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1.
Late Pleistocene and Holocene Seasonal Temperatures Reconstructed from Fossil Beetle Assemblages in the Rocky Mountains 总被引：1，自引：0，他引：1
Scott A. Elias 《Quaternary Research》1996,46(3):311-318
Mutual Climatic Range (MCR) analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14,500 to 400 yr B.P. The fossil sites represent a transect of the Rocky Mountain region from northern Montana to central Colorado. The analyses yielded estimates of mean July and mean January temperatures. The oldest assemblage (14,500 yr B.P.) yielded mean July values of 10–11°C colder than present and mean January values 26–30°C colder than present. Postglacial summer warming was rapid, as indicated by an assemblage dating 13,200 yr B.P., with mean July values only 3–4°C cooler than modern. By 10,000 yr B.P., several assemblages indicate warmer-than-modern mean summer and winter values. By 9000 yr B.P., MCR reconstructions indicate that both summer and winter temperatures were already declining from an early Holocene peak. Mean July values remained above modern levels and mean January values remained below modern levels until 3000 yr B.P. A series of small-scale oscillations followed. 相似文献
2.
Cathy W. Barnosky 《Quaternary Research》1985,23(1):109-122
A 33,000-yr pollen record from Carp Lake provides information on the vegetation history of the forest/steppe border in the southwestern Columbia Basin. The site is located in the Pinus ponderosa Zone but through much of late Quaternary time the area was probably treeless. Pollen assemblages in sediments dating from 33,000 to 23,500 yr B.P. suggest a period of temperate climate and steppe coinciding with the end of the Olympia Interglaciation. The Fraser Glaciation (ca. 25,000–10,000 yr B.P.) was a period of periglacial steppe or tundra vegetation and conditions too dry and cold to support forests at low altitudes. Aridity is also inferred from the low level of the lake between 21,000 and 8500 yr B.P., and especially after about 13,500 yr B.P. About 10,000 yr B.P. Chenopodiineae and other temperate taxa spread locally, providing palynological evidence for a shift from cold, dry to warm, dry conditions. Pine woodland developed at the site with the onset of humid conditions at 8500 yr B.P.; further cooling is suggested at 4000 yr B.P., when Pseudotsuga and Abies were established locally. 相似文献
3.
Patricia M. Anderson 《Quaternary Research》1988,29(3)
Pollen diagrams from Joe and Niliq Lakes date to ca. 28,000 and 14,000 yr B.P., respectively. Mesic shurb tundra grew near Joe Lake ca. 28,000 to 26,000 yr B.P. with local Populus populations prior to ca. 27,000 yr B.P. Shrub communities decreased as climate changed with the onset of Itkillik II glaciation (25,000 to 11,500 yr B.P.), and graminoid-dominated tundra characterized vegetation ca. 18,500 to 13,500 yr B.P. Herb tundra was replaced by shrub Betula tundra near both sites ca. 13,500 yr B.P. with local expansion of Populus ca. 11,000 to 10,000 yr B.P. and Alnus ca. 9000 yr B.P. Mixed Picea glauca/P. mariana woodland was established near Joe Lake ca. 6000 yr B.P. These pollen records when combined with others from northern Alaska and northwestern Canada indicate (1) mesic tundra was more common in northwestern Alaska than in northeastern Alaska or northwestern Canada during the Duvanny Yar glacial interval (25,000 to 14,000 yr B.P.); (2) with deglaciation, shrub Betula expanded rapidly in northwestern Alaska but slowly in areas farther east; (3) an early postglacial thermal maximum occurred in northwestern Alaska but had only limited effect on vegetation; and (4) pollen patterns in northern Alaska and northwestern Canada suggest regional differences in late Quaternary climates. 相似文献
4.
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
5.
Three atomic mass spectrometry (AMS) dates have been obtained for shell material from the bottomset beds of a glaciomarine delta at Spencers Island, Nova Scotia, near the head of the Bay of Fundy. The sediments in the delta are part of the previously undated Five Islands Formation, and are the first direct indictaion of the age of deglaciation in this region. The dates range from 14,300 to 12,600 yr B.P. and record the duration of deposition of a diamicton under the deltaic deposits and of the delta itself. The diamicton may have formed around 14,000 yr B.P. under ice-shelf or calving-bay conditions, or by a readvance of grounded ice. The Spencers Island delta is part of a prominent ice-marginal stand marked by numerous deltas along the Minas Basin. The time of formation of the deltas and the inferred ice margin is between 13,500 and 12,000 yr B.P. based on the Spencers Island dates and palynologically confirmed dates on the base of lake-sediment cores from the delta surface. Ice-marginal glaciomarine deposits near St. John, New Brunswick, record a range of radiocarbon dates similar to the Spencers Island dates. This implies that the Bay of Fundy became virtually ice free about 14,000 yr B.P. 相似文献
6.
Clay mineral assemblages of a soil chrono-association comprising five fluvial surface members (QGH1 to QGH5) of the Indo-Gangetic Plains between the Ramganga and Rapti rivers, north-central India, demonstrate that pedogenic interstratified smectite–kaolin (Sm/K) can be considered as a potential indicator for paleoclimatic changes during the Holocene from arid to humid climates. On the basis of available radiocarbon dates, thermoluminescence dates, and historical evidence, tentative ages assigned to QGH1 to QGH5 are <500 yr B.P., >500 yr B.P., >2500 yr B.P., 8000 TL yr B.P., and 13,500 TL yr B.P., respectively. During pedogenesis two major regional climatic cycles are recorded: relatively arid climates between 10,000–6500 yr B.P. and 3800–? yr B.P. were punctuated by a warm and humid climate. Biotite weathered to trioctahedral vermiculite and smectite in the soils during arid conditions, and smectite was unstable and transformed to Sm/K during the warm and humid climatic phase (7400–4150 cal yr B.P.). When the humid climate terminated, vermiculite, smectite, and Sm/K were preserved to the present day. The study suggests that during the development of soils in the Holocene in alluvium of the Indo-Gangetic Plains, climatic fluctuations appear to be more important than realized hitherto. The soils older than 2500 yr B.P. are relict paleosols, but they are polygenetic because of their subsequent alterations. 相似文献
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Shane, Linda C. K. 1987 03 01: Late-glacial vegetational and climatic history of the Allegheny Plateau and the Till Plains of Ohio and Indiana, U.S.A. Boreas , Vol. 16, pp. 1–20. Oslo. ISSN 0300–9483.
Pollen evidence from the Allegheny Plateau and the Till Plains south of the Great Lakes shows marked post-glacial vegetation gradients. C. 15,500–11,000 B.P .: On the Plateau, spruce forest was rapidly established, persisted for 2,000 years, then began a gradual change to deciduous-conifer forest. On the Till Plains, open spruce forest tundra closed slowly over 1,000 years, declined rapidly c . 13,500 B.P., and a deciduous open woodland developed. C. 11,000–10,300 B.P .: On the Till Plains, a brief cooling is recorded by increases in the abundance of spruce and fir, contemporaneous with the European Younger Dryas. No clear change is seen on the Plateau. 10,300–4,000 B.P .: Warming and/or drying occurred in both areas, as hemlock and jack/red pine trees immigrated, followed by white pine. Conifers disappeared from the Till Plains by 9,800 B.P., but pine and hemlock trees may have persisted on the Plateau. After 10,000 B.P. mixed deciduous forest was established across the entire region. Between 8,000 and 4,000 B.P., further warming/drying is indicated on the Till Plains with development of open oak forest and lake shallowing, and on the Plateau by a minor increase in herbs, lake shallowing, and reduction in pine. 相似文献
Pollen evidence from the Allegheny Plateau and the Till Plains south of the Great Lakes shows marked post-glacial vegetation gradients. C. 15,500–11,000 B.P .: On the Plateau, spruce forest was rapidly established, persisted for 2,000 years, then began a gradual change to deciduous-conifer forest. On the Till Plains, open spruce forest tundra closed slowly over 1,000 years, declined rapidly c . 13,500 B.P., and a deciduous open woodland developed. C. 11,000–10,300 B.P .: On the Till Plains, a brief cooling is recorded by increases in the abundance of spruce and fir, contemporaneous with the European Younger Dryas. No clear change is seen on the Plateau. 10,300–4,000 B.P .: Warming and/or drying occurred in both areas, as hemlock and jack/red pine trees immigrated, followed by white pine. Conifers disappeared from the Till Plains by 9,800 B.P., but pine and hemlock trees may have persisted on the Plateau. After 10,000 B.P. mixed deciduous forest was established across the entire region. Between 8,000 and 4,000 B.P., further warming/drying is indicated on the Till Plains with development of open oak forest and lake shallowing, and on the Plateau by a minor increase in herbs, lake shallowing, and reduction in pine. 相似文献
9.
Cathy W. Barnosky 《Quaternary Research》1981,16(2):221-239
Pollen and macrofossil analyses of a core spanning 26,000 yr from Davis Lake reveal late Pleistocene and Holocene vegetational patterns in the Puget Lowland. The core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units. The late Pleistocene pollen sequence records two intervals of tundra-parkland vegetation. The earlier of these has high percentages of Picea, Gramineae, and Artemisia pollen and represents the vegetation during the Evans Creek Stade (Fraser Glaciation) (ca. 25,000–17,000 yr B.P.). The later parkland interval is dominated by Picea, Tsuga mertensiana, and Gramineae. It corresponds to the maximum ice advance in the Puget Lowland during the Vashon Stade (Fraser Glaciation) (ca. 14,000 yr B.P.). An increase in Pinus ontorta pollen between the two tundra-parkland intervals suggests a temporary rise in treeline during an unnamed interstade. After 13,500 yr B.P., a mixed woodland of subalpine and lowland conifers grew at Davis Lake during a period of rapid climatic amelioration. In the early Holocene, the prolonged expansion of Pseudotsuga and Alnus woodland suggests dry, temperate conditions similar to those of present rainshadow sites in the Puget Lowland. More-mesic forests of Tsuga eterophylla, Thuja plicata, and Pseudotsuga, similar to present lowland vegetation, appeared in the late Holocene (ca. 5500 yr B.P.). 相似文献
10.
Continuous pollen and sediment records from two ∼8.5-m-long cores document late Pleistocene and Holocene sedimentation and vegetation change in the Ballston Lake basin, eastern New York State. Pebbles at the base of both cores and the geomorphology of the watershed reflect the presence of the Mohawk River in the basin prior to ∼12,900 ± 70 cal yr B.P. Ballston Lake formed at the onset of the Younger Dryas (YD) by an avulsion of the Mohawk River. The transition from clay to gyttja with low magnetic susceptibility (MS), low bulk density, and high organic carbon indicates rapid warming and increased lake productivity beginning 11,020 cal yr B.P. MS measurements reveal that the influx of magnetic particles, associated with pre-Holocene clastic sedimentation, ceased after ∼10,780 cal yr B.P. The pollen record is subdivided into six zones: BL1 (12,920 to 11,020 cal yr B.P.) is dominated by boreal forest pollen; BL2 (11,020 to 10,780 cal yr B.P.) by pine (Pinus) forest pollen; BL3 (10,780 to 5290 cal yr B.P.) by hemlock (Tsuga) and mixed hardwood pollen; BL4 (5290 to 2680 cal yr B.P.) by mixed hardwood pollen; BL5a (2680 cal yr B.P. to 1030 cal yr B.P.) by conifer and mixed hardwood pollen; and BL5b (1030 cal B.P. to present) by increasing ragweed (Ambrosia) pollen. A 62% decrease in spruce (Picea) pollen in <320 cal years during BL1 reflects rapid warming at the end of the YD. Holocene pollen zones record more subtle climatic shifts than occurred at the end of the YD. One of the largest changes in the Holocene pollen spectra began ∼5300 cal yr B.P., and is characterized by a marked decline in hemlock pollen. This has been noted in other pollen records from the region and may record preferential selection of hemlock by a pathogen or parasites. 相似文献
11.
Because of its well-developed ice-marginal zones, SW Sweden is an important reference area for the study of deglaciation, chronology and palaeoclimate 13,500-10,000 B.P. The ice-marginal zones are described and defined. Earlier research and opinions concerning the deglaciation are summarized. Based on radiocarbon dates from shells, vertebrate bones and limnic sediments, a revised deglaciation chronology is presented. This chronology is supported by biostratigraphic transects of time-space diagrams. The radiocarbon and varve chronologies are compared. Some ice-marginal zones are supposed to be 400 to 900 years older than expected from the varve chronology. The deglaciation chronology is correlated within the southern margin of the Scandinavian inland ice. Various consequences for the interpretation of glacial dynamics, shoreline displacement, and the biological environment are mentioned. 相似文献
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13.
对甘肃酉峰晚第三纪红土标准剖面的研究揭示出,该区红土下部(６．２ＭａＢ．Ｐ．前)是红化的土壤物质与其它物质一起经水流搬运(坡积作用为主)再堆积的产物;中部(６．２～３．４ＭａＢ．Ｐ．)未发现再搬运的痕迹,是风尘堆积经风化和频繁地下水位波动作用所形成,不具明显的土壤发生学层次,其中的碳酸盐富积层不是成壤碳酸盐,而与地下水作用密切相关;上部(３４～２．６ＭａＢ．Ｐ．)是典型的风尘堆积－土壤序列。由于中国西北和中亚干旱区的存在是黄河中游风尘堆积的前提条件,该区风尘物质的堆积起始于６．２ＭａＢ．Ｐ．前后标志着源区干旱化的加剧,并已达到相当高的程度。对整个序列的分析表明,源区干旱化程度在６．２～５．４ＭａＢ．Ｐ．期间较高,此后降低,在３．４ＭａＢ．Ｐ．和２．６ＭａＢ．Ｐ．又两次显著增强。上述历史与北极冰盖的起源和演化历史具有高度的一致性,若干重大转变与青藏高原隆升也有时代上的耦合性。本文认为,北极冰盖的形成演化和高原隆升都是中国西北和中亚地区干旱化发展的重要驱动因素,二者对西伯利亚高压的形成和发展的影响及高原对暖湿气流的阻挡可能是导致于旱化的重要途径。 相似文献
14.
晚第三纪中国西北干旱化的发展及其与北极冰盖形成演化和青藏高原隆升的关系 总被引：41，自引：15，他引：26
对甘肃酉峰晚第三纪红土标准剖面的研究揭示出,该区红土下部（６．２ＭａＢ．Ｐ．前）是红化的土壤物质与其它物质一起经水流搬运（坡积作用为主）再堆积的产物;中部（６．２～３．４ＭａＢ．Ｐ．）未发现再搬运的痕迹,是风尘堆积经风化和频繁地下水位波动作用所形成,不具明显的土壤发生学层次,其中的碳酸盐富积层不是成壤碳酸盐,而与地下水作用密切相关;上部（３４～２．６ＭａＢ．Ｐ．）是典型的风尘堆积－土壤序列。由于中国西北和中亚干旱区的存在是黄河中游风尘堆积的前提条件,该区风尘物质的堆积起始于６．２ＭａＢ．Ｐ．前后标志着源区干旱化的加剧,并已达到相当高的程度。对整个序列的分析表明,源区干旱化程度在６．２～５．４ＭａＢ．Ｐ．期间较高,此后降低,在３．４ＭａＢ．Ｐ．和２．６ＭａＢ．Ｐ．又两次显著增强。上述历史与北极冰盖的起源和演化历史具有高度的一致性,若干重大转变与青藏高原隆升也有时代上的耦合性。本文认为,北极冰盖的形成演化和高原隆升都是中国西北和中亚地区干旱化发展的重要驱动因素,二者对西伯利亚高压的形成和发展的影响及高原对暖湿气流的阻挡可能是导致于旱化的重要途径。 相似文献
15.
A 9300 yr-old zone of disseminated volcanic ash in North Atlantic sediments between 45° N and 65° N provides a time-synchronous reference layer against which we have compared the stratigraphic level of deglacial warming of ocean surface waters. In the Atlantic north of 45° N the most prominent feature of this warming is the replacement of low-carbonate glacial marine sediment containing only a single species of polar Foraminifera by calcareous oozes containing a diverse temperate fauna and flora. The local terminations of glacial conditions marked by this change are not synchronous at these latitudes, but range from 13,500 yr B.P. or older in the southeast near Great Britain to 6,500 yr B.P. or younger in the northwest near Greenland. Regionally, these local warmings trace the progressive westward and northward retreat of polar water from the North Atlantic. Since the withdrawal of polar water from the North Atlantic coincides with the northward shrinkage of temperate-latitude continental ice sheets, it is the best oceanic analog to continental deglaciation.Faunal, floral, lithologic, and isotopic parameters showing evidence for a sudden deglacial warming may not be time-synchronous; those parameters are subject to a range of environmental controls and may thus respond differently to the causal mechanism for global warming. 相似文献
16.
Five widespread tephra layers are found in late Quaternary sediments (0–130,000 yr B.P.) of the Eastern Mediterranean Sea. These layers have been correlated among abyssal cores and to their respective terrestrial sources by electron-probe microanalysis of glass and pumice shards. Major element variations are sufficient to discriminate unambiguously between the five major layers. Oxygen isotope stratigraphy in one of the cores studied was used to data four of the five layers. Two of the widespread layers are derived from explosive eruptions of the Santorini volcanic complex: the Minoan Ash (3370 yr B.P.) and the Acrotiri Ignimbrite (18,000 yr B.P.). An additional layer, found in one core only, is most likely correlated to the Middle Pumice Series of Santorini (approximately 100,000 yr B.P.). Two layers are correlated to deposits on the islands of Yali and Kos and date to 31,000 and 120,000 yr B.P., respectively. One layer originated from the Neapolitan area of Italy 38,000 yr B.P. 相似文献
17.
R.K. Matthews 《Quaternary Research》1973,3(1):147-153
Calculations confirm that the uplift of Barbados during the past 130,000 yr has been at nearly constant relative rates in the Clermont and Christ Church standard traverses, and that sea levels responsible for Barbados terraces I (82,000 yr B.P.) and II (105,000 yr B.P.) attained approximately the same level which was 20–25 m below the level represented by Barbados III (125,000 yr B.P.).Preference for the correlation of Barbados III with the prominent first interglacial 18O peak in stage 5 is stated once again. Further, correlation with Eemian and Pangaion of the European pollen record is suggested. 相似文献
18.
The arguments justifying the revised timing of breakup between Australia and Antarctica (Cande and Mutter, 1982) and the reconstruction of Broken Ridge and Kerguelen Plateau (Mutter and Cande, 1983) are reviewed and considered with respect to new subsidence data. The age of breakup was revised from anomaly 22 time (55 My B.P.) to anomaly 34 time (85 My B.P.). The rough topography of the Diamantina Zone can be attributed to very slow spreading (−5 mm/yr.) beginning between the times of anomaly 34 and anomaly 19. The reconstruction of Broken Ridge and Kerguelen Plateau at anomaly 34 time shows overlap of these two features, but the overlap problem is nearly resolved by anomaly 18 time ( ~ 42 My B.P.). Normal seafloor spreading rates (22 mm/yr.) commenced at anomaly 19 time ( ~ 43 My B.P.). Subsidence patterns calculated from biostratigraphic data from wells drilled along Australia's southern margin are interpreted as more consistent with the revised age of Australia-Antarctic breakup. Subsidence curves systematically show rapid subsidence associated with the rift phase of margin development followed by much slower thermally-controlled subsidence during the drift phase. The timing of the rift-to-drift transition is believed to coincide with the age of breakup ( ~ 60 to 110 My B.P.). In addition, the subsidence curves indicate a west-to-east propagation of breakup along the southern margin. Magnetic anomaly patterns and stratigraphie observations are consistent with this hypothesis. 相似文献
19.
Larry V. Benson 《Quaternary Research》1978,9(3):300-318
Samples of algal tufa, gastropods and calcite-cemented sand were collected from the Walker and Pyramid Lake areas of the Lahontan Basin, Nevada. X-ray diffraction petrographic and radiocarbon analyses show that massive forms of tufa such as the dendritic variety contain secondary carbon-bearing material and therefore yield unreliable radiocarbon dates. Dense coating of tufa (lithoid), however, gave radiocarbon ages in agreement with dates on coexisting aragonite gastropods. Radiocarbon data from the study were combined with previously dated noncarbonate materials [Born, S. M. (1972). “Lake Quaternary History, Deltaic Sedimentation, and Mudlump Formation at Pyramid Lake, Nevada”, Center for Water Resources, Desert Research Inst., Reno, Nevada] to give an internally consistent record of lake level fluctuations for the past 40,000 years. The main features of the Lahontan chronology are (1) extreme high stands (1330 m above sea level) 13,500 to 11,000 and 25,000 to 22,000 B.P., (2) a moderate high stand (1260 m above sea level) 20,000 to 15,000 B.P., (3) a low stand of unknown elevation 40,000 to 25,000 B.P., (4) an extremely low stand 9000 to 5000 B.P., and (5) an overall increase in the size of Walker and Pyramid Lakes during the past 5000 years, until the late 19th century. Pore fluid data indicate that Walker Lake desiccated sometime during the period 9050 to 6400 B.P. Salts deposited as a result of this dessication are still undergoing dissolution causing a flux of chloride, carbon, and other solute species from the sediments to the overlying lake water. Pore fluid data obtained from Pyramid Lake sediments do not indicate the presence of a concentrated brine at depth. This suggests that Pyramid Lake did not dry completely during this period although it may have been severely reduced in size. There has been considerable disagreement regarding the occurrence of extreme arid conditions (altithermal period) since 10,000 B.P. [Mehringer, P. J. (1977). “Models and Great Basin Prehistory”. Desert Research Inst. Pub, Reno, Nevada]. The data of this study suggest that such a climatic regime did occur in the western Great Basin during the period 9000 to 5000 B.P. 相似文献
20.
Richard B. Brugam 《Quaternary Research》1980,13(1):133-146
Fossil diatom assemblages from a 12-m core from Kirchner Marsh were compared with modern surface assemblages from 159 Minnesota and labrador lakes using cluster analysis. The deepest levels of the core (spruce pollen zone 13,000 to 10,200 yr B.P.) resemble modern diatom assemblages from deep oligotrophic lakes of northeastern Minnesota. Diatom assemblages of the pine pollen zone (about 10,200 to 9500 yr B.P.) have few modern analogs. In the oak zone (9500 yr B.P. to present) after a brief pulse of diatom species indicative of eutrophication, the assemblages are dominated by species characteristic of shallow lakes, suggesting a drop in the lake water level during the prairie period (5500 to 7500 yr B.P.). Macrofossil data of W. A. Watts and T. C. Winter (1966, Geological Society of America Bulletin77, 1339–1360) show that this shift to shallow-water diatoms occurred when aquatic macrophytes appeared at the site in abundance. 相似文献