Editing Stoer Group at Enard Bay, North-west Highlands - an excursion

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== Introduction ==
 
 
Park at the large lay-by [NC 0211 1241] at the road junction at Achnahaird Bay. Parties with several cars could leave one car near the bridge south of Loch Garvie [NC 0392 1300], as this saves a walk back along the road.
 
Park at the large lay-by [NC 0211 1241] at the road junction at Achnahaird Bay. Parties with several cars could leave one car near the bridge south of Loch Garvie [NC 0392 1300], as this saves a walk back along the road.
  
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== Locality 4.5 ‘Salmon Bothy’ Bay, west side: ‘drop stones’ in the Clachtoll Formation. [NC 0278 1463] ==
 
== Locality 4.5 ‘Salmon Bothy’ Bay, west side: ‘drop stones’ in the Clachtoll Formation. [NC 0278 1463] ==
Just above high-water mark, metre-sized gneiss blocks are embedded in laminated red mudstone and sandstone. These outcrops have been the source of significant controversy, with the blocks being variously interpreted as ice-rafted drop stones (Davison and Hambrey, 1996) and as mass-flow deposits (Young 1999). Bedding in the surrounding mudstone and sandstone has been deformed; generally there is more deformation on the south side, suggesting southward, lateral rather than vertical emplacement. Towards the south, at the level of the gneiss boulders, oscillation ripples and desiccation cracks occur on bedding planes; Young (1999) noted that these indicate shallow to subaerial conditions of deposition, whereas ice-rafting of dropstones >1m across would have necessitated significant water depths. To the north and on the wave-cut platform, the mudstone passes laterally into a boulder conglomerate. Young (1999) suggested that these conglomerates were formed in debris fans along the margins of lakes, with blocks of gneiss from adjacent basement highs or scarps periodically sliding into the lakes, and a similar model was favoured by Stewart (2002).
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Just above high-water mark, metre-sized gneiss blocks are embedded in laminated red mudstone and sandstone. These outcrops have been the source of significant controversy, with the blocks being variously interpreted as ice-rafted drop stones (Davison and Hambrey, 1996) and as mass-flow deposits (Young 1999). Bedding in the surrounding mudstone and sandstone has been deformed; generally there is more deformation on the south side, suggesting southward, lateral rather than vertical emplacement. Towards the south, at the level of the gneiss boulders, oscillation ripples and desiccation cracks occur on bedding planes; Young (1999) noted that these indicate shallow to subaerial conditions of deposition, whereas ice-rafting of dropstones >1m across would have necessitated significant water depths. To the north and on the wave-cut platform, the mudstone passes laterally into a boulder conglomerate. Young (1999) suggested that these conglom-erates were formed in debris fans along the margins of lakes, with blocks of gneiss from adjacent basement highs or scarps periodically sliding into the lakes, and a similar model was favoured by Stewart (2002).
  
 
Walk past the ruined salmon bothy to the east side of the bay, and cross a prominent C-shaped tidal inlet onto a small peninsula – this is possible at all but the highest tide.
 
Walk past the ruined salmon bothy to the east side of the bay, and cross a prominent C-shaped tidal inlet onto a small peninsula – this is possible at all but the highest tide.
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== Locality 4.8 Camas a’ Bhothain: Poll a’ Mhuilt Member. [NC 0301 1456]  ==
 
== Locality 4.8 Camas a’ Bhothain: Poll a’ Mhuilt Member. [NC 0301 1456]  ==
At the high-water mark are outcrops of red planar laminated algal limestone,which locally enclose clasts of gneiss up to 10cm across; please do not hammer these. The limestone is followed upwards by laminated mudstones (Poll a’Mhuilt Member), which are in turn overlain by boulder conglomerate with sandstone clasts up to 2m across, forming the cliff above (Diabaig Formation, Torridon Group).
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At the high-water mark are outcrops of red planar laminated algal limestone,which locally enclose clasts of gneiss up to 10cm across; please do not hammer these. The limestone is followed upwards by laminated mud-stones (Poll a’Mhuilt Member), which are in turn overlain by boulder conglomerate with sandstone clasts up to 2m across, forming the cliff above (Diabaig Formation, Torridon Group).
  
 
To the north, on the island of Sgeir Bhuidhe and on Rubh’ a’ Choin, note the sub-horizontal, thick-bedded sandstones of the Applecross Formation. Continue along the bay as far as a large wave-cut platform.
 
To the north, on the island of Sgeir Bhuidhe and on Rubh’ a’ Choin, note the sub-horizontal, thick-bedded sandstones of the Applecross Formation. Continue along the bay as far as a large wave-cut platform.
  
 
== Locality 4.9 Camas a’ Bhothain: Stac Fada Member. [NC 0308 1456]  ==
 
== Locality 4.9 Camas a’ Bhothain: Stac Fada Member. [NC 0308 1456]  ==
The Stac Fada Member here (stratigraphically below the Poll a’ Mhuilt Member ofLocalities 4.6 and 4.8) consists ofsandstone beds, with pea-sized accretionary lapilli in the top part, best seen on bedding surfaces. In some cases, the insides of the lapilli are seen to be concentric. Accretionary lapilli are formed when ash particles are amalgamated in moist ash clouds (sim-ilar to hailstones); they are relatively fragile and generally have a poor preservationpotential. The unit with accretionary lapilli is thicker here than at Stoer, but the volcanic fragments seen at Stoer are absent here. Thus the Stac Fada Member changes character, over a distance of ''c''.15km, from a mass-flow deposit to an ash fall dominated unit.
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The Stac Fada Member here (stratigraphically below the Poll a’ Mhuilt Member ofLocalities 4.6 and 4.8) consists ofsandstone beds, with pea-sized accretionary lapilli in the top part, best seen on bedding surfaces. In some cases, the insides of the lapilli are seen to be concentric. Accretionary lapilli are formed when ash particles are amalgamated in moist ash clouds (sim-ilar to hailstones); they are relatively fragile and generally have a poor preservationpotential.Theunitwithaccretionarylapilliis thickerherethan at Stoer, but the volcanic fragments seen at Stoer are absent here. Thus the Stac Fada Member changes character, over a distance of ''c''.15km, from a mass-flow deposit to an ash fall dominated unit.
  
 
The lower part of the member here consists of massive sandstone, locally with gneiss clasts. Continue along the bedding planes as far as a horizontal platform of breccia, just before a small inlet with loose cobbles. Some unsightly paleomagnetic drill holes are nearby. The platform [NC 0311 1457] consists of red breccia, with cobble-sized clasts which contain accretionary lapilli and are thus derived from the surrounding Stac Fada Member. The breccia, the lowest part of the Diabaig Formation, is lower than the surrounding outcrops of the Stac Fada Member and clearly occupied a palaeohollow.
 
The lower part of the member here consists of massive sandstone, locally with gneiss clasts. Continue along the bedding planes as far as a horizontal platform of breccia, just before a small inlet with loose cobbles. Some unsightly paleomagnetic drill holes are nearby. The platform [NC 0311 1457] consists of red breccia, with cobble-sized clasts which contain accretionary lapilli and are thus derived from the surrounding Stac Fada Member. The breccia, the lowest part of the Diabaig Formation, is lower than the surrounding outcrops of the Stac Fada Member and clearly occupied a palaeohollow.
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== Locality 4.10 Rubh’ a’ Choin: Torridon Group. [NC 0331 1469] to [NC 0339 1462]  ==
 
== Locality 4.10 Rubh’ a’ Choin: Torridon Group. [NC 0331 1469] to [NC 0339 1462]  ==
The cliff to the south of the cobble beach consists of conglomerate with both gneiss and sandstone cobbles and mudstone intercalations. This is Diabaig Formation, which is plastered against a paleocliff of Stoer Group conglomerates. Walk over the cobbles to a low rock wall or plateau some 50m to the north-west.
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The cliff to the south of the cobble beach consists of conglomerate with both gneiss and sandstone cobbles and mudstone intercalations. This is Diabaig Formation, which is plastered against a paleocliff of Stoer Group conglom-erates. Walk over the cobbles to a low rock wall or plateau some 50m to the north-west.
  
 
The base of this outcrop [NC 0335 1471] consists of laminated fine sandstone and red and grey siltstone and mudstone of the Diabaig Forma-tion. This is overlain by the Applecross Formation with a sharp, locally erosive contact. The Applecross Formation here consists of thick-bedded, coarse, gritty to pebbly red sandstone, with clear east-dipping cross-bed-ding, suggesting palaeocurrents to the east.
 
The base of this outcrop [NC 0335 1471] consists of laminated fine sandstone and red and grey siltstone and mudstone of the Diabaig Forma-tion. This is overlain by the Applecross Formation with a sharp, locally erosive contact. The Applecross Formation here consists of thick-bedded, coarse, gritty to pebbly red sandstone, with clear east-dipping cross-bed-ding, suggesting palaeocurrents to the east.

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