On the clay mineralogy of upper Eocene and Oligocene sediments in the Hampshire Basin

Abstract

The upper Eocene and Oligocene sediments on the Isle of Wight and adjacent mainland have been sampled and their clay mineral composition determined semi-quantitatively by X-ray diffraction. Smectite, illite and kaolinite are major components and are thought to have been mainly derived from the extensive areas of lower Eocene sediments partly surrounding the depositional basin. The clear division into western kaolinite/illite and eastern smectite/illite/kaolinite/chlorite provinces that existed during the lower Eocene did not persist in the upper Eocene and Oligocene. Neoformed illite, probably developed in calcareous lakes, resulted in a higher average illite content for upper Eocene and Oligocene sediments than for the lower Eocene source materials. In contrast to sediments of about this age in the Paris Basin, authigenic sepiolite, palygorskite and smectite do not occur in the Hampshire Basin.