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1.
Outcrop exposures of sedimentary rocks at the Opportunity landing site (Meridiani Planum) form a set of genetically related strata defined here informally as the Burns formation. This formation can be subdivided into lower, middle, and upper units which, respectively, represent eolian dune, eolian sand sheet, and mixed eolian sand sheet and interdune facies associations. Collectively, these three units are at least 7 m thick and define a “wetting-upward” succession which records a progressive increase in the influence of groundwater and, ultimately, surface water in controlling primary depositional processes.The Burns lower unit is interpreted as a dry dune field (though grain composition indicates an evaporitic source), whose preserved record of large-scale cross-bedded sandstones indicates either superimposed bedforms of variable size or reactivation of lee-side slip faces by episodic (possibly seasonal) changes in wind direction. The boundary between the lower and middle units is a significant eolian deflation surface. This surface is interpreted to record eolian erosion down to the capillary fringe of the water table, where increased resistance to wind-induced erosion was promoted by increased sediment cohesiveness in the capillary fringe. The overlying Burns middle unit is characterized by fine-scale planar-laminated to low-angle-stratified sandstones. These sandstones accumulated during lateral migration of eolian impact ripples over the flat to gently undulating sand sheet surface. In terrestrial settings, sand sheets may form an intermediate environment between dune fields and interdune or playa surfaces. The contact between the middle and upper units of the Burns formation is interpreted as a diagenetic front, where recrystallization in the phreatic or capillary zones may have occurred. The upper unit of the Burns formation contains a mixture of sand sheet facies and interdune facies. Interdune facies include wavy bedding, irregular lamination with convolute bedding and possible small tepee or salt-ridge structures, and cm-scale festoon cross-lamination indicative of shallow subaqueous flows marked by current velocities of a few tens of cm/s. Most likely, these currents were gravity-driven, possibly unchannelized flows resulting from the flooding of interdune/playa surfaces. However, evidence for lacustrine sedimentation, including mudstones or in situ bottom-growth evaporites, has not been observed so far at Eagle and Endurance craters.Mineralogical and elemental data indicate that the eolian sandstones of the lower and middle units, as well as the subaqueous and eolian deposits of the Burns upper unit, were derived from an evaporitic source. This indirectly points to a temporally equivalent playa where lacustrine evaporites or ground-water-generated efflorescent crusts were deflated to provide a source of sand-sized particles that were entrained to form eolian dunes and sand sheets. This process is responsible for the development of sulfate eolianites at White Sands, New Mexico, and could have provided a prolific flux of sulfate sediment at Meridiani. Though evidence for surface water in the Burns formation is mostly limited to the upper unit, the associated sulfate eolianites provide strong evidence for the critical role of groundwater in controlling sediment production and stratigraphic architecture throughout the formation.  相似文献   

2.
Based on a δ18O chronology,rare earth elements(REE) and other typical elements in sediments from core MD06-3047 in the western Philippine Sea were analyzed to constrain the provenances of the sediments and investigate quantitative changes in the Asian eolian input to the study area over the last 700 ka.Among the competing processes that might affect REE compositions,sediment provenance is the most important one.Provenance analysis suggests that the study sediments have two provenance end-members;local volcanic sources are dominant,and eolian dust from the Asian continent has a smaller contribution.During glacial periods,eolian input to the western Philippine Sea was enhanced.In contrast,material supply from local volcanics increased during interglacial periods.Changes in eolian input to the study area were probably related to the strength of the East Asian winter monsoon(EAWM) as well as aridity in the Asian continent on an orbital time scale,and were partly influenced by local control factors on shorter time scales.Therefore,we propose that the present study expands the application of the REE-based method for quantitatively estimating the eolian component from the mid-latitude northern Pacific to the low-latitude western Pacific.Additionally,the study preliminarily confirms the influence of EAWM-transported eolian material on sedimentation in the western Philippine Sea since 700 ka.  相似文献   

3.
Based on data from the middle Yellow River basin, a wind-water two-phase mechanism for erosion and sediment-producing processes has been found. By using this mechanism, the extremely strong erosion and sediment yield in the study area can be better explained. The operation of wind and water forces is different in different seasons within a year. During winter and spring, strong wind blows large quantities of eolian sand to gullies and river channels, which are temporally stored there. During the next summer, rainstorms cause runoff that contains much fine loessic material and acts as a powerful force to carry the previously prepared coarse material. As a result, hyperconcentrated flows occur, resulting in high-intensity erosion and sediment yield.  相似文献   

4.
Temporal constraints for the Late Pleistocene deposition of eolian dunes that occur in central and northern Alberta, Canada can be provided by dating sediments from the dune bases using luminescence techniques. In places, however, the postglacial dunes overlie glaciofluvial sands that resemble the eolian deposits in texture such that demarcating the bases of the dunes is often problematic. In this study we address the problem by employing a portable optically stimulated luminescence (OSL) reader to construct luminescence profiles that depict luminescence signal variation with depth. With the portable OSL reader, measurement can be performed on bulk sediments, negating the need for laborious separation procedures to isolate pure mineral fractions, as is required in regular luminescence dating. Measurements can also be carried out in the field, permitting quicker decision making during sample collection. Results from this study, presented as depth variations of feldspar derived infrared stimulated luminescence (IRSL) signals and predominantly quartz‐generated post‐IR blue OSL signals, show that luminescence profiling enables one to distinguish between eolian deposits that make up the dunes from the underlying non‐eolian sands. The identification of such cryptostratigraphic interfaces is made possible by differences in the dosimetric histories of the sediments. The delineation of the dune bases allows targeted sampling that yields best luminescence age approximations for the initiation of postglacial eolian deposition in the region. Luminescence profiling of eolian sequences would also, in theory, permit the identification of depositional breaks of extended duration. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

5.

Grain size of eolian deposits from the Loess Plateau in China has been widely used to reconstruct the history of the East Asian winter monsoon. However, the grain size of bulk samples is only partially indicative to the strength of the winter monsoon because post-depositional weathering processes have significantly changed the grain size of original eolian particles. Here, non-weathered loess samples were separated into eight different particle fractions, and major chemical elements were determined in order to establish a geochemical indicator of original eolian grain size. The results show that SiO2 and Al2O3 contents and the SiO2/Al2O3 ratio in different fractions vary regularly with grain size, and that a good linear relation exists between the SiO2/Al2O3 ratio and grain size for the fractions <50 μm. Because Al and Si are among the most stable elements and pedogenic processes in the Loess Plateau cannot affect the SiO2/Al2O3 ratio, this index can be used to reflect the grain size of original eolian particles. Application of this index in the Weinan and Luochuan loess sections of the last climatic cycle shows that SiO2/Al2O3 is in good agreement with median grain size (Md) in the loess units. On the contrary, SiO2/Al2O3 has documented a series of fluctuations in the soil units that are not clearly indicated by the grain-size changes of bulk samples.

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6.
A record of changes in Nd and Sr isotopic composition of the eolian deposits from the central Loess Plateau has been determined for the past 8 Ma. The isotopic records of the silicate fraction of the Quaternary and Tertiary eolian deposits allow interpreting the interplay between the Sr isotopic variations in the eolian deposits and the late Cenozoic tectonic and climatic changes. The results indicate that the temporal variations of Nd and Sr isotopes show remarkable changes around the beginning of the Quaternary. The lower values of the 143Nd/144Nd and the decreasing trend of the 87Sr/86Sr ratios after 2.58 Ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late Cenozoic uplift induced glacial grinding in the high orogenic belts in central Asia. In this context, the substantial changes in climate and tectonics have modified dust sources significantly, and the Quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the Tertiary Red Clay.  相似文献   

7.
Unlike temperate and polythermal proglacial streams, the proglacial streams in Taylor Valley (TV), Antarctica, are derived primarily from glacier surface melt with no subglacial or groundwater additions. Solute responses to flow reflect only the interaction of glacial meltwater with the valley floor surrounding the stream channel. We have investigated the major, minor and trace element 24‐h variations of two proglacial melt streams, Andersen Creek and Canada Stream, originating from the Canada Glacier in TV, Antarctica. Both streams exhibited diel mid‐austral summer diurnal flow variation, with maximum flow being more than 50 times the minimum flow. Dissolved (< 0.4 µm) major, minor and trace solute behaviors through diel periods were strongly controlled by the availability of readily solubilized material on the valley floor and hyporheic‐biological exchanges. Anderson Creek had generally greater solute concentrations than Canada Stream because of its greater receipt of eolian sediment. Andersen Creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb because of dissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic‐biological exchange. Conversely, Canada Stream had less available eolian sediment, but a greater hyporheic‐biological exchange, which preferentially removed trace and major solutes in the rising limb and released them in the falling limb. Given the dynamic nature of discharge, eolian, and hyporheic‐biological processes, solute loads in TV streams are difficult to predict. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

8.
现代风成沉积物磁化率各向异性与风向关系的研究   总被引：19，自引：3，他引：16       下载免费PDF全文
通过对风洞及室内模拟定向风条件下的风成沉积物磁化率各向异性与风向之间关系的研究,发现风成沉积物磁化率各向异性的长轴方向的偏角不仅与风向有关,而且与粉尘沉积量有关。风成沉积物磁化率各向异性的长轴方向的偏角在α95（α95≤20°）的区间范围内与粉尘沉积量大的风向一致．在干旱、半干旱区,现代风成沉积物（沙丘、黄土的表层土）的磁化率各向异性的长轴方向的偏角在此范围区间内与常年盛行风向一致,尤其与沉积物沉降时的盛行风向一致．  相似文献   

9.
The sand-hill section in Hongguang, Pengze County, Jiangxi Province is composed of eolian sand beds interbedded with 12 weakly-pedogenetic paleosols, and this sedimentary sequence was formed from about 25 to 13 kaBP. A detailed rock-magnetic study demonstrates that the magnetic minerals in the sequence are dominated by multi-domain magnetite grains in addition to small amounts of maghemite and hematite. Compared with the eolian sand beds, the paleosols are characterized by smaller magnetic particles, higher proportion of low-coercivity minerals and markedly increase in the magnetic mineral content. In the section, various magnetic parameters (K, ARM, SIRM and S ratios) display a roughly gradual increase from eolian sand beds to the overlying paleosols but an abrupt decrease from paleosols to the overlying eolian sand beds. The content of low-coercivity magnetic minerals shows the lowest values in the second eolian sand bed from the bottom of the section, and from the bed upwards it gradually increases on the whole in the eolian sand beds. These magnetic properties reflect regional climatic changes during the last glacial maximum.  相似文献   

10.
Arid alluvial fan and fluvial dry wash surfaces in Stonewall Flat, Nevada, USA, are characterized using surface geomorphic surveys, soil pits, botanical line surveys, and varnish microlamination dating techniques. Active and abandoned washes, and active fan surfaces are dominated by primary geomorphic processes of high‐energy sedimentation from flash floods. These surfaces are characterized by bar and swale topography, a lack of stone pavements, soil horizons, and rock varnish. Younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface‐modifying processes of sheet wash and eolian transport and deposition. These surfaces are characterized by faint to no bar and swale topography, incipient to moderately well‐developed pavements and soil horizons, and abundant coppices. Old and stable fan surfaces are dominated by lower energy secondary processes and manifest well‐developed pavements, soils, and sparse coppices around widely distributed shrubs. Varnish microlamination dating yields ages of 13·15 ka for intermediate fan surfaces and 25·55 to 86·75 ka for stable fan surfaces. Plant communities co‐developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes. Relatively active surfaces contain few woody species. Co‐dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes. Stable surfaces dominated by secondary processes are characterized by woody perennials, with long‐lived woody species inhabiting the oldest surfaces. Feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development. In turn, these surface features control both the composition and distribution of botanical communities on older, more stable surfaces. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

11.
Two deep-sea cores in the northwest Pacific have been analysed for sedimentology, mineralogy and environmental magnetism. The results show that after eliminating the interference from volcanism, several proxies such as quartz content, mass susceptibility and anhysteretic magnetic remanence can be used to indicate the eolian deposit from East Asia, and provide information on paleo-atmospheric circulation. A comparison of eolian record in Cure RC10-175 with its oxygen isotopic curve has revealed that the peaks of eolian accumulation occurred at the climatic “optimum” of the Holocene and the last interglaciation, showing the fairly complex nonlinear relationship between continental/pelagic eolian records and the global glacial cycles as well as within the climatic and environmental system. Project supported by the National Natural Science Foundation of China (Grant No. 9291104)  相似文献   

12.
Eolian flux in the Chinese Loess Plateau was reconstructed by measuring the dry bulk density and CaCO3 content of the late Cenozoic loess-paleosol-red clay sequences in the Lingtai profile. Comparison of eolian flux variation between the Lingtai profile and the ODP sites 885/886 in the North Pacific shows a significant wet-dry variability in addition to a gradual drying trend in the dust source regions in interior Asia. Especially, the increase of eolian fluxes from both continental and pelagic eolian sediments indicates a sharp drying of the dust source regions between 3.6 and 2.6 MaBP, which might be attributed to the tectonic uplift of the Tibetan Plateau, which cut down the moisture input to the interior Asia. The average value and variability of eolian flux are higher after 2.6 MaBP than before, which may be related to the Quaternary climatic fluctuations on the glacial-interglacial timescale after the commencement of major Northern Hemisphere Glaciations. The eolian fluxes of the Lingtai profile and Core V21-146 in northwest Pacific show a synchronous variation on the 104-105 a timescale, indicating that the flux variations from both continental and marine records are closely correlated to the Quaternary climatic fluctuation forced by the ice volume changes on a global scale.  相似文献   

13.
Eolian sand dune deposits of the Upper Cretaceous Djadokhta Formation at Tugrikiin Shiree, southern Mongolia, yield not only dinosaur skeletal remains but also numerous trace fossils produced by invertebrates. This paper describes the trace fossil Entradichnus meniscus, a long unlined and unbranched trail that is filled with meniscate laminae and occurs characteristically in positive epirelief. The trail is straight to gently meandering, parallel to the foreset laminae of the eolian dunes, and exhibits a significant preferred orientation parallel to the depositional dip of the cross‐stratification laminae. In addition, almost all the crescentic internal laminae of the trail show concave down‐dips. These features indicate that the trails were produced beneath the slipface of eolian dunes by the downward burrowing of the trace‐makers. This occurrence mode of E. meniscus of the Mongolian Cretaceous is very similar to that described from the Jurassic eolian dune deposits in North America. Hence, the downward burrowing of the E. meniscus animal might be a common feature in arid eolian dune deposits at least during the Jurassic and Cretaceous, and possibly reflecting a behavioral response to the morphology of large sand dunes under an arid climate.  相似文献   

14.
Links that have been established between the characteristic responses of hillslope drainage processes and the size of drainage catchments enable valuable extrapolations and comparisons to be made, both within and beyond the range of the field data. To date, flow through natural soil pipes has not been included in these investigations. A methodology is offered for achieving this and the first such analyses of field data on pipeflow. The results indicate that pipeflow responses follow trends which are broadly similar to other hillslope drainage processes and are intermediate between throughflow and saturation overland flow. © 1997 by John Wiley & Sons, Ltd.  相似文献   

15.
In northern China, the Quaternary loess-soil se-quences[1] and the Hipparion Red-Earth Formation in the eastern Loess Plateau[2―6] provide a continental climate record for the past 8 Ma. The recently reported Miocene[7] and Pliocene[8] loess-soil sequences near Qinan constitute an eolian record of the western Loess Plateau from 22 to 3.5 Ma. Earlier studies[9] place the Miocene loess deposits into the so-called Gansu Sys-tem. Our investigations show that the Gansu System contains inde…  相似文献   

16.
Mineralogical study of samples from depression fills on an isolated basalt plateau in Central Sardinia showed that, although the basalt is free of quartz and mica, fair amounts of these minerals occur in the finer fractions. Results from X-ray analyses of silt fractions and morphoscopical analyses of sand fractions indicate that the bulk of the quartz and mica is of eolian origin. The eolian quartz is predominantly of medium and coarse silt size and, in the upper 10 cm of the depression fills, constitutes about 20 per cent of the soil mass (approx. 20 kg/m2). Eolian mica is present in smaller amounts and is of medium silt or smaller size. The provenance of the eolian material could not be established with certainty, although a local origin can be excluded.  相似文献   

17.
The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.  相似文献   

18.
Wood WW 《Ground water》2002,40(4):438-447
Study of ground water in the Southern High Plains is central to an understanding of the geomorphology, deposition of economic minerals, and climate change record in the area. Ground water has controlled the course of the Canadian and Pecos rivers that isolated the Southern High Plains from the Great Plains and has contributed significantly to the continuing retreat of the westward escarpment. Evaporative and dissolution processes are responsible for current plateau topography and the development of the signature 20,000 small playa basins and 40 to 50 large saline lake basins in the area. In conjunction with eolian processes, ground water transport controls the mineralogy of commercially valuable mineral deposits and sets up the distribution of fine efflorescent salts that adversely affect water quality. As the water table rises and retreats, lunette and tufa formation provides valuable paleoclimate data for the Southern High Plains. In all these cases, an understanding of ground water processes contributes valuable information to a broad range of geological topics, well beyond traditional interest in water supply and environmental issues.  相似文献   

19.
Changes in vegetation cover within dune fields can play a major role in how dune fields evolve. To better understand the linkage between dune field evolution and interdune vegetation changes, we modified Werner's (Geology, 23, 1995: 1107–1110) dune field evolution model to account for the stabilizing effects of vegetation. Model results indicate that changes in the density of interdune vegetation strongly influence subsequent trends in the height and area of eolian dunes. We applied the model to interpreting the recent evolution of Jockey's Ridge, North Carolina, where repeat LiDAR surveys and historical aerial photographs and maps provide an unusually detailed record of recent dune field evolution. In the absence of interdune vegetation, the model predicts that dunes at Jockey's Ridge evolve towards taller, more closely‐spaced, barchanoid dunes, with smaller dunes generally migrating faster than larger dunes. Conversely, the establishment of interdune vegetation causes dunes to evolve towards shorter, more widely‐spaced, parabolic forms. These results provide a basis for understanding the increase in dune height at Jockey's Ridge during the early part of the twentieth century, when interdune vegetation was sparse, followed by the decrease in dune height and establishment of parabolic forms from 1953‐present when interdune vegetation density increased. These results provide a conceptual model that may be applicable at other sites with increasing interdune vegetation cover, and they illustrate the power of using numerical modeling to model decadal variations in eolian dune field evolution. We also describe model results designed to test the relative efficacy of alternative strategies for mitigating dune migration and deflation. Installing sand‐trapping fences and/or promoting vegetation growth on the stoss sides of dunes are found to be the most effective strategies for limiting dune advance, but these strategies must be weighed against the desire of many park visitors to maintain the natural state of the dunes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

20.
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