Walkable Land in the North Sea

Series Title:- The Orkney Riddle

6/29

Blog Title:- Walkable Land in the North Sea

There is an area of shallow sea that links Holland with East Anglia. It is likely that this passage would have provided walkable land between England and Holland until a time when Neolithic people were exploring Northern Europe. 

The bathymetry chart above indicates this broad area of shallow water joining Lincolnshire, and Norfolk, in England to Holland. Elsewhere, to the south of this region deep water gullies would have prevented any migration by animals, people, or plants.

The Norfolk Banks (above) are a series of ridges on the floor of the North Sea, beside the Norfolk coast.

Detailed chart, above shows bathymetry of ridges and troughs of the Norfolk

 

The location of this section of the Norfolk Banks, above, is indicated on the plan above it.

The main features of the Norfolk Banks that can be seen in the plan and section are as follows 

1- the high ridges of these banks are parallel to each other. 

2- the ridges rest on a flat surface which is about 35 metres below sea level here.

3- the ridges are also parallel to Bathymetric lows, gullies that are also linear, and run immediately beside the ridges. These gullies are cut into the flat surface upon which the ridges rest.

4- the gullies lead off in a southwestern direction, attaching to , and becoming part of the Lobourg Channel, a deep water channel in the middle of the Dover Strait. 

5- the Norfolk Banks have not moved in the last 100 years, and are unlikely to have ever moved. 

6-at nearly 2 kilometres wide these features are massive. 

My assumption is that the peaks of these ridges were once part of a land surface that joined Holland to East Anglia. Subsequent sea level rise here has partially removed seabed sediments, leaving these ridge Formations, the Norfolk Banks. 

The Lobourg Channel which merges with the Norfolk Banks is a deep gully in the floor of the Dover Strait. It connects with the Norfolk Banks at the North and with similar features in the floor of the English Channel between Dover and Southampton. 

The gullies between the banks of the Norfolk Banks are continuous with the gullies in the Dover Strait, (the Lobourg Channel, below) and also with gullies in the English Channel which have been dated to 21,200BP.

 

This date , 21,200BP, is generally accepted to be close to the coldest point in the last ice age, and the start of the process of deglaciation of ice sheets over the northern hemisphere, and the group of gullies represents the southern limit of the ice sheet over Britain that melted at that date. 

The chart of the southern North Sea, above, indicates a plausible sketch of contours for the likely depth of ice as it lay on Kent, East Anglia, the Dover Strait, and southern North Sea before 21,200BP.

The contours are for 100, 50, and for 5 metres of ice depth.

The actual weight of ice on the 100 metre contour line would have been 90 tons per square metre. The weight of ice on the 50 metre contour would have been 45 tonnes per square metre, and the 5 metre contour, 4.5 tonnes per square metre.

The effect of the thick ice on the Dover Strait would have been to compress pre-existing  sediments there. This compression of sediments squeezed out all the air and water held in them, causing a condition which geologists describe as "overconsolidated". From personal experience I can say that this overconsolidated material is as hard as hell!.

This means that sediments against the Norfolk coast would have been a rock hard material, while the sediment under the areas closest to the Dutch coastline would have remained relatively a great deal softer.

After 21,000BP the surface of Britain thawed, and the ice sheet retreated. By about 15,000BP the ice sheets were mainly restricted to the Highlands of England and Scotland, and the walkable land between Norfolk and Holland permitted the migration of herbs and trees, and animals to move north across the whole of the country.

At 7000BC the British Isles were forested, and in Orkney "A charred hazel nutshell from the mound at Long Howe produced a radiocarbon date (SUERC-15587 7900±35 BP 7030–6640 cal bc 95% confidence)." Also in Orkney there were Willow, Birch, Heather, hawthorn, Pignut. Plum/Cherry charcoal scraps present in the hearths of people living in the late 4th millennium BC. 

Herbivores, followed the plant life, while carnivores followed the herbivores.

Those animals that are known to have made this journey and to have visited Britain in around 5000BC, are recorded in "The Mesolithic mammal fauna of Great Britain", by Maroo and Yalden.

 

....and in Orkney Animal bones radiocarbon dated to the Neolithic period include:-- sheep, wild pig, auroch, Red Deer, possible wolf, dog, pine marten, wood mouse, and Orkney Vole. 

In "New evidence on the earliest domesticated animals and possible small‑scale husbandry in Atlantic NW Europe" by Philippe Crombé et al, the authors provide evidence that people in Neolithic Europe were developing forms of agriculture, including herding or shepherding of domesticated animals into the late 5th millennium.

 

The growth of herder communities in Northern Europe, described above neatly merges, in timescale, with the plan of Neolithic movement in Britain in the 4th millennium BC, as outlined by Alasdair Whittle , in "Whittle, A., Bayliss, A. & Healy, F. 2011. Gathering Time:Dating the early Neolithic enclosures of southern Britainand Ireland." See image below...

 

Crombe dates the presence of people in the Swifterbant as follows:- "It was the start of a totally new lifeway which probably would culminate into a fully agrarian society in the course of the second half of the 5th millennium cal BC, around 4000 cal BC at the latest."

He also suggests that the Neolithic people who crossed from northern Europe to south east England were animal herders, and the presence of both sheep and dogs in Neolithic Orkney rather confirms that theory. In his discussion he also offers that there was a transition away from hunter-gatherer behaviour occurring, but this is not borne out by the evidence from the middens of the Knap of Howar in Orkney where it is clear from animal bones, bird bones, and molluscs found in them that the people who lived there would eat anything that came to hand.

At a date during the 4th millennium BC sea-level rose sufficiently that it would erode soft sedimentary deposits against the Dutch coast of the North Sea. Hard deposits that had been overconsolidated by the ice sheet over England were not eroded, but remained as the ridges of the Norfolk Banks.

The woodland that had grown on this land between Norfolk and Holland was then washed away as the waters of the Atlantic Ocean pushed through to the newly developing North Sea. 

As the English Channel was scoured out ,only the compacted ridges of the Norfolk Banks remained in the floor of the southern North Sea. 

*

Recent research into the Mesolithic landscape of Doggerland is published in:-

Multi-Proxy Characterisation of the Storegga Tsunami and Its Impact on the Early Holocene Landscapes of the Southern North Sea. By Vincent Gaffney et al 

And....

"Early colonization before inundation consistent with northern glacial refugia in Southern Doggerland revealed by sedimentary ancient DNA" by Robin Allaby et al. 

The Southern River System in Doggerland

"To understand the late glacial and early Holocene environment of Southern Doggerland, the Europe’s Lost Frontiers (ELF) team undertook seismic surveys and recovery of marine sediment samples for environmental and geochemical analysis between 2016 and 2019.

Topographical reconstruction of the landscape characterized a river system, the Southern River , suitable to track the environmental changes that occurred from the Late Pleistocene to the period of inundation.

 The Southern River is around 30 km in length with a headwater area to the north close to the limit of the southern-most ice advance . The river system opened into an estuarine mouth in the south between headlands which could have been suitable for human occupation, with likely plentiful freshwater and marine resources available to inhabitants . Recently, on the basis of this topography speculative dredging of the sea floor was under-taken in the estuarine mouth area leading to the discovery of a worked lithic from the early Holocene. Consequently, the Southern River is an area of particular interest with respect to its potential to support early Mesolithic occupation. By integrating sedimentological and sedaDNA data, we distinguish secure samples in which sedaDNA derives predominantly from a local source from those in which the signal derives from influxed and reworked sediments. Secure taxonomic profiles show the transition of the landscape from one supporting temperate trees from before a time contemporaneous to the Allerød, to an inundated environment dominated by sea grass (Zostera ). The presence of thermophilous tree species too early and too far north given tree migration rates to have originated from classic glacial refugia, signal the existence of closer refugia in North-West Europe across glacial advances."

The southern river location is shown in the plan above, north of Norfolk. 

Just one boring core is examined in close detail in "Multi-Proxy Characterisation of the Storegga Tsunami......", ELF001A.

The depth of seafloor from which the core ELF001A is drilled is 24.70 metres below sealevel. The core is 3.5 metres deep. The lowest sediments (ELF001A-7) are dark grey finely laminated silts and fine sands from 3.5 to 1.52 metres depth below the sea floor. 

At 1.52 m there is a very sharp contact boundary suggestive of an erosional event, and from approximately 1.50m to 1.10 m the core suggests that the material is from a different origin to the local sediment supply.

The environment prior to this dramatic event, and recorded in the underlying stratum Unit ELF001A-7, was an estuarine mudflat with organisms consistent with brackish water nearby, including marine eelgrass and mostly freshwater pondweed as well as "Frog's Bit" and Arum. 

This mudflat was surrounded by an area of meadow influenced flora, including buttercups, orchids, mallows and asterids, with a possible open woodland close by.

Between 150 metres and 110 metres deep there is a grey, medium grain sand (ELF001A-6) with freshly broken shell fragments, whole shells and small stones (up to 3 cm in size). This unit dates to 8.04ka BP ± 0.43 ka. It is "characterized by an abrupt change in both microfossil and sedaDNA evidence. There is an absence of diatoms and pollen; an increase in outer estuarine or marine taxa of ostracods and foraminifera; the appearance of fractured molluscan shells from different and incompatible habitats including sublittoral, intertidal and brackish species; and the sudden and significant influx of all woody taxa." At 1.19 m this sequence fines to a dark grey silty sand that is moderately compact (unit ELF001A-5). Dated to 8.22ka BP ± 0.43 

(ELF001A-4) At 1.09 metres depth another sharp contact is encountered after which dark grey very well laminated silty sands once again show horizontal laminations of 2–4 mm thickness. The base of unit ELF001A-4 at 105 cm depth in core is dated to 7.16ka BP ± 0.50 ka, and at 1.00m depth to 6.03ka BP ± 0.22 ka. "Together, these proxies indicate a violent event that brought with it the terrestrially derived debris of surrounding woodland."

"After the event in units ELF001A-4 to ELF001A-1, the foraminifera and ostracod signal indicate a return to estuarine mudflats with a greater abundance of marine taxa such as Ammonia batavus indicating a more established marine signal than prior to the event. The sedaDNA signal also indicates estuarine taxa such as Zostera (seagrass) and a meadow influence, although the biogenomic mass appears greatly reduced suggesting more distant proximity of the flora. A faunal signal considerably weaker than the floral was present throughout the core, but shows a significant elevation in count towards the top units, indicating the presence of rodents and larger animals such as bear, boar and cloven hoofed ruminants, as well as higher orders of fish (Acanthomorpha, Eupercaria, Osteoglossocephalai)."

(ELF001A-3 to ELF001A-1) From 0.90 m to the surface grey to yellow medium sand is loosely consolidatedand, and shows evidence of bioturbation.

*

Two abrupt changes in the environment in the location of ELF001A are marked in the evidence presented here. These events occur at ELF001A-6, and at ELF001A-4. Dating of these events are 8000BP, and 7000BP to 6000BP, respectively 

In ELF001A-6 there is "an abrupt change in both microfossil and sedaDNA evidence". This change is dated to just after 8000BP , and is coincident with the rising of sea levels which drowned peat bogs in several other locations in the Southern Valley area. (ELF 020, ELF007, ELF009, ELF002, ELF005, ELF003, ELF 034, ELF 019, ELF 031)

Between 7000BP and 6000BP, in ELF001A-4, "a violent event that brought with it the terrestrially derived debris of surrounding woodland" occurred. 

This event coincides with significant additional sediment supply (of 2 to 3 metres thickness) to three other locations in the Southern River Valley (ELF 042, ELF 054, and ELF 059).

Sea level at 7000BP to 6000BP had risen to 5 to 7 metres below present levels, and the event that occurred between those dates is described in the report as "a violent event that brought with it the terrestrially derived debris of surrounding woodland"

Put simply, .like this, the two events found in the evidence are likely to be a two-part process in which the Atlantic Ocean, in the English Channel, and the North Sea began to nibble at land that occupied the coastal region of Lincolnshire and Norfolk which may have extended across the southern border of the North Sea. 

Breaking through from the English Channel to the North Sea may well have been a "violent event" and the timing of the second event is exact to the period in which we know that people were still moving between Britain and Europe. 

Hitherto that movement has always been attributed to boats and amphibious transport in spite of the lack of actual evidence for seagoing vehicles at the time in prehistory. 

Understanding that land that has been removed from the earth’s surface is very difficult to verify as ever having existed at all, the foregoing explanation is probably the best evidence for land between Europe and Neolithic Britain that is possible.

*

Finally,  the dates of the violent event interpreted at the Southern River Valley,  7000BP to 6000BP, and possibly later, find some agreement with strontium dating from Whitwell Cairn. 

The source is:- The Isotopic Evidence for Human Movement into Central England during the Early Neolithic by SAMANTHA NEIL CHRIS SCARRE, JANE EVANS , JANET MONTGOMERY. 

In their conclusions they write:-

"The majority of the individuals buried in the Whitwell cairn have strontium isotope ratios higher than 0.7170. High values are rare in human enamel in burials found inBritain (Evans et al., 2012), and all current evidence suggests that such values do not originate from the biosphere of central England (Evans et al., 2018).

Based on present understanding of the methodology employed and the way in which strontium isotope ratios within human enamel are derived, the results suggest that these individuals obtained the majority of their dietary resources from a geographical area in which high 87Sr/86Sr values are routinely bioavailable: for example, on granite or ancient basement gneisses. 

British bioavailable values higher than 0.7170 have been recorded in plants growing in Scotland and on granites in Dartmoor in south-west England. In these regions, however, the appearance of Neolithic features does not significantly pre-date the Whitwell burials: current modelling of radiocarbon dates suggests that Neolithic material culture and practices only began to appear in southwestern England and Scotland in the decades around 3800 cal BC (Bayliss et al.,2011: 736, 822–24, 835–40). Strontium isotope ratios higher than 0.7170, comparable to those exhibited by the group at Whitwell, have been recorded in the biosphere on the Armorican Massif in northwestern France (Négrel & Pauwels, 2004;Willmes et al., 2013, 2018). 

Recent analysis of Early Neolithic material culture found within Britain has been used to argue that there may have been population mobility between this area and Britain from approximately 3800 cal BC (Pioffet,2015; see also Sheridan, 2010a, 2010b).

Strontium isotope analysis cannot, on its own, determine the geographical source of the 87Sr/86Sr values found within human enamel at Whitwell: competing arguments for links to different source areas must, therefore, be evaluated on the basis of present archaeological and radiocarbon dating evidence. Based on current understanding of British biosphere 87Sr/86Sr data, the results do, however, provide evidence for individual human mobility over long distances during the thirty-eighth century BC, a period associated with the rapid spread of new cultural practices across Britain (Bayliss et al., 2011: 801)."

*

If i have successfully suggested that Neolithic people walked from Holland to Norfolk without getting their feet wet, it makes sense to reconsider whether the same could not be true for land between Caithness and Orkney.

For a more detailed discussion of the effect of the last ice age, see Ice Sheet Britain 

Next blog:- "Swifterbant Culture"

Back to the beginning of the Orkney Riddle

Sources

"The geology of the southern North Sea. United Kingdom offshore regional report" By T D J Cameron, A Crosby, P S Balson, D H Jeffery, G K Lott, J Bulat and D J Harrison

New evidence on the earliest domesticated animals and possible small‑scale husbandry in Atlantic NW Europe" by Philippe Crombé et al

*

All views and opinions expressed are my own.

Jeffery Nicholls 

South Ronaldsay 

Orkney 

Jiffynorm@yahoo.co.uk