Devonian, Grampian Highlands - Revision history

Dbk at 15:39, 31 January 2018

2018-01-31T15:39:09Z

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			{{GHRG}}
	'''From: Stephenson, D, and Gould, D. 1995. [[British regional geology: Grampian Highlands\|British regional geology: Grampian Highlands.]] Fourth edition. Keyworth, Nottingham: British Geological Survey.'''
	== Devonian ==		== Devonian ==
	Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).		Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).

Scotfot at 18:14, 27 July 2015

2015-07-27T18:14:46Z

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	== Devonian ==		== Devonian ==
	Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).		Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).
	[[File:P915440.png\|thumbnail\|P915440]]		[[File:P915440.png\|thumbnail\|Sedimentary and volcanic rocks of the Lower Old Red Sandstone and their relationship to the Caledonian plutons (Argyll Suite) of the South-west Highlands. P915440.]]
	[[File:P915441.png\|thumbnail\|P915441]]
	[[File:P220248.jpg\|thumbnail\|P220248]]		[[File:P915441.png\|thumbnail\|Old Red Sandstone and Permo-Triassic rocks of the northern Grampian Highlands. P915441. ]]
	[[File:P915442.png\|thumbnail\|P915442]]		[[File:P220248.jpg\|thumbnail\|Lower Old Red Sandstone unconformable on Dalradian, Ailnack Gorge, Tomintoul, Banffshire. P220248.]]
			[[File:P915442.png\|thumbnail\|Probable correlation of the lithostratigraphical divisions of the Upper Old Red Sandstone in the Nairn–Elgin area (based on Peacock et al., 1968). P915442]]
	In northern Scotland, early Devonian extensional stresses gave rise to crustal fracturing which, in places, was accompanied by short-lived volcanic episodes. A series of half-graben developed in which a variety of alluvial, aeolian and fish-bearing lacustrine sediments accumulated. The largely extensional-tectonic non-marine sedimentary regime was maintained throughout the Devonian, but differential movements and intervals of heavy precipitation periodically led to interbasinal lacustrine conditions.		In northern Scotland, early Devonian extensional stresses gave rise to crustal fracturing which, in places, was accompanied by short-lived volcanic episodes. A series of half-graben developed in which a variety of alluvial, aeolian and fish-bearing lacustrine sediments accumulated. The largely extensional-tectonic non-marine sedimentary regime was maintained throughout the Devonian, but differential movements and intervals of heavy precipitation periodically led to interbasinal lacustrine conditions.

Scotfot at 20:21, 19 July 2015

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	== Upper Old Red Sandstone ==		== Upper Old Red Sandstone ==
	The Upper Old Red Sandstone in the main part of the Orcadian Basin is characterised by coarser-grained fluvial sediments than the underlying sequence and by the development of sabkha deposits, indicative of marginal marine conditions. The only Upper Old Red Sandstone in the Grampian Highlands lies on the southern side of the Moray Firth, between Fort George in the west and Spey Bay in the east, where they are peripheral to the basinal succession (P915441).		The Upper Old Red Sandstone in the main part of the Orcadian Basin is characterised by coarser-grained fluvial sediments than the underlying sequence and by the development of sabkha deposits, indicative of marginal marine conditions. The only Upper Old Red Sandstone in the Grampian Highlands lies on the southern side of the Moray Firth, between Fort George in the west and Spey Bay in the east, where they are peripheral to the basinal succession [[Media:P915441.png\|(P915441)]].

	Although the relationship with the Middle Old Red Sandstone is generally unconformable, in the southern part of the Orcadian Basin, there is evidence to indicate that the junction largely represents a facies change without any break in sequence. In the Nairn–Elgin district, the basal beds appear to be of late Givetian age and the sedimentary sequence spans the Middle–Upper Devonian boundary. To date, no early Famennian sedimentary rocks have been recognised and there is the possibility of a sequence-break between late Frasnian and late Famennian–?Tournaisian beds around Elgin (Rogers, 1987). Because of lack of exposure, the nature of the boundary on the southern side of the Moray Firth is not resolved, although it is clear that the Upper Old Red Sandstone is diachronous from west to east and that the oldest beds are restricted to the western region (P915442). The overall shallow-water and rare dry-bed conditions are reflected by relatively rapid lateral facies changes and by some overstepping of units along the margins of fault-bounded sub-basins. The Upper Old Red Sandstone is made up essentially of sandstone and the recognised subdivisions are based mainly upon six distinctive fossil-fish assemblages (Traquair, 1896; 1897; 1905; Westoll, 1951; Tarlo, 1961; Miles, 1968) that have correlatives in Baltic, Belgium, Spitzbergen and Greenland successions.		Although the relationship with the Middle Old Red Sandstone is generally unconformable, in the southern part of the Orcadian Basin, there is evidence to indicate that the junction largely represents a facies change without any break in sequence. In the Nairn–Elgin district, the basal beds appear to be of late Givetian age and the sedimentary sequence spans the Middle–Upper Devonian boundary. To date, no early Famennian sedimentary rocks have been recognised and there is the possibility of a sequence-break between late Frasnian and late Famennian–?Tournaisian beds around Elgin (Rogers, 1987). Because of lack of exposure, the nature of the boundary on the southern side of the Moray Firth is not resolved, although it is clear that the Upper Old Red Sandstone is diachronous from west to east and that the oldest beds are restricted to the western region (P915442). The overall shallow-water and rare dry-bed conditions are reflected by relatively rapid lateral facies changes and by some overstepping of units along the margins of fault-bounded sub-basins. The Upper Old Red Sandstone is made up essentially of sandstone and the recognised subdivisions are based mainly upon six distinctive fossil-fish assemblages (Traquair, 1896; 1897; 1905; Westoll, 1951; Tarlo, 1961; Miles, 1968) that have correlatives in Baltic, Belgium, Spitzbergen and Greenland successions.
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	The oldest unit is the Nairn Sandstone Formation, which comprises an irregular basal reddish conglomerate overlain by red, grey and yellow calcareous cross-bedded and flaggy sandstones containing thin beds of conglomerate and soft or shaly limestone-bearing mudstone. Good exposures occur on the beach north-west of Nairn, in Muckle Burn, at Glenshiel and in the Findhorn area. In the Findhorn area, the sandstone is faulted against Pre-cambrian gneisses (Black and Mackenzie, 1957) and some mudstone beds have been desiccated to clay galls. High in this section, a 3 m-thick calcrete bed named the Cothall Limestone (Parnell, 1983) is succeeded by 2.6 m of red and violet marl containing fossiliferous limestone concretions veined with calcite, cherty dolomite and pyrite; there are also patches of mamillate chalcedony. The fish fauna of the Nairn Sandstone comprises two main faunules. The lower is characterised by ''Asterolepis maxima'', ''Psammolepis tesselata'' and ''P.'' ''undulata'', whilst the upper one, known as the Boghole faunule, is distinguished by ''A. alta'' and ''Eusthenopteron traquairi<nowiki>; species common to both faunules include </nowiki>''Coccosteus magnus, Polyplocodus leptognathus'' and ''Holoptychius'' ''decoratus''. The first appearance of'' Bothriolepis ''has been taken to mark the base'' ''of another unit that bears the name Whitemire Beds (P915442). The Whitemire fauna is first encountered about 7 m above the Boghole faunule (Westoll, 1951) and is transitional in type between the Boghole and the overlying Alves faunas. The diagnostic species is ''Bothriolepis taylori'' and the assemblage includes ''C.'' ex. gr. ''magnus'' and ''H. nobilissimus,'' which are common in the older faunule, and ''Psammosteus taylori, Cosmacanthus, Conchodus'' and ''H.'' ''giganteus ''present in the Alves faunule.		The oldest unit is the Nairn Sandstone Formation, which comprises an irregular basal reddish conglomerate overlain by red, grey and yellow calcareous cross-bedded and flaggy sandstones containing thin beds of conglomerate and soft or shaly limestone-bearing mudstone. Good exposures occur on the beach north-west of Nairn, in Muckle Burn, at Glenshiel and in the Findhorn area. In the Findhorn area, the sandstone is faulted against Pre-cambrian gneisses (Black and Mackenzie, 1957) and some mudstone beds have been desiccated to clay galls. High in this section, a 3 m-thick calcrete bed named the Cothall Limestone (Parnell, 1983) is succeeded by 2.6 m of red and violet marl containing fossiliferous limestone concretions veined with calcite, cherty dolomite and pyrite; there are also patches of mamillate chalcedony. The fish fauna of the Nairn Sandstone comprises two main faunules. The lower is characterised by ''Asterolepis maxima'', ''Psammolepis tesselata'' and ''P.'' ''undulata'', whilst the upper one, known as the Boghole faunule, is distinguished by ''A. alta'' and ''Eusthenopteron traquairi<nowiki>; species common to both faunules include </nowiki>''Coccosteus magnus, Polyplocodus leptognathus'' and ''Holoptychius'' ''decoratus''. The first appearance of'' Bothriolepis ''has been taken to mark the base'' ''of another unit that bears the name Whitemire Beds (P915442). The Whitemire fauna is first encountered about 7 m above the Boghole faunule (Westoll, 1951) and is transitional in type between the Boghole and the overlying Alves faunas. The diagnostic species is ''Bothriolepis taylori'' and the assemblage includes ''C.'' ex. gr. ''magnus'' and ''H. nobilissimus,'' which are common in the older faunule, and ''Psammosteus taylori, Cosmacanthus, Conchodus'' and ''H.'' ''giganteus ''present in the Alves faunule.

	In the Nairn–Findhorn area, a younger fauna occurs in a sequence of grey to reddish siliceous pebbly sandstones named the Alves Beds, which, in the Elgin area, rests unconformably on metamorphic rocks near Burgie (P915442). The diagnostic species are ''B. alvesiensis'' and ''B. gigantea'', with ''H. nobilissimus ''extending upwards into these beds. East of the Rothes Fault, the Alves'' ''succession is represented by two lithological units. The lower Scaat Craig Beds, comprising red and yellow sandstone and fine conglomerate, contain taxa such as ''Cosmacanthus malcolmsoni, Conchodus ostreiformis'' and coccosteomorph arthrodires, which are closely linked to the Whitemire fauna below. The Alves fauna, however, is distinguished by ''P.'' cf. ''falcatus, Traquairosteus pustulatus'' and ''B. paradoxa''. The influence of an active Rothes Fault on Alves sedimentation is'' ''possibly reflected by the deposition east of the fault of a more carbonate-rich succession of pale grey and reddish brown marly sandstones, which overlies the Scaat Craig Beds. This sequence is characterised by sandy cherty calcrete beds representing palaeosols and is named the Cornstone Beds.		In the Nairn–Findhorn area, a younger fauna occurs in a sequence of grey to reddish siliceous pebbly sandstones named the Alves Beds, which, in the Elgin area, rests unconformably on metamorphic rocks near Burgie [[Media:P915442.png\|(P915442)]]. The diagnostic species are ''B. alvesiensis'' and ''B. gigantea'', with ''H. nobilissimus ''extending upwards into these beds. East of the Rothes Fault, the Alves'' ''succession is represented by two lithological units. The lower Scaat Craig Beds, comprising red and yellow sandstone and fine conglomerate, contain taxa such as ''Cosmacanthus malcolmsoni, Conchodus ostreiformis'' and coccosteomorph arthrodires, which are closely linked to the Whitemire fauna below. The Alves fauna, however, is distinguished by ''P.'' cf. ''falcatus, Traquairosteus pustulatus'' and ''B. paradoxa''. The influence of an active Rothes Fault on Alves sedimentation is'' ''possibly reflected by the deposition east of the fault of a more carbonate-rich succession of pale grey and reddish brown marly sandstones, which overlies the Scaat Craig Beds. This sequence is characterised by sandy cherty calcrete beds representing palaeosols and is named the Cornstone Beds.

	The highest strata in the Upper Old Red Sandstone are preserved in the Elgin area and form the Rosebrae Beds (P915442). They are well exposed in Quarry Wood, west of Elgin, and comprise brownish grey, yellow and reddish sandstone with only scarce pebbles. The fish fauna includes ''Phyllolepis'' cf. ''woodwardi, B. cristata, B. laverocklochensis, Phaneropleuron ''cf.'' andersoni, Rhychodipterus elginensis ''and'' Glyptopomus elginensis''. Associated taxa include'' B. alvesiensis, Conchodus, Eusthenopteron ''and'' H. nobilissimus'', all present in the'' ''underlying units. Palynological evidence (Marshall ''in'' Rogers, 1987) suggests that the Rosebrae Beds are late Famennian in age at their base and that the highest strata may transgress the Devonian–Carboniferous boundary; a non-sequence may separate the Alves and Cornstone beds from the Rosebrae Beds.		The highest strata in the Upper Old Red Sandstone are preserved in the Elgin area and form the Rosebrae Beds (P915442). They are well exposed in Quarry Wood, west of Elgin, and comprise brownish grey, yellow and reddish sandstone with only scarce pebbles. The fish fauna includes ''Phyllolepis'' cf. ''woodwardi, B. cristata, B. laverocklochensis, Phaneropleuron ''cf.'' andersoni, Rhychodipterus elginensis ''and'' Glyptopomus elginensis''. Associated taxa include'' B. alvesiensis, Conchodus, Eusthenopteron ''and'' H. nobilissimus'', all present in the'' ''underlying units. Palynological evidence (Marshall ''in'' Rogers, 1987) suggests that the Rosebrae Beds are late Famennian in age at their base and that the highest strata may transgress the Devonian–Carboniferous boundary; a non-sequence may separate the Alves and Cornstone beds from the Rosebrae Beds.

Scotfot at 20:18, 19 July 2015

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	Sedimentary and volcanic rocks of Devonian age occur on both sides of the Highland Boundary Fault in the Crieff and Blairgowrie areas; they form part of the Arbuthnott Group of the Midland Valley Old Red Sandstone succession described in the Regional Guide for the Midland Valley of Scotland (Cameron and Stephenson, 1985).		Sedimentary and volcanic rocks of Devonian age occur on both sides of the Highland Boundary Fault in the Crieff and Blairgowrie areas; they form part of the Arbuthnott Group of the Midland Valley Old Red Sandstone succession described in the Regional Guide for the Midland Valley of Scotland (Cameron and Stephenson, 1985).

	In the North-east Highlands, relatively small outliers at Tomintoul, Cabrach, Rhynie, Aberdeen and Turriff [[Media:P915441.png\|(P915441)]] are considered to be remnants of a more extensive development of the Lower Old Red Sandstone. Most represent irregular infillings of half-graben on the southern periphery of the Orcadian Basin. The Tomintoul Outlier is the sedimentary fill of an irregular NE-trending depression on the Dalradian basement. In the south-west, the outlier consists of a basal breccia overlain by a considerable, but unknown, thickness of coarse angular- and rounded-clast conglomerate. The sequence is well exposed in Ailnack Gorge [[Media:~~P220488~~.jpg\|(~~P220488~~)]], where the clasts are mainly of metasedimentary lithologies and up to 1 m in diameter. To the north-east, this conglomerate is overlain by red, immature medium-grained sandstones. The Cabrach Outlier is fault-bounded on its north-western side. Here a basal conglomerate is overlain by grey and red, friable, or red micaceous sandstone intercalated with coarse conglomerate layers; an outcrop of altered amygdaloidal andesite in the northern part of the outlier may represent a lava flow.		In the North-east Highlands, relatively small outliers at Tomintoul, Cabrach, Rhynie, Aberdeen and Turriff [[Media:P915441.png\|(P915441)]] are considered to be remnants of a more extensive development of the Lower Old Red Sandstone. Most represent irregular infillings of half-graben on the southern periphery of the Orcadian Basin. The Tomintoul Outlier is the sedimentary fill of an irregular NE-trending depression on the Dalradian basement. In the south-west, the outlier consists of a basal breccia overlain by a considerable, but unknown, thickness of coarse angular- and rounded-clast conglomerate. The sequence is well exposed in Ailnack Gorge [[Media:P220248.jpg\|(P220248)]], where the clasts are mainly of metasedimentary lithologies and up to 1 m in diameter. To the north-east, this conglomerate is overlain by red, immature medium-grained sandstones. The Cabrach Outlier is fault-bounded on its north-western side. Here a basal conglomerate is overlain by grey and red, friable, or red micaceous sandstone intercalated with coarse conglomerate layers; an outcrop of altered amygdaloidal andesite in the northern part of the outlier may represent a lava flow.

	The Rhynie Outlier forms a 21 km-long NNE-trending outcrop some 12 km east of the Cabrach Outlier. It contains andesitic lavas and is fault-bounded on the western side. The rocks of this outlier may be the oldest in the Orcadian province; the sequence is (Gould, 1997):		The Rhynie Outlier forms a 21 km-long NNE-trending outcrop some 12 km east of the Cabrach Outlier. It contains andesitic lavas and is fault-bounded on the western side. The rocks of this outlier may be the oldest in the Orcadian province; the sequence is (Gould, 1997):

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	The Lower Old Red Sandstone rocks on Kerrera rest on an irregular Dalradian rock surface. They comprise a basal unit of breccia and conglomerate, which is succeeded by sandstones, shaly mudstones and up to 300 m of siltstones and thin limestones with, locally, intercalated lavas. The oldest flaggy shaly mudstones contain a varied fauna of cephalaspid and anaspid fish including ''Cephalaspis lornensis'' (Waterston ''in'' Craig, 1965), as well as the millipede ''Kampecaris obanensis'' and plant remains (Lee and Bailey, 1925). Such a fauna is considered to be Prídolí (uppermost Silurian) in age, similar to that of the Stonehaven Group in the Midland Valley succession, south of the Highland Boundary Fault. The basal beds at Oban are somewhat younger. Sections of sandstone with overlying thick grey shaly-mudstone-bearing conglomerates are well exposed. Andesite boulders within these conglomerates indicate there was volcanic activity in the Grampian region prior to sedimentation. At several localities, the mudstones have yielded fossil assemblages that include the eurypterid ''Pterygotus anglicus'' as well as ''Kampecaris forfarensis, K. obanensis, C. lornensis, Mesocanthus mitchelli, Theolodus sp., ''ostracods and plants. In Glen Coe, the oldest beds are breccias and conglomerates with green and blackish shaly mudstones; near the foot of Buchaille Etive Mòr, plant remains, including ''Pachytheca fasciculata'', occur within the blackish mudstones.		The Lower Old Red Sandstone rocks on Kerrera rest on an irregular Dalradian rock surface. They comprise a basal unit of breccia and conglomerate, which is succeeded by sandstones, shaly mudstones and up to 300 m of siltstones and thin limestones with, locally, intercalated lavas. The oldest flaggy shaly mudstones contain a varied fauna of cephalaspid and anaspid fish including ''Cephalaspis lornensis'' (Waterston ''in'' Craig, 1965), as well as the millipede ''Kampecaris obanensis'' and plant remains (Lee and Bailey, 1925). Such a fauna is considered to be Prídolí (uppermost Silurian) in age, similar to that of the Stonehaven Group in the Midland Valley succession, south of the Highland Boundary Fault. The basal beds at Oban are somewhat younger. Sections of sandstone with overlying thick grey shaly-mudstone-bearing conglomerates are well exposed. Andesite boulders within these conglomerates indicate there was volcanic activity in the Grampian region prior to sedimentation. At several localities, the mudstones have yielded fossil assemblages that include the eurypterid ''Pterygotus anglicus'' as well as ''Kampecaris forfarensis, K. obanensis, C. lornensis, Mesocanthus mitchelli, Theolodus sp., ''ostracods and plants. In Glen Coe, the oldest beds are breccias and conglomerates with green and blackish shaly mudstones; near the foot of Buchaille Etive Mòr, plant remains, including ''Pachytheca fasciculata'', occur within the blackish mudstones.

	At the southern end of Kintyre (P915443), there is a thick succession of Lower Old Red Sandstone rocks which Friend and Macdonald (1968) have subdivided into the following formations:		At the southern end of Kintyre [[Media:P915443.png\|(P915443)]], there is a thick succession of Lower Old Red Sandstone rocks which Friend and Macdonald (1968) have subdivided into the following formations:

	{\| border="1" class="wikitable"		{\| border="1" class="wikitable"
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	Sedimentary and volcanic rocks of Devonian age occur on both sides of the Highland Boundary Fault in the Crieff and Blairgowrie areas; they form part of the Arbuthnott Group of the Midland Valley Old Red Sandstone succession described in the Regional Guide for the Midland Valley of Scotland (Cameron and Stephenson, 1985).		Sedimentary and volcanic rocks of Devonian age occur on both sides of the Highland Boundary Fault in the Crieff and Blairgowrie areas; they form part of the Arbuthnott Group of the Midland Valley Old Red Sandstone succession described in the Regional Guide for the Midland Valley of Scotland (Cameron and Stephenson, 1985).

	In the North-east Highlands, relatively small outliers at Tomintoul, Cabrach, Rhynie, Aberdeen and Turriff (P915441) are considered to be remnants of a more extensive development of the Lower Old Red Sandstone. Most represent irregular infillings of half-graben on the southern periphery of the Orcadian Basin. The Tomintoul Outlier is the sedimentary fill of an irregular NE-trending depression on the Dalradian basement. In the south-west, the outlier consists of a basal breccia overlain by a considerable, but unknown, thickness of coarse angular- and rounded-clast conglomerate. The sequence is well exposed in Ailnack Gorge (~~P220248~~), where the clasts are mainly of metasedimentary lithologies and up to 1 m in diameter. To the north-east, this conglomerate is overlain by red, immature medium-grained sandstones. The Cabrach Outlier is fault-bounded on its north-western side. Here a basal conglomerate is overlain by grey and red, friable, or red micaceous sandstone intercalated with coarse conglomerate layers; an outcrop of altered amygdaloidal andesite in the northern part of the outlier may represent a lava flow.		In the North-east Highlands, relatively small outliers at Tomintoul, Cabrach, Rhynie, Aberdeen and Turriff [[Media:P915441.png\|(P915441)]] are considered to be remnants of a more extensive development of the Lower Old Red Sandstone. Most represent irregular infillings of half-graben on the southern periphery of the Orcadian Basin. The Tomintoul Outlier is the sedimentary fill of an irregular NE-trending depression on the Dalradian basement. In the south-west, the outlier consists of a basal breccia overlain by a considerable, but unknown, thickness of coarse angular- and rounded-clast conglomerate. The sequence is well exposed in Ailnack Gorge [[Media:P220488.jpg\|(P220488)]], where the clasts are mainly of metasedimentary lithologies and up to 1 m in diameter. To the north-east, this conglomerate is overlain by red, immature medium-grained sandstones. The Cabrach Outlier is fault-bounded on its north-western side. Here a basal conglomerate is overlain by grey and red, friable, or red micaceous sandstone intercalated with coarse conglomerate layers; an outcrop of altered amygdaloidal andesite in the northern part of the outlier may represent a lava flow.

	The Rhynie Outlier forms a 21 km-long NNE-trending outcrop some 12 km east of the Cabrach Outlier. It contains andesitic lavas and is fault-bounded on the western side. The rocks of this outlier may be the oldest in the Orcadian province; the sequence is (Gould, 1997):		The Rhynie Outlier forms a 21 km-long NNE-trending outcrop some 12 km east of the Cabrach Outlier. It contains andesitic lavas and is fault-bounded on the western side. The rocks of this outlier may be the oldest in the Orcadian province; the sequence is (Gould, 1997):

Scotfot at 20:14, 13 July 2015

2015-07-13T20:14:04Z

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	== Devonian ==		== Devonian ==
	Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).		Devonian rocks are largely confined to the peripheral areas of the Grampian Highlands, although scattered downfaulted outliers in the interior point to a more extensive original cover. The Caledonian Orogeny was complete by early Devonian times and the Grampian Highlands were then part of a very large landmass lying astride the equator. Under semi-arid conditions, vast thicknesses of continental sediment were deposited to form the Old Red Sandstone megafacies in two distinct basinal areas, the Argyll Basin and the Orcadian Basin. The Old Red Sandstone succession which borders the Grampian Highlands on the southern side of the Highland Boundary Fault, was deposited in the separate Midland Valley Basin (Cameron and Stephenson, 1985).
			[[File:P915440.png\|thumbnail\|P915440]]
			[[File:P915441.png\|thumbnail\|P915441]]
			[[File:P220248.jpg\|thumbnail\|P220248]]
			[[File:P915442.png\|thumbnail\|P915442]]
	In northern Scotland, early Devonian extensional stresses gave rise to crustal fracturing which, in places, was accompanied by short-lived volcanic episodes. A series of half-graben developed in which a variety of alluvial, aeolian and fish-bearing lacustrine sediments accumulated. The largely extensional-tectonic non-marine sedimentary regime was maintained throughout the Devonian, but differential movements and intervals of heavy precipitation periodically led to interbasinal lacustrine conditions.		In northern Scotland, early Devonian extensional stresses gave rise to crustal fracturing which, in places, was accompanied by short-lived volcanic episodes. A series of half-graben developed in which a variety of alluvial, aeolian and fish-bearing lacustrine sediments accumulated. The largely extensional-tectonic non-marine sedimentary regime was maintained throughout the Devonian, but differential movements and intervals of heavy precipitation periodically led to interbasinal lacustrine conditions.

Scotfot: /* Lower Old Red Sandstone */

2015-07-11T15:01:05Z

Lower Old Red Sandstone

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	\|-		\|-
	\| '''Corbie’s Tongue Conglomerate Formation'''\|\|Compact conglomerate or breccia with some pebbly sandstone interbeds\|\| 0–20		\| '''Corbie’s Tongue Conglomerate Formation'''\|\|Compact conglomerate or breccia with some pebbly sandstone interbeds\|\| 0–20
	\|
	\|}		\|}

Scotfot: /* Lower Old Red Sandstone */

2015-07-11T14:58:57Z

Lower Old Red Sandstone

← Older revision		Revision as of 15:58, 11 July 2015
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	\|-		\|-
	\| '''Corbie’s Tongue Conglomerate Formation'''\|\|Compact conglomerate or breccia with some pebbly sandstone interbeds\|\| 0–20		\| '''Corbie’s Tongue Conglomerate Formation'''\|\|Compact conglomerate or breccia with some pebbly sandstone interbeds\|\| 0–20
	\|-
	\|		\|
	\|}		\|}

Scotfot: /* Lower Old Red Sandstone */

2015-07-09T07:49:53Z

Lower Old Red Sandstone

← Older revision		Revision as of 08:49, 9 July 2015
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	\| '''Glenramsgill Formation''', Quartzite Conglomerate Member\|\|Conglomerate with mainly quartzite clasts up to 1 m in diameter overlain by 200 m of purple sandstone and siltstone \|\|300		\| '''Glenramsgill Formation''', Quartzite Conglomerate Member\|\|Conglomerate with mainly quartzite clasts up to 1 m in diameter overlain by 200 m of purple sandstone and siltstone \|\|300
	\|-		\|-

	\| '''Glenramsgill Formation''', Basal Breccia Member\|\|Poorly bedded breccia of Dalradian clasts; passing upwards into red sandstones and siltstones replete with fine-grained Dalradian detritus; lava fragments common near the top\|\|150		\| '''Glenramsgill Formation''', Basal Breccia Member\|\|Poorly bedded breccia of Dalradian clasts; passing upwards into red sandstones and siltstones replete with fine-grained Dalradian detritus; lava fragments common near the top\|\|150
	\|
	\|}		\|}

Scotfot: /* Lower Old Red Sandstone */

2015-07-09T07:48:15Z

Lower Old Red Sandstone

← Older revision		Revision as of 08:48, 9 July 2015
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	At the southern end of Kintyre (P915443), there is a thick succession of Lower Old Red Sandstone rocks which Friend and Macdonald (1968) have subdivided into the following formations:		At the southern end of Kintyre (P915443), there is a thick succession of Lower Old Red Sandstone rocks which Friend and Macdonald (1968) have subdivided into the following formations:

	{\| border="1" class "wikitable"		{\| border="1" class="wikitable"
	\| align="center" style="background:#f0f0f0;"\|'''''		\| align="center" style="background:#f0f0f0;"\|'''''
	\| align="center" style="background:#f0f0f0;"\|'''''		\| align="center" style="background:#f0f0f0;"\|'''''
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	\| '''Glenramsgill Formation''', Basal Breccia Member\|\|Poorly bedded breccia of Dalradian clasts; passing upwards into red sandstones and siltstones replete with fine-grained Dalradian detritus; lava fragments common near the top\|\|150		\| '''Glenramsgill Formation''', Basal Breccia Member\|\|Poorly bedded breccia of Dalradian clasts; passing upwards into red sandstones and siltstones replete with fine-grained Dalradian detritus; lava fragments common near the top\|\|150
	\|-

	\|		\|
	\|}		\|}