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In the late Wisconsinan, the South Thompson River valley, British Columbia, was occupied by an ice-dammed lake. After the lake drained, the exposed lacustrine silt became the source material for a Holocene loess. The purpose of this paper is to establish the stratigraphic, depositional and geomorphic framework of loess occurring along the South Thompson River valley immediately east of Kamloops, British Columbia. This montane environment of loess deposition was characterised by active slope and fluvial processes depositing sediments contemporaneously with the accumulation of loess. The loess reaches an average of 4 m in thickness in the central part of the valley and thins towards the valley sides. Two tephras—Mount St Helens Y (3.4 ka) and Mount Mazama (6.8 ka)— occur in the loess and are invaluable stratigraphic markers. Most of the loess was probably deposited between 8.2 ka and 3.4 ka, a period coinciding with mid-Holocene increased summer temperatures and decreased precipitation in south-central British Columbia. Debris flows and small streams, originating on the valley sides, flowed out on to the loess depositing sand and gravel beds. These deposits form a definite proximal—distal relation across valley with the slope-derived sediments decreasing and the loess increasing in thickness towards the centre of the valley. The lactustrine silt particles were mobilised by diurnal mountain and valley, gravity, and canalised winds flowing within the South Thompson valley. An analysis of contemporary wind-flow data was undertaken to provide a possible analogue for valley wind flows in the mid-Holocene. 相似文献
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Eolian sediments are common within the middle Gila River Valley, southern Arizona, and reflect variability in eolian and fluvial processes during the late Holocene. This study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration (SAR) protocols. Stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca. 3145 ± 220 yr, 1950-1360 yr, 800 ± 100 yr, and 690-315 yr. This nascent chronology, correlated with regional archeological evidence and paleoclimate proxy datasets, leads to two general conclusions: (1) loess deposits, transverse-dune formation and sand-sheet deposition in the late Holocene are probably linked to flow variability of the Gila River, though the last two events are concordant with regional megadroughts; and (2) the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision, resulting in Entisol formation on dunes. The prime catalyst of eolian activity during the late Holocene is inferred to be sediment supply, driven by climate periodicity and variable flow within the Gila River catchment. 相似文献
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《Quaternary Science Reviews》2003,22(18-19):1947-1986
Loess is one of the most widespread subaerial deposits in Alaska and adjacent Yukon Territory and may have a history that goes back 3 Ma. Based on mineralogy and major and trace element chemistry, central Alaskan loess has a composition that is distinctive from other loess bodies of the world, although it is quartz-dominated. Central Alaskan loess was probably derived from a variety of rock types, including granites, metabasalts and schists. Detailed stratigraphic data and pedologic criteria indicate that, contrary to early studies, many palaeosols are present in central Alaskan loess sections. The buried soils indicate that loess sedimentation was episodic, or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input. As in China, loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess/soil formation cycle. Loess deposition in central Alaska took place before, and probably during the last interglacial period, during stadials of the mid-Wisconsin period, during the last glacial period and during the Holocene. An unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period. Our studies lead us to conclude that vegetation plays a key role in loess accumulation in Alaska. Factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods. The most important of these is vegetation; boreal forest serves as an effective loess trap, but sparsely distributed herb tundra does not. Thus, thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central Alaska. Much of the stratigraphic diversity of North American loess, including that found in the Central Lowlands, the Great Plains, and Alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors. 相似文献
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Lake Houston is a man-made reservoir located northeast of Houston, Texas. The purpose of this investigation was to document
suspended sediment transport, sedimentation, and resuspension in the lake with a view towards estimating the influence of
sedimentation on water quality. Sediment traps were placed in strategic locations in the lake to collect suspended sediments.
Samples were analyzed for bulk density, grain size, organic carbon, and a number of trace elements. These data were analyzed
along with meteorological data to examine those factors which regulate suspended sediment input and dispersal, and the role
of suspended sediments in controlling water quality within the lake.
Sediment input to the lake depends primarily on the intensity of rainfall in the watershed. Sediment movement within the lake
is strongly influenced by wave activity, which resuspends sediments from shallow areas, and by wind-driven circulation. The
increased residence time of suspended sediments due to resuspension allows greater decomposition of organic matter and the
release of several trace elements from sediments to the water column.
Virtually all samples from sediment traps suspended between 1 and 5 m above the lake bottom contain medium to coarse silt,
and even some very fine sand-sized material. This implies that circulation in Lake Houston is periodically intense enough
to transport this size material in suspension. During winter, northerly winds with sustained velocities of greater than 5
m/sec provide the most suitable condition for rapid (<1 d) transport of suspended sediment down the length of the lake.
Fluctuations in current velocities and the subsequent suspension/deposition of particles may explain variations in the abundance
of coliform bacteria in Lake Houston. 相似文献
6.
The Dry Creek archeologic site contains a stratified record of late Pleistocene human occupation in central Alaska. Four archeologic components occur within a sequence of multiple loess and sand layers which together form a 2-m cap above weathered glacial outwash. The two oldest components appear to be of late Pleistocene age and occur with the bones of extinct game animals. Geologic mapping, stratigraphic correlations, radiocarbon dating, and sediment analyses indicate that the basal loess units formed part of a widespread blanket that was associated with an arctic steppe environment and with stream aggradation during waning phases of the last major glaciation of the Alaska Range. These basal loess beds contain artifacts for which radiocarbon dates and typologic correlations suggest a time range of perhaps 12,000–9000 yr ago. A long subsequent episode of cultural sterility was associated with waning loess deposition and development of a cryoturbated tundra soil above shallow permafrost. Sand deposition from local source areas predominated during the middle and late Holocene, and buried Subarctic Brown Soils indicate that a forest fringe developed on bluff-edge sand sheets along Dry Creek. The youngest archeologic component, which is associated with the deepest forest soil, indicates intermittent human occupation of the site between about 4700 and 3400 14C yr BP. 相似文献
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Loess sedimentation in Tibet: provenance,processes, and link with Quaternary glaciations 总被引：2，自引：0，他引：2
《Quaternary Science Reviews》2007,26(17-18):2265-2280
Well-preserved loess deposits are found on the foothills of mountains along the middle reaches of the Yarlung Zangbo River in southern Tibet. Optically stimulated luminescence (OSL) dating is used to determine loess ages by applying the single-aliquot regeneration technique. Geochemical, mineralogical, and granulometric measurements were carried out to allow a comparison between loess from Tibet and the Chinese Loess Plateau. Our results demonstrate that (i) the loess deposits have a basal age of 13–11 ka, suggesting they accumulated after the last deglaciation, (ii) loess in southern Tibet has a “glacial” origin, resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near-surface winds, and (iii) the present loess in the interior of Tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt. The lack of full-glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial. Such processes would have been repeated during each glacial–interglacial cycle of the Quaternary. 相似文献
9.
对青海湖沉积物进行物质来源进行聚类分析, 并对周边风成黄土与现代湖泊表层沉积物进行粒度分析, 在此基础上, 以青海湖周边典型风成黄土作为风成组分端元, 以青海湖表层沉积物作为水成组分端元, 首次利用已知端元的粒度分布特征对青海湖沉积物中典型粒度分布进行拟合, 进而估算了其中风成和水成组分的比例。结果表明, 青海湖沉积物粒度分布特征可分为三大类:1.水成组分占主导; 2.风成组分占主导(风成黄土主导); 3.两者以不同比例混合。希望此方法能成为未来湖泊沉积物中不同组分的定量判据和古环境的解读提供新途径。 相似文献
10.
Grain-size distributions of fluvial, eolian and marine sediments were explicated decades ago. For lake sediments, however, there is still great uncertainty in explaining the genesis of grain-size components due to the inherent complexity of their polymodal distributions. In this study, the grain-size components of the surface sediments of Daihai Lake, Inner Mongolia, were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated. The data indicate that the modern clastic sediments of Daihai Lake contain five distinct unimodal grain-size distributions representing five grain-size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake. These components are specified from fine to coarse modes as long-term suspension clay, offshore-suspension fine silt and medium-to-coarse silt, and nearshore-suspension fine sand and saltation medium sand. The percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed, suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past. The model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core. The coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain-size component–lake level status model for lake’s paleohydrological reconstruction. 相似文献
11.
Many Northern Hemisphere paleoclimatic records, including ice cores, speleothems, lake sediments, ocean cores and glacier chronologies, indicate an abrupt cooling event about 8200 cal yr BP. A new well-dated series of sediment cores taken from Brown's Lake, a kettle in Northeast Ohio, shows two closely spaced intervals of loess deposition during this time period. The source of loess is uncertain; however, it is likely from an abandoned drainage and former glacial lake basin located to the north of the stagnant ice topography that gave rise to the kettle lake. Strong visual stratigraphy, loss on ignition data and sediment grain size analyses dated with 3 AMS radiocarbon dates place the two intervals of loess deposition between 8950 and 8005 cal yr BP. The possibility of a two-phase abrupt climate change at this time is a finding that has been suggested in other research. This record adds detail to the spatial extent and timing as well as possible structure of the 8.2-ka abrupt climate change event. 相似文献
12.
Deglaciation chronology inferred from marine sediments in a proglacial lake basin, western Spitsbergen, Svalbard 总被引：2，自引：0，他引：2
Jan Mangerund John Inge Svendsen 《Boreas: An International Journal of Quaternary Research》1990,19(3):249-272
Sub-bottom sediment profiles and sediment cores show that the lacustrine sediments in lake Linnevatnet are underlain by marine sediments and a basal till that mantles the bedrock. The till was probably deposited by the glacier that during the Late Weichselian glacial maximum removed all pre-existing sediments from the basin. The cores were collected in closed basins, where continuous deposition is expected. The marine sediment in the studied cores is up to 8 m thick and consists of bioturbated clay and silt. Radiocarbon dates on shells from the base of the marine sequence suggest that glacial retreat from the lake basin occurred around 12,500BP. This is more than a thousand years older than basal shell dates from raised marine sediments on the slopes above the lake. Typical ice proximal litbofacies were not identified in the cores. stratigraphic record indicates both a rapid glacial retreat and that no younger glacial re-advances occurred. During the Younger Dryas local glaciers on western Svalbard were smaller than during the Little Ice Age. This is in sharp contrast to western Europe, where Younger Dryas glaciers were much larger than those the Little Ice Age. 相似文献
13.
JON TUNNICLIFFE MICHAEL CHURCH RANDOLPH J. ENKIN 《Boreas: An International Journal of Quaternary Research》2012,41(1):84-101
Tunnicliffe, J., Church, M. & Enkin, R. J. 2012 (January): Postglacial sediment yield to Chilliwack Lake, British Columbia, Canada. Boreas, Vol. 41, pp. 84–101. 10.1111/j.1502‐3885.2011.00219.x. ISSN 0300‐9483. Seismic records and evidence from sediment cores at Chilliwack Lake provide the basis for a long‐term (postglacial) sediment budget for a 324‐km2 Cordilleran catchment. Chilliwack Lake (11.8 km2 surface area), situated in the North Cascade Mountains, near Chilliwack, British Columbia, was formed behind a valley‐wide recessional moraine in the final phase of post‐Fraser alpine glaciation. Seismic surveys highlight the postglacial lacustrine record, which is underlain by a thick layer of sediments related to deglacial sedimentation. Sediment cores provide details of grain‐size fining from the delta to the distal lake basin. The cores also show a record of intermittent fire and debris flows. Magnetic measurements of lake sediments provide information on grain size, as well as a dating framework. The total postglacial lake‐floor deposit volume is estimated to be 397 ± 27 × 106 m3. Including estimates of fan and delta deposition, the specific postglacial yield to the lake is calculated to be ～86 ± 13 Mg km2 a?1. The sediment volume in the uppermost (Holocene) lacustrine layer is 128 ± 9 × 106 m3, representing ～41 ± 4 Mg km2 a?1 in the Holocene. Compared with other Cordilleran lakes of similar size, particularly those with glacial cover in the watershed, Chilliwack Lake has experienced relatively modest rates of sediment accumulation. This study provides an important contribution to a growing database of long‐term (postglacial) sediment yield data for major Cordilleran lakes, essential for advancing our understanding of the pace of landscape evolution in formerly glaciated mountainous regions. 相似文献
14.
Dust transport and the question of desert loess formation 总被引：24，自引：0，他引：24
Although contemporary dust storms are frequent in arid and semi-arid areas, desert loess deposits are poorly developed. Much of the World's loess occurs in mid-latitude areas which experienced glaciation during the Pleistocene. Ocean core evidence indicates that dust transport from sub-tropical deserts increased during cold stages of the Pleistocene, but loess formed only on certain desert margins, for reasons which have not been fully explained. This paper re-examines the mechanisms of dust transport and deposition, and the circumstances leading to the accumulation of thick loess. Typical loess is composed mainly of medium silt grains which are transported in short-term suspension a few metres above the ground. Significant thicknesses of loess form only when dust is trapped within a limited area, often relatively close to the source. Dust particles finer than 20 μm are transported mainly in long-term suspension over a greater height range and may be widely dispersed. The availability of silt and the frequency, magnitude and direction of dust-transporting winds are important factors governing the potential for loess formation, but the existence of a suitable dust trap is particularly important. Traps may be formed by topographic obstacles, areas of moist ground, or vegetated surfaces. Vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid-latitudes during the Pleistocene. Dust blown during glacial periods from certain deserts, notably in Sinai, Soviet Central Asia and China, accumulated as loess in neighbouring semi-arid regions. On the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps. During most of the Holocene net dust deposition rates in all desert-marginal areas have been too low for significant loess accumulation. This is mainly due to a reduction in silt availability and a tendency towards landscape stability. Reported dust storm frequencies during the past 50 years over-estimate the longer-term Holocene dust flux due to the effects of human activities. Much modern dust owes its origin to erosion of cultivated soils in semi-arid areas and is finer than typical loess. 相似文献
15.
Siliciclastic intervals in Lower Permian carbonate–siliciclastic cyclothems in western Kansas record climate control on facies progression, deposition and preservation. The 26 000 km2 study area comprises seven marine‐continental (carbonate–siliciclastic) cyclothems caused by glacioeustasy. Core data and a three‐dimensional geological model provide a detailed view of the sub‐surface on a gently sloping ramp. Siliciclastic intervals in the cyclothems are fine‐grained red beds with extensive pedogenic features, indicating a continental origin. Bed geometry (sheet‐like deposits that thin to the east), lateral grading, grain size (very fine‐grained sand to silt) and grain angularity (sub‐angular to angular) suggest that the sediment is loess sourced from the west, probably the Ancestral Rocky Mountains. There is a repeated record of glacial‐cycle‐scale, climate‐controlled cyclicity within siliciclastic intervals that has not been recognized previously. Aeolian silt grain size coarsens upward towards the middle, then fines upward in each siliciclastic interval. When sea‐level was high (interglacial) and carbonate production flourished, aeolian sedimentation nearly ceased, suggesting increased vegetation and rainfall at the source. As sea‐level fell, fine‐grained siliciclastic sediments were deposited under relatively dry, but seasonally wet conditions on an exposed ramp. Laterally graded coarser grained siliciclastic sediments with diagnostic fabrics indicate drier conditions with seasonal rainfall during a continued relative fall in sea‐level. The coarsest siliciclastic sediments were deposited during the lowest sea‐level and driest conditions, but still with sufficient seasonal moisture to allow vegetative cover and bioturbation. Subsequent upward fining is correlated with sedimentological indications of wetter conditions during relative sea‐level rise. Unlike common sequence stratigraphic models that relate siliciclastic sediment accumulation to base‐level rise, continental deposits were preserved because plants and pedogenesis stabilized aeolian sediment. The aggradational landscape formed by this process had several metres of positive relief that reduced accommodation for overlying marine carbonate strata. Thus, this mechanism for continental siliciclastic aggradation has a significant effect on sequence stratigraphic architecture. 相似文献
16.
通过对花海古湖泊沉积剖面8.42~0.405 m沉积物样品的矿物和化学元素测定,分析了沉积物中盐类矿物含量及化学元素K/Na比值的变化情况,结合已有的年代地层结果,重建了花海古湖泊10.47~5.5 cal ka BP湖水盐度变化. 结果表明：花海湖泊全新世湖相沉积阶段中,除个别层位以硫酸盐类矿物沉积为主外,早全新世(10.47~8.87 cal ka BP)和中全新世(8.87~5.5 cal ka BP)均以碳酸盐盐类矿物沉积为主,并且早全新世时期K/Na高于中全新世时期,揭示了早全新世时期湖水盐度高于中全新世时期. 这一结果与该湖泊沉积过程所揭示的湖泊水位变化、粒度等揭示的有效湿度变化具有一致性,表明花海湖泊早、中全新世湖水盐度的高低可以指示其湖泊水位的变化,并间接反映了有效湿度的变化. 结合花海湖泊晚全新世湖泊萎缩、气候干旱的特点,该区域早、中、晚全新世气候干湿变化变化模式可以概况为早全新世降水增强、气候呈现由干向湿的转变,中全新世有效湿度最大,晚全新世气候干旱. 这种全新世气候干湿变化模式有别于西风区,亦与季风区不完全相同,呈现出了一种季风-西风过渡带全新世气候干湿变化的模式. 相似文献
17.
黄旗海湖泊沉积记录的早中全新世大湖期环境的差异性 总被引：2，自引：0，他引：2
内蒙古黄旗海H6剖面揭示了最近间冰期古湖泊涨缩的一个完整旋回。基于OSL年代、粒度并结合沉积物地球化学等数据,分析了黄旗海在早、中全新世（约（11.4±1.1～6.7±0.7）ka）大湖期指标记录特点与环境意义。研究认为黄旗海全新世大湖期可分为三个阶段:1）（11.4±1.1～9.3±0.9） ka BP,半深水环境、湖水盐度低、流域存在有利于化学风化的湿润气候条件;2）（9.3±0.9～7.7±0.7） ka BP,湖水变浅、湖泊萎缩、湖泊盐度升高,流域可能存在不利于化学风化的干燥气候;3）（7.7±0.7～6.7±0.7） ka BP,大湖期结束,指标记录存在剧烈波动,揭示气候具有宽幅震荡特征。同时,研究初步认为Mn/Li比值可以作为流域化学风化的指标指示。 相似文献
18.
Basin evolution and palaeoenvironmental variability of the thermokarst lake El'gene‐Kyuele,Arctic Siberia 
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下载免费PDF全文 Philipp Schleusner Boris K. Biskaborn Frank Kienast Juliane Wolter Dmitry Subetto Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2015,44(1):216-229
Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene‐Kyuele in the NE Siberian Arctic (latitude 71°17′N, longitude 125°34′E). The water‐body displays thaw‐lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5‐m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ～7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ～0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin. 相似文献
19.
稳定湖相沉积物和风成黄土粒度判别函数的建立及其意义 总被引：10，自引：2，他引：8
沉积物粒度变化主要受搬运介质、搬运方式、沉积环境和气候等多种因素的控制,通过粒度分析可判别沉积物的成因类型,推断其形成的沉积环境,解释环境演变。利用统计学方法对典型稳定湖相沉积物（罗布泊湖相样品２８２块,岱海湖相样品１２３块）和典型风成黄土（甘肃兰州榆中样品２６３块）粒度参数进行定量化分析,并经稳定湖相和风成沉积物验证,获得稳定湖相与风成沉积物的判别公式:Ｆ（湖相、风成沉积物） ＝２０．３６３Ｍｚ－５６．３７１Ｓｄ－６７．９２２Ｓｋ＋２３．５１６Ｋｇ－５５．６２６,若Ｆ＞０,为稳定湖相沉积物,反之,Ｆ＜０,则为风成沉积物。这为研究地史中稳定湖泊与风成环境 沉积物的鉴别提供粒度分析定量化判别方法,它对陆相古环境、干旱化事件和尘暴事件等研究具有十分重要的借鉴价值。 相似文献
20.
The Grande Prairie region of northwestern Alberta was partially covered by glacial Lake Peace, which was dammed against the retreating Laurentide ice sheet. Two levels of glacial Lake Peace are identified in the study are by closely spaced groups of strandlines and minor deltas lying at 805 to 840 m a. s. l., and 655 to 710 m a.s.l. Sedimentation associated with the upper of the two lake levels is marked by rhythmites of silt and clay deposited by turbid underflow, interbedded with diamicton deposited by debris flow. Dropstones and dump structures indicate common ice-rafting. Thick sequences are only found on the axes of major valleys, where sediment gravity flows were concertrated. Thin sequences of ice proximal glaciolacustrine sediments reflect topographic setting and do not indicate a short-lived lake. Retreat of the ice front resulted in a decrease in ice-rafted material and diamicton in sediments. The fall in lake level to the second stage resulted in deposition of sequences of vaguely laminated silt and clay close to the modern Beaverlodge River. These sediments were deposited by suspension settling from interflow or overflow of the Beaverlodge River as it entered the lake. Lake sedimentation was dominated by inflow from unglaciated areas, rather than the ice front. 相似文献