Mid-Late Holocene sedimentary evolution process in the Qilihai area, northern Luanhe Estuary

The Holocene evolution process of the Qilihai area in the northern part of the Luanhe Estuary is the basis for division of the Luanhe River Delta.It is also a useful addition to understanding the interaction between land and sea.Detailed sedimentology, microfossils (foraminifera and ostracods), of six boreholes in the study area were analyzed, combined with 14C dating, to reveal the Late Holocene sedimentary environment evolution.In the Qilihai area, the lacustrine delta-alluvial fan was developed in the Mid-Late Holocene.The barrier-lagoon geomorphology depositional system and Marine delta were developed in the Late Holocene.The barrier-lagoon geomorphology depositional system was developed in present. 6~5 ka B.P., the alluvial fan and the lacustrine delta developed in the west, and the lacustrine delta front was developed in the east. 5~1 ka B.P., the first barrier-lagoon geomorphology depositional system was developed to form lagoon in the southern and sand barrier in the outside of the present coastline. From 19th century to 10th century, delta depositional system comprised of lagoon, supratidal zone and branch channel was formed as flooding of the Luanhe River.In 19th century, with the migration of first barrier-lagoon geomorphology depositional system landward to the Feicui Island, a shallow lake was developed in the Qilihai area.In 1883, a crevasse was developed in coastal sand dunes as the action of Luanhe River floods, and then the Qilihai lagoon was formed as the seawater flowing backward, which resulted in the formation of the current barrier-lagoon geomorphology depositional system.In 1915, the Luanhe River burst through the sand dunes south of the Emerald Island into the sea, forming the current delta.