Quaternary Sedimentary Sequences And Their Environmental Significance In Harbin Area

Research area in southeast Songnen plains, belongs to the southeast uplift area ofSongliao zone of subsidence. The uplift area approaches to Jilin province in the south,is adjacent to the east up-warping zone in the east. The development of the40-100mthick quaternary sediments, are all in fluvial predominate. Quaternary gravel detritaldeposit is widely distributed except in some local thin uplift top.Combining with the field survey data, in the use of petrology, isotope chronologytheories and methods, through the¹⁴C, thermoluminescence, and electron spinresonance and dating research, first determine the early pleistocene formation age, andspecify the quaternary strata and quaternary sedimentary lower limit. Boundary layer ofquaternary system and cretaceous system in the working area, is the the unconformitysurface between lynx group （Qp¹s） and cretaceous Nenjiang group （k₂n）. Quaternarysedimentary floor age is a real line, rather than abstract theory boundary, the earlypleistocene lynx group floor age is the lowest quaternary sedimentary age, so thatdetermined the Harbin area quaternary sedimentary lower limit for about130×10⁴a.According to the sporopollen analysis results, combining with electron spinresonance, thermoluminescence dating data, comparing sporopollen assemblage,ancient vegetation, paleoclimate at different stage of quaternary in the working area, insummary, the area can be divided11ancient vegetation, ancient climate regions,19sub-regions. Since the pleistocene, because of the changes in temperature, dry and wetchange caused by the global climate decline and ice age, interglacial period, the areaexperienced sparse scrub^steppe^meadow-needle broad mixed forest^grassland-desertification^steppe-steppe-grassy scrub^steppe-needle broad mixed forest^grassland vegetation process. The corresponding ancient climate change by cool andwet-warm and wet-cool and dry–warm and dry-warm and wet-slants cool drydevelopment process. Through the quartz sand electron microscope scanning, comprehensiveconsideration of the sediment grain size, sporopollen assemblage and animal and plantfossils characteristics, points out sedimentary facies, sedimentary environment of eachsedimentary formation, combined with the crustal movement since the early age of thequaternary, inverses the quaternary drainage rise and fall, the prosperity and death ofthe great lakes.Finally integrates ancient vegetation, ancient climate development, the rise andfall of the ancient water system and the ancient lakes, restored ancient geography,climate, vegetation, rivers and lakes landscape since quaternary period,comprehensively introduces paleoenvironment evolution process since the quaternary.