Sedimentary Record Of Chenghu Lake In Suzhou In Holocene

Holocene is a geology historical period since about 10,000a BP which has been closely influencing Mankind's Existence and Development.Study on Holocene environment changes and forecasting its trend in the future has great practical value and significance in theory.Palynology plays a important role and makes,great contributions in Holocene research by providing numerous evidences,since spore and pollen could be conserved as fossil.In 2003 the north part of Chenghu lake was enclosed to pump water out for the hard clay on bottom of the lake.Then the hard clay was extracted for building the expressway from Suzhou to Shanghai Hongqiao airport.This project offered oppommity and convenience for our field research on this area.This thesis based on the data of sediments and pollen,combining with abundant relevant documents in this region.Through the analysis of palaeo-geography, palaeo-sedimentology.Archeology and History,this thesis tries to reconstruct the sequence of fossil pollen-pollen and vegetation-paleoclimate during the prehistoric period for analyzing the environment changes,regional factors,the space-time distributed law on archaeological site,as well as the respond of human being.According to the data of granularity,pollen and charcoal of core SC1 in paleo -channel located in Chenghu lake,and abundant document in Taihu lake,it comes to 4 main conclusion as follows,First,Size analysis showed that the region's sedimentary environment can be roughly divided into five phases,below 4.4m,the main components are off-white silty sand and sand with coarse particle size and double curve,the poorly sorted,positive skewed,saltating group is divided into more than 40 percent,among many layers, environmental hydrodynamics deposition,for the shallow riverbed of the river and deposition;4.4-3.6m black grey clay of silt,clay and sand quality powder Sandy clay powder,coarse grain size,with fine bedding and dot-fine sand,separating the upper variable than good,with an average particle size decreases,partial reduction of the nearly normal distribution,rivers and lakes for the transition phase deposition; Lithology mainly black grey clay smaller size,frequency showed a total of two-step, jump to the main component-based,all-election is in the best-of,on behalf of lake sediment components increased(to clay Sandwich Increased thickening as the hallmark),the reduction under the sedimentary formation.Frequency of major components to jump mainly sediment significantly enhance color,the smallest lithology,lakes Sham deposition;2.9-0.6m dark grey transition to the clay,which mixture of fresh plant roots and iron tuberculosis,for the past An environment of the shallow lakes in shallow water deposition;Chenghu Lake SC1 experienced mainly 5 phases:fluviatile facies deposition→shallow fluviatile deposition→transition facies deposition→deep lacustrine facies deposition→shallow lacustrine facies deposition→Lake margin deposition.Second,According to the pollen map of the data analysis,we found that this area of the most warm and humid period was 7000-6000 aBP;in 6000-5000 aBP when the temperature fluctuation Obviously,there were three cool d incidents.5000-3000a BP is relatively warm and humid,but compared to 7000-6000 a BP's also a chip.3000a BP since the Holocene is the most cool of the period under woody pollen at the same time restore the climate change curve,it was obvious that the Holocene warm period of the existence of these documents and many of the region on the same results.Third,According sensitive to temperature changes in the broad-leaved species (such as Cyclobalanopsis,Castanea)and the main broad-leaved deciduous(such as Quercus)and needles(Pinus)and with woody plants and herbs to determine the percentage of relations between the temperature Changes in circumstances and in accordance with aquatic plants pollen(such as Typha,Cyperaceae)to subcontractors of the water area and precipitation changes,found in the region since the Holocene some cool events,which are about 7000 a BP.Majiabang culture Before the beginning of the cooling of the incident,5600 a.BP Songze period,the medium-term,5300 a. BP's Songze period,the cooling medium-term cultural events,5100 a BP Song-taek, the end of the cooling events,2300 a BP after the end of the warm period of cooling, these are other Regional relevant evidence,but for the famous 4000 aBP the end of the Liangzhu culture cool down the incident but performance was not obvious. Vertical,the pollen record of the core SC1 Songze period,cultural events during the cool down the recovery of the best,with the deposition rate may be related.Forth,according to the charcoal and herbs concentration of pollen found in the concentration of two percentage changes in the plan is the same as the trend reflects a natural fire and the relationship between climate,warm period,charcoal,pollen deposition rate and the total pollen deposition rate of herbal Increased,while the opposite cold period.Holocene fire events,a total of five events,namely the 6500 aBP around,5600 aBP around,5200 a BP,3100a BP and around 2300 a BP around, after four events with the relevant regional cooling.