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1.
Frost-cracking and ice-wedge growth are fundamental processes within the permafrost environment. Extensive areas of contemporary permafrost terrain are characterised by frost-fissure polygons, formed by repeated thermal contraction-cracking of the ground. The incremental growth of ice veins and wedges along the axes of contraction-cracks contributes significantly to the volume of ground ice in near-surface permafrost. In areas beyond the present limit of permafrost, the recognition of ice-wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions. An understanding of the processes of ice-wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for Pleistocene frost-fissure structures, in palaeoenvironmental reconstructions. 相似文献
2.
土楔和冰楔假形及其古气候意义 总被引：1，自引：0，他引：1
由于土楔及冰楔所处冻土的含冰状况不同,二者对冻土退化的响应不同。土楔的形状及大小乃至其中的充填物可以完整地保存下来,而冰楔在融化过程中经受强烈变形,其原形状很难保存下来,以至无法辨认。已报道的冰楔假形中,有相当部分可能是原生土脉,甚至是活动层土楔。冰楔在多年冻土环境下生长,其假形可以指示古冻土曾存在过。但它与温度之间没有简单的对应关系,因为楔形构造的形成是地-气综合因素相互作用之结果。土楔可以是原生的,也可以是次生的,它与多年冻土环境并无必然联系。 相似文献
3.
4.
Syngenetic ice wedges have been investigated on Ayon Island. Their isotope composition and the geochemical characteristics of both ice wedges and enclosing sediments have been obtained; four ice-wedge stages have been distinguished. Paleo temperature reconstructions for Ayon Island and adjacent territories of northern Chukotka have been obtained based of these results. Almost identical trends in the distribution of ice-wedge isotope characteristics in the Arctic islands and in the lower reaches of the Kolyma River were observed, as well as differences in the magnitude of isotope oscillations during the transition from the Late Pleistocene to the Holocene compared to ice wedges of the Lower Kolyma region. 相似文献
5.
Robert F. Black 《Quaternary Research》1976,6(1):3-26
Ice wedges are wedge-shaped masses of ice, oriented vertically with their apices downward, a few millimeters to many meters wide at the top, and generally less than 10 m vertically. Ice wedges grow in and are confined to humid permafrost regions. Snow, hoar frost, or freezing water partly fill winter contraction cracks outlining polygons, commonly 5–20 m in diameter, on the surface of the ground. Moisture comes from the atmosphere. Increments of ice, generally 0.1–2.0 mm, are added annually to wedges which squeeze enclosing permafrost aside and to the surface to produce striking surface patterns. Soil wedges are not confined to permafrost. One type, sand wedges, now grows in arid permafrost regions. Sand wedges are similar in dimensions, patterns, and growth rates to ice wedges. Drifting sand enters winter contraction cracks instead of ice. Fossil ice and sand wedges are the most diagnostic and widespread indicators of former permafrost, but identification is difficult. Any single wedge is untrustworthy. Evidence of fossil ice wedges includes: wedge forms with collapse structures from replacement of ice; polygonal patterns with dimensions comparable to active forms having similar coefficients of thermal expansion; fabrics in the host showing pressure effects; secondary deposits and fabric indicative of a permafrost table; and other evidence of former permafrost. Sand wedges lack open-wedge, collapse structures, but have complex, nearly vertical, crisscrossing narrow dikelets and fabric. Similar soil wedges are produced by wetting and drying, freezing and thawing, solution, faulting, and other mechanisms. Many forms are multigenetic. Many socalled ice-wedge casts are misidentified, and hence, permafrost along the late-Wisconsinan border in the United States was less extensive than has been proposed. 相似文献
6.
PETER WORSLEY 《Boreas: An International Journal of Quaternary Research》1999,28(4):543-550
Massive ice incorporating till beds and scattered erratic clasts exposed in a bimodal thaw slide displayed an association with the surrounding fluvioglacial and flow-till facies indicative of a consanguineous relationship. The massive ice cores a low ridge interpreted as a recessional moraine feature paralleling the Last Glacial Maximum advance limit. Both ice and sand wedges penetrate the massive ice and their tops are truncated by a thaw unconformity overlain by a diamicton. In a permafrost environment, relict glacial ice can persist for many millennia, and the timing of the thaw is largely determined by the vagaries of erosional processes. The age of related kettle landforms can display considerable diachronism. 相似文献
7.
Robert F. Black 《Quaternary Research》1983,20(1):74-89
Since 1965, ice-wedge casts have been reported in deposits of sand and gravel in Connecticut. These are wedge forms up to 1.1 m wide and many meters high. Most are single forms, not in polygonal array. They are found in adjoining states as well. Their distribution, dimensions, structure, and fabric and an assessment of the former physical environment preclude their origin as permafrost features. They appear to be tension fractures produced by the loading of coarse clastics on fine clastics near and below the water table where sediments creep toward a stream or depression. Locally movement started with kettle formation during deglaciation. However, some wedges cut horizontal layers of iron-coated sand and gravel and must be younger than those distinctly postglacial phenomena. Moreover, modern B horizons of the overlying soil have moved down into some wedges more than 2 m, indicating that fracturing is still active today. Complex fracture fillings in bedrock also have been attributed to a permafrost origin, but this too seems unlikely. 相似文献
8.
成都平原第四纪化石冰楔的发现及古气候意义 总被引：5，自引：0，他引：5
最近,在成都平原西缘,大邑城西氮肥厂附近,斜江河西岸,上新统-下更新统大邑砾岩剖面的北端新开挖的露头上,发现了4条化石冰楔。这里的地理坐标是30°35'N103°31'E,海拔530m.这些冰楔发育于大邑砾岩露头的顶部。其中最大的一条,顶部宽3m,向下延伸2.5m.这些冰楔垂直向下延伸,与大邑砾岩层面斜交。所以,它们是在大邑砾岩沉积之后并经过构造变动后形成的,是大邑砾岩的后生冰楔。化石冰楔的充填物的特征与大邑砾岩有明显差别:前者为棕黄色,后者为灰白-黄色;前者砾径分选较好,砾径较细,一般长5cm~15cm,而后者砾径分选较差,粗大者20cm~30cm;前者的砾石含量高,约95%,后者的砾石含量低,约85%;前者砾石ab面产状无优势方向,而后者的ab面产状显示优势方向,倾向170°~210°,倾角30°~40°.由于两者有上述差别,所以,化石冰楔在露头上可以被识别出来。采用ESR法测定冰楔充填物的时代为0.171Ma.由此看来,这些冰楔的形成时代可能相当于V28-238深海岩心氧同位素曲线第6气候期(0.195Ma~0.128Ma),也可与中国黄土L2~5(0.195Ma~0.180Ma)和L2~4(0.180Ma~0.167Ma)所记录的气候波动和青藏高原倒数第二次冰期对比。一般认为,冰楔是多年冻土的指示器,所以这些化石冰楔反映了成都平原在第四纪曾一度发育多年冻土。据研究,冰楔只能形成于年均温<-6℃的地方,高海拔多年冻土下界大致与-2℃~-4℃年均等温线相符。现今,大邑附近年均温约16℃.那么,化石冰楔形成时期,成都平原年均温至少比现今下降了18℃. 相似文献
9.
冰楔假型是反映古气候环境的重要标志,其蕴涵的气候地层信息对地貌演化过程具有重要的指示意义。通过对黄土高原北缘中部环江T1阶地上新发现的冰楔假型群特征的研究和光释光(OSL)测年,结果显示这些发育在冲积砂砾石中的冰楔假型的充填砂体的年代为 (30.01±3.31) ka B.P.,形成环境推测当时的年平均地温比现今要低17.7 ℃。该冰楔假型的发现也为末次冰期阶段性冻土南界的位置和变迁提供了证据。另外,据冰楔与阶地冲积物的关系推测,在冰楔形成的冰冻期河流阶地的堆积缓慢甚至停滞,在(28.64±3.13) ka B.P.之后的气候温暖期河流快速下切、T1阶地形成。这为河流阶地成因机制的探讨提供了依据,反映了气候波动对阶地发育的控制。 相似文献
10.
Stable isotope composition of syngenetic and epigenetic ice wedges, radiocarbon age, and pollen spectra of the surrounding deposits were studied during long term investigations at the "Belyi Klyuch" site on the first(6-8 m height) terrace of the Chara River(720 m.a.s.l.) in northern Transbaikalia to assess climatic conditions during ice-wedge formation. It was revealed that Holocene ice wedges had been formed from 10 to 7.5 ka 14 C BP. The isotope composition(δ~(18)O, δ~2 H) of relict ice wedges is the lightest and amounts-23‰ and-185‰, correspondingly. The isotopic compositions of ice lenses from sandy loam above ice wedges are-15.7‰, and-133‰; of small ice wedge in peat and sand are-15.3‰ and-117.9‰, accordingly.Interpretation of the ice wedge isotope composition has yielded that mean winter temperatures during cold stages of Holocene optimum were lower than today, during warm stages they were close to modern ones. During the coldest stages of Holocene optimum the total annual freezing index varied from-5100 to-5700 ℃ degree days, i.e. 300-600 ℃ degree days colder than during extremely severe modern winters. The total annual thawing index varied from 1300 to 1800 ℃ degree days, which was slightly higher than modern ones. 相似文献
11.
Szabolcs Ákos Fábián János Kovács Gábor Varga György Sipos Zoltán Horváth Edit Thamó‐Bozsó Gábor Tóth 《Boreas: An International Journal of Quaternary Research》2014,43(3):722-732
Wedge structures and involutions suggest that Late Pleistocene frozen ground, either permafrost or deep seasonal frost, extended at least as far south as latitude 47°N in central Europe (the Pannonian Basin). Optically stimulated luminescence dating of the sand infill from a number of wedges indicates that emplacement of the sand infill occurred during the Late Pleistocene (22.2–15.7 ka). This suggests that during this time the mean annual air temperature was depressed by at least ～15°C relative to the present. Either continuous or discontinuous permafrost was probably present in the north and NW of the Pannonian Basin. The subsequent thaw of frozen ground is indicated by the widespread occurrence of deformed sediments. The presence of soil (ground) wedges suggests conditions of deep seasonal frost probably existed during the period when climate ameliorated following the Last Permafrost Maximum (LPM). 相似文献
12.
N. J. Rowlands P. G. Blight D. M. Jarvis C. C. von der Borch 《Australian Journal of Earth Sciences》2013,60(1-2):55-68
We have reconstructed the depositional environment of sulphate‐dolomite‐sand‐mud sequences of the Callanna Beds of the late Proterozoic Adelaidean System in three areas of the Willouran Ranges, South Australia. We interpret the Callanna Beds which represent the earliest Adelaidean sediments as having been deposited in a series of discrete shallow cratonic basins. The sequences in all three areas consist of cyclic hypersaline sand‐shale‐carbonate sheets and wedges. Hypersalinity has been inferred from a study of evaporites and their pseudomorphs, which imply basin evolution in sabkha and playa palaeoenvironments. We interpret the Callanna Beds in the Willouran Ranges to have been formed in playa lake or prograding sabkha complexes, that formed in a series of yoked half‐grabens within the tectonic setting of the Adelaide palaeorift. 相似文献
13.
JULIAN B. MURTON 《Sedimentology》1996,43(4):737-760
Three stages of deposition are distinguished in thermokarst-lake-basin sequences in ice-rich permafrost of the Tuktoyaktuk Coastlands, western arctic Canada: (1) widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes, forming a distinctive basal unit of impure sand and/or diamicton; (2) a reduction or cessation of slumping-because of the pinching out of adjacent ground ice, slump stabilization or climatic cooling, that reduces the input of clastic sediment, permitting reworking of sediment around lake margins and suspension settling, principally in basin centres; (3) lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand. Radiocarbon dating of detrital peat and wood from a progradational sequence (basal unit) defines a lateral younging trend in the direction of progradation. A progradation rate is calculated to be ～ 4 cm yr?1, consistent with rapid deposition during stage (1) above. The nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents. In comparison with thermokarst-lake-basin sequences previously described in Alaska, Canada and Siberia, the middle unit of those in the Tuktoyaktuk Coastlands is similar, whereas the basal unit is generally thicker and, by contrast, often contains diamicton. These differences are attributed, respectively, to larger-scale resedimentation of upland sediments by retrogressive thaw slumping and debris-flow deposition in thermokarst lakes in the Tuktoyaktuk Coastlands. Compared with the sediments within supraglacial lakes in areas of moderate to high relief, the middle unit of thermokarst-lake-basin sequences in the Tuktoyaktuk Coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable. These differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes, which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the Tuktoyaktuk Coastlands. It may be impossible to distinguish glacial and periglacial thermokarst-lake-basin sediments in permafrost areas of incomplete deglaciation. Not only is it often difficult to distinguish intrasedimental and buried glacier ice, but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar. 相似文献
14.
中国北方地区保留了晚更新世以来大量的冰缘遗迹. 在气候变化背景下, 在寒区和干旱区分别出现冰缘地貌、正逆向沙化等问题, 综合不同区域的地质遗迹, 从时间上的对应关系可进一步分析气候环境变化问题. 2008年5-7月调查中, 在鄂尔多斯和大同地区分别发现了新的砂楔和土楔;在大兴安岭生态定位研究站设立了8个钻孔和2套自动气象站, 开启了冻土、湿地、 积雪研究以及现代陆面过程对下伏冻土影响的研究;在黄岗梁地区新发现了一个冻融褶皱;调查了松嫩沙地古沙丘及古土壤活动与冻土进退的关系;发现小兴安岭地区冻土退化显著, 岛状冻土散布于海拔相对较高的地区;三江平原西部农业开发强烈改变了地表覆盖, 冻土温度升高显著, 冻土上限下降明显, 甚至厚度较薄的冻土消失. 后期工作希望通过综合、集成分析以上结果, 探讨我国北方地区晚更新世/全新世的冻土南界及环境变迁. 相似文献
15.
James C. Walters 《Quaternary Research》1978,10(1):42-54
Polygonal patterned ground and associated sediment-filled wedges occur in thin-bedded shale in central New Jersey. During a dry growing season, numerous areas of polygonal ground were visible owing to differential growth of vegetation over the sediment-filled fractures. Construction sites where material was removed from the surface prior to excavation also revealed areas of polygonal ground. Measurements of the patterns show networks of polygons with diameters ranging from about 3 m to over 30 m, with an average of approximately 20 m. The wedges examined in vertical exposures range in depth from 25 to 260 cm (average, 125 cm) and in width from 10 to 240 cm (average, 50 cm). The infilling material of the wedges is mostly a sandy loam, although this material is not homogeneous throughout the wedges. The presence of ventifacts and frosted sand grains within the wedges indicates eolian activity during the formation of these features. The polygonal ground and wedge structures exhibit several characteristics similar to those of ice-wedge casts, and available evidence suggests they may have originated as ice-wedge polygons during the last glacial maximum. 相似文献
16.
Climate and material controls on periglacial soil processes: Toward improving periglacial climate indicators 总被引：1，自引：0，他引：1
Norikazu Matsuoka 《Quaternary Research》2011,75(2):356-365
One of the distinguished efforts of A.L. Washburn was to reconstruct mean annual air temperature using periglacial features as climate indicators. This paper reviews existing periglacial indicators and proposes a strategy to improve their thermal resolution based on recent periglacial process studies, with a focus on solifluction and thermal contraction cracking and associated landforms/structures. Landforms resulting from solifluction reflect both the depth subjected to freeze-thaw and the thickness of frost-susceptible soils. The thickness of a solifluction structure can be used to infer the dominant freeze-thaw regime and minimum seasonal frost depth. Ice-wedge pseudomorphs have limited potential as a climate indicator because (1) they mainly reflect extreme winter temperatures, (2) their thermal thresholds depend on the host material, and (3) they need to be distinguished from frost wedges of other origin produced under different thermal and/or material conditions. Monitoring studies of currently active ice wedges suggest that ice-wedge cracking requires a combination of low temperature and large temperature gradients in the frozen active layer. Further field monitoring of periglacial processes and their controlling factors under various climate conditions and in various materials are needed, however, to improve the resolution of periglacial paleoclimate indicators. 相似文献
17.
何瑞霞 金会军 蒋观利 张泽 陈雪梅 Raul David SERBAN Mihaela SERBAN Jef VANDENBERGHE Valentin V.SPEKTOR Hugh M.FRENCH 《冰川冻土》2021,43(1):263-273
冰缘遗迹（特别是冷生楔形构造及融冻褶皱）是重建古气候及第四纪晚期多年冻土环境的重要证据。内蒙古鄂尔多斯高原是我国北方地区冰缘现象最为发育的地区之一。为准确了解鄂尔多斯高原冰缘遗迹类型及其分布特征、区域冻土演化历史等,中国科学院西北生态环境资源研究院和荷兰自由大学共同组成科研小组,于2018年5—6月组织了“鄂尔多斯高原冰缘遗迹科学考察”。考察区域涉及靖边—城川—乌审旗—鄂尔多斯东胜区一带约12 000 km2的范围。考察内容主要包括鄂尔多斯高原冰缘遗迹类型及特征、分布区域、各类型冰缘遗迹所指示的气候条件的初步推断等。结果表明：冻融褶皱和冷生楔体构造是鄂尔多斯高原主要存在的两大类冰缘遗迹。基于本次考察中关于冰缘遗迹的分布与特征等新发现,并综合前人研究成果,初步推断：在气温极低、多年冻土非常发育的时段,有利于形成各类冷生楔状构造,如冰楔假形和大型原生砂楔等;在气候转暖、多年冻土退化,但还没有全部融化完阶段,可能形成融冻褶皱;区域性大面积分布和成群出现的融冻褶皱一般反映较暖气候环境下,多年冻土层上部已退化到一定程度。基于光释光（OSL）年代测试结果,结合冰缘遗迹的特征及其所指示的古气候环境,初步重建了鄂尔多斯5万年以来的冻土环境变化序列。区内多年冻土在多年冻土最大期（LPM,25~19 ka BP）时最发育,以大面积连续多年冻土为主;之后,随气温转暖,总趋势呈退化状态,多年冻土分布逐渐变为片状→岛状→零星斑状,直至现今全部融完变为深季节冻土区。 相似文献
18.
Despite a low tidal range and relatively low wave conditions, the Mackenzie Delta is not prograding seaward but rather is undergoing transgressive shoreface erosion and drowning of distributary channel mouths. In the Olivier Islands region of the Mackenzie Delta the resultant morphology consists of a network of primary and secondary channels separated by vegetated islands. New ground is formed through channel infilling and landward-directed bar accretion. This sedimentation is characterized by seven sedimentary facies: (1) hard, cohesive silty clay at the base of primary channels which may be related to earlier, offshore deposition; (2) ripple laminated sand beds, believed to be channel-fill deposits; (3) ripple laminated sand and silt, interpreted as flood-stage subaqueous bar deposits; (4) ripple laminated or wavy bedded sand, silt and clay, representing the abandonment phase of channel-fill deposits and lateral subaqueous bar deposition from suspension settling; (5) a well sorted very fine sand bed, presumed to result from a single storm event; (6) parallel or wavy beds of rooted silt, sand and clay, interpreted as lower energy emergent bar deposits; and (7) parallel or wavy beds of rooted silt and clay, believed to represent present-day subaerial bar aggradation. The distribution of sedimentary facies can be interpreted in terms of the morphological evolution of the study area. Initial bar deposition of facies 3 and channel deposition of facies 2 was followed by lateral and upstream bar sedimentation of facies 3 and 4 which culminated with the deposition of the storm bed of facies 5. Facies 6 and 7 signify bar stabilization and abandonment. Patterned ground formed by thermal contraction and preserved in sediments as small, v-shaped sand wedges provides the most direct sedimentological indicator of the arctic climate. However, winter ice and permafrost also govern the stratigraphic development of interchannel and channel-mouth deposits. Ice cover confines flow at primary channel mouths, promoting the bypassing of sediments across the delta front during peak discharge in the spring. Permafrost minimizes consolidation subsidence and accommodation in the nearshore, further enhancing sediment bypass. Storms limit the seaward extent of bar development and promote a distinctive pattern of upstream and lateral island growth. The effects of these controls are reflected in the vertical distribution of facies in the Olivier Islands. The sedimentary succession differs markedly from that of a low-latitude delta. 相似文献
19.
Subsurface large-scale patterned ground structures, observed as crop-marks in cereal fields with spring-barley and oats have been detected in southwestern Jutland. It is assumed that the structures revealed are fossil ice-wedge polygons. Mode of origin, time of formation and palneoclimatic significance of ice-wedge casts are discussed. Texture of poorly layered wedge-fill materials can be distinguished from that of the stratified materials transected by the wedges, causing stress conditions in crop, in dry summers, seen as differential growth and cereal ripening. The water-holding capacity is highest in wedge-fill materials. Plants growing above the ice-wedge casts arc able to withstand a certain deficiency in precipitation during spring and early summer. Cereals growing outside ice-wedge casts suffer owing to lack of available moisture, and growth may be restricted, even to the extent that the plants can wither. Consequently, crop-marks of variable growth appear in the fields. A growth season with high precipitation makes it difficult to trace crop marks. 相似文献
20.
Jef Vandenberghe Hugh M. French Aldar Gorbunov Sergei Marchenko Andrey A. Velichko Huijun Jin Zhijiu Cui Tingjun Zhang Xudong Wan 《Boreas: An International Journal of Quaternary Research》2014,43(3):652-666
This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice‐wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo‐temperatures that are inferred on the basis of present‐day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately <1000 m a.s.l.). Striking features that appear from the map are (i) the narrow permafrost zone in North America, which contrasts with the broader LPM permafrost zone in Eurasia (that may be related to different snow thickness or vegetation cover), (ii) the zonal extent of former LPM permafrost (that may reflect sea‐ice distribution), which contrasts with the present‐day pattern of permafrost extent (especially in Eurasia) and (iii) the relatively narrow zones of LPM discontinuous permafrost (that may indicate strong temperature gradients). 相似文献