The geochemistry and mineralogy of sediments of the Oxford clay and Kellaways formation from Southern England (Winterborne Kingston and Warlingham boreholes)

Abstract

Seventy-eight samples of the Oxford Clay and Kellaways Formations from the Warlingham Borehole (W.B.) in Surrey and sixty-three from the Winterborne Kingston Borehole (W.K.B.) in Dorset were investigated for both their geochemical and mineralogical properties. Well crystallized smectile attributed to air-fall volcanic ash occurs in the sediments of the (W.K.B.), whereas the sediments of the (W.B.) contain non-expanding mixed-laver clays. Illite and kaolinite in the (W.K.B.) sediments show a better crystailinity than the same two minerals in the (W.B.) sediments. Enriched abundances of kaolinite and chlorite in the (W.K.B.) sediments are related to the significant contribution of the igneous and low-grade metamorphic rocks of the 'Cornubian Massif', whereas enhanced abundances of degraded illite associated with a comparatively less crystalline kaolinite and non-expanding mixed-layer clays in the (W.B.) sediments point to a major contribution of re-cycled material supplied by the sedimentary rocks of Palaeozoic age in the 'East Anglian Massif'.Ten major and nineteen trace elements were analysed by X-ray spectrometry in the bulk rock and clay fraction samples of both boreholes. Sediments of the (W.K.B.), on the whole, contain enriched abundances of Fe903, CaO, Na?0, P205, S, Corg, Sr, Fe`2, Fe-3, Cr, Mn, 7.n, Pb, \i and 1{20', whereas the (W.B.) showed enrichment in Si02, T102, A1?03i K20, MgO, Ba, La, Cc, Y, Zr and Nb. There were also considerable differences in chemistry within the stratigraphic horizons represented in each borehole, and between the horizons in each borehole. Characteristic clement associations were found for different clay minerals, carbonates, sulphides, phosphates and organic carbon plus an adsorbed group possibly related to Fe-Mn oxides/hydroxides coatings.An acid-reducing agent leaching study revealed that most elements in the (W.K.B.) sediments were strongly associated with the lithogenous fraction, whereas in the (W.B.) sediments the strongly lattice-held elements were only Mg, Fe, K, Al, Cu and Cr.In general, sediments of the (W.K.B.) are less mature than those ofthe (W.B.), and experienced relatively stronger reducing conditions. The sediments of the (W.B.) were rich in detrital components and showed diagenetic formation of dolomite (ferroan). The 'Cornubian Massif' to the west and the 'East Anglian Massif' to the north were the provenances for the (W.K.B.) and (W.B.) sediments respectively.

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