GLACIGENIC RAFTING AT CASTLE HILL, GARDENSTOWN, AND ITS SIGNIFICANCE FOR THE GLACIAL HISTORY OF NORTHERN BANFFSHIRE, SCOTLAND

Reinvestigation of the lower part of the key Quaternary section at Cas tle Hill, Gardenstown, has shown that the sediments are not in stratig raphical order, bur consist chiefly of glaciotectonites, including raf ts of soft sediments, which were deposited by ice moving southeastward s from the Moray Firth. Sedimentary structures are preserved in some o f the rafts, which are separated by subhorizontal shears. The rafts ac creted subglacially under conditions of moderate to high strain, the f inal glacial event being the deposition of a thin, discontinuous sheet of till, probably derived from a more westerly direction. It is propo sed that interbedded dark grey shelly clay, till and sand elsewhere in northern Banffshire were emplaced, at least in part, by a similar mec hanism during either the Middle Devensian, or more likely, the Late De vensian. Sand and clay with paired bivalve shells, which were formerly exposed within the Quaternary successions at Castle Hill and inland a l King Edward, some 12 km to the south, are interpreted to be within g lacigenic rafts, and are not in situ deposits formed during a widespre ad marine transgression. It is suggested that the alternation of phase s of constructional and excavational deformation within a single glaci al event rather than discrete glaciations provides a useful model for glacial deposition in northern Banffshire, and more generally in north east Scotland. (C) 1997 by John Wiley & Sons, Ltd.