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1.
The position of the ice boundary around the Vestfold Hills, East Antarctica (68°30'S, 78°00'E) was observed using a 43 year record of aerial photography from 1947 to 1990. The southern boundary, formed by Sørsdal Glacier, showed two main areas of ice retreat and no areas of advance. Stagnation and retreat of this boundary is interpreted to be contraction to former limits following the Chelnok Glaciation which occurred 7lt; 700 years BP. The eastern or continental ice sheet boundary showed five sites of rapid, localised incision and downwasting around supraglacial gullies. While no area of continental ice was noted to advance, continued accumulation and firnification of wind-drifted snow in the proglacial zone of the ice sheet in the southeastern corner of the hills may signify a locally positive ice mass balance. Until ice mass balance studies are carried out in the ablation zone surrounding the hills, evidence concerning whether the ice sheet boundary is retreating, stable or advancing will remain equivocal.  相似文献   

2.
The deposits of the Toruń Basin are dominated by a few-metre thick sand series which fill up buried valley-like depressions. In many cases they underlie the Weichselian till which builds up the ice marginal streamway (pradolina) terraces or they are exposed at the basin slopes. As the results of the geological and sedimentological studies, as well as of the dating of the deposits at the sites in the Toruń Basin indicate, the deposits include two fluvial series accumulated before the advancement of the Leszno Phase ice sheet, i.e. in Middle Weichselian and at the beginning of Late Weichselian. The oldest fluvial series connected with the Saalian Glaciation was found at the mouth section of the Drwęca Valley. The fluvial system of the Toruń Basin during Middle Weichselian and at the beginning of Late Weichselian developed in two phases of the sand-bed braided river. During the first one the river channel were dominated by large mid-riverbed sandbars, while during the second phase the water flow was smaller and, as a result, low transverse sandbars and two-dimensional dunes developed. Other active river channel also showed low-energy flows, more intensive meandering than in the case of the braided rivers, as well as sandy side-bars. Analysis of the rounding and frosting of the quartz grains indicate that the studied series of the Weichselian sandy deposits represent alluvia of a river which were fed from two diverse sources. The first one might have represented the alluvia of a warm river which transformed its load, while the other one might have mainly carried the underlying Quaternary deposits.  相似文献   

3.
本文分析了陕西渭河流域新出土的更新世杨氏水牛和全新世的圣水牛头骨和颅后骨,并对比了其他地区出土的水牛标本。作者根据新的资料讨论了水牛种属的分类、进化及驯化问题。渭河流域在更新世时期至少有圣水牛,它很可能是更新世短角水牛的后代。它在进入全新世之前形体也许有所减小;但全新世早、中期(距今8000-3000年),没有迹象表明它的形体有所缩小,圣水牛的这一变化应该不是受人类活动影响(如驯化)的结果,但是否为适应气候变化而发生还有待研究。  相似文献   

4.
During the Early Pleistocene Bulgobac Glaciation, a piedmont glacial system extended into the valleys west of the West Coast Range of Tasmania. The ice that fed this extensive system originated mainly to the south and east on the western Central Highlands and northern Tyndall Mountains. The palaeo-equilibrium line lay to the east of the West Coast Range. Reconstruction of the palaeoglacial system indicates that ice-surface gradients reached only ~10–15 m km-1 over much of the system to the west of the equilibrium line, although the ice fronts were steep and rapidly ablating. The nature of the piedmont glacier is consistent with the build up of ice behind the topographic barrier of the West Coast Range. This would have resulted in ice thickening, maintained and perhaps accentuated by high precipitation as well as by the location of the equilibrium line well to the west of the western Central Highlands.  相似文献   

5.
W edge -shaped soil structures occur in many parts of southern Canada and the northern United States. These have usually been interpreted as being ice-wedge casts. Yehle (1954), however, has expressed concern over the confusion of fossil ice wedges with features he termed soil tongues, but also referred to as soil pendants (Wright 1961) or podsolschornsteine (Johnsonn 1959). Not only are soil tongues superficially similar to ice-wedge casts, but they also occur in temperate latitudes which may have experienced periglacial conditions during the Pleistocene. Soil tongues, however, are solutional features, formed by rainwater percolating through unconsolidated calcareous deposits. They may be distinguished from ice-wedge casts and other wedge-shaped structures by: (a) the presence of pebble or other marker beds extending unbroken across the wedges; (b) the absence of bed contortions or pressure features in the materials adjacent to the wedges; (c) their conical three-dimensional shape; and (d) the lower carbonate content in the sediments of the wedges than in the surrounding materials.  相似文献   

6.
Well constrained numerical ages of alluvial fan sediments are key to understanding the chronology of alluvial episodes and tectonic activity at the front of the Andean Precordillera. We tested the application of radiocarbon and optically stimulated luminescence (OSL) dating in the distal part of an alluvial fan five kilometers north of Mendoza. For OSL dating a large number of aliquots (n > 70) — each composed of ∼50 quartz grains — were measured in order to obtain reliable burial ages despite scattered dose distributions. Owing to a feldspar contamination in all samples, an infrared stimulation was inserted before each OSL measurement, which reduced the feldspar OSL signal successfully. By using the minimum age model we obtained stratigraphically consistent burial ages of alluvial deposits in a depth profile. The uppermost ∼1 m of sediment is composed of debris flow deposits buried 770±76 years ago. Three plant remnants used for radiocarbon dating from the same layer, however, yielded ages younger than 350 years, which are interpreted to underestimate the depositional age. Underneath the debris flow, a major unconformity cuts a series of distal alluvial fan sediments with interstratified floodplain deposits, which are composed of sandy and calciterich silt layers, respectively. Three samples from this unit which were distributed over one meter of sediment thickness yielded statistically concordant OSL ages of 12.3±1.2 ka, 12.3±1.2 ka, and 11.7±1.1 ka. The deposition of these sediments during the latest Pleistocene coincides with a phase of cool and humid climate, which occurred before the alluvial fan propagated farther into the foreland. The overlying debris flow sediments are associated with alluvial fan incision during the arid Late Holocene.  相似文献   

7.
The earliest Later Stone Age (LSA) industries from southern Africa are microlithic and unstandardized and include the bipolar technique. The dating of these industries is controversial and the earliest microlithic industry is said to occur at Border Cave at about 39,000 B.P. By 18,000 B.P. a bladelet tradition was established and this was replaced in many parts of southern Africa, at about 12,000 B.P., by a widespread and prolific nonmicrolithic industry, characterized by side-struck flakes. The late Pleistocene environment was colder than present, with particularly harsh conditions during the Last Glacial Maximum (LGM), between about 20,000 and 18,000 B.P. Populations may have been isolated because archaeological visibility is low during the LGM and decreases further after the LGM. After 13,000 B.P. there is a dramatic increase in sites and this implies that there may have been widespread colonization of territory previously unoccupied for tens of thousands of years. By the end of the late Pleistocene there was a change in hunting patterns, in parts of southern Africa, from an emphasis on the capture of large, gregarious grazers to an emphasis on small, solitary browsers. Social complexity increased during the late Pleistocene, and by 12,000 B.P. it seems possible that Stone Age people were observing some social practices recorded historically among Bushmen (San).  相似文献   

8.
Palaeo-environments and past human subsistence patterns are difficult to determine from dual-patterned faunal assemblages where human and non-human predators have accumulated and intensively modified animal bones. This paper examines such records in the Leeuwin–Naturaliste Region of south-western Australia, where a thin belt of coastal limestone contains caves and rock shelters with rich faunal deposits. The Late Pleistocene and Holocene part of this record derives from four archaeological sites: Devil's Lair, Tunnel Cave, Witchcliffe Rock Shelter and Rainbow Cave. Correspondence analysis combined with cluster analysis enables a preliminary assessment of habitat changes using simple species abundances in the faunal assemblages and comparison with indices of past human activity in the sites and the species’ present habitat preferences. These inferred changes, consistent with previous analyses of faunal remains and tree charcoal, suggest that late Holocene sites document Aboriginal occupation in coastal heath, scrub and woodland. Late Pleistocene deposits record hinterland occupation at times of low sea-level when the coast was up to 30 km seawards of its present position and the surrounding vegetation was open-forest or woodland. As rainfall increased and vegetation changed in the Holocene, species foraging in open-woodland declined or became locally extinct, while species requiring closed canopy habitats increased. Rank-order correlations of taxa and archaeological remains from depositional sequences before and after the environmental change indicate that the occupiers of late Holocene sites favoured the same generalist species that occupiers of Late Pleistocene sites had favoured, which were available at all times. Prey habitats, foraging behaviours and historic records of ethnographic hunting and settlement pattern suggest that this local continuity is consistent with maintenance of a “dispersive mode” subsistence pattern in the region.  相似文献   

9.
The Upper Forth Valley was glaciated on at least four occasions during the late Cainozoic. The two most extensive glaciations were no younger than early Pleistocene in age. During the last glaciation the limited ice catchment at the head of the valley nourished only a short valley glacier with separate glaciers forming in the tributary valleys to the west During earlier glaciations the Forth catchment was invaded by ice from the Mersey Valley to the east.  相似文献   

10.
Mountains     
Glacier ice from the south and west invaded upper Strathspey forming an ice sheet not less than 700m thick as it submerged the entire landscape. When the ice sheet wasted away, its meltwaters created complex sequences of fluvioglacial landforms. During the final stages of deglaciation, deposits left by the wasting ice mass were eroded by water, terraces spread out, gorges cut and the broad, low‐lying corridor on both sides of the River Spey was formed. There is evidence of a later, local readvance of the glaciers in three of the tributary valleys.  相似文献   

11.
The Sandbanks of Webb Bay, Labrador owe their origin to ice marginal conditions during the last stages of deglaciation of this section of the Labrador coast. Several phases in their evolution are recognized. Phase 1 was characterized by disintegration of the remnants of Webb Bay and Ado's Brook valley ice masses into separate local bodies with ice marginal runoff in an eastern direction. During Phase 2 the first and highest ice-dammed lake formed. Eastward ice marginal flow continued into Phase 3, when a large system of kame terraces (altitude 360 feet) formed beside the receding Webb Bay Ice. They led to new and lower ice marginal lakes in the eastern part of the Sandbanks. Phase 4 was dominated by the construction of a more extensive system of kame terraces almost 100 feet lower than those formed in Phase 3. Locally, minor moraines helped to direct runoff and control development of these newer kame terraces. In Phase 5, meltwater from the ice and runoff from the deglaciated highlands filled a large marginal lake (altitude 230 feet), which may have contributed to subglacial drainage down Port Manvers Run. Phase 6, the last of the glacial conditions associated with formation of the Sandbanks, was introduced by withdrawal of ice far enough so that the eustatically rising sea level was able to reach part of the Sandbanks. A terrace at 135 feet above sea level is believed to be the local upper marine limit. Stagnant ice still covered the floor of Hummock Valley at the western end of the Sandbanks at this time. Subsequently isostatic adjustment has lifted the last glacio-fluvial and some of the glacio-marine features above sea level.  相似文献   

12.
The geomorphological evolution of the upper Chienti river basin, during the late Pleistocene and the Holocene, was characterized mainly by numerous landslides, strongly affecting the river dynamics, that produced falls, deviations and in some cases total obstructions with the formation of lakes sometimes extending for some kilometres. Moreover, particularly during the Holocene, phytoclastic and phytohermal travertine deposits were deposited in correspondence of steps along the river bed; one of these deposits, by means of radiocarbon dating, has been dated between 8260 ± 100 yr BP and 7740 ± 80 yr BP. Stromatolithic travertine is also present at the base of Holocene channels, slightly incised on the top of the upper Pleistocene alluvial plain.  相似文献   

13.
New human remains have been found during recent excavations conducted in the lower section of Visogliano dolina (Trieste, Italy). They are represented by teeth and a fragment of particularly robust mandible that for their morphological and morphometrical characters can be generically attributed to archaic Homo sapiens. The lithic industry is formed by flakes, carinated points, scrapers, choppers and chopping tools and is characteristic of the Italian Pebble Culture. Sediments, pollen and faunal remains indicate that this part of the deposit was formed during interglacial climatic conditions in the early, but not initial phase of Middle Pleistocene (isotopic stadium 13 or 11).  相似文献   

14.
The Jebel al‐Ma'taradh and its surroundings contain exceptional deposits of lithic raw materials, including flint and chert, but especially chalcedony, agate, carnelian, and chrysoprase. These deposits were intensively exploited during the Neolithic, and some of the artefacts produced entered the trade network that included settlements on the coast and inland, sometimes as far as 300 km. During earlier periods, probably as early as the Pleistocene, only flint was used. Between the sixth and the fourth millennia, carnelian and agate were exploited to make beads, which are found in the necropolises and settlements of the UAE.  相似文献   

15.
An unusual stone tool assemblage, reported for the first time in the Arabian Peninsula, occurs at the southwest edge of the Rub'al Khali desert. The assemblage is characterized by large, unifacially worked, prominently tanged points and scrapers. An age of between about 20,000 and 35,000 years B.P., when the Rub'al Khali was a well-watered grassland, is likely. Typological affinity with the Aterian stone tool industry of North Africa is suggested. Aterian toolmakers were a vigorous population of desert hunters, ranging over much of North Africa and the Sahara during a wet phase of the late Pleistocene. Pursuit of animals running in herds may have been a hunting strategy reflected in some of the Aterian and Arabian tools. Typology of the tanged tools and the palaeogeographic context in which they occur suggest certain specific functional usage.  相似文献   

16.
Quartz sediments from the floor deposit at Jinmium rock shelter have been investigated using the multiple-grain and single-grain optical dating methods described by Galbraith et al. (1999, this volume). Here we present the results of this dating programme and argue that the artefact-bearing sediments were deposited within the last 10000 years. This time interval is consistent with the radiocarbon chronology but is much younger than previous claims for initial human occupation during the Pleistocene. Analysis of individual grains revealed also that the characteristic saturation doses of some grains are unusually high, which may permit dating of deposits older than a few hundred thousand years. Such grain-to-grain differences raise doubts, however, about the validity of using multiple-grain samples to investigate the phenomenology of quartz luminescence.  相似文献   

17.
The Mlambalasi rockshelter in the Iringa Region of southern Tanzania has rich artifactual deposits spanning the Later Stone Age (LSA), Iron Age, and historic periods. Middle Stone Age (MSA) artifacts are also present on the slope in front of the rockshelter. Extensive, systematic excavations in 2006 and 2010 by members of the Iringa Region Archaeological Project (IRAP) illustrate a complex picture of repeated occupations and reuse of the rockshelter during an important time in human history. Direct dates on Achatina shell and ostrich eggshell (OES) beads suggest that the earliest occupation levels excavated at Mlambalasi, which are associated with human burials, are terminal Pleistocene in age. This is exceptional given the rarity of archaeological sites, particularly those with human remains and other preserved organic material, from subtropical Africa between 200,000 and 10,000 years before present. This paper reports on the excavations to date and analysis of artifactual finds from the site. The emerging picture is one of varied, ephemeral use over millennia as diverse human groups were repeatedly attracted to this fixed feature on the landscape.  相似文献   

18.
Abstract

Geoarchaeological research on the southern coast of Oregon brought to light archaeological evidence of early human occupation in the late Pleistocene. Indian Sands (35CU67) lies on a highly eroded deflated headland on the Oregon coast where previous surveys had found and dated surficial cultural materials as early as 8250 b.p. (uncalibrated radiocarbon years). Prior to excavation of Indian Sands, sediment and stratigraphic analysis, along with radiocarbon and thermoluminescence dates, established the existence of late Pleistocene deposits. The excavations confirmed the presence of buried cultural deposits containing lithic artifacts, charcoal, and fire-cracked rock. Dispersed charcoal from the floor of an artifactbearing level was dated to 10,430 b.p., more than 2000 l4C years older than any other Oregon coastal site.  相似文献   

19.
We report the results of a test excavation of deposits in a limestone cave sub-chamber located beneath the main chamber of Liang Bua, Flores, Indonesia; the discovery site of the small hominin species, Homo floresiensis. Well-preserved remains of extinct Pleistocene fauna and stone artefacts have previously been identified on the surface of a sediment cone within the sub-chamber. Our excavation of the deposits, at the base of the sediment cone in the sub-chamber (to 130 cm depth) yielded only a few fragmentary bones of extant fauna. Uranium/Thorium (U-series or U/Th) dating of soda straw stalactites excavated from 20 to 130 cm in depth demonstrates that the excavated sediments were deposited during the Holocene. Red Thermoluminescence (TL) dating of the sediments at the base of the excavation (130 cm depth) indicates these sediments were last exposed to sunlight at 84 ± 15 ka (thousand years), similar to red TL ages of cave sediments from the main chamber. Together, these results indicate that the surface faunal remains, which are morphologically analogous to Pleistocene finds from the main chamber excavations, were transported to the sub-chamber relatively recently from the main chamber of Liang Bua and probably originated from conglomerate deposits at the rear of the cave and from deposits around the front entrance. There is no evidence for hominin occupation of the sub-chamber, instead it seems to have acted as a sink for cultural materials and fossil remains transported from the surface via sinkholes. Despite the small number of finds from the test excavation, it is possible that more extensive excavations may yield additional transported cultural and faunal evidence at greater depths.  相似文献   

20.
Two distinct types of rock glaciers occur in southwest Yukon. One results directly from glaciation, with the production of abundant debris over glacier ice. The other forms during and after deglaciation, when instabilities develop in deposits and when ice included in these deposits responds to climatic change.  相似文献   

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