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1.
The Tree Shelter site dates to the Early to Mid-Holocene (8000 to 4900 14C yr BP). Present conditions around the site are hyperarid, but charcoal remains indicate less severe aridity at the time of its occupation. The environment around the site then supported a rich wadi vegetation, which allowed hunting during the Epipaleolithic and herding during the Neolithic occupation. Although more favorable than today, the environmental conditions also displayed a desert character and seem to have limited the range of domestic herbivores introduced in the area.  相似文献   

2.
The last glacial-interglacial transition (LGIT; 19–9 ka) was characterized by rapid climate changes and significant ecosystem reorganizations worldwide. In western Colorado, one of the coldest locations in the continental US today, mountain environments during the late-glacial period are poorly known. Yet, archaeological evidence from the Mountaineer site (2625 m elev.) indicates that Folsom-age Paleoindians were over-wintering in the Gunnison Basin during the Younger Dryas Chronozone (YDC; 12.9–11.7 ka). To determine the vegetation and fire history during the LGIT, and possible explanations for occupation during a period thought to be harsher than today, a 17-ka-old sediment core from Lily Pond (3208 m elev.) was analyzed for pollen and charcoal and compared with other high-resolution records from the southern Rocky Mountains. Widespread tundra and Picea parkland and low fire activity in the cold wet late-glacial period transitioned to open subalpine forest and increased fire activity in the BøllingAllerød period as conditions became warmer and drier. During the YDC, greater winter snowpack than today and prolonged wet springs likely expanded subalpine forest to lower elevations than today, providing construction material and fuel for the early inhabitants. In the early to middle Holocene, arid conditions resulted in xerophytic vegetation and frequent fire.  相似文献   

3.
研究目的】在末次冰期,全球气候变化以千年尺度的快速、大幅度温度波动旋回为特征,这种波动变化在两极冰芯、深海沉积、中国黄土和洞穴石笋等诸多地质样品中均有记录。黑海位于北大西洋与东亚季风区过渡带,具有极有代表性的沉积记录。本文旨在通过对黑海沉积序列的研究,建立起其区域环境变化与北大西洋及东亚季风气候域气候变化的联系。【研究方法】研究对取自黑海西北部罗马尼亚陆坡区多瑙河峡谷北侧GAS-CS12钻孔的长22.0 m的岩芯样品,进行了粒度、矿物成分、主量元素、有机碳、总氮及碳氮同位素等分析。【研究结果】揭示出该段岩芯沉积于末次冰期中后期“Neoeuxine”湖相阶段,可划分为5个沉积单元,对应于北大西洋H4、H3、H1气候变化事件、末次冰盛期(LGM)及Bolling-Allerod气候变暖事件。【结论】建立起了其沉积序列及区域环境变化与北大西洋及东亚季风气候域气候变化的联系,印证了末次冰期千年尺度的气候变化事件在北大西洋、东亚季风区及两者过渡带上具有高度的一致性。创新点:建立了黑海西北沉积序列与区域环境变化的关系;补充了北大西洋与东亚季风区两者过渡带上气候波动事件的可靠时标。  相似文献   

4.
This paper focuses on the late Holocene occupation of hunter‐gatherers at the Marazzi 2 site located on the northwestern steppe of Tierra del Fuego, Chile. Our aim is to understand stratigraphy, formation processes, and pedogenesis with respect to human occupation over the last 3000 years. Based on archaeological excavations on a fluvial terrace of the Torcido River, we integrate soil micromorphology, mineralogy, geochemistry, magnetic susceptibility, and geomorphology, as well as the micro‐ and macrofrequency distributions of archaeological material. A micro‐taphonomical perspective is also applied to anthropogenic components recorded in sedimentary thin sections. We discuss various events in the interplay between soil development and human occupation through time. Marazzi 2 was witness to aggradation and pedogenesis with an episode of surface stability coincident with a phase of more intense human occupation at about 860 BC. Taphonomic analysis suggests that there are multiple occupation events mixed together, probably by biomechanical processes, resulting in a palimpsest with poor temporal resolution.  相似文献   

5.
Sensitive areas like oases are threatened by climatic variations and human activities that can catalyze desertification processes. Remote sensing the Earth surface from satellites is a good tool to monitor such types of change through several techniques. In this paper a remote sensing method that has been widely used for vegetated areas is adapted to study dry regions. The method consists of a combination of the Change Vector Analysis and the Tasselled Cap (TC) transform. To adapt it to dryland conditions a new set of parameters for the TC transform is hereby calculated for the Landsat 8 OLI system. The new TC parameters are tested in the analysis of the surface change in Azraq Oasis, Jordan, over a time span of 30 years (1984–2013) for Landsat satellites images. Azraq is considered a good testing site since in the early 1990s it has been subject to a complete drying up of the superficial springs, mainly due to over-exploitation of the groundwater basin. Results show that the chosen technique is able to detect the expected change on the surface, consistent with photo-interpretation and historical information available.  相似文献   

6.
High‐precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change. Although radiocarbon is the traditional method for dating late Quaternary sedimentary sequences, particularly during the last glacial–interglacial transition (LGIT; 15–9 ka), there are inherent problems with the method, particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content. An alternative method is the use of tephras that act as time‐parallel marker horizons. Within Europe, numerous volcanic centres are known to have erupted during the LGIT, providing considerable potential for high‐precision correlation independent of past radiocarbon fluctuations. Here we report the first identification of the Vedde Ash and Askja Tephra in Ireland, significantly extending the known provenance of these events. We have also identified two new horizons (the Roddans Port Tephras A and B) and tentatively recognise an additional horizon from Vallensgård Mose (Denmark) that provide crucial additional chronological control for the LGIT. Two phases of the Laacher See Tephra (LST) are reported, the lower Laacher See Tephra (LLST) and probably the C2 phase of the Middle Laacher See Tephra (MLST‐C2) indicating a more northeasterly distribution of this fan than reported previously. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

7.
Questions remain as to the nature of climatic change through the last glacial–interglacial transition in the eastern Mediterranean region, particularly the relative contribution of evaporation and precipitation to regional water balance. Here changes in oxygen isotope values through this time period from Eski Acıgöl, a crater lake in central Turkey, are investigated using hydrological and isotope mass balance models. These allow changes in evaporation and precipitation to be quantified and their relative importance evaluated. We show that it is the volumetric flux rate of water passing through the lake system and not the precipitation-to-evaporation ratio per se which controlled the stable isotope record in Eski Acıgöl. Early Holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day. We test these calculated values against other records in the same region, firstly with other lake records in Anatolia, the Konya basin and Lake Van, and secondly with isotope-inferred palaeo-precipitation data from Soreq cave in Israel. This reveals a contrast between pre- and post-LGM precipitation values in Turkey (wetter and drier, respectively) and also suggests that during the last glacial–interglacial transition there was a more marked precipitation gradient than at present between northern/interior and southern/coastal parts of the eastern Mediterranean region.  相似文献   

8.
The variability in seasonal mean and extreme precipitation is analyzed for several regions of Argentina to the north of 39º S, using long-term monthly time series data which expand from 1860 to 2006. The selected locations can be considered as representative of different climatic regions. This work focuses on the analysis of monthly rainfall distribution, significant seasonal trends, changes in variance and extreme monthly values, in order to establish the magnitude of the seasonal climatic rainfall variability through time for central Argentina. A 40-yr moving window was employed in order to analyze seasonal variability of rainfall extremes. Extremes were computed for different probability levels of a theoretical distribution function over/below the 80th/20th percentile. The gamma distribution was selected among five other theoretical distributions, and the scale and shape parameters were computed using the maximum likelihood estimation (MLE) and the bootstrap method for 1000 resample data sets, as well. Trend analysis was performed for each window on winter and summer means and tested for significance. The use of a moving window allowed detecting the window of maximum absolute values for the trends. Research results show significant temporal shifts in seasonal rainfall distribution and return values (RV) that were computed for different frequencies (once every five, 10 and 20 years). Generally, summer precipitation extremes have become wetter for the whole region. Rainfall amounts for summer wet/dry extremes (W/D) corresponding to the 90th (for W) and 10th (for D) percentiles were subjected to significant increase, but depending on the geographical area this effect spreads slightly differently over records of years. A common-for-all-stations period of such summer increase trend in extreme values spans from the window 1921-1960 to the last window analyzed: 1967-2006. This behavior was not observed for north and west Argentina during winter, except for the region represented by Bahía Blanca, where the 10% D extreme has increased throughout the study period.  相似文献   

9.
晋中盆地是位于汾渭地堑系中部的新生代陆内断陷沉积盆地,研究晋中盆地第四纪的沉积序列对于进一步认识该盆地区域构造和区域气候环境变化具有重要意义。为查明晋中盆地第四纪沉积序列结构、研究揭示晋中盆地第四纪沉积环境及演化,通过构造岩相学方法,对晋中盆地地表和钻孔内第四纪沉积物和沉积环境进行了研究。结果表明:晋中盆地清徐地区地表第四纪沉积序列结构为盆地内部沱阳组河床相和河漫滩相-盆地边缘汾河组河流相—盆山过渡带峙峪组河流相、汾河组冲积扇相及马兰组风积相-基岩山地(盆地外围)二叠系浅海相。钻孔岩芯内第四纪沉积序列结构为下更新统浅湖相和滨湖相—中更新统浅湖相和河流相—上更新统河流相和冲积扇相—全新统冲积扇相。研究认为晋中新生代陆内断陷盆地内沉积序列和演化结构为早更新世陆相湖盆沉积环境—中更新世萎缩湖泊环境—晚更新世强烈萎缩的湖泊和河流环境—全新世再度沉降的陆相湖盆;陆相湖盆从中心向山地沉积环境分带为湖泊沉积环境—河流和湖泊沉积环境—冲积扇沉积环境(盆地边缘出山口区)。盆山过渡带地区上更新世沉积物错位现象与同沉积活动断裂有关,断裂活动性揭示了晋中盆地阶梯式断陷成盆的动力学机制。这些研究成果为区域气候环境变化和晋中盆地区域构造研究提供了新证据,也为太原市城市群建设中工程场址的选择提了供参考。   相似文献   

10.
The history of variations in water level of Lake Constance, as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of Arbon-Bleiche 3, shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago (5320 yr relative to AD 1950). This event, paralleled by the destruction of the Neolithic village by fire, provoked the abandonment of this prehistoric lake-shore location established in the former shallow bay of Arbon-Bleiche, and was the last of a series of three episodes of successively higher lake level, the first occurring at 5600-5500 cal yr B.P. The dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric 14C. This supports the hypothesis of an abrupt climate change forced by varying solar activity. Moreover, the three successive episodes of higher lake level between 5600 and 5300 cal yr B.P. at Arbon-Bleiche 3 coincided with climatic cooling and/or changes in moisture conditions in various regions of both hemispheres. This period corresponds to the mid-Holocene climate transition (onset of the Neoglaciation) and suggests inter-hemispheric linkages for the climate variations recorded at Arbon-Bleiche 3. This mid-Holocene climate reversal may have resulted from complex interactions between changes in orbital forcing, ocean circulation and solar activity. Finally, despite different seasonal hydrological regimes, the similarities between lake-level records from Lake Constance and from Jurassian lakes over the mid-Holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments.  相似文献   

11.
Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatán Peninsula, México. Detailed study of dated soil‐sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices.  相似文献   

12.
Evidence from Liang Bua, a limestone cave on the island of Flores in East Indonesia, provides a unique opportunity to explore the long term relationship between hominins and their environment. Occupation deposits at the site span ~95 ka and contain abundant stone artefacts, well preserved faunal remains and evidence for an endemic species of hominin: Homo floresiensis. Work at the site included detailed geomorphological and environmental analysis, which has enabled comparisons to be drawn between changes in the occupational intensity in the cave, using stone tool and faunal counts, and changes in the environmental conditions, using the characteristics of the sedimentary layers in the cave and speleothem records. These comparisons demonstrate that H. floresiensis endured rapidly fluctuating environmental conditions over the last ~100 ka, which influenced the geomorphological processes in the cave and their occupational conditions. The intensity of occupation in the cave changed significantly between 95 and 17 ka, with peaks in occupation occurring at 100–95, 74–61 and 18–17 ka. These correlate with episodes of channel formation and erosion in the cave, which in turn correspond with high rainfall, thick soils and high bio-productivity outside. In contrast, periods of low occupational intensity correlate with reduced channel activity and pooling associated with drier periods from 94 to 75 and 36 to 19 ka. This apparent link between intensity of hominin use of the cave and the general conditions outside relates to the expansion and contraction of the rainforest and the ability of H. floresiensis to adapt to habitat changes. This interpretation implies that these diminutive hominins were able to survive abrupt and prolonged environmental changes by changing their favoured occupation sites. These data provide the basis for a model of human–environment interactions on the island of Flores. With the addition of extra data from other sites on Flores, this model will provide a greater understanding of H. floresiensis as a unique human species.  相似文献   

13.
It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

14.
北京─通县平原地区的第四纪环境演变,主要取决于气候变化和新构造运动。早更新世时,古永定河尚未形成自西向东穿越本区的河道,新构造运动和海平面变化,控制和影响了海侵事件的规模和范围。中更新世本区湖沼广布。晚更新世是本区平原化的主要时期,塑造了北京平原现时地貌的基本格架。晚更新世末,受末次冰期气候的影响,本区发生了地史时期的最后一次大事件,造成了物种迁移和绝灭,全区广泛发育黄土堆积。进入全新世,本区环境变化以河流作用最为显著,沉积物主要分布在各大水系的河谷中,构成一、二级阶地和近代河床与河漫滩淮积。  相似文献   

15.
Paleoecological data from two sites in central Pacific Panama have allowed the reconstruction of Late Pleistocene climate and vegetation in lowland areas, the timing of important environmental changes, and the generation of predictions concerning Paleoindian settlement and subsistence. The last 9000 years of the glacial period, from 20,000 B.P. until 11,050 B.P. were marked by climates cooler and drier than today's. The period from ca. 16,000 B.P. until 11,000 B.P. appears to have been the coolest and driest. We postulate that the major effects of these conditions were to have brought montane vegetation 900 m lower than its present range and to create tracts of open landscape along the Pacific coast. Forests, however, were widespread in extent and many lowland forest taxa apparently persisted, creating the basis for the rejection of refugial theory as an explanatory model for early human occupation. Neither the admittedly limited archaeological or paleoecological data indicated the presence of pre-Clovis populations in Panama, and we chose to view Clovis as the first human expression on the Isthmus. Correlation of reconstructed environmental setting with Paleoindian site location suggests that Clovis adaptations were fluid and flexible, and utilized a wide variety of vegetation types. Occupation and modification of tropical forest appear to have been integral parts of Clovis subsistence and settlement strategies.  相似文献   

16.
杨江海  颜佳新  黄燕 《沉积学报》2017,35(5):981-993
地球在晚古生代晚期—中生代早期经历最近一次从冰室到温室的气候转变,是理解未来地球冰川消融、全球变暖等气候转变的重要窗口。这一时期的沉积记录和气候模型研究揭示,冰川活动、大气pCO2和气候状态间存在复杂的耦合和反馈机制,同时伴随发生陆表植被更替和生物迁移。随冰川消融、大气pCO2升高和全球变暖,低纬大陆区干旱化趋势和季节性降雨增强,出现季风气候并在冰室之后的三叠纪温室盛行。华南和华北是位于东特提斯低纬区的主要大陆,其石炭—二叠系在沉积和生物特征上与Pangea超大陆西侧热带区差异显著,蕴含有丰富的深时气候变化信息。基于前人成果,在简述石炭—三叠纪全球气候变化的基础上,对东特提斯低纬区石炭—三叠纪沉积记录进行总结,阐明其深时古气候研究意义和研究前景。  相似文献   

17.
通过对库车河剖面下白垩统巴西改组—古近系库姆格列木群底部的沉积露头实测,分析砂岩岩性组合、沉积构造特征、砾岩特征及沉积古环境,并结合现代天山南北季节性河流沉积特征,认为干旱气候条件下发育的季节性河流及季节性河流三角洲是白垩纪库车坳陷发育的重要沉积体系.下白垩统巴什基奇克组砂岩特征与现今广泛发育的季节性河流沉积特征极为相似,既有较为典型的河流相正韵律砂体大面积沉积,河道底部内碎屑泥砾与厚层块状的大型交错层理等砂岩,又显示出高能细砂岩和高能粉砂岩沉积,并具有较低的成分成熟度和较高的结构成熟度基本特征.在此基础上,建立了库车河剖面下白垩统巴西改组—巴什基奇克组沉积相模式:巴西改组沉积时期,库车坳陷发育面积较大的宽浅型湖泊,天山前发育的季节性河流进入湖泊后形成季节性河流三角洲;巴什基奇克组沉积时期,古天山前出现了多个小型湖泊,古天山山前发育大量的季节性辫状河与多个小型季节性辫状三角洲沉积.  相似文献   

18.
Past environmental changes based on diatom relative abundances have been inferred from the maar Lake Erlongwan in northeast China. The limnology of Lake Erlongwan is affected by the strongly seasonal regional climate. The composition of diatom assemblages, in turn, responds to changes in the seasonal duration of ice cover in winter, water-column turnover in spring and autumn, and thermal stratification in summer. Statistical analysis of the sedimentary diatom assemblages reveals three significant stratigraphic zones over the past 1000 yr. The highest abundance of the planktonic species Discostella species occurs between AD 1050 and 1400 and suggests an annual ice-free period of long duration and well-developed summer stratification of the water column. This planktonic diatom peak between ca. AD 1150 and 1200 suggests that this period was the warmest over the past 1000 yr. The interval between AD 1400 and 1800 is marked by a decline in planktonic diatoms and suggests shorter duration of the ice-free season, weaker water stratification and possibly generally cold conditions. After AD 1800 relative abundances of planktonic diatoms, including Puncticulata praetermissa and Asterionella formosa, increase again, which indicates lengthening of the duration of the annual ice-free period and a stronger overturn of the water column. All these data imply that the pattern of the seasons is different between the MWP and the 20th century.  相似文献   

19.
A regional paleoenvironmental reconstruction is presented for a north-south transect of late glacial pollen and insect fossil sites from the Rocky Mountain region. Altitudinal treelines were depressed by an average of 671 m and summer temperatures were an average of 5.4° lower. the interpretation of paleoenvironmental conditions based on insect fossil evidence tends to show stronger departures from modern parameters than that based on palynology. While clear evidence for late glacial occupation of the region by Paleoindians is scarce, montane conditions were not so severe as to preclude human occupation, at least on a seasonal basis. Newly discovered sites of early occupation would benefit greatly from inter-disciplinary studies.  相似文献   

20.
《Quaternary Science Reviews》2007,26(9-10):1362-1368
Sediments deposited on the bottom of Lake Baikal have contributed to the understanding of a long-term environmental history of continents. Rare earth elements (REEs) along with major elements and loss on ignition (LOI) of Baikal sediments were determined with the aim of evaluating their suitability for a new paleoenvironmental proxy. Our interest is concentrated on paleoenvironmental change during the Last Glacial/Interglacial transition (LGIT). Chondrite-normalized REE patterns for Baikal sediments show a similar variation to those for typical upper continental crustal materials. Three parameters of (La/Yb)n (n: chondrite-normalized value) ratio, ΣREE/TiO2 and Eu anomaly were used to express detailed characteristics of Baikal sediments. Depth profile of (La/Yb)n ratio shows abrupt change, whose timing corresponds to the beginning of climatic warming inferred from the profiles of SiO2/TiO2 and LOI. In addition, (La/Yb)n ratio, ΣREE/TiO2 and the degree of Eu anomaly correlate with each other. This suggests that inflow process of particulate materials into the lake may have changed during the LGIT. The analytical results of this study lead to the conclusion that REE is a useful paleoenvironmental proxy in the Baikal region.  相似文献   

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