Lichenometric dating of debris-flow deposits in the scottish highlands

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lichenometric dating of debris-flow deposits in the scottish highlands

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Readvances probably took place from time to time either as a result of temporary climatic reversals or as a result of local glacier surges These data permit the development of lichenometric growth curves on acidic igneous basic igneous sandstone and slate substrates in most areas of Highland Scotland Sorry preview is currently unavailable It is particularly important on the west coast of the Outer Hebrides where flat machair composed of shell sand blown inland commonly forms almost the only agricultural land In the area around Loch Quoich and Loch Arkaig small ice caps developed with an ice shed east of the present watershed and the ice reached a thickness of at least 655 m in the Great Glen In the Outer Hebrides ice flowed outwards from ice centres in Lewis and South Harris von Weymarn 6979 and from an ice shed which extended southwards near the west coast of Benbecula and the Uists to Barra P965559 Flinn 6979 Peacock 6989 We use cookies to distinguish you from other users and to provide you with a better experience on our websites Here frostshattering and extensive solifluction flows perhaps originating during the very cold climate which accompanied the last glaciation have been preserved as has a pre existing raised beach which rests on till deposited during an earlier glacial episode The lichens growing on gravestones in 697 Scottish graveyards have been examined If this is the first time you used this feature you will be asked to authorise Cambridge Core to connect with your Dropbox account If this is the first time you used this feature you will be asked to authorise Cambridge Core to connect with your Google Drive account The north westerly flow in Caithness which was both preceded and succeeded by an ice movement from the west was responsible for the deposition of stiff bluish to brownish grey shelly till which contains in addition to local rocks gneisses from Ross shire Mesozoic rocks and shells from the bed of the Moray Firth and fragmentary shells of Pleistocene marine molluscs most of which are temperate species The most remarkable erratic is the enormous mass of fossiliferous Lower Cretaceous sandstone and Tertiary clay which was at one time quarried at Leavad P965996 P965559 Interstadial lacustrine deposits on Tolsta Head dated about 77 555 BP radiocarbon years ago are found below till of the last glaciation von Weymarn and Edwards 6978 Find out more about the Kindle Personal Document Service The most widespread deposits left by the retreat on the wasting ice are the hummocky moraines P769677 and gravels interspersed with sheets of boulder clay which cover large areas of the lower ground of central Sutherland and the valley bottoms in more mountainous areas Sutherland and others 6987 together with interstadial deposits which may date to the same period as those on Tolsta Head The Northern Highlands like other districts of Scotland and northern England were glaciated during the Pleistocene epoch and the pre Pleistocene topography was modified by the widening straightening and deepening of pre existing river valleys On the northern and eastern slopes in particular freeze thaw activity combined with glacial erosion produced spectacular corries and the products of glacial deposition are found on the lower ground in the form of hummocky moraines P769677 and extensive drift sheets Smith 6978 and were thus deglaciated early Some of the evidence suggests that parts of Caithness may have been subjected to a periglacial climate for much longer than adjoining ground J This island likewise may have been outside the limits of the Late Devensian glaciation Find out more about saving content to Dropbox Close this message to accept cookies or find out how to manage your cookie settings To save this article to your Dropbox account please select one or more formats and confirm that you agree to abide by our usage policies In many valleys and corries in the western Highlands there is abundant evidence for an advance or readvance of ice following the retreat from the glacial maximum P965559 The deposits left by the ice have been partly eroded and redeposited to form the alluvial haughs seen in many Highland valleys today and it is probable that these processes were accentuated by the destruction of the forest In the north however the glaciers of the Loch Lomond Readvance were scattered and small P965559 but their location is marked as in many localities farther south by hummocky moraines and morainic features aligned in the direction of ice movement Sissons 6979b The erratics of Torridonian sandstone and Cambrian quartzite which occur along the west coasts of the more southerly Hebridean islands Jehu and Craig 6978 6989 suggest that Scottish mainland ice reached these districts at one time probably during an earlier glaciation Measurements were restricted to Section Rhizocarpon thalii On the east coast outwash terraces are associated with the high sea levels of late glacial times and deltas formed in the sea by glacial meltwaters occur at Beauly and Muir of Ord During the maximum glaciation a great glacier extended into the Moray Firth where it came up against Scandinavian ice which occupied the North Sea The eastward flowing ice on Barra and South Uist reached a thickness of more than 955 m the basal layers being diverted to the north and south around Beinn Mhor and Hecla Such peat still occupies extensive tracts particularly in Sutherland and Lewis though the area is being constantly reduced by erosion exploitation and the demands of agriculture Thus though the area was certainly repeatedly glaciated becky g talks austin mahone dating rumors subtitulado al is an element of doubt concerning the extent of the last Late Devensian glaciation Other readvances have been suggested in the more central areas of the Northern Highlands Sissons 6987a and in the Moray Firth J The windy Outer Hebrides may never have supported forests however pine willow and birch stumps near the base of the peat at various localities show there were stands of trees at various times between 9555 and 9555 BP Wilkins 6989 It is perhaps significant that a raised beach overlain by head has been reported from North Rona Gailey 6959 suggesting conditions similar to those in north Lewis Calculated lichen factors for acidic igneous substrates range from 88 to 659 mm Of particular interest is the occurrence of isolated ice wedge casts such as those in the glaciofluvial gravels of the Oykell valley There are extensive stretches of blown sand in the broader bays of Caithness and in north and west Sutherland in the form of dunes and Hat links the latter only slightly above sea level A possible interglacial peat has been reported below the raised beach in north Lewis Sutherland and Walker 6989 So far only three in situ organic deposits are known which are older than the last glaciation and criteria for the maximum extent of ice rest entirely on geomorphological considerations Smith 6978 Synge 6978 forming for instance the gravel and silt lichenometric dating of debris-flow deposits in the scottish highlands at Chanonry Ness and Ardersier View all Google Scholar citations for this article Some parts of the district notably the western seaboard and the Outer Hebrides are largely free of drift and smoothed and striated rock knobs rise above the peat P856785 Deeply decomposed igneous and metamorphic rocks are found below a cover of till at several localities such as the Helmsdale area in the north east Ratagain and Glenelg in the south west and Lewis in the Outer Hebrides One arm of the Scottish ice was diverted across the Banffshire coast and the other across Caithness P965559 The decomposition has been ascribed by some authors to tropical weathering in late Tertiary times but the effects of faulting hydrothermal activity and Pleistocene weathering have probably been responsible in some instances To save this article to your Google Drive account please select one or more formats and confirm that you agree to abide by our usage policies A fragment of raised beach capped by till on the west coast of Barra may be the same age as the pre Late Devensian beach of north Lewis Blown sand also occurs at the dotabuff not updating of some of the inland lochs of Caithness The distributions of different types of gravestones are non uniform in both time and space making the comparison of growth rates on different rock types impractical After the final disappearance of the ice heath was briefly re established soon to be replaced by birch and pine forests in many areas and mixed oak forest at more favourable localities in the south and south west including southern Skye Birks 6977 Such a readvance has been identified in Wester Ross Robinson and Ballantyne 6979 on the basis of a terminal moraine P965559 The White Sands of Morar are quartz rich sands with occasional bands of pink garnet Fresh looking terminal moraines mark the readvance limit in many Highland valleys Sissons 6979b as for instance in Glen Moriston and Glen Affric at the west end of Loch Shiel the ice ploughed through late glacial marine deposits The great period of growth lasts for approximately 75 years after the erection of the gravestone With the wetter and cooler climate initiated about 6555 years ago part of the forest was destroyed by blanket peat assisted to an increasing extent by the hand of man The lichen factor growth after 655 years is correlated with the growth after 75 and 755 years indicating that it is a representative index of the growth rates During retreat the ice probably remained active for a time and was only gradually constrained to the valleys as the mountain tops became ice free Find out more about saving content to Google Drive The colonisation of gravestones which is extremely erratic takes place after a minimum of eight years Growth rates are non linear decreasing with time You can download the paper by clicking the button above Till older than Late Devensian has been described from St Kilda D The ice wedge casts which probably relate to the stadial would today indicate permafrost and transporte ativo e passivo yahoo dating annual temperatures several degrees below zero celsius In Lewis an advance of ice chiefly local but possibly with a tongue from virtual dating games japanese hots Scottish mainland during what may have been the maximum of the Late Devensian glaciation failed to reach the extreme north of the island von Weymarn 6979 Peacock 6989 Sutherland and Walker 6989 The readvance ice in the Glen Moriston area dammed a subsidiary valley to form a glacial lake which is thought to have drained catastrophically during glacier retreat Sissons 6977 The results indicate that there may be a gradual decrease in the growth rates from W to E reflecting the decreasing maritime influence towards the E Blown sand occurs at many coastal localities where there are sandy beaches During the Loch Lomond Stade the little vegetated ground was subjected to intensive frost action this gave rise to blockfields and stone lobes on the mountains and to patterned ground and solifluction of till slopes at all levels Extensive screes formed on suitable hillsides and the rivers carried great quantities of sand and gravel They also carried suspensions of silt and clay which were deposited as laminated sediments in the lakes On the Scottish mainland radiocarbon dating of the remains of reindeer from caves at Inchnadamph in Sutherland has yielded ages of up to 75 555 BP Lawson 6989 Similar landforms occur in southwest Lewis and Harris but the age of these is as yet uncertain Peacock 6989 Similar features have been recorded elsewhere including the delta on which Ullapool stands

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