Holocene Environmental Changes Of Liao River Delta

Holocene is a relatively short geological period which began at10000a B.P. andcontinued till now and is very important to mankind’s development.The research onHolocene environmental Changes has become one of the hot problems in earthsciences.Through mechanical drilling of No.LZK03and comprehensive analysis on thedata of sedimentary facies,grain-size parameter, pollen combination, fossils and14Cdating, Holocene environmental Changes have been studied in this paper.The Holocene environmental Changes can be divided into three phases.1.The limnetic stage (10700-8000aB.P.):The beginning time of this period isearlier than the start time of Holocene and it has continued to the time while Holocenetransgression reached this region at approximate8kaB.P.. The sediments of thisperiod were buried at depth of18.10-22.70m.There were Typha and Cyperaceae inwater-covered lowlands and some herb plants composed mainly of Chenopodiaceae,Artemisia and Compositae in plain during the period.The climate was moderate andhumid.2.Transgressive period (8000-3000aB.P.): the Holocene transgression(also calledPanshan transgression in Liaodong bay) beginning at11ka B.P. reached this region atapproximate8kaB.P..With the extending of transgression toward inland, the limneticperiod ended in this area and a series of marine tidal flat deposits were formed.Thestrata were buried at depth of18.10-13.50m.The shells taken respectively at14.29mand15.80m were dated by14C method and had the ages of Cal BP3360-3070and CalBP8190-7950. The deposits were mainly silts and very fine sands and the sortingcoefficients were bad.The vegetation landscapes were grass land dashed by trees andthe climate was warm and humid.3.Salt marshes period (3000B.P.-present): About3,000years ago, the sea waterhas retreated to the position out of the hole LZK03and the salt marshe layers wereyellow brown showing oxidized environment and prolonged exposure to the surface.There were a lot of broken shells in the salt marshe layers which also contained somemuddy gravels,showing that after sea water retreating the lowland was covered once in a while by sea water which carried some broken shells into the area.The strata wereburied at depth of13.50-6.50m. The shells taken at the depth of4.60m and the peattaken at the depth of6.90m were dated by14C method and had the ages of CalBP200-190and Cal BP520-480. The deposits formed during this period were mainlysands and silts.The vegetation landscapes were needles-broadleaf mixed forests withthe Quercus as the main partner and the climate was warm and wet.