Archaeology in the North Sea
Archaeology in the North Sea
The Orkney Vole is thought to have been imported, by uncertain means, to the archipelago from mainland Europe without setting foot on mainland Britain.
How this happened is a bit of a mystery.
At present, the scope for a small rodent to migrate between Denmark, Germany, the Netherlands, or France, and Orkney, without touching Britain seems a bit limited.
I can suggest here two possibilities for the means by which a landscape may have been accessible for plants and animals to forage and survive and migrate across Britain and the North Sea.
The first is perhaps the most obvious, that the animals were on Dogger Bank from about 10,000BP, with Mesolithic people, and were able to walk northwards to the Atlantic coast of the North Sea, along the west coast of the Norwegian Channel, and were then able to cross an as yet unspecified piece of land westward, to reach Orkney. This first theory is difficult to prove because even though it is possible to give evidence that land of some sort was present there, besides the finding of a flint artefact, there is no other evidence, as the whole geological sediment bank has been stripped by marine currents.
The second means by which the rodent may have reached Orkney relies on the possibility that rather than being completely frozen , or iced over the region between the ridge of land that bordered the Norwegian Channel, and the English and Scottish coasts was a lagoon of shallow water. There is evidence, that is undeclared, that suggests that this Lagoon was associated with a shoreline around it, with vegetation of various sorts on it. The date for the migration of the Orkney Vole into this lagoon environment may have been at any time when England and Scotland were covered in ice-sheets of any thickness. The ice would have prevented the vole from foraging.
Initially, in order to establish the possibility of land being present in the middle of the North Sea in prehistoric times the undersea features there need to be recognised. These are in simple terms, Dogger Bank, the Witch Ground and the Norwegian Channel.
Fig. 1, The British Isles and North Sea (Emodnet)
The Norwegian Channel is a deep water trench that follows the Norwegian Coast from the Skaggerak, an even deeper section of the same trench, between Norway and Denmark, out to the North Atlantic Ocean.
Dogger Bank is an area of shallow water in the southern North Sea known to have been walkable land in prehistoric times, Doggerland.
The Witch Ground is one of a group of deep water features in the North Sea. These gullies are cut into older sediments, and are all the result of impact erosion. Ice sheet edges collapsed, between around 21,000BP and 17,000BP, cutting valleys in underlying ground that was at that time mostly dry land.
A sea-level surge along the Norwegian Channel suggests that its' westwall was once considerably higher than it presents at present.
The Norwegian Channel is also an impact valley that has for millions of years been cut out by ice sheets on Norway and scoured by mobile ice streams rolling off from Sweden, into the Skaggerak, and out to the Atlantic Ocean.
The sea level charts for points along the Norwegian Coast, are published in "Post Glacial Relative Sea Level Change in Norway" by Roger C. Creel. These charts are attached to the map of the Norwegian Channel below.
Fig. 2, Sea level charts for the Norwegian Coast (Creel)
There is, on the charts, a consistent pulse of 10 metres higher water level onto the Norwegian coast at 12,000BP when the ice sheets on Sweden were melting and draining into the Skaggerak.
The sea level in the Norwegian Channel, inferred from "Global sea-level rise in the early Holocene revealed from North Sea peats" by Marc P. Hijma, et al, was 60 metres below present at 12,000BP, but the peak of the meltwater surge out of the Skaggerak was then 10 metres above 60, therefore 50 metres below our sea level.
This surge of 50 metres below sea level was supported at the Skaggerak between the coasts of Norway and Denmark, and not diminished in any way until it had followed the Norwegian Coast and reached the Atlantic.
This means that there was land along the west bank of the Norwegian Channel at better than 50 metres below current sea level, where the seabed is now over 100 below.
This suggests that there was land at the west coast of the Norwegian Channel at shallower that 50 metres below sea-level that people and animal may have used to walk from Doggerland north to the Atlantic coast of the North Sea.
To confirm this possibility, There is evidence of human activity in the middle of the North Sea.
In a report entitled "A flint artifact from the northern North Sea" . Caroline Wickham-Jones discusses a struck flint artefact found in a borehole in the North Sea, half way between Shetland and the North Sea, ("A flint artifact from the northern North Sea" By Long, D., Wickham-Jones, C.R. and Ruckley, N.A. 1986).
The location of the find is indicated in the map above, and the artefact itself is drawn. This may indicate that people were foraging in this area in prehistory. It is certainly difficult to conceive how a knapped flint got to that place otherwise.
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That high ground that bordered the west coast of the Norwegian Channel, and where the flint was found, was not attached to the east coast of England, though it may have had a tenuous link with Scotland, and/or Orkney and Shetland. It was separated from the English coast by a series of shallow water inland seas. These developed, and were maintained between (roughly) 60,000BP and 10,000BP.
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| Fig. 4 |
They were in the locations of geological features known as the Swatchway Formation, the Marr Bank Formation, the Wee Bankie Formation (not shown) and the Bolders Bank Formations. These interconnected features were enclosed at the north by the Capeshore Formation, which was a meltwater runoff deposit accumulated throughout MIS 5, 4, and 3, as the Shetland ice cap collapsed.
As continued melting water drained into the Marr Bank Lagoon from the north, and from all sides, it overflowed out to the Norwegian Channel around the south coast of Dogger Bank, as the Bolders Bank Formation.
Establishing the status of the Shetland icecap
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| Fig, 5. Location map of Capeshore Formation (blue) in sea floor of the northern North Sea |
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| Fig. 6. Section east to west from Shetland to the Norwegian Channel in the sea floor of the North Sea |
The plan and section of the formations around Shetland are presented here. They demonstrate that the Ferder Formation (FD) encircles and is derivetd from he Shetland islands.
The Capeshore Formation material is described as "Soft to firm, highly to moderately silty clay with sporadic shell fragments and pebbles." (BGS)
"The foraminiferal assemblage is dominated by E. clavatum, Cassidulina reniforme Norvang and Protelphidium orbiculare . " (The geology of the northern North Sea. United Kingdom Offshore Regional Report", By H Johnson,)
In "Distribution of recent Benthic foraminifera in Kongsfjorden and Krossfjorden; North-West Svalbard, High Arctic"by Debolina Chatterjee et al, the presence of E, clavatum in Svalbard, the high arctic, is discussed.
"The Cassidulina reniforme–Elphidium clavatum, Textularia spp. assemblage dominates the foraminifera fauna near the glacier proximal that indicates increased sedimentation and meltwater runoff." (Chatterjee)
This marker species confirms that meltwater was running away from Shetland probably through MIS 5, 4, and 3. Further though this soft to firm material would have covered the cropped surface of the Ferder Formation, all around the Shetland islands. This material would have been washed away when sea-level rose between 20,000BP and 5000BP.
The Swatchway Formation, the Witch Ground, and how these relate to features in the southern North
The Swatchway Formation
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| Fig. 7. Plan and section of sea floor deposits , including the Swatchway Formation, demonstrating its' proximity to Orkney. |
In "The geology of the central North Sea. United Kingdom offshore regional report", by R W Gatliff, the Swatchway Formation is described as follows,
"......the sparse, benthonic foraminiferal assemblage is dominated by the cold-water species E excavatum var. clavatum, which suggests deposition in boreal to arctic seas (Stoker et al., 1985). Perhaps more significantly, the foraminifera are accompanied by moderately abundant populations of dinoflagellate cysts; a limited spectrum is co-dominated by O. centrocarpum and Bitectatodinium tepikiense Wilson, indicating northern cool-temperate conditions without significant sea-ice cover (Harland, 1988a). The formation can be broadly assigned a late Weichselian age (Stoker et al., 1985)."
"The Lower Swatchway Beds are heavily overconsolidated, shallow marine sediments which form pronounced ridges, interpreted as ice-pushed ridges.
The Upper Swatchway Beds, filling in the hollows between the ridges, are composed of usually normally consolidated glaciomarine deposits, with locally some probably subglacially folded structures.
The Swatchway Beds are roughly 50 m thick.
A core in the Swatchway Beds nearby Old Devil's Hole (74-J62-Z, Fig. I) contains still unidentified peaty material as an admixture in fine sands, which was 14C dated. The section between 130 and 166 cm below the seafloor yielded a conventional radiocarbon age of 33 800 (+2600, --2000) y BP and the sample from 248 to 251 cm of 37 500 (+ 1800, --1500) y BP (Gr N-7934 and Gr N-7935 respectively 1. The small downward ageing over such a short interval enhances the reliability of the datings and, if correct, they refer to the Upper Swatchway Beds and support the supposed Middle Weichselian age.
From the upper sample of the Josephine Field boring a.o. large fragments of Taxus were dated which is a thermophilic tree. An early glacial age of 23 170 y BP, as was measured, is therefore impossible for biological reasons, and the material most probably was contaminated with younger carbon. If this is the case, the older dates of the boring are also suspect. The radiocarbon dates from the boring off Aberdeen are uncertain as well. They resulted in a youngest age for the deepest sample which makes the ages of the upper two samples questionable too. These upper datings form the main reason to assume that the incision of the Middle Series (Fig. 11) took place after 17 700 y BP.
It is therefore most likely that the Swatchway Beds cover a much longer period than was stated by HOLMES (1977). The Lower Swatchway Beds probably are of at least Early Weichselian age, an Eemian age being within the range of possibility. As a consequence the last main Weichselian glaciation of about 20 000 to 18 000 y BP is most probably represented by the sediments around the transition of the Upper Swatchway Beds into the Hills Deposits." (Jansen)
The Witch Ground, which is the deep feature cutting into the Swatchway Formation was not present at the same period as that in which the Swatchway Formation was part of an inland sea. This is dated to 18,000BP, and is an impact valley group caused by the collapse of the ice sheet, which was probably retreating north-east towards Norway.
The Lower Swatchway Formation was overconsolidated, and was therefore overlaid by an ice sheets, and the Upper Swatchway Formation resulted from the cutting of the impact valleys into it.
The Witch Ground, a deep impact valley group in the middle of the North Sea, cut into and through the Swatchway Formation, which was laterally equivalent to the Marr Bank Formation, a large area of seabed deposits in the central North Sea beside the Scottish and English coasts.
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| Fig. 8, Plan of sea floor deposits outcropping on the east coast of Scotland and England. Showing locations of section drawings below, and location of Marr Bank Formation. |
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| Fig. 9, Sections of Marr Bank Formation |
The Marr Bank Formation comprises glacigenic sediments of late Weichselian age (Stoker et al., 1985; BGS Farne and Marr Bank Quaternary Geology sheets). A sheet-like deposit generally some 10 m to 25 m thick, it is confined to the west-central part of the report area, where it crops out extensively (Figure 67) and (Figure 72). It has a characteristically flat or slightly undulating seismic reflector at its base in the west that commonly truncates any Pleistocene or older deposits below it ((Figure 73); BGS Marr Bank Quaternary Geology sheet). The reflector becomes discontinuous eastwards, rendering the formation acoustically indistinguishable from the upper part of the Coal Pit Formation into which it locally grades laterally (BGS Devil's Hole Quaternary Geology sheet). This basal reflector represents a surface of marine planation or deposition which dips from 60 m below mean sea level in the south-west to more than 100 m in the north-east, probably as a result of tectonic subsidence and isostatic adjustment (Holmes, 1977).
On sparker and boomer records, the formation has an acoustic signature that varies from amorphous to parallel bedded, or displays groups of inclined reflectors resembling the large-scale internal cross-bedding of sand bars (Stoker et al., 1985; BGS Marr Bank Quaternary Geology sheet). The formation has been sampled in a number of boreholes, and although including muddy sediments, especially towards the north-west (Holmes, 1977), it is generally formed of sands of varying grain sizes and degrees of sorting (Stoker et al., 1985). Gravelly layers contain a variety of lithic clasts of Scottish provenance, and wood fragments and clay balls occur sporadically. No dinoflagellate cysts have been recovered from the formation. A poor ostracod fauna and a moderately abundant population of foraminifera (Thomson, 1978) indicate that the shallow waters in which the formation was deposited were high-boreal to arctic in temperature, and inner shelf to estuarine in character.
Thomson (1978) and Thomson and Eden (1977) inferred a Weichselian age for the Marr Bank Formation (then termed the Marr Bank beds) because the acoustic base appeared to be at the same level as the base of the Wee Bankie Formation (Figure 73). The western edge of the Marr Bank Formation is commonly a low scarp, probably an ice-contact face, and lateral passage by interdigitation between the two formations has been argued on seismostratigraphical grounds by both Stoker et al. (1985) and Stewart (1991).
The Wee Bankie Formation (Stoker et al., 1985) occurs near the east coast of Scotland (Figure 72), where it has a sheet-like geometry but an uneven, ridged, upper surface. It is up to 40 m thick. On sparker records, point-source reflectors can give a chaotic acoustic response pattern. Its lithology is of stiff, variably matrix-dominated polymictic diamicton with some interbeds of sand, pebbly sand and silty clay; there is a lack of significant in-situ fauna or flora, although reworked biological material is common. The formation may have originated as a basal till, perhaps in part as a lodgement till, and is assumed to be of late Weichselian age by correlation both with the Marr Bank Formation and onshore tills (Goste ow and Browne, 1986; Paterson et al., 1981). The eastern boundary of the Wee Bankie Formation in the Forth Approaches could mark the maximum extent of late Weichselian grounded ice (Stewart, 1991), as inferred by Thomson and Eden (1977).
The Bolders Bank Formation forms the south-eastward extension of the Wee Bankie Formation to the south of 56°N and east of 0° (Figure 67) and (Figure 72); BGS Swallow Hole Quaternary Geology sheet). The formation is typically not more than 1 m thick, but locally attains 40 m in an over-deepened trough. It typically has a chaotic to poorly ordered internal seismic: reflector configuration, and is characterised by reddish to greyish brown, stiff, massive diamictons in which the pebble content tends to diminish eastwards" (Gatliff)
"The Bolders Bank Formation characteristically consists of reddish to greyish brown, stiff diamictons that are generally massive but in places possess distinct, commonly arenaceous layering, and deformational structures. The majority of its pebbles, of which chalk is the most conspicuous component, are derived from the sedimentary rocks of eastern England. The pebble content tends to diminish eastwards. In general, the formation is less than 5 m thick, and commonly less than 1 m is preserved in deep-water areas west of the Dogger Bank, although to the east of Lincolnshire it may be 15 to 20 m thick (BGS Spurn Quaternary Geology sheet). " ("The geology of the southern North Sea. United Kingdom offshore regional report" By T D J Cameron et al)
The full sequence of deposits offshore from England and Scotland consist of just the four formations that are dated to the period after 60,000BP. They are the Swatchway Formation, the Marr Bank Formation, the Wee Bankie Formation, and the Bolders Bank Formation. This group are blocked at the north by the meltwater runoff derived from the collapsing Shetland icecap, and retained at the south by rising seabed around the south coast of Dogger Bank.
There is little evidence of ice cover on the Marr Bank Formations, which were laid in conditions that were markedly warmer than might be expected in the middle of an ice age:-
"Fluvial sand and gravel exposed in quarries near Tattershall contain evidence of a short but marked mid-Devensian climatic amelioration (Girling, 1974). An organic silt bed within involuted gravel overlying the Ipswichian peat has yielded insects indicative of a high-latitude continental tundra environment, but a slightly higher bed contains a thermophilous insect fauna—some taxa of which are now confined to southern Europe—implying summer temperatures at least as warm as those of southern England today. Radiocarbon dates from these deposits and correlatives elsewhere in England show that this warm interval, the initial phase of the Upton Warren Interstadial Complex, occurred around 43 000 years ago. It was too brief for the climatic improvement to be reflected in the flora. The overlying sand and gravel in the Tattershall area are appreciably cryoturbated and contain numerous remains of mammoth (Mammuthus primigenius), woolly rhinoceros (Coelodonta antiquatis), bison, reindeer and other tundra-favouring mammals.” (Eastern England from the Tees to The Wash. British regional geology, by Sir Peter Kent)
The Orkney Vole was present in the Orkney archipelago in the human Neolithic period, but not present in the remainder of Britain at any time. An explanation for the vole being in Orkney but not Britain may be as follows:- The shores of these inland seas were warm enough that , even when the last glacial maximum began to develop, they were favourable to the survival of the small rodent, and other prehistoric animals.
In addition to this though, during the cold period of the last glacial maximum, all of eastern Britain from Dover to Orkney was ice covered. The Orkney Vole would have been restricted in its range to the shores of the inland seas, and unable to make landfall on mainland Britain due to the snow cover.
Summary
The North Sea, in the post-glacial period, was divided into two parts during the closing events of the glaciation. A ridge of land linked Dogger Bank to the Atlantic Ocean, dividing the North Sea between the Norwegian Channel at the east, and a sequence of features against the east coast of Britain.
At the north of the sequence the Shetland icecap is collapsing, dumping glacial sediment, in the form of the Capeshore Formation, which formed a barrier, enclosing lagoons from the Swatchway Formation towards the south.
There is no evidence that the Marr Bank Formation was ever iced over. Its' low altitude would have tended to maintain low temperatures at ground level.
The decreasing pebble content eastward in the Bolders Bank Formation also rather suggests that overflowing meltwater from the Marr Bank Formation was running around the south coast of Dogger Bank during, and after, the deglaciation of the British ice sheets. This would support the theory that there was containment for any lagoons , including the Marr Bank Formation lagoon at the end of the ice age.
The Inundation of the North Sea
The ridge of land that separated the Marr Bank Lagoon from the Norwegian Channel has been removed as a result of rising sea levels.
The date at which this happened may be found in a report of excavations of raised beaches on the Norwegian Coast that was carried out by Lisbeth Prøsch-Danielsen (Sea-level studies along the coast of south-western Norway, by Lisbeth Prøsch-Danielsen) At the "Stavanger Airport Sola Site"
Fig, 11. The Rogaland coast of Norway (Prøsch-Danielsen)
Danielsen demonstrated that there were a couple of transgressive rises in sea level after the end of the last ice age. She also found an anomalous event which she could give no explanation for, in which an alder tree was ripped from its roots at a site in Rogaland, near Stavanger. “The layer consisted of organic and sand (mica schist) lenses sandwiched on top of each other, dipping towards the east. Between layer 3 and layer 4 there is an erosional angular unconformity. Also roots of black alder (Alnus glutinosa) (identified by Aud Simonsen) penetrating into the upper part of the marine gyttja have been cut of discordantly. A piece of root has been dated to 4320±70 yr BP (ß-171185).”. The date was calibrated to just after 3000BC, and I interpret that the roots may have been stripped of their tree by a very local tsunami wave, rolling across the Norwegian Channel.
Similar results to those at Stavanger airport Sola site, were found at other archaeological sites in Rogaland, where tsunami-type deposits are found.
Talking to Bård Amundsen, a journalist for sciencenorway.no , Svein Vatsvåg Nielsen and his German colleague Martin Hinz say:- "We now consider it certain that the sea level rise was brief. It also seems likely that a tsunami struck the Stone Age people in Rogaland – and probably also Vest-Agder – sometime between 3445 and 3396 BCE,"
Nielsen and Hinz suspect that it may have been the Garth tsunami, named after the Garth Loch lake in Shetland.
Jåsund 2 is the name archaeologists have given to one of the most well-known Stone Age settlements in Rogaland. It is located on the Tananger Peninsula in Sola municipality, just outside Stavanger. Evidence suggests Jåsund 2 was flooded by a wave possibly as high as 10 metres.
They have also discovered evidence of the Garth tsunami, which may have hit southwestern Norway 5,400 years ago, on Shetland. The sediments left behind by this tsunami are similar to those from the Storegga tsunami. In this case, the wave run-up on land is over 10 metres.
Håkon Glørstad, who first proposed the tsunami theory in the 1990s, is pleased that Nielsen and Hinz have now confirmed it in a new scientific article. "At the time, much of what we uncovered in archaeological digs in Rogaland didn’t make sense," Glørstad tells sciencenorway.no. "But I realised something dramatic must have happened, something involving water, that was unique to Rogaland. It had to be a fairly local phenomenon," he says. (Amundsen, edited)
Fig. 12. The bathymetry of the Norwegian Channel
The position of this coastal region of Norway which makes it likely to have been affected by such a wave is exactly opposite the narrowest neck of land between the Witch Ground and the Norwegian Channel.
Fig. 14, A section along the length of the Norwegian Channel
A dump of sedimentary material is to be found in the floor of the Norwegian Channel at this location, and is likely to have been caught up with the collapse of the side wall of the channel. It is recorded in a section along the channel surveyed by Hans Petter Sejrup in "Quaternary of the Norwegian Channel: glaciation History and palaeoceanography”
When the tidal waters of the Atlantic reached into the non-tidal flow of the Norwegian Channel they rapidly stripped the seabed of most of the northern North Sea of over 50 metre depth of deposits.
At the same time similar quantities of structural land-based sediments are likely to have been removed by marine erosion from the locations that link Scotland to Orkney and Shetland.
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The last ice age is not well understood at present, but the research that has been necessary to plot a path by which the European Vole transformed itself into the Orkney Vole required a series of shifts in my perception of Quaternary landscapes.
One of the significant understandings that i needed to develop, in order to make sense of our landscape, and the geology that we live amongst was a novel idea about the formation of valleys . This i have defined in "Ice-sheetBritain".
"Interpretations" looks over the fine detail of the sediments on the floor of the North Sea, using BGS, and other primary sources to re-interpret the story of features there.
In addition, the better understanding of Ice Age Britain is attempted in "Ice Age Beginnings"
"Archaeology in the North Sea"
I was not just looking to understand what happened to the Orkney Vole. There is also the problem that people are supposed to have had boats in prehistory, at a time when there is little evidence of their existence. To plot the route by which people would have walked between Holland and Norfolk, I wrote "Walkable Land in the North Sea" which charts the existence of a land bridge allowing flora, fauna, and people, to commute between Europe and Britain.
The existence of land between Holland and Norfolk makes it easier to explain that a similar corridor of land would have linked Orkney to Scotland. This also explains how huge monuments could have been constructed by Neolithic people in a sparsely populated Orcadian environment.
Using archaeological evidence "Neolithic Migration to Orkney" tracks the occupation of Orkney from Neolithic to Bronze Age. It describes how the more sophisticated structures there, including Skara Brae, and the Ness of Brodgar, were the creation of small groups of people who became stranded on the islands when the link that joined them to Scotland was washed away by rising sea levels.
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All views and opinions expressed are my own. Many assertions stated have not been thoroughly justified here, simply because space prohibits it in this format. The evidence exists elsewhere to demonstrate that these assertions are, at their core, valid.
Jeffery Nicholls
South Ronaldsay
Orkney
Jiffynorm@yahoo.co.uk
Adjacent to the Marr Bank Formation is the Wee Bankie Formation.
"The Wee Bankie Formation (Stoker et al., 1985) occurs near the east coast of Scotland, where it has a sheet-like geometry but an uneven, ridged, upper surface. It is up to 40 m thick. On sparker records, point-source reflectors can give a chaotic acoustic response pattern. Its lithology is of stiff, variably matrix-dominated polymictic diamicton with some interbeds of sand, pebbly sand and silty clay; there is a lack of significant in-situ fauna or flora, although reworked biological material is common." (Gatliff)
The Marr Bank Formation merges with the Wee Bankie Formation, which then merges with the Bolders Bank Formation.
The Bolders Bank Formation also merges with the Dogger Bank.
"The Bolders Bank Formation characteristically consists of reddish to greyish brown, stiff diamictons that are generally massive but in places possess distinct, commonly arenaceous layering, and deformational structures. The majority of its pebbles, of which chalk is the most conspicuous component, are derived from the sedimentary rocks of eastern England. The pebble content tends to diminish eastwards. In general, the formation is less than 5 m thick, and commonly less than 1 m is preserved in deep-water areas west of the Dogger Bank, although to the east of Lincolnshire it may be 15 to 20 m thick (BGS Spurn Quaternary Geology sheet). " (Cameron)
Section of the sea floor in the southern North Sea. It shows that the base of the Bolders Bank Formation is 45 metres below sea level.
Referring back to Figure 8, the base of the Marr Bank Formation, which is continuous with the Bolders Bank Formation, is 90 to 100 metres below sea level.
"The majority of its pebbles, of which chalk is the most conspicuous component, are derived from the sedimentary rocks of eastern England. The pebble content tends to diminish eastwards."
This description of the Bolders Bank Formation in which pebble content is diminishing away from the English coast suggests that, as sand would move readily in flowing water than pebbles, the water was flowing in an easterly direction around the southern end of Dogger Bank.
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