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.