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1.
南海东北部末次冰期以来的沉积环境演变   总被引：1，自引：0，他引：1  
利用南海东北部上陆坡处所取的D孔柱样进行硅藻分析,结合粒度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孔柱样可分为上下两层.上表层（0～2 cm）的砂质沉积层为冰后期海进过程改造的晚更新世残留沉积层,即变余沉积;下层（2～130 cm）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MIS 4期海退至MIS 3期海进与MIS 2期海退至冰后期海进的沉积变化韵律.  相似文献   

2.
根据1996年"中－法合作东海计划",在东海大陆架打钻一口,取一长196cm的岩芯。对该岩芯样品粒度分析结果和现场生物种属记录综合研究,表明此岩芯属浅海沉积,既有波浪多次往返搬运沉积的特点,又有河流砂沉积的特点。以74cm为界,上层为冰后期海进滨海相沉积,下层为晚更新世末冰期海退海相沉积。  相似文献   

3.
通过对神狐海域SH1B孔硅藻丰度和生态类群组成的研究,探讨了该海域MIS 6期以来古生产力及古环境变化特征。硅藻丰度变化表明MIS 6期以来古生产力具有显著的冰期高-间冰期低旋回特征。末次冰期(MIS2-4)和MIS 6时低海平面导致河流剥蚀作用增强,并可能存在季风驱动的上升流,使得营养物质输入增加引发高生产力。MIS 5和MIS 1期硅藻丰度低,与高海平面时期河流输入的营养物质相对减少,对表层生产力的影响减弱有关。MIS 6期热带远洋种含量偏高,反映硅藻分布主要受盐度控制。MIS 5期半咸水沿岸种含量增加,可能是由降雨量增加引起。  相似文献   

4.
西菲律宾海15万年以来的浊流沉积及其成因   总被引：2，自引：0，他引：2  
MD06-3052孔取自西菲律宾海吕宋岛岸外上陆坡,通过AMS14 C测年、沉积物粒度和浮游有孔虫氧同位素记录,揭示了15万年以来5个浊流沉积层的特征和浊积事件的发生时间。浊流沉积物粒度明显较上下层的粗,主要组分为砂质和粉砂质沉积。通过AMS14 C测年和氧同位素年代标尺,计算了5个浊流沉积层发生的时间分别为13.3、20.4、34.3、41.7和121.8kaBP,其中上部4次浊积事件发生于末次冰期,特别是MIS 3晚期和MIS 2期的低海平面时期,仅底部一次出现于末次间冰期MIS 5e中期相对低海平面时期,因而推测研究区浊流沉积事件的主要诱因是低海平面时期的海平面波动造成临近陆架上的沉积物不稳定,同时较陡的陆坡为浊流沉积提供了有利地形,因而造成了向陆坡方向的浊流搬运。  相似文献   

5.
为了解南海北部陆坡末次间冰期以来的古海洋沉积环境演化特征,对研究区ZSQD196PC柱状样有孔虫、硅藻及有孔虫氧同位素资料开展了分析。依据沉积有孔虫、硅藻主要属种的百分含量、丰度及组合特征,将有孔虫划分为3个组合,分别对应于氧同位素MIS1、2、3~4期;将硅藻划分为4个组合,大致对应于MIS1~4期。MIS1期有孔虫以暖水种占优势,Pulleniatina obliquiloculata百分含量显著升高;硅藻丰度低且以热性种占优势,其中冷期出现大量沿岸种,反映相对温暖的气候条件。MIS2~4期有孔虫以冷水种占优势,温跃层种含量相对较高;硅藻丰度高且以广布种占优势,出现沿岸种含量的升高,反映较冷的气候条件。通过对比浮游有孔虫氧同位素,分析讨论了末次盛冰期、Blling—Allerd暖期和新仙女木事件在ZSQD196PC柱状样的沉积响应,揭示了末次冰期中的气候波动。  相似文献   

6.
IODP347航次的目标是在波罗的海不同的地点获取末次间冰期—冰期时期的沉积物,重点解决4个主要科学问题。它们是:(1)气候和海平面动态变化,包括MIS 5期的起始与结束;(2)末次冰期MIS4-MIS 2期变化的复杂性;(3)冰期和全新世(MIS 2-MIS1)的气候特征;(4)波罗的海盆地(BSB)深部生物圈。BSB作为欧洲最大的陆内海盆地,巨厚、连续且完整的沉积记录时限可达14万年,这里的高沉积速率提供了一个  相似文献   

7.
南海深水区末次冰期和冰后期沉积物堆积速率的特征   总被引：3，自引：0，他引：3  
黄维  汪品先 《海洋学报》2007,29(5):69-73
通过统计南海100 m以下深水区的136个沉积柱状样的分析数据,对南海末次冰期以来的堆积速率进行了统计.计算出MIS(marine isotope stage)1期的年均沉积量为152.3 Mt/a,2期的为215.2 Mt/a,主要为陆源物质的贡献.无论在末次冰期还是在冰后期,堆积速率均在南海西南部最高,其次是在东北部,在其他地区较低.由于侧向搬运和顺坡搬运频繁,虽然整体上末次冰期的堆积速率高于冰后期的,但在沉积物高速堆积地区附近有相反的变化趋势.  相似文献   

8.
利用最新采集的高分辨率浅地层剖面资料,结合SHD-1钻孔岩心资料,对东海北部外陆架MIS 6以来的地层结构进行了分析,建立了MIS 6以来的沉积地层格架,并对地层的地质年代进行了厘定。根据Octavian Catuneanu(2005)的层序地层学理论,研究区地层划分出海侵和高位体系域、下降期体系域、海退和低位体系域。研究表明,过孔的浅地层剖面与钻孔岩心的沉积地层有很好的对应关系。东海北部外陆架MIS 6以来可划分出7个不整合界面(D7—D1)和7个地震单元(SU_7—SU_1)。东海外陆架的海进层序与海退层序有规律地交替发育,它们与海平面变化曲线也有很好的对应关系。其中,地震单元SU_1、SU_5分别为MIS 1、MIS 5形成的海侵沉积,主要发育浅海沉积层,100 m以浅的位置发育潮流沙脊;地震单元SU_2、SU_4、SU_6分别对应MIS 2、MIS 4和MIS 6低海平面时期形成的河流/河口—三角洲沉积;地震单元SU3、SU4为下降期体系域,这两个亚单元分别对应MIS 3和MIS 4晚期。MIS 4—MIS 3发育厚层且分布广泛的水下三角洲,但MIS 4发育的水下三角洲的规模不及MIS 3大。总之,对MIS 6以来沉积地层格架的建立和古环境研究可为东海外陆架晚第四纪地层的海平面变化、古环境演化等相关研究提供参考。  相似文献   

9.
基于国际海洋古全球变化研究项目(IMAGES)在西菲律宾海本哈姆海台获取的高质量柱状沉积物岩芯MD06-3047(17°00.44′N、124°47.93′E),利用颗石藻下透光带属种Florisphaera profunda的相对丰度以及初级生产力转换函数,恢复了260 ka以来西菲律宾海上部水体营养跃层以及初级生产力的变化历史。发现该区域26万年以来初级生产力冰期-间冰期变化特征较不明显,冰期生产力平均值略高于间冰期。通过与前人已发表的指示东亚冬季风强弱的伊利石/蒙脱石记录和热带太平洋纬向表层海水温度梯度记录的对比,提出MIS 8期以来,热带西菲律宾海古生产力变化的主要受控因素在MIS 5a左右发生明显转变。在MIS 8后期至MIS 5a之间,初级生产力受到长期类ENSO过程的影响较为显著,当热带东西太平洋海水表层温度梯度较小的时期,认为热带太平洋处于类El Niňo状态,此时西菲律宾海营养跃层相对较浅,生产力较高,反之则相反。而在MIS 5末期至末次冰消期时段,生产力受东亚冬季风的影响相对于长期ENSO过程更强,可能掩盖了后者的古生产力信号。冰期东亚冬季风加强,一方面,可以引起上部水体混合加强,增加下部营养物质向上的输送,另一方面大量风尘物质的输入可以刺激颗石藻的生长;反之在冰消期,水体混合较弱,风尘输入显著减少,生产力也随之降低。  相似文献   

10.
硅藻在全球碳循环中发挥着重要的作用。"树荫种"硅藻在次表层水体中的勃发成席,并迅速埋藏成为硅藻席沉积,使人们逐渐意识到次表层生产在整个生产力及输出生产中起着重要作用。介绍了首次在低纬度西太平洋区域发现的硅藻席沉积的分布特征,硅藻席发现站位呈带状分布,大致呈北西-南东向展布,大部分散布在17.5°～20°N之间。采集到硅藻席沉积物的站位其水深在碳酸钙补偿深度(CCD)以下4837～6150m的深水区,多分布在较平坦的海底,且受风力和陆源物质输入影响相对较强的区域。该区域硅藻席的形成可能是由于末次冰期时该海区有大洋锋面的形成所致。该区域的成席硅藻Ethmodiscus rex(Wallich)Hendey为典型的"树荫种"硅藻,可以通过自身调节浮力的作用,在水体相对稳定的贫氧大洋中生存并勃发成席。末次冰期低纬度西太平洋硅藻席沉积的发生,可能使该区成为CO2的汇。  相似文献   

11.
The sedimentary sequences since the Late Pleistocene can be divided into Layers E, D, C, B, A from old to young according to systematic analysis of grain-size, pollen and spore, diatom, foraminifera, radiocarbon dating and paleogeomagnetism of 16 sedimentary cores from the sea area of the western Taiwan Strait. The results proved the existences of the Langqi transgression (upper section of Layer D) formed in middle and late stages of early Wurm glacial period, Fuzhou transgression (Layer C) formed in Wurm sub-interglacial period and Changle transgression (Layer A) formed in postglacial period. It was also the first time to discover the Jinmen transgression (Layer E) formed in Riss -Wurm interglacial period. In this paper it is proposed that most part of the Taiwan Strait emerged as land in the early stage of early Wurm glacial period, and was still under sublittoral environment in late Wurm glacial period, as well as the existence of Dongshan Continental Bridge was in 8×103 a BP.  相似文献   

12.
Sea surface temperatures (SSTs) in the southwestern South China Sea have been reconstructed for the past 160 ka using the Uk37 paleothermometer from the core MD01-2392. The temperature differences between glacial times (MISs 6 and 2) and interglacial times (MISs 5.5 and 1) are 2.2~2.5 ℃. Younger Dryas event during the last deglaciation was documented in both the planktonic foraminiferal δ18O and SST records. After MIS 5.5, SSTs displayed a progressive cooling from 28.6 to 24.5 ℃, culminating at the LGM. During this gradual cooling period, warm events such as MISs 5.3, 5.1 and 3 were also clearly documented. By comparison of SST between the study core and Core 17954, a pattern of low or no meridional SST gradients during the interglacial periods and high meridional SST gradients during the glacial periods was exhibited. This pattern indicates the much stronger East Asian winter monsoon at the glacial than at the interglacial periods. Spectral analysis gives two prominent cycles: 41 and 23 ka, with the former more pronounced, suggesting that SSTs in the southern SCS varied in concert with high-latitude processes through the connection of East Asian winter monsoon.  相似文献   

13.
末次冰盛期后黄河三角洲沉积物的磁性特征及其沉积环境   总被引：1，自引：0，他引：1  
On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe(Yellow River) Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay(4 μm)and the fine-grained size(32 μm). The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak-strong, which has been proved by the Flemming triangular schema.  相似文献   

14.
Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2–1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties.  相似文献   

15.
研究钻孔DGKS-9602位于冲绳海槽中部,岩芯长度为931 cm,钻孔年代覆盖了氧同位素1～4阶段,年代可追溯至距今73 ka.孢粉分析结果证明,孢粉带与氧同位素阶段有较好的对应关系,其中松属花粉与蒿属花粉比值(P/A)与海平面变化曲线相互吻合.应用非相似性类比法将钻孔孢粉样品与陆地表土孢粉样品进行欧氏距离计算,从而...  相似文献   

16.
The distribution of diatoms, radiolarians, planktonic and benthic foraminifers, and sediment components in the fraction >0.125 mm was analyzed in the core obtained from the central Sea of Okhotsk within the frameworks of the Russian-German KOMEX project. The core section characterizes the period 190–350 ka, which corresponds to marine-isotopic stages (MIS) 7 to 10. During glacial MIS 10 and MIS 8, the basin accumulated terrigenous material lacking microfossils or containing them in low abundance, which reflects, along with their composition, heavy sea-ice conditions, suppressed bioproductivity, and bottom environments aggressive toward calcium carbonate. Interglacial MIS 9 was characterized by elevated bioproductivity with accumulation of diatomaceous ooze during the climatic optimum (328 to 320 ka). The water exchange with the Pacific was maximal from 328 to 324 ka ago. Environments became moderate and close to the present-day ones at the end of the optimum exhibiting the possible existence of a dichothermal layer with substantial amounts of the surface Pacific water still flowing into the basin. Similar to interglacial MIS 5e and MIS 1, the “old” Pacific water determined near-bottom environments in the central Sea of Okhotsk during that period, although the influx of terrigenous material was higher, probably reflecting a more humid climate of the region. Slight warming marked the terminal MIS 8 (approximately 260 ka ago). The paleoceanographic situation during interglacial MIS 7 was highly variable: from warm-water to almost glacial. The main climatic optimum of MIS 7 occurred within 220–210 ka, when the subsurface stratification increased and the dichothermal layer developed. Bottom environments during the studied time interval, except for the optimum of interglacial MIS 9, resembled those characteristic of glacial periods: the actively formed “young” Okhotsk water displaced the “old” Pacific deep water.  相似文献   

17.
Abundant evidences of higher sea levels from Jiangsu and Fujian coasts have proved a marine transgression event during 30–40 ka BP, suggesting that there was a stage with high sea level and a warm climate when ice sheets shrank in the Northern Hemisphere. The duration of 30–40 ka BP spanned a period in the late Marine Isotope Stage 3(MIS 3) and was in nature an interstadial epoch during the Last Glacial period of the Quaternary. Different from the glacial period with a cold climate, this marine transgression considered as a penultimate higher sea level during the Quaternary remains a puzzle that why the evidence is contrary to the Quaternary glacial theory. It is important to understand sea level rise for these areas sensitively responding to the global changes in the future. To recognize the key issues on sea level changes, the eustatic sea level(H_S) was defined as the glaciation-climateforced sea levels, and the relative sea level change(H_R) was defined as that a sea level record was preserved in sediment that experienced multiple secondary actions of land and sea effects. On the basis as defined above, we constructed multi-level models of climate-driven glacio-eustatic changes and land-sea systems. By integrating data sets from eight borehole cores and prescribing the boundary conditions, we simulated the changes of HS and HR in the East China Sea and southern Yellow Sea areas in the late MIS 3. The marine transgression strata from the borehole core data was identified at ca. 30 m below present sea level as a result of the collective influence of ice melting water, neotectonic subsidence, sediment compaction and terrestrial sediment filling since ca. 35 ka ago,whereas the simulated relative sea-levels turned out to be –26.3––29.9 m a.s.l. The small error involved in the simulation results of ±(2.5–4.5) m demonstrated the credibility of the results. Our results indicated that sea level change in the late MIS 3 was dominated by glacial effects, in which the eustatic sea-level was between –19.2––22.1m a.s.l. The study sheds light on the nature of sea-level changes along the east coast of China in the late MIS 3 and contributes to understanding the characteristics of marine transgression under the effects of multiple complex land-sea interactions.  相似文献   

18.
波弗特环流(Beaufort Gyre)是 决定北冰洋海冰运移方向和滞留时间的主要因素。依据沉积物的颜色旋回、Mn元素含量和有孔虫丰度,本文建立了阿尔法洋脊(Alpha Ridge)B85-D孔轨道尺度上的年龄框架,并深入分析了该孔晚第四纪以来冰筏碎屑(IRD>154 μm)含量、组分及其源区的变化特点。结果表明,350ka以来最显著的变化发生在末次冰期(MIS2~4期),期间沉积物中Ca元素和白云石含量都接近于零,大部分来自班克斯岛、维多利亚岛和麦肯齐地区的碳酸盐岩碎屑没有在阿尔法洋脊沉积;随着波弗特环流的消亡,搬运陆源碎屑的海冰很可能沿着北美海岸线直接进入了欧亚海盆。而在末次间冰期(MIS5期),波弗特环流却十分流畅,并将大量碳酸盐岩碎屑限制在美亚海盆内,导致阿尔法洋脊沉积物中Ca元素含量急剧升高,与之对应的白云石含量高达16.4%。通过类比可知,在MIS6期波弗特环流的状态可能与MIS2~4期相似,而在MIS8和MIS10这两大冰期,波弗特环流却类似于MIS5期。显然,波弗特环流的存在与否并不严格遵循“冰期-间冰期”旋回,这种变化很可能是风场强度和海冰浓度双重作用的结果。  相似文献   

19.
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   

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