THE LAMINATED SEDIMENTS OF LOCH-NESS, SCOTLAND - PRELIMINARY-REPORT ON THE CONSTRUCTION OF A CHRONOLOGY OF SEDIMENTATION AND ITS POTENTIAL USE IN ASSESSING HOLOCENE CLIMATIC VARIABILITY

Two sediment cores, ca. 6 m long, have been recovered from the north b asin of Loch Ness, Scotland. Each consists of ca. 4.5 m of laminated g yttja, terminating in a basal grey, unlaminated clay. A suite of three C-14 AMS dates have been obtained, and place the base of the gyttja a t ca. 9500 yr B.P. Investigations into the structure, composition and formation of the laminae are in progress. Analysis by Backscatter Scan ning Electron Microscopy (BSEM) has demonstrated that they consist of couplets comprising dark, clay-rich sediments thought to be deposited from spring to autumn, and pale, silt-rich layers believed to represen t sedimentation through winter. The laminae are thus thought to record incidence and intensity of streamflow into the Loch over the past nin e millennia, and thus illustrate environmental change over the region for most of the Holocene. X-ray densitometry has been utilised in orde r to count the laminations and test the hypothesis that they are varve s. It has, however, proved difficult to obtain a continuous sequence o f countable laminations, although it has been possible to construct a fragmented, floating chronology which indicates that the hypothesis ma y be correct. Examination of lamination thickness reveals that althoug h the average rate of sedimentation throughout the time periods studie d seems to have remained fairly constant, significant variations have occurred. As Loch Ness is located on the northwest oceanic fringe of E urope, any climatic signal which the laminations contain will be close ly related to even larger scale events over and within the North Atlan tic Ocean, which is a major controller of global climate. Preliminary statistical investigation of sequences of laminae is being carried out in order to search for periodicity of sedimentation which may then be related to appropriate climatic indices. (C) 1998 Elsevier Science B. V. All rights reserved.