Geology of Hampshire

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The geology of Hampshire in southern England broadly comprises a gently folded succession of sedimentary rocks dating from the Cretaceous and Palaeogene periods. The lower (early) Cretaceous rocks are sandstones and mudstones whilst those of the upper (late) Cretaceous are the various formations which 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.

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Hampshire Basin

In the south, along the coast, soft Eocene and Oligocene clays and gravels form low flat terrain, the Hampshire Basin. Protected from sea erosion by the Isle of Purbeck, Dorset, and the Isle of Wight, this land supports heathland and woodland habitats, a large area of which form part of the New Forest.

Much of the coastal landscape of the Hampshire Basin results from sea level rise in the Flandrian (after the last ice age) some 6000 years BP. There are several large estuaries and rias, notably the 12 mile long Southampton Water and the large convoluted Portsmouth Harbour. The Solent, which separates the Isle of Wight from the coast of Hampshire, is itself a flooded river valley, further erosion having broken the remaining chalk link with the mainland.

Chalk Downs

In the centre and north of the county the substrate is the chalk of the Hampshire Downs and the South Downs. These are high hills with steep slopes where they border the clays to the south. The downland supports a calcareous grassland habitat, important for wild flowers and insects, as well as arable agriculture. The hills dip steeply forming a scarp onto the Kennet valley to the north, and dip gently to the south. The highest point in the county is Pilot Hill, which reaches the height of 286m/938 ft. The rivers Test and Itchen flow from the downland through green valleys, both supporting trout and other wildlife.

A series of east-west trending folds in the chalk to the north of the Hampshire Basin is controlled by faults in the underlying Jurassic strata. From south to north these are the Winchester-East Meon Anticline, the Winchester-King's Somborne Syncline/Alderbury - Mottisfont Syncline, the Stockbridge Anticline and the Micheldever Syncline. [1] The Winchester-East Meon Anticline in particular gives rise to many hills including Yew Hill, Compton Down, Oliver's Battery, Magdalen (Morn) Hill, Chilcomb Down, Cheesefoot Head, Telegraph Hill, Deacon Hill, Twyford Down, St. Catherine's Hill, Beacon Hill, Old Winchester Hill and Henwood Down. [2] [3] [4]

Around the chalk margins to the north are the Pewsey-Kingsclere Anticline and to the south the Dean Hill Anticline, Portsdown Anticline, Forest of Bere Syncline and Chichester Syncline.

Further north, beyond the downs, the landscape is again lowland clay and gravel heathland, though the north is generally greener and more diverse than the south.

See also

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The Winchester-East Meon Anticline is one of a series of parallel east–west trending folds in the Cretaceous chalk of Hampshire. It lies at the western end of the South Downs, immediately to the north of the Hampshire Basin and south-east of Salisbury Plain.

The Winchester-King's Somborne Syncline is one of a series of parallel east-west trending folds in the Cretaceous chalk of Hampshire. It lies at the western end of the South Downs, immediately to the north of the Winchester-East Meon Anticline and east of Salisbury Plain.

The Stockbridge Anticline is one of a series of parallel east-west trending folds in the Cretaceous chalk of Hampshire. It lies at the western end of the South Downs, immediately to the north of the Winchester-King's Somborne Syncline and east of Salisbury Plain.

The Micheldever Syncline is one of a series of parallel east-west trending folds in the Cretaceous chalk of Hampshire. It lies at the western end of the South Downs, immediately to the north of the Stockbridge Anticline and east of Salisbury Plain.

The Dean Hill Anticline is an east-west trending fold in the Cretaceous chalk of Hampshire, England. It lies immediately to the north of the Hampshire Basin and south of Salisbury Plain.

The Alderbury-Mottisfont Syncline is an east–west trending fold in the Cretaceous chalk of Hampshire. It lies to the north of the Dean Hill Anticline and south of Salisbury Plain.

The geology of West Sussex in southeast England comprises a succession of sedimentary rocks of Cretaceous age overlain in the south by sediments of Palaeogene age. The sequence of strata from both periods consists of a variety of sandstones, mudstones, siltstones and limestones. These sediments were deposited within the Hampshire and Weald basins. Erosion subsequent to large scale but gentle folding associated with the Alpine Orogeny has resulted in the present outcrop pattern across the county, dominated by the north facing chalk scarp of the South Downs. The bedrock is overlain by a suite of Quaternary deposits of varied origin. Parts of both the bedrock and these superficial deposits have been worked for a variety of minerals for use in construction, industry and agriculture.

The geology of the South Downs National Park in South East England comprises a gently folded succession of sedimentary rocks from the Cretaceous and early Palaeogene periods overlain in places by a range of superficial deposits from the last 2.6 million years. Whereas the South Downs are formed from the Late Cretaceous age chalk, the South Downs National Park extends into the Weald to the north of the range and thereby includes older rock strata dating from the Early Cretaceous including sandstones and mudstones. The youngest solid rocks are found on the southern fringes of the National Park in the eastern extension of the Hampshire Basin and include sand, silt and clay deposited during the Palaeocene and Eocene epochs.

References

  1. ↑ Booth, K.A. (2002). Geology of the Winchester district - a brief explanation of the geological map. British Geological Survey. ISBN   0-85272-429-2.
  2. ↑ Winchester (Map). 1:50000. British Geological Survey England and Wales. British Geological Survey. 2002. ISBN   0-7518-3340-1.
  3. ↑ Alresford (Map). 1:50000. British Geological Survey England and Wales. British Geological Survey. 1999. ISBN   0-7518-3250-2.
  4. ↑ Fareham (Map). 1:50000. British Geological Survey England and Wales. British Geological Survey. 1998. ISBN   0-7518-3167-0.
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