Compton Bay on the west coast of the Isle of Wight, faces towards the prevailing southwesterly winds. It is thus a place of rapid erosion and coastal retreat. The strata are all Cretaceous in this area, with the major units being the Lower Cretaceous Wealden Group, and the Chalk. Between the two there is Lower Greensand and Gault and Upper Greensand, well-exposed in the centre of Compton Bay.

There is a car park at Compton Chine (SZ368852), near Compton Farm, and this used to be used for easy access to the bay. However, recent cliff erosion has steepened the cliff. At many places on the Isle of Wight turned chines or access valleys into hanging valleys with steep cliffs at the foot. Access here will depend upon the state of the cliff at the time, and tide and weather conditions. It may or often may not be safe to descend here. It it not then access is possible, at least at the time of writing, at Shippards Chine (SZ378841) further to the southeast near Compton Grange (do not confuse Shippards Chine, near Brook, with Sheppards Chine, much further southeast and near Atherfield Point).

LOCATION:

Compton Bay - Coastal Recession at Shippards Chine

The southwest coast of the Isle of Wight has long been an area of major erosion. It is only about 10,000 years ago, at the end of the Pleistocene, since the valley of the English Channel was dry land. The rising sea level with wave erosion has destroyed large areas of soft Wealden strata. A substantial land area of Wealden clay and sands is now reduced to the relatively small southern part of the Isle of Wight. In due course, thousands of years ahead (a short time geologically, of course), Vectis will disappear, probably with the central Chalk ridge surviving last as some residual Chalk stacks and small islands. In the near future (in geological terms) the Military Road will be destroyed in part, and indeed some has already been lost at Blackgang. Shippards Chine shown above, is a place where the Military Road is very close to the cliffs; it might be broken through in merely a few decades (or even less). Such coastal retreat is quite normal, and fortunately there are very few buildings close to the cliff top in this region.

Compare the two photographs, which are of the same locality. The earlier one is from 2008 and the later from 2011. There has been a change and more of the car has been lost by the date of the second image.

LOCALITIES

Compton Bay - Cretaceous Cliffs - View from Afton Down
(western Isle of Wight, near Brook)

Go also to: Geology of the Isle of Wight - General - Compton Bay

LOCALITIES

Compton Bay - Cliff Views

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Compton Bay is an important locality because it shows a section from the Wealden Group, Wessex Formation up into the Lower Greensand, the Gault and Upper Greensand, and then to the Lower Chalk. Parts of it, though, are obscured by landslide debris. The exposure is good because this locality, facing southwest, is subjected to major wave erosion. There is considerable contrast between the resistance to erosion of the Chalk, relatively harder, and the softer Wealden, LGS, Gault and UGS strata. The result of this is the Chalk cliff remains more or less in place, but with some retreat, while the cliffs of older Cretaceous strata move rapidly landward. Presumably at one time the Greensands etc were exposed as a cliff at High Down near the Needles and have been eroded back about 6.5 km.

The cliff exposures in Compton Bay can be accessed by walking at low tide from Shippards Chine. In the past it was possible to descend to the shore direclty at Compton Chine. Cliff erosion means that may not be possible now. If walking from Shippards Chine take care not to be cut off by a rising tide.

LOCATION:

Compton Bay - Lower-Greensand

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LOCATION:

Compton Bay continued: Lower Greensand Succession

The following is a modified, and slightly updated, version of an old log of the succession of the Lower Greensand at Compton Bay, based on White (1921), turn based on Bristow et al. (1889). This log is still valid, although the original thickness figures are given in old-fashioned feet and inches (1 metre equals 3.28 feet, or 1 foot equals 0.3048m; in round figures 3 feet equals 1 metre, and this will serve because the original figures will not usually be accurate to less than one inch.)

Brown sand with a 3 inch pebble-band at the base, containing rounded quartzite pebbles up to three-quarters of an inch in diameter, some phosphatic pebbles, and many pieces of wood. Cylindrical phosphate nodules also occur. [The base of this bed is the major, Late Cimmerian unconformity. At Sandown the equivalent pebble bed contains reworked Kimmeridge Clay fossils. In the northern Isle of Wight, as shown in diagrams above this bed rests unconformably on Upper Jurassic strata.]

Sandrock Series 81 ft., 6 inches [Aptian]

Blue Clay .. 2 ft 6 ins.

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Pebble band with quartzites etc. - 0 to 3 ins.
Grey and greenish sand, with a layer of pyritised wood 8 and a half feet from the top, and scattered fragments near the top, about 12 and a half ft.
Pebble band as above, 6 inches.
Thickness of the above, including the two pebbles beds - 13 ft.
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Bright yellow sand with a ferruginous seam at the base - 10 ft.

Clean white sand and blue clay, interbedded in wavy laminae [rippled? flaser or linsen?], and producing copious chalybeate springs [ferruginous, sulphate-rich springs resulting from oxidation of pyrite]. ("foliated series") [of the old literature].

Ferruginous Sands 251 ft, 6.5 inches
[in part - oolitic iron ore, probably berthierine sands]

LOCATION:

Lower Greensand - Ferruginous Sand

LOCATION

Compton Bay - Chalk

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[END OF COMPTON BAY SECTION]

Hanover Point Area (Compton Grange or Shippard's Chine to Brook Bay)

Hannover Point

The Pine Raft

The "Pine Raft" at Hanover Point near Brook consists of gymnosperm tree remains that can be seen at low tide. They come from a Wealden plant bed. The tree remains are either compressed or in solid uncompressed form, as in the case of tree trunk shown above. Examples like this one have been impregnated by calcite at a very early stage, and thus have avoided compaction.

LOCALITIES:

Sheppard's Chine to Barnes High (northwest of Atherfield Point)

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