Palynological Characters of Late Quaternary in the South Flank of the Oujiang River Delta and Their Paleoclimate Implications

详细信息   

• 责任者：Zhang Mengying (State Key Laboratory of Marine Geology ; Tongji University ; Shanghai 200092 ; China) ; Fan Daidu
• 刊名：Quaternary Sciences
• 出版年：2012
• 卷期：32(6)
• 关键词：晚第四纪 ; Late Quaternary ; 孢粉组合 ; palynological assemblage ; 古气候 ; paleoclimate ; 浙江 ; Zhejiang Province
• 页码：p.1234-1247
• 图表：6 illus., 2 tables, 68 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

摘要

Borehole YQ0902（27°55＇N, 120°51＇E） was drilled from the southern coastal plain of Oujiang River delta,with a total length of 41.9m.Sediment cores were split and described in detail,including color,sedimentary texture and structure,and stratigraphical boundaries before sampling.Fourteen AMS14C dating samples were collected and sent to Beta Analytic Company for dating.Forty-five samples were collected with roughly 1-m sampling interval for palynological studies.

    

Facies analysis together with AMS 14C age data showed that the lower section of the core was deposited during MIS 3 in a fluvial-lacustrine environment,topped by the paleosol formed during the MIS 2 low sea-level stage.A complete transgressive-regressive succession of 29m thick overlying the paleosol,was presumed to deposit after 10cal.kaB.P. when the transgression reached the area.Pollen-spore analysis suggested that the Late Quaternary paleoenvironmental evolution can be divided into eight stages.1）Between 50cal.kaB.P. and 35cal.kaB.P., the climate was cool and dry,and the sea-level was at least 40m lower than the present.2）During the period of 35～25cal.kaB.P.,it was a warm and humid interval.3）From the beginning of MIS 2 to 10.0cal.kaB.P.,the climate changed into cold and dry,and the study area was exposed to undergo long-term pedogenesis before terminated by the last deglacial transgression.4）In the interval of 10.0～9.0cal.kaB.P.,the climate was still cool and dry but the area was flooded by the transgression to deposit an intertidal-flat succession.5）The period of 9.0cal.kaB.P. to 6.5cal.kaB.P. was warm and wet,corresponding to the mid-Holocene Climatic Optimum,and the sea-level gradually reached its highest position（close to or a little higher than the present）,resulting in maximum transgression to deposit neritic facies in the study area.6）During 6.5cal.kaB.P. to 4.8cal.kaB.P.,the climate became cool and dry after termination of the mid-Holocene Climatic Optimum,and a shoaling-upward succession was initiated after the delta development and the consequent shoreline progradation.7）After 4.8cal.kaB.P.,the climate became warm and wet again.8）But it turned into cool,similar to the present climate,from 1.8cal.kaB.P. on,and the depositional environment changed from the open-coast intertidal flat into the barred lagoon setting,finally silted to become dry land.

    

Palynological data demonstrated the timing of weakening precipitation ca.6.5cal.kaB.P.,falling within the time intervals recorded by the two（Sanbao and Dongge）cave-stagmalite stable oxygen isotopes in the region.The finding iterated the viewpoint that the decrease in precipitation by the weakening East Asian summer monsoon during the Holocene commenced earlier in the lower latitude.Additionally,two centennial-scale cooling events were identified during 6.9～7.3cal.kaB.P. and 5.0～5.5cal.kaB.P.,corresponding well with the two widely-recognized global cooling events.It is therefore indicated that the Late-Quaternary strata in the study area are highly potential to decode high-resolution Late Quaternary climate change.