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Glacial Deposition (glacial + deposition)

Distribution by Scientific Domains
Humanities and Social Sciences75%

Selected Abstracts

A Polygenetic Landform At Stígá, Örćfajökull, Southern Iceland

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2004
Tim Harris
Abstract Recent research has identified problems inherent in the identification and description of landforms. Morphologically similar small-scale glacial and periglacial landforms can be misinterpreted, thus hindering environmental reconstruction. This study reveals that a landform resembling a moraine at Stígárjökull, southern Iceland, is the product of both glacial deposition and mass movement. The landform has two distinct morphological and sedimentological components: a basal, lithologically diverse component, and an upper, lithologically homogenous component. Clast lithological analysis, particle shape and particle size measurements demonstrate that the basal component of the landform consists of sediment whose characteristics match nearby moraines. In contrast, the source of the upper component is a narrow outcrop of rock above the valley floor. Evidence suggests that frost-shattered material was transported across a perennial snow patch to a small moraine, leading to growth of the ,moraine'. This combination of processes is unlikely to be unique, but the geological peculiarities of the field site permitted their identification. It is possible that many similar ,moraines' could be enlarged by subaerial feeding, leading to false reconstruction of glacier form and/or associated rates of erosion and sedimentation. Such polygenetic landform genesis therefore has implications for environmental reconstruction. [source]

Recognition and palaeoclimatic implications of late Quaternary niche glaciation in eastern Lesotho,

JOURNAL OF QUATERNARY SCIENCE, Issue 7 2009
Stephanie C. Mills
Abstract Geomorphic evidence of former glaciation in the high Drakensberg of southern Africa has proven controversial, with conflicting glacial and non-glacial interpretations suggested for many landforms. This paper presents new geomorphological, sedimentological and micromorphological data, and glacier mass-balance modelling for a site in the Leqooa Valley, eastern Lesotho, preserving what are considered to be moraines of a former niche glacier that existed during the Last Glacial Maximum (LGM). The geomorphology and macro-sedimentology of the deposits display characteristics of both active and passive transport by glacial processes. However, micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes. The application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude (ELA) of 3136,m a.s.l. and palaeoglacier mass balance characteristics comparable with modern analogues, reflecting viable, if marginal glaciation. Radiocarbon dates obtained from organic sediment within the moraines indicate that these are of LGM age. The reconstructed palaeoclimatic conditions during the LGM suggest that snow accumulation in the Drakensberg was significantly higher than considered by other studies, and has substantial relevance for tuning regional climate models for southern Africa during the last glacial cycle. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Glaciomarine deposition around the Irish Sea basin: some problems and solutions

JOURNAL OF QUATERNARY SCIENCE, Issue 5 2001
Dr. Jasper Knight
Abstract Reconstructing the depositional processes and setting (marine or terrestrial depositional environment) of late Devensian age glacigenic sediments around the Irish Sea basin (ISB) is critical for developing an all-embracing and consistent glacial model that can account for all observed field evidence. Identifying episodes of marine and terrestrial glacial deposition from field data is considered the first step in achieving this goal. Criteria for distinguishing marine and terrestrial glacial environments in the ISB include the geomorphology, sedimentology and faunal content (biofacies) of the associated deposits. Exposures of glacigenic sediments around the ISB are very diverse in terms of their morphosedimentary characteristics and associated biofacies, and thus inferred depositional processes and setting. Possible reasons for the diverse geological record include the differing geometry of eastern and western ISB coasts, time-transgressive ice retreat, and differential land rebound effects as a result of forebulge collapse and neotectonics. Poor geochronometric control on ice sheet events has not helped the correlation of ISB events with glacial and climatic events elsewhere. Future investigations of glacial sites around the ISB should use an integrated methodological approach involving a range of geomorphological, sedimentary and biofacies data, and dating control where possible. This will help in developing a more precise and holistic late Devensian glacial model that is constrained rigorously by field geological evidence. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Modification of sediment characteristics during glacial transport in high-alpine catchments: Mount Cook area, New Zealand

BOREAS, Issue 4 2004
MICHAEL J. HAMBREY
The Mount Cook area in the Southern Alps of New Zealand is heavily glacierized with numerous peaks over 3000 m a.s.l. feeding several large valley glaciers. The region is subject to rapid tectonic uplift and heavy precipitation (up to 15 m per year). This paper describes the clast roundness, clast shape and textural characteristics associated with five glaciers (Fox, Franz Josef, Hooker, Mueller and Tasman) in terms of inputs to the glacier system, transport by the glaciers and reworking following glacial deposition. Inputs include rockfall, alluvial fan and avalanche material delivered to the surface of valley glaciers. Basal debris, where observed at the terminus of two glaciers, consists mainly of incorporated fluvial material. Following deposition, reworking is mainly by subglacial and proglacial streams. The dominant facies are (i) boulder gravel with mainly angular clasts on the steep slopes above the glaciers, (ii) sandy boulder gravel, with mainly angular and subangular clasts, forming lateral and end moraines, and (iii) sandy boulder/cobble gravel with mainly subrounded clasts, and sand, which represent glacially transported sediment reworked by braided rivers. Diamicton is rare in the contemporary glacial environment. Since most sediment associated with glaciers in the Southern Alps lacks unambiguous indications of glacial transport, interpretation of similar sediments in the geological record should not necessarily exclude the involvement of glacial processes. [source]