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1.
Sediment cores from the Norwegian Sea were studied to evaluate interglacial climate conditions of the marine isotope stage 5e (MIS 5e). Using planktic forminiferal assemblages as the core method, a detailed picture of the evolution of surface water conditions was derived. According to our age model, a step-like deglaciation of the Saalian ice sheets is noted between ca. 135 and 124.5 Kya, but the deglaciation shows little response with regard to surface ocean warming. From then on, the rapidly increasing abundance of subpolar forminifers, concomitant with decreasing iceberg indicators, provides evidence for the development of interglacial conditions sensu stricto (5e- ss ), a period that lasted for about 9 Ky. As interpreted from the foraminiferal records, and supported by the other proxies, this interval of 5e- ss was in two parts: showing an early warm phase, but with a fresher, i.e., lower salinity, water mass, and a subsequent cooling phase that lasted until ca. 118.5 Kya. After this time, the climatic optimum with the most intense advection of Atlantic surface water masses occurred until ca. 116 Kya. A rapid transition with two notable climatic perturbations is observed subsequently during the glacial inception. Overall, the peak warmth of the last interglacial period occurred relatively late after deglaciation, and at no time did it reach the high warmth level of the early Holocene. This finding must be considered when using the last interglacial situation as an analogue model for enhanced meridional transfer of ocean heat to the Arctic, with the prospect of a future warmer climate.  相似文献   

2.
通过对海南岛三亚地区铁炉港海湾TLG01钻孔沉积物的AMS 14C和OSL测年,以及对地层岩性特征、亮度、粒度、海生贝壳、有孔虫丰度等进行研究,发现全新世海相层较薄,以砂质潮坪相沉积为主;而下伏晚更新世海相层厚度超过38 m,OSL测年结果显示为MIS-5e及MIS-5d沉积。晚更新世海进―海退系列自下而上依次为砂质潮坪―潮下带―泥质潮坪―砂质潮坪,其中可见较深水的软体动物。MIS-5e细粒的粉砂黏土体积分数先陡增、后缓降,结合粒度及有孔虫丰度、亮度L*等指标,判断MIS-5e初期为最高海平面时期,水深较大,其后海平面逐渐降低;沉积物中陆源粗砂的体积分数不断增加,显示进入了MIS-5d相对低海面时期。MIS-1及MIS-5沉积物粒度三角图,分别与湛江海岛潮间带及不同深度南海表层沉积物同类沉积环境有较好的对照,指示2类不同水深的海相环境。  相似文献   

3.
选择位于福建平潭岛北部芦洋埔海积平原的PT01钻孔,岩芯长度28.3 m,采用加速器碳同位素（AMS 14C）和光释光（OSL）测年建立地层年代框架,认为晚更新世富含有孔虫等海相生物化石的地层应归属于MIS 5高海面期,即MIS 5e的潮下带滨海相沉积。结合岩性特征、古生物化石、沉积物色度、粒度分析及其参数等指标,进行了沉积单元的划分,重建了MIS 6末期以来的沉积相变化过程,揭示出MIS 5期间的多次海平面波动变化,即MIS 5高海面期沉积环境仍存在滨海、潮坪、潟湖、风成砂等沉积相之间的转换,并可能存在短暂的陆相或风化过程。而该区整个末次冰期的沉积缺失或较薄,上部全新世沉积也不发育,厚度仅为3.79 m,以沼泽相―风成砂相为主。  相似文献   

4.
对采自西南极布兰斯菲尔德海峡ＰＣ１０孔的５１个硅藻样品进行了氧同位素分析，结果揭示，柱状样氧同位素曲线可划分为５期，记录了区内近１１２．５ｋａ来的沉积，包括了一个冰期／间冰期旋回和一个冰后期。间冰期的沉积速率高于冰期，推测这与间冰期（暖期）筏冰物质及生物硅质源的供应较冰期（冷期）更丰富所致。  相似文献   

5.
青藏高原湖泊沉积研究主要围绕青藏高原隆升和全球变化响应开展的。研究揭示了青藏高原隆升具有整体性、阶段性和后期加速性。中晚更新世以来和末次间冰期一冰期气候演化过程得到重建,并能够与冰芯和深海氧同位素记录对比;同时也存在MIS3阶段强烈暖湿和末次冰盛期冷湿等区域特征;新仙女木事件在湖泊沉积物也有明显记录。全新世研究表明青藏高原早期暖湿并经历冷事件,大暖期普遍出现高水位,后期气候向于冷化方向发展。湖泊沉积环境定量化重建也得到研究。青藏高原湖泊沉积应在高分辨率纹层沉积和环境指标定量分析基础理论方面加强研究。  相似文献   

6.
Two raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by 14C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions.  相似文献   

7.
ＳｉｌｉｃａｏｘｙｇｅｎｉｓｏｔｏｐｅｒｅｃｏｒｄｏｆｃｏｒｅＰＣ１０ｄｉａｔｏｍｓｆｒｏｍｔｈｅＢｒａｎｓｆｉｅｌｄＳｔｒａｉｔ,Ａｎｔａｒｃｔｉｃａａｎｄｉｔｓａｐｐｌｉｃａｔｉｏｎｉｎｓｅｄｉｍｅｎ┐ｔｏｌｏｇｙＤｕａｎＷｅｉｗｕ（段威武）ａｎ...  相似文献   

8.
青藏高原湖泊沉积研究及其进展   总被引：3，自引：0，他引：3  
青藏高原湖泊沉积研究主要围绕青藏高原隆升和全球变化响应开展的。研究揭示了青藏高原隆升具有整体性、阶段性和后期加速性。中晚更新世以来和末次间冰期-冰期气候演化过程得到重建,并能够与冰芯和深海氧同位素记录对比;同时也存在M IS3阶段强烈暖湿和末次冰盛期冷湿等区域特征;新仙女木事件在湖泊沉积物也有明显记录。全新世研究表明青藏高原早期暖湿并经历冷事件,大暖期普遍出现高水位,后期气候向干冷化方向发展。湖泊沉积环境定量化重建也得到研究。青藏高原湖泊沉积应在高分辨率纹层沉积和环境指标定量分析基础理论方面加强研究。  相似文献   

9.
Ten meters of lacustrine deposits retrieved from Lake Pergusa (Sicily, southern Italy) were investigated through stable isotope composition (carbon and oxygen) of authigenic carbonate (calcareous muds) and freshwater shells. The core chronology was established through three AMS dates, and by correlation with a previously dated nearby core. Stable isotope data show that the lake water evolution was mainly dominated by evaporation. Between ca. 20 and 28 ka the recovered sediments have very high δ18O values, likely corresponding to very dry climatic conditions. The observed rapid oscillations in the δ18O of the recovered sediments during this period also suggest important climatic fluctuations. More humid conditions dominated during the Holocene period, with the wettest interval occurring between ca. 9000 and 3000 years BP. Late Holocene sediments represent a substantial return to drier conditions. The available pollen data from a nearby core substantially confirm this general climatic trend during the Holocene. The positive correlation between δ13C of the calcareous muds and carbonate content suggests that biological activity played a key role in the carbon isotope evolution of dissolved inorganic carbon. However, a clear climatic signal is not evident from the δ13C record.  相似文献   

10.
Quaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 103 to 105 year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year?1 during the late Holocene, ca. 0.03 mm year?1 during the last glacial and at least 0.07 mm year?1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.  相似文献   

11.
Biogenic silica contents of sediments on the lower Selenga Delta and Buguldeika saddle in Lake Baikal show distinct fluctuations that reflect changes in diatom productivity, and ultimately, climate. The pattern of the upper 50 m of the section, dating from about 334 ka, is similar to that of the marine oxygen-isotope record, increasingly so as the younger sediments become progressively finer grained and less locally derived with time. The last two interglaciations are marked by biogenic silica abundances similar to those of the Holocene. The equivalent of marine oxygen-isotope stage 3 is distinctly intermediate in character between full glacial and full interglacial biogenic silica values. Following near-zero values during the last glacial maximum, biogenic silica began to increase at about 13 ka. The rise in biogenic silica to Holocene values was interrupted by an abrupt decrease during Younger Dryas time, about 11 to 10 14C ka.  相似文献   

12.
中国第四纪冰川作用与深海氧同位素阶段的对比和厘定   总被引：1，自引：0，他引：1  
随着冰期(阶)与间冰期(阶)旋回的不断细化,第四纪冰期系列与深海氧同位素阶段(MIS)对比之间所反映的问题开始逐步显现。通过中国第四纪冰期与MIS阶段对比,结合分析气候旋回与构造运动对地貌演化的控制作用,研究表明:①冰期(阶)或者间冰期(阶)发生的时段应尽可能对应于MIS的偶数或奇数阶段,有助于MIS框架下新的冰期(阶)的发现;②中更新世以来,中国第四纪冰期-间冰期旋回可能受控于100 ka轨道偏心率变化的气候大背景,昆仑冰期-倒数第二次冰期的冰川规模总体上与全球冰量变化一致。然而,末次冰期早、中期的冰川规模却与MIS所记录的全球冰量变化不尽一致,强烈显示气候与构造环境对冰川作用的影响;③目前在中国第四纪冰期划分方案中,存在着冰期系列由时间和地点双重命名的现象,建议用大理冰期、古乡冰期分别代替末次冰期和倒数第二次冰期。  相似文献   

13.
张信宝 《中国沙漠》1995,15(3):207-209
黄土高原晚更新世末次冰期时期,冬季风强盛,马兰黄土堆积;全新世以来的间冰期时期,夏季风强盛,降水较丰,侵蚀强烈。晚更新世以来的中国东部海岸线40°N 一带变化最大,同纬度晋陕蒙接壤区是黄土高原季风气候变化最剧烈的地区,致使该区成为黄土高原沙黄土区中现代降水最多的地区。沙黄土和较多降水的组合,使晋陕蒙接壤区成为黄土高原现代侵蚀最剧烈的地区。  相似文献   

14.
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen, and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm) overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca. 7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year. Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms. During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface, ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher than during the coastal marine period.  相似文献   

15.
Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry 14C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.  相似文献   

16.
The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns. This is the seventh in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

17.
由极地冰芯记录、中纬黄土记录和深海沉积记录的对比可得，１５万年以来全球变化的基本框架为：末次间冰期，从距今１４万年开始到约１２．５万年达鼎盛，可分为五个阶段，即冰芯中三次高温期夹两次低温期；黄土中三层古土壤夹两层黄土；深海沉积中三次高海面夹两次低海面。末次冰期，距今８万年到１万年，可分为三个阶段，早、晚冰段和中间的间冰段。早、晚冰段盛期气候寒冷程度相当，但晚冰段最低温持续期更长，造成海面比早期更低。中间的间冰段，至少可分为７个亚段，即４次暖期（４次弱成土古土壤）夹３次冷期。全新世与末次间冰期对比，总体气候变化较平缓。在上述基本框架中，近几年发现，在末次冰期存在许多短周期、高频快速变化事件。这些事件，温度变化幅度达７℃，变化速率为几年到几十年，对应的环境变化速率可能更快。这些事件的引发机理目前还不清楚，有待进一步研究。  相似文献   

18.
The geomorphology of a coarse clastic coastal landscape at Tuapaat (69°24'N 52°36'W), southeastern Disko Island, central West Greenland, is described, and a coastal morpho-stratigraphy of the landscape is constructed. 14C ages on marine shells, whale bones, peat and gyttja are used to construct relative sea level changes throughout the Holocene. The emergence of SE Disko Island occurred in the early part of the Holocene. The Holocene marine limit is situated ca. 80m a.s.l. Between 4.7 and 1.0ka BP, the relative sea level approached the present sea level and it has probably been below present sea level between 4.7 ka BP and the present. The morpho-stratigraphy in the lowest part of the coastal landscape at Tuapaat suggests a complex late Holocene relative sea level history which includes at least 3-4 transgressions during the last ca. 2.5 ka.  相似文献   

19.
白令海北部陆坡晚第四纪的古海洋与古气候学记录   总被引：3，自引：0，他引：3       下载免费PDF全文
白令海北部陆坡B2 9柱状样中放射虫Cycladophoradavisiana含量曲线和深海SPECMAP氧同位素记录的对比 ,为该柱状样建立了晚第四纪约 1 0万年以来的地层年代框架。该柱状样中微体化石、碳屑颗粒、筏冰碎屑 (石英和岩屑颗粒 )的定量分析结果表明 ,作为表层生产力指标的粗组份自氧同位素 5 .3期以来呈阶梯状增加 ,反映表层生产力阶段式的增长 ;碳屑颗粒丰度自氧同位素 5 .3期至末次冰消期的增加说明白令海末次冰消期以前气候较全新世干冷 ,天然火灾发生的概率较全新世大大增加 ;冰期和早、中全新世较高的筏冰碎屑反映了冰期和早、中全新世白令海陆架海冰的扩大以及气候转暖所导致的海冰消融的过程 ,揭示了白令海对过去全球气候变化的响应。  相似文献   

20.
Varnish microlamination (VML) dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts. In this study, we establish a generalized late Quaternary (i.e., 0–300 ka) varnish layering sequence for the drylands of western USA and tentatively correlate it with the SPECMAP oxygen isotope record. We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region. VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5–15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation. During the Holocene interglacial time, however, 0.5–1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate. VML dating of alluvial desert pavements in Death Valley and the Mojave Desert reveals that pavements can be developed rapidly (< 10 ky) during the Holocene (and probably late Pleistocene) in the arid lowlands (< 800 m msl) of these regions; but once formed, they may survive for 74–85 ky or even longer without being significantly disturbed by geomorphic processes operative at the pavement surface. Data from this study also support the currently accepted, “being born at the surface” model of desert pavement formation. VML dating of colluvial boulder deposits on the west slope of Yucca Mountain, southern Nevada, yields a minimum age of 46 ka for the emplacement of these deposits on the slope, suggesting that they were probably formed during the early phase of the last glaciation or before. These results, combined with those from our previous studies, demonstrate that VML dating has great potential to yield numerical age estimates for various late Quaternary geomorphic features in the western USA drylands.  相似文献   

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