Editing East Grampian Drift Group, Quaternary lithostratigraphy, Cainozoic of north-east Scotland

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= East Grampian Drift Group  =
 
= East Grampian Drift Group  =
[[File:P915251.png|thumbnail|Generalised flow-lines of ice during the Main Late Devensian glaciation. P915251.]]
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This group is broadly equivalent to the sediments that were previously referred informally to the ‘Inland Series’ (Hall, 1984a; Sutherland and Gordon, 1993). The deposits contain clasts that have been carried by ice flowing from the eastern Grampian Highlands during several glaciations (Figure 4). Although erratics from farther afield do occur [[Media:P915294.png|(P915294)]], the colour and clast composition of the tills closely reflect the nature of underlying bedrock (commonly deeply weathered), or of rocks cropping out within a few kilometres to the west. The tills are generally sandy, thin (less than 2 m) and patchy, especially across central Buchan, where they are normally pale yellowish brown in colour. Thicker and more widespread tills occur in the valleys of the Dee and Don, where colour ranges from brown to grey. Glaciofluvial and glaciolacustrine deposits are relatively uncommon across large tracts of countryside, especially in central Buchan. The uppermost metre or so of all materials is commonly severely disturbed by periglacial activity (Connell and Hall, 1987).[[File:P915294.png|thumbnail|Transport paths of some indicator erratics in north-east Scotland. P915294.]]
This group is broadly equivalent to the sediments that were previously referred informally to the ‘Inland Series’ (Hall, 1984a; Sutherland and Gordon, 1993). The deposits contain clasts that have been carried by ice flowing from the eastern Grampian Highlands during several glaciations [[Media:P915251.png|(P915251)]]. Although erratics from farther afield do occur [[Media:P915294.png|(P915294)]], the colour and clast composition of the tills closely reflect the nature of underlying bedrock (commonly deeply weathered), or of rocks cropping out within a few kilometres to the west. The tills are generally sandy, thin (less than 2 m) and patchy, especially across central Buchan, where they are normally pale yellowish brown in colour. Thicker and more widespread tills occur in the valleys of the Dee and Don, where colour ranges from brown to grey. Glaciofluvial and glaciolacustrine deposits are relatively uncommon across large tracts of countryside, especially in central Buchan. The uppermost metre or so of all materials is commonly severely disturbed by periglacial activity (Connell and Hall, 1987).[[File:P915294.png|left|thumbnail|Transport paths of some indicator erratics in north-east Scotland. P915294.]]
 
  
 
The sandy nature and pale colour of the tills occurring in central Buchan have led some authors to conclude that they have been weathered since their deposition. These attributes, together with inferred relationships to incorrectly dated organic sediments ([[Geomorphological features of glacial or glaciofluvial deposition, Cainozoic of north-east Scotland#Erratics|Crossbrae]]), led some to conclude that they were laid down either during an early Devensian glaciation (Hall, 1984; Sutherland, 1984a; Hall and Connell, 1991) or during a pre-Devensian one (Charlesworth, 1956; Synge, 1956, Fitzpatrick, 1958, 1972; Galloway, 1961a, b, c). The sandiness and colour are equally likely, however, to result from the incorporation of significant proportions of deeply weathered bedrock or previously weathered deposits, in which case the tills need be no older than Late Devensian in age (Clapperton and Sugden, 1977; Hall and Bent, 1990). For example, pedological studies of a till (possibly Hythie Till Formation) near Mintlaw suggest that the soil-forming processes occurred during the Holocene (Van Amerongen, 1976).
 
The sandy nature and pale colour of the tills occurring in central Buchan have led some authors to conclude that they have been weathered since their deposition. These attributes, together with inferred relationships to incorrectly dated organic sediments ([[Geomorphological features of glacial or glaciofluvial deposition, Cainozoic of north-east Scotland#Erratics|Crossbrae]]), led some to conclude that they were laid down either during an early Devensian glaciation (Hall, 1984; Sutherland, 1984a; Hall and Connell, 1991) or during a pre-Devensian one (Charlesworth, 1956; Synge, 1956, Fitzpatrick, 1958, 1972; Galloway, 1961a, b, c). The sandiness and colour are equally likely, however, to result from the incorporation of significant proportions of deeply weathered bedrock or previously weathered deposits, in which case the tills need be no older than Late Devensian in age (Clapperton and Sugden, 1977; Hall and Bent, 1990). For example, pedological studies of a till (possibly Hythie Till Formation) near Mintlaw suggest that the soil-forming processes occurred during the Holocene (Van Amerongen, 1976).

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