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1.
Thermokarst landforms and processes in Ares Vallis, Mars   总被引：1，自引：0，他引：1  
With a length of 1500 km, Ares Vallis is one of the largest martian outflow channels, and is inferred to have been formed by cataclysmic floods of water conveyed from source areas, which are marked by chaotic terrain, to Chryse Planitia. Near its downstream outlet (14°N, 28°W), the floor of Ares widens to 100 km from its average 25 km width. This area of widened channel floor is marked by a complex of irregular terraces, elongated depressions, linear ridges, sinuous ridges, and other indicators of highly irregular dissection of a formerly continuous surface. Thermokarst processes, following either glacial or alluvial histories, seem best to explain these relationships. Various indicators of fluctuating discharge for water and sediment, ponding of debris, and prolonged flow suggest the emplacement of ice-rich debris in the anomalous reach of Ares Vallis. Post-flood or post-glacial thawing of the ice-rich sediments would then generate the thermokarst landscape. These processes, which are consistent with other indicators of anomalously warm climatic conditions, imply a profound change from the modern martian environment.  相似文献   

2.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants.  相似文献   

3.
Vegetation, microclimate, seedling frequency, freezing tolerance, and cold acclimation were compared for seedlings of Artemisia tridentata collected from 1775, 2175, and 2575 m elevation in the eastern Sierra Nevada, California. Data were used to test the hypothesis that ecotypic differences in stress physiology are important for seedling survival along gradients from desert to montane ecosystems. The vegetation canopy cover and A. tridentata seedling frequency were greatest at 2575 m, compared to 1775 and 2175 m. Snow cover ameliorated temperatures near the soil surface for part of the winter and depth varied across elevations. Freezing tolerance was compared for seedlings maintained in growth chambers at day/night air temperatures of 25°C/15°C. The temperature at which electrolyte leakage and Photosystem II function (FV/FM) from leaves were half-maximum was approximately −13·5°C for leaves of seedlings from all three elevations. Shifting day/night air temperatures from 25°C/15°C to 15°C/5°C initiated about 1·5° of acclimation by plants from all three altitudes, with seedlings from the highest elevation exhibiting the greatest acclimation change. Measurements of ambient air and canopy temperatures at the three elevations indicated that wintertime average low temperatures were consistent with the measured degree of freezing tolerance. At small spatial scales used in this study, pollen and seed dispersal between study sites may have precluded resolution of ecotypic differences. Patterns of freezing tolerance and cold acclimation may depend on a combination of mesoclimate and microclimate temperatures, canopy cover, snow depth, and snow melt patterns.  相似文献   

4.
The distribution of mountain permafrost along Trail Ridge Road (TRR) in Rocky Mountain National Park, Colorado, was modeled using ‘frost numbers’ and a ‘temperature of permafrost model’ (TTOP) in order to assess the accuracy of prediction models. The TTOP model is based on regional observations of air temperature and heat transfer functions involving vegetation, soil, and snow; whereas the frost number model is based on site-specific ratios of ground temperature measurements of frozen and thawed degree-days. Thirty HOBO© temperature data loggers were installed near the surface as well as at depth (30 to 85 cm). From mid-July 2008 to 2010, the mean annual soil temperature (MAST) for all surface sites was − 1.5 °C. Frost numbers averaged 0.56; TTOP averaged − 1.8 °C. The MAST was colder on western-facing slopes at high elevations. Surface and deeper probes had similar MASTs; however, deeper probes had less daily and seasonal variation. Another model developed at the regional scale based on proxy indicators of permafrost (rock glaciers and land cover) classified 5.1 km2 of permafrost within the study area, whereas co-kriging interpolations of frost numbers and TTOP data indicated 2.0 km2 and 4.6 km2 of permafrost, respectively. Only 0.8 km2 were common among all three models. Three boreholes drilled within 2 m of TRR indicate that permafrost does not exist at these locations despite each borehole being classified as containing permafrost by at least one model. Addressing model uncertainty is important because nutrients stored within frozen or frost-affected soils can be released and impact alpine water bodies. The uncertainty also exposes two fundamental problems: empirical models designed for high latitudes are not necessarily applicable to mountain permafrost, and the presence of mountain permafrost in the alpine tundra of the Colorado Front Range has not been validated.  相似文献   

5.
Jason R. Janke   《Geomorphology》2005,67(3-4):375-389
Permafrost distribution, or ground that remains frozen for at least 2 years, has been modeled using a combination of Geographic Information System (GIS) techniques, Digital Elevation Model (DEM) variables, and land cover in alpine regions of the world. In the Front Range, however, no such empirical models have been developed, and field data are restricted in spatial extent, but rock glaciers are in abundance. Here, I present a probabilistic logistic regression model that is based on topoclimatic information (elevation and aspect) for rock glaciers derived from U.S. Geological Survey (USGS) 10-m DEMs. Classes of land cover, obtained from an Enhanced Thematic Mapper Plus (ETM+) image classification, were assigned weights and were then multiplied by the regression results to refine estimates. The effectiveness of the model was evaluated by comparing mean probability scores with rock glacier activity categories, Mean Annual Air Temperature (MAAT) from climatic stations on Niwot Ridge, and Bottom Temperature of winter Snow (BTS) measurements, while a Monte Carlo simulation was used to detect uncertainty associated with the original DEM. Permafrost scores >50% covered about 8.9% (242 km2) of the study area (2722 km2) with the highest scores clustered around Longs and Rowe Peaks. Permafrost locations showed a strong correlation with rock glacier activity classes, the −1.0 °C MAAT isotherm, and BTS measurements less than −3.0 °C. The uncertainty analysis revealed that slight global differences exist between the original and error prone DEM; however, local variations in aspect caused the most uncertainty. These results indicate that the model accurately represents regional distribution of permafrost. Therefore, topoclimatic information from rock glaciers and land cover, when combined with an uncertainty analysis, can effectively be used to map the occurrence of Front Range permafrost, providing an imperative tool for cartographers, planners, and geocryologists.  相似文献   

6.
Three-week old soybean (Glycine max) plants were subjected to a factorial combination of four regimes of soil matric water potential (ψm=−0·03, −0·5, −1·0 and −1·5 MPa), two levels of supplementary Zn (O and 20 mgl−1) and two levels of foliar IAA application (O and 10 mgl−1). Under control conditions (no Zn, no IAA), increasing soil drying progressively retarded shoot and root growth (length and dry mass production), reduced leaf relative water content (RWC) and decreased the contents of chlorophyll (Chl) and shoot soluble sugars (SS), but increased soluble sugar content of roots and lowered osmotic water potential of shoots and roots (osmotic adjustment). Total free amino acid (TAA) content increased in shoots but decreased in roots whereas contents of soluble proteins (SP) decreased in shoots and roots. The effect of water stress was statistically significant (p<0·05) and had a major effect (as indicated by η2values) on leaf RWC, shoot and root dry masses and osmotic potential. Supplementary Zn improved root growth at all levels of stress and shoot growth under severe stress. Improvement of growth was positively correlated with the internal tissue Zn concentrations (r=0·91 and 0·86 for shoot and 0·94 and 0·82 for root length and dry mass respectively). Exogenous IAA raised (p<0·05) RWC, Chl, DM (slightly), root SS, and SP, whereas shoot TAA was lowered. Effects on root TAA and shoot SS were more complex: they were lowered at zero stress and raised under severe stress. IAA and Zn in combination had additive effects on Chl, growth and osmotic potential, but their combined effects on SP and TAA were more complex. It is concluded that the treatment of soybean plants grown under conditions of low soil water potentials and Zn deficiency with Zn and IAA solutions counteracted the deleterious effects of stress, especially at high stress levels, and helped stressed plants to grow successfully under these adverse unfavourable conditions.  相似文献   

7.
The standard metabolic rate ofUromastyx philbyiwas measured at 20–40 °C, using constant pressure manometric respirometers. Standard metabolic rate was mass-dependent. Values for the mass exponent ‘b’ ranged from 0·75 at 20 °C to 0·82 at 40 °C. Standard metabolic rate increased as temperature increased with high Q10values at low temperatures (20–25 °C). Low standard metabolic rates in this species are probably an adaptation to herbivory in hot desert environments.  相似文献   

8.
The water status of Terminalia brownii seedlings was assessed in relation to incident microclimate and initial irrigation treatments, during establishment at Olorgesailie in the Rift Valley of Kenya. Experimental treatments involved incorporation of a water-absorbing polymer with the root systems of the plants during establishment, and repeated irrigation, in a factorial design. The maximum photosynthetically active radiation of over 2500 μmol/m2/s recorded during the first 9 days after outplanting was associated with air temperatures of up to 47·4°C, and leaf-to-air vapour pressure deficits (VPDs) of up to 8·04 kPa. Water potentials declined to a minimum of -3·7 MPa, 9 days after outplanting, indicating severe water deficits. Stomatal conductances were generally below 0·2 cm/s, reflecting a high degree of stomatal closure. However, conductances of over 1·3 cm/s were observed on the 6th day after outplanting, associated with VPDs below 1·5 kPa. These relatively high conductances were restricted to plants which had received irrigation; overall, irrigation was found to significantly increase stomatal conductance on three of the four measurement days. Although the application of synthetic polymers increased stomatal conductances on two of the measurement days, the effects were very slight (treated means 0·02-0·03 cm/s higher than controls). These results indicate the severity of the transplant shock in semi-arid sites for seedling water status, and imply that initial irrigation treatments are more likely to increase establishment rates of tree seedlings than application of synthetic polymers.  相似文献   

9.
The profile distribution of total, diethylene triamine penta-acetic acid (DTPA)- and 0·1 HCl-extractable Fe and Mn were determined in 12 pedons formed on three contiguous sand dunes in the semi-arid savanna of Nigeria. The total Fe and Mn contents varied from 100 to 3750 and 40 to 11,375 μg g−1, respectively. Values of 0·1 HCl-extractable Fe and Mn varied from 8·0 to 123 and 1·5 to 43·5 μg g−1, respectively. The corresponding values of DTPA-extractable Fe and Mn were 4·5 to 16·0 and 1·0 to 38·8 μg g−1. Total Fe and Mn correlated significantly with clay in nearly all the dunes (p≤ 0·01) but were not significantly correlated with organic matter. The 0·1 HCl-extractable Mn had a positive significant correlation with soil pH (r= 0·58*) in Illela dunes but a negative significant correlation with pH in the Sangiwa dunes (r= −0·75***). The values of extractable Fe and Mn in the sand dune soils are above the critical limits reported in other literature, thus deficiencies of these micronutrients do not pose a problem to crop production in the study area.  相似文献   

10.
Characterizing spatial variability of soil nutrients in relation to site properties, including climate, land use, landscape position and other variables, is important for understanding how ecosystems work and assessing the effects of future land use change on soil nutrients. In order to assess the effects of land use and landscape position on soil nutrients consisting of soil organic matter (SOM), total N (TN), total P (TP), available N (AN) and available P (AP), soil samples were collected in August and October 1998 and July 1999 from three transects in a small catchment on the loess plateau, China. The three transects consisted of typical land use structure from the top to foot of hillslope in the study area: fallow land – cropland – woodland – orchard (T1), fallow land – shrub land – fallow land – cropland – woodland – orchard (T2) and intercropping land – woodland (T3). Significant differences among land uses were found for SOM, TN and AN. Woodland, shrub land and grassland had the higher levels for them compared to fallow land and cropland. Use of soil deterioration index showed that soils deteriorated moderately (−17·05%) under orchard and seriously (ranging from −29·91% to −20·32%) under fallow land, cropland and intercropping land, while soils had no deterioration (−0·74%) under shrubland and (−0·69%) grassland. This study indicated that the cultivated hilly lands must be abandoned before a critical minimum SOM of 0·492%. Soil nutrient responses to landscape positions were variable depending on transect and the location of land use types. The highest levels in SOM, TN and AN were observed at middle slope position on T1, while they occurred at foot slope position on T3. However, an increasing trend from upper slope to foot slope for five nutrients were found on T2.  相似文献   

11.
The columnar cactus Polaskia chende, endemic to Central Mexico, occurs in the wild and in silviculturally managed populations where artificial selection for better edible fruits operates by sparing and favouring desirable phenotypes during vegetation clearance. Wild and managed populations were compared in morphology and reproductive biology to analyse if human selection has influenced phenotypic divergence, if it has modified breeding systems and if reproductive isolation exists between them. Fruits from managed populations were larger (6·36±0·17 cm3), heavier (19·62±1·32), sweeter (9·07±0·25 °Brix), and with thinner peel (2·09±0·13 mm) than those from wild populations (5·77±0·18 cm3, 15·73±0·85 g, 8·23±0·31 °Brix, and 2·58±0·14 mm, respectively). Both population types bloom synchronically, show diurnal anthesis, with bees as the most likely pollinators, and have breeding system predominantly self-incompatible. Spatial and temporal barriers to pollen exchange between wild and managed populations are unlikely, and morphological differences would be related with an ongoing process of artificial selection.  相似文献   

12.
Four sets of remote sensing images from 1987, 1994, 2000, and 2006, 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the Qinghai–Tibetan Plateau (QTP). It showed that surface soil temperature in the region has increased at an average rate of 0.6 °C per decade between 1980 and 2005, the thawing days on the surface have increased by 60 days from 1983 to 2001, and the depth of the seasonal thawing layer has increased by 54 cm, 102 cm and 77 cm in April, May and June, respectively, from 1983 to 2003. As a result, the upper soil layer has become drier due to the thickening active layer and soil water infiltration. These changes, in turn, have inhibited the growth of alpine meadow vegetation that has shallow root systems. It is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the Qinghai–Tibetan Plateau (QTP).  相似文献   

13.
The fjord landscape of South America, stretching ~ 1500 km between Golfo Corcovado (~ 43°S) and Tierra del Fuego (~ 56°S), is the largest continuous fjord landscape on Earth. This paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models. First-order geological structures are represented by strike-slip faults forming lineaments up to hundreds of kilometres long. The strike-slip faulting has been active since Late Cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to ~ 10 km long. A detailed analysis of these second-order lineaments from digital image data was carried out in three sectors. In Sector 1, located northwest of the North Patagonian Icefield, there are three distinct mean orientations, characterized by a main nearly orogen-parallel orientation (az. ~ 145°) and two orogen-oblique secondary orientations (az. ~ 20° and az. ~ 65°). In Sector 2, located west of the South Patagonian Icefield, there are also three separate mean orientations, with most of the lineaments concentrated between azimuths 0° and 80° (mean at ~ 36°); and two other orogen-oblique means at azimuth ~ 122° and ~ 163°. In Sector 3, around the Cordillera Darwin, there is a single main orogen-parallel mean at ~ 100–115°. In all three sectors, mapped fjord orientations bear a striking similarity to the structural data, with fjords orientated preferentially in the same direction as structural lineaments. We infer that successive glaciations followed the same ice-discharge routes, widening and deepening pre-existing geological structures at the expense of the surrounding terrain to create the fjord landscape. This study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological.  相似文献   

14.
Effects of salinity, temperature, light and their interactions on the rate and final percentage of germination were evaluated for the invasive shrub Prosopis juliflora, grown under arid environmental conditions of the United Arab Emirates (UAE). Seeds that were not treated with NaCl germinated well in a wide range of temperatures and in both full light and complete dark. Seed germination decreased significantly with the increase in both NaCl concentration and temperature. Optimal germination percentage occurred at 25 °C. The inhibitory effect of high salinity on final germination percentage was greater at 40 °C than at 15 and 25 °C. Germination was completely inhibited in 400 mM NaCl at 40 °C and in 600 mM NaCl at 25 °C. However, germination rate was significantly greater at 40 °C than at 15 and 25 °C in lower salinities and the reverse was true at higher salinities. Germination in light was significantly greater than in the dark at lower salinity levels and high temperature.  相似文献   

15.
Lake Lisan, the lake that filled the Jordan graben during the Last Glacial, left behind a well developed sequence of erosional and depositional shore terraces in the south east of the current Dead Sea. These terraces record a series of stillstands that were caused by small transgressions within an overall trend of falling lake levels. The terraces were observed in places where they had not been identified previously. The morphology of the terraces was investigated in six cross-sections using differential GPS altimetry. The levels of the terraces range between − 370 and − 148 m a.s.l. The high stand of Lake Lisan at − 148 m correlates well with the high level of − 150 m reported by Bowman and Gross [Bowman, D., Gross, T., 1992. The highest stand of Lake Lisan: ~ 150 meters below MSL. Israel Journal of Earth-Science 41, 233–237.] along the western coast of Lake Lisan. The lake terraces are horizontal, elongated and tectonically undisturbed, and have a sub-horizontal foreshore (tread) with an average slope of 8.2° and steep backshore cliff (riser) with an average slope of 17.7°. The six cross-sections show a good altitudinal correlation between their terraces. Moreover, the terraces appear in undisturbed continuity on the aerial photos. These morphological characteristics demonstrate that the retreat of the lake was a result of substantial climatic changes, not of tectonic subsidence.In-situ stromatolites were found on most of the terraces, reflecting a shallow water environment and emphasizing that these terraces are recessional. Well-developed desert varnish and Tafoni observed on blocks sitting on the terrace surfaces imply a long period of exposure and a low rate of post lacustrine erosion. The formation of Lisan terraces is constrained mainly by coastal slope, water depth and underlying lithology. The morphological analysis of these terraces allows identification of two kinds of pseudo-terraces, which were formed as a result of tread or riser destruction.U/Th and OSL dating allowed the dating of three events within the lake level curve more precisely. The high level of − 148 m occurred at 30.5 ± 0.22 ka BP, consistent with the Heinrich Event 3 and Dansgaard–Oeschger stadial 5, the coldest period in the NGRIP Greenland Ice Core record. The next lower terrace at − 154 m was formed at 22.9 ka BP ± 0.29 and corresponds to the stadial 2C, the final phase of the Last High Glacial. The correlation between the Lisan high stands and climatic stadials suggests that Northern-Hemispheric cold periods led to periods with a more positive water balance in the Near East. At ~ 10 ± 0.8 ka BP Lake Lisan experienced a sharp drop to − 200 m followed by a transgression between 9.5 to 7 ka BP.  相似文献   

16.
On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.  相似文献   

17.
Addition and incorporation of organic fertilizers is known to improve the properties of agricultural soils. Therefore, during 22 weeks of field incubation we studied the biodegradation (measured by static absorption of CO2) of two organic manures viz. municipal refuse and chicken manure incorporated into sandy soils, under sprinker irrigation, at the rates of 0, 16·5, 33·0, 49·5 and 66·0, and 0, 4·1, 8·25, 16·5, and 33·0 tonnes/ha, respectively.The results obtained indicated that the cumulative amount of CO2 respired was linearly correlated with the rate of organic material applied (p < 0.001). Statistical analysis of the data obtained showed that both the intercept (rate of decomposition) and the slope (rate of reaction with time) increased with increasing rate of application of organic manure. The magnitude of increment was highest at the application rates of 33·0 and 8·25 tonnes/ha for municipal refuse and chicken manure, respectively. The rate of increment, generally, declined thereafter thus indicating that these two rates are the optimum levels of incorporation of the appropriate organic manures under the conditions of this study.The maximum organic-carbon mineralized, accounting for 10·5 and approximately 50%, was obtained at the optimum rates for municipal refuse and chicken manure, respectively. Both simple and multiple regression equations describing the relationship between soil temperature and soil-moisture content each separately and in combination, as independent variables, and the cumulative rate of CO2 production were computed. A substantially strong relationship with soil temperature but inconsistent and contradicting results with soil moisture were obtained. Inclusion of soil temperature and moisture in a single model as an independent variable in relation to cumulative CO2 as a dependent variable improved the soil moisture-CO2 production relationship.  相似文献   

18.
In vitro mass propagation of Acacia seyal Del. was achieved using seedling shoot tip explants on Murashige and Skoog (MS) medium supplemented with 6-benzyladenine (BA) or Thidiazuron (TDZ) with ∝-Naphtalene acetic acid (NAA). The best result was obtained with BA in the presence of NAA. The greatest shoot multiplication with long shoots was observed on media containing (mg l-1) 2·0 BA with 0·1 or 0·5 NAA and 4·0 BA with 0·1 NAA; with 6·4 and 6·7 mean number of shoots, respectively. TDZ also induced multiple shoots but most of the shoots were stunted. Microshoots were rooted better on half-MS salts supplemented with Indole-3-butyric acid (IBA). The highest rooting percentage (80%) and root number (4·9 roots/microshoot) were promoted by 4·0 mg IBA. The plantlets (90%) successfully survived acclimatization ex vitro.  相似文献   

19.
This study investigates the origin and regional tectonic implications of high-altitude Plio (?)–Quaternary fluvial deposits developed over the Bozdağ horst which is an important structural element within the horst–graben system of western Anatolia, Turkey.A total of 23 deposits occur near the modern drainage divide comprising fluvial to occasionally lacustrine deposits. The deposits are all elongated in N–S direction with a width / length ratio of 1 / 10. The largest of them is of 13 km in length with a maximum observable thickness of about 100–110 m. Morphological, lithological, deformational characteristics of these deposits and the drainage system of the area all suggest that the deposits were formed due to uplift and southward tilting of the Bozdağ horst. This tilting which is estimated as 1.2° to 2.2° caused accumulation of the stream load along channels flowing from south to north. All the deposits were later dissected by the same streams with the exception of one deposit which still preserves its original lake form. These deposits are of Quaternary age, which corresponds to the latest N–S directed extensional tectonic phase in the region.  相似文献   

20.
The selective use by cattle of range resources in the Sahel was assessed in terms of quantity and nutritional quality of the herbage grazed and diet selected. Peak standing crop was 1951 kg ha−1dry matter (DM) with 47·9 kg nitrogen (N) ha−1and 7·4 kg phosphorus (P) ha−1. Esophageally fistulated cattle diets were consistently (p<0·05) higher in N, P and organic matter digestibility (OMD) than the herbage grazed. Cattle consumed 48% of the mean annual herbage production. The results indicate grazing ruminants select a higher quality diet from Sahelian rangelands than can be predicted on the basis of pasture evaluation alone. Therefore, the foraging behaviour of the animals needs to be considered in the evaluation of Sahelian rangelands for animal production.  相似文献   

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