When amateur geologist Samuel Hazzledine Warren was collecting Ice Age fossil mammal bones from gravel pits in the terrace gravels of the River Lea in north-east London at the turn of the 20th century, he discovered peat horizons sandwiched between layers of gravel. These contained plant assemblages characteristic of a cold climate or ‘full glacial’ environment, and are part of the ‘Lea Valley Arctic Bed’. This distinctive vegetation of the Arctic Bed is known as the ‘tundra steppe’, the main habitat of the woolly mammoth.

During the early to mid 20th century Arctic Bed deposits were recorded at a number of sites in the Lea Valley, but the absence of recent discoveries has precluded modern scientific analysis.

One of the key aims of investigation by OA for Cascade Consulting Ltd on behalf of Thames Water at Deephams Sewage Treatment Works, Enfield, has been to locate and investigate similar deposits, described by J F Hayward during development of the site in the 1950s.

Initial work in 2010 comprised desk-based assessment of historical borehole data in order to model the sequence of sediments and predict the likely location of Arctic Bed deposits. In 2011 excavation of a deep pump shaft successfully identified a sequence of organic deposits radiocarbon dated to the period immediately following the Last Glacial Maximum (c 18,000 years BP). Although slightly later than Heyworth’s sequence, in 2015 a series of deep boreholes were drilled to recover core samples suitable for detailed analysis.