Age and relationships of the Chillesford Clay (early Pleistocene: Suffolk, England)

Abstract

The distribution, lithology, palaeontology (pollen and spores, foraminifera molluscs and dinoflagellate cysts), heavy mineral content and palaeomagnetic properties of the Chillesford Clay Member of the Norwich Crag Formation are described, and compared with those of the Easton Bavents Clay that outcrops further north. The Chillesford Clay is a discrete unit forming the top of the marine Plio-Pleistocene sequence between Aldeburgh and Orford, Suffolk; it rests conformably on the Chillesford Sand Pollen spectra are dominated by non-arboreal pollen. Two local pollen assemblage biozones are recognized; the lower is similar to that of the Baventian, and the upper to that of the Pre-Pastonian a . A deterioration in climate from cool oceanic to cold is indicated. Foraminifera assemblages preserved in one sequence suggest a decline from temperate to cool conditions. Restricted mollusc assemblages found in one sequence may signify low temperatures. Dinoflagellate cyst floras differ from those of the Chillesford Sand and Easton Bavents Clay, and in all these deposits suggest warmer conditions than the other biological indicators, although their absence from part of the Chillesford Clay may indicate low temperatures. Heavy mineral suites from the Chillesford Clay, Easton Bavents Clay, Chillesford Sand and Red Crag Formation are similar and are more diverse than those of the overlying fluviatile Middle Pleistocene Kesgrave Formation; thus, the earlier concept of a distinctive mineralogy of the Easton Bavents Clay is refuted. Palaeomagnetic measurements were inconclusive. The Chillesford Clay is interpreted as a temporal correlative of the Easton Bavents Clay. Both deposits are thought to have been deposited in high intertidal conditions during the major marine regression that accompanied transition from the Bramertonian Stage (warm) to the Baventian cold Stage and Pre- Pastonian a cold Substage. This suggests that these two cold stages/substages are more closely related in time than previously thought, and that the relative stratigraphical positions of the Bramertonian and Baventian stages are the reverse of those originally envisaged. The Baventian to Pre-Pastonian a interval probably correlates with the Tiglian C4c Substage of the Netherlands sequence, and should be considered as part of a single cold stage, for which the Baventian has nomenclatural priority.

Integrated chronostratigraphy of the Pliocene-Pleistocene interval and its relation to the regional stratigraphical stages in the southern North Sea region

“…Gibbard et al (1991) focussed more on regional interpretations and correlations of the Pliocene and Pleistocene time interval. Until now chronostratigraphical interpretations of Late Pliocene to Early Pleistocene sediments widely refer to the subdivision of the Dutch and British 'Quaternary' (Fig.…”

“…The British stages are also primarily based on pollen studies (West, 1961;Beck et al, 1972). Both schemes were further developed with respect to faunal and floral data and correlated by Gibbard et al (1991) (Fig. 2) to the Netherlands scheme.…”

The sedimentology and palaeoecology of the Westleton Member of the Norwich Crag Formation (Early Pleistocene) at Thorington, Suffolk, England

“…Both Hey (1967) and West (1980) suggested that the deposits may have formed under the influence of glaciation, on the basis of exotic minerals introduced from Britain and/or Scandinavia, although this has been questioned in later studies (e.g. Zalasiewicz et al 1991). Hey (1982) concluded that the gravels of the Norwich Crag Formation may have been supplemented by material introduced by both the ancestral Thames and a precursor to the River Trent, whilst Burger (pers.…”

“…The Norwich Crag Formation comprises fine-to medium-grained, well-sorted, micaceous sands with a maximum total thickness of 40 m (Hamblin, 1992). and Zalasiewicz et al (1991) recognized four stratigraphical units within the Norwich Crag Formation: the Chillesford Sand; the overlying Easton Bavents Clay and Chillesford Clay, which are geographically separated clay units thought to be of the same age; and the Westleton Beds (Prestwich, 1871), which are wellsorted, clast-to matrix-supported gravels dominated by well-rounded, high-sphericity, chattermarked flint pebbles and cobbles (Hey, 1967).…”

“…The deposits are characterized by a temperate mixed forest flora (West, 1961), although vertebrate remains imply that open woodland was also present (Stuart, 1982). The overlying Easton Bavents Clay and Chillesford Clay members were analysed by Zalasiewicz et al (1991), who concluded that they Geol. Mag.…”