Geology Site Account

Site name: Bradwell Gravel Quarry, near Braintree

Grid reference: TL 819 215

Brief description of site:

Bradwell Quarry is a working gravel quarry with fine sections through Kesgrave Sands and Gravels (Thames gravel) and boulder clay (till). The quarry has been the source of a large number of fossils from the till during successive organised visits by members of the Essex Rock and Mineral Society, mostly during the 1990s.

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Details

The quarry works the Kesgrave Sands and Gravels (Kesgrave Formation) which were laid down during the early Ice Age by the River Thames when it flowed through north Essex and Suffolk and out across what is now the southern North Sea to become a tributary of the Rhine. The gravel is mostly flint but also contains exotic pebbles of rocks from far upstream, some of which are ignimbrite (a volcanic rock) from North Wales.

Above the Kesgrave Formation is a thickness of boulder clay, or till, which was laid down on top of these gravels about 450,000 years ago by an ice sheet during the Anglian glaciation, the most severe cold period of the whole of the Ice Age (Allen 1999).

Beneath the Kesgrave Formation is London Clay bedrock which is exposed in drainage trenches in the quarry floor. These have yielded fossils, mostly of pyritised wood.

Bradwell Quarry. The photograph shows the Kesgrave Gravel being worked after the overburden of till has been removed. London Clay bedrock forms the floor of the quarry. Photo: G.Lucy