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1.
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. 相似文献
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3.
Rock magnetic properties of unconsolidated sediments from the Korea Deep Ocean Study area of the northeastern equatorial Pacific were analyzed to trace the time-dependent variations of sedimentary environments. For upper Pleistocene sediments, light-brown sediments predominate, whereas the lower sediments deposited in the late Pliocene are dark brown. Rock magnetic properties also clearly differ among the two distinct color environments. Values of anhysteretic remanent magnetization and low-field magnetic susceptibility are highly responsive to changes in the color of the sediment. For example, comparatively low values denote a dominance of coarse-grained magnetic minerals as observed in the lower dark-brown layers. With respect to the content of magnetic minerals, coarse magnetic grains are highly concentrated in the darker-colored sediment layers. However, both the magnetic mineral dependent parameter (S ratio) and results of the scanning electron microscope observation indicate that magnetic mineral changes did not occur along the core depth, which means that there was no apparent source change. Without distinctive source changes, the variations in the rock magnetic properties likely reflect a process by which the magnetic grains were primarily transported by enhanced wind and bottom currents and affected by diagenetic dissolution as a function of both the time from burial and the extremely low sedimentation rates after deposition. 相似文献
4.
Sedimentological and faunal records from the transitional period marking the onset of widespread northern hemisphere glaciation have been investigated at Ocean Drilling Program Site 984. The late Pliocene interglacial sediments of the northeast Atlantic are carbonate rich and show evidence of vigorous bottom water circulation at intermediate water depths. Contrasting this, the late Pliocene glacial sediments are characterised by carbonate dissolution and slower bottom current velocities. Weak or “leaky” Norwegian Sea overflows, undersaturated with respect to carbonate, influenced this region during the late Pliocene glacials. The early Pleistocene pattern of intermediate water circulation appears to have changed radically in the northeast Atlantic. At this time, interglacial carbonate values and inferred bottom current velocities are low. This suggests slow-flowing, undersaturated Norwegian Sea water bathing the site. The overflow increased during the early Pleistocene interglacials as the exchange between the Atlantic and Norwegian-Greenland Seas improved. The most significant feature of the early Pleistocene glacials is the increase in inferred bottom current velocity. These changes reflect a switch in deep North Atlantic convection to shallower depths during glacial periods, possibly in a manner similar to the increasing contribution of glacial intermediate water to the North Atlantic during the late Pleistocene glacials. Our results suggest that the late Pleistocene climate variability of the North Atlantic is a pervasive feature of the late Pliocene–early Pleistocene record. 相似文献
5.
Ho Il Yoon Kyu-Cheul Yoo Young-Suk Bak Yong Il Lee Jae Il Lee 《Geo-Marine Letters》2009,29(5):309-320
A deep-sea sediment core (GC98-06) from the southernmost Drake Passage, West Antarctica, shows late Quaternary depositional
environments distinctly different from sedimentary drifts commonly found along the southwestern Pacific margin of the Drake
Passage. The chronology of the core has been inferred using geochemical tracers of paleoproductivity and diatom biostratigraphy,
and represents the paleoceanographic conditions in a continental rise setting during the last 150,000 years. Three dominant
sediment types associated with distinct sedimentary processes have been identified using textural/compositional analyses:
(1) hemipelagic mud (interglacial sediments) deposited from pelagic settling of bioclasts, meltwater plumes, and ice-rafted
detritus; (2) terrigenous mud (glacial sediments) delivered by turbid meltwater plumes; and (3) massive muds marking the boundaries
from interglacial to glacial periods. The succession of the sedimentary facies in core GC98-06 is interpreted to reflect temporal
changes in environmental conditions prevailing on the continental rise of the southern Drake Passage in the course of successive
climatic stages over the last 150 ka: from the bottom upward, these are glacial, interglacial, glaciation, glacial, and interglacial
episodes. Variability in sediment flux and diatom abundance seem to have been related to changes in glacial advance, sea-ice
extent, and specific sedimentary environments, collectively influenced by mid- to late Quaternary climatic changes. 相似文献
6.
临夏盆地王家山剖面沉积物地球化学元素特征与季风演化 总被引：9，自引：0，他引：9
位于青藏高原东北边缘临夏盆地王家山剖面（上新统以上段）的沉积物地化元素含量波动特征表明，上新世气候频繁、剧烈和大幅度波动体现了上新世气候演化的过渡性特征，与第四纪早期相对稳定的湖相沉积地球化学元素的波动明显不同。这种差异的产生具有深刻的环境及构造背景，一定程度上反映了亚洲季风从上新世开始不稳定过渡到第四纪早期相对稳定的动态过程，与青藏高原隆升有密切的内在关系。 相似文献
7.
Xidong Chen Douglas F. Williams Yuan Youren Wang Baogui Tang Xianzan Fan Shiqing Liu Zongyang 《海洋学报(英文版)》1992,11(4):573-581
Signal processing techniques of cross-correlation, power spectral analysis and cross-power spectral analysis are used to determine the relationships between paleomagnetic properties and the oxygen isotope record of the South China Sea during the late Pleistocene. On the basis of correlation tests between the δ18O time series of cores V3 and A15 with the paleomagnetic properties of core SCS01, five events of susceptibility and intensity of natural remanent magnetization are identified as glacial events corresponding to δ18O positive events. The magnetic properties of the sediments which are independent of the geomagnetic field are sensitive climatic indicators which have frequencies corresponding to the Milankovitch orbital parameters. 相似文献
8.
渤海湾海陆交互相沉积的磁性地层学 总被引：23，自引：0，他引：23
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。 相似文献
9.
Late Cenozoic sedimentation from four varied sites on the continental slopes off southeastern Canada has been analysed using high-resolution airgun multichannel seismic profiles, supplemented with some single channel data. Biostratigraphic ties are available to exploratory wells at three of the sites. Uniform, slow accumulation of hemipelagic sediments was locally terminated by the late Miocene sea-level lowering, which is also reflected in changes in foraminiferan faunas on the continental shelf. Data are very limited for the early Pliocene but suggest a return to slow hemipelagic sedimentation. At the beginning of the late Pliocene, there was a change in sedimentation style marked by a several-fold increase in accumulation rates and cutting of slope valleys. This late Pliocene cutting of slope valleys corresponds to the onset of late Cenozoic growth of the Laurentian Fan and the initiation of turbidite sedimentation on the Sohm Abyssal Plain. Although it corresponds to a time of sea-level lowering, the contrast with the late Miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline, perhaps as a result of increased rainfall or development of valley glaciers. High sedimentation rates continued into the early Pleistocene, but the extent of slope dissection by gullies increased. Gully-cutting episodes alternated with sediment-draping episodes. Throughout the southeastern Canadian continental margin, there was a change in sedimentation style in the middle Pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope. 相似文献
10.
Seamounts are ubiquitous topographic units in global oceans, and their influences on local oceanic circulation have attracted great attention in physical oceanography; however, previous efforts were less made in paleoclimatology and paleoceanography. The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount, and in this study, we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes. The principal results are as follows: (1) the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range, probably including a biogenic contribution; (2) the variabilities of magnetic parameters can be clustered into two sections at ～500 ka, and the differences between the two units are evident in amplitudes and means; (3) changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO2 in the middle Pleistocene. Based on these results, a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes. This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals, responding to changes in marine productivity and deep-sea circulation and displaying a major change in the Mid-Brunhes climate event. Therefore, we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes, providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales. 相似文献
11.
楚科奇海盆M04柱晚更新世以来沉积古环境记录 总被引：1，自引：0，他引：1
对"中国第五次北极科考"采自楚科奇海盆的M04柱进行粒度、冰筏碎屑、黏土矿物、岩心XRF扫描、沉积物颜色分析,初步建立了楚科奇海盆晚更新世MIS4期以来的沉积地层框架。MIS4期以来,楚科奇海盆M04柱沉积物粒度和黏土矿物组成具有明显的冰期/间冰期变化特征,冰期沉积物粒度分布以双峰态为主,由洋流搬运和海冰搬运沉积组分组成,伊利石含量高、高岭石含量低;间冰期沉积物具有三峰态粒度分布特征,由海冰搬运、洋流搬运和冰山搬运沉积组分组成,伊利石含量低、高岭石含量高。通过M04柱黏土矿物组合类型与北冰洋边缘海盆的表层沉积物黏土矿物组合类型对比表明,晚更新世以来楚科奇海盆沉积环境发生显著变化:温暖的间冰期受波弗特涡流驱动,波弗特海为研究区的物源输入提供了主要贡献;寒冷的冰期表层环流呈反向输运,细颗粒物源碎屑以东西伯利亚海的输入为主。 相似文献
12.
晚更新世末期地磁短期游移的研究 总被引：1，自引：0，他引：1
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。 相似文献
13.
南海北部陆架柱状沉积物记录的残留沉积 总被引：3，自引：0，他引：3
对南海北部外陆架珠江口西南的E602孔进行了粒度分析和AMS14C年龄测定,通过沉积学分析,认为该孔沉积物形成于近滨环境,时间为全新世初期。根据岩性的变化将该孔分为上下2段,下段岩性较均匀,粒度参数变化较小,主要是风暴成因的递变悬浮沉积序列,形成于近滨上部环境;上段为均匀悬浮,为近滨下部环境。该孔下段的沉积作用主要是对晚更新世低海平面时沉积物的改造和再沉积,基本没有新的陆源物质加入,属于残留沉积或准残留沉积,只是在晚期的上段沉积中才有少量以细粒物质为主的新物源加入。 相似文献
14.
Research on Lamelllbranchiate fossils of the Huanghai Sea started rather late in China and data on this subject are scarce. During the large-scale investigation of the Huanghai Sea sediment in the late 1970s, a large number of surface and core samples of the sea-floor sediment were obtained and a considerable number of Lamellibranchiatc fossils were found. A preliminary identification reveals that there are 46 species of the fossils.The Lamellibranchiate fossils in the Huanghai Sea are composed of different species: the shallow water species, the littoral species and the fossils reflecting the environment of the estuary where freshwater flows, or of the tidal zone having brackish water.Through the studies of the Lamellibranchiate fossils and their ecological environment, not only the features of the Lamellibranchiate groups of the Upper Pleistocene have been restored, but also some relatively important data of the investigation of paleo-current and paleo-temperature during late Pleistocene have been obt 相似文献
15.
The Ocean Drilling Program Leg 175 recovered a unique series of stratigraphically continuous sedimentary sections along the SW African margin, an area which is presently affected by active coastal upwelling. The accumulation rates of organic and inorganic carbon are a major component of this record. Four Leg 175 sites (1082, 1084, 1085, 1087) are chosen as part of a latitudinal transect from the present northern to southern boundaries of the Benguela Current upwelling system, to decipher the Pliocene–Pleistocene history of biogenic production and its relationship with global and local changes in oceanic circulation and climate. The pattern of CaCO3 and Corg mass accumulation rates (MARs) over 0.25-Myr intervals indicates that the evolution of carbon burial is highly variable between the northern and the southern Benguela regions, as well as between sites that have similar hydrological conditions. This, as well as the presence over most locations of high-amplitude, rapid changes of carbon burial, reflect the partitioning of biogenic production and patterns of sedimentation into local compartments over the Benguela margin. The combined mapping of CaCO3 and Corg MARs at the study locations suggests four distinct evolutionary periods, which are essentially linked with major steps in global climate change: the early Pliocene, the mid-Pliocene warm event, a late Pliocene intensification of northern hemisphere glaciation and the Pleistocene. The early Pliocene spatially heterogeneous patterns of carbon burial are thought to reflect the occurrence of mass-gravitational movements over the Benguela slope which resulted in disruption of the recorded biogenic production. This was followed (3.5–3 Ma) by an episode of peak carbonate accumulation over the whole margin and, subsequently, by the onset of Benguela provincialism into a northern and a southern sedimentary regime near 2 Ma. This mid and late Pliocene evolution is interpreted as a direct response to changes in the ventilation of bottom and intermediate waters, as well as to dynamics of the subtropical gyral circulation and associated wind stress. 相似文献
16.
G. P. Glasby 《Geo-Marine Letters》1986,5(4):247-252
A histogram of the frequency of distribution of hiatuses in deep-sea manganese nodules shows that these hiatuses occur dominantly in the outer 5 mm of the nodules and that their frequency falls off sharply below this depth. It is believed that these hiatuses are of primary origin and are related to changes in ocean bottom current velocity caused by major changes in global climate occurring mainly during the Pleistocene and late Pliocene. 相似文献
17.
G. P. Glasby 《Geo-Marine Letters》1985,5(4):247-252
A histogram of the frequency of distribution of hiatuses in deep-sea manganese nodules shows that these hiatuses occur dominantly in the outer 5 mm of the nodules and that their frequency falls off sharply below this depth. It is believed that these hiatuses are of primary origin and are related to changes in ocean bottom current velocity caused by major changes in global climate occurring mainly during the Pleistocene and late Pliocene. 相似文献
18.
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. 相似文献
19.
利用南海东北部上陆坡处所取的D孔(21°23′02″N,116°47′13″E,水深405m)进行硅藻分析,结合粒度分析与碎屑矿物分析结果,探讨该海域末次冰期以来沉积环境演变过程。结果表明:粒度与硅藻分析结果较为吻合,共同显示D孔可分为上下两层,上层(0-2cm)的砂质沉积层为经冰后期海进过程改造的晚更新世残留沉积层;下层(2-130cm)主要是末次冰期形成的浅海沉积。整个柱样可反映出海洋同位素MIS4期海退至MIS3期海进与MIS2期海退至冰后期海进的沉积韵律。 相似文献
20.
根据北仑河口3个钻孔柱状沉积物的粒度分析结果,结合14C测年和210Pb测年资料,分析了钻孔沉积物的粒度特征,结果表明：KL1柱样沉积物主要为粉砂质砂、砂质粉砂、中细砂、细中砂,沉积物由下到上由细到粗再变细,经历了2个沉积变化;KL2柱样沉积物单一,为细中砂;KL3柱样沉积物由下到上依次为砾石、砂砾、粗中砂、细中砂、砾砂、粉砂质砂、粘土质粉砂、砂-粉砂-粘土,沉积物粒度由下到上逐步细化,该孔早期离物源较近.3个孔的沉积物分选大多很差,反映当时水动力作用较强或者离物源较近.这些沉积物类型为晚更新世末次冰期以来的沉积,记录了晚更新世以来2个沉积变化. 相似文献