The Red Crag Formation is a geological formation in England. It outcrops in south-eastern Suffolk and north-eastern Essex. The name derives from its iron-stained reddish colour and crag which is an East Anglian word for shells. 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. This bay would have been subjected to enlargement and contraction brought about by transgressions and regressions driven by the 40,000-year Milankovitch cycles .
8-432: The sediment in the outcrops mainly consists of coarse-grained and shelly sands that were deposited in sand waves ( megaripples ) that migrated parallel to the shore in a south-westward direction. The most common fossils are bivalves and gastropods that were often worn by the abrasive environment. The most extensive exposure is found at Bawdsey Cliff , which is designated a Site of Special Scientific Interest (SSSI); here
16-404: A laminae similar to caternary and sinuous ripples. Linguoid ripples generate an angle to the flow as well as downstream. Linguoid ripples have a random shape rather than a "W" shape, as described in the catenary description. Lunate ripples, meaning crescent shaped ripples, are exactly like linguoid ripples except that the stoss sides are curved rather than the lee slope. All other features are
24-625: A segment of time from about 3.3 to 2.5 mya . It is considered that the Red Crag at Walton-on-the–Naze is the oldest and that it was deposited in only a few decades at some time between 2.9 and 2.6 mya. This has led to the UK stratigraphic stage name Waltonian , which is usually correlated with the final Pliocene Reuverian Stage in the Netherlands. There are difficulties in reconciling how the Red Crag equates with international chronological stages. In particular,
32-483: A width of around 2 kilometres (1.2 miles) of Crag is exposed. At the coastline by Walton-on-the-Naze, remains of megalodon were found. The Red Crag Formation at depth in eastern Suffolk clearly has one member, the Sizewell Member , a coarse shelly sand with thin beds of clay and silt. It was interpreted as having been deposited in large scale sand waves where the sea bed was deeper. The overlying Thorpeness Member ,
40-501: The flow as well as downstream. These laminae are also formed by the unidirectional current. [REDACTED] Catenary ripples generate cross-laminae that are curvy but have a unidirectional swoop. They show a pattern similar to what a repeated "W" would look like. Like the sinuous ripples, this form of ripple is created by unidirectional flow with the dip at an angle to the flow as well as downstream. [REDACTED] Linguoid ripples have lee slope surfaces that are curved generating
48-563: The lower flow regime ) and indicate agitation by water ( current or waves ) or directly by wind . [REDACTED] Straight ripples generate cross-laminae that all dip in the same direction, and lie in the same plane. These forms of ripples are constructed by unidirectional flow of the current. [REDACTED] Sinuous ripples generate cross-laminae that are curvy. They show a pattern of curving up and down as shown in picture. Sinuous ripples produce trough cross lamination. All laminae formed under this type of ripple dip at an angle to
56-457: 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. It can also be difficult to separate the Red Crag from the overlying Norwich Crag Formation. 51°59′58″N 1°25′16″E / 51.9994°N 1.4211°E / 51.9994; 1.4211 Megaripple In geology , ripple marks are sedimentary structures (i.e., bedforms of
64-541: Was provisionally assigned to the Red Crag based on its lithology but there is more evidence to suggest that it is part of the Norwich Crag Formation . 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. According to the British Geological Survey , the Red Crag sits within
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