OR/15/026 Cenozoic superficial deposits - Revision history

Ajhil: /* Paleogene/Neogene deep weathering deposits */

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Paleogene/Neogene deep weathering deposits

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	Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983"></ref>, fig. 12.6.iv).		Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983"></ref>, fig. 12.6.iv).

	‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name="Hall 1986"></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.		‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name="Hall 1986">HALL, A M. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. Zeitschrift für Geomorphologie, Vol. 30, 407–422.</ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.

	Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989"></ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.		Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989"></ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.

Ajhil at 11:11, 3 December 2019

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	==Palaeogene/Neogene==		==Palaeogene/Neogene==
	===Palaeogene/Neogene gravels and deep weathering===		===Palaeogene/Neogene gravels and deep weathering===
	Within the Huntly and Turriff districts are occurrences of unconsolidated deposits that appear to predate the Pleistocene glacial and glaciofluvial deposits. Their exact age is uncertain but they are considered to be largely of Palaeogene and Neogene age. They include the Buchan Gravels Formation and spreads of intensely and deeply weathered bedrock (saprolite) that can be divided into two distinct types: clayey gruss and sandy gruss (Hall, 1986<ref name="HALL~~, A M~~">Hall. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie,'' Vol. 30, 407–422.</ref>). Clayey gruss resulted from deep weathering under humid, warm climatic conditions, probably during the Miocene. Comparison of the saprolite mineralogy with that of North Sea sediments suggests that highly kaolinitic weathering mantles formed prior to the Pliocene in north-east Scotland (Hall et al., 1985<ref name="Hall 1985">HALL, A M, THOMAS, M F, and THORP, M B. 1985. Late Quaternary alluvial placer development in the humid tropics: the case of the Birim diamond placer, Ghana. ''Journal of the Geological Society of London'', Vol. 142, 777–787.</ref>). The sandy gruss resulted from less intense weathering under humid temperate conditions and is considered to be Pliocene to Early Pleistocene in age. The deeply weathered rocks are best developed in the south-east part of the Turriff district on the higher metamorphic grade Strichen Formation and on parts of the Insch Pluton and related mafic intrusions.		Within the Huntly and Turriff districts are occurrences of unconsolidated deposits that appear to predate the Pleistocene glacial and glaciofluvial deposits. Their exact age is uncertain but they are considered to be largely of Palaeogene and Neogene age. They include the Buchan Gravels Formation and spreads of intensely and deeply weathered bedrock (saprolite) that can be divided into two distinct types: clayey gruss and sandy gruss (Hall, 1986<ref name="HALL 1986">Hall. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie,'' Vol. 30, 407–422.</ref>). Clayey gruss resulted from deep weathering under humid, warm climatic conditions, probably during the Miocene. Comparison of the saprolite mineralogy with that of North Sea sediments suggests that highly kaolinitic weathering mantles formed prior to the Pliocene in north-east Scotland (Hall et al., 1985<ref name="Hall 1985">HALL, A M, THOMAS, M F, and THORP, M B. 1985. Late Quaternary alluvial placer development in the humid tropics: the case of the Birim diamond placer, Ghana. ''Journal of the Geological Society of London'', Vol. 142, 777–787.</ref>). The sandy gruss resulted from less intense weathering under humid temperate conditions and is considered to be Pliocene to Early Pleistocene in age. The deeply weathered rocks are best developed in the south-east part of the Turriff district on the higher metamorphic grade Strichen Formation and on parts of the Insch Pluton and related mafic intrusions.

	==== Buchan Gravels Formation ====		==== Buchan Gravels Formation ====

Ajhil: /* Paleogene/Neogene deep weathering deposits */

2019-12-03T11:10:20Z

Paleogene/Neogene deep weathering deposits

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	Within the Huntly and Turriff districts, most saprolites are sandy grusses with low fines, considered to have formed under the humid temperate conditions in the Pliocene and during warmer periods of the Pleistocene (Hall et al., 1985<ref name="Hall 1985"></ref>). The clay mineralogy of grusses is closely controlled by bedrock composition. Granitic saprolite clay mineral assemblages are dominated by kaolinite and white mica (Hall et al., 1989<ref name="Hall 1989"></ref>), whilst basic igneous saprolites contain a wide range of clay minerals. Plagioclase feldspar and hornblende in the Insch Pluton are largely unaffected by weathering. Pyroxene alters first to iron oxides and then vermiculite, whilst biotite weathers to hydrobiotite and vermiculite and, locally, kaolinite and gibbsite (Basham, 1974<ref name="Basham 1974">BASHAM, I R.1974. Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire. Clay Minerals, Vol. 10, 189–202. </ref>). Kaolinite and mica clays predominate in weathered metamorphic quartzo-feldspathic rocks, but the presence of ferro-magnesian minerals results in an increased smectite content (Hall et al., 1989<ref name="Hall 1989"></ref>).		Within the Huntly and Turriff districts, most saprolites are sandy grusses with low fines, considered to have formed under the humid temperate conditions in the Pliocene and during warmer periods of the Pleistocene (Hall et al., 1985<ref name="Hall 1985"></ref>). The clay mineralogy of grusses is closely controlled by bedrock composition. Granitic saprolite clay mineral assemblages are dominated by kaolinite and white mica (Hall et al., 1989<ref name="Hall 1989"></ref>), whilst basic igneous saprolites contain a wide range of clay minerals. Plagioclase feldspar and hornblende in the Insch Pluton are largely unaffected by weathering. Pyroxene alters first to iron oxides and then vermiculite, whilst biotite weathers to hydrobiotite and vermiculite and, locally, kaolinite and gibbsite (Basham, 1974<ref name="Basham 1974">BASHAM, I R.1974. Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire. Clay Minerals, Vol. 10, 189–202. </ref>). Kaolinite and mica clays predominate in weathered metamorphic quartzo-feldspathic rocks, but the presence of ferro-magnesian minerals results in an increased smectite content (Hall et al., 1989<ref name="Hall 1989"></ref>).

	Deep weathering profiles are highly variable (Hall, 1983<ref name="Hall 1983"></ref>). Weathering of igneous rocks normally leaves a residual coarse grit, with or without core stones. Weathering of metamorphosed pelitic and psammitic rocks results initially in deep blocky disintegration with the progressive development of fines as weathering becomes more intense. Borehole intersections of the weathering profile and the bedrock show that typically there is a gradational contact. However, in rare cases a sharp contact is observed (Hall, 1986<ref name=""></ref>).		Deep weathering profiles are highly variable (Hall, 1983<ref name="Hall 1983"></ref>). Weathering of igneous rocks normally leaves a residual coarse grit, with or without core stones. Weathering of metamorphosed pelitic and psammitic rocks results initially in deep blocky disintegration with the progressive development of fines as weathering becomes more intense. Borehole intersections of the weathering profile and the bedrock show that typically there is a gradational contact. However, in rare cases a sharp contact is observed (Hall, 1986<ref name="Hall 1986"></ref>).

	==Quaternary ==		==Quaternary ==

Ajhil: /* Paleogene/Neogene deep weathering deposits */

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Paleogene/Neogene deep weathering deposits

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	Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983"></ref>, fig. 12.6.iv).		Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983"></ref>, fig. 12.6.iv).

	‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name=""></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.		‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name="Hall 1986"></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.

	Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989"></ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.		Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989"></ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.

Ajhil at 11:09, 3 December 2019

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	Almost continuous vegetation cover was established during the Windermere Interstadial, following the final retreat of the Late Devensian ice sheets from north-east Scotland. Peats and organic muds from this period and the later Loch Lomond Stadial are known from excavations at Woodhead, Fyvie [NJ 788 384] (Connell and Hall, 1987<ref name="Connell 1987">CONNELL, E R, and HALL, A M. 1987. The periglacial stratigraphy of Buchan. 277–285 in ''Periglacial processes and landforms in Britain and Ireland. ''BOARDMAN, J (editor). (Cambridge: Cambridge University Press.)</ref>), Fisherie Green [NJ 791 589] and North Gorrachie [NJ 7385 5857] (Whittington et al., 1998<ref name="Whittington 1998"></ref>).		Almost continuous vegetation cover was established during the Windermere Interstadial, following the final retreat of the Late Devensian ice sheets from north-east Scotland. Peats and organic muds from this period and the later Loch Lomond Stadial are known from excavations at Woodhead, Fyvie [NJ 788 384] (Connell and Hall, 1987<ref name="Connell 1987">CONNELL, E R, and HALL, A M. 1987. The periglacial stratigraphy of Buchan. 277–285 in ''Periglacial processes and landforms in Britain and Ireland. ''BOARDMAN, J (editor). (Cambridge: Cambridge University Press.)</ref>), Fisherie Green [NJ 791 589] and North Gorrachie [NJ 7385 5857] (Whittington et al., 1998<ref name="Whittington 1998"></ref>).

	The Loch Lomond Stadial was a period of intense cold that resulted in permafrost conditions in north-east Scotland. Ice wedge casts are commonly present in sand and gravel quarries and at least some these structures formed during this period (Gemmell and Ralston 1984<ref name="Gemmell 1984">GEMMELL, A M D, and RALSTON, I B M. 1984. Some recent discoveries of ice-wedge cast networks in north-east Scotland. Scottish Journal of Geology, Vol. 20, 115–118. </ref>). Examples have been noted in gravel pits south of Turriff [NJ 736 493] and elsewhere (Connell and Hall, 1987<ref name="Connell 1987">CONNELL, E R, and HALL, A M. 1987. The periglacial stratigraphy of Buchan. 277–285 in Periglacial processes and landforms in Britain and Ireland. BOARDMAN, J (editor). (Cambridge: Cambridge University Press.) </ref>; Galloway, 1961<ref name="Galloway 1961">GALLOWAY, R W. 1961. Ice wedges and involutions in Scotland. ''Biuletyn Peryglacjalny,'' Vol. 10, 169–193.</ref>). Involutions and vertically orientated clasts, rotated as a result of freeze-thaw action, are also widespread in gravel pits in the Turriff area (Connell and Hall, 1987<ref name="Connell 1987"></ref>). However, the finest example of rotated clasts in the districts occurs in the quartzite gravels at Windy Hills (see above). Here, the entire upper metre of the deposit locally consists of sub-vertically orientated clasts.		The Loch Lomond Stadial was a period of intense cold that resulted in permafrost conditions in north-east Scotland. Ice wedge casts are commonly present in sand and gravel quarries and at least some these structures formed during this period (Gemmell and Ralston 1984<ref name="Gemmell 1984">GEMMELL, A M D, and RALSTON, I B M. 1984. Some recent discoveries of ice-wedge cast networks in north-east Scotland. Scottish Journal of Geology, Vol. 20, 115–118. </ref>). Examples have been noted in gravel pits south of Turriff [NJ 736 493] and elsewhere (Connell and Hall, 1987<ref name="Connell 1987"></ref>; Galloway, 1961<ref name="Galloway 1961">GALLOWAY, R W. 1961. Ice wedges and involutions in Scotland. ''Biuletyn Peryglacjalny,'' Vol. 10, 169–193.</ref>). Involutions and vertically orientated clasts, rotated as a result of freeze-thaw action, are also widespread in gravel pits in the Turriff area (Connell and Hall, 1987<ref name="Connell 1987"></ref>). However, the finest example of rotated clasts in the districts occurs in the quartzite gravels at Windy Hills (see above). Here, the entire upper metre of the deposit locally consists of sub-vertically orientated clasts.

	Frost shattering of rock is also widespread. Some shattering predates the last glaciation, as with the shattered quartzite as Newbigging [NJ 527 591], which is overlain by till (Galloway 1958<ref name="Galloway 1958"> GALLOWAY, R W. 1958. Periglacial phenomena in Scotland. Unpublished Ph.D thesis, University of Edinburgh. </ref>). Shattering is particularly well developed on the Durn Hill Quartzite, for example, at Gallowhill [NJ 484 525] and it reaches a reported depth of 8 m on Sillyearn Hill [NJ 507 514] (Galloway 1958<ref name="Galloway 1958"></ref>). The phyllitic semipelitic rocks around the headwaters of the Ythan and in the Glens of Foudland also show shattering to depths of 3 to 5 m (Galloway 1958<ref name="Galloway 1958"></ref>).		Frost shattering of rock is also widespread. Some shattering predates the last glaciation, as with the shattered quartzite as Newbigging [NJ 527 591], which is overlain by till (Galloway 1958<ref name="Galloway 1958"> GALLOWAY, R W. 1958. Periglacial phenomena in Scotland. Unpublished Ph.D thesis, University of Edinburgh. </ref>). Shattering is particularly well developed on the Durn Hill Quartzite, for example, at Gallowhill [NJ 484 525] and it reaches a reported depth of 8 m on Sillyearn Hill [NJ 507 514] (Galloway 1958<ref name="Galloway 1958"></ref>). The phyllitic semipelitic rocks around the headwaters of the Ythan and in the Glens of Foudland also show shattering to depths of 3 to 5 m (Galloway 1958<ref name="Galloway 1958"></ref>).

Ajhil at 11:09, 3 December 2019

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	Deep weathering affects almost all rock types to varying depths (Fitzpatrick, 1963<ref name="Fitzpatrick 1963">FITZPATRICK, E A. 1963. Deeply weathered rock in north-east Scotland, its occurrence, age and contribution to the soils. ''Journal of Soil Science'', Vol.14, 33–42. </ref>). The distribution of weathered bedrock is governed mainly by rock type, structure, topography and the variable intensity of glacial erosion. The mafic-ultramafic igneous rocks of the Insch Pluton and the Aberchirder biotite granite are widely and deeply weathered. In contrast, Southern Highland Group rocks and Devonian sandstones and conglomerates are less significantly affected (Hall, 1986<ref name="">HALL, A M. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie'', Vol. 30, 407–422.</ref>), although geophysical surveys suggest that in parts of the Turriff outlier alteration extends down to 10 m (Ashcroft, personal communication to A Hall, 1983). Beds of quartzo-feldspathic psammite within the Dalradian quartzites are frequently kaolinised.		Deep weathering affects almost all rock types to varying depths (Fitzpatrick, 1963<ref name="Fitzpatrick 1963">FITZPATRICK, E A. 1963. Deeply weathered rock in north-east Scotland, its occurrence, age and contribution to the soils. ''Journal of Soil Science'', Vol.14, 33–42. </ref>). The distribution of weathered bedrock is governed mainly by rock type, structure, topography and the variable intensity of glacial erosion. The mafic-ultramafic igneous rocks of the Insch Pluton and the Aberchirder biotite granite are widely and deeply weathered. In contrast, Southern Highland Group rocks and Devonian sandstones and conglomerates are less significantly affected (Hall, 1986<ref name="">HALL, A M. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie'', Vol. 30, 407–422.</ref>), although geophysical surveys suggest that in parts of the Turriff outlier alteration extends down to 10 m (Ashcroft, personal communication to A Hall, 1983). Beds of quartzo-feldspathic psammite within the Dalradian quartzites are frequently kaolinised.

	Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983">~~HALL, A M. 1983. Deep weathering and landform evolution in north-east Scotland. Unpublished PhD thesis, University of St. Andrews.~~</ref>, fig. 12.6.iv).		Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983"></ref>, fig. 12.6.iv).

	‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name=""></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.		‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name=""></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.

Ajhil at 11:08, 3 December 2019

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	‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name=""></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.		‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name=""></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.

	Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989">~~HALL, A M, MELLOR, T, and WILSON, M J. 1989. The clay mineralogy and age of deeply weathered rock in north-east Scotland. ''Zeitschrift der Geomorphologie Supplement Bund'', Vol. 72, 97–108.~~</ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.		Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989"></ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.

	Within the Huntly and Turriff districts, most saprolites are sandy grusses with low fines, considered to have formed under the humid temperate conditions in the Pliocene and during warmer periods of the Pleistocene (Hall et al., 1985<ref name="Hall 1985"></ref>). The clay mineralogy of grusses is closely controlled by bedrock composition. Granitic saprolite clay mineral assemblages are dominated by kaolinite and white mica (Hall et al., 1989<ref name="Hall 1989"></ref>), whilst basic igneous saprolites contain a wide range of clay minerals. Plagioclase feldspar and hornblende in the Insch Pluton are largely unaffected by weathering. Pyroxene alters first to iron oxides and then vermiculite, whilst biotite weathers to hydrobiotite and vermiculite and, locally, kaolinite and gibbsite (Basham, 1974<ref name="Basham 1974">BASHAM, I R.1974. Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire. Clay Minerals, Vol. 10, 189–202. </ref>). Kaolinite and mica clays predominate in weathered metamorphic quartzo-feldspathic rocks, but the presence of ferro-magnesian minerals results in an increased smectite content (Hall et al., 1989<ref name="Hall 1989"></ref>).		Within the Huntly and Turriff districts, most saprolites are sandy grusses with low fines, considered to have formed under the humid temperate conditions in the Pliocene and during warmer periods of the Pleistocene (Hall et al., 1985<ref name="Hall 1985"></ref>). The clay mineralogy of grusses is closely controlled by bedrock composition. Granitic saprolite clay mineral assemblages are dominated by kaolinite and white mica (Hall et al., 1989<ref name="Hall 1989"></ref>), whilst basic igneous saprolites contain a wide range of clay minerals. Plagioclase feldspar and hornblende in the Insch Pluton are largely unaffected by weathering. Pyroxene alters first to iron oxides and then vermiculite, whilst biotite weathers to hydrobiotite and vermiculite and, locally, kaolinite and gibbsite (Basham, 1974<ref name="Basham 1974">BASHAM, I R.1974. Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire. Clay Minerals, Vol. 10, 189–202. </ref>). Kaolinite and mica clays predominate in weathered metamorphic quartzo-feldspathic rocks, but the presence of ferro-magnesian minerals results in an increased smectite content (Hall et al., 1989<ref name="Hall 1989"></ref>).

Ajhil: /* Palaeogene/Neogene */

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Palaeogene/Neogene

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	==Palaeogene/Neogene==		==Palaeogene/Neogene==
	===Palaeogene/Neogene gravels and deep weathering===		===Palaeogene/Neogene gravels and deep weathering===
	Within the Huntly and Turriff districts are occurrences of unconsolidated deposits that appear to predate the Pleistocene glacial and glaciofluvial deposits. Their exact age is uncertain but they are considered to be largely of Palaeogene and Neogene age. They include the Buchan Gravels Formation and spreads of intensely and deeply weathered bedrock (saprolite) that can be divided into two distinct types: clayey gruss and sandy gruss (Hall, 1986<ref name=">HALL, A M. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie,'' Vol. 30, 407–422.</ref>). Clayey gruss resulted from deep weathering under humid, warm climatic conditions, probably during the Miocene. Comparison of the saprolite mineralogy with that of North Sea sediments suggests that highly kaolinitic weathering mantles formed prior to the Pliocene in north-east Scotland (Hall et al., 1985<ref name="Hall 1985">HALL, A M, THOMAS, M F, and THORP, M B. 1985. Late Quaternary alluvial placer development in the humid tropics: the case of the Birim diamond placer, Ghana. ''Journal of the Geological Society of London'', Vol. 142, 777–787.</ref>). The sandy gruss resulted from less intense weathering under humid temperate conditions and is considered to be Pliocene to Early Pleistocene in age. The deeply weathered rocks are best developed in the south-east part of the Turriff district on the higher metamorphic grade Strichen Formation and on parts of the Insch Pluton and related mafic intrusions.		Within the Huntly and Turriff districts are occurrences of unconsolidated deposits that appear to predate the Pleistocene glacial and glaciofluvial deposits. Their exact age is uncertain but they are considered to be largely of Palaeogene and Neogene age. They include the Buchan Gravels Formation and spreads of intensely and deeply weathered bedrock (saprolite) that can be divided into two distinct types: clayey gruss and sandy gruss (Hall, 1986<ref name="HALL, A M">Hall. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie,'' Vol. 30, 407–422.</ref>). Clayey gruss resulted from deep weathering under humid, warm climatic conditions, probably during the Miocene. Comparison of the saprolite mineralogy with that of North Sea sediments suggests that highly kaolinitic weathering mantles formed prior to the Pliocene in north-east Scotland (Hall et al., 1985<ref name="Hall 1985">HALL, A M, THOMAS, M F, and THORP, M B. 1985. Late Quaternary alluvial placer development in the humid tropics: the case of the Birim diamond placer, Ghana. ''Journal of the Geological Society of London'', Vol. 142, 777–787.</ref>). The sandy gruss resulted from less intense weathering under humid temperate conditions and is considered to be Pliocene to Early Pleistocene in age. The deeply weathered rocks are best developed in the south-east part of the Turriff district on the higher metamorphic grade Strichen Formation and on parts of the Insch Pluton and related mafic intrusions.

	==== Buchan Gravels Formation ====		==== Buchan Gravels Formation ====

Ajhil at 11:07, 3 December 2019

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	Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983">HALL, A M. 1983. Deep weathering and landform evolution in north-east Scotland. Unpublished PhD thesis, University of St. Andrews.</ref>, fig. 12.6.iv).		Rocks in shear zones in the low relief depression at the eastern end of the Insch Pluton are weathered to depths of about 50 m (Leslie, 1984<ref name="Leslie 1984">LESLIE, A G. 1984. Field relations in the north-eastern part of the Insch igneous mass, Aberdeenshire. ''Scottish Journal of Geology'', Vol. 20, 215–235. </ref>). Similar depths of weathering may also occur along the northern margin of the Insch depression and beneath the floor of the Drumblade depression (Ashworth, 1975<ref name="Ashworth 1975">ASHWORTH, J R. 1975. The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland. ''Geological Magazine'', Vol. 112, 113–136.</ref>). Boreholes in the Knock Pluton east of Ruthven also reveal 20 to 30 m of weathered basic igneous rock, although weathering depths are highly variable (Hall, 1983<ref name="Hall 1983">HALL, A M. 1983. Deep weathering and landform evolution in north-east Scotland. Unpublished PhD thesis, University of St. Andrews.</ref>, fig. 12.6.iv).

	‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name="Hall 1986">~~HALL, A M. 1986. Deep weathering patterns in north-east Scotland and their geomorphological significance. ''Zeitschrift für Geomorphologie'', Vol. 30, 407–422.~~ </ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.		‘Scarp-foot’ zones of enhanced weathering occur along the northern margin of the Insch depression at the foot of the Slate Hills (Hall, 1986<ref name="Hall 1986"></ref>, fig. 5). Glacial erosion was variably effective but did result in the stripping of weathered rock in some areas. Ice-moulding generally increases eastward along the Insch depression and the distribution of weathered rocks becomes more restricted, although numerous deep pockets and zones still remain. Similarly, weathered rock profiles appear to be less commonly preserved north of Huntly in the area affected by the relatively vigorous eastward flowing Moray Firth ice stream. Outcrops of fresh rock are also more abundant in this area in addition to the fewer occurrences of weathered rock.

	Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989">HALL, A M, MELLOR, T, and WILSON, M J. 1989. The clay mineralogy and age of deeply weathered rock in north-east Scotland. ''Zeitschrift der Geomorphologie Supplement Bund'', Vol. 72, 97–108.</ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.		Very intense weathering during the Miocene produced clayey gruss that is dominated by kaolinite and illite and small amounts of hematite. Examples of this degree of weathering are known only from the pelitic rocks beneath the Buchan Gravels and silicate clasts within the gravels themselves (Hall et al., 1989<ref name="Hall 1989">HALL, A M, MELLOR, T, and WILSON, M J. 1989. The clay mineralogy and age of deeply weathered rock in north-east Scotland. ''Zeitschrift der Geomorphologie Supplement Bund'', Vol. 72, 97–108.</ref>; Koppi, 1977<ref name="Koppi 1977"></ref>). Koppi (1977) also described a highly weathered biotite-bearing feldspathic psammite from Clashindarroch Forest at [435 305], just within the Glenfiddich district.