It is part of the Crag Group, a series of notably marine strata which belong to a period when Britain was connected to continental Europe by the Weald–Artois Anticline, and the area in which the Crag Group was deposited was a tidally dominated marine bay.

[1] This bay would have been subjected to enlargement and contraction brought about by transgressions and regressions driven by the 40,000-year Milankovitch cycles.

[1] The most extensive exposure is found at Bawdsey Cliff, which is designated a Site of Special Scientific Interest (SSSI);[4] here a width of around 2 kilometres (1.2 miles) of Crag is exposed.

It has been proposed that the Red Crag started in the late Pliocene and to have possibly extended up into the early Pleistocene, but there is disagreement on more precise dating.

In particular, the start and end dates are poorly defined due to the general paucity of age-diagnostic stratigraphic indicators and the fragmentary nature of the geology.