]. For the Hanjiang River Delta, [PERSON] (1984) established five major sedimentary cycles according to the vertical variation in the grain size of the Quaternary sediments. Each cycle shows a sedimentary rhythm of coarse (gravel, sand) and fine (silt, clay) sediments [11]. There are currently four viewpoints on the age of the Hanjiang River Delta: Early Pleistocene, Middle Pleistocene, Early Late Pleistocene and Holocene. There is considerable controversy among these viewpoints [9; 10; 11]. We believe that the accuracy of dating needs to be further discussed due to the limitations of current dating techniques. In addition, the drilling data based on previous studies are mostly distributed in the plain area of the Hanjiang River Delta, and there is a relative lack of research on the sea area. In this research, we used geological drilling information to establish the stratigraphic structure of the sea area outside the Hanjiang Estuary. To define the stratigraphic age before the Holocene and the postglacial delta construction time, the characteristics of late Quaternary sedimentary evolution in the sea area outside the Hanjiang Estuary were analyzed by means of: sediment lithology division; AMS\({}^{14}\)C and optically stimulated luminescence dating; foraminiferal and ostracod identification; particle size testing; and clay mineral content determination. According to the analysis of strata and sedimentary environment, the period and age of late Quaternary transgression were analyzed, and the paleoenvironment and paleoclimate changes were speculated. These results were combined with the results of previous calculations of regional relative sea level height for a discussion on the characteristics of regional sea level change. Based on accurate dating data and sedimentary facies analysis results, the sedimentary evolution characteristics of the Hanjiang Delta since the late Quaternary are discussed. Importantly, the OSL age of the underlying marine strata of ZK03 borehole also confirms the high sea level phenomenon in the study area during MIS5. In addition, the rich information of sedimentary environment changes in the Hanjiang River Delta revealed in this study, such as sea level changes, can provide the possibility for extracting historical environmental change information. It also provides support for delta land use and future development planning of coastal zone.