Quaternary Strata、Sea-level Change And Neotectonism Of Suzhou And Adjacent Area

Suzhou area locates at the posterior margin of the southern flank of YangtzeRiver Delta and its tectonic position is the eastern Lower Yangtze–Qiantang Fold Beltof Yangtze Para-platform.The main geological units are NE-trending rifts and uplifts.Geomorphologically, the research area can be divided into hilly area and sedimentaryplain.Quaternary standard drilling BK2is on the transitional zone of the hilly area andsedimentary plain, BK1and SZ03is on the sedimentary plain.we conducted detailedcore description and sedimentary cycle division of the drilling cores and obtainedreliable chronological data by¹⁴C、OSL and ESR testing of the samples from thedrilling cores. Paleomagnetic measurement, pollon assemblage, micropaleontologyand grain size analysis were also carried out. We use the testing results of BK1andBK2as the main material of the thesis.Based on the sedimentary cycle division, chronological testing, paleomagneticmeasurement, pollon assemblage analysis and micropaleontology and grain sizeanalysis of the sediments from the cores and combined with regional Quaternarystrata comparison, we divided lithostratigraphy, chronostratigraphy, magneticstratigraphy and biostratigraphy of the studied cores. Using all data of the studiedcores and the previous achievements of other researchers, this paper studied theintegrated stratigraphic division of Suzhou area and the drilling section Quaternarystratigraphic correlation. All the research provides primitive data and reliable scale forgeophysical data interpretation and seismic hazard analysis.Four of the five marine transgressions occurred in the Yangtze River Delta duringthe Quaternary period strongly influenced the research area. Since Middle Pleistocene,despite of the various scales of the marine transgressions, the oceanity grainedgradually.Continuous neotectonic movement caused frequent earthquake and controlled thetopographic development of the hilly area and the sedimentary plain. The sedimentaryplain is tectonic subsidence area, subsided slowly and continuously with local relativeuplift. The hilly area and island hills are tectonic uplifting areas, uplifted slowly andcontinuously with the feature of oscillation. The scale of neotectonics of earlyPleistocene is smaller than that in Middle and Late Pleistocene.Quaternary formation perfectly recorded the climate change, sea level fluctuation and neotectonic movement. Generally, the Quaternary sedimentation of theresearch area was controlled by tectonic movement in Early Pleistocene andconstrained by climate change and sea level fluctuation in Middle and LatePleistocene. In Early Pleistocene, the research area is closed small watershed area andbegan to receive the deposits from The Yangtze River in late Early Pleistocene, sincethen, the eastern area developed as alluvial plain and delta plain. Since MiddlePleistocene， the sedimentary process of the area is a periodic cycle of“incision-filling-marine ingression-incision” which is in accordance with the land-seachange cycle of “transgression–high sea level-regression-low sea level” anddeveloped related sedimentary facies and accumulated related deposits.