Quaternary Characteristics And Lithofacies Paleogeography Of Ningbo Area In ZheJiang

Quaternary, which closely related to human, is the latest period of the earthhistory. The climate of Quaternary, especially the late Quaternary, has thecharacteristic of cold and cyclic variation, alternating glacial and interglacial greatlyaffect Earth's environment and climate.Lithofacies paleogeography is to analysissedimentary facies of the stratum which formated in certain geologic history, theninvestigate the sedimentary environmental conditions in different regions, in order toreconstruct the distribution of land and sea, natural geography and the climate feature.Therefore, external environment during Earth's history to infer the direction of futuredevelopment have a decisive reference to the survival and development of humansociety.Ningbo located in eastern Zhejiang provice, lies to the southern bank ofHangzhou bay and face East China sea. Ningbo was important port, manufacturingbase and high-tech zone. This area was in a constant process of alternating land andsea in recent 150K years. The Lithofacies paleogeographic study in this area canguide the development and planning for the eastern coastal areas.Plenty of geologic work have done before in this area, but lack of LithofaciesPaleogeographic study. Based on the "Minghechang town, Xiepu town, Cicheng town,Yinjiang town, Jiangshan town of regional geological survey of Zhejiang 1:50000"project, a large number of core have been done in Ningbo area. combined with variethof geological data has been make, we can reconstruct the environment between landand sea in late 150 thousands year.based on the 61 cores which this project made and 88 cores we collected,combined with anlysis of data included date, paleontology, paleomagnetic and ancient human culture, we set up lithostratigraphy, chronostratigraphy, biostratigraphy,magnetostratigraphy and archaeological strata. Sediment in plain is divided intoQiangang group of mid-Pleistocene, Dongpu group and Ningbo group ofupper-Pleistocene, Zhenhai group of Holocene; sediment in valley is divided intoZhijiang group of mid-Pleistocene, Lianhua group of upper-Pleistocene andYinjiangqiao group of Holocene. According to the data of lithostratigraphy andbiostratigraphy, the sedimentary facies can divided into slope facies, alluvial facies,fluvial facies, lacustrine facies, shallow marine facies and lagoonal facies, the fluvialfacies can divided into river bed subfacies, marginal bank subfacies, floodplainsubfacies and oxbow lake subfacies, the lacustrine facies can divided into shallowlake subfacies, deep lake subfacies and the lake delta subfacies.According to the multiple stratigraphy, the Quaternary sediment in Ningbo areawas deposited from mid-Pleistocene. There are 3 transgressions at least in last 150thousands years, the time is from 125KaBP to 70KaBP, from 50KaBP to 25KaBP,from 11KaBP to 6KaBP, and the transgression scale increased, the last transgressionin Holocene almost flood all the plain in Ningbo area. On the paleoclimate aspect, theclimate in mid-Pleistocene was cold and dry, there are two warm-cold cyle inlate-Pleistocene. Hard clay sediment was at the top of Pleistocene stratum, it wasdeposited in Last Glacial Maximum. The temperature in Holocene increased, a few ofclimatic fluctuations are revealed in this time.Based on the data and analysis above, this article reconstruct the sedimentaryenvironment of Ningbo area from mid-Pleistocene and draw lithofaciesPaleogeographic map in different period.