Case Studies:Case study 44

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Allochthonous and autochthonous mire deposits, slope instability and palaeoenvironmental investigations in the Borve Valley, Barra, Outer Hebrides, Scotland
P. Ashmore, B.A. Brayshay, K.J. Edwards, D.D. Gilbertson, J.P. Grattan, M. Kent, K.E. Pratt and R.E. Weaver

Abstract
This case study suggests that sediment depth-age anomalies, and the lithological and palaeoecological properties of a peat core from Borve mire on the Outer Hebridean island of Barra, reflect the episodic impacts of rapid mass-movement of superficial peats and mineral soils from the adjacent hillslopes in the period 3000 to 1750BP. The studies involved gathering Russian cores for EDMA (energy-dispersive x-ray micro-analysis) investigations and x-radiography, mineral magnetism, and LOI, radiocarbon dating, and pollen analysis. The samples for pollen analysis and radiocarbon dating at the cairn site were obtained using a monolith tray inserted into an excavated peat. The environmental and vegetational history of this exposed and isolated Atlantic island is shown to have not been one of treeless homogeneity. A variety of deciduous and coniferous tree species colonized early in the Holocene, with distinctive birch-hazel woodland developing at one point in time. The landscape became increasingly treeless in the Bronze Age, with most but not all trees having been lost by the Medieval period. Valley side peats provide palynological evidence of pastoral and arable farming on poor soils in the Dark Age-Early Medieval period, at sites beyond the present limits of cultivation.

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Allochthonous and autochthonous mire deposits, slope instability and palaeoenvironmental investigations in the Borve Valley, Barra, Outer Hebrides, Scotland.

Keywords: Mass-movement, palaeoenvironments, pollen analysis, farming, mineral magnetism, Outer Hebrides, Scotland, Bronze Age, Medieval, x-radiography

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