Rhins of Galloway - an excursion - Revision history

Scotfot at 20:01, 6 November 2015

2015-11-06T20:01:29Z

← Older revision		Revision as of 21:01, 6 November 2015
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	By By J A McCurry and P Stone. Excursion 15. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey.		By By J A McCurry and P Stone. Excursion 15. From: Stone, P (editor). 1996. [[Geology in south-west Scotland: an excursion guide]]. Keyworth, Nottingham: British Geological Survey.

	== Rhins of Galloway:a coastal traverse across the Northern and Central belts of the Southern Uplands ==		== Rhins of Galloway:a coastal traverse across the Northern and Central belts of the Southern Uplands ==

JenniferFindlay1 at 09:52, 13 October 2015

2015-10-13T09:52:41Z

JenniferFindlay1 at 12:41, 6 October 2015

2015-10-06T12:41:42Z

Scotfot at 17:34, 3 April 2015

2015-04-03T17:34:14Z

← Older revision		Revision as of 18:34, 3 April 2015
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	[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]		[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]
	Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.		Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.
	[[File:P008478.jpg\|~~right~~\|thumbnail\|Corsewall Point, Well Isle. Corsewall Conglomerate. A very coarse, boulder conglomerate of Ordovician age.]]		[[File:P008478.jpg\|left\|thumbnail\|Corsewall Point, Well Isle. Corsewall Conglomerate. A very coarse, boulder conglomerate of Ordovician age. P008478]]

	The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.		The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.

Scotfot at 17:33, 3 April 2015

2015-04-03T17:33:27Z

← Older revision		Revision as of 18:33, 3 April 2015
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	[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]		[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]
	Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.		Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.
	[[File:P008478.jpg\|thumbnail\|Corsewall Point, Well Isle. Corsewall Conglomerate. A very coarse, boulder conglomerate of Ordovician age.]]		[[File:P008478.jpg\|right\|thumbnail\|Corsewall Point, Well Isle. Corsewall Conglomerate. A very coarse, boulder conglomerate of Ordovician age.]]

	The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.		The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.

Scotfot: /* 3 Corsewall Point: Corsewall Conglomerate */

2015-04-03T16:30:37Z

3 Corsewall Point: Corsewall Conglomerate

← Older revision		Revision as of 17:30, 3 April 2015
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	[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]		[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]
	Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.		Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.
			[[File:P008478.jpg\|thumbnail\|Corsewall Point, Well Isle. Corsewall Conglomerate. A very coarse, boulder conglomerate of Ordovician age.]]

	The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.		The conglomerates are variably clast and matrix supported and consist of well-rounded pebbles and boulders up to 1.5 m in diameter set in a sandy matrix (3a''' '''and 3b). Granites and acid volcanic clasts predominate, but spilites, gabbros, greywackes and cherts are also found. Although mostly disorganised, the conglomerates display increased organisation eastwards across the three promontories. Organisation is shown by the alignment of the long axes of clasts parallel to bedding and, in places, by a crude lamination in the matrix. Both normal and reverse grading are present, but rare. Bedding is lenticular and channelised, in places clearly eroding the underlying unit (3c). The massive sandstone units are coarse grained and frequently contain outsize extrabasinal clasts. Rare sole markings indicate palaeoflow from the NW. Further east the boulder conglomerates are less common so that massive and graded sandstone units predominate. At Ochley Point (NW 986 728), about 300 m east of the parking area, fine-grained sandstone, laminated silt-stone and mudstone form interbedded units up to 1.5 m thick in an overall fining-and thinning-up sequence (3d). This facies assemblage represents an interchannel environment on a submarine fan.

Scotfot at 16:25, 3 April 2015

2015-04-03T16:25:37Z

← Older revision		Revision as of 17:25, 3 April 2015
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	=== Main points of interest ===		=== Main points of interest ===
	[[File:RhinsOfGallowayExcursionMap.jpg\|~~300px~~\|thumbnail\|Locality map and outline geology for the Rhins of Galloway.]]		[[File:RhinsOfGallowayExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Rhins of Galloway.]]
	Ordovician and Silurian structure; turbidite sedimentology (conglomerate, greywacke and shale) and stratigraphy; Caledonian folding and thrusting.		Ordovician and Silurian structure; turbidite sedimentology (conglomerate, greywacke and shale) and stratigraphy; Caledonian folding and thrusting.

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	=== Introduction ===		=== Introduction ===
	[[File:RhinsOfGallowayLowerPalaeozoicStratigraphy.jpg\|thumbnail\|Summary of Lower Palaeozoic stratigraphy on the Rhins of Galloway.]]		[[File:RhinsOfGallowayLowerPalaeozoicStratigraphy.jpg\|400px\|thumbnail\|Summary of Lower Palaeozoic stratigraphy on the Rhins of Galloway.]]
	The coast sections of the 45 km-long Rhins of Galloway peninsula provide an unsurpassed traverse through the Lower Palaeozoic outcrop of south-west Scotland. The sections chosen (Figure 45) build up a complete cross-strike traverse through the imbricate thrust sheet of late Ordovician and early Silurian turbidite strata. Biostratigraphical ages quoted are based largely on recent determinations by A W A Rushton and S P Tunnicliff summarised in Stone (1995). The summary of tectonostratigraphy given in Figure 46 encapsulates the stratigraphical paradox of the Southern Uplands: within each fault-bounded tract the exposed strata become younger towards the NW, though the tracts themselves become sequentially younger towards the SE. The strike faults separating the tracts are therefore thrust faults which originally propagated mostly towards the SE, carrying older beds over younger. Each thrust slice steepened upwards before its sole thrust stuck and was replaced at a lower level by a new thrust. In some interpretations one of the faults is given special importance as a possible terrane boundary along which a large displacement has occurred. This structure, the Orlock Bridge Fault, is examined in Excursion 17. In the Rhins of Galloway traverse described here Localities 1-5 are within the Ordovician Northern Belt of the Southern Uplands and Localities 6-10 are in the Silurian Central Belt to the south.		The coast sections of the 45 km-long Rhins of Galloway peninsula provide an unsurpassed traverse through the Lower Palaeozoic outcrop of south-west Scotland. The sections chosen (Figure 45) build up a complete cross-strike traverse through the imbricate thrust sheet of late Ordovician and early Silurian turbidite strata. Biostratigraphical ages quoted are based largely on recent determinations by A W A Rushton and S P Tunnicliff summarised in Stone (1995). The summary of tectonostratigraphy given in Figure 46 encapsulates the stratigraphical paradox of the Southern Uplands: within each fault-bounded tract the exposed strata become younger towards the NW, though the tracts themselves become sequentially younger towards the SE. The strike faults separating the tracts are therefore thrust faults which originally propagated mostly towards the SE, carrying older beds over younger. Each thrust slice steepened upwards before its sole thrust stuck and was replaced at a lower level by a new thrust. In some interpretations one of the faults is given special importance as a possible terrane boundary along which a large displacement has occurred. This structure, the Orlock Bridge Fault, is examined in Excursion 17. In the Rhins of Galloway traverse described here Localities 1-5 are within the Ordovician Northern Belt of the Southern Uplands and Localities 6-10 are in the Silurian Central Belt to the south.

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	===Excursion ===		===Excursion ===
	[[File:RhinsOfGallowayFinnartsBayExcursionMap.jpg\|~~500px~~\|thumbnail\|Locality map and outline geology for the Finnarts Bay area (Locality l).]]		[[File:RhinsOfGallowayFinnartsBayExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Finnarts Bay area (Locality l).]]

	==== 1 Finnarts Bay: Kirkcolm Formation ====		==== 1 Finnarts Bay: Kirkcolm Formation ====
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	==== 3 Corsewall Point: Corsewall Conglomerate ====		==== 3 Corsewall Point: Corsewall Conglomerate ====
			[[File:RhinsOfGallowayCorsewallPointExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Corsewall Poinr area (Locality 3).]]
	Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.		Return to the parking area in Lady Bay and retrace the route to the KirkcolmCorsewall Point road. Turn right and continue towards the lighthouse. Just over 1 km NW from the Lady Bay road junction be sure to take the right fork; thereafter the route is fairly obvious, though occasionally gated. At Corsewall Point park on the right side of the road by the wildlife information board (NW 982 727). From there walk NW on to the fault-bounded promontory (3a on Figure 48). On this and the two promontories to the east (3b and 3c) the sedimentary features of the conglomeratic member of the Corsewall Formation (late Llandeilo—early Caradoc) can be examined. This site has been mapped and logged in detail by Holroyd (1978) who interprets its rocks as an inner fan channel sequence deposited at the base of a deep-sea slope. The steeply SE-dipping beds are slightly overturned and young north. The sequence consists of extrabasinal conglomerates interbedded with coarse, massive sandstone units. Individual units are up to 4 m thick. Tertiary igneous activity is evidenced by thin cross-cutting dolerite dykes and, offshore to the north, by the microgranitic plug of Ailsa Craig.

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	==== 4 Killantringan: Portpatrick Formation ====		==== 4 Killantringan: Portpatrick Formation ====
			[[File:RhinsOfGallowayKillantringanExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Killantringan area (Locality 4).]]
	From Corsewall Point return via minor roads to the A718 north of Kirkcolm. Drive south through the village to the Craigencross roundabout and proceed straight on along the Glenstockadale road; at the end turn left on to the A764 towards Portpatrick. After about 3 km turn right on to a single-track road signposted for Killantringan Lighthouse. This road forms part of the Southern Upland Way footpath and is marked accordingly. When the road reaches the coast cars should be parked on the right-hand side overlooking Killantringan Bay (NW 982 567). At low tide a broad sweep of sandy beach allows easy access to the cliffs; when the tide is high the sea reaches the foot of the cliffs and isolates a number of small coves. These may then be accessed via the cliff top path.		From Corsewall Point return via minor roads to the A718 north of Kirkcolm. Drive south through the village to the Craigencross roundabout and proceed straight on along the Glenstockadale road; at the end turn left on to the A764 towards Portpatrick. After about 3 km turn right on to a single-track road signposted for Killantringan Lighthouse. This road forms part of the Southern Upland Way footpath and is marked accordingly. When the road reaches the coast cars should be parked on the right-hand side overlooking Killantringan Bay (NW 982 567). At low tide a broad sweep of sandy beach allows easy access to the cliffs; when the tide is high the sea reaches the foot of the cliffs and isolates a number of small coves. These may then be accessed via the cliff top path.

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	==== 7. Drumbreddan Bay: Gala and Moffat Shale groups ====		==== 7. Drumbreddan Bay: Gala and Moffat Shale groups ====
			[[File:RhinsOfGallowayDrumbreddanBayExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geo logy for the Drumbreddan Bay area (Locality 7) .]]
	Drive back to Clachanmore crossroads, turn right and proceed SE for 1.5 km to a prominent left-hand bend. Turn right at the bend and continue first south and then SW for 2 km to Drumbreddan Farm where permission to park and to visit Drumbreddan Bay should be obtained. Walk west through the farm for 150 m to the track which leads past the cattle sheds (083 439). Follow this track SW for 600 m to the coast.		Drive back to Clachanmore crossroads, turn right and proceed SE for 1.5 km to a prominent left-hand bend. Turn right at the bend and continue first south and then SW for 2 km to Drumbreddan Farm where permission to park and to visit Drumbreddan Bay should be obtained. Walk west through the farm for 150 m to the track which leads past the cattle sheds (083 439). Follow this track SW for 600 m to the coast.

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	==== 9 Clanyard Bay: Gala and Moffat Shale groups ====		==== 9 Clanyard Bay: Gala and Moffat Shale groups ====
			[[File:RhinsOfGallowayClanyardBayExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the Clanyard Bay area (Locality 9).]]
	To reach the next locality, Clanyard Bay, continue SE along the B7065 for 3.5 km to an offset crossroads. Turn right and drive for 800 m to just beyond the point where the road bends sharply south. Branching off to the right is the track to Low Clanyard Farm (NX 107 376). Park carefully at the road adjacent to the track, or drive to the farm where permission should be obtained to visit Clanyard Bay. This locality provides evidence for the reversed sense of D1 thrusting and allows a comparison with the Drumbreddan Bay Imbricate Zone (Locality 7).		To reach the next locality, Clanyard Bay, continue SE along the B7065 for 3.5 km to an offset crossroads. Turn right and drive for 800 m to just beyond the point where the road bends sharply south. Branching off to the right is the track to Low Clanyard Farm (NX 107 376). Park carefully at the road adjacent to the track, or drive to the farm where permission should be obtained to visit Clanyard Bay. This locality provides evidence for the reversed sense of D1 thrusting and allows a comparison with the Drumbreddan Bay Imbricate Zone (Locality 7).

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	==== 10 West Tarbet: Hawick Group ====		==== 10 West Tarbet: Hawick Group ====
			[[File:RhinsOfGallowayWestTarbetExcursionMap.jpg\|400px\|thumbnail\|Locality map and outline geology for the West Tarbet area (Locality 10).]]
	From Low Clanyard continue south and then east on the minor road to join the B7041 at Kirkmaiden. Drive south on the B7041 for 3 km and take the left-hand fork for the Mull of Galloway. On reaching the narrow isthmus at West Tarbet (Figure 52) turn right and park at the side of the road next to the track (142 309). This locality must be visited within three hours either side of low tide.		From Low Clanyard continue south and then east on the minor road to join the B7041 at Kirkmaiden. Drive south on the B7041 for 3 km and take the left-hand fork for the Mull of Galloway. On reaching the narrow isthmus at West Tarbet (Figure 52) turn right and park at the side of the road next to the track (142 309). This locality must be visited within three hours either side of low tide.

Scotfot at 16:19, 3 April 2015

2015-04-03T16:19:03Z

← Older revision		Revision as of 17:19, 3 April 2015
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	=== Main points of interest ===		=== Main points of interest ===
			[[File:RhinsOfGallowayExcursionMap.jpg\|300px\|thumbnail\|Locality map and outline geology for the Rhins of Galloway.]]
	Ordovician and Silurian structure; turbidite sedimentology (conglomerate, greywacke and shale) and stratigraphy; Caledonian folding and thrusting.		Ordovician and Silurian structure; turbidite sedimentology (conglomerate, greywacke and shale) and stratigraphy; Caledonian folding and thrusting.

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	=== Introduction ===		=== Introduction ===
			[[File:RhinsOfGallowayLowerPalaeozoicStratigraphy.jpg\|thumbnail\|Summary of Lower Palaeozoic stratigraphy on the Rhins of Galloway.]]
	The coast sections of the 45 km-long Rhins of Galloway peninsula provide an unsurpassed traverse through the Lower Palaeozoic outcrop of south-west Scotland. The sections chosen (Figure 45) build up a complete cross-strike traverse through the imbricate thrust sheet of late Ordovician and early Silurian turbidite strata. Biostratigraphical ages quoted are based largely on recent determinations by A W A Rushton and S P Tunnicliff summarised in Stone (1995). The summary of tectonostratigraphy given in Figure 46 encapsulates the stratigraphical paradox of the Southern Uplands: within each fault-bounded tract the exposed strata become younger towards the NW, though the tracts themselves become sequentially younger towards the SE. The strike faults separating the tracts are therefore thrust faults which originally propagated mostly towards the SE, carrying older beds over younger. Each thrust slice steepened upwards before its sole thrust stuck and was replaced at a lower level by a new thrust. In some interpretations one of the faults is given special importance as a possible terrane boundary along which a large displacement has occurred. This structure, the Orlock Bridge Fault, is examined in Excursion 17. In the Rhins of Galloway traverse described here Localities 1-5 are within the Ordovician Northern Belt of the Southern Uplands and Localities 6-10 are in the Silurian Central Belt to the south.		The coast sections of the 45 km-long Rhins of Galloway peninsula provide an unsurpassed traverse through the Lower Palaeozoic outcrop of south-west Scotland. The sections chosen (Figure 45) build up a complete cross-strike traverse through the imbricate thrust sheet of late Ordovician and early Silurian turbidite strata. Biostratigraphical ages quoted are based largely on recent determinations by A W A Rushton and S P Tunnicliff summarised in Stone (1995). The summary of tectonostratigraphy given in Figure 46 encapsulates the stratigraphical paradox of the Southern Uplands: within each fault-bounded tract the exposed strata become younger towards the NW, though the tracts themselves become sequentially younger towards the SE. The strike faults separating the tracts are therefore thrust faults which originally propagated mostly towards the SE, carrying older beds over younger. Each thrust slice steepened upwards before its sole thrust stuck and was replaced at a lower level by a new thrust. In some interpretations one of the faults is given special importance as a possible terrane boundary along which a large displacement has occurred. This structure, the Orlock Bridge Fault, is examined in Excursion 17. In the Rhins of Galloway traverse described here Localities 1-5 are within the Ordovician Northern Belt of the Southern Uplands and Localities 6-10 are in the Silurian Central Belt to the south.

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	===Excursion ===		===Excursion ===
			[[File:RhinsOfGallowayFinnartsBayExcursionMap.jpg\|500px\|thumbnail\|Locality map and outline geology for the Finnarts Bay area (Locality l).]]

	==== 1 Finnarts Bay: Kirkcolm Formation ====		==== 1 Finnarts Bay: Kirkcolm Formation ====

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2015-04-03T15:40:24Z

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	== Rhins of Galloway:a coastal traverse across the Northern and Central belts of the Southern Uplands ==		== Rhins of Galloway:a coastal traverse across the Northern and Central belts of the Southern Uplands ==

	''OS 1:50 000 sheets 76 Girvan and 82 Stranraer; Glen Luce surrounding area		OS 1:50 000 sheets 76 Girvan and 82 Stranraer; Glen Luce surrounding area

	BGS 1:50 000 Sheet 1 and 3 with parts of 7 and 4W The Rhins of Galloway		BGS 1:50 000 Sheet 1 and 3 with parts of 7 and 4W The Rhins of Galloway
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	The introductory section of this guide which deals with the Lower Palaeozoic regional geology is particularly relevant to this excursion. Also of great value is the BGS 1:50 000 Rhins of Galloway map, but note the alternative interpretation at Locality 9. Much of the evidence to be seen is pertinent to the debate over the origin of the Southern Uplands: forearc accretionary prism or backarc to foreland basin thrust belt. The regional palaeocurrent pattern (at least in the Ordovician) and the interdigitating siliceous and volcaniclastic turbidites at locality 4 provide evidence of a volcanic source to the south of a backarc Southern Uplands (Stone et al., 1987); the opposing younging and vergence of D1 thrusting and folding on either side of the Port Logan Fault (Localities ''7, ''8 and 9) provide evidence of obduction accretion comparable with that in the Washington—Oregon forearc (McCurry and Anderson, 1989). Descriptions for Localities 1, 2 and 5 have been prepared by P Stone, for Localities 3, 7, 9 and 10 by J McCurry, and for Localities 6 and 8 jointly.		The introductory section of this guide which deals with the Lower Palaeozoic regional geology is particularly relevant to this excursion. Also of great value is the BGS 1:50 000 Rhins of Galloway map, but note the alternative interpretation at Locality 9. Much of the evidence to be seen is pertinent to the debate over the origin of the Southern Uplands: forearc accretionary prism or backarc to foreland basin thrust belt. The regional palaeocurrent pattern (at least in the Ordovician) and the interdigitating siliceous and volcaniclastic turbidites at locality 4 provide evidence of a volcanic source to the south of a backarc Southern Uplands (Stone et al., 1987); the opposing younging and vergence of D1 thrusting and folding on either side of the Port Logan Fault (Localities ''7, ''8 and 9) provide evidence of obduction accretion comparable with that in the Washington—Oregon forearc (McCurry and Anderson, 1989). Descriptions for Localities 1, 2 and 5 have been prepared by P Stone, for Localities 3, 7, 9 and 10 by J McCurry, and for Localities 6 and 8 jointly.

			===Excursion ===

	==== 1 Finnarts Bay: Kirkcolm Formation ====		==== 1 Finnarts Bay: Kirkcolm Formation ====

Scotfot: Created page with "By By J A McCurry and P Stone. Excursion 15. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey..."

2015-04-03T15:39:40Z

Created page with "By By J A McCurry and P Stone. Excursion 15. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey..."

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← Older revision		Revision as of 13:41, 6 October 2015
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	Regain the track and continue south for a short distance and descend into the next small inlet. The most prominent feature here (f) is a 2 m-thick felsic dyke containing abundant feldspar phenocrysts. At first sight the dyke appears compound, with a discrete central zone, but examination of thin sections has proved it to be a homogeneous porphyritic microdiorite. There is no cleavage in the dyke and so, like the first example seen, it is probably post-tectonic.		Regain the track and continue south for a short distance and descend into the next small inlet. The most prominent feature here (f) is a 2 m-thick felsic dyke containing abundant feldspar phenocrysts. At first sight the dyke appears compound, with a discrete central zone, but examination of thin sections has proved it to be a homogeneous porphyritic microdiorite. There is no cleavage in the dyke and so, like the first example seen, it is probably post-tectonic.

	The less agile should retrace their route to the parking area, but the more sure-footed can scramble over the next two rocky spurs; the distance is only about 50 m but is quite arduous at anything but very low tide. The reward is a magnificent array of flute casts on the base of a greywacke bed, slightly overturned to dip steeply SE (g). The rock face must therefore be viewed looking north. The linear nested flutes indicate a current flow from top right to bottom left. If you imagine the bedding plane restored to the horizontal, an original eroding current flowing from the SE is suggested.		[[File:P008425.jpg\|300px\|thumbnail\|left\|Finnarts Bay, Loch Ryan. Flute casts on the base of a greywacke bed. A linear bottom structure produced by current flow, in this case from top right to bottom left. When bedding is restored from subvertical to horizontal the original current flowed from the south. P008425]]The less agile should retrace their route to the parking area, but the more sure-footed can scramble over the next two rocky spurs; the distance is only about 50 m but is quite arduous at anything but very low tide. The reward is a magnificent array of flute casts on the base of a greywacke bed, slightly overturned to dip steeply SE (g). The rock face must therefore be viewed looking north. The linear nested flutes indicate a current flow from top right to bottom left. If you imagine the bedding plane restored to the horizontal, an original eroding current flowing from the SE is suggested.

	Return to the raised beach at Finnarts Bay. If several vehicles are being used the party should walk back to the A77 and '''proceed with care '''(the road carries '''much heavy traffic '''to and from the Irish ferry terminals) to the entrance track for the large disused quarry (NX 053 720). One or two vehicles can be parked in the rough track entrance or on the hard shoulder area on the opposite (seaward) side of the road. The quarry itself is structurally complex and has loose, dangerous faces. It should not be entered. Fortunately the more accessible cliffs forming the roadside section running south from the quarry (Figure 47) are both secure and instructive.		Return to the raised beach at Finnarts Bay. If several vehicles are being used the party should walk back to the A77 and '''proceed with care '''(the road carries '''much heavy traffic '''to and from the Irish ferry terminals) to the entrance track for the large disused quarry (NX 053 720). One or two vehicles can be parked in the rough track entrance or on the hard shoulder area on the opposite (seaward) side of the road. The quarry itself is structurally complex and has loose, dangerous faces. It should not be entered. Fortunately the more accessible cliffs forming the roadside section running south from the quarry (Figure 47) are both secure and instructive.
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	From Corsewall Point return via minor roads to the A718 north of Kirkcolm. Drive south through the village to the Craigencross roundabout and proceed straight on along the Glenstockadale road; at the end turn left on to the A764 towards Portpatrick. After about 3 km turn right on to a single-track road signposted for Killantringan Lighthouse. This road forms part of the Southern Upland Way footpath and is marked accordingly. When the road reaches the coast cars should be parked on the right-hand side overlooking Killantringan Bay (NW 982 567). At low tide a broad sweep of sandy beach allows easy access to the cliffs; when the tide is high the sea reaches the foot of the cliffs and isolates a number of small coves. These may then be accessed via the cliff top path.		From Corsewall Point return via minor roads to the A718 north of Kirkcolm. Drive south through the village to the Craigencross roundabout and proceed straight on along the Glenstockadale road; at the end turn left on to the A764 towards Portpatrick. After about 3 km turn right on to a single-track road signposted for Killantringan Lighthouse. This road forms part of the Southern Upland Way footpath and is marked accordingly. When the road reaches the coast cars should be parked on the right-hand side overlooking Killantringan Bay (NW 982 567). At low tide a broad sweep of sandy beach allows easy access to the cliffs; when the tide is high the sea reaches the foot of the cliffs and isolates a number of small coves. These may then be accessed via the cliff top path.

	Walk north on to the sea cliffs, either at beach level or by way of the cliff path, where thinly bedded greywackes and silt-stones of the Portpatrick Formation are extensively exposed (4a in Figure 49). Sporadic thicker greywacke beds are also present and isoclinal fold structures can be picked out in places by careful examination. However, the probability of folding is most readily deduced from the sedimentary younging indicators, mostly grading, which show local reversals. Despite these, the dominant younging direction is to the north. Structural complexity is illustrated at one place (4b) where a synclinal hinge is exposed in a section which the sedimentary younging indicators show is broadly anticlinal. A strong slaty cleavage dips moderately to the SE, compatible with the bedding attitude in an axial-planar relationship. A fragmentary graptolite fauna recovered from this vicinity indicates a ''linearis ''Biozone age (Figure 46).		[[File:P008516.jpg\|300px\|thumbnail\|left\|Killantringan Bay. Synclinal fold hinge in greywackes of the Portpatrick Formation, Ordovician. P008516]]Walk north on to the sea cliffs, either at beach level or by way of the cliff path, where thinly bedded greywackes and silt-stones of the Portpatrick Formation are extensively exposed (4a in Figure 49). Sporadic thicker greywacke beds are also present and isoclinal fold structures can be picked out in places by careful examination. However, the probability of folding is most readily deduced from the sedimentary younging indicators, mostly grading, which show local reversals. Despite these, the dominant younging direction is to the north. Structural complexity is illustrated at one place (4b) where a synclinal hinge is exposed in a section which the sedimentary younging indicators show is broadly anticlinal. A strong slaty cleavage dips moderately to the SE, compatible with the bedding attitude in an axial-planar relationship. A fragmentary graptolite fauna recovered from this vicinity indicates a ''linearis ''Biozone age (Figure 46).

	Return past the parking area and move on to the rocky outcrops around high water mark to the west. A different facies of the Portpatrick Formation is exposed with thicker greywacke beds ranging up to 1 m. Cleavage is still strong but is generally confined to the finer-grained, upper part of the greywacke beds and is markedly curved, refracting through the bed as the grain size varies. Some beds preserve bottom structures on their bases (the south side of the bed so view looking north) including some large flute casts indicating current flow from the SW (4c). The greywackes are dark and immature, and on fresh surfaces it may be possible to discern with a hand lens the abundant detrital mafic minerals, dominantly pyroxene and amphibole. This composition, rich in andesitic debris, is characteristic of the Portpatrick Formation.		Return past the parking area and move on to the rocky outcrops around high water mark to the west. A different facies of the Portpatrick Formation is exposed with thicker greywacke beds ranging up to 1 m. Cleavage is still strong but is generally confined to the finer-grained, upper part of the greywacke beds and is markedly curved, refracting through the bed as the grain size varies. Some beds preserve bottom structures on their bases (the south side of the bed so view looking north) including some large flute casts indicating current flow from the SW (4c). The greywackes are dark and immature, and on fresh surfaces it may be possible to discern with a hand lens the abundant detrital mafic minerals, dominantly pyroxene and amphibole. This composition, rich in andesitic debris, is characteristic of the Portpatrick Formation.
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	==== 5 Portpatrick: Portpatrick Formation, folding and fault zone ====		==== 5 Portpatrick: Portpatrick Formation, folding and fault zone ====
	Drive back along the lighthouse road to the A764 and turn right for Portpatrick. After about 4km turn right again into the village. Part of the described route requires a lowish tide and it may be necessary to arrange the sequence of localities to accommodate this. If time allows, a walk south along the cliff path to Dunskey Castle (NX 004 534) is a worthwhile diversion from the geology. The path is reached via steep steps just beyond the SE margin of the main car park on the south side of the harbour. The castle is about 500 in from the top of the steps. It occupies an impressive position on the cliff edge and is built mainly of local greywacke, with dressed corner stones and lintels of Permian red sandstone most probably brought in from Dumfries. It was built around 1510 by Adair of Kilhilt on the site of an earlier stronghold but was in a ruinous condition by 1684 and has remained so.		Drive back along the lighthouse road to the A764 and turn right for Portpatrick. After about 4km turn right again into the village. Part of the described route requires a lowish tide and it may be necessary to arrange the sequence of localities to accommodate this. If time allows, a walk south along the cliff path to Dunskey Castle (NX 004 534) is a worthwhile diversion from the[[File:P001122.jpg\|300px\|thumbnail\|right\|Morroch Bay, Wigtownshire viewed from the north-west. The bay and the smaller Port of Spittal Bay beyond are eroded along the outcrop of shale sequences which alternate with Portpatrick Formation (Ordovician) greywackes. The rocks are all steeply inclined ranging from vertical in the foreground to overturned towards Port of Spittal Bay. The bay has a low raised beach and old cliff line. P001122]]geology. The path is reached via steep steps just beyond the SE margin of the main car park on the south side of the harbour. The castle is about 500 in from the top of the steps. It occupies an impressive position on the cliff edge and is built mainly of local greywacke, with dressed corner stones and lintels of Permian red sandstone most probably brought in from Dumfries. It was built around 1510 by Adair of Kilhilt on the site of an earlier stronghold but was in a ruinous condition by 1684 and has remained so.

	Folded Portpatrick Formation greywackes are well exposed in and around Portpatrick Harbour and exposure is more or less complete southwards to Morroch Bay. At Morroch Bay the basal beds of the Portpatrick Formation conformably overlie the Moffat Shale Group and are interbedded with shales containing ''clingani ''Biozone graprolites (Figure 46). Full details are given in Excursion 18.		Folded Portpatrick Formation greywackes are well exposed in and around Portpatrick Harbour and exposure is more or less complete southwards to Morroch Bay. At Morroch Bay the basal beds of the Portpatrick Formation conformably overlie the Moffat Shale Group and are interbedded with shales containing ''clingani ''Biozone graprolites (Figure 46). Full details are given in Excursion 18.

	A spectacular exposure of the greywackes is provided by an old quarry, 250 m SE from the southern harbour car park. The quarry is paved and landscaped. The main face, viewed looking east, exposes a magnificent F1 monoclinal fold. Remember, as you view the fold, that north is to your left. On the left the beds are vertical at ground level but higher in the cliff face assume a more gentle northward dip. The axial plane of the monocline dips moderately south (towards your right) and so the upper, gently dipping limb of the fold descends to ground level in that direction. A fine selection of turbidite features includes gravelly bed bases, shale rip-up clasts and cross-laminated bed tops. These make it easy to confirm the younging directions. In the north of the quarry the bedding at ground level is vertical and youngs north; in the south of the quarry it is the right way up and dips gently northwards.		[[File:P008429.jpg\|300px\|thumbnail\|left\|Portpatrick Quarry. Monocline in greywackes. The attitude of the Portpatrick Formation greywackes changes from sub-horizontal at the top of the cliff to vertical at the base. P008429]]A spectacular exposure of the greywackes is provided by an old quarry, 250 m SE from the southern harbour car park. The quarry is paved and landscaped. The main face, viewed looking east, exposes a magnificent F1 monoclinal fold. Remember, as you view the fold, that north is to your left. On the left the beds are vertical at ground level but higher in the cliff face assume a more gentle northward dip. The axial plane of the monocline dips moderately south (towards your right) and so the upper, gently dipping limb of the fold descends to ground level in that direction. A fine selection of turbidite features includes gravelly bed bases, shale rip-up clasts and cross-laminated bed tops. These make it easy to confirm the younging directions. In the north of the quarry the bedding at ground level is vertical and youngs north; in the south of the quarry it is the right way up and dips gently northwards.

	Continue NW across the intertidal rocks towards Portpatrick Harbour. Bedding dip is variable and by applying younging criteria it can be seen that the beds are right way up and are folded about several open F1 synclines and anticlines. The hinges are mostly replaced by faults or shear zones but one good example of an open syncline is preserved slightly farther north in the back wall of the outer harbour and, at lowish tide, is accessible from the beach. The hinge plunges about 15° NE. A strong slaty cleavage is developed throughout this section, striking NE, and is either vertical or dips steeply SE.		Continue NW across the intertidal rocks towards Portpatrick Harbour. Bedding dip is variable and by applying younging criteria it can be seen that the beds are right way up and are folded about several open F1 synclines and anticlines. The hinges are mostly replaced by faults or shear zones but one good example of an open syncline is preserved slightly farther north in the back wall of the outer harbour and, at lowish tide, is accessible from the beach. The hinge plunges about 15° NE. A strong slaty cleavage is developed throughout this section, striking NE, and is either vertical or dips steeply SE.