Glaucony from the Eocene of the Isle of Wight (southern UK): implications for basin analysis and sequence-stratigraphic interpretation

Abstract

The Lower-Middle Eocene sequence of the Hampshire Basin, which includes an alternation of sands, silts and clays, interpreted as fluvial to open-marine deposits, is exposed at two locations on the western (Alum Bay) and eastern (Whitecliff Bay) margin of the Isle of Wight. Glaucony is encountered throughout the study units: sand-clay alternations of lagoonal origin and estuarine channel-fill sands include less than 10% of predominantly poorly evolved, allochthonous glaucony; shelf silts and sands generally comprise more than 20% of evolved, mostly autochthonous glaucony. Vertical changes in maturity of glaucony confirm the trend predicted by recent models, indicating an overall upward increase in the transgressive systems tracts and decrease in the highstand systems tracts, with maximum values in coincidence with the condensed sections, where a remarkable peak in glaucony concentration is invariably recorded. Comparison of glaucony characteristics at different sites of depositional sequences shows a slight increase in maturity and abundance from the proximal to the distal areas. This lateral tendency is interpreted to reflect more suitable conditions for glauconitization in open-marine environments than in shallow waters. Despite documented intrasequential variability of glaucony characteristics, glaucony assemblages from distinct depositional sequences may be generally identified on the basis of more pronounced differences in maturity. Consequently, glaucony attributes can be used as an index for characterization of third-order sedimentary cycles.