Middle Old Red Sandstone of Orkney - Revision history

Dbk at 15:19, 31 January 2018

2018-01-31T15:19:57Z

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	~~'''From: Mykura, W. 1976. [[British regional geology: Orkney and Shetland\|British regional geology: Orkney and Shetland]]. Edinburgh, Her Majesty's Stationery Office.'''~~		{{OSRG}}
	__FORCETOC__		__FORCETOC__
	== Stromness Flags ==		== Stromness Flags ==

Dbk: /* References */

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References

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	This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson 1935"></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.		This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson 1935"></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.

	==~~References~~==		==Bibliography==

	[[Category:Orkney and Shetland]]		[[Category:Orkney and Shetland]]

Dbk: /* Conditions of deposition */

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Conditions of deposition

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	The Upper Eday Sandstone crops out in two areas: a northern area which comprises the outcrops in Eday and south-west Sanday, and a southern area around the south shore of Scapa Flow, which includes the outcrops on Burray, north-westem South Ronaldsay and Flotta. In the southern area the group consists of beds of soft, cross-bedded, red, pink and yellow sandstone alternating with bands of red and green ‘marl’. The latter are most common and thickest at the base of the formation. In Eday, where the group reaches a thickness of more than 300 m, it falls into two lithological divisions. The lower division consists of beds of red and yellow sandstones with scattered pebbles, which pass upwards into more massive trough-cross-bedded pebbly sandstones alternating with beds of marl. The pebbles and sedimentary structures in the latter are closely comparable to those found in the Middle Eday Sandstones. The upper division shows a reversion to finer-grained sediments and consists of bright red and purple sandstones with thin bands of suncracked sandy marl.		The Upper Eday Sandstone crops out in two areas: a northern area which comprises the outcrops in Eday and south-west Sanday, and a southern area around the south shore of Scapa Flow, which includes the outcrops on Burray, north-westem South Ronaldsay and Flotta. In the southern area the group consists of beds of soft, cross-bedded, red, pink and yellow sandstone alternating with bands of red and green ‘marl’. The latter are most common and thickest at the base of the formation. In Eday, where the group reaches a thickness of more than 300 m, it falls into two lithological divisions. The lower division consists of beds of red and yellow sandstones with scattered pebbles, which pass upwards into more massive trough-cross-bedded pebbly sandstones alternating with beds of marl. The pebbles and sedimentary structures in the latter are closely comparable to those found in the Middle Eday Sandstones. The upper division shows a reversion to finer-grained sediments and consists of bright red and purple sandstones with thin bands of suncracked sandy marl.

	=== Conditions of deposition ===		5=== Conditions of deposition ===
	No modern account of the lithology and palaeogeography of the Eday Beds has as yet been published, and the following suggestions as to the environment of deposition and direction of palaeocurrents are based on observations made by the author and Dr N. G. T. Fannin during a brief spell of field work in 1972.		No modern account of the lithology and palaeogeography of the Eday Beds has as yet been published, and the following suggestions as to the environment of deposition and direction of palaeocurrents are based on observations made by the author and Dr N. G. T. Fannin during a brief spell of field work in 1972.

	The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.		The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.

	This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson ~~1932~~"></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.		This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson 1935"></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.

	==References==		==References==

	[[Category:Orkney and Shetland]]		[[Category:Orkney and Shetland]]

Dbk: /* Conditions of deposition */

2015-11-26T14:59:46Z

Conditions of deposition

← Older revision		Revision as of 15:59, 26 November 2015
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	The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.		The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.

	This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson ~~19352~~></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.		This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970)<ref name="Fannin 1970">FANNIN, N. G. T. 1970. The sedimentary environment of the Old Red Sandstone of western Orkney. Ph.D. thesis, University of Reading (unpublished).</ref> and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935)<ref name="Wilson 1932"></ref>. Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.

			==References==

	[[Category:Orkney and Shetland]]		[[Category:Orkney and Shetland]]

Dbk at 14:58, 26 November 2015

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Dbk at 12:12, 1 September 2015

2015-09-01T12:12:58Z

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	In the past the Sandwick Fish Bed was worked in a large number of small quarries in West Mainland for paving flags and roofing slates. At present only the quarry at Quoyloo (P915581) is still active. This still yields abundant fish remains, though modern methods of quarrying are less conducive to the preservation of good specimens. The fish bed can be recognised on the quarry face by its rusty weathering. Fish remains may be evenly scattered on some bedding planes, on others they may be so abundant as to form a matted mass. On joint faces the fish can be recognised as black coal-like lenses, sometimes up to 1 cm thick. Black bituminous matter is often present along the joint planes of the fish bed, and in the more compact carbonate—rich portions of the bed a little oil is also found.		In the past the Sandwick Fish Bed was worked in a large number of small quarries in West Mainland for paving flags and roofing slates. At present only the quarry at Quoyloo (P915581) is still active. This still yields abundant fish remains, though modern methods of quarrying are less conducive to the preservation of good specimens. The fish bed can be recognised on the quarry face by its rusty weathering. Fish remains may be evenly scattered on some bedding planes, on others they may be so abundant as to form a matted mass. On joint faces the fish can be recognised as black coal-like lenses, sometimes up to 1 cm thick. Black bituminous matter is often present along the joint planes of the fish bed, and in the more compact carbonate—rich portions of the bed a little oil is also found.


	== Rousay Flags ==		== Rousay Flags ==
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	=== Palaeogeography ===		=== Palaeogeography ===
	No detailed account of the lithology and palaeogeography of the Rousay Flags has as yet been published. The lithology of this formation is, however, so similar to that of the Stromness Flags that the general conclusions concerning the environment of deposition of the latter (see pp. 74-77) must also apply. Without a detailed knowledge of the lithological variations within the cycles in space and time and without palaeocurrent data, nothing can be said at this stage about the shape and extent of the Orcadian lake or lakes in Rousay times or of the directions from which rivers entered the area.		No detailed account of the lithology and palaeogeography of the Rousay Flags has as yet been published. The lithology of this formation is, however, so similar to that of the Stromness Flags that the general conclusions concerning the environment of deposition of the latter (see pp. 74-77) must also apply. Without a detailed knowledge of the lithological variations within the cycles in space and time and without palaeocurrent data, nothing can be said at this stage about the shape and extent of the Orcadian lake or lakes in Rousay times or of the directions from which rivers entered the area.


	== Eday Beds ==		== Eday Beds ==
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	The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.		The sandstones and red ‘marls’ of the Eday Beds were deposited in the channels, alluvial fans and flood plains of fairly large rivers which entered the area from the south-west and either filled up the Orcadian lake or at least encroached upon its margin. The presence within the Eday Flags of grey thinly bedded lacustrine flagstones, which alternate with channel sandstones and lake delta deposits, indicates that there was a time when the waters of a lake again covered the greater part of the Orkney area. This lake was fed by swifter and more active rivers than those which entered the lake at the time the Stromness and Rousay flags were laid down. They regularly built out deltas into the lake and these pushed its margin north-eastwards beyond the limits of the present area. The lithology of the higher beds of the Eday group indicates that a fluvial regime was soon re-established, first in the north, but then over the whole area. The Eday Sandstones were probably laid down by swift, braided and straight rivers which formed alluvial fans, but the Eday Marls were formed in the channels and alluvial plains of slower meandering streams. The appearance of swift-flowing rivers is probably the result of differential vertical movements along faults which were responsible for the tectonic uplift of the source area or areas.


	This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970) and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935). Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.		This article is based to a large extent on the work of Dr N. G. T. Fannin (Fannin 1970) and the section on the Eday Beds incorporates data supplied by Miss J. M. Ridgway. In consequence the classiﬁcation used in this account differs in some respects from that published by Wilson and others (1935). Information provided by Mr U. McL. Michie of the Institute’s Geochemical Division has been used throughout article.

	[[Category:Orkney and Shetland]]		[[Category:Orkney and Shetland]]

Dbk: 1 revision imported

2015-09-01T11:05:17Z

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Lmo at 12:14, 29 July 2015

2015-07-29T12:14:17Z

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