Boundaries of the Pleistocene

Boswell Reference Boswell ¹ has dealt fully with the question of where to draw the Plio-Pleistocene boundary in East Anglia. Criteria used to determine the boundary include the presence of a strati-graphical break, marked increase of the proportion of northern forms of marine molluscs, indicative of a refrigeration of the climate, and the first arrival of elephant and horse. Such criteria seem best satisfied by placing the boundary between the Coralline and Red Crags. The correlation of this boundary with the continental Plio-Pleistocene boundary has been summarized by Voorthuysen.Reference Voorthuysen ²

The Pleistocene-Holocene (Recent) boundary may be taken at the transition between the Late- and Post-glacial Periods, between Zones III and IV of the north-west European pollen zonation. The youngest Pleistocene deposits considered here are those of the most recent glaciation in East Anglia, although Late-glacial deposits are known in East Anglia.Reference Tallantire ³

Glacial and Pre-Glacial

Although far-travelled erratics occur in the Crags, the oldest true glacial deposits in East Anglia are the tills of the North Sea Drift. Thus the Pleistocene deposits in East Anglia may be divided broadly into a “glacial” series, including the North Sea Drift and younger deposits, and a “pre-glacial” series, including the Leda-myalis Bed, Cromer Forest Bed Series and older deposits. These terms are naturally of local significance only; what is pre-glacial in East Anglia is not necessarily so on the continent. As the correlations in the table suggest, the early Pleistocene glaciations of the continent Reference Zagwijn ⁴ do not appear to be represented by glacial deposits in East Anglia. Instead there is the extensive sequence of the marine and estuarine Crag deposits. There is not yet sufficient evidence to make any detailed correlation of these deposits with the continental early Pleistocene glacial and interglacial deposits.

Ice Advances

Tills of a number of ice advances have been distinguished in East Anglia. The earliest tills are those of the North Sea Drift, including the Cromer Till and the Norwich Brickearth. It is possible that the tills of this age in north-east Norfolk may have been formed by more than one advance.Reference Solomon ⁵ The direction of movement of the ice which laid down the North Sea Drift, the Cromer Advance,Reference West and Donner ⁶ appears to have been from the north-west. The next ice advance to be distinguished is the Lowestoft Advance,Reference West and Donner ⁶ which deposited Baden-Powell’sReference Baden-Powell ⁷ Lowestoft Till, a chalky boulder clay. Evidence from erratics and stone orientation measurements of this till suggest that the ice which deposited it moved across East Anglia from west to east. An upper chalky boulder clay, the Gipping Till of Baden-Powell Reference Baden-Powell ⁷ is the youngest widespread till-sheet in East Anglia. The till was deposited during the Gipping Advance.Reference West and Donner ⁶ Both erratics and stone orientation measurements suggest a north to south movement for this advance.

There is some evidence of a final ice advance in north Norfolk, where certain features of the landscape described by West Reference West ⁸ suggest a recent, Newer Drift, glaciation, in contrast to the Older Drift formed by the previous ice advances. Possibly this ice advance also deposited the Hunstanton Brown Boulder Clay, supposed by many Reference Solomon ^5, Reference Baden-Powell ⁷ to be younger than the chalky boulder clays.

Interglacials

Professor van der Vlerk Reference Vlerk ⁹ has pointed out that the wealth of information about fauna, flora and climate provided by fossiliferous interglacialFootnote * sediments makes such deposits more significant than glacial deposits for subdividing the Pleistocene. This is certainly true in East Anglia. The classification of the glacial deposits has been simplified by the identification of three distinct richly fossiliferous interglacial horizons, each of which appears to have a characteristic vegetational development. The oldest, the Cromerian, is represented by the Cromer Forest Bed Series. A pollen diagram from this deposit Reference Woldstedt ¹¹ shows a lower coniferous phase, a middle mixed oak forest phase, and an upper coniferous phase, a type of sequence which is indicative of climatic amelioration and then deterioration and is characteristic of interglacial deposits. The pollen diagram differs from those of both the younger interglacial periods in various ways, principally in the low values of Corylus, and from the pollen diagram of the Hoxnian Interglacial in the absence of any quantity of Abies pollen.

In the sense that there are no glacial deposits below the Cromer Forest Bed Series, the deposit may be considered “pre-glacial”. However, the typical interglacial sequence mentioned above, and the fact that early continental glaciations are supposed to have occurred before the Cromerian,Reference Zagwijn ⁴ suggests that the Cromer Forest Bed Series was deposited in an interglacial period.

The middle interglacial horizon, the Hoxnian, includes deposits at Hoxne,Reference West ¹² ClactonReference Pike and Godwin ¹³ and several other sites in East Anglia. The pollen diagrams from this interglacial period are different from those from the earlier and later interglacials, notably in the slow rise of Corylus to a maximum long after the rise to dominance of the mixed oak forest and in the presence of rather high percentages of Abier pollen in the latter part of the interglacial.

The youngest interglacial, the Ipswichian, with deposits at CambridgeReference Walker ¹⁴ and Ipswich,Reference West ¹⁵ gives pollen diagrams with an early high percentage of Corylus, with low values of Alnus and a distinct Carpinus-dominant zone, all features apparently absent from the older interglacials.

Glaciations

If the three interglacial horizons already described are taken as limiting glaciations, then evidence for two, and possibly three, glaciations can be distinguished in East Anglia. The first, the Lowestoft Glaciation,Reference West and Donner ⁶ is between the Cromerian and Hoxnian Interglacials; the second, the Gipping Glaciation,Reference West and Donner ⁶ is between the Hoxnian and Ipswichian Interglacial; a third, later than the Ipswichian Interglacial, is possibly represented by the fresh drift features, and perhaps by the Hunstanton Brown Boulder Clay, of the north Norfolk coast.

Marine Horizons

The “pre-glacial” Pleistocene deposits, confined to the eastern part of East Anglia, are, apart from the freshwater beds of the Cromer Forest Bed Series, predominantly marine and estuarine. Two series of Crag deposits can be distinguished: the Red Crag, and the Icenian Crag, which includes the Norwich Crag, Chillesford Beds and Weybourne Crag. The Red Crag is a shore deposit, while the Icenian Crag is supposed to have been deposited in “a shallow open sea that lay near the estuary of a large northward-flowing river that was probably a forerunner of the Rhine”.Reference Chatwin ¹⁶ Alterations in the conditions of deposition and the changes of sediment type in these Crag deposits suggest changes of relative land- and sea-level during Crag times.Reference Chatwin ¹⁶ These changes are not known in any great detail, but it appears that they were superimposed upon a relative depression of the land, part of the general Pleistocene subsidence in the southern part of the North Sea basin.Reference Voorthuysen ¹⁷

ReidReference Reid ¹⁸ described a middle estuarine bed of the Cromer Forest Bed Series. The exact position of this horizon in the interglacial sequence shown by the pollen diagram is not known. A further comparatively unknown marine deposit is the Leda-myalis Bed, lying above the Cromer Forest Bed Series, but below the glacial deposits.

A series of sands, the Corton Beds of Baden-Powell and Reid Moir,Reference Baden-Powell and Moir ¹⁹ lies between the North Sea Drift and the Lowestoft Till. These sands contain a fauna of marine molluscs described by Baden-Powell.Reference Baden-Powell ²⁰ It is not certain to what extent the fauna is contemporary with the deposit. No organic deposits are known from the interval between the North Sea Drift and the Lowestoft Till, and there appears to be no evidence from the Corton Beds of the kind that shows the Cromerian and Hoxnian deposits to be interglacial and that would merit the characterization of the Corton Beds as interglacial, except in a strictly stratigraphical sense.

A comparison of the pollen diagrams from the interglacial beds at HoxneReference West ¹² and ClactonReference Pike and Godwin ¹³ indicates that the estuarine deposits of the Clacton Channel were formed during a phase of declining warmth within the Hoxnian Interglacial. It appears that during this interglacial relative land- and sea-level changes in East Anglia resulted in a transgression relatively later in the interglacial, compared with the earlier transgression in the Eemian Interglacial.Reference Brelie ²¹

The March Gravels, a marine horizon described by Baden-Powell,Reference Baden-Powell ²² have been tentatively correlated with the Eemian (= Ipswichian) Interglacial.Reference Woldstedt ¹¹ This seems the most probable correlation in view of the fact that these gravels lie in the Fenland basin apparently undisturbed by a glacial advance, and thus later than the latest widespread advance in the Fenland, the Gipping Advance.

SolomonReference Solomon ⁵ described a raised beach deposit beneath Hunstanton Brown Boulder Clay at Morston, on the north Norfolk coast. If this till is of Last Glaciation age, then possibly the raised beach was formed during the Ipswichian Interglacial.

Climate

The increasing proportion of species of northern marine mollusca in the Pleistocene Crags suggests a gradual refrigeration of the climate during their deposition.Reference Boswell ¹ The pollen diagram from the Cromer Forest Bed Series shows an amelioration of the climate from a basal boreal phase to a middle temperate phase, and then a deterioration to an upper boreal phase. The Arctic Freshwater Bed, described by ReidReference Reid ¹⁸ from between the Cromer Forest Bed Series and the North Sea Drift, contains dwarf birch, Betula nana, and an arctic willow, Salix polaris, indicators of cold conditions. The climatic cycle shown by the interglacial deposits at Hoxne has been described by West.Reference West ¹² There is a sequence from cold conditions at the base through a temperate phase back to a cold periglacial climate at the top. A similar sequence is known from the Eemian Interglacial on the continent, but in the Ipswichian deposits only the amelioration of the climate at the beginning of the interglacial at Ipswich,Reference West ¹⁵ and zones somewhat later in the interglacial at Cambridge,Reference Walker ¹⁴ have so far been recorded. A comparison between the pollen diagrams of the Hoxnian and Ipswichian Interglacials suggests that the climate became warmer, and the vegetation more open, during the temperate phase of the latter interglacial.

Indications of a periglacial climate with frozen ground phenomena during the Late Pleistocene are described in the next section.

Periglacial Features

Features indicative of a periglacial climate are abundant in East Anglia. Disturbance of the deposits is frequently seen near the surface in sections in the East Anglian drifts. In the Breckland magnificent stone stripes have been identified by Watt,Reference Watt ²³ and these are often associated with large-scale polygon-type surface patterns. PatersonReference Paterson ²⁴ has given an account of frost phenomena seen in gravels near Cambridge. Periglacial valleys have been described from the eastern part of the Cromer Ridge by West.Reference West ⁸

It is evident that severe periglacial conditions were present in East Anglia at some time later than the Gipping Advance, possibly during the Last Glaciation, since many of these features disturb the deposits of this advance.

Correlations

The correlations with the continental sequence made in the table (p. 215) are those suggested by West Reference West ^{15 ,} Reference West ²⁵ and by various authors in the symposium on Pleistocene correlations between the Netherlands and adjacent areas conducted by van. der Vlerk. ²⁶

Table I