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1.
Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.  相似文献   

2.
《Quaternary Science Reviews》2003,22(8-9):823-837
Some syntheses of lake-level data for the Last Glacial Maximum (LGM) in East Africa (10°N and 30°S, East of 25°E) show apparently wetter conditions than present for some basins, whereas palaeovegetation reconstruction indicates a generally dry climate. PMIP GCM simulations for the LGM support both scenarios for this region when run under different boundary conditions. Here, we compare three new records from lakes in the data-poor southern part of East Africa; Lake Malawi, Lake Massoko, and Lake Rukwa. We also re-assess previously published lake-level data and apply a salinity transfer function to the diatom record from Lake Manyara. Our results show that in contrast to previous interpretations, these lakes were at least as low as today at the LGM and are thus in agreement with the palaeovegetation data. Relative drought across East Africa is best simulated by GCMs that use computed SSTs rather than the higher CLIMAP values. Lower SSTs and the presence of the Northern Hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern African tropics.  相似文献   

3.
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4.
《Quaternary Science Reviews》2007,26(9-10):1369-1383
Paleoenvironmental records in Europe describing paleofires extending back to the Last Interglacial have so far been unavailable. Here, we present paleofire results from the combined petrographic and automated image analysis of microcharcoal particles preserved in marine core MD95-2042 retrieved off southwestern Iberia and covering the last climatic cycle. The variability of microcharcoal concentrations reveals that the variability of fire emissions is mainly imprinted by the 23 000 yr precessional cycle. A focus on the Last Glacial Period further shows that paleofires follow the variability of Dansgaard–Oeschger oscillation and Heinrich events and, therefore, parallel the variability of atmospheric temperatures over Greenland detected in ice cores. There is no evidence for fire increase related to human activity. The variability of fire emission by-products for the Last Glacial Period is interpreted in terms of changes in biomass availability. Low fire activity is associated with periods of drought which saw the development of semi-desert vegetation that characterised stadial periods. Fire activity increased during wetter interstadials, related to the development of open Mediterranean forests with more woody fuel availability.  相似文献   

5.
The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 °N, 61.0157 °W, 884 m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from ～15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200 m elevation above the lake, suggesting a cooling‐driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
This study presents a multi‐proxy record from Lake Kotokel in the Baikal region at decadal‐to‐multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000‐year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, cold steppe associations typical for northern Mongolia, and mountain tundra vegetation. The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase (c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid‐based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice‐cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity.  相似文献   

7.
末次盛冰期华北平原古气候古环境演化   总被引：3，自引：0，他引：3       下载免费PDF全文
华北平原宁晋泊南王庄剖面的^14C和光释光年代测定表明宁晋泊地区在末次盛冰期有连续的湖相沉积。依据孢粉、碳酸盐、有机碳含量（TOC）及C／N值的高分辨率分析与综合判识，末次盛冰期并不是一个持续的干冷时期，而是存在从凉湿-冷偏湿-冷干的波动变化过程。其中早期明显降温事件，可以与Heinrich事件2（H2）对比，说明全球降温的同步性。本研究说明末次盛冰期（20-16ka BP），在全球气候变冷的背景下，存在一个冬季风不断加强夏季风逐渐变弱的过程。  相似文献   

8.
Mongolian glaciers have been the subject of relatively little research, resulting in less geochronological constraint than other parts of Central Asia. The Khentey Mountains (latitude 47–51°N, longitude 105–112°E) are a typical landlocked mountain range exhibiting clear geomorphic evidence of late Quaternary glaciation. Yet, compared to western parts of Mongolia such as the Mongolian Altay, Gobi Altay, Khangay, and Khovsgol, glacial history of the Khentey Mountains is poorly understood. To address this, and permit comparison of the Khentey glacier–climate record with other alpine regions in Mongolia, we performed geomorphological mapping and cosmogenic 10Be surface‐exposure dating in two glaciated regions of the Khentey Mountains: Yestii and Khagiin Khar. Specifically, we measured 10Be in 34 samples collected from five moraine sequences, which, together with morphostratigraphy, correspond to four main glacial stages: (i) The My1 terminal moraine sequence for Yestii (21.0±4.9 ka) and the Mk1 moraine for Khagiin Khar (19.6±2.6 ka), both of which represent the Last Glacial Maximum; (ii) the Lateglacial Mk2 moraine, dated to 16.0±3.5 ka; (iii) the Mk3 moraine, dated to either 17.6±7.0 ka (Lateglacial) or 12.1±1.1 ka (Younger Dryas); and (iv) the currently undated Mk4 moraine (~2200 m a.s.l.), to which we assign a Holocene age. Our results suggest that the timing of maximum glacier extent in Mongolia was regionally variable. In the Khentey Mountains, maximum glaciation occurred during Marine Isotope Stage (MIS) 2, whereas the maximum occurred during MIS 3 in Khangay and Khovsgol and during MIS 4 in the Altay. The MIS 2 glacial maximum in the Khentey Mountains coincided with the global sea level minimum during the Last Glacial Maximum, and was followed by at least three glacial re‐advances during the Lateglacial to possibly the Holocene.  相似文献   

9.
J.L. Ripley 《Geoarchaeology》1998,13(8):793-818
Archaeological sites that have only surface scatters are usually considered to be of little or no use in reconstructing paleoenvironmental conditions during episodes of human occupation. However, geoarchaeological research at the Skare site in south-central Wisconsin reveals that these sites can be used to provide information about the timing of paleoenvironmental changes and their affect on the location of human occupations. Geomorphic investigations revealed the presence of Alfisols formed in late Wisconsin loess on upland and low bench positions; morphologically younger Mollisols formed in alluvial and colluvial sediments on low alluvial plain positions; and beach sediments that represent the low-water stand of Glacial Lake Yahara. Semiquantitative age control for timing the formation of these soils and the lake level(s) of Glacial Lake Yahara is based on the location of diagnostic artifacts (Early Paleoindian to Late Woodland) recovered during ten separate surface collections. Early and Late Paleoindian artifacts all occur on Alfisols and are only found above the low-water stand of Glacial Lake Yahara, indicating that loess deposition and subsequent soil formation happened sometime between 12,000 and 11,000 yr B.P., and that Glacial Lake Yahara remained near the low-water stand at least until ∼9500 yr B.P. Early Archaic artifacts are present below the low-water stand and provide ages for lowering of the lake to be between 8000 and 9500 yr B.P. Middle Archaic artifacts are present on Mollisols and provide an age of soil formation to be between 5000 and 3000 yr B.P. A majority of Woodland artifacts occur on these Mollisols and are present along the floodplain of the Yahara River, possibly representing a change in subsistence strategy and settlement patterns relative to Paleoindian and Archaic occupations. The agreement of soil morphological and sedimentological data with semiquantitative age data of diagnostic artifacts provides evidence that archaeological surface scatters can be useful tools in dating soils and landforms associated with these sites. © 1998 John Wiley & Sons, Inc.  相似文献   

10.
Relict permafrost structures (ice-wedge casts and cryoturbation structures) are present in the Gobi of southern Mongolia. Luminescence dates of sediments are presented to constrain the age of formation of permafrost structures. These data show that there was a phase of permafrost development during the latter part of the Last Glacial (after about 22 to 15 ka) that resulted in cryoturbated sediments and ice-wedge casts. Furthermore, permafrost degradation occurred during late Pleistocene times (13–10 ka) and was absent during the early Holocene. These permafrost structures mark the southernmost evidence of permafrost in northern Asia during late Quaternary times and indicate that the mean annual air temperature was below approximately −6°C during their formation. © 1998 John Wiley & Sons, Ltd.  相似文献   

11.
The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age arte‐facts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U‐series dating analyses. Tufa is identified in four sites: Nyamita (94·0 ± 3·3 and 111·4 ± 4·2 ka); Kisaaka, Aringo (455 ± 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring‐fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with δ13C values of ca 10‰ indicative of C3 plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C3/C4 signature consistent with a semi‐arid C4 grassland surrounding these spring‐fed rivers. The δ18O values of tufa from Nyamita are on average ca 1‰ more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface‐collected artefacts indicate that early modern humans were utilizing these spring‐fed rivers. The presence of spring?fed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment.  相似文献   

12.
河西走廊末次冰期芒硝和砂楔与古气候重建   总被引：10，自引：0，他引：10  
芒硝和砂楔是冷干气候环境的典型标志。河西走廊砂楔主要形成在晚更新世冲洪积砾石层中 ,楔体内充填的风成砂14 C年龄证明其是末次冰期的产物 ,古砂楔所对应的年均气温为- 5 6℃左右。芒硝主要分布在内陆河终端的盐湖中 ,花海芒硝矿粘土夹层中的陆生树枝残条普通14 C和AMS14 C年龄分别为 (116 0 0± 2 80 )aB .P .和 (11181± 54)aB .P .,证明芒硝层为末次盛冰期 (LGM )和新仙女木期 (YD)异常冷干气候的产物。计算表明 ,该区LGM年均气温较现在低 11～ 15℃ ,YD年均气温比现代低约 6～ 8℃。这一降温幅度与中国北方根据孢粉、砂楔、冰芯等所推测的气温下降值大体一致 ,亦与最近有关北半球高、中纬度冰期降温幅度的研究相符合  相似文献   

13.
Lacustrine, alluvial terraces and sediments record at least one Holocene glacially dammed lake in Songzong Basin immediately upstream of the Purlung TsangpoRiver, a main tributary of the downstream of Yarlung Tsangpo River, at the northeastern syntaxis of the Himalaya. The lacustrine deposit is more than 88 meters thick at the SongzongLandslide. There is an 18.33 meters thick layer of lacustrine silt within the lacustrine terrace. The Optical Simulated Luminescence (OSL) ages at the bottom and top of the lacustrine silt layerare 22.5±3.3ka B.P., and 16.1±1.7ka B.P., respectively, which indicates that the lacustrine deposits were formed during the Last Glacial Maximum ranging from 25kaB.P. to 15kaB.P.The ancient shorelines and the lake erosion zone confirm the preexistence of Songzong Lake. There are also terraces formed by moraines in the Songzong Basin. The high and large moraineterrace seen near the mouth of the Dongqu Valley is very prominent. The special characteristics of thelacustrine sediment and the ancient lake line in the Songzong Basin indicate that the lacustrinesediments are related to the blocking of the Purlung Tsangpo River by a glacier from DongquValley during Last Glacial Maximum.  相似文献   

14.
Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 106 km2 to a maximum of 19 × 106 km2 during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ～61°S to ～52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ～30 ka and 22 ka that extended to ～59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.  相似文献   

15.
Establishing the precise timing of continental glacial dynamics and abrupt high‐latitude climate events is crucial to understanding the causes of global climate change. Here we present multi‐proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at ～26.2–21.8 and ～17.3–11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at ～24–23.5, 17.3–17 and 15.6–14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill‐slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier‐derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high‐ and mid‐latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier‐related processes in arid Inner Mongolia, further well‐dated records are clearly needed to re‐evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
The causes of large animal extinctions at the end of the Pleistocene remain a hotly debated topic focused primarily on the effects of human over hunting and climate change. Here we examine multiple, large radiocarbon data sets for humans and extinct proboscideans and explore how variation in their temporal and geographic distributions were related prior to proboscidean extinction. These data include 4532 archaeological determinations from Europe and Siberia and 1177 mammoth and mastodont determinations from Europe, Siberia, and North America. All span the period from 45,000 to 12,000 calendar years BP. We show that while the geographic ranges of dated human occupations and proboscidean remains overlap across the terminal Pleistocene of the Old World, the two groups remain largely segregated and increases in the frequency of human occupations do not coincide with declines in proboscidean remains. Prior to the Last Glacial Maximum (LGM; ca 21,000 years BP), archaeological 14C determinations increase slightly in frequency worldwide while the frequency of dated proboscidean remains varies depending on taxon and location. After the LGM, both sympatric and allopatric groups of humans and proboscideans increase sharply as climatic conditions ameliorate. Post-LGM radiocarbon frequencies among proboscideans peak at different times, also depending upon taxon and location. Woolly mammoths in Beringia reach a maximum and then decline beginning between 16,000 and 15,500 years BP, woolly mammoths in Europe and Siberia ca 14,500 and 13,500 BP, and Columbian mammoth and American mastodont only after 13,000 BP. Declines among woolly mammoths appear to coincide with the restructuring of biotic communities following the Pleistocene–Holocene transition.  相似文献   

17.
Two Gravity cores (AAS 38-4 and AAS 38-5) recovered from the eastern Arabian Sea were analyzed for calcium carbonate (CaCO3), organic carbon, aluminium (Al) and titanium (Ti) in order to understand the calcium carbonate and terrigenous fluctuations during the Holocene and Last Glacial Period. High CaCO3 and low Al and Ti during the Holocene, and low CaCO3 and high Al and Ti during the Last Glacial Period suggest that CaCO3 content in these two cores appears to be controlled by the dilution of terrigenous material. The supply of terrigenous material to the core sites was higher during the Last Glacial Period than in the Holocene. Organic carbon values were lower (<2%) during the Holocene and higher (>2%) during the Last Glacial Period in core AAS 38-4; but the opposite was found in core AAS 38-5. This inconsistent pattern of organic carbon changes in the two cores studied indicates that the distribution of organic carbon in the eastern Arabian Sea is controlled not only by the supply of organic matter from the water column but also by sediment texture and dilution of sediment components.  相似文献   

18.
Radiocarbon-dated pollen records of two adjacent sediment cores from Canal de la Puntilla (40°57′09″S, 72°54′18″W) in the Chilean Lake District reveal that a sparsely vegetated landscape prevailed during the portion of the Last Glacial Maximum between 20200 and about 14800 14C yr BP. Dominating the vegetation was Nothofagus, Gramineae and Compositae, along with taxa commonly found today above the Andean treeline (Perezia-type, Valeriana) and in Magellanic Moorlands (Donatia, Astelia). Nothofagus expanded between 20200 and 15800 14C yr BP, interrupted by a reversal at 19200 14C yr BP and followed by a prominent increase in Gramineae pollen between 15800 and about 14800 14C yr BP. A major increase in Nothofagus started at about 14800 14C yr BP, followed by an abrupt expansion of thermophilous Valdivian/North Patagonian Rain Forest taxa (Myrtaceae, Lomatia/Gevuina, Hydrangea, etc.) at about 14000 14C yr BP. An opening of the rain forest and an expansion of Podocarpus nubigena, Misodendrum, and Maytenus disticha-type subsequently occurred between 11000 and 10000 14C yr BP. These results suggest that mean annual temperature was 6–7°C colder than at present, with twice the modern annual precipitation between 20200 and 14000 14C yr BP, implying a northward shift and intensification of the westerlies storm-tracks. Slight climate warming occurred between 20200 and 15800 14C yr BP, featuring cooling reversals at 19200 14C yr BP, and later at 15800 14C yr BP. The warming of the last termination started at about 14800 14C yr BP, and reached a total temperature rise of ≥5°C by 12400 14C yr BP, followed by cooling between 11000 and 10000 14C yr BP. © 1997 John Wiley & Sons, Ltd.  相似文献   

19.
Surface exposure dating of boulders on an exceptionally well‐preserved sequence of moraines in the Peruvian Andes reveals the most detailed record of glaciation heretofore recognised in the region. The high degree of moraine preservation resulted from dramatic changes in the flow path of piedmont palaeoglaciers at the southern end of the Cordillera Blanca (10° 00′ S, 77° 16′ W), which, in turn, generated a series of cross‐cutting moraines. Sixty 10Be surface exposure ages indicate at least four episodes of palaeoglacier stabilisation (>65, ca. 65, ca. 32 and ca. 18–15 ka) and several minor advances or stillstands on the western side of the Nevado Jeulla Rajo massif. The absence of ages close to the global Last Glacial Maximum (ca. 21 ka) suggests that if an advance culminated at that time any resulting moraines were subsequently overridden. The timing of expanded ice cover in the central Peruvian Andes correlates broadly with the timing of massive iceberg discharge (Heinrich) events in the North Atlantic Ocean, suggesting a possible causal connection between southward migration of the Intertropical Convergence Zone during Heinrich events and a resultant increase in precipitation in the tropical Andes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
Glaciers are retreating and thinning in the high altitude of the Himalayas due to global warming, causing into formation of numerous glacial lakes. It is necessary to monitor these glacial lakes consistently to save properties and lives downstream from probable disastrous glacial lake outburst flood. In this study, image processing software ArcGIS and ERDAS Imagine have been used to analyse multispectral image obtained by Earth resource satellite Landsat for delineating the glacial lakes with the help of image enhancement technique like NDWI. Landsat data since 1972 through 2013 have been used and maximum seven glacial lakes (L1–L7) have been detected and delineated in Dhauliganga catchment, they are situated above 4000 masl. The Glacial Lake L2 (Lat 30°26′45″E and Long 80°23′16″N) is the largest whose surface area was 132,300 m2 in Sept 2009, and L6 (Lat 30°23′27″E and Long 80°31′52″N) is highly unstable with variation rate ?55 to +145 % with increasing trend. Additionally, glacial lakes L2 (Lat 30°26′45″E and Long 80°23′16″N) and L6 (Lat 30°23′27″E and Long 80°31′52″N) have been identified as potentially hazardous. These lakes may probably burst; as a result, huge reserve of water and debris may be released all on a sudden. This may transform into hazardous flash flood in downstream causing loss of lives, as well as the destruction of houses, bridges, fields, forests, hydropower stations, roads, etc. It is to note that Dhauliganga river considered in this study is a tributary of Kaliganga river, and should not be confused with its namesake the Dhauliganga river, which is a tributary of Alaknanda river.  相似文献   

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