Sedimentary Evolution And Source Analysis In Laizhou Bay Since Late Pleistocene

Because of paleoclimate and sea level variation,the sedimentary environment of multi-source fluvial delta sedimentary system,formed along the bank of Laizhou Bay,is complex and changeable since late Pleistocene.The stratum results from multi-source sedimentary contribution.Although Yellow River is the main sedimentary source of the formation in Laizhou Bay,the contribution from small and medium-sized rivers in the southwest coast is also worth paying attention.In this thesis,on the basis fully digesting and absorbing predecessors'research achievements and collected materials,using the lithology characteristics,sediment color,grain size and structure characteristics of borehole,combined with the AMS¹⁴C dating and optically stimulated luminescence?OSL?dating data,we carry on studies on division of sedimentary units,sedimentary facies analysis and strata division and comparison,which aims to establishing sedimentary stratigraphic framework of Laizhou Bay;Besides,we focus on analyzing the geochemical element characteristics of each sedimentary unit of core 07 in estuary of Bailang River.Combined with the surface of sediments of Bailang River and the clay mineral combination features,we probes the sources of sediments extracted from core 07.Based on paleoclimate and sea level change characteristics and above research findings,we explore the sedimentary evolution of Laizhou Bay since late Pleistocene.The results show that there are difference in sedimentary characteristics and stratum structure of five sedimentary units,formed in Laizhou Bay since the late Pleistocene.The depth of stratum is relatively stable,ranging from several meters to tens of meters.The depth of formation tends to decreasing from seawards to landwards.And it develops fluvial facies,deltas or tidal flat,littoral neritic facies from southern to northern.Through the provenance analysis,it is concluded that the main provenance of borehole 07 are Bailang River and Yellow River,which play an important role in multi-source fluvial delta sedimentary system of southern coast of Laizhou Bay since Late Pleistocene.Although the sedimentary formation provenance of Laizhou Bay is mainly controlled by terrigenous clastic input of Yellow River,there also exist differences.Whereas,the Yellow River rechannelled frequently in geological history,and influenced by sea level change,river runoff and clastic input,tectonic movement,wave and tide effects,the main provenance of sedimentary strata shows characteristics of generation and segment.According to element variation characteristics in the vertical direction and clay mineral combination features,it can be divided into two glacial periods and three interglacial periods,corresponding to three transgression events and two regression events in Laizhou Bay since late Pleistocene.In 124.6⁷2.0 ka B.P.,60.0²4.4 ka B.P.and10.2⁴.0 ka B.P.,it occurred three times warm-wet periods,respectively corresponding to the Cangzhou transgression,Xianxian transgression,and Huanghua transgression;In 72.0⁶0.0 ka B.P.and 24.4¹0.2 ka B.P.,two dry and cold periods,it was continental sedimentary environment,corresponding to Wurm early glacier age and Wurm late glacial age.During transgression period,it always developed littoral-neritic facies in marine area,gradually transition to delta and fluvial facies in land field,and with sediment showing retrogradation superposition pattern.Contribution that near source rivers and distant origin Yellow River makes to strata,gradually reduces from land to sea.During regression period,it forms fluvial and delta facies in most area of Laizhou Bay.Terrigenous input of near source rivers increased,with sediment showing progradational sequences.From late Pleistocene to Holocene,this region go through sedimentary evolution of littoral neritic facies-delta-continental facies-tidal flat-littoral neritic facies-delta-continental facies.