A palynological investigation of the Oxford Clay Formation and Quaternary succession of Northamptonshire : sheets 171 and 186

The samples examined in this study are from an area of Northamptonshire where the youngest unit of the solid geology is the Peterborough Member (Oxford Clay Formation). This, and the overlying Quaternary sediments, were studied. The Quaternary succession comprises till overlain by chalky till. In the Biggin Grange 1 Borehole, possible glaciofluvial sands and clays are intercalated between the till and chalky till. The in situ Peterborough Member samples from the Biggin Grange 1 Borehole are probably referable to the Jason Zone. All the samples of the Quaternary units have similar palynomorph signatures. These are characterised by low proportions of Carboniferous and early Toarcian palynomorphs and extremely high levels of Callovian (Oxford Clay Formation) palynomorphs. However, the till in the Biggin Grange 1 borehole lacks early Toarcian palynomorphs. Of the allochthonous Oxford Clay Formation palynomorphs, the majority are interpreted as having been derived from the Peterborough Member. The chalky till samples are, surprisingly, entirely devoid of Late Cretaceous palynomorphs. However, the sands/clays and chalky till of the Biggin Grange 1 borehole and the till of the Woodford borehole contain late Callovian dinoflagellate cysts, that indicate input from the Stewartby Member. The dominance of the Peterborough Member (Oxford Clay Formation) indicates that the majority of the material in the Quaternary units was derived locally. However, the early Toarcian material is more far-travelled. The closest in situ early Toarcian strata in this area is to the north-west in the Welland valley. It is also possible that this material was sourced from further north, possibly from the Cleveland Basin. Early Toarcian palynomorphs are well known from the tills of East Anglia. It is possible that the tenacious lithologies which characterise strata of this age are especially conducive to the preservation of their palynofloras during glacial reworking processes. The Carboniferous spores may have been sourced from in situ outcrops or from allochthonous Carboniferous spores that have been reworked into the Oxford Clay Formation. If the Carboniferous material, which is most likely to be all Westphalian, was sourced directly, the closest outcrops are the West Midlands coalfield, again to the north-west. However, it is also possible that they were sourced from coalfields further north. In conclusion, the non-local Carboniferous and early Toarcian palynomorphs are consistent with ice movement from the north-west.