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Glacial Deposits (glacial + deposit)
Selected AbstractsRegolith and soils in Bhutan, Eastern HimalayasEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2004I. C. Baillie Summary Bhutan lies at altitudes of 100,7500 m on the steep, long and complex southern slopes of the Eastern Himalayas. Soil surveys show that, despite steep gradients, there are many moderately or deeply weathered soils. Many slopes are mantled with polycyclic, layered drift materials, so soil horizons owe as much to regolith heterogeneity as to pedogenesis. In the limited arable areas soil profiles are further complicated by rice cultivation and the construction, maintenance and irrigation of flat terraces on steep slopes. Some natural pedogenic horizonation is apparent, and there is an altitudinal zonation of soil types. Although the climate is warm and seasonally wet, most soils on the subtropical southern foothills are not particularly weathered and leached. The foothills are seismically active, and many soils are formed in unstable landslide debris. Elsewhere the regoliths are more stable. The main soils up to about 3000 m in the inner valleys are moderately weathered and leached, and have bright subsoil colours and thin dark topsoils. Above these there is a zone of bright orange-coloured non-volcanic andosolic soils. Further upslope there are acid soils with thick surface litter, stagnogleyic topsoils, and drab brown subsoils with organic cutans. These grade to weak podzols, which extend from about 3500 m up to the treeline, around 4000 m. Above this, alpine turf soils, with deep, dark, and friable topsoils and yellowish friable subsoils, are intermixed with unweathered glacial deposits. The interactions between pedogenesis and the deposition of the varied and layered drift materials complicate mapping and classification of the soils. [source] The effect of terrace geology on ground-water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake, New Hampshire, USA,HYDROLOGICAL PROCESSES, Issue 1 2008Thomas C. Winter Abstract The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north-west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground-water flow in a mountainside indicated that the presence of a terrace can cause local ground-water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water-table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow-through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground-water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain. Copyright © 2007 John Wiley & Sons, Ltd. [source] Biostratigraphic and aminostratigraphic constraints on the age of the Middle Pleistocene glacial succession in north Norfolk, UK,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2009Richard C. Preece Abstract Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north-western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ,Sidestrand Unio -bed', here defined as the Sidestrand Hall Member of the Cromer Forest-bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio -bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomyssavini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ,Cromerian Complex' and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial , probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ,new glacial stratigraphy' during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd. [source] Marine Isotope Stage 7,6 transition age for beach sediments at Morston, north Norfolk, UK: implications for Pleistocene chronology, stratigraphy and tectonics,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2009P. G. Hoare Abstract Optically stimulated luminescence age estimates for the Pleistocene beach at Morston, north Norfolk, UK, obtained by the single-aliquot regenerative-dose protocol, indicate a Marine Isotope Stage (MIS) 7,6 transition date. The view that the beach is of Ipswichian (MIS 5e) age, held virtually unanimously for the last 75 years, may now be discarded. The extant beach sequence lies up to ,5,m OD, yet global models suggest that MIS 7,6 sea levels were typically substantially below that of today. The explanation may lie with poorly understood regional tectonic movements. The MIS 7,6 date helps to constrain the ages of glacial deposits that bracket the beach sediments at Morston. The underlying Marly Drift till cannot be younger than MIS 8; this may also be true for the complex assemblage of glaciogenic landforms and sediments, including the Blakeney esker, in the adjacent lower Glaven valley. The well-established Late Devensian (MIS 2) age of the Hunstanton Till is not compromised by the date of the Morston beach. There is no indication of a proposed Briton's Lane glaciation during MIS 6 times. Copyright © 2009 John Wiley & Sons, Ltd. [source] Late- and postglacial history of the Great Belt, DenmarkBOREAS, Issue 1 2004OLE BENNIKE On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200,300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP. [source] | ||||||||||