浙江宁波地区Z03孔第四纪磁性地层研究

Quaternary magnetostratigraphic study of the Ningbo area in Zhejiang using borehole Z03

浙江宁波地区第四纪以来沉积了较大厚度的海陆交替沉积物,对其进行划分和对比,对研究该区第四纪地层至关重要。宁波南部滨海平原Z03孔揭示该区伴随多次海侵—海退,形成数个沉积旋回,其岩性多变,沉积相复杂。文章通过对Z03孔进行磁性地层研究,结合钻孔岩性特征、光释光测年和^(14)C测年数据,建立可靠的磁性地层框架。结果显示,Z03孔所有样品均位于布容正向时内,且包含了3个全球性极性漂移事件和1个地方性亚时,自下而上分别为布莱克事件、拉尚事件、哥德堡事件以及宁波亚时;80.0~87.0 m样品记录了中更新世和晚更新世之交的布莱克事件,上更新统底界定于79.2m处;42.2~44.0m样品记录了拉尚事件;21.0~23.0m样品记录了全新世和更新世之交的哥德堡事件,全新统底界定于23.6m处。

A large amount of thick marine and continental sediments had deposited in the Ningbo area since the Quaternary,and its classification and comparison is vital to study of the Quaternary sedimentary environment.Borehole Z03 located in the southern Ningbo coastal plain reveals that the area contains several sedimentary cycles due to several transgressive-regressive activities,with variable lithologic characteristics and complicated sedimentary facies.Combined with lithological features,OSL and ^（14）C dating data of the drilling core,the study established a reliable magnetic stratigraphic framework.The results show that all the samples of borehole Z03 fall into the Brunhes normal polarity zone,and record three global magnetic excursion events and one regional event,including Blake,Laschamp and Guthenberg events from bottom to top.80.0~87.0 mdeep samples record the Blake event occurring between Middle Pleistocene and Late Pleistocene,with the bottom of upper Pleistocene defined at a depth of 79.2 m.42.2~44.0 m deep samples record the Laschamp event and 21.0~23.0 mdeep samples record the Guthenberg occurring between Pleistocene and Holocene,with the bottom of Holocene located at a depth of 23.6 m.