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Spindle- and parabolic-shaped drumlins examined at fifty-five localities in northern Ireland possess stratification sequences on their lee-side flanks. These forms lack the distinctive steep stoss- and tapering lee-ends of classical drumlins and tend to occur in linear zones transverse to late Pleistocene ice-flow. In most cases (90 per cent) the stratified deposits infill embayments excavated in the lee-side of barkhanoid forms and, in the remainder (10 per cent), they are superimposed on the lee-side of whaleback forms. The stratification sequences developed as a result of sedimentation in interconnected subglacial water-filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form. Stratigraphic evidence indicates that the lee-side sequences developed during drumlin streamlining, which supports the view that subglacial hydraulic processes played an important role in drumlin formation. 相似文献
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Physical properties (Schmidt hammer in situ rock strength; degree of weathering; orientation, spacing, width and continuity of joints, bedding planes and faults; groundwater flow) of bedrock-incised rills and gullies were ecamined at selected localities in southern Africa. The resulting data was compared to froms of erosion observed in the field to test for possible influences of rock physical properties on rill and gully development. Bedrock-incised rill erosion occurs at low RMS (Rock Mass Strength) values (40–50). Rills generally do not form where RMS values are high (> 50). Though V-shaped bedrock-incised gullies form in lithologies with a wide range of RMS values (40–69), these values exert strong control on longitudinal morphometry. Future studies should concentrate on establishing a database on properties of erosion forms to aid identification of lithological conditions (e. g. deep regolith) which are potentially susceptible to accelerated erosion. 相似文献
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A fossil dune complex on the east coast of southern Africa is presently undergoing extensive accelerated erosion, with concomitant dune reactivation and degradation, unconfined erosion (sheetwash and wind deflation) and extensive development of V-shaped, ravine-type gully forms on hillslopes composed of thick sequences of Quaternary (Berea Formation?) dune sands. The sands comprise a thick, reddened, ferralitic sand carapace overlying white, poorly cemented quartzitic sands. Soil erosion has resulted from degradation of the red dune sand cover. Despite the cohesionless nature of the host materials, gully forms developed on dune sands are typologically similar to those developed in regolith or soft bedrock. This demonstrates that gully forms are influenced by the degree of homogeneity, rather than the absolute strength, of the host material subject to erosion. Factors which have contributed to erosion are discussed. 相似文献
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The mesoscale (time) control of annual storm-surge activity on quasi-annual saltmarsh (tidal marsh) deposition is studied from two estuarine saltmarshes on the high-energy NW coast of Ireland. Both saltmarshes exhibit a cliffed edge where maximum sedimentary variation is expressed in the form of lamination. Sections were logged and characterised by lithofacies based on grain-size determinations. Sections dated using Cs and Pb determinations indicated deposition records of decadal to century scale (c. 0.5 cm a-1). Linear multiple regression explains (p< 0.05) half the variation of the deposition rate by annual coastal forcing (surge frequency and magnitude) and sediment modes (coarse silt to clay). Further variability in deposition rate is partially reflected in the non-linear response between forcing and deposition that is affected by mesoscale (30, 11 and 5-year) periodicities in forcing. Increased annual surge activity appears to be associated with a coarsening of, and reduction in annual deposition. A relationship between annual deposition rate and fractal dimension of surge timing (i.e. the clustering of surge events) is identified. 相似文献
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George Dardis 《GeoJournal》1988,17(2):308
Reports
Symposium on the Geomorphology of Southern Africa 相似文献7.
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George F. Dardis 《地球表面变化过程与地形》1985,10(5):483-495
Four genetic varieties of ice-marginal cross-valley moraine ridge have been identified in south-central Ulster, Northern Ireland. Type I ridges are flat topped, composed of stratified, water-lain sediments and formed by coalescence of a series of supraaquatic deltas. Type II ridges are sharp crested, composed of stratified, water-lain sediments and formed by coalescence of a series of subaquatic deltas. Type III ridges show mixed morphological and sedimentological characteristics of type I and II ridges. Type IV ridges are sharp crested or hummocky, composed of poorly-sorted and poorly-stratified water-lain sediments and formed by coalescence of a series of subaquatic sediment gravity flow cones. Field evidence indicates that cross-valley moraine ridges in south-central Ulster were deposited in proglacial lacustrine environments. Ridge type depended principally on (1) the nature of the proglacial bedrock slope; (2) the manner in which meltwater entered the proglacial zone; and (3) ice-sheet behaviour during deglaciation, particularly within the ice-sheet terminus zone. 相似文献
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