Temporary Desert Lake Deposits, Lower Permian (Rotliegendes) Southern Scotland, U.K.

• Autores: Michael E. Brookfield
• Localización: Lake basins through space and time / coord. por Elizabeth H. Gierlowski-Kordesch, K. Kelts, 2000, ISBN 0891810528, págs. 67-73
• Idioma: inglés
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• Resumen

  • During the Late Carboniferous to Early Permian, a large lowland desert developed over the whole of southern Scotland. Several desert basins were eroded into softer Carboniferous sediments preserved in post depositional grabens within the lower Paleozoic Southern Uplands massif (Figure 1) (Brookfield, 1978, 1980; Glennie,1982). Early Permian eruptions of basaltic lavas occurred in the Thornhill basin where they were accompanied by pediment formation and the deposition of thin pediment and desert floor stream and lake sediments. These interfinger with, and are overlain by, thick eolian sands.

    Northwesterly directed faulting then formed the isolated grabens of the Moffat, Lochmaben, and Dumfriesbasins to the south and east. In these grabens, marginal alluvial fan sequences are dominated by immature streamflood and sheetflood breccias and sandstones with interbedded eolian sandstones that pass basinwardinto massive dune sandstones. Depositional facies are those of very arid intermontane basins summarizedin Figure 2 (Brookfield, 1980;Nilsen 1982). The fan deposits have angular, poorly sorted clasts and often contain abundant well-rounded, reworked, coarse eolian sand and reworked ventifacts derived from the fan surfaces. Silt and clay are rare and probably were mostly removed by the wind; nevertheless ,rare silt and clay beds are occasionally interbedded with the pediment, alluvial fan, and eolian deposits.

    These fine-grained sediments were deposits inephemeral ponds and lakes and provide additional data on paleoenvironments. Such deposits are rarelydescribed from sections of ancient arid desert deposits because the most impressive units are the alluvial and eolian deposits (cf. Brookfield, 1984).The purpose of this paper is to record the facies