宁波沿海平原Z02孔第四纪地层及古环境演变

宁波沿海平原第四纪沉积物属于海陆交互沉积,记录了良好的古气候变化信息,是研究古气候冷暖变化、沉积物沉积特征的良好载体。对位于宁波沿海平原东南部的Z02孔进行¹⁴C和古地磁测年,根据钻孔岩性、孢粉组合、有孔类和介形类组合、粒度等环境替代指标特征,确定了Z02孔第四纪地层划分,揭示了研究区第四纪以来的古环境演变信息。结果表明:Z02孔全新统与上更新统界线位于30.5 m,上更新统与中更新统界线位于82.65 m,第四系与下白垩统界线为90 m,中更新统沉积较少,下更新统全部缺失。Z02孔晚更新世经历水动力条件变化过程为中能-中低能-中能,沉积相为冲湖积-河漫滩-河流-湖沼-冲湖积-湖沼-河漫滩,全新世经历的水动力条件变化为中低能-低能-中能,沉积相为滨海-浅海-海沼。Z02孔记录了宁波沿海平原早中更新世处于构造抬升风化剥蚀阶段、晚更新世由温暖湿润到干燥、全新世由温湿到干凉的变化过程。该研究为我国亚热带东部沿海地区的古环境演变研究提供了有益信息。

Quaternary stratigraphy and paleoenvironmental evolution of the Ningbo Coastal Plain revealed by core Z02

The Quaternary sediment in the Ningbo Coastal Plain was the deposit due to sea-land interaction, which recorded information of past climate changes. The region is therefore an ideal area to study paleoclimate changes and sedimentary characteristics. We determined the stratigraphic division and paleoenvironmental evolution based on 14C and paleomagnetic dating, along with detailed analyses of lithology, pollen assemblage, foraminifera and ostracodes assemblage, and grain size of sediment in core Z02 located in the southeastern Ningbo Coastal Plain. The results showed that the boundary between the Holocene and Upper Pleistocene in the core Z02 record was at 30.5 m, the boundary between the Upper and Middle Pleistocene was at 82.65 m, and the boundary between the Quaternary and Lower Cretaceous was at 90 m. The Middle Pleistocene section of the core contained few sediments, while the Lower Pleistocene section was completely missed. During the late Pleistocene, the hydrodynamic conditions experienced energy levels of medium to medium low to medium, and sedimentary facies changed from alluvial lake to overbank to river to lake to alluvial lake to lake to overbank. During the Holocene, the hydrodynamic changes experienced energy levels of medium low to low to medium, and the sedimentary facies changed from shoreland to shallow sea to shoreland lake. The Ningbo Coastal Plain had experienced tectonic uplift, weathering and erosion stage in the Early and Middle Pleistocene, from warm and humid to dry in the Late Pleistocene, and from warm and humid to dry and cool in the Holocene, as revealed by the core Z02 record. This study provided useful information in investigating past environmental changes in the subtropical coastal region of eastern China.