OR/15/017 Field survey - May 2014 - Revision history

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Unst

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	At Norwick the peat is 8 m thick and two sand units were sampled at about 4 m depth beneath ground and dated 6840±40 years 14C (Smith et al., 2004). At Site 2, the lower part of the Burn of Norwick valley landward of coastal dunes is widely occupied by peat (Smith, 1993<ref name="Smith 1993a">~~SMITH, D E. 1993a. Norwick, Unst; Burragarth, Unst; Sullom Voe, Mainland.~~ </ref>; Smith et al., 1995). In the centre of the valley at its seaward end, the peat rests upon a thin (ca 10–20 cm) layer of grey, micaceous, sand with angular clasts and organic fragments, beneath which is a laminated, grey-green, silty clay. The top of the silty clay is relatively uniform, lying at -3.38m (-4.70 m) to -4.17m (-5.49 m), with the top ca 25 cm not laminated, and contains a scatter of angular clasts (the largest 4 cm in its greatest dimension). Above these basal deposits, the peat is woody at its base and above this contains silty horizons. The sand continues up-valley forming a tapering wedge in the peat. Throughout, the sand contains peat intraclasts as well as many organic fragments. In the sand, the pollen includes ''Chenopodiaceae ''and ''Plantago maritima'',, which may indicate a marine origin, given that the sites probably lay a considerable distance from the shore at time of deposition. There are exceptionally high percentages of corroded pollen and spores in the sand and at the top of the underlying grey-green, silty clay. A 14C (AMS) date of 6840±40 (7748–7589) was obtained for the base of peat overlying the sand layer at borehole 140.
			At Norwick the peat is 8 m thick and two sand units were sampled at about 4 m depth beneath ground and dated 6840±40 years 14C (Smith et al., 2004). At Site 2, the lower part of the Burn of Norwick valley landward of coastal dunes is widely occupied by peat (Smith, 1993<ref name="Smith 1993a"></ref>; Smith et al., 1995). In the centre of the valley at its seaward end, the peat rests upon a thin (ca 10–20 cm) layer of grey, micaceous, sand with angular clasts and organic fragments, beneath which is a laminated, grey-green, silty clay. The top of the silty clay is relatively uniform, lying at -3.38m (-4.70 m) to -4.17m (-5.49 m), with the top ca 25 cm not laminated, and contains a scatter of angular clasts (the largest 4 cm in its greatest dimension). Above these basal deposits, the peat is woody at its base and above this contains silty horizons. The sand continues up-valley forming a tapering wedge in the peat. Throughout, the sand contains peat intraclasts as well as many organic fragments. In the sand, the pollen includes ''Chenopodiaceae ''and ''Plantago maritima'',, which may indicate a marine origin, given that the sites probably lay a considerable distance from the shore at time of deposition. There are exceptionally high percentages of corroded pollen and spores in the sand and at the top of the underlying grey-green, silty clay. A 14C (AMS) date of 6840±40 (7748–7589) was obtained for the base of peat overlying the sand layer at borehole 140.

	At Burragarth the northwestward-facing bay (Lunda Wick) is backed by dunes, landward of which a peat moss occupies the lower end of Vinstrick valley. At the base of the sequence lies a sand and gravel surface, overlain to seaward by a grey, silty clay which forms a gently sloping surface and thins out landward, reaching a maximum observed altitude of –3.65m (-4.88 m). Above the silty clay is a widespread layer of grey micaceous sand, up to 0.75 m thick, containing fragments of vegetation (roots, stems and twigs). Above the sand, peat with horizons of organic silt and sand extends to the surface. Towards the head of the valley, the sand layer attains an altitude of at least 4.11 m (2.88m) (Burragarth E., Table 4). The sand shows high values for corroded pollen and spores and at the top contains Chenopodiaceae (see Fig. 10, below). There are no diatoms in the fine sand, but the silty clay contains a few broken and eroded pennate forms, mainly ''Pinnularia viridis. ''Pinnularia occurs widely in Storegga tsunami deposits in eastern Scotland, incorporated into the tsunami sand as the tsunami moved across underlying freshwater sediments. The presence of Pinnularia fragments in the silty clay at this site could indicate re-working of the upper layers of that deposit as freshwater (possibly peaty) sediments either down valley or towards the valley sides were reworked. A radiocarbon date of 7215±60 (8165–7878) was obtained for the base of the peat at 4 m depth, overlying the fine sand in borehole 108 (Smith, 1993<ref name="Smith 1993a"></ref>).		At Burragarth the northwestward-facing bay (Lunda Wick) is backed by dunes, landward of which a peat moss occupies the lower end of Vinstrick valley. At the base of the sequence lies a sand and gravel surface, overlain to seaward by a grey, silty clay which forms a gently sloping surface and thins out landward, reaching a maximum observed altitude of –3.65m (-4.88 m). Above the silty clay is a widespread layer of grey micaceous sand, up to 0.75 m thick, containing fragments of vegetation (roots, stems and twigs). Above the sand, peat with horizons of organic silt and sand extends to the surface. Towards the head of the valley, the sand layer attains an altitude of at least 4.11 m (2.88m) (Burragarth E., Table 4). The sand shows high values for corroded pollen and spores and at the top contains Chenopodiaceae (see Fig. 10, below). There are no diatoms in the fine sand, but the silty clay contains a few broken and eroded pennate forms, mainly ''Pinnularia viridis. ''Pinnularia occurs widely in Storegga tsunami deposits in eastern Scotland, incorporated into the tsunami sand as the tsunami moved across underlying freshwater sediments. The presence of Pinnularia fragments in the silty clay at this site could indicate re-working of the upper layers of that deposit as freshwater (possibly peaty) sediments either down valley or towards the valley sides were reworked. A radiocarbon date of 7215±60 (8165–7878) was obtained for the base of the peat at 4 m depth, overlying the fine sand in borehole 108 (Smith, 1993<ref name="Smith 1993a"></ref>).

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Unst

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	== Unst ==		==Unst==
	We carried out a reconnaissance visit to Unst to survey potential coastal sites (see locations on Figs 91 and 92) where tsunami sands might be preserved. Previous visits to the island (Smith, 1993b<ref name"Smith 1993b">SMITH, D E. 1993b. Norwick, Unst; Burragarth, Unst; Sullom Voe, Mainland. 52–56 in The Quaternary of Shetland. BIRNIE, J, GORDON, J, BENNETT, K, and HALL, A M (editors). (Quaternary Research Association Field Guide.) </ref>) had not found sands in the coastal peats, but deposits in cores had been found and dated at Norwick, Burragarth and Snarravoe (Fig. 91). Like Fetlar, the south eastern part of Unst is oceanic crust and composed of Ophiolite and gabbro, so peat is not present here, but seems to be well developed elsewhere, where the tsunami sands were cored.		We carried out a reconnaissance visit to Unst to survey potential coastal sites (see locations on Figs 91 and 92) where tsunami sands might be preserved. Previous visits to the island (Smith, 1993b<ref name"Smith 1993b">SMITH, D E. 1993b. Norwick, Unst; Burragarth, Unst; Sullom Voe, Mainland. 52–56 in The Quaternary of Shetland. BIRNIE, J, GORDON, J, BENNETT, K, and HALL, A M (editors). (Quaternary Research Association Field Guide.) </ref>) had not found sands in the coastal peats, but deposits in cores had been found and dated at Norwick, Burragarth and Snarravoe (Fig. 91). Like Fetlar, the south eastern part of Unst is oceanic crust and composed of Ophiolite and gabbro, so peat is not present here, but seems to be well developed elsewhere, where the tsunami sands were cored.

Dbk: /* Age dating of the tsunami sands */

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Age dating of the tsunami sands

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	The evidence on the tsunami source from Yell at this stage, is inconclusive. The sand at Whale Firth is remarkably similar to the sands at Sullom Voe (except for the absence of large rip-up clasts); it lies within a woody peat, so a Storegga source seems to be most likely, except the one date here is mid-Holocene (4760±30 cal yr BP). There is no sequence, similar to those cored at Loch Benston and Garth Loch, which would provide a firmer context (two sand layers at one site with different ages). Thus the identification in 2013 of three sand layers within one stratigraphic sequence at Mid Yell promised to provide a firmer basis for a mid-Holocene event. It is thus unfortunate that the results from our 2014 visit do not confirm the presence of more than one tsunami sand at this location. The thick sand at the base of the peat, because of its’ thickness and stratigraphic position (at the base of the peat) where it overlies till or bedrock (not within it as seen elsewhere at Whale Forth and Sullom Voe), is probably not a tsunami deposit. We suggest it is weathered bedrock, mineralogenic sand laid down before the peat formed (as described by Flinn, 1994<ref name="Flinn"></ref>), a lacustrine sediment (Fraser Milne, ''Pers. Comm''.) or a combination of all three processes. Only one tsunami sand therefore is confirmed at Mid Yell, its origin interpreted as such because it is preserved fully within the peat and because of its lateral extent along the section; its variable elevation, high in the east, but below ground level in the west supporting a tsunami origin.		The evidence on the tsunami source from Yell at this stage, is inconclusive. The sand at Whale Firth is remarkably similar to the sands at Sullom Voe (except for the absence of large rip-up clasts); it lies within a woody peat, so a Storegga source seems to be most likely, except the one date here is mid-Holocene (4760±30 cal yr BP). There is no sequence, similar to those cored at Loch Benston and Garth Loch, which would provide a firmer context (two sand layers at one site with different ages). Thus the identification in 2013 of three sand layers within one stratigraphic sequence at Mid Yell promised to provide a firmer basis for a mid-Holocene event. It is thus unfortunate that the results from our 2014 visit do not confirm the presence of more than one tsunami sand at this location. The thick sand at the base of the peat, because of its’ thickness and stratigraphic position (at the base of the peat) where it overlies till or bedrock (not within it as seen elsewhere at Whale Forth and Sullom Voe), is probably not a tsunami deposit. We suggest it is weathered bedrock, mineralogenic sand laid down before the peat formed (as described by Flinn, 1994<ref name="Flinn"></ref>), a lacustrine sediment (Fraser Milne, ''Pers. Comm''.) or a combination of all three processes. Only one tsunami sand therefore is confirmed at Mid Yell, its origin interpreted as such because it is preserved fully within the peat and because of its lateral extent along the section; its variable elevation, high in the east, but below ground level in the west supporting a tsunami origin.

	Our interpretation of a single, laterally extensive mid-peat sand is hard to reconcile with the logs of the Mid Yell 7a and 7b logs reproduced in Dawson et al. (2013)<ref name="Dawson 2013"></ref>. The sequence we identify most resembles Mid Yell 7b with an upper sand preserved in woody peat and overlain by fibrous peat. The lithology of the sand we describe within the woody peat is different to the sand at Whale Firth (and hence Sullom Voe) in that it is thinner, muddier, the upper and lower peat contacts are not as sharp, and in places it is contorted. Not being able to relate our results to 14C dates of Mid Yell 7a compromises our interpretation of the age dating from this section. If we are correct that the basal sand in Mid Yell 7a is not from a tsunami, then the lower of the overlying two sands should be Storegga and the upper a mid-Holocene event based on the peat age of 8120±40 cal yr BP for the lowest peat and the 5800±40BP age from the peat immediately below the upper sand. From a similar location, Milne et al. (2014) identify in a gouge core two 5–6 cm intra-peat sands above the basal sand in Mid-Yell Log 7 (contorted sands location).		Our interpretation of a single, laterally extensive mid-peat sand is hard to reconcile with the logs of the Mid Yell 7a and 7b logs reproduced in Dawson et al. (2013)<ref name="Dawson 2013">DAWSON, A, and COSTA, P J M. 2013. Field Report 2. Will climate change in the Arctic increase the landslide tsunami risk for the UK? Shetland Fiedlwork June 2013</ref>. The sequence we identify most resembles Mid Yell 7b with an upper sand preserved in woody peat and overlain by fibrous peat. The lithology of the sand we describe within the woody peat is different to the sand at Whale Firth (and hence Sullom Voe) in that it is thinner, muddier, the upper and lower peat contacts are not as sharp, and in places it is contorted. Not being able to relate our results to 14C dates of Mid Yell 7a compromises our interpretation of the age dating from this section. If we are correct that the basal sand in Mid Yell 7a is not from a tsunami, then the lower of the overlying two sands should be Storegga and the upper a mid-Holocene event based on the peat age of 8120±40 cal yr BP for the lowest peat and the 5800±40BP age from the peat immediately below the upper sand. From a similar location, Milne et al. (2014) identify in a gouge core two 5–6 cm intra-peat sands above the basal sand in Mid-Yell Log 7 (contorted sands location).

	The other dates from Mid Yell of 6060±40 cal yr BP at Mid Yell 1 (by the road) and 780±30 cal yr BP from Mid Yell 3 (at the west end) do not really provide any further confirmatory evidence on the likelihood of additional tsunami events, except that at these locations there is only one sand within the peat, that perhaps confirms a single laterally extensive event.		The other dates from Mid Yell of 6060±40 cal yr BP at Mid Yell 1 (by the road) and 780±30 cal yr BP from Mid Yell 3 (at the west end) do not really provide any further confirmatory evidence on the likelihood of additional tsunami events, except that at these locations there is only one sand within the peat, that perhaps confirms a single laterally extensive event.

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Dbk: /* Other locations on Yell */

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Other locations on Yell

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	Gutcher (HU549993) (Fig. 78). No sign of potential preservation at Gutcher even in coastal inlet (Loch of Gutcher) at the ferry terminal.		Gutcher (HU549993) (Fig. 78). No sign of potential preservation at Gutcher even in coastal inlet (Loch of Gutcher) at the ferry terminal.

	[[Image:OR15017_fig77.jpg\|thumb\|right\|~~100px~~\| '''Figure 77''' Other Locations on Yell.]]		[[Image:OR15017_fig77.jpg\|thumb\|right\|200px\| '''Figure 77''' Other Locations on Yell.]]

	[[Image:OR15017_fig78.jpg\|thumb\|center\|400px\| '''Figure 78''' View from road to east across Loch of Gutcher.]]		[[Image:OR15017_fig78.jpg\|thumb\|center\|400px\| '''Figure 78''' View from road to east across Loch of Gutcher.]]

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Other locations on Yell

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	Gutcher (HU549993) (Fig. 78). No sign of potential preservation at Gutcher even in coastal inlet (Loch of Gutcher) at the ferry terminal.		Gutcher (HU549993) (Fig. 78). No sign of potential preservation at Gutcher even in coastal inlet (Loch of Gutcher) at the ferry terminal.

	[[Image:OR15017_fig77.jpg\|thumb\|right\|~~400px~~\| '''Figure 77''' Other Locations on Yell.]]		[[Image:OR15017_fig77.jpg\|thumb\|right\|100px\| '''Figure 77''' Other Locations on Yell.]]

	[[Image:OR15017_fig78.jpg\|thumb\|center\|~~100px~~\| '''Figure 78''' View from road to east across Loch of Gutcher.]]		[[Image:OR15017_fig78.jpg\|thumb\|center\|400px\| '''Figure 78''' View from road to east across Loch of Gutcher.]]

	The coast along Bluemull Sound (Fig. 77) didn’t show promise. It was noted that this area had had improvements to the agriculture quality of the land such that blanket peat was rare and that worked fields extended to the coast.		The coast along Bluemull Sound (Fig. 77) didn’t show promise. It was noted that this area had had improvements to the agriculture quality of the land such that blanket peat was rare and that worked fields extended to the coast.

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Other locations on Yell

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	[[Image:OR15017_fig77.jpg\|thumb\|right\|400px\| '''Figure 77''' Other Locations on Yell.]]		[[Image:OR15017_fig77.jpg\|thumb\|right\|400px\| '''Figure 77''' Other Locations on Yell.]]

	[[Image:OR15017_fig78.jpg\|thumb\|center\|~~400px~~\| '''Figure 78''' View from road to east across Loch of Gutcher.]]		[[Image:OR15017_fig78.jpg\|thumb\|center\|100px\| '''Figure 78''' View from road to east across Loch of Gutcher.]]

	The coast along Bluemull Sound (Fig. 77) didn’t show promise. It was noted that this area had had improvements to the agriculture quality of the land such that blanket peat was rare and that worked fields extended to the coast.		The coast along Bluemull Sound (Fig. 77) didn’t show promise. It was noted that this area had had improvements to the agriculture quality of the land such that blanket peat was rare and that worked fields extended to the coast.

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Fetlar

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	A day was spent on Fetlar (Fig. 86) conducting a reconnaissance survey for tsunami sediments. Fetlar is mainly composed of obducted oceanic crust, predominantly ophiolites, so soils are thin, peat is not well developed on the island. The land is mainly pasture.		A day was spent on Fetlar (Fig. 86) conducting a reconnaissance survey for tsunami sediments. Fetlar is mainly composed of obducted oceanic crust, predominantly ophiolites, so soils are thin, peat is not well developed on the island. The land is mainly pasture.

	[[Image:~~15017_fig86~~.jpg\|thumb\|center\|400px\| '''Figure 86''' Locations visited on Fetlar.]]		[[Image:OR15017_fig86.jpg\|thumb\|center\|400px\| '''Figure 86''' Locations visited on Fetlar.]]

	On the southwest coast we visited the Wick of Triesta and Papil Water (WPs 686-688), here the coastal sand dunes directly overlie bedrock (Figs. 87 and 88).		On the southwest coast we visited the Wick of Triesta and Papil Water (WPs 686-688), here the coastal sand dunes directly overlie bedrock (Figs. 87 and 88).

Dbk: /* Kirkabister 1 and Burra Ness (Kirkabister 2) */

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Kirkabister 1 and Burra Ness (Kirkabister 2)

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	[[Image:OR15017_fig66.jpg\|thumb\|center\|400px\| '''Figure 66''' Kirkabister to the right of Fig 5865. Beneath the weathered peat (where Dave Long’s arm is resting and bottom of spade handle) there is a sandy gravelly section (on the ledge) underlain by muddy brown peat within which is a thin (2-3cm) grey muddy sand that overlies till.]]		[[Image:OR15017_fig66.jpg\|thumb\|center\|400px\| '''Figure 66''' Kirkabister to the right of Fig 5865. Beneath the weathered peat (where Dave Long’s arm is resting and bottom of spade handle) there is a sandy gravelly section (on the ledge) underlain by muddy brown peat within which is a thin (2-3cm) grey muddy sand that overlies till.]]

	[[Image:~~R15017_fig67~~.jpg\|thumb\|center\|400px\| '''Figure 67''' The Storegga tsunami deposit at Maryton in Scotland (Location on Fig.1).]]		[[Image:OR15017_fig67.jpg\|thumb\|center\|400px\| '''Figure 67''' The Storegga tsunami deposit at Maryton in Scotland (Location on Fig.1).]]


	== Kirkabister 2 – Burra Ness ==		== Kirkabister 2 – Burra Ness ==

Dbk: /* Mid Yell Voe */

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Mid Yell Voe

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	At the location of the western pit (Fig. 34) there was no sand in the peat at beach level, but at the base of the pit we found sand at ~ 1m depth that we interpret as a continuation of the sand bed traced to the east. The sand is up to 10 cm thick, the base is sharp and undulating with faint internal lamination; it is very micaceous with organic clay or peat clasts. Above the sand there is a peat bed (~50 cm) with sparse twigs and then a peat layer with contains numerous twigs and logs (10-15cm diameter). A gouge core taken at the base of the pit sampled a sand layer 60-90cm extending below the base of the pit. Lack of core penetration suggests this sand immediately overlies till or bedrock. Above beach level the peat has a different texture (?Sphagnum moss blanket peat) and extends to top of the cliff which has a hummocky topography and is, covered with modern grass.		At the location of the western pit (Fig. 34) there was no sand in the peat at beach level, but at the base of the pit we found sand at ~ 1m depth that we interpret as a continuation of the sand bed traced to the east. The sand is up to 10 cm thick, the base is sharp and undulating with faint internal lamination; it is very micaceous with organic clay or peat clasts. Above the sand there is a peat bed (~50 cm) with sparse twigs and then a peat layer with contains numerous twigs and logs (10-15cm diameter). A gouge core taken at the base of the pit sampled a sand layer 60-90cm extending below the base of the pit. Lack of core penetration suggests this sand immediately overlies till or bedrock. Above beach level the peat has a different texture (?Sphagnum moss blanket peat) and extends to top of the cliff which has a hummocky topography and is, covered with modern grass.
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	Image:OR15017_fig38.jpg\|'''Figure 38''' West Pit (location Fig. 28) detail on Fig. 32.		Image:OR15017_fig38.jpg\|'''Figure 38''' West Pit (location Fig. 28) detail on Fig. 32.
	Image:OR15017_fig39.jpg\|'''Figure 39''' West pit sand at base – note the birch wood in the peat.		Image:OR15017_fig39.jpg\|'''Figure 39''' West pit sand at base – note the birch wood in the peat.
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	[[Image:OR15017_fig40.jpg\|thumb\|center\|400px\| '''Figure 40''' View north across Mid Yell Voe to main section with tsunami sands (outlined) and the laminated sand location to the east.]]		[[Image:OR15017_fig40.jpg\|thumb\|center\|400px\| '''Figure 40''' View north across Mid Yell Voe to main section with tsunami sands (outlined) and the laminated sand location to the east.]]

	[[Image:~~OR15017_fi41~~.jpg\|thumb\|center\|400px\| '''Figure 41''' Laminated sand located east of mid-peat sands - location Fig. 40.]]		[[Image:OR15017_fig41.jpg\|thumb\|center\|400px\| '''Figure 41''' Laminated sand located east of mid-peat sands - location Fig. 40.]]

	[[Image:OR15017_fig42.jpg\|thumb\|center\|400px\| '''Figure 42''' Gouge core at traverse inland of east pit.]]		[[Image:OR15017_fig42.jpg\|thumb\|center\|400px\| '''Figure 42''' Gouge core at traverse inland of east pit.]]