摘要
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.
引文
[1]赵勇,蔡向民,王继明,等.北京平原顺义ZK12-2钻孔剖面第四纪磁性地层学研究[J].地质学报,2013,87(2):288-294.
[2]苗巧银,朱志国,陈火根,等.镇江地区长江南北两岸第四纪地层结构划分与沉积特征对比[J].华东地质,2017,38(3):175-183.
[3]蒋仁,杨祝良,于俊杰,等.长江三角洲北翼兴化—通州地区第四纪地层划分及古环境分析[J].华东地质,2014,35(4):263-269.
[4]邹亮,张志忠,韩月.长江口外海区DZS2孔第四纪磁性地层[J].海洋地质与第四纪地质,2015,35(2):43-52.
[5]王开发,张玉兰.宁波平原晚第四纪沉积的孢粉、藻类组合及其古地理[J].地理科学,1985,5(2):145-152.
[6]王宗涛.浙江北仑港地区的第四纪海相地层及其古地理意义[J].海洋地质与第四纪地质,1986,6(1):45-54.
[7]王建华,周洋,郑卓,等.杭州湾晚第四纪沉积与古环境演变[J].古地理学报,2006,8(4):551-558.
[8]刘锐,覃军干.宁绍平原末次冰盛期以来的沉积环境演化[J].海洋地质与第四纪地质,2013,33(3):37-46.
[9]骆丁,肖渊甫,叶思源,等.宁波平原晚第四纪的古气候变化[J].海洋地质与第四纪地质,2013,33(5):155-161.
[10]陈德昌,陈俊仪.浙江宁波地区第四纪磁性地层的初步研究[J].海洋地质与第四纪地质,1988,8(4):101-109.
[11]Creer K M,Readman P W,Jacobs A M.Palaeomagnetic and paleontological dating of a section at Gioia Tauro,Italy:identification of the Blake event[J].Earth and Planetary Science Letters,1980,50(1):289-300.
[12]Tric E,Laj C,Valet J P,et al.The Blake geomagnetic event:transition geometry,dynamical characteristics and geomagnetic significance[J].Earth and Planetary Science Letters,1991,102(1):1-13.
[13]Fang X M,Li J J,Voo R V D,et al.A record of the Blake event during the last interglacial paleosol in the western plateau of China[J].Earth and Planetary Science Letters,1997,146(1/2):73-82.
[14]王润华,郭坤一,于振江,等.长江三角洲地区第四纪磁性地层学研究[J].地层学杂志,2005,29(Z):612-617.
[15]黄湘通,郑洪波,杨守业,等.长江三角洲DY03孔磁性地层研究及其意义[J].海洋地质与第四纪地质,2008,28(6):87-93.
[16]Bard E,Rostek F,Ménot-Combes G.Radiocarbon calibration beyond 20 000 14 C yr B.P.by means of planktonic foraminifera of the Iberian margin[J].Quaternary Research,2004,61(2):204-214.
[17]Laj C,Kissel C,Beer J.High resolution global paleointensity stack since 75kyr(GLOPIS-75)calibrated to absolute values[J].Conference on Timescales of the Internal Geomagnetic Field,2004,145:255-265.