Research On Sand Hills And Their Environmental Significance In Poyang Lake Region Since Last Glacial Period

Aeolian deposits (including aeolian sand and loess deposits) are widely distributed inPoyang Lake region in the middle reaches of the Yangtze River. Longitudinal ridge-liketopography has been formed with grooves, dish pits and other erosional landforms in the upwindand longitudinal dunes in the leeward of the sand hills. Sand Hills has attracted scholarlyattention. In earlier studies, researchers have focused on the strata of sand dune, sedimentaryfacies and the investigation and analysis of regional physiognomy, they also expound the themechanism of formation of the aeolian deposits. And then there are two opposite views“hypothesis of current origin for sand hill”and“hypothesis of eolian origin for sand hill”. Thus,this kind of sand stratigraphy was an archive recorded the past regional climate change.Thechronology and its environmental implications of these aeolian sediments have been debated fordecades.Existing studies suggest that the Poyang Lake Lake Sand Hills is the handling by the wintermonsoon in the last glacial- specific climatic conditions. The Sand Hills in Poyang Lake is theideal material for recording climate change and regional environmental evolution. Longitudinaldunes, with appreciably tilting forest and backeset beds, have clear and stable beddingaccumulates in the strong winter wind states.Here we present four sedimentarys. Section HG and Section PH are located on the secondterrace on the south bank of the Yangtze River. Section PBL is beside the Poyang Lake. SectionSM1 is located on the Centre Island of Songmen in Poyang Lake. Based on OSL chronology,sedimentology, grain size, and elementary data, we conclude:(1) The evolution of winter monsoon climate in the late Little Ice Age recorded in Botou Liprofile in Xingzi County is conducted in this research. It is strong winter monsoon climate periodfrom 1650 to 1700 years. It is weak winter monsoon climate period from 1700 to 1810 years, but there is the event of winter monsoon enhance. The winter monsoon has enhanced gradually trend.And the winter monsoon enhanced events is independent of the later cold period of little ice age.there existed obvious winter monsoon weak period.It is very strong winter monsoon periodduring 1810 to 1860. The winter monsoon presents a waning characteristics form 1860 to 1920.the winter monsoon evolution recorded by profile SM1 and the winter temperature of Hankou,Shanghai and North China were compared. and found that the evolution of winter monsoonrecorded in sand hills in Poyang Lake and the temperature of the North China and the middle andlower Yangtze has sensitive response characteristics. In our research, an enhanced monsoonevent in the late Little Ice Age was recorded. The cold event indicated an abrupt start and agradual end, which suggested an abrupt winter monsoon climate change at that time. Combinedwith existing researches, we conclude the point of abrupt change was 1815 A.D or 1816 A.D,which may be related with the eruption of volcanoes.(2) Characteristics of depositional sequence of Sand Hills in the middle reaches of theYangtze River are loess- mud- loess, sand- sandy silt- mud- sandy silt- sand since LastGlaciation. Except for the early-middle Holocene (10-5 ka), aeolian deposition was overallappeared continually throughout the last 110 ka and no significantly concentrating trend.However, sand layers clearly clustered into three periods: 60- 75 ka, 18- 24 ka and 0.1- 0.4ka.Loess deposition in the area started in the early Last Glaciation. the formation of sand hillsrevealed by age dating distinctively clusters at 0- 1.0 ka, 17- 24 ka, and 60- 75 ka, respectively,roughly synchronous responses to the great stadials of the last glaciation.. aeolian deposit isprobably derived exclusively from the floodplains of the Yangtze River and its tributaryGanjiang Rive.(3) We compiled and rebuilt the timing limits of aeolian deposits, together withδ18Orecord from GISP2 and sea level change during the last 125 ka reconstructed by Chappell andShackleton. And found that the winter wind and sea-level fluctuations have an effect upon thedevelopment of the Sand Hill. The active accumulation of sand hills on the second terrace of theYangtze River during 85-80 ka means that the channel of the Yangtze River (between Hukouand Pengze Town) shifted southward form the late Megainterstadial of last glacial period to LastGlacial Maximum. As a result, aeolian deposits in this area might provide a long termperspective on hydrographical change and paleoclimatic implications.