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1.
The deglaciation history and Holocene environmental evolution of northern Wijdefjorden, Svalbard, are reconstructed using sediment cores and acoustic data (multibeam swath bathymetry and sub-bottom profiler data). Results reveal that the fjord mouth was deglaciated prior to 14.5±0.3 cal. ka BP and deglaciation occurred stepwise. Biomarker analyses show rapid variations in water temperature and sea ice cover during the deglaciation, and cold conditions during the Younger Dryas, followed by minimum sea ice cover throughout the Early Holocene, until c. 7 cal. ka BP. Most of the glaciers in Wijdefjorden had retreated onto land by c. 7.6±0.2 cal. ka BP. Subsequently, the sea-ice extent increased and remained high throughout the last part of the Holocene. We interpret a high Late Holocene sediment accumulation rate in the northernmost core to reflect increased sediment flux to the site from the outlet of the adjacent lake Femmilsjøen, related to glacier growth in the Femmilsjøen catchment area. Furthermore, increased sea ice cover, lower water temperatures and the re-occurrence of ice-rafted debris indicate increased local glacier activity and overall cooler conditions in Wijdefjorden after c. 0.5 cal. ka BP. We summarize our findings in a conceptual model for the depositional environment in northern Wijdefjorden from the Late Weichselian until present.  相似文献   

2.
Philips Inlet and Wootton Peninsula are located at 82°N and 85°W on the northwest coast of Ellesmere Island and are composed of three bedrock controlled zones: (1) 900 m undulating plateau dissected by fiords; (2) a deeply fretted cirque terrain >1200m; (3) a 300m plateau bounded by coastal cliffs. Each zone contains different glacier morphologies and these control glacigenic sediment and landform assemblages. The extent of the last glaciation is mapped using the distribution of moraines, kames, meltwater channels and glacimarine sediments. Glaciers advanced on average <10 km from their present margins and many piedmont lobes coalesced and floated in the sea. Morainal banks were deposited at the grounding lines of floating glaciers, and where debris-charged basal ice occurred, subaqueous fans were deposited upon deglaciation. Marine shells dating 20.2 ka BP (<2km from present ice margin) and 14.9ka BP (from a morainal bank) document full glacial marine fauna. Thirty-three radiocarbon dates document glacier retreat patterns and are used to reconstruct the postglacial sea level history (glacioisostatic rebound pattern). An equidistant shoreline diagram is constructed using the 8.5ka BP shoreline as a guide. Tilts from 0.73-0.85m/km are calculated for this shoreline. Using two firm control points and tilts from elsewhere on northern Ellesmere Island, the 10.1 ka BP (full glacial) marine limit descends from 117m as at the fiord heads to 63 m asl at the north coast. Deglaciation started with a pronounced calving phase throughout the field area between 10.1 and 7.8ka BP. This chronology is similar to that from northeast Ellesmere Island and attests to an early Holocene warming trend recorded in high arctic ice cores. A maximum lag of 2.1 ka exists between the field area and locations to the south of the Grant Land Mountains suggesting differences in glacioclimatic regimes on either side of the mountain range. Persistent reconstructions of all-pervasive ice sheets for the last glaciation of the area are obsolete and should be abandoned.  相似文献   

3.
以渤海湾西岸现代岸线附近的NP3、CH110和BT113三个钻孔全新世岩心为研究对象,采用沉积岩石学、AMS 14C(accelerator mass spectrometry 14C,加速器质谱14C)测年、微体生物聚类分析等方法精细判别沉积相,重建渤海湾西岸全新世沉积演化历史,并利用微体生物组合分带对水深变化的指示,定量讨论全新世相对海面变化。结果表明:渤海湾西岸全新世受海陆交互作用影响,经历了沼泽-潮滩-浅海-前三角洲-三角洲前缘-三角洲平原环境的演化过程。全新世初始阶段,研究区中部和北部发育沼泽环境,南部未见沉积,与上更新统河流相沉积呈不整合接触。全新世早期,研究区潮滩环境发育。潮滩层厚度约1 m,历时数百至1千余年。至7000 cal BP前后水深增大,研究区进入浅海环境。约6000 cal BP,沿岸南北两端先后进入三角洲过渡环境,中部三角洲环境约开始于1500 cal BP。渤海湾西岸地区全新世的环境演化同时记录了该地区的相对海面变化:约10000 cal BP前后,渤海湾相对海平面已接近21.3~20.4 m。约8000 cal BP,相对海平面介于18.6~17.0 m。约6000 cal BP时相对海平面低于6.8 m,5000~1000 cal BP,相对海平面高于-2.5 m,1000~800 cal BP,相对海平面介于-1.3~-0.4 m。8000~5000 cal BP时,相对海面上升约15.0 m,上升速率达5 m/1 ka。  相似文献   

4.
Recessional positions of the Newfoundland ice sheet 14-9 ka BP are represented by fjord-mouth submarine moraines, fjord-head emerged ice-contact marine deltas, and inland moraine belts. The arcuate submarine moraines have steep frontal ramparts and comprise up to 80 m of acoustically incoherent ice-contact sediment (or till) interfingered distally with glaciomarine sediment that began to be deposited c. 14.2 ka BP. The moraines formed by stabilization of ice that calved rapidly back along troughs on the continental shelf. The ice front retreated to fjord-heads and stabilized to form ice-contact delta terraces declining in elevation westward from +26 m to just below present sea level. Stratified glaciomarine sediments accumulated in fjords, while currents outside fjords eroded the upper part of the glaciomarine deposits, forming an unconformity bracketed by dates of 12.8 and 8.5 ka BP. The delta terraces are broadly correlated with the 12.7 ka BP Robinson's Head readvance west of the area. The ice front retreated inland, pausing three or four times to form lines of small bouldery stillstand moraines, heads of outwash, sidehill meltwater channels, and beaded eskers. Lake-sediment cores across this belt yield dated pollen evidence of three climatic reversals to which the moraines are equated: the Killarney Oscillation c. 11.2 ka BP, the Younger Dryas chronozone 11.0-10.4 ka BP, and an unnamed cold event c. 9.7 ka BP. Relative sea level fell in the early Holocene because of crustal rebound, so that outwash and other alluvium accumulated in deltas now submerged due to relative sea-level rise.  相似文献   

5.
This study presents a detailed reconstruction of the sedimentary effects of Holocene sea‐level rise on a modern coastal barrier system. Increasing concern over the evolution of coastal barrier systems due to future accelerated rates of sea‐level rise calls for a better understanding of coastal barrier response to sea‐level changes. The complex evolution and sequence stratigraphic framework of the investigated coastal barrier system is reconstructed using facies analysis, high‐resolution optically stimulated luminescence and radiocarbon dating. During the formation of the coastal barrier system starting 8 to 7 ka rapid relative sea‐level rise outpaced sediment accumulation. Not before rates of relative sea‐level rise had decreased to ca 2 mm yr?1 did sediment accumulation outpace sea‐level rise. From ca 5·5 ka, rates of regionally averaged sediment accumulation increased to 4·3 mm yr?1 and the back‐barrier basin was filled in. This increase in sediment accumulation resulted from retreat of the barrier island and probably also due to formation of a tidal inlet close to the study area. Continued transgression and shoreface retreat created a distinct hiatus and wave ravinement surface in the seaward part of the coastal barrier system before the barrier shoreline stabilized between 5·0 ka and 4·5 ka. Back‐barrier shoreline erosion due to sediment starvation in the back‐barrier basin was pronounced from 4·5 to 2·5 ka but, in the last 2·5 kyr, barrier sedimentation has kept up with and outpaced sea‐level. In the last 0·4 kyr the coastal barrier system has been prograding episodically. Sediment accumulation shows considerable variation, with periods of rapid sediment deposition and periods of non‐deposition or erosion resulting in a highly punctuated sediment record. The study demonstrates how core‐based facies interpretations supported by a high‐resolution chronology and a well‐documented sea‐level history allow identification of depositional environments, erosion surfaces and hiatuses within a very homogeneous stratigraphy, and allow a detailed temporal reconstruction of a coastal barrier system in relation to sea‐level rise and sediment supply.  相似文献   

6.
The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).  相似文献   

7.
Based on geological and archaeological proxies from NW Russia and NE Estonia and on GIS‐based modelling, shore displacement during the Stone Age in the Narva‐Luga Klint Bay area in the eastern Gulf of Finland was reconstructed. The reconstructed shore displacement curve displays three regressive phases in the Baltic Sea history, interrupted by the rapid Ancylus Lake and Litorina Sea transgressions c. 10.9–10.2 cal. ka BP and c. 8.5–7.3 cal. ka BP, respectively. During the Ancylus transgression the lake level rose 9 m at an average rate of about 13 mm per year, while during the Litorina transgression the sea level rose 8 m at an average rate of about 7 mm per year. The results show that the highest shoreline of Ancylus Lake at an altitude of 8–17 m a.s.l. was formed c. 10.2 cal. ka BP and that of the Litorina Sea at an altitude of 6–14 m a.s.l., c. 7.3 cal. ka BP. The oldest traces of human activity dated to 8.5–7.9 cal. ka BP are associated with the palaeo‐Narva River in the period of low water level in the Baltic basin at the beginning of the Litorina Sea transgression. The coastal settlement associated with the Litorina Sea lagoon, presently represented by 33 Stone Age sites, developed in the area c. 7.1 cal. ka BP and existed there for more than 2000 years. Transformation from the coastal settlement back to the river settlement indicates a change from a fishing‐and‐hunting economy to farming and animal husbandry c. 4.4 cal. ka BP, coinciding with the time of the overgrowing of the lagoon in the Narva‐Luga Klint Bay area.  相似文献   

8.
The history of sea‐level change and sediment accumulation since the last deglaciation along the German North Sea coast is still controversial because of a limitation in the quantity and quality of chronological data. In the current study, the chronology of a 16‐ka coastal sedimentary record from the Garding‐2 core, retrieved from the Eiderstedt Peninsula in Schleswig‐Holstein, northern Germany, was established using OSL and AMS 14C dating techniques. The robust chronology using 14 radiocarbon and 25 OSL dates from the Garding‐2 core is the first long‐term record that covers the Holocene as well as the last deglaciation period in one succession in the German North Sea area. It provides a new insight into understanding the Holocene transgression and coastal accumulation histories. The combined evidence from the sedimentology and chronology investigations indicates that an estuarine environment dominated in Eiderstedt Peninsula from 16 to 13 ka, followed by a depositional hiatus between 13 and 8.3 ka, attributed to erosion caused by the Holocene transgression; the onset of the Holocene transgression at the core site occurred at around 8.3 ka. The sea level continued to rise with a decelerated rate until around 3 ka. Since 3 ka, the shoreline has begun to prograde. Foreshore (tidal flat) sediments have been deposited at the drilling site with a very high sedimentation rate of about 10 m ka?1. At around 2 ka, a sandy beach deposit accumulated in the sedimentary succession, indicating that the coastline shifted landward, which may represent a small‐scale transgression in the late Holocene. At around 1.5 ka, terrestrial clastic sediment started to accumulate, indicating a retreat of the relative sea level in this area, which may be related to local diking activities undertaken since the 11th century.  相似文献   

9.
This paper presents an overview of the evolution of the Nile deep‐sea turbidite system during the last 200 kyr, over a series of glacial to interglacial cycles. Six individual deep‐sea fans were identified from an extensive field data set. Each fan comprises a canyon, channel system and terminal lobes. Two of these fan systems were possibly active at the same time, at least during some periods. Large‐scale slope failures destroyed channel segments and caused the formation of new submarine fan systems. These slope failures thus played an important role in the overall evolution of the turbidite system. During the last glacial maximum (ca 25 to 14·8 ka) the central and eastern parts of the Nile deep‐sea turbidite system were relatively inactive. This inactivity corresponds to a lowstand in sea‐level, and a period of arid climate and relatively low sediment discharge from the Nile fluvial system. Rapid accumulation of fluvial flood‐derived deposits occurred across the shallower part of the submarine delta during sea‐level rise between ca 14·8 and 5 ka. The most recent deep‐sea channel–lobe system was very active during this period of rising sea‐level, which is also associated with a wetter continental climate and increased sediment and water discharge from the Nile. Increased sediment deposition in shallower water areas led to occasional large‐scale slope failure. The Nile deep‐sea turbidite system was largely inactive after ca 5 ka. This widespread inactivity is due to retreat of the coastline away from the continental shelf break, and to a more arid continental climate and reduced discharge of sediment from the Nile. The Nile deep‐sea turbidite system may be more active during periods of rising and high sea‐level associated with wetter climates, than during lowstands, and may rapidly become largely inactive during highstands in sea‐level coupled with arid periods. These acute responses to climate change have produced sedimentary/stratigraphic features that diverge from traditional sequence models in their nature and timing. This large‐scale sedimentary system responded to monsoon‐driven climate change and sea‐level change in a system‐wide and contemporaneous manner.  相似文献   

10.
渤海湾西岸BT113孔35ka以来的沉积环境演化与海陆作用   总被引：1，自引：0，他引：1  
根据渤海湾西岸有孔虫和介形虫与年代学(AMS14C和OSL测年)研究,将该段岩心自下而上划分为6个沉积单元(U1—U6),它们依次形成于晚更新世的河流及全新世的潮滩、浅海、前三角洲、三角洲前缘和三角洲平原沉积环境,结束于约35 ka的U1单元的陆相环境,证实晚更新世低海面时渤海湾西岸未受海水影响。U1和U2单元之间,存在历时约27 ka的沉积间断(35～8.5 ka cal BP),研究区因此缺失早全新世沉积。U2单元的潮滩环境指示全新世海侵于8.5 ka cal BP到达渤海湾西岸,当时相对海平面为-16.7 m。U3单元为浅海环境,约6 ka cal BP时相对海平面上升到-6.8～-1.8 m。8.5～6 ka cal BP期间的海面上升速率是0.4～0.6 cm/a,可能与MWP1C事件有关。U4—U5单元,转为三角洲环境,沉积速率增大,反映自3.7 ka cal BP河流输入影响加强,约1.3 ka cal BP时成陆,形成U6单元。晚更新世35 ka以来的陆海环境演化,总体上是对气候变化控制下的海面变化的响应。  相似文献   

11.
Clastic, depositional strandplain systems have the potential to record changes in the primary drivers of coastal evolution: climate, sea‐level, and the frequency of major meteorological and oceanographic events. This study seeks to use one such record from a southern Brazilian strandplain to highlight the potentially‐complex nature of coastal sedimentological response to small changes in these drivers. Following a 2 to 4 m highstand at ca 5·8 ka in southern Brazil, falling sea‐level reworked shelf sediment onshore, forcing coastal progradation, smoothing the irregular coastline and forming the 5 km wide Pinheira Strandplain, composed of ca 500 successive beach and dune ridges. Sediment cores, grab samples and >11 km of ground‐penetrating radar profiles reveal that the strandplain sequence is composed of well‐sorted, fine to very‐fine quartz sand. Since the mid‐Holocene highstand, the shoreline prograded at a rate of ca 1 to 2 m yr?1 through the deposition of a 4 to 6 m thick shoreface unit; a 1 to 3 m thick foreshore unit containing ubiquitous ridge and runnel facies; and an uppermost beach and foredune unit. However, the discovery of a linear, 100 m wide barrier ridge with associated washover units, a 3 to 4 m deep lagoon and 250 m wide tidal inlet within the strandplain sequence reveals a period of shoreline transgression at 3·3 to 2·8 ka during the otherwise regressive developmental history of the plain. The protected nature of Pinheira largely buffered it from changes in precipitation patterns, wave energy and fluvial sediment supply during the time of its formation. However, multiple lines of evidence indicate that a change in the rate of relative sea‐level fall, probably due to either steric or ice‐volume effects, may have affected this coastline. Thus, whereas these other potential drivers cannot be fully discounted, this study provides insights into the complexity of decadal‐scale to millennial‐scale coastal response to likely variability in sea‐level change rates.  相似文献   

12.
Late Quaternary landscape development along the Rancho Marino coastal range front in the central‐southern Pacific Coast Ranges of California has been documented using field mapping, surveying, sedimentary facies analysis and a luminescence age determination. Late Quaternary sediments along the base of the range front form a single composite marine terrace buried by alluvial fans. Marine terrace sediments overlie two palaeoshore platforms at 5 m and 0 m altitude. Correlation with the nearby Cayucos and San Simeon sites links platform and marine terrace development to the 125 ka and 105 ka sea‐level highstands. Uplift rate estimates based on the 125 ka shoreline angle are 0.01–0.09 m ka?1 (mean 0.04 m ka?1), and suggest an increase in regional uplift along the coast towards the NW where the San Simeon fault zone intersects the coastline. Furthermore, such low rates suggest that pre‐125 ka uplift was responsible for most of the relief generation at Rancho Marino. The coastal range front landscape development is, thus, primarily controlled by post 125 ka climatic and sea‐level changes. Post 125 ka sea‐level lowering expanded the range front piedmont area to a width of 7.5 km by the 18 ka Last Glacial Maximum lowstand. This sea‐level lowering created space for alluvial fan building along the range front. A 45 ± 3 ka optically stimulated luminescence (OSL) age provides a basal age for alluvial fan building or marks the time by which distal alluvial fan sedimentation has reached 300 m from the range front slope. Fan sedimentation is related to climatic change, with increased sediment supply to the range front occurring during (1) glacial period cold stage maxima and/or (2) the Late Pleistocene–Holocene transition, when respective increases in precipitation and/or storminess resulted in hillslope erosion. Sea‐level rise after the 18 ka lowstand resulted in range front erosion, with elevated localised erosion linked to the higher relief and steeper slopes in the SE. This study demonstrates that late Quaternary coastal range front landscape development is driven by interplay of tectonics, climatic and sea‐level change. In areas of low tectonic activity, climatic and sea‐level changes dominate coastal landscape development. When the sea‐level controlled shoreline is in close proximity to the coastal range front, localised patterns of sedimentation and erosion are passively influenced by the pre‐125 ka topography. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

13.
末次冰消期以来东海内陆架古环境演化   总被引：18，自引：2，他引：16  
通过对位于浙—闽沿岸泥质带的EC2005孔岩性、粒度以及AMS14C年代分析,探讨了研究区自末次冰消期以来的古沉积环境演化,认为是湖水或海水深度、气候变化等综合影响的结果。岩芯底部60.20～41.00 m（17.3～13.1 ka BP）为湖泊三角洲沉积序列,可划分为前三角洲—三角洲前缘—三角洲平原三个沉积亚相,物质来源主要是湖盆流域物质的输入。随着海平面的逐渐上升,海水自13.1 ka BP开始侵入研究区,形成了41.00 m的海相沉积地层,可划分为前滨—近滨—浅海三个沉积亚相,与海平面变化曲线具有良好的对应。自12.3 ka BP开始,研究区受到沿岸流影响,长江物质开始影响研究区,7.3 ka BP以来主要是来自长江的悬浮体在沿岸流作用下输送沉积而形成,稳定的泥质沉积物开始形成。全球性重要气候事件如新仙女木事件、8.2 ka冷事件在东海内陆架沉积物中也得到了良好揭示。  相似文献   

14.
Wagner, B., Bennike, O., Cremer, H. & Klug, M. 2010: Late Quaternary history of the Kap Mackenzie area, northeast Greenland. Boreas, Vol. 39, pp. 492–504. 10.1111/j.1502‐3885.2010.00148.x. ISSN 0300‐9483. The Kap Mackenzie area on the outer coast of northeast Greenland was glaciated during the last glacial stage, and pre‐Holocene shell material was brought to the area. Dating of marine shells indicates that deglaciation occurred in the earliest Holocene, before 10 800 cal. a BP. The marine limit is around 53 m a.s.l. In the wake of the deglaciation, a glaciomarine fauna characterized the area, but after c. one millennium a more species‐rich marine fauna took over. This fauna included Mytilus edulis and Mysella sovaliki, which do not live in the region at present; the latter is new to the Holocene fauna of northeast Greenland. The oldest M. edulis sample is dated to c. 9500 cal. a BP, which is the earliest date for the species from the region and indicates that the Holocene thermal maximum began earlier in the region than previously documented. This is supported by driftwood dated to c. 9650 cal. a BP, which is the earliest driftwood date so far from northeastern Greenland and implies that the coastal area was at least partly free of sea ice in summer. As indicated by former studies, the Storegga tsunami hit the Kap Mackenzie area at c. 8100 cal. a BP. Loon Lake, at 18 m a.s.l., was isolated from the sea at c. 6200 cal. a BP, which is distinctly later than expected from existing relative sea‐level curves for the region.  相似文献   

15.
The stratigraphy of lake Endletvatn on northern Andøya, northern Norway, has been revisited to improve the understanding of the palaeoenvironment in the region during the Last Glacial Maximum (LGM). Four high‐quality cores were analysed with respect to various lithological parameters and macrofossil content, supplemented by 47 AMS radiocarbon dates. The sediments indicate a low‐energy environment with a mean sedimentation rate of 0.5 mm a?1. We infer perennially frozen ground in the surroundings during the LGM. Climate proxies indicate a high arctic climate (i.e. July mean temperatures between 0 and 3°C) throughout most of the LGM. The warmest periods are marked by a rise in seed, moss and animal fossils, and often also by higher organic production in the lake. These periods took place from 21.4 to 20.1, from 18.8 to 18.1, around 17 and from 16.4 cal. ka BP onwards. The shifts between the different climatic regimes occurred rapidly – probably during one or two decades. The present data do not support recently published conclusions stating that Picea, Pinus and Betula pubescens grew on Andøya during parts of the LGM. The highest relative sea level after the final deglaciation on northern Andøya is bracketed between 36 and 38 m a.s.l. It occurred between 21.0 and 20.3 cal. ka BP, peaking around 20.7 cal. ka BP. The final deglaciation of the northern tip of Andøya occurred 22.2 cal. ka BP. Then the western margin of the Andfjorden ice stream receded to the Kjølhaugen Moraine and shortly thereafter to the Endleten Moraine. Our research confirms that northern Andøya is a key location for understanding the natural environment in northwestern Europe during the LGM.  相似文献   

16.
In spite of a widespread distribution, the way in which plateau icefields affect the glaciation and deglaciation of adjacent terrains is not particularly well‐known. This paper aims to identify how the deglaciation of the fjord and plateau terrain of north Norway has influenced the glacial geomorphology and relative sea‐level history of both local and adjacent areas and so serve as a model for interpreting similar areas along the continental margins of northwest Europe and elsewhere. The identification of moraines and their relationships with the Main shoreline of northern Norway allows the margins of the Øksfjordjøkelen, Svartfjelljøkelen and Langfjordjøkelen plateau icefields to be identified in the adjacent terrains. In locations where ice margins are uncertain, it is also possible to reconstruct ice limits by means of glacier models appropriately constrained by known local conditions and dates. Earlier glacier margins, characterised in north Norway by ice shelves floating in the local inlets of major fjords, also can be related to known regional shorelines. The distribution of high shoreline fragments, augmented by radiocarbon dates, helps show the extent to which inter‐island channels and outermost parts of fjords can become deglaciated relatively early in comparison with published maps of regional deglaciation. Plateau‐icefield‐centred glaciation became important sometime after 14 000 14C yr BP and was characterised by glacier readvances up to, and in some locations beyond, earlier moraines and raised marine features. Although overlooked until recently, the identification of the influence of plateau icefields on local glaciation, and their interaction with local and regional marine limits, is of great importance in accurate palaeoenvironmental reconstruction. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
It is shown that sediments accumulated in the Southern Novaya Zemlya Trench at both deglaciation and marine stages. Permanent sea ice sheet existed during the deglaciation, and glacier meltwater was intensely delivered to the bottom layer. Along with the dominant sediment supply from the Southern Island of Novaya Zemlya, southern continental sources also played a noticeable role at that stage. Seasonal sea ice freezing led to the formation of cold brines at the marine stage. Like paleoproductivity, these processes were irregular. Dissolution of calcareous benthic foraminiferal tests considerably intensified after about 7 ka BP owing to a stronger Atlantic water advection into the Western Arctic and consequent increase in paleoproductivity, whereas the relative role of southern sedimentary provenances decreased. Sedimentation rates were constant (45 cm/ka) during the entire marine stage.  相似文献   

18.
Seismostratigraphical studies of the 11.8‐km2‐large and ~140‐m‐deep Lake Bolshoye Shchuchye, Polar Ural Mountains, reveal up to 160‐m‐thick acoustically laminated sediments in the lake basin. Using a dense grid of seismic lines, the spatial and temporal distributions of the sedimentary history have been reconstructed. Three regional seismic horizons have been identified and correlated with the well‐dated 24‐m‐long sediment core retrieved from the lake. Isopach maps constructed from the seismic data show four phases of sedimentation. A contour map of the deepest regional seismic reflector represents the earliest hemipelagic sedimentation in the lake. Three contour maps represent time intervals covering the last 23 cal. ka based on the well‐dated core stratigraphy from the lake. The detailed time constraints on the upper stratigraphical units in the lake allow calculation of the lake's development in terms of sediment fluxes and the denudation rates from the Last Glacial Maximum (LGM) to the present. The sedimentation in Lake Bolshoye Shchuchye has been dominated by hemipelagic processes during at least the last 24 cal. ka BP only locally interrupted by delta progradation and slope processes. A major shift in the sediment accumulation at c. 18.7 cal. ka BP is interpreted to mark the end of the local glacial maximum, greatly reduced denudation and the onset of the deglaciation period; this also demonstrates how fast the glaciers melted and possibly disappeared at the end of the LGM. The denudation rate during the Holocene is only a fifth of the LGM rate. The age of the oldest stratified sediments in Lake Bolshoye Shchuchye is not well constrained, but estimated as c. 50–60 ka.  相似文献   

19.
Knowledge of the glaciation of central East Iceland between 15 and 9 cal. ka BP is important for the understanding of the extent, retreat and dynamics of the Icelandic Ice Sheet. Crucially, it is not known if the key area of Fljótsdalur‐Úthérað carried a fast‐flowing ice stream during the Last Glacial Maximum; the timing and mode of deglaciation is unclear; and the history and ages of successive lake‐phases in the Lögurinn basin are uncertain. We use the distribution of glacial and fluvioglacial deposits and gradients of former lake shorelines to reconstruct the glaciation and deglaciation history, and to constrain glacio‐isostatic age modelling. We conclude that during the Last Glacial Maximum, Fljótsdalur‐Úthérað was covered by a fast‐flowing ice stream, and that the Lögurinn basin was deglaciated between 14.7 and 13.2 cal. ka BP at the earliest. The Fljótsdalur outlet glacier re‐advanced and reached a temporary maximum extent on two separate occasions, during the Younger Dryas and the Preboreal. In the Younger Dryas, about 12.1 cal. ka BP, the outlet glacier reached the Tjarnarland terminal zone, and filled the Lögurinn basin. During deglaciation, a proglacial lake formed in the Lögurinn basin. Through time, gradients of ice‐lake shorelines increased as a result of continuous but non‐uniform glacio‐isostatic uplift as the Fljótsdalur outlet glacier retreated across the Valþjófsstaður terminal zone. Changes in shoreline gradients are defined as a function of time, expressed with an exponential equation that is used to model ages of individual shorelines. A glaciolacustrine phase of Lake Lögurinn existed between 12.1 and 9.1 cal. ka BP; as the ice retreated from the basin catchment, a wholly lacustrine phase of Lake Lögurinn commenced and lasted until about 4.2 cal. ka BP when neoglacial ice expansion started the current glaciolacustrine phase of the lake.  相似文献   

20.
YQ0902孔位于浙江南部瓯江三角洲南侧温瑞平原上。沉积相、粒度分析以及AMS 14C测年数据表明,硬土层之下为海洋氧同位素3阶段(MIS 3）形成的潟湖相沉积,据此推测MIS 3高海平面至少达到现今海平面之下30m左右(未经构造升降和沉积物压实作用等影响的校正,下同）。硬土层的成土过程发生于MIS 2,其母质部分为MIS 3的潟湖沉积,部分为河漫滩沉积。硬土层之上是一套形成于全新世的海侵—海退旋回,与长江三角洲南翼前缘的沉积相组合类似。研究钻孔初始海泛面约形成于9 cal ka BP,推算当时的海平面约低于现今海平面25 m。中全新世最大海侵前后,东亚季风较强,通过径流或沿岸流输入本区的沉积物较充足,沉积速率较大。随着海平面相对稳定或略有下降,东亚季风减弱,可容空间减小,中晚全新世(5～2 cal ka BP）沉积速率较低。高分辨率的XRF岩心扫描获得的元素相对含量是古环境与古气候研究的重要指标,其中Cl/Ti、Fe/Ti值可分别作为海相性(与海洋联通程度）与东亚季风强弱的替代指标。  相似文献   

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