福州市马尾地区第四纪地层划分及海相层分析

通过对该区钻孔剖面贡料,结合~(14)C、古地磁、孢粉及微体古生物等资料综合分析研究,对该区第四纪地层提出划分意见和自第四纪晚期以来,地层中存在着典型两期海侵所形成的海相层。     

中国北方沿海两个沉积岩芯的古地磁研究

为编制中国北方沿海地区的古地磁年表,并为该区第四纪地层的划分与对比提供年代地层上的依据,我们选择了辛集孔(沦-13)和 H-70孔沉积岩芯进行了古地磁研究。根据磁倾角的正、反向变化,绘成了古地磁极性变化(柱状)年表。辛集孔位于华北平原东部仅有的两个出露死火山(即大山和小山)之间。该孔井深600米,下部未见到基岩,全部岩芯均为松散沉积,不含玄武岩及其他喷发岩层。全岩芯共制成136块标本进行了天然剩余磁性测量。     

东海北部海域DZS1钻孔孢粉记录与古环境研究

利用在东海北部海域获取的全取芯钻孔DZS1孔202.1 m深沉积物岩芯进行孢粉分析鉴定,通过对松散地层的孢粉研究自下而上划分出了7个孢粉组合带、8个气候期,由孢粉组合带反映出的该区第四纪早更新世以来的气候冷干-温凉湿润-温暖略干-温暖湿润-温凉偏干-温和略干-寒冷干燥-转暖、温暖湿润的气候特点与区域性的气候变化特征比较符合。借助AMS14C、光释光测年和古地磁测试结果,分析了东海北部海域早更新世以来的气候、环境演化特征,进一步丰富了该海区第四纪孢粉学资料,为该海区第四纪地层划分和对比提供了证据。     

福建沿海下更新统的磁性地层学研究

通过对下更新统海湾相的“镇海组”（Q1^m？）建组剖面--福建龙海市关头剖面进行古地磁测量，配合K-Ar法测年、粒度、矿物和孢粉等分析资料，确认该剖面中部的灰绿色粘土粉砂质砂层属于早更新世，其沉积相应为冲-洪积相，仍沿用“镇海组”（Q1^al pl）之名。研究表明第四纪下界存在于该剖面的灰绿色粘土粉砂质砂层与红褐色粉砂粘土质砂层之间（即M/G面上）。这是福建首次用年代地层学手段发现的第四纪下界。     

南黄海4个沉积岩芯的热释光测年及地层划分

本文利用热释光技术对南黄海4个柱状岩芯样品进行测年,结果与其他方法所获年代相符甚好;并综合岩性、古地磁和~(14)C等资料对该海区第四纪地层进行划分。对此,初步确定其全新世地层厚度变化于十几厘米至几米之间。     

滦河三角洲地区第四纪海相地层及其古地理意义的初步研究

第四纪海相地层是第四纪地层学研究的重要内容之一,它对第四纪地层的划分和对比有重要的作用,也有助于进一步了解海面变化、海侵海退过程以及古地理环境的演变。我们在开展滦河三角洲地区第四纪地质调查研究工作中,通过对该区东麦港(乐7孔)、坨     

青海柴达木盆地西部上新世以来的地质环境与成盐期

对柴达木盆地西部大浪滩及察汗斯拉图地区的上新世晚期以来的沉积物及其孢粉化石的研究,结合古地磁、同位素年代测定,建立了九个孢粉带、九个植被演变期、三十次气候波动及三个成盐阶段。分析了本区主要成盐时期的古气候特征。 第四纪下限位于Ⅲ/Ⅱ孢粉带之间,对应于古地磁的M/G界面。中更新世底界位于Ⅵ/Ⅴ孢粉带之间,对应于古地磁的B/M界面。晚更新世底界位于Ⅷ/Ⅶ孢粉带之间,铀系测年为距今15—17万年。     

我国海洋地质与第四地质研究的新进展

80年代以来,国内外在海洋地质和第四纪地质研究方面取得了重要进展。本文着重从我国第四纪全球变化;应用第四纪地质;第四纪突变事件;海洋地质调查研究诸方面进行了概述。     

晚更新世末期地磁短期游移的研究

本文根据对胶州湾至丁字湾岸段的6个柱状岩芯古地磁标本系统测量结果,结合地层、古生物、古气候及~(14)C年代测定,确定了该区晚更新世末期哥德堡短期游移的存在。     

中太平洋柱样430的古地磁和沉积间断研究

根据中太平洋柱样430的古地磁测量结果并结合柱样的岩性、生物地层学和同位素年代学的研究资料,讨论了钻孔所在海域的沉积史。结果表明,中新世中期至上新世早期(约距今1500—340万年)和晚第四纪末(约距今4万年)以采存在明显的沉积间断。在上新世晚期末至第四纪早期(约距今240—90万年)之间的沉积物中可能存在沉积间断。上述有关时期内出现的深海底侵蚀和沉积间断与地史时期南极底层环流形成和增强有关。作者认为古地磁应作为研究太平洋沉积间断的一种重要工具。     

渭南阎村W7孔岩心样品的古地磁学研究

对渭南阎村W7孔岩心地层样品的磁性地层学研究,确定了黄土组、三门组地层的时代。这一地区的黄土/古土壤层形成始于松山反极性时晚期,约为1.1MaB.P.。按照地层样品的剩磁特征和岩性特征对黄土/古土壤层作更精细地划分,这一地区的黄土/古土壤层相当于马兰黄土、离石黄土层,缺失午城黄土。地层的剩磁极性资料表明,三门组地层形成于高斯极性时晚期—松山极性时中期,按照奥尔都维正极性亚时为第四纪下限的年代准则,确定三门组地层的时代为晚上新世。 W7孔岩心的地层样品的剩磁极性序列与已有的地磁极性年代表的磁极性序列大体相当,本项研究也揭示了二个短周期极性事件的存在,位于第5黄土层的安比拉事件(Emperor)发生的年代约为0.445—0.458Ma B.P.。位于第9黄土层的后期哈拉米洛事件(Post-Jaramillo)发生的年代约为0.77—0.81MaB.P.。 磁性地层学研究表明这一地区在松山反极性时中晚期出现过沉积间断,持续时约0.5Ma。 根据W7孔的地层学研究认为,选择以奥尔都维正极性亚时末期的年代(1.60MaB.P.)作为第四纪下限是有利于第四纪地层的划分和对比的。     

渤海湾海陆交互相沉积的磁性地层学

渤海湾的海陆交互相沉积对研究海陆环境变化、新构造活动及华北平原的演化历史等均有重要意义,而建立可靠的年代地层框架是上述研究的前提。对取自渤海湾西岸天津市深度为203.57 m的BZ2钻孔进行了详细的磁性地层学研究,结果表明,钻孔岩心包含4个正极性段,分别可与标准极性柱中布容(Brunhes)、贾拉米洛(Jaramillo)、奥尔都维(Olduvai)和高斯(Gauss)正极性世对比;获得的3个负极性段则与松山(Matuyama)和凯纳(Kaena)事件对应,从而获得钻孔岩心底部年龄约为3.18 MaBP。磁性界限之间平均沉积速率的相对一致性,指示了渤海湾在晚上新世以来总体稳定的下沉趋势。     

Magnetic polarity sequences from downhole measurements in ODP holes 998B and 1001A,leg 165, Caribbean Sea

The magnetostratigraphy of sediments drilled at two sites (998 and 1001) in the Caribbean Sea during the Ocean Drilling Program (ODP) Leg 165 is established directly from downhole measurements. For the first time in the ODP, the magnetostratigraphy of sediments is determined from both logging magnetic data and paleomagnetic analysis of core material for an age interval of about 16 m.y. across the Cretaceous/Tertiary boundary. The total magnetic induction and the susceptibility of the surrounding sediment were recorded in situ and continuously by the GHMT (Geological High-sensitivity Magnetic Tool). The aim of processing these data is to determine the magnetic polarity. At Site 998 (Cayman Rise), no paleomagnetic results are available from the recovered cores given a hard secondary overprint. Nonetheless, a magnetostratigraphic sequence from early Miocene to late Oligocene is proposed from the analysis of the GHMT data. The comparison with biostratigraphic results shows the accuracy of the resulting magnetic polarity. At Site 1001 (Hess escarpment), cores were recovered in two holes thus allowing the comparison of the magnetostratigraphic results obtained from the GHMT data and from paleomagnetic analysis of core samples over a length of 200 m representing about 16 m.y. from early Eocene to late Cretaceous times. The sedimentation rates computed from the determined magnetochrons are very similar and correspond to the ones obtained from shipboard biostratigraphic results. One of the most striking result obtained from the magnetostratigraphic results, especially the GHMT data, at Site 1001, is the abrupt decrease in the sedimentation rate across the K/T boundary. This suppressed sedimentation lasted at least 4 Ma after the K/T event.     

PALEOMAGNETIC STUDY OF Dc1 AND Dc2 CORES IN THE EAST CHINA SEA

We got two cores from 10 miles east of Zhoushan islands about 29 m in water depth in 1979 and 1980.Dc1 core, 26 m long, can be divided into two layers; 0-19.4 m, brown-yellow, silty-clay, rich in foraminifera, 19.3-26 m, grey silt. DC1 core, 91 m long, 7 miles south of DC1 core. The colour for 0-16.6 m is the same as for 0-19.4 m of Dc2 core, brown silty-clay, rich in foraminifera too. The results of paleomagnetic measurements show: there are 464 specimens in DC1 and Dc2 cores altogether; AF demagnetization often shows that 95 % of all the specimens belong to normal polarity epoch, and the others are reversal ones.We consider that more stranger intensity may represent the warming period and transgression period, and vice versa. At least DC, and Dc2 cores provide such an evidence for this. It is obvious that glacial period should be low peak period of intensity, and interglacial period should be its high peak period.     

东海DC-1, DC-2孔古地磁研究

本文报道了东海DC-1,DC-2孔古地磁研究结果,表明DC-l孔26.9m岩芯及DC-2孔61.0m岩芯段均以正极性为主,属布容正极性世 (Brunhcs)。其中DC-l孔18.86-19.18m的反向磁化带(倾角为—49.29°),经~(14)C测年为距今115lO土570a;DC-2孔29.95—30.54m处反向磁化带(倾角为—40.5°),经~(14)C测年为距今10250±lOOa。可与哥德堡事件(Gǒthcnburg)对比。对比地磁年表,DC-2孔37.80—38.0m为反极性事件与蒙哥事件(Mungo event)相当,7l.20—74.44m划为布莱克事件(B1akc event)。据此计算全新世沉积速率为2.12—2.84m/1000a,晚更新世沉积速率为O.65一O.69m/1000a。     

太平洋中部磁性地层学研究

本文通过太平洋中部５个长柱状岩心古地磁样品的测量分析，对区内早中新世以来的松散沉积层进行了磁性地层的划分对比，确定了各孔研究深度内沉积层的时代，认识到太平洋中部新世以来主要有两个沉积时期和两个沉积间断时期。第一沉积期分别到早中新世末或中中新世初停止沉积，为主沉积期，沉积了岩心的大部分。从晚上新世或第四纪初开始沉积到第四纪中晚期停止沉积的是第二沉积期，从早中新世末或中中新世初至早上新世或第四纪初为主     

Paleomagnetic results from deep-sea sediment of the Korea Deep Ocean Study (KODOS) area (northern equatorial Pacific) and their paleodepositional implications

Paleomagnetic properties of sediment cores were examined to reconstruct paleodepositional conditions in the Korea Deep Ocean Study (KODOS) area, located in the northeastern equatorial Pacific. The studied KODOS sediments have a stable remanent magnetization with both normal and reversed polarities, which are well correlated with the geomagnetic polarity timescale for the late Pliocene and Pleistocene. Average sedimentation rates are 1.56 and 0.88 mm/kiloyear for the Pleistocene and late Pliocene, respectively. Clay mineralogy and scanning electron microscope analyses of the sediments indicate that terrestrial material was transported to the deep-sea floor during these times. The variations of sedimentation rates with age may be explained by the onset of the northern hemisphere glaciation and subsequent climatic deterioration during the Pliocene and Pleistocene. For the Pleistocene, an increasing sedimentation rate implies that input of terrestrial materials was high, and also a high input of biogenic materials was detected as a result of increased primary production in the surface water. The down-core variations in paleomagnetic and rock-magnetic properties of the KODOS sediments were affected by dissolution processes in an oxic depositional regime. As shown by magnetic intensity and hysteresis parameters, the high natural remanent magnetization (NRM) stability in the upper, yellowish brown layers indicates that the magnetic carrier was in pseudo-single domain states. In the lower, dark brown sediments, only coarse magnetic grains survived dissolution and the NRM was carried by more abundant, multi-domain grains of low magnetic stability. The down-core variation of magnetic properties suggests that the KODOS sediments were subjected to dissolution processes resulting in a loss of the more stable components of the magnetic fraction with increasing core depth.     

南沙群岛海域磁性地层学初步研究

根据南沙群岛海域NS89-76,NS90-103和NS84-38柱样的古地磁研究结果,三柱样终孔深度内均属布容正极性期沉积,较完整地记录了布容期约20万年以来5个短期极性事件。结合地层、古生物资料,~(230)Th及~(14)C年代测定,推断这些极性事件可分别与哥德堡、蒙哥、拉尚、布莱克、琵琶湖C事件对比。依极性事件的年代界限推算3个柱样的底界年龄分别为15ka,202ka,191ka。并对海域大陆架、大陆坡及海盆等地貌单元晚更新世以来的沉积作用进行了初步探讨。     

Paleomagnetic records and mineral-magnetic properties of deep-sea sediments in the NW pacific: Paleoenvironmental implication

The paleomagnetic records and mineral-magnetic properties of unconsolidated core sediment from the east Mariana Basin of the western Pacific have been analyzed to trace the time-dependent variations in sedimentary environments. Progressive alternating field demagnetization effectively extracts a stable remanent magnetization showing both normal and reverse polarities. Comparison of successive polarity changes, recorded in the sediment core, with reference magnetic polarity time-scale, reveals that the recovered sediment column was deposited since the late Pliocene. From the sediment age model, calculated sedimentation rate during the late Pliocene was 9.8 times higher than that during the Pleistocene. Considering the oceanic environments and geologic setting in the study area, the anomalous high sediment flux during the late Pliocene was probably caused by enhanced current flows, such as North Equatorial Current, associated with atmospheric circulation as well as by debris flows from adjacent sea mounts. In addition, the systematic variation of mineral-magnetic properties indicates periodical fluxes of coarse and magnetically stable particles, on the fine-grained dominant sedimentary environments. Such influxes, however, would not be related to syn-volcanic activities, because the summits of seamounts were totally blanketed by biogenic Pliocene-Pleistocene sediments. It is, hence, reasonable to interpret that paleomagnetic and mineral-magnetic data probably reflect drastic paleoenvironmental changes at the boundary between the Pliocene and Pleistocene, where strong current and atmospheric circulations decreased.     

西菲律宾海盆XT06孔第四纪磁性地层与深海沉积动力过程

菲律宾海是西太平洋典型的风尘汇集区,也是南极底层水影响的远端地区.由于水深较大等原因,这一热点地区沉积物的古环境研究尚未全面展开.本文对菲律宾海中部XT06孔沉积物开展了磁性地层和粒度测试工作,分析了XT06孔沉积记录的年代学特征和沉积过程,初步探讨了区域沉积演化的控制因素与古环境意义.结果表明:(1)通过系统交变退磁...