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1.
Pollen analysis of the organic surface (FH) horizon of a radiocarbon-dated palaeopodzol buried beneath the 'Little Ice Age' outer moraine of Haugabreen west of the Jostedalsbrecn ice-cap, southern Norway, provided evidence for environmental change in the area between ca. 4,000 B. P. and the 13th century A. D. Radiocarbon dating of the profile, apart from providing a chronology for the changes interpreted, also allowed estimation of pollen incorporation rates into the soil which can be compared with pollen influx rates established elsewhere. Two periods of local woodland recession were identified, the first between ca. 3,300 B. P. and ca. 3,600 B. P., after the initiation of the FH horizon, and the second in the 13th century A. D. at the onset of the Little Ice Age.  相似文献   

2.
14C dating and pollen analysis of the surface organic (LFH) horizons of several humo-ferric podzol profiles forming a soil catena close to the 'Little Ice Agc' outer moraine ridge of Haugabreen, southern Norway, are used to examine the timing and nature of podzol development at the low-/sub-alpine margin of the Jostedalsbreen area. Comparison with results from a palaeosol buried beneath the outer moraine shows that FH horizon development began as early as 5,265 ± 65 B.P., but that it was not synehronous across the profiles, the latest profile having a date of 3,590 ± 65 B.P. It is argued that surface organic horizons developed as a response to a deterioration of climate and possibly the recrudescence of the Myklebustbreen ice cap at c . 5,000 B.P., and that the dates for horizon initiation vary according to local topographic and soil-hydrologic conditions. It is still uncertain whether the hump-ferric podzols were preceded by brown earths or weakly podzolised sub-alpine podzolic soils, but at all sites where pollen evidence is available it appears that FH initiation took place beneath Betula woodland.  相似文献   

3.
At The Rustad Quarry Site (32RI775), in southeastern North Dakota, Early Archaic artifacts, bison bone, and hearth features were found in the lowest of three Boroll-like buried soils formed in alluvial fan sediments. Alluvial fan sediments were deposited from 8000 to 4925 B.P., and were then buried by eolian sand. The alluvial fan sediments (mudflows) bury lacustrine sediments (Sherack Formation deposited from 9900 to 9500 B.P. in Glacial Lake Agassiz II), both of which overlie a Moorhead Phase fluvial terrace deposited from 10,900 to 9,900 B.P. Cultural remains were associated with five radiocarbon ages, three on archaeological charcoal (7180 B.P., 7240 B.P., and 7550 B.P.) and two on organic carbon from two welded A-horizons containing the cultural remains (7370 B.P. and 7675 B.P.). A well-developed Aquoll-like soil formed in the lacustrine sediments from 9500 to 8000 B.P. Soil morphology and chemistry of the Boroll-like fan soils, the Aquoll-like lacustrine soil, and other Boroll-like soils formed in eolian and deltaic sediments nearby suggest a subhumid, cool continental climate with riparian woodland and mixed prairie vegetation at the site and surrounding area from 11,400 B.P. to the present. This partially contradicts paleoenvironmental reconstruction from pollen sites nearby that suggest the area was covered by a closed canopy spruce forest from terminal late-Pleistocene to 10,000 B.P. Alluvial fan formation and eolian activity on the adjacent Sheyenne Delta occurred from 8000 to 5000 B.P., which indicates greater landscape instability and drier conditions during the mid-Holocene (Altithermal).  相似文献   

4.
Continuous core samples were taken through the unsaturated zone at three sites on the outcrop of Permo-Triassic sandstone in the British West Midlands. Sample sites were chosen for lack of recent, direct anthropogenic disturbance, and for differing vegetation: heathland, birch woodland and conifer forest. Interstitial water was extracted and analyzed for 32 major and trace elements. Solid phases were analyzed for exchangeable cations and mineralogy. The rate of recharge calculated using a Cl mass balance method was three times greater below heathland than below afforested sites owing to higher evapotranspiration rates in the woodlands.Carbonate minerals were absent from the unsaturated zone at each site. Soil solutions were acidic and soils at the woodland sites were more acidic (pH 4.0) than those at the heathland site (pH 4.5). Acidic interstitial water solutions were found to up to 5.0 m depth in the unsaturated zone and are partially neutralized by two aluminosilicate mineral reactions in the unsaturated zone: cation exchange and K-feldspar dissolution. The rate at which these acid neutralizing reactions act to neutralize acidity is revealed by the rate of depletion of base cations from the unsaturated zone in recharge solutions; K+ (dissolution), Ca+2 + Mg+2 (cation exchange). The total base cation depletion rate was greatest below heathland; this can be attributed mainly to the greater rate of SO4 assimilation by the woodland biome.  相似文献   

5.
Dodson, John R. & Bradshaw, Richard H. W. 1987 06 01: A history of vegetation and fire, 6,600 B.P. to present, County Sligo, western Ireland. Boreas , Vol. 16, pp. 113–123. Oslo. ISSN 0300–9483.
Two lake sites on metamorphic rocks with small catchments and one mor humus deposit have been analysed to assess the relative influences of fire, man and climate upon the regional and local vegetation of the Lough Gill region of County Sligo. The vegetation of the area was dominated by mixed woodland from 6,600 B.P. to 600 B.P. The first evidence of human impact on the forests was around 5,400 B.P. in the form of clearance for pasture. The intensity of human impact varied between sites, and there were periods of forest recovery as well as decline. From 600 B.P. widespread forest destruction took place, and pasture with heathland became predominant. Pinus sylvestris had a major presence until about 5,400 B.P. It declined from this time and had a patchy distribution by 2,000 B.P. The decline of Pinus was linked with the expansion of treeless peatland in what are presumed to be wet periods, and Pinus recovery in drier periods. Fire may have encouraged the spread of heathland at the expense of Pinus . Arbutus unedo pollen was found at Slish Lake as early as 1,900 B.P., suggesting that it is native to this area. Isolated trees survive today at woodland edges. Charcoal particles occurred in all the profiles. Fire was particularly associated with heathland communities, and may have been used as a management tool to improve grazing conditions. Some of the phases of woodland decline correlate strongly with charcoal input suggesting forest destruction by fire.  相似文献   

6.
Two buried paleocatenas were studied to determine some features and techniques by which buried soils could be recognized, and to define their pedological characteristics, their lateral variation, and their contemporary environment. At Woodhall Spa, Lincolnshire, a ferric podzol to sandy gley sequence was developed in sands under marine clay and fen peat. The peat was radiocarbon dated at about 4100 yr BP. The buried soil was evident from its obvious catenary character and the soil characteristics and contemporary environment were determined using sand mineralogy, micromorphology, and pollen analysis. At West Runton, Norfolk, an apparently similar ferric podzol sequence occurred in Beestonian sands and gravels under a layer of Cromerian organic muds. However, only the uppermost profile contained definite evidence of soil formation. Other lower profiles contained pseudosoil features produced by sedimentation or diagenetic subsurface iron mobilization. It is suggested that the occurrence of a paleocatena is the most important criterion for the identification of a buried soil. Sedimentation and diagenesis cannot reproduce this lateral variation.  相似文献   

7.
如同137Cs和210Pbex核尘埃,土壤和坝库沉积物中的孢粉也源于大气沉降,是否能用于侵蚀产沙的示踪研究?在陕北吴旗周湾水库采集了一些表层土壤和现代淤地坝、古代聚湫坝沉积泥沙的样品,尝试土地利用/覆被变化和侵蚀产沙的孢粉示踪研究。初步研究表明:草地表土孢粉丰富,平均浓度为26077粒/g;有33个科属的花粉,孢粉组合反映了当地以蒿属为主的半干旱温带草原植被;坡耕地表土的孢粉组合和草地一致,但孢粉平均浓度远低于草地,仅5844粒/g。坝库沉积剖面中,和137Cs核素一样,孢粉也富集于每一洪水沉积旋迴的上部层位,可用于沉积旋迴的区分。现代沉积旋迴的孢粉平均浓度,远低于草地和坡耕地表土,这表明草地和坡耕地土壤不是沉积泥沙的主要来源。古代沉积物的孢粉平均浓度高于现代沉积,表明流域内300年前的植被好于现代,或300年前沟谷地的相对产沙量低于现代。古代孢粉组合中十字花科花粉比例高达36·85%,明显高于现代的0·58%含量,这表明草地退化严重,十字花科植物比例急剧降低。孢粉示踪技术在植被环境恢复,沉积旋迴区分,和泥沙来源确定等方面具有一定的潜力,但应建立针对土地利用/覆被变化和侵蚀产沙研究的孢粉示踪技术方法。  相似文献   

8.
14C dating and pollen analytical evidence is presented relating to the usefulness of arctic-alpine Brown Soils for palaeoenvironmental reconstruction. A present-day soil has been examined together with its continuation beneath the outermost ?Little Ice Age’? end moraine of the glacier Vestre Memurubreen at a location well above the tree-line in the mid-alpine belt of southern Norway. Fourteen 14C dates from chemically-fractionated soil samples, which range in age from 495 ± 55 14C yr in the uppermost 1 cm to > 4000 14C yr within 13 cm of the buried soil surface, demonstrate near-linear age/depth gradients in the palaeosol. Continuous development of the palaeosol over at least 5000 calendar yr prior to burial confirms that Vestre Memurubreen attained its Neoglacial maximum extent in the ?Little Ice Age’?. Pollen stratification in buried and unburied profiles indicates a single vegetation change from a low-alpine dwarf-shrub heath to a mid-alpine ?grass’? heath, reflecting an altitudinal lowering of vegetation belts and a possible climatic cooling of 2-4°C. Surface additions of allochthonous (aeolian) mineral particles appear to have contributed to soil development, whilst mixing processes have been relatively unimportant at this site. The immobilisation of resistant organic residues and the ineffectiveness of biological and chemical activity are major reasons for the preservation of a palaeoenvironmental record in these high altitude soils.  相似文献   

9.
Deposits beneath Mubwindi Swamp provide a partial record of vegetation history since at least 43,000 yr ago. We studied pollen from two cores and obtained nine radiocarbon ages from one of these cores and three radiocarbon ages from the other. Pollen deposited before and soon after the last glacial maximum represents vegetation very different from the modern vegetation of the Mubwindi Swamp catchment. Although species now associated with higher altitudes were dominant some elements of moist lower montane forest persisted, possibly because of favorable soils or topography. The pollen data provides evidence for a late glacial montane forest refuge near Mubwindi Swamp. Moist lower montane forest became much more widespread soon after the glacial maximum. The only irrefutably Holocene sediments from Mubwindi Swamp date to the past 2500 yr. During this time a combination of climatic and human-induced changes in vegetation can be seen in the pollen records.  相似文献   

10.
Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg−1. Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants’ roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of serpentine soils.  相似文献   

11.
《Organic Geochemistry》2011,42(12):1519-1528
On-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13C-labelled tetramethylammonium hydroxide (TMAH) was used to assess the relative contributions of phenolics (lignin, demethylated lignin and non-lignin phenolics) in a peaty gley soil profile beneath an unimproved grassland (LL), from a study site located at Harwood (Northumberland, northeast England, UK). This site also includes an unforested moorland (ML) and a second rotation Sitka spruce stand (SS). The common lignin proxies have been corrected for contributions of non-lignin phenols and demethylated lignin in the LL ecosystem and then compared with those from the ML and SS ecosystems. The phenolic compositions from the contributory vegetation inputs (i.e. grasses, heather and Sitka spruce) to all three soils (LL, ML and SS) were also analysed. By using 13C-labelled TMAH it was possible to show that the chemical composition of soil organic matter (SOM) reflected the different vegetation inputs in each of the L/F layers but these characteristics were lost from the deeper organic and mineral layers. Similar changes in the yield of lignin monomers (Λ) with increasing soil depth were displayed in the LL soil profile as reported previously in the ML soil in that no maxima were observed in these amount-depth profiles. The tannin input to the LL soil is low and as a consequence, unlike the ML and SS soils, there is no progressive decrease in the amounts of these non-lignin phenolics with increasing depth. Finally the methylated carbohydrate derivatives (MC) become more abundant relative to the phenolics with increasing soil depth in all three ecosystems (LL, ML and SS).  相似文献   

12.
On-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13C-labelled tetramethylammonium hydroxide (TMAH) was used to assess the relative contributions of phenolics (lignin, demethylated lignin and non-lignin phenolics) in a peaty gley soil profile beneath an unimproved grassland (LL), from a study site located at Harwood (Northumberland, northeast England, UK). This site also includes an unforested moorland (ML) and a second rotation Sitka spruce stand (SS). The common lignin proxies have been corrected for contributions of non-lignin phenols and demethylated lignin in the LL ecosystem and then compared with those from the ML and SS ecosystems. The phenolic compositions from the contributory vegetation inputs (i.e. grasses, heather and Sitka spruce) to all three soils (LL, ML and SS) were also analysed. By using 13C-labelled TMAH it was possible to show that the chemical composition of soil organic matter (SOM) reflected the different vegetation inputs in each of the L/F layers but these characteristics were lost from the deeper organic and mineral layers. Similar changes in the yield of lignin monomers (Λ) with increasing soil depth were displayed in the LL soil profile as reported previously in the ML soil in that no maxima were observed in these amount-depth profiles. The tannin input to the LL soil is low and as a consequence, unlike the ML and SS soils, there is no progressive decrease in the amounts of these non-lignin phenolics with increasing depth. Finally the methylated carbohydrate derivatives (MC) become more abundant relative to the phenolics with increasing soil depth in all three ecosystems (LL, ML and SS).  相似文献   

13.
Pleistocene sediments and soils exposed at Stebbing in central Essex, England are described, analysed and interpreted. The sand and gravel units above Eocene London Clay and Upper Pliocene Red Crag are shown to be a high level member of the Kesgrave Formation, with a surface immediately beneath that of the Westland Green Gravels, which are tentatively assigned to the Pre-Pastonian ‘a’ Stage of the British Quaternary succession. The rubified, argillic soil developed in the surface of these fluvial deposits is a composite of the Valley Farm and Barham Soils and displays micromorphological evidence of several phases of clay illuviation, gleying and clay coating disruption. Originally truncated and buried beneath Anglian gelifluction deposits, cover sand and till, the soil has been exhumed in most places by subsequent erosion. The full succession, however, is preserved within large gulls that formed by periglacial cambering prior to this erosion. More recent loess incorporation and pedogenesis have modified the exhumed soil and the materials within the gulls.  相似文献   

14.
重庆金佛山表层岩溶生态系统土壤的CO2释放规律   总被引:3,自引:2,他引:3  
采用碱溶液吸收法通过对重庆金佛山林地、裸地表层岩溶生态系统土壤CO2释放量进行野外监测,研究了影响土壤CO2释放量变化的主要因素,揭示土壤CO2释放变化规律。土壤CO2释放量的变化主要随着温度而变化,即气温降低,土壤CO2释放量减少,在昼夜时段,土壤CO2也随温度而变化,但相比温度变化有明显滞后性;降雨对土壤CO2释放有比较复杂的影响,但非简单的线性相关;同时植被也会影响到土壤CO2的释放,总体上,相比裸地而言,林地的土壤CO2的释放量大,但在不同时间段内土壤CO2释放强度与气温的关系有较大差异。一天时间段内林地土壤CO2释放强度与温度的关系较裸地灵敏,这是因为林地本身生物量大,对温度反应敏感,温度很小的变化就能引发土壤CO2释放量的大幅度地改变。而在以月为单位观测时间段时,裸地土壤CO2释放强度与气温的关系较林地灵敏,这可能是因为植被覆盖减缓气温对土温的影响,对土温有较强的调节作用。这种不同植被系统下,在不同时段土壤的CO2释放量动态差异在讨论岩溶作用与碳循环时应充分注意。  相似文献   

15.
The reliability of phytolith assemblage analysis for characterizing Mediterranean vegetation is investigated in this study. Phytolith assemblages are extracted from modern and buried Holocene soils from the middle Rhône valley (France). The relation between modern phytolith assemblages and the surrounding vegetation, as well as between fossil assemblages and contemporaneous vegetation, already reconstructed through other proxies, is discussed. We demonstrate that the main northwestern Mediterranean biomes are well distinguished by soil phytolith assemblage analysis. In particular, the density of pine and nonconiferous trees (densities expressed relatively to the grass cover) and the overall degree of opening of the vegetation appear well recorded by three phytolith indexes. North Mediterranean vegetation changes during the Holocene period, mainly tree line shifts, pine wood development and deforestation are poorly documented, due to the scarcity of proxy-preserving sites. Phytolith assemblage analysis of soils, buried soils, and sediments appears to be a promising technique to fill this gap.  相似文献   

16.
At Green Pond, a small permanent sinkhole pond in Bartow County, northwest Georgia, organic silty clays are buried by up to 2 m of colluvium. Pollen from the clays shows that a Pinus-Quercus-herb (pine-oak-herb) flora was present before 29,630 radiocarbon yr ago. It is interpreted as the product of a xeric woodland with prairie-like openings. Between 29,630 and approximately 25,000 BP, pollen of Pinus and herbs was sparse; Quercus and Carya (hickory) predominated in the pollen rain. There were few other deciduous trees. Oak-hickory forest is thought to have been present. From 25,000 to 23,000 BP, more diverse forest with pines and some Picea (spruce) became established. At the same time Taxodium (swamp cypress) was locally abundant, as were shrubs characteristic of Coastal Plain swamps. Some time after 23,000 BP, the pond basin filled with colluvium and no further sedimentation took place, other than thin muck sedimented on the bottom of the present Green Pond.The sediments were first thought to be of Sangamon age because the pollen sequence has many of the characteristics of an interglacial cycle, but the radiocarbon dates correlate them firmly with the Farmdalian Interstadial. A comparison with known Farmdalian sites is made, but the important sites are in the northern United States and adjacent Canada, too far away to make a useful comparison of the details of pollen diagrams from the two areas. At another Bartow County pond site, Bob Black Pond (Watts, 1970), a flora predominantly of pine with spruce and oak was present immediately before 22,900 BP and a strikingly cold flora with jack-pine, spruce and northern herbs followed immediately after. The radiocarbon dates indicate that the sedimentary sequence at Bob Black Pond immediately follows that at Green Pond.  相似文献   

17.
Andersen, S. Th. 1979 03 01: Brown earth and podzol: soil genesis illuminated by microfossil analysis. Boreas , Vol. 8, pp. 59–73. Oslo. ISSN 0300–9483.
Pollen and other plant microfossils were studied in soil profiles from a Fagus-Quercus petraea woodland in eastern Jutland, Denmark. Fungal hypha fragments in the soil show characteristic length frequency distributions, which indicate comminution by large arthropods and microarthropods (Oribatei) during the burial. Distribution of the hypha fragments within the podzol indicates development from a former brown earth. The pollen sequence in a humus deposit reflects recent vegetational development. Modification of pollen assemblages in the mineral soils can be explained by mixing during burial by soil fauna. Development from brown earth to podzoloid and podzol follows the models assumed by pedologists. The various stages are related to vegetational changes and the processes were completed within a few hundred years.  相似文献   

18.
Pollen taphonomy in a canyon stream   总被引:1,自引:0,他引:1  
Surface soil samples from the forested Chuska Mountains to the arid steppe of the Chinle Valley, Northeastern Arizona, show close correlation between modern pollen rain and vegetation. In contrast, modern alluvium is dominated by Pinus pollen throughout the canyon; it reflects neither the surrounding floodplain nor plateau vegetation. Pollen in surface soils is deposited by wind; pollen grains in alluvium are deposited by a stream as sedimentary particles. Clay-size particles correlate significantly with Pinus, Quercus, and Populus pollen. These pollen types settle, as clay does, in slack water. Chenopodiaceae-Amaranthus, Artemisia, other Tubuliflorae, and indeterminate pollen types correlate with sand-size particles, and are deposited by more turbulent water. Fluctuating pollen frequencies in alluvial deposits are related to sedimentology and do not reflect the local or regional vegetation where the sediments were deposited. Alluvial pollen is unreliable for reconstruction of paleoenvironments.  相似文献   

19.
Marine erosion at Clettnadal, West Burra island off the west coast of Shetland, caused the drainage of a small water body at Clettnadal, exposing deposits of Late Devensian and Holocene age. Pollen, diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event GI‐1. Event GS‐1 is revealed by the non‐pollen evidence, especially by Coleoptera, by sediment stratigraphy, and by radiocarbon dating. In contrast, the pollen evidence indicates that an arctic tundra flora, in which dwarf shrubs were prominent, persisted throughout the Late‐glacial. The Holocene brought colonisation by tree birch, but by ca. 9000 14C yr BP the taxon had almost disappeared. This contrasts strongly with other Holocene pollen records for Shetland where both Betula and Corylus avellana‐type survived longer—at some sites, for example, until ca. 2900 yr BP. The extreme westerly and exposed coastal situation of Clettnadal appears to be responsible both for a muted Late‐glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland. The results provoke questions concerning biological stability at times of marked climatic change. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

20.
Anthrosols (cf. plaggen soils) are commonly found across the homefields of Norse farms, yet the extent to which these taphonomically complex and heterogeneous deposits provide reliable archives of environmental change and vegetation history has rarely been investigated. This paper compares the palynological signature contained within an anthrosol located beside Norse farm ruins in the Eastern Settlement of Greenland, with that from a mire situated ~400 m from the nearest archaeological remains. The investigation covers a period of ~1000 years leading into, through, and beyond the Greenlandic landnám of AD 985. The results demonstrate that, as anticipated, the anthrosol contains a strong signal for human impact associated with settlement and occupation, although changes in both pollen percentages and accumulation rates (influx) through the profile appear smooth, not erratic, and radiocarbon dates are conformable. Thus the palynological signature contained in the anthrosol is broadly comparable to the patterns characteristic of stratified natural contexts (e.g. mires) with small pollen source areas that are located in close proximity to former Norse structures. Nevertheless, it is also demonstrated that secondary microfossils are a major component of the pollen assemblages within the anthrosol, and pollen influx is notably an order of magnitude higher when compared against the peat core taken from the mire. It is suggested that this may result from the addition of pollen contained in animal dung, augmenting that accumulating through the natural accretion of pollen derived from the surrounding vegetation and landing on the surface of the anthrosol. Although this complicates any palynological interpretation, by adopting a cautious approach we argue that anthrosols can be used to extract useful information about vegetation history at a local scale, as well as providing indirect evidence of landscape impacts and resource use around farmsteads.  相似文献   

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