CAJ | 학술논문

通过对永定河冲洪积物的研究发现,永定河形成前后的沉积环境明显不同.钻探资料表明永定河形成前本地区沉积环境主要为湖泊相,当时湖水宁静,沉积物主要为泥岩和粉砂.永定河形成时洪水裹携大量碎屑形成巨厚的泥石流堆积,沉积环境为冲洪积相,主要为砂砾石、砂、粉砂和粘土互层,形成巨大的冲洪积扇.通过新5孔钻孔岩芯273块古地磁样品的系统剩磁测试,获得了该钻孔岩芯的古地磁极性序列,对比国际地磁极性年表,认为该钻孔岩芯剖面0～96.59m以正极性带为主,对应布容正极性时,其地质时代为0～0.78Ma;96.59～246.79m则以反极性带为主,对应松山反极性时,其地质时代为0.78～2.58Ma;246.79～413.64m以正极性带为主,则对应高斯正极性时,其地质时代为2.58～3.58Ma,属于新近纪上新世.研究推测永定河最早的沉积物为上新世形成,距今3.33～3.58Ma.
통과대영정하충홍적물적연구발현,영정하형성전후적침적배경명현불동.찬탐자료표명영정하형성전본지구침적배경주요위호박상,당시호수저정,침적물주요위니암화분사.영정하형성시홍수과휴대량쇄설형성거후적니석류퇴적,침적배경위충홍적상,주요위사력석、사、분사화점토호층,형성거대적충홍적선.통과신5공찬공암심273괴고지자양품적계통잉자측시,획득료해찬공암심적고지자겁성서렬,대비국제지자겁성년표,인위해찬공암심부면0～96.59m이정겁성대위주,대응포용정겁성시,기지질시대위0～0.78Ma;96.59～246.79m칙이반겁성대위주,대응송산반겁성시,기지질시대위0.78～2.58Ma;246.79～413.64m이정겁성대위주,칙대응고사정겁성시,기지질시대위2.58～3.58Ma,속우신근기상신세.연구추측영정하최조적침적물위상신세형성,거금3.33～3.58Ma.
As the most important river in Beijing City,the Yongdinghe river carried much alluvium and proluvium and shaped the Beijing Plain.Lots of borehole data show that the sedimentary environment was obviously different before and after the formation of the Yongdinghe River.Before its formation,the lake facies dominated this region,depositing mudstone and siltstone.After its formation,the alluvial and pluvial facies dominated this region,forming vast alluvial and pluvial fans consisting of interbedded gravel,sand,silt,and clay.This paper provided a detailed magnetostratigraphic record based on 273 samples from New Borehole 5 in the Beijing plain area.Stepwise alternating field(AF) demagnetization is used to isolate the magnetic component in these samples.The pattern of magnetic polarity sequence given by the record is well matched with the geomagnetic polarity timescale.0～96.59m.The rock core of depth 0～96.59m is mainly of normal polarity,corresponding to the Brunhes chrons with an age of 0 to 0.78Ma.The rock core of depth 96.59～246.79m is mainly of reversed polarity,corresponding to the Matuyama chrons,with an age of 0.78Ma to 2.58Ma.The rock core of depth 246.79～413.64m is mainly of normal polarity,corresponding to the Gilbert chrons,with an age of 2.58Ma to 3.58Ma.The gompholite at the bottom of the borehole should be the oldest sediment by the Yongdinghe River,so it should he formed about 3.00MaB.P.,that is,in the Pliocene Epoch.