Wednesday, 24 September 2014

Of chalk and ice: the white cliffs of Louth in the Palaeolithic era

The previous post in 'The History of the Louth Region' discussed the earliest evidence for human activity in eastern Lincolnshire, with a particular focus on the handaxes found in Welton le Wold quarry, which were probably used by pre- or ancestral Neanderthal hunters in the Hoxnian Interglacial around 400,000 years ago. This second posting continues the tale, discussing the period after the Hoxnian Interglacial through to the end of the last glacial period, nearly 15,000 years ago.

The climatic fluctuations of the last 800,000 years, with the present warm-period being stage 1 on the right-hand side of the graph (drawn by C. R. Green, based on Gibbard & Cohen). The climatic changes are based on the Marine Oxygen Isotope Record, with the Marine Isotope Stage numbering shown: cold stages are assigned even MIS numbers, warm stages odd ones. The Anglian glaciation is MIS 12, the Hoxnian Interglacial is MIS 11, and the warm Ipswichian Interglacial is MIS 5e. 

It is likely that the Louth region—like Britain as a whole—was largely abandoned by humans after the Hoxnian Interglacial ended, about 374,000 years ago. At that point, the global climate grew significantly colder as part of its regular oscillation between hot and cold periods over the past million years or so (see the above graph; the post-Hoxnian cold stage is MIS 10). Quite what happened after the climate warmed once more, nearly 40,000 years later, is difficult to say for sure, as we lack further, well-stratified Palaeolithic artefacts of the kind found at Welton. However, there have been other finds of Lower Palaeolithic handaxes from the Louth region. These have been made in Legbourne, Maidenwell, and Calcethope & Kelstern parishes, with the handaxe found in the latter parish believed to date, typologically, from around 280,000 years ago. As such, it is probable that early humans did continue to occasionally visit the region after the Hoxnian Interglacial, at least when the climate was warm enough to render the area reasonably habitable to them.

A Lower Palaeolithic handaxe from Calcethorpe & Kelstern (PAS)

Needless to say, such early humans—probably ancestral Neanderthals—are likely to have only been infrequent visitors to the region, and this irregular visitation probably ceased entirely around 191,000 years ago, when Britain once again entered a glacial epoch. The MIS 6 cold period has been recently defined as the Tottenhill Glaciation and appears to have been especially severe, with ice sheets once more flowing right over the top of the Wolds (as they did during the Anglian glaciation, 478,000–424,000 years ago) to cover the entire Louth region. In addition to probably eroding the Wolds further, these ice sheets are thought to have deposited the Welton Till on the Wolds as they melted and probably the Calcethorpe Till too ('glacial till', or boulder clay, is the sediment left behind by a glacier as it melts or retreats).

Lower Palaeolithic finds from the Louth region, set against a map of the modern region (drawn by C. R. Green, contains Ordnance Survey data © Crown copyright and database right 2011). Any evidence for Lower Palaeolithic human activity east of the line running northwest-southeast is irretrievably lost, as this was eroded away by the sea around 115,000 years ago, during the Ipswichian Interglacial. The line marks the Ipswichian cliff-edge, which would have had a flint beach at its foot. As sea-levels fell again after this time, the exposed wave-cut platform become a flat plain.

The subsequent Ipswichian Interglacial (MIS 5e), beginning around 130,000 years ago, was even more significant for this region. This period was one of the warmest in recent geological history, and Britain from Yorkshire southwards was inhabited by exotic fauna including lions, hyenas, hippopotamuses, elephants and rhinoceroses—although humans appear not to have made it across to Britain from the Continent before Britain became an island due to rising sea-levels after the end of the Tottenhill Glaciation (MIS 6). It was also the era in which around half of the Palaeolithic landscape of our region disappeared. As was noted in the previous post, the Wolds originally extended well to the east of the current coastline, but in the Ipswichian Interglacial the sea gradually eroded this landscape away until it reached the modern eastern edge of the Wolds. The last glaciation, which saw ice sheets reach the Lincolnshire Wolds around 17,000 years ago, has covered the resultant Ipswichian landscape with glacial till (see below), but around 115,000 years ago the edge of the Wolds would have been marked by a line of white cliffs with a flinty beach at its foot and a wave-cut chalk platform extending eastwards from this: the present-day Louth hospital and cemetery stand roughly on this cliff-edge, and the Lincolnshire Marshes now lie above the ancient wave-cut platform.

Schematic cross-section of eastern Lincolnshire in the Palaeolithic period, showing how the Wolds once extended to the present coastline and beyond, and how they were eroded away around 115,000 years ago. From the landscape evolution of eastern Lincolnshire (drawn by C. R. Green).

The approximate coastline of Lincolnshire and Yorkshire around 115,000 years ago during the Ipswichian Interglacial; the current coastline is shown as a grey line (drawn by C. R. Green, based on IECS, 1994 with modifications).

After this period of warm temperatures and relatively high sea-levels came to an end, there was an erratic decline into the next cold epoch, MIS 4 (71,000–57,000 years ago). During this new cold period, both Britain and the Louth region probably experienced a climate close to that now found in northern Scandinavia, with temperatures dropping to about –20°C in winter months. Only after MIS 4 ended, around 57,000 years ago, did humans return to Britain once more. These new inhabitants were true Neanderthals, Homo neanderthalensis, and they were joined around 35,000 years ago by our own species of human, Homo sapiens. The period in which this recolonisation of Britain and Lincolnshire took place is sometimes termed a 'failed interglacial'—the climate then was unstable and swung from relatively mild to cold, with significant amounts of water remaining locked up in the ice sheets so that sea-levels remained as much as 80 metres lower than today. As a result, the Ipswichian wave-cut platform below the white cliffs of the Wolds would have been exposed as a dry, flat plain sloping gently eastwards in this epoch.

Schematic cross-section of eastern Lincolnshire, showing how the Ipswichian wave-cut platform became a dry, flat plain that was later scoured by the advance of the Late Devensian ice sheet to the Lincolnshire Wolds. From the landscape evolution of eastern Lincolnshire (drawn by C. R. Green).

Whilst it is likely that the flat plain to the east of the Wolds saw human activity as a result of the recolonisation of Britain, the evidence that might be used to confirm this has long-since been destroyed. The cause of this loss was the Late Devensian glaciation. This final 'Ice Age' before the current warm Holocene epoch saw Britain emptied of people once more approximately 25,000 years ago, with mean annual temperatures dropping as low as –6 or –7°C and midwinter temperatures of around –40°C, colder than parts of Siberia today! Radiocarbon dating indicates that the Late Devensian ice sheet arrived in Holderness around 22,000 years ago and and reached the Lincolnshire Wolds sometime around 17 ka BP, where it rose to a maximum of about 114 metres above the current sea-level (Ordnance Datum). At the same time, the development of these massive ice sheets both here and elsewhere led to global sea-levels dropping to approximately –120 metres (–395 feet) OD. As a direct result, the bottom of the North Sea became dry land as far north as Shetland, although both this plain and those parts of modern Britain that remained ice-free formed an uninhabitable arctic desert at the height of the Ice Age.

Lincolnshire and the surrounding region c. 17,000 years ago (drawn by C. R. Green, based on a map for Origins of Louth and Clark et al, 2004). The present-day coastline is shown as a grey line; areas covered by the ice sheet are in white, areas covered by probable or possible glacial lakes are in blue, and ice- and water-free land is in green. It should be noted that the large glacial lake to the south of the Wash is speculative and its existence has been disputed. No Vale of York ice is shown, as this had probably retreated north by this point.

This glaciation had a number of important effects on the Louth region. First, the advance of the massive ice sheet to the Lincolnshire Wolds would have scoured the flat plain that stretched eastwards from the sea-cliff edge of the Wolds and destroyed any archaeological remains that might have existed there. Second, the ice sheet prevented the rivers in this part of Britain draining properly, so that massive lakes such as ‘Lake Humber’ built up, inundating vast swathes of land (see the map, above). A similar effect at the local level led to the creation of Hubbard's Hills gorge—the blocking of the Hallington valley by decaying ice and its thick deposits of till meant that the water that would have drained along this valley from the springtime snowmelt on the Wolds backed up to form a large lake covering Hallington and Raithby, which then overflowed northwards across the chalk ridge. The resulting waterfall off the ridge into the Welton valley rapidly cut a steep-sided channel—Hubbard's Hills—backwards through the chalk over the course of perhaps as little as two or three hundred years, which thereafter acted as the new permanent channel for the Hallington and Raithby/Tathwell Becks.

The landscape of the Louth area at the time the Hubbard's Hills gorge was cut by water draining from a glacial lake covering Hallington and Raithby (drawn by C. R. Green, after Robinson, 2007; contains Ordnance Survey data © Crown copyright and database right 2014). Glacial ice is depicted as white, glacial moraine as brown and the glacial lake and meltwater river is shown in blue.

Third and finally, the ice sheet retreated northwards to leave the flat plain east of the Lincolnshire Wolds buried under a thick layer of glacial till—this undulating till forms the present Middle Marsh and underlies the Outmarsh, whilst also extended out beyond the current coastline onto the then-exposed North Sea plain, which began to slowly flood in the north around Scotland as sea-levels rose due to the glacial melt. Needless to say, the next post in the current series will be concerned with the early history of this newly created landscape in the eastern part of the Louth region, examining how it developed after the ice-sheet retreated and how the rising sea-levels of the present Holocene interglacial affected this region over the subsequent millennia.

Schematic cross-section of eastern Lincolnshire, showing how the post-Ipswichian flat plain east of the Wolds and the former sea-cliff were buried beneath a thick layer of glacial till as the ice-sheet melted. From the landscape evolution of eastern Lincolnshire (drawn by C. R. Green).

Possible stages in the retreat of the Devensian ice at the end of the last glaciation, with the maximum extent of the glaciation shown as the unbroken line (drawn by C. R. Green after IECS, 1994).

Next: North Somercotes, the drowning of Doggerland, & the Mesolithic Louth region (#3)
Previous: The Welton le Wold handaxes & the earliest human activity in the Louth region (#1)

Post Index of  'The History of the Louth Region'

'The History of the Louth Region' is based in part on The Origins of Louth: Archaeology and History in East Lincolnshire, 400,000 BC–AD 1086, which offers additional details and analysis, along with suggested further reading. The content of this page, including any original illustrations, is Copyright © Caitlin R. Green, 2014, All Rights Reserved, and should not be used without permission.