Sand and gravel resources, Sheet 77 Aberdeen, Cainozoic of north-east Scotland
|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).
Contributors: J F Aitken, D F Ball, D Gould, J D Hansom, R Holmes, R M W Musson and M A Paul.
Sheet 77 Aberdeen
Significant spreads of sand and gravel are present on Sheet 77 (P915379). Their proximity to Aberdeen, and the major market for building aggregate in north-east Scotland, has meant that many of the more attractive resources, such as those in the vicinity of Leuchlands (NJ 934 133), have been worked out; others have been sterilised by urban expansion. Mapping, undertaken as part of the Aberdeen sand and gravel assessment (MAR 146) and as part of an on-going programme of continuous revision, indicate that the resources on Sheet 77 are much less extensive than might be inferred from the 1:50 000 drift geological map published in 1980. The principal resources occur in three main areas.
- An arcuate spread of glaciofluvial sediments that stretches from Newburgh to Bridge of Don.
- Spreads of sand and gravel that flank the River Don upstream of Dyce and across the interfluve between Dyce and Corby Loch (NO 925 145) to merge with those of 1. above.
- Scattered spreads within the valleys of tributaries of the River Don and River Dee, beyond the City of Aberdeen.
Other resources are present within the sand dunes that extend southwards from Sands of Forvie to Bridge of Don. They constitute a potential resource of clean, medium- to fine-grained quartz sand, which, in places, overlies post-glacial raised beach deposits and glaciofluvial sands and gravels. Although the blown sand and underlying deposits have in the past been worked in pits at Blackdog Rifle Ranges (NJ 962 153) and Blackdog Rock (NJ 964 138), much of the remaining resource occurs within environmentally sensitive areas, such as nature reserves, or underlies golf courses.
Most of the sand and gravel deposits within the City of Aberdeen have either been worked or sterilised by urban and industrial development. These include the terraced spreads on the northern side of the Dee floodplain downstream of Peterculter, the moundy deposits near Nigg Bay (NJ 967 047), and those between Denmore (NJ 936 111) and Bridge of Don. Much of the urban development in the latter area has taken place since the summary assessment was made in 1988.
The sand and gravel between Newburgh and Denmore forms discontinuous mounds and ridges along the boundary between the Logie-Buchan and East Grampians drift groups. The potentially workable deposits are generally thin and sandy, but gravelly units are also present locally. Much of the resource is concealed beneath a variable thickness of overburden, comprising sandy till or a mixture of till and silty glaciolacustrine sediment; waste partings of till and silt are also common. The thickest gravel deposits form a steep-sided discontinuous ridge, 8 to 10 m high, between Hatterseat (NJ 982 215) and Newburgh; they have been worked in several pits near Drums (NJ 986 226). The resources are less extensive than might be inferred from the 1:50 000 drift map, but a BGS borehole at the southern end of the ridge, near Hatterseat, proved 7.1 m of poorly sorted sandy gravel resting on bedrock (Auton and Crofts, 1986). Another BGS borehole, near Pitscaff Croft (NJ 989 235), proved 9.4 m of sandy gravel beneath 4.7 m of overburden. The gravels are composed mainly of clasts of quartzite, psammite and vein quartz.
Little remains of the former thick deposits of glaciofluvial sand and gravel between Corby Loch and the coast, which have been exploited for aggregate in 19 major workings (see Auton and Crofts, 1986, tables 24 and 25). Few of these pits are now active, but currently notable amounts of coarse- and fine-grained aggregate are being extracted at Lochhills (Bishops Loch) pit. The sands and gravels formed a complex pattern of mounds and ridges (see Munro, 1986, fig.36) but the exact distribution of sheet and moundy ice-contact deposits is now difficult to determine, owing to the extent of worked-out and reinstated ground. The workable material ranged from 1.0 to over 13.9 m, averaging about 6 m in thickness.
The deposits forming the flat-topped mounds generally coarsen upwards, from ripple-laminated fine-grained sand and silt, into well sorted coarse gravel and sand with planar and trough cross-bedding. These workable resources are commonly concealed by thin discontinuous spreads of sandy ‘flow till’. The sand and gravel forming the ridges is generally more poorly sorted and cobbly than that underlying the mounds and discontinuous waste partings of clayey gravel and till are common. Exposures in some of the sequences are illustrated in Aitken (1998).
The terraced spreads of sand and gravel in the valley of the River Don contain significant resources of coarse and fine aggregate, lying above the water table. Similar water-saturated material is present beneath the flood-plain. The terraced deposits were formerly worked in pits at Nether Kirkton (NJ 880 143). Larger workings occur nearby, at Mill of Dyce (St Fergus), within moundy ice-contact sand and gravel that locally exceeds 16.2 m in thickness. These deposits, which are largely worked out, were seen to coarsen upwards, from silty and clayey sand into poorly sorted cobble and boulder gravel; they are described in detail in Site 18 Mill of Dyce.
Attractive resources of aggregate lying above the water table are present within the dissected glaciofluvial terraces on the southern side of the valley of the River Dee, downstream of Templar’s Park (NJ 845 999). The deposits average 4.3 m in thickness, but over 10 m of fine-grained silty sand were exposed in abandoned workings 200 m east of Templar’s Park, in 1999; up to 6 m of clast-supported gravel was recorded from working faces in Blairs Quarry (NJ 880 011) during 1988. Major resources of water-saturated gravel (with a mean thickness of 9.4 m) are also present beneath the river flood-plain, overlain by thin clayey alluvium.
Minor resources of moundy sand and gravel, which have been worked in places, are present on the Don–Dee interfluve near Borrowstone (NJ 849 078), Cairdhillock (NJ 848 068), East Brotherfield (NJ 844 043), Foggieton (NJ 867 038) and Easter Auguston (NJ 823 017), near Peterculter. Small deposits of sand and gravel forming mounds and esker ridges, were identified in the valley drained by the Green Burn, in the vicinity of Craibstone College of Agriculture (NJ 866 112), during surveys undertaken as part of the summary assessment study (Merritt et al., 1988). Up to 4 m of poorly sorted cobble gravel was exposed near the crest of the largest esker, and degraded faces in workings at the western end of the ridge indicate that the deposits have been exploited to depths of 12 to 15 m.
The grading of the most notable deposits of sand and gravel on Sheet 77 is illustrated in Mineral Assessment Report 146 (fig.4). This shows that gravels and sandy gravels predominate in the valleys of the rivers Don and Dee and their main tributaries, and that coarsening-upward successions dominate the more sandy sequences between Balmedie, Bridge of Don and Dyce.
The gravels on Sheet 77 are similar in composition to the bulk of those on the adjoining Sheet 76E Inverurie. Clasts of psammitic and granitic rocks predominate (P915335, P915336). Much of the granitic material is derived from the local granite intrusions at Clinterty, Crathes and Aberdeen; the clasts of basic and ultrabasic igneous rocks are probably derived mainly from the intrusion at Belhelvie. Small numbers of limestone and calcareous siltstone pebbles are present in gravels within the Logie-Buchan Drift Group along the coast north of Bridge of Don.
The gravels between Hatterseat and Newburgh and those within the valley of the River Dee, downstream of Peterculter, appear to be particularly suitable for coarse aggregate for road sub-base, asphalt and concrete. The workable deposits around Corby Loch, together with those in the valley of the River Don, between Mill of Dyce Pit and Aryburn (NJ 898 131) are potentially suitable for most end uses. The sandy deposits between Sheilhill (NJ 935 129) and Millden (NJ 971 163) were particularly suitable for use as asphalting sand, but the resource is largely worked out.