Sand and gravel resources, Sheet 66E Banchory, 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 66E Banchory
The principal resources of the northern part of Sheet 66E (P915380) occur within glaciofluvial and alluvial deposits in the valleys of the River Dee, Burn of Sheeoch and Burn of Canny. Extensive spreads of sand and gravel are also present in the valley of the Water of Feugh, in the vicinity of Strachan. Minor resources occur within terraced alluvial deposits and moundy glaciofluvial deposits in Glen Dye and as flat-lying spreads of sand, in a small lake basin near Lochhead of Leys (NO 695 979) and in a larger basin around Loch of Park (NJ 770 990).
Some potentially workable coarse aggregate, mixed with bouldery diamicton, is present within the moundy glacial deposits forming moraines to the north and east of Loch of Park. Similar morainic sediments also occur in the valleys of the Water of Aven, the Burn of Melmannoch, the Burn of Knock, and on the southern side of the valley of the Water of Feugh, in the vicinity of Powlair (NO 620 912). All are potential sources of low-grade aggregate. Discrete areas of deeply decomposed granitic bedrock, around Loch of Park, Powlair and the upper reaches of Garrol Burn also constitute sources of aggregate suitable for use as fill and road base.
In the southern part of Sheet 66E, the main spreads of sand and gravel form moundy topography on the northern margin of Strathmore, notably between Auchenblae and Drumlithie, and around Fettercairn. Less attractive deposits are present beneath the floodplains of the Bervie Water, Luther Water, Black Burn, Devilly Burn and Burn of Cauldcots, as well as in the discontinuous terraced spreads on the sides of the valleys. Deeply weathered exposures of Lower Devonian conglomerate north of the Glen of Drumtochty, constitute a resource of cobbly gravel which, in places, exceeds 3 m in thickness.
The sand and gravel resources in the Dee valley, downstream of Banchory and within the valley of the Burn of Sheeoch, were evaluated as part of Mineral Assessment Report 148. Those in the vicinity of Strachan and in Strathmore were included in MAR 149. The sands and gravels that crop out in the south-west corner of Sheet 66E have not been assessed in detail. They are described in Carroll (1995d).
The kettled terraces that flank the Dee, between Banchory and the eastern margin of Sheet 66E, contain extensive resources of well stratified gravel and sand, lying above the water table; they average 7.4 m in thickness. Gravelly deposits, beneath negligible overburden are also present underlying the floodplain; they average 10.4 m in thickness. The terraced glaciofluvial gravels have been worked to a depth of greater than 10 m in Park Quarry, near Gallow Hill (NO 806 978), where they merge into mounds and ridges of ice-contact gravel. The upper part of the sequence at Park Quarry is described in Brown (1993); nearby boreholes indicate that the workable material reaches a thickness of between 15.8 and 19.7 m.
The discontinuous spreads of glaciofluvial sand and gravel in the valley of the Burn of Sheeoch form flat-topped mounds and sinuous esker ridges trending north-eastwards. The sediments underlying the flat-topped mounds are typified by the coarsening upward deltaic sequence that was formerly exposed in Lochton Pit (NO 752 929). Up to 5.4 m of sandy gravel was recorded overlying laminated glaciolacustrine silt and clay in the floor of the pit; the uppermost parts of the Lochton sequence are described in Brown (1994). The esker deposits are characterised by interdigitating sequences of poorly sorted gravel, fine-grained sand and laminated silt and clay. They are more heterogeneous and hence less attractive sources of aggregate than some of the deltaic deposits.
The most extensive spreads of sand and gravel in the valley of the Water of Feugh underlie the floodplain and river terraces upstream of Heugh-head (NO 687 928). Much of this material lies close to or below the water table, but mounds and kettled terraces on the southern side of the river valley, upstream of its confluence with the Burn of Knock, contain thick deposits of potentially workable sand and gravel. These deposits are typified by the glaciofluvial deltaic sediments exposed in the working pit at Cammie Wood (NO 695 920), where 12.8 m of sand and gravel occurs above the water table (P220858). The deposits coarsen upwards, from pebbly sand with partings of silt and clay into cross-bedded, fining-upward graded units of sandy gravel. The sandy gravel is overlain by up to 3 m of subhorizontally bedded coarse gravel that was laid down as the topset beds of the former ice-contact delta. The top of the sequence at Cammie Wood is described further in Brown (1994). Similar upward-coarsening sequences characterise many of the moundy glaciofluvial deposits between Scolly’s Cross (NO 642 877) and Pitdelphin Farm (NO 654 912), and also those forming large kames in the valley of the Devilly Burn, near Clatterin’ Brig (NO 665 782), in the southern part of Sheet 66E.
Small but attractive resources of coarse gravel, lying above the water table are present within esker systems in the vicinity of Strachan. Gravels forming the esker ridges, have been worked in pits north of Waulkmill (NO 647 923) and near Templeton (NO 671 916); however, significant unworked resources are present, within discontinuous esker ridges between Powlair and Greendams (NO 649 901).
The sands and gravels that form the undulating topography between Auchenblae and Drumlithie, and around Fettercairn, were laid down by meltwaters draining between ice in Strathmore and ice in the upland area to the north, which retreated north-westwards. These deposits characteristically occur as coarsening-upward sequences, which were laid down as deltas and fans into bodies of standing water between the two ice masses. The sands and gravels commonly contain thin waste partings of laminated silt and clay and some workable deposits (notably those south-east of Drumlithie) extend beneath a thin overburden of sandy ‘flow till’. These glaciofluvial sediments are assigned to the Drumlithie Sand and Gravel Formation of the Mearns Drift Group. They contain a mixed assemblage of clasts with tough granitic and psammitic pebbles being derived from igneous and metamorphic terrain to the north and less resistant clasts of sandstone and andesitic volcanic rocks derived from the Old Red Sandstone succession in Strathmore.
The most laterally extensive resources lying above the water table in the vicinity of Auchenblae, occur as flat-topped mounds. These deposits were worked in a large pit at Drumsleed (NO 733 776), where 5 m of sandy gravel was formerly exposed, overlying 13 m of pebbly sand. Exposures in other disused workings indicate that some of the nearby flat-topped deposits are much thinner, and range in composition from clayey gravel, to medium- and coarse-grained sand. Farther to the east, the glaciofluvial deposits become more hummocky and form a series of east-trending ridges that are extensively dissected by glacial drainage channels. The workable deposits of sand and gravel within the ridges range from 1.8 m to over 23.1 m in thickness, and have a similar range of grading characteristics to the deposits forming the flat-topped mounds.
The discontinuous spreads of sand and gravel beneath the floodplains of the Bervie Water, Luther Water, Black Burn, Devilly Burn and Burn of Cauldcots are relatively unattractive sources of aggregate as most lie beneath the water table. However, the last two named burns dissect extensive deposits of sand and gravel of the Drumlithie Sand and Gravel Formation that form moundy and terraced spreads around Fettercairn. None of these deposits has been assessed in detail, but notable resources are thought to occur on the lower flanks of Tor Hill, between Thornhill (NO 630 725) and Fettercairn, around Stankeye (NO 643 745), Kincardine Castle (NO 671 751), and at Nether Thainston (NO 634 750).
Sands and gravels lying above the water table are present within ice-contact glaciofluvial sequences in two areas at the eastern edge of Sheet 66E. Significant resources of gravel and coarse-grained sand have been worked in several small pits in the valley of the Cowie Water, around Snob Cott (NO 801 885). They also extend downstream on to the adjoining Sheet 67 Stonehaven. The surrounding moundy glacial deposits have also been worked on a small scale, though the resource is commonly thin, bouldery and laterally discontinuous.
Mounds and ridges of ice-contact sand and gravel on the eastern side of the valley drained by the Carron Water, and the Forthie Water between Brenzieshill (NO 799 792) and Pitdrichie (NO 795 825), have been worked for gravel in several places. The deposits forming the Bridge of Fiddes Esker are largely worked out, whereas up to 18.7 m of gravel was recorded in 1989 from active workings in an esker ridge near Pitdrichie. In contrast, the Little Wards Esker, which forms a discontinuous ridge, extending south-south-westwards for a distance of 1.5 km from the vicinity of Bridgend (NO 803 789), had only been exploited in small piecemeal workings at the time of the assessment. Noteworthy resources were also present within the more extensive glaciofluvial spreads, but the deposits are generally thinner and more sandy than those forming the eskers.
The gravels in the northern portion of Sheet 66E are of similar composition to most of those in the southern part of Sheet 76E, to the north. Clasts of granite and felsite (microgranite) predominate (P915336). Most are derived from the Mount Battock Granite, which forms the high ground between the catchments of the Dee, Bervie Water, Carron Water and Cowie Water. Psammitic clasts become more numerous within the glaciofluvial and alluvial gravels in the Dee valley, downstream of Banchory and significant numbers of pebbles of basic igneous rocks are present in gravels forming south-east-trending eskers in the vicinity of Strachan.
The glaciofluvial deposits of the Drumlithie Sand and Gravel Formation in the southern part of Sheet 66E contain a high proportion of quartzite and andesite pebbles, many of which have been reworked from local Devonian conglomerates. Some granitic clasts are also present, but the gravels contain a much higher proportion of deleterious material than those in the northern part of Sheet 66E. The friable clasts, which are mainly Devonian mudstone and sandstone pebbles, significantly reduce the strength of the aggregate and its suitability for use in concrete and road construction (see aggregate test results below).
End-use suitability data are only available for the sand and gravel resources in the valley of the River Dee downstream of Banchory, the valley of Burn of Sheeoch, and the sandy lacustrine sediments near Lochhead of Leys and Loch of Park. The glaciofluvial deposits, downstream of Banchory appear to be suitable for most end uses and as ‘all in’ concrete aggregate. The resources in the valley of the Burn of Sheeoch are more variable, with the glaciofluvial sheet deposits near Mains of Blairydrine (NO 742 943) being the most attractive as a source of fine aggregate for asphalt, plaster, mortar and concrete. Some of the lacustrine sediments are also suitable for use as asphalt, plaster, mortar and concrete sand, but the deposits are generally rather thin and variable.