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Summary accounts of the Anglian in Essex, usually within a wider context, are given by
Bridgland (1988, 1994, 1995a), Gibbard (1994, 1995a), Sumbler et al. (1996) and Lucy (1999).
The most recent terminology for the stratigraphy is given by Gibbard (1999) and Lewis (1999).
A summary stratigraphy is given in Table 1.
Climatic change and geological activity in the Anglian
Whilst oxygen isotope variation gives a good record of temperature change (Fig. 1), knowledge
of precipitation is more difficult to determine. Unfortunately pollen-bearing sediments,
indicating the nature of the contemporaneous vegetation and hence climate, are rare in the cold
stages. The environments of deposition are too vigorous, particularly the flood gravels of
braided rivers and the tills laid down by glaciers, for such sediments to be preserved. However,
certain sediments and structures do enable to us go some way to inferring the detail of the
climate.
Prior to the Anglian, northern and central Essex had been covered by vast spreads of gravel, the
Kesgrave Formation (Whiteman, 1992), laid down by an early Thames which flowed from the
Reading area, past Watford, St Albans, Hertford/Ware, Chelmsford, Colchester, into Suffolk and
Norfolk (Fig. 2). Over time, the river migrated southeastwards, so that by the Anglian it was
flowing across the present coast in the Clacton area. The gravels formed flat surfaces (terraces)
at various heights, getting lower to the south in a series of steps, as the river downcut. The
surfaces of the terraces were protected to a certain extent by clay-enriched soils (the Valley
Farm and Barham Soils) (Whiteman & Kemp, 1990) that had developed on them and the
vegetation they supported. The terraces and their associated soils are now largely buried by later
deposits. This early Thames received a number of south bank tributaries several of which
originated in Kent (Green et al., 1982; Bridgland, 1988, 1999). Of particular importance was an
extended Medway which deposited the High-level East Essex Gravels through the Rayleigh
Hill, Canewdon and Bradwell and was confluent with the early Thames in the Clacton area
(Bridgland 1988)
Tundra desert phase
As the climate deteriorated at the end of the Cromerian, vegetation declined and an open, largely
unprotected, landscape developed. At Newney Green and Broomfield, sand wedges (Plate 9)
cutting through the buried terrace (Kesgrave Formation) surfaces and soils give important
climatic information. The sand (the Broomfield Member) could also be seen in places to overlie
the soil and originally must have formed a thin blanket over much of the landscape. The texture
of, and the heavy minerals in, the sand indicate that it was wind-derived, mostly from the
exposed terrace surfaces, but there was a significant increase of weatherable heavy minerals,
notably epidote, garnet, chlorite, apatite and collophane (Catt, in Rose et ai, 1978) which can be
matched with the outwash and tills of the Anglian glaciers.
For a wedge to form, mean annual sub-zero temperatures are required. At such temperatures the
ground can shrink and crack open as the groundwater loses volume (as do most materials at
lower temperatures). Initially on freezing, water actually expands, by up to 9%, but a further
sharp drop of temperature or a prolonged period below -22°C leads to contraction. Given the
widespread occurrence of the wedges in Essex and East Anglia, the latter is thought to have
been the case. For the sand to accumulate in the wedges, the surrounding land surface has to be
free of vegetation, to allow it to be picked up by the wind and moved freely. Also there cannot be
Essex Naturalist (New Series) 16 (1999)