Coldingham - an excursion - Revision history

Scotfot at 21:48, 6 November 2015

2015-11-06T21:48:58Z

← Older revision		Revision as of 22:48, 6 November 2015
Line 1:		Line 1:

	'''By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [http://www.edinburghgeolsoc.org/ Edinburgh Geological Society]), 1972.'''		'''By D.C.Greig. From [[Scottish Borders geology: an excursion guide]] edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [http://www.edinburghgeolsoc.org/ Edinburgh Geological Society]), 1972.'''

	O.S. 1:50 000 Sheet 67 Duns and Dunbar		O.S. 1:50 000 Sheet 67 Duns and Dunbar

JenniferFindlay1 at 14:27, 19 July 2015

2015-07-19T14:27:15Z

← Older revision		Revision as of 15:27, 19 July 2015
Line 9:		Line 9:

	===Introduction===		===Introduction===
	The Silurian rocks which crop out around Coldingham differ in character from those seen to north-west, as at Fast Castle, and to south-east, near Eyemouth (Greig 1988)<ref>Greig, D.C. 1988. Geology of the Eyemouth district. Mem. Brit. Geol. Surv. Hutton, J. 1795. Theory of the Earth. William Creech, Edinburgh.</ref>. The main object of this excursion is the examination of these rocks on the shore. Fluvioglacial deposits and drainage developments in the area are also worth examining.		The Silurian rocks which crop out around Coldingham differ in character from those seen to north-west, as at Fast Castle, and to south-east, near Eyemouth (Greig 1988)<ref name="Greig88">Greig, D.C. 1988. Geology of the Eyemouth district. Mem. Brit. Geol. Surv. Hutton, J. 1795. Theory of the Earth. William Creech, Edinburgh.</ref>. The main object of this excursion is the examination of these rocks on the shore. Fluvioglacial deposits and drainage developments in the area are also worth examining.

	The village of Coldingham, of ecclesiastical importance in mediaeval times, lies about 2 km south-west of St Abbs on the A1107 Cockburnspath to Eyemouth road. From the centre of the village (NT 902 660) the road to the Sands should be taken, at first to the left, and after about 500 m turning off to the right. Cars may be parked in the centre of the village or close to the Sands, about 1 km beyond. Prior enquiry should be made locally regarding the parking of coaches.		The village of Coldingham, of ecclesiastical importance in mediaeval times, lies about 2 km south-west of St Abbs on the A1107 Cockburnspath to Eyemouth road. From the centre of the village (NT 902 660) the road to the Sands should be taken, at first to the left, and after about 500 m turning off to the right. Cars may be parked in the centre of the village or close to the Sands, about 1 km beyond. Prior enquiry should be made locally regarding the parking of coaches.
Line 31:		Line 31:
	Towards the south end of the Sands the greywackes are less reddened and their stratification is evident. In the extreme corner of the Sands, west of a N-S fault which passes 15 m west of a short set of steps, they are cut by two sill-like microdioritic intrusions separated by 1.5 m of greywacke. The more northerly is 5 m thick, includes many irregular xenoliths of contorted sediment, and locally interdigitates with the greywacke; the more southerly sill is at least 3 m thick. Homeli Knoll, the conical hill above, marks the seaward limit of the fluvioglacial sands described above, and a narrow strip of blown sand is seen to north-west, along the back of the beach.		Towards the south end of the Sands the greywackes are less reddened and their stratification is evident. In the extreme corner of the Sands, west of a N-S fault which passes 15 m west of a short set of steps, they are cut by two sill-like microdioritic intrusions separated by 1.5 m of greywacke. The more northerly is 5 m thick, includes many irregular xenoliths of contorted sediment, and locally interdigitates with the greywacke; the more southerly sill is at least 3 m thick. Homeli Knoll, the conical hill above, marks the seaward limit of the fluvioglacial sands described above, and a narrow strip of blown sand is seen to north-west, along the back of the beach.

	The greywackes at the southern end of the Sands are cut by several N-S and E-W faults. The thin beds dip generally at 50o to north or NNW, but many small folds are clearly visible, plunging at various angles, locally steeply, and in several different directions. No clear pattern is immediately apparent. Eastward, on Milldown Point, the greywackes are intruded by a very pale yellow close-jointed felsite, approximately concordant and extensively altered to carbonate and sericite. The intrusion can be followed south-westward from Milldown Point for 150 m, to the left bank of the Milldown Burn near its mouth, its width varying from 6 m on the point to 2 m beside the burn and up to 17 m nearby. The margins of this intrusion follow the intricacies of the bedding, either because the two rock-types have been folded together or because the magma has been preferentially intruded along already folded bedding-planes. Shiells and Dearman (1963<ref>Shiells, K.A.G. and Dearman, W.R. 1963. Tectonics of the Coldingham Bay area of Berwickshire, in the Southern Uplands of Scotland. Proceedings of the Yorkshire Geological Society, 34, 209-224 </ref>, 1966<ref>Shiells, K.A.G. and Dearman, W.R. 1966. On the possible occurrence of Dalradian rocks in the Southern Uplands of Scotland. Scottish Journal of Geology, 2, 231-242.</ref>) postulated that the Coldingham Beds, and the intrusion, might be pre-Silurian but subsequent structural and metamorphic studies (Oliver et al. 1984)<ref>Oliver, G.J.H., Smellie, J.L., Thomas, L.J., Casey, D.M., Kemp, A.E.S., Evans, L.J., Baldwin, J.R. and Hepworth, B.C. 1984. Early Palaeozoic metamorphic history of the Midland Valley, Southern Uplands, Longford-Down massif, and the Lake District, British Isles. Trans. R. Soc. Edinb: Earth Sci. 75, 245-258.</ref> suggest that the greywackes are of late Silurian age and that large-scale slumping caused the complex folding prior to complete lithification. Radiometric dating shows the Milldown Point intrusion was emplaced at or before 398+13Ma.(Greig 1988, p.30). It is thus essentially coeval with the various "Caledonian" intrusive swarms of wide occurrence in the south of Scotland. Particularly striking examples of the complex folding of the greywackes are to be seen immediately east of the Milldown Point intrusion.		The greywackes at the southern end of the Sands are cut by several N-S and E-W faults. The thin beds dip generally at 50o to north or NNW, but many small folds are clearly visible, plunging at various angles, locally steeply, and in several different directions. No clear pattern is immediately apparent. Eastward, on Milldown Point, the greywackes are intruded by a very pale yellow close-jointed felsite, approximately concordant and extensively altered to carbonate and sericite. The intrusion can be followed south-westward from Milldown Point for 150 m, to the left bank of the Milldown Burn near its mouth, its width varying from 6 m on the point to 2 m beside the burn and up to 17 m nearby. The margins of this intrusion follow the intricacies of the bedding, either because the two rock-types have been folded together or because the magma has been preferentially intruded along already folded bedding-planes. Shiells and Dearman (1963<ref name="ShiellsDearman63">Shiells, K.A.G. and Dearman, W.R. 1963. Tectonics of the Coldingham Bay area of Berwickshire, in the Southern Uplands of Scotland. Proceedings of the Yorkshire Geological Society, 34, 209-224 </ref>, 1966<ref>Shiells, K.A.G. and Dearman, W.R. 1966. On the possible occurrence of Dalradian rocks in the Southern Uplands of Scotland. Scottish Journal of Geology, 2, 231-242.</ref>) postulated that the Coldingham Beds, and the intrusion, might be pre-Silurian but subsequent structural and metamorphic studies (Oliver et al. 1984)<ref>Oliver, G.J.H., Smellie, J.L., Thomas, L.J., Casey, D.M., Kemp, A.E.S., Evans, L.J., Baldwin, J.R. and Hepworth, B.C. 1984. Early Palaeozoic metamorphic history of the Midland Valley, Southern Uplands, Longford-Down massif, and the Lake District, British Isles. Trans. R. Soc. Edinb: Earth Sci. 75, 245-258.</ref> suggest that the greywackes are of late Silurian age and that large-scale slumping caused the complex folding prior to complete lithification. Radiometric dating shows the Milldown Point intrusion was emplaced at or before 398+13Ma.(Greig 1988, p.30)<ref name="Greig88" />. It is thus essentially coeval with the various "Caledonian" intrusive swarms of wide occurrence in the south of Scotland. Particularly striking examples of the complex folding of the greywackes are to be seen immediately east of the Milldown Point intrusion.

	From the mouth of Milldown Burn cross the pebble beach and follow the path up the cliff to south-east and then descend again to the shore level after rounding Yellow Craig Head. From here to Linkim Well the complexities of folding may be examined at many points; notable features include closely-spaced, flat-lying, tight similar folds and concentric folds showing extreme variation in angle of plunge. Discordance between adjacent folds and discontinuity of bedding are common, and there is a significant absence of cleavage associated with the folds. All these features support the hypothesis of soft-sediment deformation resulting from gravity-induced slump movement.		From the mouth of Milldown Burn cross the pebble beach and follow the path up the cliff to south-east and then descend again to the shore level after rounding Yellow Craig Head. From here to Linkim Well the complexities of folding may be examined at many points; notable features include closely-spaced, flat-lying, tight similar folds and concentric folds showing extreme variation in angle of plunge. Discordance between adjacent folds and discontinuity of bedding are common, and there is a significant absence of cleavage associated with the folds. All these features support the hypothesis of soft-sediment deformation resulting from gravity-induced slump movement.

	==== 4. Linkim Shore: Intrusions ====		==== 4. Linkim Shore: Intrusions ====
	[[File:P218963.jpg\|300px\|thumbnail\|left\|Linkim Shore, Yellow Craig. Looking SE. Tight folding in greywackes of 'Coldingham Beds' (Silurian). The axial plane and the bedding dip at c. 50 degrees to north-east: the fold axes plunge northwards at about 40 degrees. P218963]]Linkim Shore, which is backed by a storm-beach grading into a low raised beach, the rounded stack known as Leader Kip stands up prominently from the rocky intertidal ‘platform'. It forms part of a NE-SW trending dyke of closely jointed pale microdiorite similar to that of Milldown Point (Shiells and Dearman, 1963). The Geological Survey map groups it with the quartz-porphyries but in places it is more even-grained and albitic. The dyke's boundary with the greywackes is locally obscure but it appears to vary in width between 40 and 100 m with a 60 m wide offshoot, exposed at L.W.M. just to north.		[[File:P218963.jpg\|300px\|thumbnail\|left\|Linkim Shore, Yellow Craig. Looking SE. Tight folding in greywackes of 'Coldingham Beds' (Silurian). The axial plane and the bedding dip at c. 50 degrees to north-east: the fold axes plunge northwards at about 40 degrees. P218963]]Linkim Shore, which is backed by a storm-beach grading into a low raised beach, the rounded stack known as Leader Kip stands up prominently from the rocky intertidal ‘platform'. It forms part of a NE-SW trending dyke of closely jointed pale microdiorite similar to that of Milldown Point (Shiells and Dearman, 1963)<ref name="ShiellsDearman63" />. The Geological Survey map groups it with the quartz-porphyries but in places it is more even-grained and albitic. The dyke's boundary with the greywackes is locally obscure but it appears to vary in width between 40 and 100 m with a 60 m wide offshoot, exposed at L.W.M. just to north.

	Near the south-eastern end of Linkim Shore two sill-like intrusions less than 1 m wide cut the greywackes, which in this area are more regularly folded, with N-S trending hinges and steeply dipping limbs. The more westerly sill, which extends northwards from a wider somewhat circular outcrop, has small phenocrysts of plagioclase and mica. The second sill, 30 m to the east, is 0.6 m wide and follows bedding in the greywackes around the axis of an asymmetric anticline. This observation is more plausibly interpreted as an instance of the intrusion following folded strata, rather than subsequent folding of the intruded rock.		Near the south-eastern end of Linkim Shore two sill-like intrusions less than 1 m wide cut the greywackes, which in this area are more regularly folded, with N-S trending hinges and steeply dipping limbs. The more westerly sill, which extends northwards from a wider somewhat circular outcrop, has small phenocrysts of plagioclase and mica. The second sill, 30 m to the east, is 0.6 m wide and follows bedding in the greywackes around the axis of an asymmetric anticline. This observation is more plausibly interpreted as an instance of the intrusion following folded strata, rather than subsequent folding of the intruded rock.

JenniferFindlay1 at 14:04, 19 July 2015

2015-07-19T14:04:50Z

← Older revision		Revision as of 15:04, 19 July 2015
Line 26:		Line 26:

	==== 2. St Abbs Haven: Volcanic Vent ====		==== 2. St Abbs Haven: Volcanic Vent ====
	Follow the footpath to the beach and examine the rocks at the northern end of the Sands. In this area lies the NE-trending fault which separates the Lower Devonian volcanic vent of St Abbs from the Silurian greywackes to the south, the Coldingham Beds. The rocks of the vent are an assemblage of intrusive porphyrite and volcanic agglomerate, all fine-grained lithologies and somewhat reddened, like the greywackes, and not always readily distinguishable from them in the field. A helpful characteristic of the igneous rocks is the occurrence of phenocrysts of ferro-magnesian minerals, altered to iron oxides, visible under the hand-lens.		[[File:P000812.jpg\|300px\|thumbnail\|right\|Oblique aerial view of Coldingham Bay viewed from the east. Berwickshire. The white buildings with the red roofs are at St. Abb's Haven. Intrusive porphyrites and agglomerates. The rocks on the shore are intrusive porphyrites and unbedded agglomerates, probably within a volcanic vent, of Lower Old Red Sandstone age. Coldingham Sands, on the left, marks the local southern limit of these rocks. Silurian greywackes form the high ground on the right. P000812]]Follow the footpath to the beach and examine the rocks at the northern end of the Sands. In this area lies the NE-trending fault which separates the Lower Devonian volcanic vent of St Abbs from the Silurian greywackes to the south, the Coldingham Beds. The rocks of the vent are an assemblage of intrusive porphyrite and volcanic agglomerate, all fine-grained lithologies and somewhat reddened, like the greywackes, and not always readily distinguishable from them in the field. A helpful characteristic of the igneous rocks is the occurrence of phenocrysts of ferro-magnesian minerals, altered to iron oxides, visible under the hand-lens.

	==== 3. Milldown Point: Coldingham Beds ====		==== 3. Milldown Point: Coldingham Beds ====
Line 36:		Line 36:

	==== 4. Linkim Shore: Intrusions ====		==== 4. Linkim Shore: Intrusions ====
	Linkim Shore, which is backed by a storm-beach grading into a low raised beach, the rounded stack known as Leader Kip stands up prominently from the rocky intertidal ‘platform'. It forms part of a NE-SW trending dyke of closely jointed pale microdiorite similar to that of Milldown Point (Shiells and Dearman, 1963). The Geological Survey map groups it with the quartz-porphyries but in places it is more even-grained and albitic. The dyke's boundary with the greywackes is locally obscure but it appears to vary in width between 40 and 100 m with a 60 m wide offshoot, exposed at L.W.M. just to north.		[[File:P218963.jpg\|300px\|thumbnail\|left\|Linkim Shore, Yellow Craig. Looking SE. Tight folding in greywackes of 'Coldingham Beds' (Silurian). The axial plane and the bedding dip at c. 50 degrees to north-east: the fold axes plunge northwards at about 40 degrees. P218963]]Linkim Shore, which is backed by a storm-beach grading into a low raised beach, the rounded stack known as Leader Kip stands up prominently from the rocky intertidal ‘platform'. It forms part of a NE-SW trending dyke of closely jointed pale microdiorite similar to that of Milldown Point (Shiells and Dearman, 1963). The Geological Survey map groups it with the quartz-porphyries but in places it is more even-grained and albitic. The dyke's boundary with the greywackes is locally obscure but it appears to vary in width between 40 and 100 m with a 60 m wide offshoot, exposed at L.W.M. just to north.

	Near the south-eastern end of Linkim Shore two sill-like intrusions less than 1 m wide cut the greywackes, which in this area are more regularly folded, with N-S trending hinges and steeply dipping limbs. The more westerly sill, which extends northwards from a wider somewhat circular outcrop, has small phenocrysts of plagioclase and mica. The second sill, 30 m to the east, is 0.6 m wide and follows bedding in the greywackes around the axis of an asymmetric anticline. This observation is more plausibly interpreted as an instance of the intrusion following folded strata, rather than subsequent folding of the intruded rock.		Near the south-eastern end of Linkim Shore two sill-like intrusions less than 1 m wide cut the greywackes, which in this area are more regularly folded, with N-S trending hinges and steeply dipping limbs. The more westerly sill, which extends northwards from a wider somewhat circular outcrop, has small phenocrysts of plagioclase and mica. The second sill, 30 m to the east, is 0.6 m wide and follows bedding in the greywackes around the axis of an asymmetric anticline. This observation is more plausibly interpreted as an instance of the intrusion following folded strata, rather than subsequent folding of the intruded rock.
Line 45:		Line 45:
	==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====		==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====

	[[File:P005896.jpg\|thumb\|~~200px~~\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]		[[File:P005896.jpg\|thumb\|300px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]
	Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.		Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.

Scotfot at 20:23, 7 March 2015

2015-03-07T20:23:50Z

← Older revision		Revision as of 21:23, 7 March 2015
Line 1:		Line 1:

	'''By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [http://www.edinburghgeolsoc.org/ ~~Edonburgh~~ Geological Society]), 1972.'''		'''By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [http://www.edinburghgeolsoc.org/ Edinburgh Geological Society]), 1972.'''

	O.S. 1:50 000 Sheet 67 Duns and Dunbar		O.S. 1:50 000 Sheet 67 Duns and Dunbar

Scotfot at 20:23, 7 March 2015

2015-03-07T20:23:22Z

← Older revision		Revision as of 21:23, 7 March 2015
Line 1:		Line 1:

	'''By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press, 1972.'''		'''By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [http://www.edinburghgeolsoc.org/ Edonburgh Geological Society]), 1972.'''

	O.S. 1:50 000 Sheet 67 Duns and Dunbar		O.S. 1:50 000 Sheet 67 Duns and Dunbar

Scotfot: /* 5. Bennison's Brae: Linkim Beds */

2015-03-07T20:21:19Z

5. Bennison's Brae: Linkim Beds

← Older revision		Revision as of 21:21, 7 March 2015
Line 43:		Line 43:
	This name is given to the 30-m cliff which forms the right bank of the Fleurs-Hallydown Dean at its mouth. From the west the red colour of the rocks is very striking, and close examination shows that the burn runs very close to the boundary between the highly contorted Coldingham Beds to north-west and an apparently less deformed group of massive red greywackes and siltstones, the Linkim Beds to south-east. The name is taken from Linkim Kip and the formation lies entirely outwith Linkim Shore. Among the well-exposed rocks on the foreshore east of the mouth of the burn the precise boundary between the two formations is difficult to trace, but it may be marked by an irregular intrusion of feldspar-porphyry. The beds to the west of this intrusion, although reddened, show in places the isoclinal folding typical of the Coldingham Beds and not generally seen in the Linkim Beds. From general considerations the boundary is thought to be essentially a NE-SW fault with downthrow to NW. The Linkim Beds are characteristically red or purplish and consist of alternating bands of greywacke and siltstone, which are in general thicker than those of the Coldingham Beds but seldom exceed 0.6 m. The greywackes lack the extensive development of carbonate which distinguishes the Coldingham Beds and are, in some cases at least, rich in quartz grains. The greywackes at the foot of the Bennison's Brae cliff have a massive appearance and their structure is not readily apparent, but at localities 80 m and 120 m beyond the south-eastward bend in the cliff-line, minor folds are developed in thin strata on the shore. At the second locality two folds about 6 m apart occur in beds dipping generally to north and north-west. The more northerly is an antiform plunging at about 20° to north-east. Other examples of folds of this type and on this scale are common farther to south-east. Just north-west of the two folds the greywackes are cut by a 7.5 m-wide dyke, which can be followed north-eastwards across the shore, and south-westwards and westwards into the cliff, along the face of which it is exposed for a further 50 m to south-east. Described as an altered quartz-diorite, this dyke is among the more acid of the Lower Devonian suite and it may be continuous with a similar 20 m dyke seen north-east of Linkim Kip.		This name is given to the 30-m cliff which forms the right bank of the Fleurs-Hallydown Dean at its mouth. From the west the red colour of the rocks is very striking, and close examination shows that the burn runs very close to the boundary between the highly contorted Coldingham Beds to north-west and an apparently less deformed group of massive red greywackes and siltstones, the Linkim Beds to south-east. The name is taken from Linkim Kip and the formation lies entirely outwith Linkim Shore. Among the well-exposed rocks on the foreshore east of the mouth of the burn the precise boundary between the two formations is difficult to trace, but it may be marked by an irregular intrusion of feldspar-porphyry. The beds to the west of this intrusion, although reddened, show in places the isoclinal folding typical of the Coldingham Beds and not generally seen in the Linkim Beds. From general considerations the boundary is thought to be essentially a NE-SW fault with downthrow to NW. The Linkim Beds are characteristically red or purplish and consist of alternating bands of greywacke and siltstone, which are in general thicker than those of the Coldingham Beds but seldom exceed 0.6 m. The greywackes lack the extensive development of carbonate which distinguishes the Coldingham Beds and are, in some cases at least, rich in quartz grains. The greywackes at the foot of the Bennison's Brae cliff have a massive appearance and their structure is not readily apparent, but at localities 80 m and 120 m beyond the south-eastward bend in the cliff-line, minor folds are developed in thin strata on the shore. At the second locality two folds about 6 m apart occur in beds dipping generally to north and north-west. The more northerly is an antiform plunging at about 20° to north-east. Other examples of folds of this type and on this scale are common farther to south-east. Just north-west of the two folds the greywackes are cut by a 7.5 m-wide dyke, which can be followed north-eastwards across the shore, and south-westwards and westwards into the cliff, along the face of which it is exposed for a further 50 m to south-east. Described as an altered quartz-diorite, this dyke is among the more acid of the Lower Devonian suite and it may be continuous with a similar 20 m dyke seen north-east of Linkim Kip.

	==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====[[File:P005896.jpg\|thumb\|200px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]		==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====


			[[File:P005896.jpg\|thumb\|200px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]
	Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.		Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.

Scotfot at 20:20, 7 March 2015

2015-03-07T20:20:49Z

← Older revision		Revision as of 21:20, 7 March 2015
Line 44:		Line 44:

	==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====[[File:P005896.jpg\|thumb\|200px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]		==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====[[File:P005896.jpg\|thumb\|200px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]


	Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.		Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.

Scotfot: /* References */

2015-03-07T20:19:59Z

References

← Older revision		Revision as of 21:19, 7 March 2015
Line 59:		Line 59:
	[[Category:6. The South of Scotland]]		[[Category:6. The South of Scotland]]

	~~===References===~~

	~~<References/>~~
	~~{{EGwalks}}~~
	[[Category:6. The South of Scotland]]		[[Category:6. The South of Scotland]]

Scotfot: /* 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions */

2015-03-07T20:19:11Z

6. Linkim Kip: Linkim Beds, Porphyrite Intrusions

← Older revision		Revision as of 21:19, 7 March 2015
Line 43:		Line 43:
	This name is given to the 30-m cliff which forms the right bank of the Fleurs-Hallydown Dean at its mouth. From the west the red colour of the rocks is very striking, and close examination shows that the burn runs very close to the boundary between the highly contorted Coldingham Beds to north-west and an apparently less deformed group of massive red greywackes and siltstones, the Linkim Beds to south-east. The name is taken from Linkim Kip and the formation lies entirely outwith Linkim Shore. Among the well-exposed rocks on the foreshore east of the mouth of the burn the precise boundary between the two formations is difficult to trace, but it may be marked by an irregular intrusion of feldspar-porphyry. The beds to the west of this intrusion, although reddened, show in places the isoclinal folding typical of the Coldingham Beds and not generally seen in the Linkim Beds. From general considerations the boundary is thought to be essentially a NE-SW fault with downthrow to NW. The Linkim Beds are characteristically red or purplish and consist of alternating bands of greywacke and siltstone, which are in general thicker than those of the Coldingham Beds but seldom exceed 0.6 m. The greywackes lack the extensive development of carbonate which distinguishes the Coldingham Beds and are, in some cases at least, rich in quartz grains. The greywackes at the foot of the Bennison's Brae cliff have a massive appearance and their structure is not readily apparent, but at localities 80 m and 120 m beyond the south-eastward bend in the cliff-line, minor folds are developed in thin strata on the shore. At the second locality two folds about 6 m apart occur in beds dipping generally to north and north-west. The more northerly is an antiform plunging at about 20° to north-east. Other examples of folds of this type and on this scale are common farther to south-east. Just north-west of the two folds the greywackes are cut by a 7.5 m-wide dyke, which can be followed north-eastwards across the shore, and south-westwards and westwards into the cliff, along the face of which it is exposed for a further 50 m to south-east. Described as an altered quartz-diorite, this dyke is among the more acid of the Lower Devonian suite and it may be continuous with a similar 20 m dyke seen north-east of Linkim Kip.		This name is given to the 30-m cliff which forms the right bank of the Fleurs-Hallydown Dean at its mouth. From the west the red colour of the rocks is very striking, and close examination shows that the burn runs very close to the boundary between the highly contorted Coldingham Beds to north-west and an apparently less deformed group of massive red greywackes and siltstones, the Linkim Beds to south-east. The name is taken from Linkim Kip and the formation lies entirely outwith Linkim Shore. Among the well-exposed rocks on the foreshore east of the mouth of the burn the precise boundary between the two formations is difficult to trace, but it may be marked by an irregular intrusion of feldspar-porphyry. The beds to the west of this intrusion, although reddened, show in places the isoclinal folding typical of the Coldingham Beds and not generally seen in the Linkim Beds. From general considerations the boundary is thought to be essentially a NE-SW fault with downthrow to NW. The Linkim Beds are characteristically red or purplish and consist of alternating bands of greywacke and siltstone, which are in general thicker than those of the Coldingham Beds but seldom exceed 0.6 m. The greywackes lack the extensive development of carbonate which distinguishes the Coldingham Beds and are, in some cases at least, rich in quartz grains. The greywackes at the foot of the Bennison's Brae cliff have a massive appearance and their structure is not readily apparent, but at localities 80 m and 120 m beyond the south-eastward bend in the cliff-line, minor folds are developed in thin strata on the shore. At the second locality two folds about 6 m apart occur in beds dipping generally to north and north-west. The more northerly is an antiform plunging at about 20° to north-east. Other examples of folds of this type and on this scale are common farther to south-east. Just north-west of the two folds the greywackes are cut by a 7.5 m-wide dyke, which can be followed north-eastwards across the shore, and south-westwards and westwards into the cliff, along the face of which it is exposed for a further 50 m to south-east. Described as an altered quartz-diorite, this dyke is among the more acid of the Lower Devonian suite and it may be continuous with a similar 20 m dyke seen north-east of Linkim Kip.

	==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====		==== 6. Linkim Kip: Linkim Beds, Porphyrite Intrusions ====[[File:P005896.jpg\|thumb\|200px\|right\|Linkim Kip. Sea stack. Stack in greywackes of Linkim Beds (Silurian). The beds have a low inverted dip to north-north-west and are traversed by a drag-fold whose axial planes dip at about 50 degrees to north-north-east. This fold possibly induced by a thick dyke which forms the basal left-hand part of the stack. [http://194.66.252.158/asset-bank/action/viewAsset?id=5145 P005896]]]
	Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.		Within the shore outcrop of the Linkim Beds the stack known as Linkim Kip is the most prominent topographic feature. On its triangular western face the stratification is clearly seen, dipping to north-north-west at 30°, conspicuously modified by two closely spaced folds similar in style to those seen on the shore to west. The beds round the base of the stack yield sufficient evidence of grading and cross-lamination to show that they are inverted. Evidence of this type at other exposures indicates that, except at the south-eastern end of the outcrop, the Linkim Beds are in general inverted and that the minor folds face downwards, the beds in the cores of synforms, for example, being older than those farther out on the fold limbs. A graptolite collected near Linkim Kip, poorly preserved and doubtfully allocated to the genus ''Monograptus'', indicates a probable Silurian age for the rocks (Strachan, 1982)<ref>Strachan, I. 1982. The distribution of graptolites in south-east Scotland, with notes on the fauna of Old Cambus Quarry. Scottish Journal of Geology, 18, 157-165.</ref>. More recent work by Molyneux (1987)<ref>Moleneux, S.G. 1987. Probable early Wenlock acritarchs from the Linkim Beds of the Southern Uplands. Scottish Journal of Geology, 23, 301-313.</ref> has shown that beds at the base of the stack contain an assemblage of microscopic acritarchs comparable with that found elsewhere in the lower part of the Wenlock Series.

Scotfot at 20:15, 7 March 2015

2015-03-07T20:15:36Z

← Older revision		Revision as of 21:15, 7 March 2015
Line 31:		Line 31:
	Towards the south end of the Sands the greywackes are less reddened and their stratification is evident. In the extreme corner of the Sands, west of a N-S fault which passes 15 m west of a short set of steps, they are cut by two sill-like microdioritic intrusions separated by 1.5 m of greywacke. The more northerly is 5 m thick, includes many irregular xenoliths of contorted sediment, and locally interdigitates with the greywacke; the more southerly sill is at least 3 m thick. Homeli Knoll, the conical hill above, marks the seaward limit of the fluvioglacial sands described above, and a narrow strip of blown sand is seen to north-west, along the back of the beach.		Towards the south end of the Sands the greywackes are less reddened and their stratification is evident. In the extreme corner of the Sands, west of a N-S fault which passes 15 m west of a short set of steps, they are cut by two sill-like microdioritic intrusions separated by 1.5 m of greywacke. The more northerly is 5 m thick, includes many irregular xenoliths of contorted sediment, and locally interdigitates with the greywacke; the more southerly sill is at least 3 m thick. Homeli Knoll, the conical hill above, marks the seaward limit of the fluvioglacial sands described above, and a narrow strip of blown sand is seen to north-west, along the back of the beach.

	The greywackes at the southern end of the Sands are cut by several N-S and E-W faults. The thin beds dip generally at 50o to north or NNW, but many small folds are clearly visible, plunging at various angles, locally steeply, and in several different directions. No clear pattern is immediately apparent. Eastward, on Milldown Point, the greywackes are intruded by a very pale yellow close-jointed felsite, approximately concordant and extensively altered to carbonate and sericite. The intrusion can be followed south-westward from Milldown Point for 150 m, to the left bank of the Milldown Burn near its mouth, its width varying from 6 m on the point to 2 m beside the burn and up to 17 m nearby. The margins of this intrusion follow the intricacies of the bedding, either because the two rock-types have been folded together or because the magma has been preferentially intruded along already folded bedding-planes. Shiells and Dearman (1963<ref>Shiells, K.A.G. and Dearman, W.R. 1963. Tectonics of the Coldingham Bay area of Berwickshire, in the Southern Uplands of Scotland. Proceedings of the Yorkshire Geological Society, 34, 209-224 </ref>, 1966<ref>Shiells, K.A.G. and Dearman, W.R. 1966. On the possible occurrence of Dalradian rocks in the Southern Uplands of Scotland. Scottish Journal of Geology, 2, 231-242.</ref>) postulated that the Coldingham Beds, and the intrusion, might be pre-Silurian but subsequent structural and metamorphic studies (Oliver et al. 1984) suggest that the greywackes are of late Silurian age and that large-scale slumping caused the complex folding prior to complete lithification. Radiometric dating shows the Milldown Point intrusion was emplaced at or before 398+13Ma.(Greig 1988, p.30). It is thus essentially coeval with the various "Caledonian" intrusive swarms of wide occurrence in the south of Scotland. Particularly striking examples of the complex folding of the greywackes are to be seen immediately east of the Milldown Point intrusion.		The greywackes at the southern end of the Sands are cut by several N-S and E-W faults. The thin beds dip generally at 50o to north or NNW, but many small folds are clearly visible, plunging at various angles, locally steeply, and in several different directions. No clear pattern is immediately apparent. Eastward, on Milldown Point, the greywackes are intruded by a very pale yellow close-jointed felsite, approximately concordant and extensively altered to carbonate and sericite. The intrusion can be followed south-westward from Milldown Point for 150 m, to the left bank of the Milldown Burn near its mouth, its width varying from 6 m on the point to 2 m beside the burn and up to 17 m nearby. The margins of this intrusion follow the intricacies of the bedding, either because the two rock-types have been folded together or because the magma has been preferentially intruded along already folded bedding-planes. Shiells and Dearman (1963<ref>Shiells, K.A.G. and Dearman, W.R. 1963. Tectonics of the Coldingham Bay area of Berwickshire, in the Southern Uplands of Scotland. Proceedings of the Yorkshire Geological Society, 34, 209-224 </ref>, 1966<ref>Shiells, K.A.G. and Dearman, W.R. 1966. On the possible occurrence of Dalradian rocks in the Southern Uplands of Scotland. Scottish Journal of Geology, 2, 231-242.</ref>) postulated that the Coldingham Beds, and the intrusion, might be pre-Silurian but subsequent structural and metamorphic studies (Oliver et al. 1984)<ref>Oliver, G.J.H., Smellie, J.L., Thomas, L.J., Casey, D.M., Kemp, A.E.S., Evans, L.J., Baldwin, J.R. and Hepworth, B.C. 1984. Early Palaeozoic metamorphic history of the Midland Valley, Southern Uplands, Longford-Down massif, and the Lake District, British Isles. Trans. R. Soc. Edinb: Earth Sci. 75, 245-258.</ref> suggest that the greywackes are of late Silurian age and that large-scale slumping caused the complex folding prior to complete lithification. Radiometric dating shows the Milldown Point intrusion was emplaced at or before 398+13Ma.(Greig 1988, p.30). It is thus essentially coeval with the various "Caledonian" intrusive swarms of wide occurrence in the south of Scotland. Particularly striking examples of the complex folding of the greywackes are to be seen immediately east of the Milldown Point intrusion.

	From the mouth of Milldown Burn cross the pebble beach and follow the path up the cliff to south-east and then descend again to the shore level after rounding Yellow Craig Head. From here to Linkim Well the complexities of folding may be examined at many points; notable features include closely-spaced, flat-lying, tight similar folds and concentric folds showing extreme variation in angle of plunge. Discordance between adjacent folds and discontinuity of bedding are common, and there is a significant absence of cleavage associated with the folds. All these features support the hypothesis of soft-sediment deformation resulting from gravity-induced slump movement.		From the mouth of Milldown Burn cross the pebble beach and follow the path up the cliff to south-east and then descend again to the shore level after rounding Yellow Craig Head. From here to Linkim Well the complexities of folding may be examined at many points; notable features include closely-spaced, flat-lying, tight similar folds and concentric folds showing extreme variation in angle of plunge. Discordance between adjacent folds and discontinuity of bedding are common, and there is a significant absence of cleavage associated with the folds. All these features support the hypothesis of soft-sediment deformation resulting from gravity-induced slump movement.