Raised marine deposits, Quaternary, Cainozoic of north-east Scotland
From: Merritt, J W, Auton, C A, Connell, E R, Hall, A M, and Peacock, J D. 2003. Cainozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, sheets 66E, 67, 76E, 77, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland).
Raised marine deposits
In addition to present-day coastal sediments, two distinct sets of raised marine deposits are present in the district. The sets were formed during periods of relatively high sea level, in Late-glacial times and in the mid-Holocene (Chapter 7; Figure 48). Sea level was appreciably lower than it is today between these periods. Each set of deposits is capable of being divided lithologically into ‘shoreface and beach deposits’ (mainly shingle and sand) and quiet-water sedimentary facies formed in tidal-flat, brackish lagoon and estuarine environments (mainly fine-grained sand and silt). Only the raised glaciomarine deposits are described here; the raised beaches and associated deposits, rock platforms and other features of coastal erosion are described in Chapter 7.
Late Devensian raised marine and glaciomarine deposits
Raised marine beds, mainly silty clay, are known between Elgin and Lossiemouth, from north of Peterhead, and possibly between Ellon and Stonehaven. In the Elgin area, the Spynie Clay Formation underlies much of the low-lying ground around Loch Spynie (NJ 237 667) (Chapter 8; Map 1). It occurs also below Lossiemouth Airfield where it is overlain by sand and gravel forming Late-glacial and Flandrian raised beaches. The maximum recorded thickness is 12.5 m (Peacock et al., 1968). North of the Spynie basin the formation attains a minimum level of 10 m above OD, and possibly reaches over 20 m OD, but on the south side of the basin the mapped level is only a little above present sea level, probably because the sea was partly excluded by stagnant ice from this area when sedimentation had begun elsewhere.
North of Peterhead, on Sheets 87E and 97, the dark grey silts, clays and fine-grained sands of the St Fergus Silt Formation extend up to about 16 m above OD (Chapter 8). Most of the formation is concealed by lacustrine alluvium (peat and silt) or blown sand. It borders red diamicton, clay and sand of the Logie-Buchan Drift Group to the west, whereas seawards, it appears to be banked against, or to have been deformed into, an end moraine (Hall and Jarvis, 1989; Anderson in Scott, 1890; Glentworth and Muir, 1963; Map 4). Their lithology suggests that the St Fergus Silts are glaciomarine in origin. Most of the marine bivalves, foraminiferids and ostracods in it belong to boreal or boreal-arctic taxa, and two adjusted radiocarbon dates of about 14.9 and about 14.3 ka BP indicate that it was laid down prior to the Windermere Interstadial (Appendix 1 St Fergus).
Some of the isolated deposits of red clay that have been mapped as glaciolacustrine deposits along the coast between Peterhead and Stonehaven may also be partly glaciomarine. These deposits, the Tullos Clay Member of the Logie-Buchan Drift Group (Chapter 8), contain a macrofauna and microfauna that is predominantly derived from reworked older deposits (Jamieson, 1882b; Bremner, 1916; Simpson, 1948; Munro, 1986). The clays lie between present sea level and about 30 m OD and may correlate with the Errol Clay Formation of eastern Scotland (Peacock, 1999). Early workers recorded the skull of a seal at Westfield (NJ 993 308), near Kirkton of Logie-Buchan on Sheet 87W (Nicol, 1860; Jamieson, 1882b), a fish at Tipperty (NJ 971 268) (Map 9), and remains of Ophiura from the clay at Clayhills (NJ 941 055), in Aberdeen. The red clays on the south side of the city of Aberdeen reach over 18 m above OD at Tullos (Simpson, 1948), where they were worked for making bricks (NJ 949 052) (Chapter 2).