Quaternary Sediments and Paleoenvironmental Evolution in Suqian Region

Abstract

Based on the BK2 hole of Suqian active fault detection and seismic hazard assessment project, The Quaternary comprehensive geological profile of Suqian area is analyzed and presented by the methods of lithology description, lithofacies classification, stratigraphy dating, grain size analysis and palaeospheric sporopollen sample analysis, the Quaternary Sediments and Paleoenvironmental Evolution in Suqian area are discussed. The main achievements and understandings obtained are as follows: 1. Through the grain size test and analysis, we can conclude the changes of sedimentary motivation and sedimentary environment: the sections generally experienced Qp1-2 (alluvial-diluvial of medium and high energy) → Qp2-1 zone (high-energy alluvial-diluvial) → Qp2-2 zone (middle-high energy alluvial-diluvial) → Qp2-3 zone (middle-low energy alluvial-diluvial) → Qp3-1 zone (Alluvial-diluvials→ Qp3-2 (middle and high energy alluvial-diluvials) →Qh-1 (low-lying lacustrine sediments) →Qh-2(Middle and low energy fluvial deposit) .2. According to the sporopollen map, the sporopollen assemblage of BK2 borehole since Quaternary in Suqian area was divided into 9 sporopollen assemblage zones. Based on the sporopollen assemblage, lithology and dating data, the sporopollen assemblage zone I, II represents the last interglacial age and the last glacial age respectively; The sporopollen assemblage zones III, IV and V represent warm and dry in the early postglacial stage, warm and humid in the middle, and warm and wet in the late stage, respectively.3, Palynological assemblages reflect the vegetation types and climate evolution during Quaternary period in Suqian city, BK2 hole of 9 Palynologicalassemblages corresponding to the type of vegetation and climate types: the early Pleistocene (coniferous and broad-leaved mixed forest, warm and humid), the earlier of mid-Pleistocene (coniferous-steppe, cold-dry), the mid of mid-Pleistocene (coniferous-broad-leaved mixed forest, warm and humid), the later of Middle Pleistocene (coniferous forest-steppe, warm and dry), the earlier of Late Pleistocene (coniferous and mixed forest, warm and humid), the later of Late Pleistocene (coniferous and mixed forest-grassland, cool and wet.) the early Holocene (spare deciduous broad-leaved forest-grassland, cool and dry) the mid-Holocene (spare deciduous broad-leaved forest-grassland, warm and moist, coniferous and broad-leaved mixed grassland,) the late Holocene (spare deciduous broad-leaved forest - grassland, warm and humid).