Geology of Mull - an outline - Revision history

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	A small outcrop of baked blue shale just west of Duart Bay has yielded ammonites and other fossils of Kimmeridgian age (mutabilis Zone).		A small outcrop of baked blue shale just west of Duart Bay has yielded ammonites and other fossils of Kimmeridgian age (mutabilis Zone).

	= Cretaceous =		== Cretaceous ==

	At Gribun, Cenomanian glauconitic sandstone (6 m thick) is overlain by 3 m of white sandstone and 3 m of silicified chalk with flints (possiby Santonian). The chalk is overlain by breccia containing angular pebbles and cobbles of silicified chalk, sandstone with chert nodules, and 2 m of weakly bedded, red mudstone. The beds above the chalk have been formally designated the Gribun Conglomerate Formation by Hancock (2000), but have been equated with the Clach Alasdair Conglomerate Member and Beinn Iadain Mudstone Formation by Mortimore et al. (2001). The succession is overlain by Paleocene lavas (Plate 4). A rich bivalve fauna is known from the glauconitic sandstone, including ''Rhynchonella'', ''Exogyra conica'', and ''Pecten asper''. ''Ostrea'' and ''Pecten'' have been found in the chalk. Glauconitic sandstone occurs at Auchnacraig, south of Loch Don, and also at Carsaig where it reaches about 13 m, its greatest thickness in the district.		At Gribun, Cenomanian glauconitic sandstone (6 m thick) is overlain by 3 m of white sandstone and 3 m of silicified chalk with flints (possiby Santonian). The chalk is overlain by breccia containing angular pebbles and cobbles of silicified chalk, sandstone with chert nodules, and 2 m of weakly bedded, red mudstone. The beds above the chalk have been formally designated the Gribun Conglomerate Formation by Hancock (2000), but have been equated with the Clach Alasdair Conglomerate Member and Beinn Iadain Mudstone Formation by Mortimore et al. (2001). The succession is overlain by Paleocene lavas (Plate 4). A rich bivalve fauna is known from the glauconitic sandstone, including ''Rhynchonella'', ''Exogyra conica'', and ''Pecten asper''. ''Ostrea'' and ''Pecten'' have been found in the chalk. Glauconitic sandstone occurs at Auchnacraig, south of Loch Don, and also at Carsaig where it reaches about 13 m, its greatest thickness in the district.

Scotfot at 12:10, 19 July 2023

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	[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]		[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]
	[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]		[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]
	[[File:P914133.png\|thumbnail\|~~File:P914133.png~~ Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]		[[File:P914133.png\|thumbnail\|Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]
	[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]		[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]
	[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]		[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]

Scotfot at 12:05, 19 July 2023

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← Older revision		Revision as of 13:05, 19 July 2023
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	[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]		[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]
	[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]		[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]
			[[File:P914133.png\|thumbnail\|File:P914133.png Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]
	[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]		[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]
	[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]		[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]

Scotfot: /* Dykes, dyke swarms and volcanic plugs */

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Dykes, dyke swarms and volcanic plugs

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	== Dykes, dyke swarms and volcanic plugs ==		== Dykes, dyke swarms and volcanic plugs ==
			Numerous dykes of Palaeogene age are present throughout western Scotland and the Hebrides. The dykes commonly occur in parallel, north-west- to north-north-west-trending regional swarms, becoming more numerous and varied in direction near to and within the central complexes (Speight et al., 1982)

			The dykes in and near the central complexes are generally less than 2 m in thickness. However, injection of dykes side by side into the same fissure can result in thick multiple intrusions, which are most common close to the central complexes. Large numbers of multiple dykes also occur close to the Mull Central Complex.
			The distribution of the dyke swarms was controlled by a regional north-east–south-west extensional stress field, and the over-riding control on the orientation of the swarms is considered to have been the orientation of lower crustal intrusions that fed the dykes. Locally, subsidiary swarms are orientated approximately north–south, for example in the Outer Hebrides, and between south Skye and Morvern where the subsidiary swarm forms an en échelon link between the Skye and Mull swarms. Echelons of the Cleveland Dyke are up to 25m thick in County Durham and north Yorkshire, some 350 to 400 km from Mull.

			The majority of the dykes in the linear regional swarms are of basaltic or slightly more evolved composition. In and around the central complexes there are, additionally, dykes of silicic, intermediate and, less commonly, ultrabasic composition (Gibb, 1968, 1969). The basaltic dykes of the regional swarms are predominantly of tholeiitic basalt or tholeiitic olivine basalt, or of mildly alkaline olivine basalt. Dyke compositions may remain fairly uniform over considerable distances, as has been well demonstrated in regional dykes that extend across the Southern Uplands and into north Yorkshire (Macdonald et al., 1988).

			Tholeiitic basalts and related, more evolved, lithologies predominate in the Mull Dyke Swarm. However, alkali olivine-dolerites, locally termed ‘crinanites’, are common as far southeast as Loch Fyne, and the swarm contains silicic and intermediate dykes in the vicinity of Oban and on Mull.

			The majority of the plugs are basaltic in composition, but a few of trachyte composition have been recorded. On Mull, a large trachyte plug intrudes lavas and is, itself, intruded by north-west-trending dykes at Druim Buidhe, south-east of Tobermory.

	== Sills and sill-complexes ==		== Sills and sill-complexes ==

Scotfot: /* References */

2023-07-19T11:41:29Z

References

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	BAILEY, E B. 1962. Early Tertiary fold movements in Mull. Geological Magazine, Vol. 99, 478–479.		BAILEY, E B. 1962. Early Tertiary fold movements in Mull. Geological Magazine, Vol. 99, 478–479.

	BAILEY, E B, CLOUGH, C T, WRIGHT, W B, RICHEY, J E, and WILSON, G V. 1924. Tertiary and Post-Tertiary geology of Mull, Loch Aline, and Oban. Memoir of the Geological Survey of Great Britain, Sheet 44 (Scotland).		BAILEY, E B, CLOUGH, C T, WRIGHT, W B, RICHEY, J E, and WILSON, G V. 1924. [https://webapps.bgs.ac.uk/Memoirs/docs/B01951.html Tertiary and Post-Tertiary geology of Mull, Loch Aline, and Oban.] Memoir of the Geological Survey of Great Britain, Sheet 44 (Scotland).

	BOULTER, M C, and KVACEK, Z. 1989. The Palaeocene flora of the Isle of Mull. Palaeontological Association Special Papers in Palaeontology, No. 42.		BOULTER, M C, and KVACEK, Z. 1989. The Palaeocene flora of the Isle of Mull. Palaeontological Association Special Papers in Palaeontology, No. 42.

Scotfot: Created page with "== Geology of Mull - Palaeogene volcanic districts of Scotland == Table 10 Mineralogical and petrographical characteristics of the principal lava types of the Hebridean Igneous Province. Table 15 The Mull Lava Group. File:P914125.jpg|thumbnail|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick..."

2023-07-19T11:32:21Z

Created page with "== Geology of Mull - Palaeogene volcanic districts of Scotland == thumbnail|Table 10 Mineralogical and petrographical characteristics of the principal lava types of the Hebridean Igneous Province. thumbnail|Table 15 The Mull Lava Group. File:P914125.jpg|thumbnail|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick..."

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← Older revision		Revision as of 13:10, 19 July 2023
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	[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]		[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]
	[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]		[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]
	[[File:P914133.png\|thumbnail\|~~File:P914133.png~~ Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]		[[File:P914133.png\|thumbnail\|Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]
	[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]		[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]
	[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]		[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]

← Older revision		Revision as of 13:05, 19 July 2023
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	[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]		[[File:P914125.jpg\|thumbnail\|Figure 7 Upper Cretaceous of the Inner Hebrides Group, exposed at the south-east corner of Beinn Iadain, Morvern (after Mortimore et al., 2001, fig.6.29). The thick sandstones of the Loch Aline White Sandstone and Morvern Greensand formations are obscured beneath steep grassy slopes at X and Y, respectively. Age of the deposits: A Lavas of Paleocene age; B Beinn Iadain Formation, generally assumed to be of Paleocene age; D Judd (1878) recorded Belemnitella (Campanian) from the Chalk, but the exact horizon is uncertain; E Sponges dated as Santonian; F undated, generally considered to be Turonian (but may be Cenomanian; Braley,1990); G probably upper Cenomanian; H probably middle Cenomanian (compare with similar, better dated, site in Northern Ireland); I uncertain, possibly lower Cenomanian; J Lias and Permo-Triassic rocks seen in track section leading to Beinn Iadain ]]
	[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]		[[File:P914131.png\|thumbnail\|Figure 13 Hydrothermal circulation in and around the Mull Central Complex. Diagrammatic cross-section showing the hydrothermal mineral zones in the lava succession and the superimposed alteration zones developed about the central complex in response to the circulation of heated meteoric water (based on Walker, 1971;Taylor and Forester, 1971; Bell and Williamson, 2002). From: Emeleus, C H, and Bell, B R. 2005. British regional geology: The Palaeogene volcanic districts of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.]]
			[[File:P914133.png\|thumbnail\|File:P914133.png Dilation axes of the Palaeogene dyke swarms in the Hebridean area. Broader lines indicate the main axes of the regional swarms; broken lines indicate less certain axes (based on Speight et al., 1982, fig. 33.5).The Minch Linear Magnetic Anomaly is also interpreted as a dyke or dyke swarm]]
	[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]		[[File:P914146.jpg\|thumbnail\|Figure 27 Principal components of the Mull Central Complex. ]]
	[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]		[[File:P914147.png\|thumbnail\|Figure 28 Mull Central Complex: Centre 1, the Glen More Centre and early Caldera]]