共查询到20条相似文献，搜索用时 828 毫秒
1.
David R. Gaylord Franklin F. Foit Jr. Jeffrey K. Schatz Angela J. Coleman 《Journal of Arid Environments》2001,47(4):403
Sedimentary deposits from the Smith Canyon dune field, south-central Columbia Basin, Washington, U.S.A. document climatically-influenced Late Pleistocene and Holocene aeolian and fluvial deposition in a region impacted by glacial outburst floods and tephra falls. The depositional history is summarized by five environmentally distinctive and climatically sensitive sedimentary units (temporal limits estimated): Unit 1 (c. 15·5–8 ka), pedogenically altered glacial outburst flood and minor aeolian silt and clay; Unit 2 (c. 8–6·9 ka), fluvial and minor aeolian sand; Unit 3 (c. 6·9–6·8 ka), flood-induced fluvial sand with gravel-sized tephra clasts; Unit 4 (c. 6·8–3·9 ka), aeolian dune sand; Unit 5 (c. 3·9 ka to present), pedogenically altered, stabilized dune sand. Estimated age ranges are based on stratigraphic position, tephrochronology, and correlation with temporally constrained strata from elsewhere in the region. 相似文献
2.
A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried
out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by
stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both
lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late
Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic
matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are
separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper
sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing
water.
At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon
dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth
of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year
BP).
Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in
the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine
sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments
began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between
9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year
BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year
BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred
bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year.
These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake
brine for manufacturing salt. 相似文献
3.
Wisconsin's Central Sand Plain east of the Wisconsin River is composed of eolian sand forming high-relief dunes surrounded by sand sheets and scattered low-relief dunes. To establish a maximum age for dune formation, three samples for optical dating were taken from glacial Lake Wisconsin lacustrine sediment that underlies eolian sand. These age estimates range from 19.3 to 13.6ka. Age estimates taken from within or at the base of the dunes range from 14.0 to 10.6ka. Samples taken from < 2m of the ground surface were slightly younger, indicating dunes were stabilized between 11.8 and 5.5ka. The younger ages near the surface of some dunes were most likely the result of pedoturbation or localized problems with applying the optical dating method. The majority of the optical age estimates from dunes (18 of 21) indicated that most of the dunes were active between 14 and 10ka and that most dune activity ended by 10ka. These ages suggest that localized activity on dune crests may have occurred in the Holocene but would have been limited to < 1m of sand accumulation. The timing of dune activity and the lack of any significant Holocene reactivation suggest that dune activation in this setting cannot be attributed solely to changes in aridity. Instead, we attribute dune formation to changes in sediment availability from either sand inputs from the Wisconsin River or the melting of permafrost. 相似文献
4.
Several sand flats located on the northern shores of the Late Pleistocene palaeolake of the Konya plain (inner Anatolia, Turkey), are related to changes in lake levels. In this paper, the two main dune systems are mapped according to their geomorphological, sedimentological and dynamic characteristics, and their significance is discussed with regard to the environmental changes since the Late Pleistocene, both at time of the former lake and during the drier periods of the Holocene. Cross-sections show the relationship of the dunes to the topography of the basement. Analyses of the sand fraction show distinct characteristics in size distribution, quartz and shell contents, wind erosion effects on the quartz grains and petrographic composition. Interpretation of the results, coupled with information provided by the geomorphology of the dune systems studied in the field and from aerial photographs and satellite images, highlights the importance and variations in time of local factors such as prevailing winds, sand sources, changes in lake levels and vegetation. A chronology of the main sand fields is proposed, based on the evidence of three main droughts during the Upper Pleistocene. The older one, much eroded (maximum height=3 m), covers a limestone surface at +50 m above the bottom of the dried lake. An Optical Scanning Luminescence (OSL) date shows a last period of accumulation at 14,328±3220 years. The younger one (maximum height=12 m) has moved over the emerged Late Pleistocene lacustrine marls. An OSL date gives an age of 5674±988 years for the last accumulation period. Evidence of very recent activation of this younger dune system is apparent as a result of overgrazing and excessive land reclamation. A third period of dominant wind action and dune construction is responsible for the installation of a younger and thin dune field over the Mid-Holocene lacustrine deposits of the Karapinar lake. The success of the stabilization programme of the dunes over the last 30 years shows that the last period of dune movement is not related to climate change but to overpressure on the land due to the needs and activities of an increasing population. 相似文献
5.
青海湖滨土地沙漠化驱动机制 总被引：1，自引：1，他引：0
在自然因素和不合理人为活动的影响下,青海湖流域及其周边地区正面临土地沙漠化、湿地萎缩、草场退化、水土流失等严重的生态环境问题。本文分析了青海湖滨土地沙漠化现状及其驱动因素。结果表明:青海湖滨广泛分布的古风沙沉积物是现代沙漠化的沙物质来源,现代流动沙丘的粒度特征与古风成沙丘粒度极为相似,两者的继承与改造关系极为明显。草皮层及其下的粉沙土层是古沙丘的保护层。保护层的机械破坏,使下伏松散的古风沙沉积物暴露,是形成沙漠化的关键一步。随后在风蚀、雨水冲刷及其他因素的共同作用下,松散的古风沙沉积物被侵蚀,引起草皮层坍塌,导致古沙丘活化,风沙活动加剧,形成风沙沉积。流水侵蚀和地层沉陷是导致草皮层机械破坏的主要因素。青海湖水位下降,河流沉积,风沙入湖,都可使沙地面积增加,但仅限于湖边局部地方。 相似文献
6.
禹门口南黄河东岸沙丘初步研究 总被引：2，自引：1，他引：1
在禹门口南山西省河津、万荣县境内黄河阶地上发育了一些固定、半固定沙丘,注入黄河的汾河将这些沙丘分成了南北两部分。北部的沙丘多在海拔400m左右,高出现代黄河约35m,位于黄河的第二级阶地上,由两条南北向的沙垄和两垄之间分布的抛物线形沙丘构成特殊的景观。这些抛物线形沙丘一般高度约7~8m,背风面突出,迎风坡坡度一般为15°~20°,背风坡坡度一般大于40°。风沙堆积下伏的河流堆积物的14C年龄为26.40±0.8kaBP,表明沙丘形成于距今26ka以来。南部沙丘海拔高度近500m,高出现代黄河水面150m,覆盖于黄河第三级阶地之上。一个天然剖面揭示,第三阶地的底部为黄色中粗砂与灰绿色粉砂粘土互层,中部为灰黄色黄土,顶部为黄色风沙层。在黄土地层中可以识别出S1古土壤和位于风沙堆积下面的可能为L1SS1的弱成土层。由此推断风沙堆积于距今3万a以来。黄河阶地上的沙丘是在特殊的地区和特定的时期;强大的风力、丰富的沙源和气候变干条件下形成的。虽然东岸沙丘已是固定、半固定沙丘,但沙化仍然是该地区的一个问题。由于3~4a前开始在丘前洼地栽种苹果树,破坏了下风向沙丘迎风面的植被,造成了原来已固定沙丘的活化,在沙丘顶部生成了新的小抛物线形沙丘,高度大于1 m。沙丘上裸露的树根指示表土已被侵蚀0.3 m。南部沙丘区的风蚀作用也很强,例如,万荣县裴庄乡西范村北一片柿树林的树根由于风蚀已经裸露1.2 m。 相似文献
7.
近40ka来海南岛海岸沙地气候与环境演变 总被引：1，自引：0，他引：1
选择海南岛东、西海岸具有代表性和高分辨率特征的木堆、棋子湾等地层剖面,在建立年代序列的基础上,对风成沙粒度组成与参数、SC/D值及磁化率等代用指标的研究表明,末次冰期间冰阶时气候相对温暖,滨海平原上河流三角洲前移,湿地、沙丘与交错分布;末次盛冰期时气候干凉,海岸沙地上形成了多道平行延伸的古沙垄(丘),并与大陆架古沙丘形成连续性沉积;末次冰消期时气候快速变化,古沙垄(丘)或加积发育或固定成壤;全新世以来气候回暖并波动变化,次生沙丘经历多次半固定、固定－沙丘加积、活化的演变。 相似文献
8.
Saline playas in north-western Nevada, U.S.A., remnants of pluvial periods of the Pleistocene, represent a tremendous source of unconsolidated sediments available for aeolian transport. This study investigated the transport of aqueous-soluble solutes in dust from July 1994 through June 1996 along a transect from a barren salt-encrusted playa surface (elevation=1224 m), to a former pluvial lake beach (elevation=1228 m), to a dune-mantled upland (elevation=1248 m). The content of aqueous-soluble solutes in aeolian dust showed a significant (p≤0·05) interaction with dust trap location (playa, beach, dune) and time of collection. Dust collectors on the playa surface generally contained significantly more aqueous-soluble solutes and had greater total flux of solutes than either the beach or the dune locations. The solute content of aeolian dust was usually higher, in some cases several orders of magnitude, than that in the surface 5 cm of soil. Recent changes in playa hydrology may explain this result. Pulses of nitrate-rich dust, synchronous with spring emergence, and other nutrient additions via aeolian dust may have stimulated invasion of dune-mantled uplands by the weedSalsola paulsenii (barb-wire Russian thistle). 相似文献
9.
Susan Ringrose Philippa Huntsman-Mapila William Downey Stephan Coetzee Martin Fey Cornelis Vanderpost Bernard Vink Thebe Kemosidile Dikitso Kolokose 《Geomorphology》2008,101(4):544-557
This work considers the spatial distribution and ages of western MOZ basin siliclastic sediments prior to providing insights into the diagenesis of degraded dune and alluvial fan sands. Previously published and new TL/OSL ages imply that extensive over-washing of dune sands took place at least 100 ka ago while ages on Okavango floodplains imply that the fan was formed ca. 40 ka and has since undergone periods of higher and lower flood regimes. Sediment analyses indicate that both dune and fan sands contain a diagenetic matrix of clay-enhanced amorphous silica (CEAS) which bonds weakly formed aggregates. The time of formation of diagenetic matrix products is inconclusive but may have been accelerated during or shortly after events dated using OSL/TL techniques. Hence earlier dune over-washing may have led to greater porewater of an acidic to near neutral nature which in turn promoted smectite formation and silicic acid precipitation > 100 000 years ago. The relatively abundant CEAS matrix in floodplain sands implies more recent semi-continuous flood events again of an acidic-near neutral nature leading to the formation of smectite. In this case the floodplain sediments are dated as having been deposited around 40 and 11 ka, when porewater content may have accelerated clay formation and silica dissolution. The dual nature of the CEAS in the islands reflects a changing environment from smectite-dominated flooding events to sepiolite-dominated desiccation events. Flooding may also correspond to TL/OSL ages over the past 40 000 years which contributed to accelerated CEAS formation. The sepiolite is associated with a Ca-rich matrix implying desiccation which may relate to drying events over the 40 000 year period or to riparian tree root pumping and selective salt accumulation. This work shows that sedimentation in incipient rifts is complex and rarely explained totally in terms of primary depositional events. The implications of different stages of sand diagenesis may be significant in enhancing palaeo-environmental interpretations in semi-arid fluvial environments. 相似文献
10.
Sediment cores collected from embayed lakes along the east-central coast of Lake Michigan are used to construct aeolian sand
records of past coastal dune mobility, and to constrain former lake levels in the Lake Michigan basin. Time series analysis
of sand cycles based on the weight-percent aeolian sand within lacustrine sediment, reveals statistically significant spectral
peaks that coincide with established lake level cycles in Lake Michigan and the Gleissberg sunspot cycle of minima. Longer
cycles of ~ 800 and ~ 2200 years were also identified that correspond to solar cycles. Shorter cycles between 80 and 220 years
suggest a link between coastal dune mobility, climate, and lake levels in the Lake Michigan basin. Radiocarbon-dated sedimentary
contacts of lacustrine sediment overlying wetland sediment record the Nipissing transgression in the Lake Michigan basin.
Lake level rise closely mimics the predicted uplift of the North Bay outlet, with lake level rise slowing when outflow was
transferred to the Port Huron/Sarnia outlet. The Nipissing highstand was reached after 5000 cal (4.4 ka) BP. 相似文献
11.
海岸是陆、海、气相互作用的地带。海岸风沙沉积是这一特殊动力环境的产物,是研究海岸环境演变及海平面变化的良好信息载体。中国海岸主要存在3种风沙沉积,分别为“老红砂”、沙丘岩及海岸沙丘。本文通过比较已报道的风沙堆积的物质组成、地层变化等,进一步总结了海岸风沙沉积的特征;选择已开展绝对测年的沉积剖面,利用概率密度函数分析了风沙沉积年代的分布特征,考察了中国海岸风沙活动历史,结合其他气候记录,探讨了不同地质历史时期海岸风沙堆积的关键影响因素。结果表明：“老红砂”沉积主要记录了冰期-间冰期尺度的风沙活动,在120 ka BP前后、73—55 ka BP等时期,风沙活动主要与海平面下降时陆架提供的丰富沙源和强盛的冬季风有关;而在105 ka BP、80 ka BP前后,风沙活动与高海平面时期丰富的沙源或季风气候的季节性增强有关;55 ka BP以来风沙活动强度降低更多地反映了沉积记录保存环境的变化,末次冰期海岸风沙沉积大多分布在现代海面之下,并不代表实际的海岸风沙活动减弱。相比之下,海岸沙丘沉积所记录的风沙活动主要发生在近3 000 a,可能与中国海岸冬季风的增强有关。 相似文献
12.
青海湖东岸的风沙堆积 总被引：15，自引：5，他引：10
风沙堆积和风成沙丘的发育在分布上服从于两条规律, 一条是地带性规律, 即绝大多数沙漠均分布于干旱地区, 或在副热带高压带及其产生的信风带, 或在温带干旱大陆中心, 另一条是非地带性规律, 即在某些非干旱区域如河流、海岸或湖泊的沙质滨岸地带, 只要有一定的风力条件也可形成风沙堆积。 相似文献
13.
The Mudui stratigraphic section represents the typical records of sedimentation processes of sand dunes and interdune depressions on the east coast of Hainan Island.Based on high-density sampling and optically stimulated luminescence(OSL) dating of the strata of the section,the grain-size composition,grain-size parameters,cumulative distribution probability curve,and grain-size-sensitivity indexes(SC/D) were analyzed.The analyzed results show that the grain-size features of aeolian sand,weakly developed sandy paleosol,two-facies(aeolian and aqueous) deposits,and lagoon deposits are all different.This indicates four evolutionary phases of the sedimentary environment of the east coast of Hainan Island since 38 ka B.P.Phase I:38-22 ka B.P.;phase II:22-17 ka B.P.;phase III:17-10 ka B.P.;phase IV:10 ka B.P.-present.The climate experienced the hot-wet/hot-dry,hot-wet/hot-dry,and warm-wet/hot-wet fluctuations,and the sedimentary environment also underwent lagoon deposition,dune and interdune depression deposition,dune stabilization and soil development,shifting sand deposition,and evolutionary processes. 相似文献
14.
新月形沙丘顶部稳定性是风沙地貌学尚未解决的科学问题。研究新月形沙丘的顶部稳定性,对于绿洲边缘风沙运动规律揭示、防沙工程建设和沙区生态环境保护等具有重要的现实意义。选择民勤沙区新月形沙丘,通过测定沙丘各部位风速、风蚀风积和粒度等,分析了新月形沙丘顶部稳定机理。主风向（NW）作用是新月形沙丘最高点与沙脊线重合、沙丘前移和高度降低的过程;反向风（SE）作用是沙丘最高点与沙脊线分离、沙丘背风坡风蚀与沙丘增高的过程。由于研究区以NW风为主,新月形沙丘沿NW-SE方向前移,SE风只能风蚀减缓沙丘背风坡的坡度。人为干预将会阻止或减少从迎风坡向沙丘顶部输送沙量,使得新月形沙丘背风坡尤其是背风坡上部风蚀过程增强,新月形沙丘逐渐过渡为抛物线形沙丘。 相似文献
15.
Yuan Shang RuiJie Lu FeiFei Ji LiHui Tian QingLiang Tang Yuan Chen Chao Zhao WangYang Wu 《寒旱区科学》2013,5(3):0301-0308
As the largest inland lake of China, along with its unique landscape and geographical location, Qinghai Lake has got much attention of the scientists for a long time. The precursors have done substantive researches by using the lake sediment, which deepen our understanding of the climate changes in this region. Although sand dunes and loess sediment are widely distributed around the lake, so far the researches on geochemical elements from aeolian sediment have been less reported. In this paper, we selected a typical aeolian profile on the east of Qinghai Lake. Based on systematic sampling and analysis of seven major geochemical elements, combined with OSL dating and previous researches, this paper discusses climate changes in the Qinghai Lake area since 12.5 ka B.P.. Our conclusions are: (1) Before 12.5 ka B.P., the climate in this region was dry, cold, and accompanied by strong wind-sand activities. (2) During 12.5–11.9 ka B.P., the climate became warm and wet. However, there was an abrupt climate cooling event during 12.2–11.9 ka B.P., which likely corresponded to the Younger Dryas event. (3) During 11.9–8.0 ka B.P., the climate fluctuated greatly and frequently from warm to cold, and three cooling events occurred. (4) During 8.0–2.6 ka B.P., the climate was warm and humid. (5) Since 2.6 ka B.P., similar to the modern climate, the climate was mainly dry and cold. 相似文献
16.
17.
察尔汗盐湖北侧沙丘沉积物颗粒微结构特征 总被引：1，自引：1，他引：0
利用扫描电镜对比分析了柴达木盆地察尔汗盐湖北侧线形沙丘和新月形沙丘沉积物颗粒的表面显微特征。结果表明：柴达木盆地察尔汗盐湖北侧线形沙丘和新月形沙丘沉积物石英颗粒表面具有明显的风成特征。颗粒以次棱角状为主,普遍发育典型的碟形撞击坑、麻坑和新月形撞击坑;察尔汗盐湖北侧沙丘沉积物以物理分解和机械搬运作用为主,化学风化作用较低,反映了当时干旱炎热的沉积环境;贝壳状断口、平行擦痕及V形坑的存在表明柴达木盆地沙丘沉积物前期曾受到冰川或流水的作用,推断出柴达木盆地周围高山的剥蚀产物或察尔汗盐湖的湖相沉积物可能是察尔汗盐湖北侧沙丘沉积物的来源之一。 相似文献
18.
沙丘内部沉积构造保存了沙丘动力演变过程的重要信息。以古尔班通古特沙漠西南缘固定、半固定新月形沙丘区为研究区域,利用探地雷达在春、秋两季对固定、半固定新月形沙丘内部构造进行探测,获取了不同规模形态的固定、半固定新月形沙丘深约8 m的内部构造图像信息。通过图像增益处理、解译和对比分析表明：（1） 古尔班通古特沙漠固定、半固定新月形沙丘共有5种沙丘内部构造雷达相,即高倾角斜层理、楔状交错层理、上凸形交错层理、低倾角-近水平层理和块状层理,其中前4种主要分布在3~5 m的浅层,而块状层理主要分布在4~5 m以下的深度。（2） 高倾角斜层理、楔状交错层理主要分布在高大新月形沙丘（链）的迎风坡上部和丘顶地带,前者为背风坡前积层埋藏而成,反映高大新月形沙丘迎风坡上部和丘顶风沙活动较频繁,沙丘“固身缩顶”后埋藏的前积纹层因风蚀而出露,后者为迎风坡风蚀坑和风蚀槽中由风沙流充填而成的构造或在丘顶风向的季节性变化形成的构造。（3） 与灌丛沙丘相关的上凸形交错层理广泛分布在新月形沙丘的迎风坡中下部,在背风坡也有局部出现,表明灌丛沙丘在沙丘表层的风沙过程中占有重要地位;而深部的块状层理可能是早期风积层受到强烈的生物扰动,原生层理消失而产生。（4） 以上沙丘内部构造的类型与组合分布特点,反映了研究区新月形沙丘总体上趋于稳定或衰退状态,这与现代沙丘“固身缩顶”的地貌变化特征相一致。例如,迎风坡中上部和丘顶常见风蚀槽,背风坡因坡度变缓、前积层发育趋缓,现代风沙活动主要集中于新月形沙丘的上部和丘顶等。由此可见,研究区固定、半固定新月形沙丘内部构造及其组合分布特征异于流动新月形沙丘,也与半个多世纪以来北疆沙漠气候变暖变湿、平均风速减弱、植被盖度增加的区域自然地理环境变化趋势有一定的吻合性。 相似文献
19.
《自然地理学》2013,34(3):233-244
Relatively low (<25 m) parabolic dunes and dune ridges occur inland of massive parabolic dunes in many dune complexes along the southeastern shore of Lake Michigan. The major study of these backdunes (Tagues, 1946) concluded, based on field criteria, that they were older than the massive parabolic dunes and originate at the Calumet and Algonquin stages of ancestral Lake Michigan (~14-10 ka). Younger ages are indicated by this study in which Optically Stimulated Luminescense (OSL) ages were obtained from the crest of three backdunes southwest of Holland, Michigan. All ages are within statistical error of each other and indicate dune stabilization at ~4 ka. Similarities in surface soil development throughout the backdunes support the conclusion that they all stabilized at about the same time. Radiocarbon ages from paleosols indicate that the massive parabolic dunes were active at 4 ka and that this activity persisted after the back dunes had stabilized. In the Holland area, dune growth and migration occurred in a broad zone, including both back and massive parabolic dunes, immediately after the rise to and drop from Nipissing II high lake levels but became confined to a narrower zone closer to shore after ~4 ka. 相似文献
20.
高精度光释光测年揭示的晚第四纪毛乌素和浑善达克沙地沙丘的固定与活化过程 总被引：13，自引：3，他引：13
利用光释光测年技术对毛乌素沙地和浑善达克沙地7个地点的沉积剖面进行了年代测试,结合地层特征,获得了最近60kaBP以来两个沙地沙丘固定与活化时间的年代学控制60kaBP以来毛乌素沙地的固定期分别为距今37.71ka、8.54ka、8.32ka、7.93ka、7.77ka、7.57ka、7.39ka和2.39ka以后;活化的时间分别为距今57.08ka、52.50ka、13.65ka、13.13ka、7.20ka前后、2.39ka以前和0.29ka以来。在10.97kaBP、10.04kaBP、9.81kaBP和8.67kaBP前后沙地处于气候干湿交替时期。全新世期间,浑善达克沙地在距今8.74～8.72ka、7.79ka前后,沙丘活化;5.69kaBP、4.25kaBP、2.75kaBP、1.53kaBP和0.71kaBP前后,沙丘处于相对固定阶段,0.15kaBP以来,沙丘处于半固定状态。晚第四纪气候千年至百年尺度的变化可能是两个沙地沙丘活化与固定的主导因素。 相似文献