Unravelling the Sedimentary Structure of Coastal Alluvial Fan and its Origin in the Northern Haitan Island, Fujian, Using Ground Penetrating Radar

Key words: 
• ground penetrating radar (GPR) /
• alluvial fan /
• sedimentary structures /
• coastal zone /
• Haitan Island of Fujian

Abstract: Alluvial fan could provide valuable information in recording local climate change, reflecting neotectonic movement and rebuilding paleogeographic environment. Compared with inland areas, coastal zone as the interface of three layers of atmosphere, ocean and land has distinct differences in depositional environment, resulting in unique material sources and dynamic condition. Thus, alluvial fan in coastal zone may have special geological landscape process and sedimentary structure characteristics. There is a great sandy hill which covered by grayish yellow eolian sand layer in the northern Junshan along the coast of Haitan island, Fujian Province. It seems to be a big aeolian dunes, but in fact alluvial fan shape. In this paper, we used the ground penetrating radar (GPR) to detect the internal sedimentary structure of the great sandy hill, and tried to find out its origin. Detection results show that in the middle-upper part of the great sandy hill, there developed sedimentary cycle composed of angular gravel or coarse to fine sand and groove depositional structure, which presents the depositional characteristics of traditional alluvial fan; in the middle-lower part of the great sandy hill, there developed curved depositional structure presented alternately in the layer. Based on the results, we also found that detecting depth of the alluvial fan record the wide range of three to five times of piedmont ancient flood sedimentary history. Combining the geological investigation in the great sandy hill, we assumed that the great sandy hill is the remnant of alluvial fan, which contains the characteristics of aeolian sediments along the coastal zone. The research is benefit for further understanding of the evolution of paleogeographic environment in the coastal zone of South China, and enriching the research of dynamic geomorphological processes on coastal zone and the sedimental structures of alluvial fan.