Quaternary Strata And Paleoenvironmental Evolution In Coastal Plain Of Wenzhou

Based on the study of Global Change,Earth System Science has become a new research hotspot.As an important interface between the Land System and the Ocean System,the study on the evolution of the paleoenvironment in the coastal plain has a pivotal academic status.Since the Quaternary period,because of the influenced by climate and sea level changes,there are alternating changes of cold and warm which lead to geological events such as Transgression and Regression.The strong interaction between sea and land resulted in the development of extremely complex sedimentary strata in the study area,which included many records of climate change,sedimentary environment evolution and Transgressive history.Therefore,under the strategic background of Marine Economic Construction,Wenzhou city,as the link between the Yangtze river delta Economic Zone and the West-Straits Economic Zone,is also the weak area in Zhejiang coastal of Quaternary studies.It is of great academic value and practical significance to study the Quaternary environmental evolution history of this region in order to explore the temporal and spatial changes of human activities.The Quaternary geological boreholes QTZ1 and QTZ3 in the coastal plain to the north and south of the Oujiang estuary in Wenzhou city,Zhejiang province were selected in this paper.On the basis of stratigraphic classification,through pollen and microfossil,special algae and sediment grain size substitute indexes such as the environment,reconstruction of the coastal plain in Wenzhou region since the Quaternary environmental evolution history,and thoroughly discusses the ancient vegetation succession in the study area-the relationship of the ancient climate change,Marine strata characteristics and its environmental significance.The research results are as follows:(1)In Quaternary stratigraphic division.The results indicated by rock stratum,magnetic stratum,climatic stratum and special algal transgression stratum are basically consistent.Based on the regional comparison and comprehensive analysis,it is considered that the geological age reflected by the stratigraphic results in this paper is reasonable under the background of multiple stratigraphic division theory.It can be pointed out that for QTZ1 boreholes,the Q_h/Q_p~3 boundary is located at 37.90 m;The Q_p~3/Q_p~2 boundary is located at 94.90 m.And forQTZ3 boreholes,the Q_h/Q_p~3 boundary is located at 35.20 m;The Q_p~3/Q_p~2 boundary is located at 110.30 m.(2)In Vegetation succession and climate change.Since the Quaternary period,vegetation succession and climate change in the coastal plain of Wenzhou have experienced five major evolutionary stages(The early Pleistocene strata were missing,which is why the evolution history of climate and vegetation during this period could not be reconstructed):The climate of the middle Pleistocene was moderate,coniferous trees dominated by pinus were flourishing in the western mountainous and hilly regions,deciduous broad-leaved forest was developed in the coastal plain,and wetland and grassland environment were developed on both sides of the coast and river;In the early stage of the late Pleistocene,it is a warmer climate,affected by invasion or flooding,wetland lacustrine environment is widely developed in coastal plain and woody woodland disappears;In the middle of the late Pleistocene,the seawater retreated and the typical broad-leaved forest and grassland landscape appeared;Since the Last Glacial Maximum,the relatively cold climate conditions have led to the decline of temperate forests in coastal plains,and steppe-wetland-marsh has become the main environment;In the Holocene,when the climate became warmer,coniferous forests retreated to alpine areas,and several deciduous tree species and herbaceous communities appeared in coastal plains.(3)Marine stratigraphic features.The QTZ1borehole can identified two sets of Marine units,which can be divided into three Marine layers;And the QTZ3 borehole can identified one set of Marine units,which can be divided into two Marine layers.The Marine sedimentary records of late Pleistocene and Holocene in Wenzhou coastal plain are good.The results of foraminifera and ostracoda identification showed that from theLast Glacial Maximum to the present,the study area changed from the littoral-shallow sea environment to the shallow sea sedimentary environment.The Marine stratigraphic characteristics of hole 89 m in QTZ1 borehole indicate that the coastal area of Wenzhou had a Transgressive history in the early late Pleistocene and developed a shallow sea shelf environment.The lack of microfossils in other periods,combined with the special algae distribution characteristics,can be inferred as continental sedimentation.(4)The paleomagnetic polarity sequence in the study area in Wenzhou shows that intermittent polarity reversal events are common in the middle and upper part of the Holocene,which is not corresponding to any known global polarity events,but can have a good correspondence with the"Ningbo polarity subchron"found by predecessors in Ningbo area of Zhejiang Province.Whether this polar event is common in the east coast of China remains to be systematically studied.Based on the theory of multiple stratigraphic division,this paper makes a comparative analysis of Quaternary strata along the coast of Wenzhou with a variety of stratigraphic means,and takes this as a time scale to qualisatively describe the environmental evolution process of the coastal plain of Wenzhou,and at the same time provides a comparative basis for the possible"Ningbo polarity subchron"in the East coast of China.The research results can first provide basic data for the comparison of regional environmental evolution,enrich the paleoenvironment research in coastal areas of Zhejiang province,and make the paleoenvironment evolution results of Wenzhou play a role in the face to Ocean Earth System science research.Secondly,the possible research value is to make demand guidance for the development of Marine economic construction in coastal areas such as reclamation and development of underground space,predict the changes of human habitat in the future,and put forward reasonable development Suggestions.