Grampian Caledonides—introduction - Revision history

Dbk at 15:40, 31 January 2018

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	'''From: Stephenson, D, and Gould, D. 1995. [[British regional geology: Grampian Highlands\|British regional geology: Grampian Highlands.]] Fourth edition. Keyworth, Nottingham: British Geological Survey.'''		{{GHRG}}

	== Introduction ==		== Introduction ==
	The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in [[Media:P915427.png\|P915427]].		The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in [[Media:P915427.png\|P915427]].

Dbk at 12:56, 26 November 2015

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	In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this ''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.		In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this ''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.
	[[File:P915450.png\|thumbnail\|Distribution of lineaments, shear zones and major brittle faults in the Grampian Highlands. P915450.]]		[[File:P915450.png\|thumbnail\|Distribution of lineaments, shear zones and major brittle faults in the Grampian Highlands. P915450.]]
	The main outcrop pattern of the Dalradian as depicted in P915411 is largely governed by the major folds described above. During the later stages of orogenesis, many of these structures were further modified by block uplift and faulting, which occurred at different rates and at different times throughout the Dalradian outcrop (Harte et al., 1984; Dempster, 1985). The differential uplift resulted in an outcrop pattern that reveals wide variations in levels of exposure. Later, post-orogenic, brittle fault movements have displaced boundaries, by several kilometres in some cases (Chapter 16). Between the major boundary faults of the Great Glen and the Highland Boundary lie a whole series of parallel, NE-trending faults showing sinistral displacement. Of these, the ''Glen Markie, Ericht–Laidon, Tyndrum, Bridge of Balgie'' and ''Loch Tay faults'' have particularly significant displacements [[Media:P915450.png\|(P915450)]]. In some areas, appreciable displacements, largely of a vertical nature, also occur on NW-trending faults such as the ''Rothes'' and ''Pass of Brander faults'', some of which may reflect fundamental deep level tectonostratigraphical lineaments (Chapter 6).		The main outcrop pattern of the Dalradian as depicted in [[Media:P915411.png\|P915411]] is largely governed by the major folds described above. During the later stages of orogenesis, many of these structures were further modified by block uplift and faulting, which occurred at different rates and at different times throughout the Dalradian outcrop (Harte et al., 1984; Dempster, 1985). The differential uplift resulted in an outcrop pattern that reveals wide variations in levels of exposure. Later, post-orogenic, brittle fault movements have displaced boundaries, by several kilometres in some cases (Chapter 16). Between the major boundary faults of the Great Glen and the Highland Boundary lie a whole series of parallel, NE-trending faults showing sinistral displacement. Of these, the ''Glen Markie, Ericht–Laidon, Tyndrum, Bridge of Balgie'' and ''Loch Tay faults'' have particularly significant displacements [[Media:P915450.png\|(P915450)]]. In some areas, appreciable displacements, largely of a vertical nature, also occur on NW-trending faults such as the ''Rothes'' and ''Pass of Brander faults'', some of which may reflect fundamental deep level tectonostratigraphical lineaments (Chapter 6).

	The Dalradian rocks occur at the surface in a variety of metamorphic states, illustrated best by the pelitic rocks which range from slate and phyllite, especially in the south and east, to coarse-grained schists, gneisses and migmatites in the north. In detail, as outlined in Chapter 7, the metamorphic development in space and time was complex, but the overall pattern exposed can be described in terms of two main components:		The Dalradian rocks occur at the surface in a variety of metamorphic states, illustrated best by the pelitic rocks which range from slate and phyllite, especially in the south and east, to coarse-grained schists, gneisses and migmatites in the north. In detail, as outlined in Chapter 7, the metamorphic development in space and time was complex, but the overall pattern exposed can be described in terms of two main components:

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	== Introduction ==		== Introduction ==
	The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in P915427.		The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in [[Media:P915427.png\|P915427]].
	[[File:P915417.png\|thumbnail\|Lithostratigraphical units in the Grampian Group. P915417.]]		[[File:P915417.png\|thumbnail\|Lithostratigraphical units in the Grampian Group. P915417.]]

Jeth1 at 09:42, 19 November 2015

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	Continuing detailed stratigraphical and structural studies have resulted in further refinements to the Bailey model. Several alternative structural models have emerged, although many of the major fold structures originally named by Bailey are still recognised. However, detailed interpretations of the relative ages and original geometry of differing sets of folds and their overall tectonic significance remain problematical. Many of Bailey’s slides are still recognised as important and complex zones of low-angled tectonic dislocation and stratigraphical attenuation. However, it has been shown that, on a regional scale, both the structure and the stratigraphy of the Grampian Highlands are more integrated and continuous than inferred by Bailey, with elements of the succession being traced vertically through the nappe pile as well as laterally along the full strike length. Hence most of the Dalradian must be regarded as autochthonous or parautochthonous and the slides may have lost much of their original significance as major tectonic and stratigraphical boundaries. In most current models, where tectonostratigraphical boundaries are recognised they are commonly defined by cross-strike lineaments. Such lineaments are taken to represent fundamental, deep-seated crustal fractures which have influenced sedimentation, igneous activity and structural development over a long period of time. They can have a marked influence on the outcrop pattern and are recognised by various combinations of features such as abrupt lateral facies changes in the metasedimentary sequence, sites of igneous activity, geochemical and geophysical changes and zones of structural discontinuity.		Continuing detailed stratigraphical and structural studies have resulted in further refinements to the Bailey model. Several alternative structural models have emerged, although many of the major fold structures originally named by Bailey are still recognised. However, detailed interpretations of the relative ages and original geometry of differing sets of folds and their overall tectonic significance remain problematical. Many of Bailey’s slides are still recognised as important and complex zones of low-angled tectonic dislocation and stratigraphical attenuation. However, it has been shown that, on a regional scale, both the structure and the stratigraphy of the Grampian Highlands are more integrated and continuous than inferred by Bailey, with elements of the succession being traced vertically through the nappe pile as well as laterally along the full strike length. Hence most of the Dalradian must be regarded as autochthonous or parautochthonous and the slides may have lost much of their original significance as major tectonic and stratigraphical boundaries. In most current models, where tectonostratigraphical boundaries are recognised they are commonly defined by cross-strike lineaments. Such lineaments are taken to represent fundamental, deep-seated crustal fractures which have influenced sedimentation, igneous activity and structural development over a long period of time. They can have a marked influence on the outcrop pattern and are recognised by various combinations of features such as abrupt lateral facies changes in the metasedimentary sequence, sites of igneous activity, geochemical and geophysical changes and zones of structural discontinuity.

	The structure of the Grampian Caledonides is discussed in detail in Chapter 6. However, in order to describe the stratigraphy of the area in Chapter 5 it is necessary to have some knowledge of the major fold structures and tectonic dislocations that influence the disposition of the lithostratigraphical units. Most were established by E B Bailey and are shown on P915427. They are described below without recourse to complex and controversial discussions of deformation phases, relationships with adjacent or other structures, metamorphic textures or related fabrics.		The structure of the Grampian Caledonides is discussed in detail in Chapter 6. However, in order to describe the stratigraphy of the area in Chapter 5 it is necessary to have some knowledge of the major fold structures and tectonic dislocations that influence the disposition of the lithostratigraphical units. Most were established by E B Bailey and are shown on [[Media:P915427.png\|(P915427)]]. They are described below without recourse to complex and controversial discussions of deformation phases, relationships with adjacent or other structures, metamorphic textures or related fabrics.

	The overall structure of the Grampian Highlands is most easily described and understood with reference to structures in the South-west Highlands (Roberts and Treagus, 1977). Here the major folds are seen to diverge on either side of a central ''Loch Awe Syncline'' which is interpreted as an early primary structure. Apparently geometrically similar structures farther to the north-east include the ''Ben Lawers Synform'' and ''Sron Mhor Syncline'' but these are actually due to later refolding events. To the south-east of the Loch Awe Syncline, the ''Ardrishaig Anticline'' is interpreted as the core of a large SE-facing nappe, the ''Tay Nappe'', which dominates the overall structure of the Southern Highlands. The Tay Nappe is flat-lying, although in the south-west it is folded across a broad arch known as the ''Cowal Antiform''. The erosion level is such that most of the outcrop constitutes part of the inverted limb of the nappe, so that stratigraphical sequences are inverted. Structures underlying this inverted limb are seen only in the area of the Angus glens, where a largely right-way-up sequence has been interpreted as a separate ''Tarfside Nappe'' (Harte, 1979). Close to the Highland Boundary Fault Zone, the Tay Nappe is bent downwards to form the ''Highland Border Steep Belt''. The hinge zone of the nappe thus becomes downward facing as a synformal anticline, recognised in the Southern Highlands as the ''Aberfoyle Anticline'' (Shackleton, 1958).		The overall structure of the Grampian Highlands is most easily described and understood with reference to structures in the South-west Highlands (Roberts and Treagus, 1977). Here the major folds are seen to diverge on either side of a central ''Loch Awe Syncline'' which is interpreted as an early primary structure. Apparently geometrically similar structures farther to the north-east include the ''Ben Lawers Synform'' and ''Sron Mhor Syncline'' but these are actually due to later refolding events. To the south-east of the Loch Awe Syncline, the ''Ardrishaig Anticline'' is interpreted as the core of a large SE-facing nappe, the ''Tay Nappe'', which dominates the overall structure of the Southern Highlands. The Tay Nappe is flat-lying, although in the south-west it is folded across a broad arch known as the ''Cowal Antiform''. The erosion level is such that most of the outcrop constitutes part of the inverted limb of the nappe, so that stratigraphical sequences are inverted. Structures underlying this inverted limb are seen only in the area of the Angus glens, where a largely right-way-up sequence has been interpreted as a separate ''Tarfside Nappe'' (Harte, 1979). Close to the Highland Boundary Fault Zone, the Tay Nappe is bent downwards to form the ''Highland Border Steep Belt''. The hinge zone of the nappe thus becomes downward facing as a synformal anticline, recognised in the Southern Highlands as the ''Aberfoyle Anticline'' (Shackleton, 1958).

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	== Stratigraphy ==		== Stratigraphy ==
	Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.		Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.
	[[File:P915411.png\|thumbnail\|P915411]]		[[File:P915411.png\|thumbnail\|Solid geology of the Grampian Highlands. P915411.]]
	[[File:P915427.png~~\|600px~~\|thumbnail\|P915427]]		[[File:P915427.png\|thumbnail\|Block diagram of major structures in the Grampian Highlands. P915427.]]
	It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.		It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.

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	== Structure and metamorphism ==		== Structure and metamorphism ==
	Current structural interpretations of the Grampian Caledonides are still based upon those proposed by E B Bailey, which drew on the results of the primary mapping by the Geological Survey. In a series of papers, from 1910 to 1938, Bailey demonstrated that the rocks of the South-west and Southern Highlands are disposed in large recumbent folds. The lower limbs of many of these folds are partly replaced by low-angled, extensional faults, termed ‘slides’, with postulated movements of several kilometres. In 1922 Bailey produced a comprehensive synthesis in which major slides were perceived as fundamental tectonic dislocations separating nappe complexes, each complex having its own stratigraphical succession and structural style. Initially three such nappe complexes were recognised and named, in ascending structural order, the ''Ballappel Foundation'' (from the type areas of Ballachulish, Appin and Loch Eilde), the ''Iltay Nappe'' (from Islay and Loch Tay), and the ''Loch Awe Nappe'', but these were subsequently reduced to two when Bailey (''in ''Allison, 1941) accepted the stratigraphical correlations of other investigators which removed the need to invoke a separate Loch Awe Nappe.		Current structural interpretations of the Grampian Caledonides are still based upon those proposed by E B Bailey, which drew on the results of the primary mapping by the Geological Survey. In a series of papers, from 1910 to 1938, Bailey demonstrated that the rocks of the South-west and Southern Highlands are disposed in large recumbent folds. The lower limbs of many of these folds are partly replaced by low-angled, extensional faults, termed ‘slides’, with postulated movements of several kilometres. In 1922 Bailey produced a comprehensive synthesis in which major slides were perceived as fundamental tectonic dislocations separating nappe complexes, each complex having its own stratigraphical succession and structural style. Initially three such nappe complexes were recognised and named, in ascending structural order, the ''Ballappel Foundation'' (from the type areas of Ballachulish, Appin and Loch Eilde), the ''Iltay Nappe'' (from Islay and Loch Tay), and the ''Loch Awe Nappe'', but these were subsequently reduced to two when Bailey (''in ''Allison, 1941) accepted the stratigraphical correlations of other investigators which removed the need to invoke a separate Loch Awe Nappe.
	[[File:P915415.png\|thumbnail\|P915415]]		[[File:P915415.png\|thumbnail\|Diagram to illustrate the concept of facing direction of folds as defined by Shackleton (1958). P915415. P915415.]]
	A better understanding of the stratigraphy, following the recognition of sedimentary structures in quartzitic rocks as way-up indicators, led to modifications of the early structural models. Bailey himself used such observations in the Loch Leven area to completely reverse the order of superposition used in his 1922 paper and revised his structural interpretation in a further major review paper (Bailey, 1934). Further developments and modifications resulted from the recognition of graded units and other internal structures in turbiditic rocks, first applied by Shackleton (1958) to the structure of the Southern Highlands and the Highland Border. The concept of ‘facing’ was introduced as a means to describe the structural ‘way-up’ of strata [[Media:P915415.png\|(P915415)]]. Shackleton (1958) defined ‘facing’ geometrically as ‘the direction normal to the fold axis, along the axial plane, and towards the younger beds’. Thus a synclinal synform is described as ‘upward facing’, whereas an anticlinal (i.e. inverted) synform is ‘downward facing’. Asymmetrical and recumbent folds have a sideways component of facing which is an important descriptive parameter, and which is commonly used to infer the direction of tectonic transport. H H Read, who had commenced work in the north-east Grampians as a member of the Geological Survey, initiated research which resulted in several detailed studies of the Banff Nappe and related structures.		A better understanding of the stratigraphy, following the recognition of sedimentary structures in quartzitic rocks as way-up indicators, led to modifications of the early structural models. Bailey himself used such observations in the Loch Leven area to completely reverse the order of superposition used in his 1922 paper and revised his structural interpretation in a further major review paper (Bailey, 1934). Further developments and modifications resulted from the recognition of graded units and other internal structures in turbiditic rocks, first applied by Shackleton (1958) to the structure of the Southern Highlands and the Highland Border. The concept of ‘facing’ was introduced as a means to describe the structural ‘way-up’ of strata [[Media:P915415.png\|(P915415)]]. Shackleton (1958) defined ‘facing’ geometrically as ‘the direction normal to the fold axis, along the axial plane, and towards the younger beds’. Thus a synclinal synform is described as ‘upward facing’, whereas an anticlinal (i.e. inverted) synform is ‘downward facing’. Asymmetrical and recumbent folds have a sideways component of facing which is an important descriptive parameter, and which is commonly used to infer the direction of tectonic transport. H H Read, who had commenced work in the north-east Grampians as a member of the Geological Survey, initiated research which resulted in several detailed studies of the Banff Nappe and related structures.

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	In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this ''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.		In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this ''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.
	[[File:P915450.png\|thumbnail\|P915450]]		[[File:P915450.png\|thumbnail\|Distribution of lineaments, shear zones and major brittle faults in the Grampian Highlands. P915450.]]
	The main outcrop pattern of the Dalradian as depicted in P915411 is largely governed by the major folds described above. During the later stages of orogenesis, many of these structures were further modified by block uplift and faulting, which occurred at different rates and at different times throughout the Dalradian outcrop (Harte et al., 1984; Dempster, 1985). The differential uplift resulted in an outcrop pattern that reveals wide variations in levels of exposure. Later, post-orogenic, brittle fault movements have displaced boundaries, by several kilometres in some cases (Chapter 16). Between the major boundary faults of the Great Glen and the Highland Boundary lie a whole series of parallel, NE-trending faults showing sinistral displacement. Of these, the ''Glen Markie, Ericht–Laidon, Tyndrum, Bridge of Balgie'' and ''Loch Tay faults'' have particularly significant displacements [[Media:P915450.png\|(P915450)]]. In some areas, appreciable displacements, largely of a vertical nature, also occur on NW-trending faults such as the ''Rothes'' and ''Pass of Brander faults'', some of which may reflect fundamental deep level tectonostratigraphical lineaments (Chapter 6).		The main outcrop pattern of the Dalradian as depicted in P915411 is largely governed by the major folds described above. During the later stages of orogenesis, many of these structures were further modified by block uplift and faulting, which occurred at different rates and at different times throughout the Dalradian outcrop (Harte et al., 1984; Dempster, 1985). The differential uplift resulted in an outcrop pattern that reveals wide variations in levels of exposure. Later, post-orogenic, brittle fault movements have displaced boundaries, by several kilometres in some cases (Chapter 16). Between the major boundary faults of the Great Glen and the Highland Boundary lie a whole series of parallel, NE-trending faults showing sinistral displacement. Of these, the ''Glen Markie, Ericht–Laidon, Tyndrum, Bridge of Balgie'' and ''Loch Tay faults'' have particularly significant displacements [[Media:P915450.png\|(P915450)]]. In some areas, appreciable displacements, largely of a vertical nature, also occur on NW-trending faults such as the ''Rothes'' and ''Pass of Brander faults'', some of which may reflect fundamental deep level tectonostratigraphical lineaments (Chapter 6).

Scotfot at 17:28, 27 July 2015

2015-07-27T17:28:29Z

← Older revision		Revision as of 18:28, 27 July 2015
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	== Introduction ==		== Introduction ==
	The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in P915427.		The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in [[Media:P915417.png\|P915417]] and [[Media:P915418.png\|(P915418)]]. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in [[Media:P915411.png\|(P915411)]] and the generalised overall structure in P915427.
	[[File:P915417.png\|thumbnail\|P915417]]		[[File:P915417.png\|thumbnail\|Lithostratigraphical units in the Grampian Group. P915417.]]
	[[File:P915418.png\|thumbnail\|P915418]]
			[[File:P915418.png\|thumbnail\|Composite lithostratigraphical sections (not to scale) of the Appin, Argyll and Southern Highlands groups. P915418.]]

	== Stratigraphy ==		== Stratigraphy ==

Scotfot at 14:06, 11 July 2015

2015-07-11T14:06:00Z

Scotfot at 21:39, 10 July 2015

2015-07-10T21:39:22Z

← Older revision		Revision as of 22:39, 10 July 2015
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	Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.		Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.
	[[File:P915411.png\|thumbnail\|P915411]]		[[File:P915411.png\|thumbnail\|P915411]]
	[[File:P915427.png\|thumbnail\|P915427]]		[[File:P915427.png\|600px\|thumbnail\|P915427]]
	It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.		It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.

Scotfot at 21:38, 10 July 2015

2015-07-10T21:38:18Z

← Older revision		Revision as of 22:38, 10 July 2015
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	== Introduction ==		== Introduction ==
	The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in P915417 and P915418. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in P915411 and the generalised overall structure in P915427.		The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in P915417 and P915418. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in P915411 and the generalised overall structure in P915427.
			[[File:P915417.png\|thumbnail\|P915417]]
			[[File:P915418.png\|thumbnail\|P915418]]

	== Stratigraphy ==		== Stratigraphy ==
	Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.		Much of the Grampian Highlands is underlain by a wide variety of metasedimentary and metavolcanic rocks which are now mostly assigned to the Dalradian Supergroup. However, the basal Grampian Group was previously considered to be part of an older succession which was equated with the Moine north-west of the Great Glen. Migmatites, which are spatially associated with the Grampian Group metasedimentary rocks in the northern part of the Grampian Highlands, were also correlated originally with the Moine (Hinxman and Anderson, 1915; Horne, 1923). Subsequent detailed studies of the migmatites, which referred to them as the Central Highland Division, retained their correlation with the Moine. However, this correlation has been questioned and their stratigraphical position is not fully resolved, as the following summary of the history of stratigraphical studies will show.
			[[File:P915411.png\|thumbnail\|P915411]]
			[[File:P915427.png\|thumbnail\|P915427]]
	It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.		It was in 1891 that Sir Archibald Geikie first introduced the name ‘Dalradian’ for the varied group of metamorphic rocks which lies to the east of the Great Glen and which was thought to be younger than the Lewisian Gneiss of the North-west Highlands. The 1892 and 1910 editions of Bartholomew’s 10-miles-to-one-inch Geological Map of Scotland, compiled under Geikie’s direction, extended the name ‘Dalradian’ to include all the metamorphic strata east of the Moine Thrust. However, Geikie made it clear in his explanatory notes to the map that the ‘Moine Schists’ of the Northern Highlands were different in character from the ‘Dalradian’ rocks south-east of the Great Glen. As research proceeded, quartzofeldspathic rocks of ‘Moine Schist’ facies were mapped and described south-east of the Great Glen where they were variously referred to as, from north-east to south-west, ‘Granulitic Schists of the Central Highlands’ (Hinxman and Anderson, 1915), ‘Struan Flags’ (Barrow, 1904) and ‘Eilde Flags’ (Bailey, 1910). This left the Dalradian ''sensu stricto ''as an assemblage of rocks lying mainly in the south-western and'' ''south-eastern parts of the Grampian Highlands, and characterised by the presence of black schists, quartzites and limestones with, in its upper part, metagreywackes.

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	== Structure and metamorphism ==		== Structure and metamorphism ==
	Current structural interpretations of the Grampian Caledonides are still based upon those proposed by E B Bailey, which drew on the results of the primary mapping by the Geological Survey. In a series of papers, from 1910 to 1938, Bailey demonstrated that the rocks of the South-west and Southern Highlands are disposed in large recumbent folds. The lower limbs of many of these folds are partly replaced by low-angled, extensional faults, termed ‘slides’, with postulated movements of several kilometres. In 1922 Bailey produced a comprehensive synthesis in which major slides were perceived as fundamental tectonic dislocations separating nappe complexes, each complex having its own stratigraphical succession and structural style. Initially three such nappe complexes were recognised and named, in ascending structural order, the ''Ballappel Foundation'' (from the type areas of Ballachulish, Appin and Loch Eilde), the ''Iltay Nappe'' (from Islay and Loch Tay), and the ''Loch Awe Nappe'', but these were subsequently reduced to two when Bailey (''in ''Allison, 1941) accepted the stratigraphical correlations of other investigators which removed the need to invoke a separate Loch Awe Nappe.		Current structural interpretations of the Grampian Caledonides are still based upon those proposed by E B Bailey, which drew on the results of the primary mapping by the Geological Survey. In a series of papers, from 1910 to 1938, Bailey demonstrated that the rocks of the South-west and Southern Highlands are disposed in large recumbent folds. The lower limbs of many of these folds are partly replaced by low-angled, extensional faults, termed ‘slides’, with postulated movements of several kilometres. In 1922 Bailey produced a comprehensive synthesis in which major slides were perceived as fundamental tectonic dislocations separating nappe complexes, each complex having its own stratigraphical succession and structural style. Initially three such nappe complexes were recognised and named, in ascending structural order, the ''Ballappel Foundation'' (from the type areas of Ballachulish, Appin and Loch Eilde), the ''Iltay Nappe'' (from Islay and Loch Tay), and the ''Loch Awe Nappe'', but these were subsequently reduced to two when Bailey (''in ''Allison, 1941) accepted the stratigraphical correlations of other investigators which removed the need to invoke a separate Loch Awe Nappe.
			[[File:P915415.png\|thumbnail\|P915415]]
	A better understanding of the stratigraphy, following the recognition of sedimentary structures in quartzitic rocks as way-up indicators, led to modifications of the early structural models. Bailey himself used such observations in the Loch Leven area to completely reverse the order of superposition used in his 1922 paper and revised his structural interpretation in a further major review paper (Bailey, 1934). Further developments and modifications resulted from the recognition of graded units and other internal structures in turbiditic rocks, first applied by Shackleton (1958) to the structure of the Southern Highlands and the Highland Border. The concept of ‘facing’ was introduced as a means to describe the structural ‘way-up’ of strata (P915415). Shackleton (1958) defined ‘facing’ geometrically as ‘the direction normal to the fold axis, along the axial plane, and towards the younger beds’. Thus a synclinal synform is described as ‘upward facing’, whereas an anticlinal (i.e. inverted) synform is ‘downward facing’. Asymmetrical and recumbent folds have a sideways component of facing which is an important descriptive parameter, and which is commonly used to infer the direction of tectonic transport. H H Read, who had commenced work in the north-east Grampians as a member of the Geological Survey, initiated research which resulted in several detailed studies of the Banff Nappe and related structures.		A better understanding of the stratigraphy, following the recognition of sedimentary structures in quartzitic rocks as way-up indicators, led to modifications of the early structural models. Bailey himself used such observations in the Loch Leven area to completely reverse the order of superposition used in his 1922 paper and revised his structural interpretation in a further major review paper (Bailey, 1934). Further developments and modifications resulted from the recognition of graded units and other internal structures in turbiditic rocks, first applied by Shackleton (1958) to the structure of the Southern Highlands and the Highland Border. The concept of ‘facing’ was introduced as a means to describe the structural ‘way-up’ of strata (P915415). Shackleton (1958) defined ‘facing’ geometrically as ‘the direction normal to the fold axis, along the axial plane, and towards the younger beds’. Thus a synclinal synform is described as ‘upward facing’, whereas an anticlinal (i.e. inverted) synform is ‘downward facing’. Asymmetrical and recumbent folds have a sideways component of facing which is an important descriptive parameter, and which is commonly used to infer the direction of tectonic transport. H H Read, who had commenced work in the north-east Grampians as a member of the Geological Survey, initiated research which resulted in several detailed studies of the Banff Nappe and related structures.

Line 47:		Line 50:

	In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this		In the north-east Grampians, recumbent folds which may be correlated with those of the Tay Nappe have been identified in sections around Collieston on the east coast. However, the area is dominated by broad NNE-trending late folds, principally the ''Turriff Syncline'' and ''Buchan Anticline''. Within these structures the upper parts of the Dalradian succession occur in right-way-up sequences. Early interpretations classed this succession as a separate ‘Banff division’ in an allochthonous ‘Banff Nappe’, which was separated by a slide from an underlying Dalradian sequence continuous with that of the Central Highlands (Read, 1955; Read and Farquhar, 1956). Although other authors have also suggested that this area is allochthonous (Sturt et al., 1977; Ramsay and Sturt, 1979), current interpretations suggest that the succession is essentially autochthonous, passing downwards from the Southern Highland Group into an Argyll Group succession which correlates with that farther to the south-west (Harris and Pitcher, 1975; Ashworth, 1975; Harte, 1979; Treagus and Roberts, 1981; Ashcroft et al., 1984). If this is so, then it is not necessary to invoke the presence of a Banff Nappe and underlying slide. However, the area is bounded to the west and south by major shear belts and it is distinguished from the remainder of the Scottish Dalradian by different stratigraphical, metamorphic, igneous and geophysical features. The western boundary of this
			[[File:P915450.png\|thumbnail\|P915450]]
	''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.		''Buchan Block ''is marked by the'' Portsoy–Duchray Hill Lineament'', a major tectonic'' ''and stratigraphical boundary which can be traced from the north coast to the Glen Shee area (Fettes et al., 1986). To the west of this lineament Appin and Argyll group rocks are involved in a series of NW-facing folds which can be traced down sequence into the underlying Grampian Group.

Scotfot at 18:04, 8 July 2015

2015-07-08T18:04:37Z

← Older revision		Revision as of 19:04, 8 July 2015
Line 1:		Line 1:
	'''From: Stephenson, D, and Gould, D. 1995. [[British regional geology: Grampian Highlands\|British regional geology: Grampian Highlands.]] Fourth edition. Keyworth, Nottingham: British Geological Survey.'''		'''From: Stephenson, D, and Gould, D. 1995. [[British regional geology: Grampian Highlands\|British regional geology: Grampian Highlands.]] Fourth edition. Keyworth, Nottingham: British Geological Survey.'''

			== Introduction ==
	The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in P915417 and P915418. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in P915411 and the generalised overall structure in P915427.		The last two editions of this regional guide emphasised that, despite a long and distinguished history of research, aspects of the stratigraphy and structure of the Grampian sector of the Caledonides remained controversial. To a lesser extent that remains the position today. Continuous geological work since the publication in 1966 of the third edition of this guide has certainly led to an improved understanding of Grampian geology. The general outlines of the stratigraphy and structure are now well established. However, the precise status of a number of stratigraphical units, and the relationships between some of the major divisions still remain conjectural. Also there is no overall consensus about the detailed structural evolution of the Grampian Caledonides. We do now have a reasonably consistent correlation of local successions of metamorphic rocks throughout the Grampian Highlands, as shown in P915417 and P915418. The distribution of the major lithostratigraphical units across the Grampian Highlands is illustrated in P915411 and the generalised overall structure in P915427.