A palynological investigation of diamictons from the Britons Lane Borehole, north Norfolk

The ten samples studied produced extremely abundant palynofloras of high diversity with a wide overall stratigraphical range. Typically the assemblages contain Carboniferous (mainly Westphalian spores), Permo-Triassic, Jurassic (largely miospores), Cretaceous (chiefly Chalk Group dinoflagellate cysts), Palaeogene (Eocene), Quaternary and non-age diagnostic taxa. The most persistent and common forms are Carboniferous, Jurassic and Late Cretaceous. Many grains are not age diagnostic forms. These associations are generally typical of the Tills of North Norfolk and area significant contribution to the database. Certain familiar patterns were observed, for example while a wide range of Carboniferous ages were observed, spores of Westphalian age tend to dominate. The Carboniferous input is most likely to have been derived from the Northumberland-Durham area of north-east England and/or southern Scotland. Permo-Triassic input was extremely rare and probably reflects the organic-lean nature of much of this succession in the UK. The provenance of this is likely to be the Yorkshire Basin or the East Midlands Shelf. The consistently abundant associations of Jurassic miospores indicate significant input of Early and Mid-Late Jurassic strata; the Yorkshire Basin and/or the East Midlands Shelf are the most likely sources of these forms. When Jurassic marine microplankton are present, early Toarcian and Kimmeridgian dinoflagellate cysts tend to dominate. This is probably related to the mechanically tenacious and organic-rich, nature of lithological units of these ages. These units are relatively resistant to weathering as compared to other, softer units. This means that the eroded fragments of early Toarcian mudstones have the propensity to travel long distances while retaining their organic contents. Additionally, the Kimmeridge Clay Formation outcrops extensively in and around the Wash area (Cox and Gallois, 1981). Characteristically Early Cretaceous marker are either entirely absent or are present in low proportions. This is somewhat surprising as the Early Cretaceous succession of eastern England is known to be highly palyniferous. Late Cretaceous dinoflagellate cysts derived from the Chalk Group are present throughout in varying proportions. They occur in the normal grey/brown diamictons in relatively low numbers, however in the highly chalky diamictons they are unsurprisingly dominant. The Chalk Group dinoflagellate cyst floras are deemed to be of Campanian-Maastrichtian age based on the occurrences of key dinoflagellate cyst taxa. There appears to have been virtually no mixing of the Chalk Group input and indicates that the derivation is entirely from local sources of Upper Chalk. Other chalky diamictons from north Norfolk have yielded similar Campanian and Maastrichtian markers. Most of the Palaeogene dinoflagellate cysts tend to be of Eocene age, which is consistent with previous studies. The majority of the relatively sparse Quaternary spores, pollen and dinoflagellate cysts are not environmentally or biostratigraphically significant.
It is possible to subdivide this succession based on the palynofloras. The grey diamicton between 32.00 and 23.00 yields small proportions of Carboniferous spores and Chalk Group dinoflagellate cysts, moderate levels of Jurassic palynomorphs and consistently relatively high numbers of Quaternary spores/pollen. The light grey diamicton at 18.00 m is dominated by Quaternary spores and pollen; Carboniferous, Jurassic and Late Cretaceous species are rare. The highly chalky diamicton between 17.00-19.90 m and 22.95 and 21.50 m is overwhelmingly dominated by abundant, diverse and well preserved dinoflagellate cysts characteristic of the local Upper Chalk. Other elements are relatively sparse due to the diluting effect of the Chalk Group input. The grey/brown diamicton between 6.50 and 2.70 m is characterised by the highest proportions of Carboniferous spores and Jurassic palynomorphs in this succession. Late Cretaceous and Eocene dinoflagellate cysts and Quaternary palynomorphs are consistently relatively sparse.