Site 4 King Edward

King Edward [NJ 722 561], midway between Turriff and Banff (Map 5), is a long recognised locality for the presence there of a Quaternary marine shell bed containing whole arctic marine shells beneath dark grey shelly till (Jamieson, 1866; Sutherland, 1984c). Opinion has been divided over the origin of the shell bed. The state of preservation of the shells and the extent of the shell bed led to the view that this was an in situ marine deposit (Jamieson, 1866; Sutherland, 1981). Alternatively, the intimate association of the shell bed with shelly till led others to consider it to be a glacial raft or rafts (Read, 1923; Peacock and Merritt, 1997).

Jamieson gave details of a section beside the Burn of King Edward about 100 m south-west of the old bridge over the Banff–Turriff road in a series of papers spanning almost 50 years (Jamieson, 1858, 1865, 1866, 1906). Today the section is obscured and forested. The upper part comprised up to 8 m of coarse glaciofluvial gravel penetrated by ice-wedge casts. It cropped out along the sides of the burn and its tributaries below high terraces (Read, 1923; Sutherland, 1984c). Below the gravel lay up to 9 m of dark grey pebbly mud, with striated shells towards its base. This diamicton, here named the Castleton Memberof the Whitehills Glacigenic Formation (Castleton Formation of Sutherland, 1999), is typical of the shelly till found widely in the King Edward area (Read, 1923). The base of the section revealed a thin (60 cm thick) layer of brown shelly sand interstratified with more than 3 m of stoneless dark grey silt. The silt contained arctic shells in a crushed and decayed state, but apparently in situ. Jamieson regarded the lowermost shelly silt as representing a marine submergence under arctic conditions that occurred prior to glaciation of the area.

Recent excavation of a river bank 200 m south-east of the original locality [NJ 7236 5604] has confirmed the general succession of terrace gravel resting on dark grey muddy diamicton. The latter rested on over 6 m of intercalated brown sand, grey silt and mud, and dark grey muddy diamicton. Shell fragments occur in varying concentrations and states of preservation throughout these layers. Whole shells, including specimens of Lunatia pallida and valves of Arctica islandica and Macoma balthica were recovered from a sand layer at a depth of 12 m (Table A1.4). The base of the mud sequence was not seen, but a pit beneath the adjacent floodplain of the Burn at [NJ 7234 5602] showed that it rests on coarse glaciofluvial gravel and on bedrock. Although not conclusive evidence, the presence of disturbed contorted and steeply dipping beds is strongly suggestive of glacial disturbance, possibly rafting.

Jamieson (1865) noted that the faunas from King Edward and Gardenstown (see below) are similar. He tabulated the then known modern distributions in terms of those living:

1. on the British coast
2. south of Britain
3. within the Arctic Circle
4. on the east coast of North America
5. in the north Pacific.

Item (3) unfortunately gives a misleading 'cold' impression because 'within the Arctic Circle' includes the coast of Norway with its boreal fauna (Zenkevitch, 1963). Of the shells in Jamieson's list, only two (Tachyrhynchus reticulata and Serripes greenlandicus) can be classed as truly arctic to subarctic. Another (Yoldia limatula) is an American species that may be confused with the arctic to subarctic Y. hyperborea (Ockelmann, 1954). Excepting these arctic species, a deep-water taxon (Yoldiella lucida) and two boreal taxa (Polinices nanus and Turritella communis), all the molluscs listed in (Table A1.4) have been recorded in the Late-glacial (Windermere) Interstadial (13 000–11 000 BP) Clyde Beds of western Scotland (Smith et al., 1904). The fauna may thus be taken as generally of non-arctic, interstadial, offshore aspect.

It seems likely that the shell-bearing sands and muds at King Edward are glacially transported rafts within a sequence of glacial deposits derived largely from the bed of the Moray Firth (see Chapter 8; Whitehills Glacigenic Formation). King Edward lies only 1 km north-west of Plaidy (Map 5) where a large erratic of Oxfordian mudstone was worked in the 19th century (Jamieson, 1859). Other shell-bearing marine deposits previously thought to be in situ (Sutherland, 1981) have since been shown to be erratic masses, for example at Clava (Merritt, 1992b), Gardenstown (Peacock and Merritt, 1997) and the Boyne Limestone Quarry (Peacock and Merritt, 2000a).

At King Edward, amino-acid ratios between 0.073 and 0.095 (mean value 0.078 + 0.010) have been obtained from five Arctica shells collected from till at a site 200 m north-east of Jamieson's section. Uncalibrated AMS radiocarbon ages of greater than 44 200 BP (AA–1323) and greater than 41 500 BP (AA–1324) are reported on two of the analysed shells (Miller et al., 1987). On this basis the shells in the Castleton Member of the Whitehills Glacigenic Formation have been assigned to the interval between 40 and 80 ka BP (Miller et al., 1987). This age is consistent with the faunal evidence at King Edward of interstadial conditions. It appears on current evidence that these marine muds and sands were originally deposited on the floor of the Inner Moray Firth during OIS 4 or 3.

The timing of the glacial phase or phases that emplaced the rafts of marine sediment is uncertain. While some tills and rafts derived from the Moray Firth are thought to have been deposited during the Late Devensian (Merritt, 1992b), the possibility remains that some were transported during a Middle Devensian glacial phase equivalent to the Norwegian Skjonghelleren glaciation (Figure 43). The dark grey shelly tills of the Whitehills Glacigenic Formation around King Edward are covered in places, or merge upwards into, red-brown sandy till (Read, 1923). The latter is probably laterally equivalent to the Crovie Till Formation at Gardenstown and the Old Hythe Till Formation at the Boyne Limestone Quarry, but the exact age of all these units is unclear (Table 7).

References