Evolution Of Sedimentary Environment And Storm Deposition At The Lunden Bay In The Southern Nortl Sea During Holocene

The North Sea is a marginal sea between Eurasia plate and the Atlantic Ocean plate,with an area of around 5×105 km2 and its average depth less than 100 meters.There are large area of low tidal flats and marshes around it.Wadden Sea is an intertidal zone in the southeastern part of the North Sea,and it is the typical barrier-lagoon coast and the most integrated mudflat ecosystem.The Lunden Bay,an ancient barrier-lagoon,which is located near the western coast of the Jutland Peninsula along the Southern North Sea.Now the bay has become a coastal plain.Restoring the depositional environment and kowning the effects of storms about the Lunden Bay during Holocene is beneficial to research other developing barrier-lagoon in Wadden Sea.And it has a great significance for the studies of other barrier-lagoon coasts.In September 2015,we had a field survey in Lunden Bay,an ancient lagoon in the eastern suburb of Lunden Town.It is located near the western coast of the Jutland Peninsula.A non-disturbance core LN(54°19.80° N,9°03.87?E),in the length of 719 cm and the diameter of 10 cm,was obtained with the gravity core sampler from the depth of-53 cm.The coring rate is 93.9%.Based on the petrographic,the grain size,loss on ignition(LOI)and EMMA,combined with 14C dating and species of integrated bivalve in the core LN,we analyze the storms,sedimentary facies and long term evolution of Lunden Bay.The main conclusions of the analysis are as follows:(1)According to the End-Member Modeling Analysis,it is clear that the core is mainly composed of fluvial deposition(EMI),tidal deposition(EM2)and wave deposition/storm deposition(EM3).Along with the evolution of the regressive barrier-lagoon coast,the fluvial effects became stronger,and marine effects became weaker and vanish finally.The results of EMMA,sedimentary structure and dates of LOI reveal that storm deposition appeared at the depth 522?542 cm,567?577 cm,678?688 cm and 750?760 cm of the core LN.Storm deposit had the important influence on the barrier-lagoon coast in Lunden Bay.(2)The sedimentary facies of the core LN are tidal flat facies,submarine bar facies,storm facies,lagoon facies and estuarine swamps facies,which reconstructed the evolution processes of the coast along the Lunden Bay since 6050 cal.a BP.About 8000 cal.a BP,seawater entered the Wadden Sea area,and the study area developed into tidal flat with tidal current effect.Along with the sea-level rises,the shoreline reaches the moraine area in the eastern part,and the study area became fjord coast.Then submarine sand barrier was forming and developing form south to north with the work of horizontal wave and the littoral current.Controlled by the river-sea interactions,the embayment coast,submarine sand bar-lagoon,semi-enclosed barrier-lagoon and enclosed barrier-lagoon have been formed in the Lunden Bay successively.Meanwhile,the Elbe River's effect had becamed weaker,but Eider River's effect had becamed stronger.It showed the typical processes for the changes of the regressive barrier-lagoon coast.Finally,the ancient lagoon was filled and developed into coastal wetland in 5150 cal.a BP.(3)Buried peat on the top of the core LN revealed that the ancient lagoon was filled and developed into coastal wetland in 5150 cal.a BP.However,the area had appeared marshes in some existing studies in 3000 cal.a BP,the time of 5150 cal.a BP is so early.Maybe the fluvial transport affected local coast.In addition,the upper part of the core LN which lacked the nearest sediment revealed that lagoons had been filled and Eider River changed its channel,because of lacking sediment input in this area.