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New stratigraphic and geochronologic data from the Killpecker Dunes in southwestern Wyoming facilitate a more precise understanding of the dune field’s history. Prior investigations suggested that evidence for late Pleistocene eolian activity in the dune field was lacking. However, luminescence ages from eolian sand of ∼15,000 yr, as well as Folsom (12,950-11,950 cal yr B.P.) and Agate Basin (12,600-10,700 cal yr) artifacts overlying eolian sand, indicate the dune field existed at least during the latest Pleistocene, with initial eolian sedimentation probably occurring under a dry periglacial climate. The period between ∼13,000 and 8900 cal yr B.P. was characterized by relatively slow eolian sedimentation concomitant with soil formation. Erosion occurred between ∼8182 and 6600 cal yr B.P. on the upwind region of the dune field, followed by relative stability and soil formation between ∼5900 and 2700 cal yr B.P. The first of at least two latest Holocene episodes of eolian sedimentation occurred between ∼2000 and 1500 yr, followed by a brief (∼500 yr) episode of soil formation; a second episode of sedimentation, occurring by at least ∼700 yr, may coincide with a hypothesized Medieval warm period. Recent stabilization of the western Killpecker Dunes likely occurred during the Little Ice Age (∼350-100 yr B.P.). The eolian chronology of the western Killpecker Dunes correlates reasonably well with those of other major dune fields in the Wyoming Basin, suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late Quaternary. Similar to dune fields on the central Great Plains, dune fields in the Wyoming Basin have been active under a periglacial climate during the late Pleistocene, as well as under near-modern conditions during the latest Holocene. 相似文献
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以54个浅层新钻孔和多个野外露头为研究对象,综合沉积物粒度、薄片、微体古生物、孢粉、14C测年及静力触探等资料,分析了鲁北平原晚第四纪的地层结构和沉积类型,总结了晚更新世晚期以来的沉积演化。研究表明,末次冰期盛冰期到冰后期,受地势、气候条件控制的黄河河道迁移和海水进退是影响地层结构和沉积特征的主要因素,南北地层结构差异明显,发育古河道、湖沼、黄土、三角洲、潮坪和滨浅海等沉积类型,其中古河道分布面积最广,自下而上可划分为三期。晚更新世晚期至早全新世早期,受干冷气候影响,发育第Ⅰ期古河道,小清河以南沉积黄土层;早全新世晚期至中全新世,气候转暖导致海平面升高,沿海地区形成海侵层和三角洲,内陆地区继承性发育第Ⅱ期古河道和湖沼沉积;中全新世末期或晚全新世以来,受黄河泛滥影响,沉积第Ⅲ期古河道和现代黄河三角洲。地层结构和沉积物分布的研究对于分析地下水位的变化规律,以及选择合适的地震激发层等均有重要的指导意义。 相似文献
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Climate change and population history in the Pacific Lowlands of Southern Mesoamerica 总被引：1，自引：0，他引：1
Hector Neff Deborah M. Pearsall John G. Jones Brbara Arroyo de Pieters Dorothy E. Freidel 《Quaternary Research》2006,65(3):390-400
Core MAN015 from Pacific coastal Guatemala contains sediments accumulated in a mangrove setting over the past 6500 yr. Chemical, pollen, and phytolith data, which indicate conditions of estuarine deposition and terrigenous inputs from adjacent dry land, document Holocene climate variability that parallels the Maya lowlands and other New World tropical locations. Human population history in this region may be driven partly by climate variation: sedentary human populations spread rapidly through the estuarine zone of the lower coast during a dry and variable 4th millennium B.P. Population growth and cultural florescence during a long, relatively moist period (2800–1200 B.P.) ended around 1200 B.P., a drying event that coincided with the Classic Maya collapse. 相似文献
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Camila Rodrigues Costa Cynthia Fernandes Pinto da Luz Ingrid Horák-Terra Plínio Barbosa de Camargo Uidemar Morais Barral Carlos Victor Mendonça-Filho Thamyres Sabrina Gonçalves Alexandre Christófaro Silva 《第四纪科学杂志》2023,38(1):61-75
The Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central-eastern Brazil. A multi-proxy approach was used that involved palynological analysis, stable isotopes (δ13C, δ15N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub-humid climatic conditions seem to have been established in the mid-/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc. 相似文献
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Bradley G. Johnson Martha Cary Eppes John A. Diemer Gonzalo Jiménez-Moreno Anthony L. Layzell 《Quaternary Research》2011,76(3):352-362
Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene–Holocene transition (~ 12.5–9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2–1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins. 相似文献
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Phytolith data from Poyang Lake, southern China, indicate that significant natural and human‐induced vegetational changes have occurred in the middle Yangtze River valley, the likely hearth of rice (Oryza sativa L.) domestication, during the Late Pleistocene and Holocene periods. During the Late Pleistocene (from >13,500 to ca. 10,500 yr B.P.) the climate was cooler and drier than today's. Oryza appears to have been a natural component of the vegetation at that time, but may not have been well adapted to the glacial climatic conditions. The early Holocene climate may have been wetter and more markedly seasonal that at present, and wild Oryza species may have been distributed further north than seen today. By 4000 yr B.P., rice agriculture appears to have been well developed in the middle Yangtze River Valley. Environmental factors such as atmospheric CO2 concentrations and the seasonality of precipitation and temperature in addition to overall cooler and drier Pleistocene climates may have significantly influenced human exploitation of Oryza during the Late Pleistocene and early Holocene in southern China. © 2000 John Wiley & Sons, Inc. 相似文献
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Charles E. Mear 《Geoarchaeology》1995,10(6):457-480
Controlled by a local base level of downfaulted Edwards and Comanche Peak limestone, and aided by landsliding in Glen Rose marl, the Sabinal River and its tributaries have developed a large valley in the Edwards Plateau. Extensive soil-covered pediments that cut Glen Rose bedrock and Pleistocene terrace gravels are present along each side of the valley. Six alluvial deposits of late Pleistocene and Holocene age were recognized in the upper Sabinal River valley. The Holocene series is represented by three deposits. The oldest of these exhibits a Stage II calcic horizon and appears to have been deposited before ca. 5000 yr B.P. The Pleistocene deposits have a calcrete zone (calcic Stage IV and III horizon) in the upper 3-4 m. The Holocene alluviums, locally beveled by stream action, parallel the river's course and contain Archaic and younger artifacts, which in central Texas range in age from about 8000-350 yr B.P. One of the Holocene deposits (Q2) is correlated with the Georgetown and Fort Hood alluviums of the Cowhouse Creek at Fort Hood, which range in age from 11,000 yr B.P. to 5200 yr B.P., with the Wilson-Leonard terrace site in the Lampasas Cut Plain that ranges from about 11,000 to 5000 yr B.P., and with Unit E of Blum and Valastro (1989) in the Pedernales River valley, ranging from 10,550 to 7150 yr B.P. Modern climate in the valley is drought-prone, and fluctuates from semiarid to dry subhumid. Paleoclimate has ranged from much drier during the Middle Holocene to much cooler and wetter during the Late Pleistocene. 相似文献
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Field, micromorphological, pollen, whole soil (XRF), and stable isotope geochemical methods were used to evaluate the latest Pleistocene to Holocene climate record from a floodplain-terrace system in southeastern West Virginia. A late Pleistocene (22,940 ± 150 14C yr B.P.) silt paleosol with low-chroma colors formed from fluviolacustrine sediment deposited during the last glacial maximum (Wisconsinan) and records a cooler full-glacial paleoclimate. Fluvial gravel deposited between the latest Pleistocene and earliest Holocene (prior to 6360 ± 40 14C yr B.P.) was weathered in the middle Holocene under warmer, drier climate conditions, possibly correlated with the Hypsithermal and Altithermal Events of the eastern and southwestern United States, respectively. The glacial to interglacial climate shift is recorded by: (1) changes from a poorly drained landscape with fine-textured soil, characterized by high organic C and redoximorphic features related to Fe removal and concentration, to a well-drained, coarse-textured setting without gley and with significant argillic (Bt) horizon development; (2) changes from a high Zr and Ti silt-dominated parent material to locally derived, coarse fluvial gravels lower in Zr and Ti; (3) a shift from dominantly conifer and sedge pollen in the paleosol to a modern oak/hickory hardwood assemblage; and (4) a shift in δ13C values of soil organic matter from −28‰ to −24‰ PDB, suggesting an ecosystem shift from cooler, C3-dominated flora to one that was mixed C3 and C4, but still predominantly composed of C3 plants. A root-restrictive placic horizon developed between the late Pleistocene silt paleosol and the overlying fluvial gravel because of the high permeability contrast between the two textures of soil materials. This layer formed a barrier that effectively isolated the Pleistocene paleosol from later Holocene pedogenic processes. 相似文献
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Brendon J. Quirk Glen N. Mackey Diego P. Fernandez Andy Armstrong Jeffrey R. Moore 《第四纪科学杂志》2020,35(6):776-790
Rapid and high-magnitude North Atlantic climate oscillations following the Last Glacial Maximum have been correlated to climate change events in western North America. However, the strength of teleconnections between the North Atlantic and the interior of western North America remains poorly understood. We present a U-series calibrated speleothem record from Timpanogos Cave National Monument, located at 2040 m asl in the Wasatch Mountains of Utah, spanning 13.5–10.6 ka. Additionally, we carried out a climate reconstruction for a coeval glacier advance in the Wind River Range of Wyoming. Our results indicate that between 13.5 and 12.8 ka, the Wasatch was probably first cool and dry and then warmed. After 12.8 ka, our record suggests cool and/or wetter conditions followed by reduced moisture until 11.8 ka, followed by an early Holocene wet period. The Timpanogos record exhibits few similarities with those from the North Atlantic. Climate reconstructions of the Titcomb Basin glacier suggest modest temperature depressions relative to modern (<−3 °C) were necessary to sustain the glacier with a moderate increase in precipitation (>150%). The high-altitude speleothem record presented here provides a valuable basis for understanding latest Pleistocene–early Holocene glacial episodes in western North America. 相似文献
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Late Pleistocene organic-rich sediments exposed in coastal bluffs near the head of Plaza Creek, East Falkland, have yielded conventional and AMS 14C dates of between 36 and 28 ka BP, and possess a pollen spectrum dominated by grasses, indicating a vegetation assemblage similar to that of the present day. Although some sample dates are anomalous and contamination by non-contemporaneous carbon cannot be ruled out entirely, the age estimates are consistent with evidence and dates from Antarctica, South America and the amphi-North Atlantic for climate shifts to interstadial conditions at around that time. The organic-rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting. Grain-size characteristics suggest that these sediments may have been emplaced by solifluction, shallow translational landsliding and surface wash in at least five mass-wasting episodes. Some of the mass-wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka BP at San Carlos, East Falkland, and with periods of cirque and valley glaciation identified in the uplands of the Falkland Islands. The similarity between late Pleistocene interstadial, Holocene and present-day pollen assemblages, and the lack of vegetation change within these periods, is characteristic of most cool temperate Southern Ocean islands, and may reflect the lack of sensitivity of the vegetation to climate change and/or a lack of climate variability for the time intervals covered. © 1998 John Wiley & Sons, Ltd. 相似文献
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两护村ZKC1孔位于洞庭盆地安乡凹陷的东南部,孔内第四系(底部跨上新世)厚达294 m,为河流和湖泊沉积,自下而上依次为上新世—早更新世华田组、早更新世汨罗组、中更新世洞庭湖组、晚更新世坡头组以及全新统等。对ZKC1孔第四系进行了详细的孢粉分析,自下而上划分出16个孢粉组合带。ESR年龄和孢粉组合及其反映的气候特征指示华田组下段形成于上新世末。根据孢粉组合特征,结合构造—沉积演化和区域气候背景,重塑洞庭盆地上新世末以来的气候演化过程:上新世末期由孢粉带Ⅰ和Ⅱ指示具暖干气候。早更新世经历了凉干(孢粉带Ⅲ、Ⅳ)→暖湿间凉干(孢粉带Ⅴ～Ⅶ)→冷干间温湿(孢粉带Ⅷ～Ⅹ)→暖较湿(孢粉带Ⅺ,Ⅻ)的气候演变过程。中更新世早期无孢粉样品(洞庭湖组下部砾石层),其沉积环境暗示冷干气候条件;中期由孢粉带ⅩⅢ反映出暖稍湿的气候特征;晚期因构造抬升缺失沉积,同期湿热化事件指示暖湿气候。晚更新世早期缺乏沉积,据区域对比应为寒冷气候;中期由孢粉带ⅩⅣ指示温较湿的气候特征;晚期缺失沉积,系寒冷气候下区域海平面下降所致。全新世经历了暖稍湿(孢粉带ⅩⅤ)→暖稍干(孢粉带ⅩⅥ)的演变。上述气候演变过程与ZKC1孔化学蚀变指数曲线反映的气候演变过程以及中国东部第四纪气候演化基本吻合。以孔深140 m为界,上部孢粉数量显著高于下部,种属也更为丰富。这一变化很可能对应于一次重要的地质事件,其成因有待今后深入研究。 相似文献
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Jingxing Lin Shanlin Zhang Jinbo Qiu Biaoyun Wu Huanzhong Huang Huizhen Huang Jianguo Xi Baogen Tang Zuren Cai Yubao He 《Quaternary Research》1989,32(3)
Eight marine transgressions have been recognized from more than 30 deep drill holes (ca. 300 m deep) through Quaternary sequences in the Yangtze River delta region. These are, in ascending order, the Rugao and Zhoupe transgressions (early Pleistocene); the Shanghai, Jiading, and Wangdian transgressions in the middle Pleistocene; the Jiangyin and Gehu transgressions in the late Pleistocene; and the Zhenjiang transgression in the Holocene. The transgressions correspond to warm periods and regressions to cold periods. The younger transgressions were not only of shorter duartion, but also of larger magnitude. The findings verify that there were five moderately warm periods during the early to middle Pleistocene and two very warm periods during the late Pleistocene in the Yangtze River delta region. 相似文献
15.
Alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores, tree rings, and speleothems are not available. About 20 years have passed since a special issue of Quaternary Science Reviews was published to review the worldwide evidence for Holocene glacier fluctuations. Since that time, numerous sites have been discovered, new dating techniques have been developed, and refined climatic hypotheses have been proposed that contribute to a better understanding of Earth's climate system. This special volume includes 12 papers on Holocene and latest Pleistocene alpine glacier fluctuations that update the seven review papers from 1988.Major findings of these 12 papers include the following: many, but certainly not all, alpine areas record glacier advances during the Younger Dryas cold interval. Most areas in the Northern Hemisphere witnessed maximum glacier recession during the early Holocene, with some glaciers disappearing, although a few sites yield possible evidence for advances during the 8.2 ka cooling event. In contrast, some alpine areas in the Southern Hemisphere saw glaciers reach their maximum post-glacial extents during the early to middle Holocene. In many parts of the globe, glaciers reformed and/or advanced during Neoglaciation, beginning as early as 6.5 ka. Neoglacial advances commonly occurred with millennial-scale oscillations, with many alpine glaciers reaching their maximum Holocene extents during the Little Ice Age of the last few centuries. Although the pattern and rhythm of these glacier fluctuations remain uncertain, improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for Holocene and latest Pleistocene glacial activity and perhaps predict glacier response to future impacts from human-induced climate change. 相似文献
16.
洞庭盆地第四纪红土地层及古气候研究 总被引：1，自引：0，他引：1
洞庭盆地周缘广泛发育着第四纪红土地层,我们在野外对典型红土剖面进行了考察,并在岳阳市月山红土剖面进行了取样,在室内对土壤样品进行了磁化率、粘土矿物和粒度等实验分析,从而对洞庭盆地第四纪红土地层的剖面特征进行了研究,在此基础上,对洞庭盆地第四纪古气候变迁进行了探讨。月山红土剖面地层界限清晰,剖面特征明显,与中国南方其它的红土地层具有较好的地层对比性。月山红土剖面磁化率和粘土矿物分析表明:中更新世早期洞庭盆地气候干凉,中更新世晚期转为湿热;晚更新世早期气候仍保持湿热,晚更新世晚期则转为干凉;全新世以来洞庭盆地的气候再次转为湿热。粒度分析表明月山红土剖面第四纪沉积物的沉积环境为洪水盆地中的泛滥平原环境。 相似文献
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We report high-resolution macroscopic charcoal, pollen and sedimentological data for Agua Caliente, a freshwater lagoon located in southern Belize, and infer a late Holocene record of human land-use/climate interactions for the nearby prehistoric Maya center of Uxbenká. Land-use activities spanning the initial clearance of forests for agriculture through the drought-linked Maya collapse and continuing into the historic recolonization of the region are all reflected in the record. Human land alteration in association with swidden agriculture is evident early in the record during the Middle Preclassic starting ca. 2600 cal yr BP. Fire slowly tapered off during the Late and Terminal Classic, consistent with the gradual political demise and depopulation of the Uxbenká polity sometime between ca. 1150 and 950 cal yr BP, during a period of multiple droughts evident in a nearby speleothem record. Fire activity was at its lowest during the Maya Postclassic ca. 950–430 cal yr BP, but rose consistent with increasing recolonization of the region between ca. 430 cal yr BP and present. These data suggest that this environmental record provides both a proxy for 2800 years of cultural change, including colonization, growth, decline, and reorganization of regional populations, and an independent confirmation of recent paleoclimate reconstructions from the same region. 相似文献
18.
Richard F. Madole 《Quaternary Research》2012,78(2):197-208
Stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the Roaring River, Colorado, lead to three principal conclusions: (1) the opinion that stream channels in the higher parts of the Front Range are relics of the Pleistocene and nonalluvial under the present climate, as argued in a water-rights trial USA v. Colorado, is untenable, (2) beds of clast-supported gravel alternate in vertical succession with beds of fine-grained sediment (sand, mud, and peat) in response to centennial-scale changes in snowmelt-driven peak discharges, and (3) alluvial strata provide information about Holocene climate history that complements the history provided by cirque moraines, periglacial deposits, and paleontological data. Most alluvial strata are of late Holocene age and record, among other things, that: (1) the largest peak flows since the end of the Pleistocene occurred during the late Holocene; (2) the occurrence of a mid- to late Holocene interval (~ 2450–1630(?) cal yr BP) of warmer climate, which is not clearly identified in palynological records; and (3) the Little Ice Age climate seems to have had little impact on stream channels, except perhaps for minor (~ 1 m) incision. 相似文献
19.
南迦巴瓦峰西北坡末次冰期以来的冰川变化 总被引：5，自引：2，他引：5
本区自晚更新世以来的冰川变化可分为距今25000—10000年的末次冰期、距今3500—1000年的新冰期和距今400—200年的小冰期,冰川面积逐次减小,雪线上升,与气候变化具同步性。 相似文献
20.
Statigraphic exposures, fluvial archives and borehole data have been allowed to reconstruct the alluvial history of Late Pleistocene to Early Holocene and climate changes in the monsoonal wet–dry region of lower Damodar Basin (West Bengal, India). The facies architectures and climate proxies suggest that five to six climate changes occurred in between ～14 and 6 kiloannum (ka). Supporting evidence from the floodplain of Damodar River demonstrates that the successive phases of aggradation and incision were linked to the south-west monsoonal variability of Late Quaternary period. The onset of semi-arid climate was associated with caliches, pond and backswamp deposits of waning low-energy floods. The relatively warm-humid climate was associated with sandy bedforms, valley fills, slack water deposits and ferruginous nodules. This paper presents a synthesis of the available palaeoclimatic records from the lower Ganga Basin and the rivers of western and central India for the palaeoenvironmental significance of Late Quaternary deposits and discusses the influence of palaeoclimatic controls on the fluvial architectures and archives that developed below the floodplain of Damodar River. We have taken some representative studies from the region to reveal the spatial variability in fluvial successions in response to climate changes during this period. 相似文献