A RECORD OF LATE CENOZOIC STRATIGRAPHY, SEDIMENTATION AND CLIMATE-CHANGE FROM THE HEBRIDES SLOPE, NE ATLANTIC-OCEAN

A punctuated 103.3 m thick succession of upper Palaeogene to Quaternar y sediments has been recovered in a borehole from the upper Hebrides S lope, west of Britain. The borehole proved 11.2 m of upper Oligocene, carbonate-rich muds at the base, unconformably overlain by 2.85 m of m iddle to upper Miocene, glauconitic sands. This is in turn unconformab ly overlain by 89.25 m of predominantly Plio-Pleistocene sands and mud s, with a Holocene sea-bed veneer. The post-Miocene succession is subd ivided into two units: the sand-dominated, Pliocene to lower middle Pl eistocene. Lower MacLeod sequence between 89.25 and 67.82 m, and the m ud-dominated, middle Pleistocene to Holocene, Upper MacLeod sequence a bove 67.82 m. Regional mapping indicates that these sequences are comm only associated with large-scale shelf-margin progradation and slope-f ront fan construction. The borehole core provides an excellent record of the transition from pre-glacial to glacial conditions in the mid-la titude NE Atlantic Ocean. Climatic conditions warmer than present prev ailed in the late Oligocene, mid- to late Miocene and Pliocene, althou gh the influx of ice-rafted detritus in the late Pliocene marks the on set of climatic deterioration. This deterioration continued, in a fluc tuating manner, until the early mid-Pleistocene (0.44 Ma) when fully g lacial conditions were established on the Hebridean Margin.