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Purfleet Chalk Pits SSSI, , Thurrock District, TQ569786, Site of Special Scientific Interest
Site of Special Scientific Interest designated for the importance of its geology.
Greenlands Quarry at Purfleet (sometimes called Dolphin Pit) is of critical importance for interpreting the sequence of events in the Lower Thames valley during the middle of the Ice Age. Here, sediments are banked up against the northern side of the Purfleet anticline, an east-west ridge formed by a fold in the Chalk strata, and contain a record of three separate periods of early human occupation that makes this site unique in Britain. Greenlands Quarry, and three adjacent disused quarries (Bluelands Quarry, Botany Pit and Esso Pit), have, for this reason, been designated as a Site of Special Scientific Interest (the Purfleet Chalk Pits SSSI).
The area to the north is now drained by the Mar Dyke, a westward-flowing tributary of the present Thames. It has therefore been suggested that the Purfleet deposits are a terrace of the Mar Dyke and not the Thames. This suggestion is supported by bedding structures in the sediments that indicate that they were deposited by a westward-flowing river. However, as a result of evidence gathered over a wider area, geologists have now come to the remarkable conclusion that the Thames did in fact once flow in a westerly direction along the north side of this chalk ridge which accounts for the great width of the Mar Dyke valley at this point. It is now known that from the Hornchurch area the Thames flowed south east until it turned around on itself in the Ockendon area, flowed west along the present Mar Dyke valley to Purfleet where it looped back to resume its eastward course. During the forma-tion of the next terrace of the Thames the river abandoned this loop and took a straighter route that more closely resembles the course that it has today. The Mar Dyke is therefore a minor stream that has only recently occupied this abandoned valley.
The Purfleet sediments are part of the Corbets Tey Formation (a downstream equivalent of the Lynch Hill Terrace of the Thames) and the central part of the sequence was deposited during an interglacial period. Unfortunately the sediments have been almost entirely quarried away and those that remain have largely been destroyed or obscured by new access roads and embankments as the floors of the quarries have been developed. However, a section was created by geologists for research.
At the base of this section is a layer of gravel resting on shattered and disturbed chalk known as ‘coombe rock’, both indicating a cold climate at the time of deposition. This is followed by several layers, mostly of gravel or silty clay, which contain fossils that indicate the much warmer climate of an interglacial stage, at one point implying summer temperatures at least as warm as the present day. The most interesting of these layers is the Greenlands Shell Bed which contains conspicuous shells and also (very rarely) the bones of deer, bison, monkey, beaver and straight-tusked elephant, which together suggest that at that time there was mixed woodland close by. Also found was a single 3 centimetre diameter coprolite (fossilised faeces) of a hyena. Capping the sequence is gravel which may indicate the return of cold conditions.
The sequence of sediments at Purfleet has produced numerous broken flints which are undoubtedly of human workmanship. These artefacts come from three separate layers of gravel and the different styles of workmanship indicate that three distinct Palaeolithic cultures are present. The lowest gravel contains flint flakes that are characteristic of a ‘Clactonian’ industry, a middle gravel contains hand-axes which is characteristic of an ‘Acheulian’ industry, and in the topmost gravel there is evidence of a ‘prepared core’ or ‘Levallois’ industry. This locality was clearly used as a site of occupation by early humans over a long period and is therefore important for establishing the timing of the various phases of early human colonisation of Britain from continental Europe. The lowest gravel is thought to be an upstream equivalent of the gravel at Globe Pit in Grays (see separate site entry) which also contains Clactonian flint tools.
Based on the fossils and other evidence geologists have concluded that the warm climate sediments at Greenlands Quarry were laid down by the Thames during an as yet un-named interglacial stage (provisionally called the ‘Purfleet Interglacial’ after this site) that is thought to be over 280,000 years old and correlated with Oxygen Isotope Stage 9 of the marine record. This means that the older cold climate gravel at the base of the section was deposited during the latter part of the previous glacial stage (Oxygen Isotope Stage 10) and the gravel at the top of the sequence with the early part of the succeeding glacial stage (Oxygen Isotope Stage 8).
For safety and security reasons the Greenlands Quarry section is not accessible to the public and is only accessed via a locked gate in Armor Road. Visits, however, are periodically arranged for organised groups.
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Reference: Bridgland 1994 (p. 218-228), Bridgland et al. 2003, Schreve et al. 2002, Schreve 2004 (p. 49-67), Prosser et al. 2006 (p. 110-111), Clements 2010.
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