日照近岸海域晚更新世以来地层结构及沉积环境演化

根据在日照近岸海域施工的地质钻孔和浅地层剖面测量资料,对比南黄海已有钻孔成果,系统地开展日照近岸海域晚更新世以来地层结构特征识别和沉积环境演化重建。结果表明:日照近岸海域沉积地层中见含有有孔虫化石的第二海相层,形成年代介于34.3~41.4 cal.ka B.P.,对应MIS3的暖湿阶段,该层位可能与古三角洲有关。沉积层从上往下分别为:滨海相细砂混杂泥质沉积层(命名为DU1沉积单元);河流-河口相粉砂质黏土夹粗砂、粉砂层(DU2沉积单元);浅海相粉砂质黏土夹粗砂层(DU3沉积单元);河流-湖泊相粗砂夹黏土层(DU4沉积单元)。晚更新世以来日照东部南黄海海域主要经历了2~3次显著的海侵和海退,各区域因条件不同表现有所差异:日照近岸浅水区主要表现为两次海侵和海退,东部深水区主要表现为三次海侵和海退,由于地势高低和侵蚀破坏等原因,总体表现为从离岸深水区域向近岸浅水区域海相地层厚度逐渐减少的趋势,部分地层出现尖灭消失。

Analysis of stratigraphic configuration characteristics and sediment evolution since the Late Pleistocene in the offshore area of Rizhao

Based on the comprehensive analysis of the geological drilling and shallow stratigraphic seismic profile data obtained from the offshore area of Rizhao, the authors studied the stratigraphic characteristics identification and sedimentary evolution environment rebuilding by comparing the results of other boreholes in the Continental Shelf of South Yellow Sea. The second marine layer containing foraminiferal fossils was discovered in the seabed strata. This layer may be related to ancient deltals. The dating results of the samples collected form the second marine layer show that the ages range from 34.3 to 41.4 cal. ka B.P., which indicates that the formation of the second marine layer occurred in MIS3. The stratum in Rizhao offshore area was divided into four main sedimentary stratigraphical units (DU1, DU2, DU3, DU4 from top to bottom). DU1 sedimentary unit is a littoral facies containing fine sand mixed with argillaceous deposits; DU2 sedimentary unit is river and estuary facies of silty clay intercalated with coarse sand and fine sand layer; DU3 sedimentary unit is shallow sea layer of dark gray silty clay with coarse sand; DU4 sedimentary unit is fluvial and lacustrine facies of coarse sand with clay. Two or three marine strata are mainly developed in the eastern sea area of Rizhao, corresponding to MIS1, MIS3, or MIS5. Regional differences due to different conditions, two transgressions and regressions happened in shallow water area of Rizhao coastal, and yet three transgressions and regressions in deep water area of eastern Rizhao. Due to the height of the terrain or erosion and destruction, it shows a decreasing trend of thickness for marine strata from offshore area to near-shore area, and some strata have disappeared.