The visible geology of Hampshire in southern England broadly comprises a folded succession of sedimentary rocks dating from the Cretaceous and Palaeogene periods – mostly gentle folding in the north, more complex folding along the south coast. The lower (early) Cretaceous rocks are sandstones and mudstones whilst those of the upper (late) Cretaceous are the various formations that comprise the Chalk Group and give rise to the county's downlands. Overlying these rocks are the less consolidated Palaeogene clays, sands, gravels and silts of the Lambeth, Thames and Bracklesham Groups which characterise the Hampshire Basin.
Hampshire’s geological ‘basement’ was probably formed in the early Devonian or late Silurian periods, then folded during the later Devonian and early Permian periods.[1] Two faults have driven much of its later geological development. The county’s near-surface geology was built up in three stages: first, when layers of clay, limestone and mudstone were laid down in and around Jurassic seas; then, when sands and clays washed off the London Platform early in the Cretaceous period; and finally, as the sea rose again and covered southern England to a considerable depth, great thicknesses of chalk were laid down. This was later shaped in two further stages; first the Alpine orogeny, which inverted the London Platform to become a London Basin, then the Anglian glaciation. The Anglian and later glaciations moved the course of the Thames (southwards) and the Solent (eastwards),[2] and during this time the rivers that run between them were opened by melting glacial outwash, bringing sands, clays, gravels and some iron down these rivers.
Oil has been extracted from Triassic strata, and natural gas from the Great Oolite, at Humbly Grove[3] and oil continues to be drawn from the Great Oolite at more than eighteen smaller wells near Horndean, Stockbridge and Andover.[4]