Sedimentary Response Research Of Major Climate Transition Events Since Pliocene,Changjiang Delta

The geological environment is relatively fragile,in Changjiang delta.The pore water in loose layer was abundant,and the soft soil layers are widely distributed.To fully understand the geological conditions,we can't separate from the east China,and even global climate evolution since the Cenozoic framework.Since the Pliocene,the present Changjiang estuary has gradually formed a loose deposit of nearly 500 m,and the sedimentary environment evolution is not accidental,but an inevitable phenomenon caused by the climate and other factors.However,due to the influence of many factors,the global climate change research is relatively weak and controversial.Therefore,the paper makes a comprehensive research on paleoclimate evolution of sedimentary,aiming at the LZK1 hole of alluvium 395.4 m in Hengsha island.This paper focus on the introduction of linear and nonlinear mathematical methods,such as particle size-standard deviation,end members simulation,orbital tuning,digital filtering,R/S analysis,power spectrum and wavelet analysis,and so on.Try to establish the astronomical timescale,make a comprehensively comparison with the sedimentary records of climatic events,carry out the study on the climate cycle change and the relationship between sedimentary environment and climate.The results show that the methods are effective in the area with temporary depositional hiatus and can obtain more effective results.The main results of this research includ the followings:1.The sedimentary circle is obvious,sediment types are complicated,sedimentary environment and deposition rate is changeable.The study section can be divided into 213 small layers and 15 big layers.The sediment types include clayey silt,sandy silt,silty sand,clay silt sand,fine sand,medium sand,coarse sand,sandy gravel,muddy sandy gravel,etc.The sedimentary environments include alluvial fan,braided river,meandering river,lake,estuary,shallow sea,delta,etc.Since late Pleistocene,The deposition rate is higher than before.During Holocene,it reached the maximum,the average was 4.1~8.5 m/ka.Before the late Pleistocene,the average sedimentation rate is similar.During 1076~1787 ka and 5232~6033 ka,the deposition rate is lowest,about 0.011 m/ka.2.The correlation between the mass susceptibility,the frequency magnetic susceptibility and the grain size is different.Frequency magnetic susceptibility has specific climate indicator.There is a negative correlation between the mass susceptibility and the frequency susceptibility,but no significant correlations between them in some segments.The magnetic susceptibility and the frequency magnetic susceptibility changed abruptly at the depth of 13~15 m,80~90 m,220~230 m,290~295 m.Meanwhile,at the depth of the first three,the average particle size,clay content,silt content and sand content are aslo changed.The mass susceptibility is controlled by grain size,with 250 ?m grain size is positively correlated.The frequency magnetic susceptibility controlled by grain size is not obvious,but a moderate correlation in some segments.The climatic implications of susceptibility is uncertain,indicating dry and cold climate or a warm and wet climate,while the frequency magnetic susceptibility is distinct,high value indicates warm and wet climate,low value indicates cold and dry climate.3.This paper established a time scale since 6.3 Ma and recognized 16 polarity drift or subchron events.In the continuous subsidence area with short time deposition,a reliable framework can be established by means of the orbital tuning method.The bottom boundary of Holocene,upper Pleistocene,middle Pleistocene Quaternary is about at 41.6 m,107.1 m,143 m,219 m,respectively.Gi/Ga bondary is about 296.6 m,The Gilbert negative polarity extends 369.6 m.Polarity drift or subchron events include The Holocene I,Holocene II,Mono lake,Laschamp,Blake,M/B Precursor,Kamicatsura,Santa Rosa,Jaramillo-cobb mountain,Olduvai,Feni-Reunion,Keana,Mammoth,sidufjall,Thvera.The tuned frequency dependent susceptibility record is correlated with ETP curves enormously in orbital periods which the confidence interval exceeds 95%.The band-pass filtering curves of 100 ka,41ka,23 ka circles coincide with the corresponding orbital parameter curve in phase and amplitude in total,while existing some inconformities at certain times.The inconformities may be caused by low sedimentary rate or abrupt change of sedimentary rate.4.The sensitive particle size and end members are etracted by analysis of size-standard deviation and end members simulation.Two grouped end members are constructed as the indicator for summer monsoon and winter monsoon,respectivly.In the analysis of size-standard deviation,the sensitive grain size differences are bigger between the whole section and segmented calculation,but in the analysis of end members simulation,the results is similar by whole section and segments.This paper draw a clusion that EM1(2.7~3.9 ?m),EM2(10.8~14.3 ?m),EM3(33.1~36.2 ?m),EM4(76.7~83.9 ?m)end members can indicate climate change direcly or indirecly,and construct two grouped end members of EM1+EM2,EM3+EM4,which were thought as summer monsoon and winter monsoon indicators respectively.5.The H value of EM1+EM2,average particle size,magnetic susceptibility,frequency susceptibility and EM3+EM4 are very close to the modern climate index in the region,so they can be used as to indicate the change of climate.R/S analysis showed that the H value of the EM1+EM2,average particle size,magnetic susceptibility,frequency dependent susceptibility values are relatively close,and close to 1.which are closely related with the intensity of summer monsoon.The H value of EM3+EM4 has big differences with others,which is closely related with the intensity of the winter monsoon.6.All kinds of climate proxy indicators are comparable,and the climate change time of 5.2 Ma,3.5 Ma,2.7 Ma,2.2 Ma,1.5 Ma,1.1 Ma,0.5 Ma,and so on,are consistent with the results of the research on the regional and global scale.During 6.3~5.2 Ma,the climate is mainly warm and humid,and the winter and summer monsoon are strong,but gradually decreased.During 5.2~3.5 Ma,the climate is still warm and humid.At about 4.7 Ma,4.2 Ma,the summer monsoon appears the process of weakening-enhancement-weakening,while the winter monsoon is relatively stable,only slightly weakened after 4.1 Ma.During 3.5~2.7 Ma,the climate gets cooler,dryer,the summer monsoon fluctuates increasely compared with the previous climate.When the summer monsoon slightly increases,the winter monsoon is rapidly increasing and plays the leading role,but near 3.0~3.1 Ma,the winter and summer monsoon occurred large amplitude fluctuations.About 2.7~2.2 Ma,the weather is getting warmer than the previous stage,with the winter and summer monsoon strengthen significantly meanwhile,but the winter monsoon is dominant,the climate is dry.About 2.2~1.5 Ma,the climate is warmer,but increases volatility.Summer monsoon remains stable and slightly enhances.The winter monsoon significantly weakens.The both have a negative correlation.About 1.5~1.1 Ma,the climate is cool dry compared with the previous stage.With 1.2~1.3 Ma as the boundary,the summer monsoon is from volatility to gradually weakens,meanwhile,the winter wind begins to increase.But the summer monsoon is dominant.About 1.1~0.6 Ma,the climate is warm and wet and dry alternate is further increased.The winter monsoon continues to fluctuate,the summer monsoon continues to weaken,both continue to show the anti related.About 0.6~0.2 Ma,the climate is warm and wet,cold and dry for alternating volatility,but overall it is warm and wet.On the whole,the summer monsoon becomes weak,the winter monsoon is enhanced,both of them are inverse.From 0.2 Ma,the warm wet,cold dry climate is alternating volatility.The winter and summer monsoons appear an inverse relationship,but on the whole,the summer monsoon weakens,and the winter monsoon strengthens.The climate is warm and wet in MIS5.There are three stages(MIS5e,MIS5 d and MIS5c).The climate got colder in MIS4.At MIS3,the temperature is slightly warmer.The summer monsoon intensity keep stable,comparing with the MIS4,but fluctuates significantly.The climate gets warmer at this stage,which may be related with the winter monsoon relatively decreased.The last deglaciation period begins with 18 ka.The climate gets warmer rapidly at around 14 ka,which may indicate B/A warm period start.The Holocene climate is divided three characteristics.The summer monsoon dominates at about 11~5.5 ka.At about 5.5~2.0 ka,the climate gets dry obviously.From about 2.0 ka,it appears to be a cooling and colding process.7.The preliminary climatic cycles analysis indicats that the climatic cycles recorded by different indices are different,but all with intense precession,semi precession cycles.The circle values fluctuate rapidly.A preliminary spectrum analysis of the frequency susceptibility,particle size of EM1+EM2 end member,Rb/Sr shows the cliamte circle is dominated by approximate long eccentricity(330 ka),approximate 200 ka circle(166~250ka),approximate short eccentricity(72~125 ka)?approximate obliquity(38~50 ka and 26~33 ka)?approximate precession(16~23 ka)and semi precession(10~13 ka),and so on.In addition to a long cycle,the other cycles fluctuate largely,especially the precession cycle,which may be affected by the deposition rate or short time scale of erosion.There are eccentricity and slope cycle development differences in around 600 ka and 1100 ka,which may be the Middle Pleistocene climatic revolution records.8.The sedimentary environment is closely related to the climate change.During MIS5,MIS3,MIS1,three transgression events controlled by climate have been recorded since the last interglacial period.Some short time scales of erosion in the climate transition period is recorded.