By Dr. Ian West,
Romsey, Hampshire
and:
Ocean and Earth Science ,
Faculty of Natural and Environmental Sciences
Southampton University,
Website hosted by iSolutions, Southampton University
Website archived at the
British Library
With some aerial photographs by Alan Holiday
|Home and List of Webpages |Isle of Wight Geological Bibliography |Alum Bay |The Needles - Chalk Stacks |Whitecliff Bay |Brighstone-Bay, Isle of Wight |Solent - Hurst Spit, Barrier Beach, Geomorphology and Rocks.
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| Needles from Alum Bay cliff top | Needles from Alum Bay beach | Compton Bay |
"In examining the natural productions of a country or district, one of the first objects that strikes the attention is that of the geological structure of its surface. What a field this opens for enquiry! What can exceed the interest naturally excited in the mind when it reverts back to ages which have no place in this world's history? Thought itself becomes bewildered by the speculation which oppresses it...
Few spots in Britain of similar size contain more objects of geological interest than the Isle of Wight. It presents the characters of the tertiary formations (the Eocenic period of Lyell), consisting of depositions partly derived from the sea, and containing detritus of various kinds, such as shells and plants, the bones of fish and turtles, of saurians, or animals of the lizard tribe, and also of some extinct mammalia. Teeth of the crocodile and shark are also found in this division, as well as wood and the fruit of some former species of the Cycadeae or Pine tribe.
Immediately below the Tertiary Eocene lies the Cretaceous group, which consists of the marine deposits of former oceans, many of them highly fossiliferous. This series is made up of the two beds of Chalk, Upper and Lower, superimposed on Chalk Marl; then follows the Upper Greensand, with its various strata of Chert, Firestone, Limestone, Freestone etc.; and to this succeeds the argillaceous bedsd of Gault, which again rest upon the Lower Greensand, or Ferruginous sand, as it was formerly called; below which we find the Wealden or Hastings sand, which crops out at various parts of the Island, as at Sandown Bay, and along portions of the south-western coast from Atherfield Bay westward, forming as it were a transition-series between the last-named and the Oolitic formation. "
"The Country of the Iguanodon. .. Whether that country was an Island or a Continent cannot be determined; but that it was diversified by hills and valleys, and irrigated by streams and rivers and enjoyed a climate of a higher temperature than any part of modern Europe, is most evident..."
( Martin, 1849).
( Mantell)
INTRODUCTION:
Location Maps and Geological Maps
INTRODUCTION CONTINUED:
General Introduction
The Isle of Wight is often described as being lozenge or diamond shaped with concave sides (White, 1921) , (Bird, 1997) . Its long axis runs approximately east-west and is 23 and a half miles. It is nearly 14 miles at right angles. The island is fairly evenly divided into two parts by the roughly north-south Medina River. A more prominant feature is the range of Chalk downs extending east-west from the Needles (shown above) in the west to Culver Cliff in the east.
The Isle of Wight in its southern half is mostly of Cretaceous strata, whereas north of the Chalk ridge it is of Tertiary sands, clays and some limestones. The oldest Cretaceous strata is Wealden, a continental, fluvial deposit of mudstones and sandstones that is famous for its dinosaur remains. The coast near Brook is of particular interest. The Lower Greensand above has a good assemblage of marine fossils and has ferruginous sands (with chamosite or berthierine oolites partly oxidised to limonite). The Gault and Upper Greensand are fossiliferous and well-seen in coastal exposures such as Compton Bay (see above). The Chalk is fossiliferous and very well-exposed in the west of the island in the region of Freshwater, the Needles and Alum Bay and in the east at Whitecliff Bay and Culver Cliff, as shown below (left photograph).
Above the Chalk come the Tertiary strata which include fossiliferous, marine, Eocene sands and clays, seen in the right-hand photograph above at Whitecliff Bay in the east of the island. This is an excellent reference section but they are also well-seen at Alum Bay in the west. Whereas the Bracklesham Group of the Middle Eocene is most fossiliferous at Whitecliff Bay, it is the overlying Barton Clay which is better exposed and more fossiliferous at Alum Bay. At both the eastern and western ends of the Island the lacustrine and lagoonal Solent Formation is well-exposed north of these marine Eocene cliff sections, particularly at Headon Hill just north of Alum Bay and in the northern part of Whitecliff Bay.
The marls, clays and limestones of the Solent Group are also exposed at various places, mostly coastal sections, around the northern part of the Island. In particular, the Bembridge Limestone of the Solent Group is a prominant freshwater limestone with ancient pondsnails and there are several places like west Cowes and Gurnard where it forms a natural sea-wall. In the Bembridge area it forms extensive ledges. The Bouldnor Formation includes the strata referred to in the older publications as the Bembridge Marls and Hamstead Beds. An insect bed occurs in the Bembridge Marls and there is a variety of mollusc shells to be found and occasional remains of turtles. Salinity conditions varied from fresh to brackish to marine. At Hamstead and Bouldnor Cliff some of the youngest of these Oligocene strata contain abundant remains of the small marine bivalve Corbula .
There are no strata on the island of late Oligocene or of Miocene age. In the Eocene succession of the northern part of the Isle of Wight there is evidence of early folding. This would have intensified in the late Oligocene. By the Miocene Epoch there was uplift and major folding associated with the Alpine Orogeny, and the effects of this are clearly visible. In the photographs above you will notice that the Chalk is steeply dipping towards the north. There is a continuation of this Chalk outcrop eastward under the seafloor to the Isle of Purbeck, and there, as Ballard Cliff, Swanage and at Lulworth Cove, the Chalk is vertical or overturned. This steeply north-dipping or vertical Chalk is within the middle limb of the Purbeck - Isle of Wight Monocline (or "Purbeck - Isle of Wight Disturbance" in some oil-industry and structural publications). The structure is easily understood in the Isle of Wight because the south limb of the fold is seen as gently south-dipping Chalk at St. Catherine's Down. To the north the Chalk descends deeply beneath the Solent and the New Forest, eventually coming to the surface again in Salisbury Plain. The nature of the folding is somewhat more complicated than it first appears. It is due to compression from the south, but not in a simple manner. Deep-seated thrust faults, of Hercynian origin (Hercynian - of the Carboniferous-Permian Hercynian Orogeny or mountain-building movements, about 300 million years ago), in the Palaeozoic basement have been reactivated as an effect of the distant impact of the African Plate on the European Plate (i.e. northward movement of Africa and collision with Europe). Although this was distant it still had some effect in southern England. The thrust faults are not seen at the surface here but the visible monoclinal folding is above them and results from uplift and northward movement of the block under the southern half of the Isle of Wight. The Inversion Structure and the Late Cimmerian (or Late Kimmerian or Intra-Cretaceous movements will be considered in more detail below.
PETROLEUM GEOLOGY - ISLE OF WIGHT
The Arreton Borehole (old studies)
Several exploratory boreholes for oil have been drilled in the Isle of Wight. Before 1960 the exploration commenced at Arreton (Falcon and Kent, 1960). The structure was a closed, east-west elongate dome south of the Chalk Ridge. The strata at the surface is Lower Greensand and the borehole extended down to the Inferior Oolite at 5161 feet (1573 metres). This is not as deep as most modern petroleum boreholes in the region, and therefore did not test Bridport Sands or Sherwood Sandstone (the reservoirs at Wytch Farm).
The first exploratory wells in the Wessex region in 1936 in obvious anticlines at Portsdown and Poxwell were disappointing and proved dry. Unlike Iran, where the geologists had been exploring, there was no significant oil in these anticlines. None was found in other similar folds in the area. Already, in 1960, Falcon and Kent (1960), both very notable petroleum geologists, realised that most of the Tertiary structures investigated (Poxwell Pericline, Portsdown Anticline, Chaldon Anticline etc) had developed too late to act as traps for oil migrating towards the edge of the Wessex Basin. Without enormous quantity of seismic data that exists today they did not have a good knowledge of the Cretaceous structure at depth, and the English Channel Inversion theory so familiar now, was not well-understood at the time (although intra-Cretaceous tectonism had been recognised since well before the 1930s).
Of course, it well-known now that oil did migrate towards the margin of the English Channel (Wessex in part) Basin. The Wytch Farm Oilfield is proof of this. Similarly oil migrated towards the margins in the Weald Basin (or Inversion). The Middle Jurassic oilfields of West Sussex and East Hampshire are proof of this. Now it is known that the migration was Cretaceous in age and was into Cretaceous fault traps (the intra-Cretaceous or Late Cimmerian structure are largely extensional faults, unlike the compressional folds of the Tertiary). Thus, although the Arreton Borehole was not targeted at Cretaceous traps, it was planned in the 1950s to find oil that had migrated to the edge of the basin. The general theory was correct but the exact location was not. Oil had not accumulated in the Corallian (as seen in small quantities at Osmington Mills) or the Cornbrash (as at Kimmeridge), and nothing seems to have been found in Middle Jurassic limestones, the reservoirs of the West Sussex and East Hampshire fields. These Middle Jurassic limestones were found to be more muddy and less suitable as reservoirs than in Portsdown and Henfield (Weald Basin).
Of general geological interest, it was noted that the Wealden had a thickness of 2010 feet (612 metres) and thus was like the thick succession at Swanage, Dorset. Only the upper part of the Wealden is exposed in the Isle of Wight cliff sections. The Purbeck was found to be 343 feet (104 metres), only a little thinner than in the type section at Durlston Bay. Data for depth of formation tops will found in Falcon and Kent (1960), Table 1. There is not a detailed log in this report though.
Most of the recent exploratory wells of the 1980s and 90s etc seem to have been targeted at fault structures north of the main Purbeck-Isle of Wight Disturbance (i.e. north of the line of the re-activated Variscan faults). There are major unconfomities beneath the Albian, as shown in a sub-Albian map above. The structural similarity with the Wytch Farm area is obvious, and the hope of finding another highly-successful Wytch Farm Oilfield has clearly been a driving force. Most boreholes seems to have been concentrated in the western part of the island, and thus closer to Wytch Farm. Theories of migration from an area with mature source rocks southwest of the Isle of Wight is a factor. Surprisingly the wells have proved dry so far. The problem might be one of migration. Even in the area south or southeast of Wytch Farm there are problems about a migration fairway. Appropriate juxtaposition of permeable strata at the right time was essential.
Another possible complication might be the regional easterly tilt during Aptian-Albian times. This is seen in the coast from Dorset to Devon as the westerly overstep of the Albian. If migration coincided with this movement, then there may have been not just a tilt up towards the high north of the basin, but also a tilt up westwards. In simple terms there could have been migration in the Cretaceous towards the northwest, rather than just northward. Undoubtedly though there is no simple pattern and the details have to be established.
The state of the reservoirs or potential reservoirs is not considered in any detail here. The Isle of Wight is fairly close to the eastern margins of the Triassic Basin and thus Triassic reservoir facies may be different from Wytch Farm (i.e. more marginal in facies). The Bridport Sand facies is finer-grained and a less satisfactory potential reservoir at the Marchwood Borehole, compared to the Dorset area. The Middle Jurassic is "muddy" according to the records of the Arreton Borehole. There are only very general comments here though, without technical detail and without conclusions. Obviously those who have studied the Isle of Wight boreholes will have a much clearer knowledge not only of the reservoir aspect but also of the possible migration aspect.
PETROLEUM GEOLOGY - ISLE OF WIGHT:
Borehole Details:
Sandhills - 2 Borehole
A exploratory borehole Sandhills No. 2 has been sited at Sandhills near Porchfield, in the northern part of the Isle of Wight, not far from Newport (A Sandhills No.1 Borehole had been drilled before 2001). The licences here had exploration targets for Sandhills No. 2 in both the Middle Jurassic Great Oolite (a major reservoir rock in the western Weald area such as Horndean and Singleton) and in the Triassic Sherwood Sandstone formations (the major and lower reservoir of the Wytch Farm oilfield). Before drilling the estimated potential recoverable reserves at Sandhills-2 were believed to be 10-15 million barrels in the Great Oolite and 20-80 millions barrels in the Sherwood Sandstone. Before the drilling the structure was well-established from seismic and the formations which could be oil-bearing were expected to be present.
In 2005, Northern Petroleum began exploratory drilling for oil, with its Sandhills-2 borehole at Porchfield. However, there was no success in finding useful oil reserves, even though the prospect initially seemed very promising. Northern Petroleum ceased operations at Sandhills in October 2005.
STRUCTURE
The English Channel Inversion Structure
By Barremian (Cretacous, top Wealden) times the Blue Lias and Shales-with-Beef, the source rocks for the Wytch Farm oilfield had been buried, WSW of the Isle of Wight, to more than 2250 metres, as shown by the map above. This seems marginal for oil generation, although an additional minor factor was that this was at about the time of the Cretaceous thermal maximum. Thus the average surface temperature was higher than normal. The Lias source rocks are believed to thermally mature in the dark blue area of the map, but not so to any signficant distance beyond this. The Kimmeridge Clay was probably not, in general, thermally mature.
An interesting feature related to the Inversion Structure, partly explained in the diagram above, is the occurrence of reworked Jurassic (Kimmeridge Clay) ammonites in the Cretaceous strata of Redcliff, Sandown. Beneath the southern Isle of Wight, concealed and known only from boreholes and seismic is a thick sequence of Lower Cretaceous and Jurassic strata; in the northern part of the island, however, about a kilometre of this is missing. This large gap is the result previous extensional movements on the same faults producing depression to the south and uplift to the north. The northern uplifted area, similar to the structure at Wytch Farm Oilfield, was eroded in Cretaceous times. The southern area is part of the English Channel Basin and this was uplifted, thus becoming an inversion structure during the Tertiary tectonism.
If the middle Tertiary uplift had happened as a sudden brief event after deposition of the Tertiary strata, then these poorly consolidated sands and clays would have been uplifted as a mountain of more than 600m in height in the southern part of the Isle of Wight. There probably never was much of a "soft mountain of Wight", a topic I discussed briefly in print as far back as in the 1960s West, 196 ? . The uplift probably started in the Eocene Epoch and the Tertiary strata almost certainly thinned or disappeared because of non-deposition or progressive erosion over the slowly rising anticline. Creechbarrow Hill in Dorset provides evidence of angular unconformity between Tertiary strata and the Chalk in the similar Purbeck Monocline. As in the case of the older (Bartonian) Creechbarrow Limestone, the Bembridge Limestone is probably the result of a lacustrine deposition in proximity to eroded Chalk (on the anticline to the south) providing very carbonate-rich water for the pondsnail limestones (cf. the Holocene "shell marls" of the Test Valley in Hampshire). It is of interest, though, that the large quantity of reworked subangular flint that would be expected to be present in the Upper Eocene and Oligocene has not been found.
An interesting sideline to the history of folding is origin of the coloured sands of parts of the Bracklesham Group at Alum Bay and Redend Point, Studland in Dorset. Both of these localities are close to the middle limb of the monocline. At Studland previously vertical, cylindrical pipes of limonitic sandstone in the Redend Sandstone have been tilted from the vertical ( Arkell, 1947). This suggest that there, at least, some weathering and oxidation took place quite early, before the folding was completed. Probably there was some limited early uplift on the northern margin of the anticline at Studland and Alum Bay and this resulted in the oxidation that gives the reds and yellows of these sands. It was followed later by the main folding, the effects of which were slight at Studland Bay, but major (vertical) at Alum Bay. The coloured sands are not developed at Whitecliff Bay because the anticlines plunge eastward and there was probably insufficient early uplift in this lower eastern region. The Bracklesham (including "Bagshot Beds") are not brightly coloured elsewhere and are largely grey or green and glauconitic; there is much iron but it is mostly not in ferric condition.
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Usually, as at Alum Bay, the uppermost zone of the Chalk is that of Belemnitella mucronata. Rowe (1908) considered that in certain places Tertiary strata either rest directly on the next zone down, that of Actinocamax quadratus and in some others only a thin representative of the mucronata Zone separates the quadratus zone from the Tertiary. White (1908) did not agree with this and considered that the mucronata Chalk is continuous from Alum Bay to Whitecliff Bay. He recognised, however, that there has been drastic thinning due to Pre-Tertiary erosion with the mucronata Zone being 145m at Alum Bay and only 46m at Whitecliff Bay. It would be interesting to know whether there is a marked topographic unconformity beneath the Tertiary, rather than just a gradational change due to regional uplift over some distance, and whether there is any truth in the old theory of a rather deep sub-Tertiary valley at Freshwater Gate. This data, however, does not see, to help a theory of the Alum Bay coloured sands being oxidised by fairly early Tertiary uplift because the greater thickness of the last Chalk zone here, seems to oppose uplift at the very beginning of the Tertiary here.
After the Miocene folding there is no record of deposition on the Isle of Wight until Pleistocene times. Obviously much major erosion took place over several million years. It is possible that, at a time of relatively high sea-level, there was some Pliocene marine deposition, as the products of it are known elsewhere in the southern part of Britain (in East Anglia and at St. Erth in Cornwall), but no Isle of Wight Pliocene sediments have been discovered. By comparision with other regions Pliocene deposits, had they existed, would probably have been present on the Chalk downs, such as St. Catherine's Down, perhaps 130m or more above sea-level.
Pleistocene deposits include a raised beach of the Foreland near Bembridge, and this was formed by an Interglacial sea-level that was a little higher than that at present. During the many glacial phases, which severely affected northern Britain, the Isle of Wight area was not glaciated but was in periglacial tundra conditions. During the melting of the snow each Spring the flooded rivers transported much flint downstream from the source areas of the Chalk uplands. As in nearby areas, such as the New Forest, there are, as a result, various subangular flint gravels that originated as braided river deposits of flood origin. Some of these are associated with the Solent River, a major Pleistocene river that once flowed on what is now the bed of the Solent eastward round the Isle of Wight and then southwestward down the English Channel. This was, of course, at a time of lower sea-level during glacial advance. Other gravels have originated on the flood plains of local northward-flowing tributaries to the Solent River.
There has been a suggestion that during the Pleistocene there was an English Channel Glacier approaching the area of the Isle of Wight from the west and blocking river inflow to so as to form a glacial Lake Solent ( Kellaway, 1975 ). This seems unlikely, at least partly because of lack of a sufficiently high ice source area in the west. Erratics at low levels on the Hampshire-Sussex coast can be adequately explained by the presence of pack-ice in the sea at times and needed no glacier for their transport. Elephants, particularly mammoths, and other large mammals lived in the periglacial tundra of the Isle of Wight (not at that time an island). Their remains are found in Pleistocene chalky gravel and loam on both sides of Freshwater Bay, in brickearth near Shide in the Medina Valley, and in old river gravels at Grange Chine near Brighstone and at Brook Chine. See White (1921).
STRATIGRAPHY:
Strata of the Isle of Wight
Footnote: How deep has been the Pre-Tertiary erosion?
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Quaternary
- Holocene (Recent)
Landslips
Blown Sand
Tufa
Alluvium and Peat
Quaternary
- Pleistocene
Raised Beach
Valley Gravel
Plateau Gravel
Angular Flint Gravel
Palaeogene
(Tertiary)
Solent Group
Barton Sand Formation
Barton Clay Formation
Bracklesham Group
"Bagshot Sands"
Thames Group
Reading Formation
Bouldnor Formation (Bembr. Marls & Hamstead)
Bembridge Limestone Fmt.
Headon Hill Fmt. (Headon & Osborne)
Elmore Formation
Selsey Formation
Marsh Farm Formation
Earnley Formation
Wittering Formation
London Clay Formation
(Oldhaven Formation)
Cretaceous
Upper Chalk
Middle Chalk
Lower Chalk
Upper Greensand
Gault
Lower Greensand
Wealden Group
(Purbeck Fm. - in boreholes)
(Chalk with flints)
Carstone
Sandrock
Ferruginous Sands
Atherfield Clay
Vectis Formation ("Wealden Shales")
Wessex Formation ("Wealden Marls")
Jurassic
(Jurassic underground only)
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PALAEONTOLOGY:
Some Fossils of the Isle of Wight
Silicified remains of the tree-fern Tempskya are widespread in the British Wealden (Watson and Alvin (1996). Radley (2005) reported a gastrolith of Tempskya from a Wealden plant bed at Yaverland, near Sandown, Isle of Wight. Examples from elsewhere on the south coast of England are shown for comparison.
A gastrolith from an overlying plant debris bed comprises a fragment of the tree-fern Tempskya schimperi Corda (M. Munt, pers. comm.). Portions of silicified Tempskya, some preserving lignitized “bark”, are widespread in the southern English Wealden (White, 1928 and Watson and Alvin, 1996). This suggests an intrabasinal, early Cretaceous source for the gastrolith.
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STRATIGRAPHY - EOCENE
Eocene Fossils
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Various fossils from the Cretaceous and Tertiary strata of the Isle of Wight (and other regions) are shown here. Note the lagoonal Purbeck Formation is underground and is not present in the cliff, but known from the Arreton Boreholes. The mainly fluvial Wealden consists of mottled marls, yellowish sandstone beds, some shales and thin limestones. It has some very interesting non-marine faunas, including remains of Unio-like bivalves, ostracods and gastropods (Viviparus) It is particularly notable for dinosaur remains and such creatures as Polacanthus, Brachiosaurus, Iguandodon and Hypsilophodon have left their bones in these strata. The main exposures are near Brook in the southwest and around Sandown in the southeast. The Lower Greensand is a notable fossiliferous formation in the Isle of Wight with remains of marine organisms such as lobsters and various molluscs, including the robust Mulletia mulleti, formerly known as Perna. The unit can be seen at Compton Bay, Atherfield area (where it is particularly well-developed) and at Sandown. The Gault Clay is fossiliferous in places, but because this "Blue Slipper" is often associated with landslides it is not usually cleanly exposed. The Upper Greensand forms prominant cliffs and is particularly fossiliferous. Some examples of Upper Greensand fossils are shown here. They are of marine origin. Chalk fossils are present at Compton Bay, Culver Cliff, the St. Catherine's Down area and at many other places.
Fossils of the Tertiary strata include the Eocene fossils of Alum Bay and Whitecliff Bay. The London Clay, the Bracklesham Group and the Barton Clay contain fossils (although Bracklesham fossils are rare at Alum Bay).
PALAEONTOLOGY:
Fossils of the Solent Group
A selection of just some of the many species of Solent Group (Upper Eocene to Oligocene) fossils are shown here. Most, but not all, of the common ones are included, together with a few rarer species. Some of the diagrams are very old, with a few names updated. The nomenclature on the figures should be treated with caution.
The molluscan fossils of the Solent Group are generally different from those of the marine Eocene strata beneath. They are most frequently found to be fairly small, white and thin-shelled and occur, often in abundance, in thin-bedded strata. They are preserved as aragonite, but usually without any preservation of shell colour. Most of them lived in lacustrine conditions or brackish, lagoonal water. Gastropords such as Galba ( Lymnaea ) or Viviparusare common in freshwater strata such as the Bembridge Limestone. Planorbis - type gastropods are also typical of freshwater strata, and charophyte algae may be present with them. Brackish water molluscs include Corbicula and various cerithid (ornamented and turreted) gastropods. There are some truely marine horizons, usually fairly thin and particularly recognised by the presence of oyster shells or "Barton Clay - type" gastropods such as Athleta.
The Solent Group is very well exposed on the Isle of Wight and this is the best place in the country to see fossils of Upper Eocene to Oligocene age. The Group includes the Headon Hill Formation, particular well seen at Headon Hill, near Alum Bay in the west of the Isle of Wight. It is also present at Colwell Bay, Totland Bay and elsewhere. There are freshwater lacustrine, brackish water and some marine fossils. The Bembridge Limestone Formation is present around the shores of much of the northern (Solent) coast of the island. It contains various freshwater pondsnails. The Bouldnor Formation contains freshwater to marine molluscs. It also contain fossil insects, not shown here. Remains of crocodile (rare) and turtle (fairly common) are present in the Solent Group.
Younger strata than the Solent Group are Pleistocene and Holocene. These Quaternary deposits contain remains of elephants (as at Freshwater Bay), bison (as at Newtown Estuary), hazelnuts (near Brook) and other fossils.
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LOCATIONS:
Headon Hill and Totland Bay
LOCATION:
Colwell Bay (near Freshwater, Western Isle of Wight)
For more go to:
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LOCATION:
Freshwater Bay (Southwestern I.O.W.) - Introduction
The Upper Chalk is well exposed in Freshwater Bay. It dips steeply towards the north. There is little evidence of faulting. Brown Pleistocene deposits, in which mammoth teeth have been found, lie above the eroded surface of the Chalk. They are from the lower valley slopes of the old Western Yar, now truncated by coast erosion at Freshwater Bay.
LOCATION:
FRESHWATER BAY, Western Side
(beneath Fort Redoubt)
The western side of Freshwater Bay is easily reached by a very short walk from the car park. After the sea defences are passed, there is a cliff of south-dipping, Micraster Zones Chalk, with reddish-brown Quaternary
deposits cutting down toward the centre of the bay. The exposure is beneath a mid-Victorian fort, now a private residence. The place is Fort Redoubt. The name "Redoubt" refers, according to Wikipedia, to:
"a fort or fort system usually consisting of an enclosed defensive emplacement outside a larger fort, usually relying on earthworks, though others are constructed of stone or brick. It is meant to protect soldiers outside the main defensive line and can be a permanent structure or a hastily-constructed temporary fortification..."
This redoubt has a deep cutting on the landward side which descends through the thin edge of brown Quaternary deposits into the steeply-dipping Chalk.
LOCATION:
Freshwater Bay - Eastern Chalk Stacks
LOCATION:
Freshwater Bay - Quaternary Deposits
Pleistocene River Gravel at Freshwater Bay
Pleistocene river gravel, Valley Gravel, occurs at the Freshwater gap. Osborne White (1921), pp 166-167, commented on this:
"Much of the superficial material mapped as Valley Gravel on the sides of Freshwater Gap is of a different character from any of the deposits in that class described in the preceding pages. Valley gravel, consisting of partly-worn flints with chert and ironstone, in places cemented by iron oxide, is seen low down on the sides of the gap; the bulk of it is probably derived from older gravels in the country that once existed to the south; but the superficial deposit most in evidence in the cliff section is a banded chalky wash, or rubble drift which overlies parts of the gravel and was formed under different conditions."
Pleistocene Head at Freshwater Bay
Here are some comments of Osborne White (1921), p. 167, on the Head deposits at Freshwater Bay.
"On the eastern side of Freshwater Bay, a sheet of the chalky gravel and loam, mentioned in connection with the Valley Gravel, occurs on the top of the cliff, and a little outlier of it, which has long seemed in imminent danger of destruction, clings with remarkable tenacityto the apex of the Stag Rock. The deposit thickens as it descends into the valley at Freshwater Gate, and is well seen in the cliff near the protective fascines. A tooth of Elephas primigenius has been obtained from it on both sides of the valley, and Godwin Austen, by whom these finds were recorded, observed numerous shells of the land molluscs, "Pupa muscorum" and "Succinea oblonga" in the wash on the eastern slope. The deposit belongs to the widely-represented class of late Pleistocene "heads" of which the well-known Elephant Bed, overlying the Brighton raised beach at Kemp Town, is a type."
More on Freshwater Quaternary - Forbes
(The following is from p.2 et seq. of Forbes (1856), edited by Godwin-Austen.)
" II. 1. The Gravel of Freshwater Gate, with Elephant's Remains
"These gravels are well exhibited in the cliff sections of Freshwater Bay, and are interesting and instructive, as they show most clearly that the superficial accumulations such as those which cover so large a portion of the surface of the Isle of Wight, and which to the casual observer would hardly seem capable of subdivision, are yet separable into groups referabletro very distinct periods of past time.
Freshwater Gate is situated in the most western of the several transverse depressions which the range of the highly inclined chalk strata presents in its course through the Isle of Wight; and the only difference is to be remarked upon is this, - that the Freshwater depression is the deepest of these, extending down to the present sea level. The highest portion of the chalk range, as Beacon Down on the West and Afton Down on the east, present only a thin coating of angular flints, the residue of that portion of chalk which has been dissolved away. Thes downs are good illustrations of the rate of waste over calcareous surfaces from the action of rain-water alone. Detritus and gravel beds occupy the lower slopes, as shown in woodcuts Nos. II and III.
On the west side of the valley (Vignette III [- shown as an illustration above, re stacks]) the superficial beds reach a considerable elevation, descending thence continuously to sea level. Starting from this lower line, it will be seen that the gravel beds which rest immediately on and against the chalk are composed of coarse sub-angular and water-worn flints, with chert and ironstone from the lower cretaceous beds; the whole coloured and somewhat cemented by iron.
[Sequence on the West Side of Freshwater Bay.
1. West Side; Older Gravel, Red: Basal, Horizontal, Dark Gravel Beds, without Chalk Pebbles - channel deposits up to about 4m thick]
The lower gravel beds conform to the irregular surface of the chalk, but higher up the mass has a marked horizontal arrangement with occasional bands of coarse sand. These lines of successive accumulation, when traced out toward the valley, end abruptly along a line which slopes at an angle of 30 degrees, and which is distinctly marked through a vertical height of 14 feet (4.26m).
[2. West Side; The Diagonal Bed on an Erosional Slope]
The bed which follows next on this slope is rather more than an a foot (0.3m) in thickness, and agrees so completely with the gravels against which it rests, that it could not be distinguished from it but for the arrangement of the materials which is in accordance with the slope.
[3. West Side; Newer Gravel: Younger Horizontal, Cross-Bedded, Sandy Gravel, Valley Fill with Chalk Pebbles (lighter-coloured gravel)]
The diagonal bed here described separates the dark gravel from another horizontal series, which is very distinguishable both by colour and composition. The materials are generally finer, and the thickness and number of sand beds greater. These last, more particularly in the lower portion, show the cross bedding which is produced by drifting currents having opposite sets at different times. There occur throughout this newer gravel a considerable admixture of small rounded detritus of white chalk, which is wholly wanting in the older gravel.
[4. West Side; Late Transgressive Phase - Coarser Gravel]
After the newer series had been raised to the level of the older one, it appears to have spread out [transgressed] over it. This portion, which is not thick, resembles the older gravel in coarseness and the newer in colour, and consists, in fact, of the re-arranged surface of the older gravel beds.
[5. West Side; Brickearth with angular flint - near the top]
These accumulation are overlain by the brick-earth deposit, which contains here, as elsewhere, the usual disseminated fragments of angular flint.
[6. West Side; Top Chalk Talus
The newest bed to be noticed here is that which occurs in superposition on the foregoing, along a line at the base of the chalk hills. It consists largely of chalk rubble and detritus with angular flints. It has a marked banded arrangement, conforming to the slopes above it, all of which is talus. It must not be confounded with the underlying gravel beds, and considered portion of them as has sometimes been done elsewhere.
[end of West Side Quaternary Sequence]
.
[Freshwater Bay Quaternary - East Side]
The Newer Gravel series has been cut out along the central line of the valley, just as the older ones had been in some earlier time. The superficial deposits on the east side of the valley (Woodcut II) do not correspond exactly with those on the west. The removal of the Older or Red-Gravel series has taken place to a much greater extent and the bulk of the mass consists of the Newer Gravel and brick-earth.
LOCATION:
Freshwater Bay
Shear Planes and Fracture of the Chalk
Freshwater Bay has unusual Chalk cliffs in which the bedding planes are not clearly conspicuous in much of the Bay. They are best seen in the southern part of the eastern cliffs, as in the photograph above. Even there, in the Micraster coranguinum Chalk (Seaford Chalk Formation), were it not for the flint (enhanced in the photograph) the bedding would be much less conspicuous than the shear planes or joints. There are numerous fractures, especially ones dipping at a low angle to the north, but displacement on them is minute or zero.
At some other parts of the bay it is difficult to see the bedding at all. The sequence of Chalk from the Marsupites testudinarius Zone up to the Actinocamax quadratus Zone (Newhaven Chalk Formation) consists of white chalk that has few flint bands and therefore does not show the bedding very clearly. The junction with the Newer Gravel (rather sandy) is clearly seen. There is not much Brickearth just here.
Freshwater Bay is an interesting locality because the overlying land surface has not been appreciably eroded down here since the late Pleistocene glacial phase. Solifluction has not removed the uppermost exposed Chalk. In addition the cliff erosion provides good sections through the fractured Chalk.
(Problem: In the stacks (see photographs above) the shear planes or fractures clearly dip south at low angles, whereas here in the coranguinum Zone in the eastern cliffs the dominant dip of fracture planes is northward at low angles. More study is needed!)
LOCATION:
Chalk Road Cutting, Compton Down and Afton Down (between Freshwater Bay and Compton Bay)
There is a road cutting in the Chalk on the A3055 (Military Road) above Freshwater Cliff. The cutting is into Afton Down and Compton Down between Freshwater Bay and Compton Bay (near Brook). It is on the main route southwestward from Freshwater Bay. The road, just here, has been threatened by cliff falls of chalk. The exposure is not particularly impressive and gradually becoming weathered and overgrown. Note that there is risk of accident due to passing vehicles. However, the cutting may be of interest to specialists working on the Chalk.
The cutting in the Lewes Nodular Chalk Formation exposes chalk of the St. Margaret's Member (Sternotaxis planus and Micraster cortestudinarium, and adjacent. This is approximately Turonian to Coniacian; in old terminology this would be the top part of the Middle Chalk to the lower part of the Upper Chalk. See: Insole et al. (1998) for more details. They mentioned (see p.100) that at the eastern (Brook) end of the cutting the St. Margaret's Member is visible (or was visible) just above the scree. 3.5 m above the top of the hardground lies the "Black Band", a thin marl correlatable with the Southerham Marl in Sussex, and that 4.5m higher there is a bed rich in the bryozoan Bicavea.
More on Compton Bay? Go to: Geology of the Isle of Wight - Brighstone, Compton and Chale Bays
(End of Freshwater Bay Section)
LOCATION:
Compton Bay, ESE of Freshwater.
For more detail go to:
Geology of the Isle of Wight - Brighstone, Compton and Chale Bays
LOCATION:
Hanover-Point
The coast continues southeast from Compton Bay to Hanover Point, an interesting Wealden, Wessex Formation, locality, and then on the large Brighstone Bay.
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.
For more on Brighstone Bay, and Hanover Point etc., go to:
Brighstone-Bay, Isle of Wight - new webpage
Brighstone Bay is about 9 km. long. It extends from Hanover Point to Atherfield Point. It is mainly of Wealden strata and is a notable area for collecting dinosaur bones. There is access to the beach from several chines or small stream valleys, but the details of these may change with coast erosion. In general chines are now being progressively cut back, and with time, access to the coast will become more difficult. If exploring this stretch of coast, find out the tide conditions in advance and arrange your visit at low tide. There may be real difficulties at high tide and in stormy conditions.
For more on Brighstone Bay, and Hanover Point etc., go to:
Brighstone-Bay, Isle of Wight - new webpage
LOCATION:
Blackgang Chine and Gore Cliff,
Blackgang Chine is a famous locality on the Isle of Wight and once used to be a major chine or valley giving access by a path to the beach. It was a place for fisherman, and also for smugglers to land their goods and get them up the cliffs. A sad event here was the wrecking of the East Indiaman, Clarendon during a storm in October, 1836. An old etching, modified and shown above reveals something of the coastal geomorphology at the time.
The original chine was natural, undeveloped and scenically very attractive. Landsliding and cliff retreat in recent years has caused loss of the original chine. The area on the cliff top has been changed into Blackgang Chine Theme Park, a good place for children to enjoy.
Blackgang area is one of the most notable places for landslides on the Isle of Wight. The Upper Cretaceous Gault Clay underlies a well-developed sequence of porous and permeable Upper Greensand, with Chalk above. The Sandrock of the Lower Greensand forms the lower part of the cliff with some Ferruginous Sands
at the base. Most the strata low in the cliff, though are covered by landslide debris that has slipped down from above. Because of the landslides the area is quite complex to explore because original roads and paths have been cut or destroyed.
A major landslide in January 1994 has been well-described by Mark Davies (1994), who was at that time an Environmental Science student at Southampton University. Shown above are the remains of Gore Cliff Cottage, adversely affected by the landslide of 1994. For another photograph of this building (at a slightly earlier stage) see the document Understanding Demolition Costs for Properties Affected by Coastal Erosion, March 2010 (Final Report by Scott Wilson).
See particularly the detailed map of the landslides of Blackgang and Gore Cliff provided by Bromhead et al. (1991). A modified version of this map can be seen as Fig. 19 on page 74 of Insole et al., 1998 (The Isle of Wight, GA Guide).
LOCATION:
Gore Cliff and Sandrock Road
Originally, the Victorian coast road, the Military Road (now the A3055) extended the western Undercliff slopes to Blackgang Chine (it still extends along the Undercliff from Ventor in the east to Niton in the west, and it has not yet been broken through). In part of Knowles Farm (now National Trust), at the southern end of Gore Cliff (Windy Corner), it was broken through by a major rock fall and landslide in September 1928. In spite of the name "Sandrock Road" the road is largely on Gault rather than Lower Greensand Sandrock.
The photographs above show the same location at Windy Corner and Sandrock Road (part of Knowles Farm) and Gore Cliff in 1928, 1992 and 2011. Rock debris from the upper part of the landslide can be seen in front of what is now the car park, but to some extent it seems to have subsided. This presumably the result of continued movement on the the underlying landslide.
Rocken End is a promontory almost at the southern end of the Isle of Wight. It is less than a kilometre from St. Catherine's Lighthouse at St. Catherine's Point, the southernmost part of the island. Rocken End is composed of fallen debris from landslides. Beneath the debris Gault Clay is above Sandrock (Lower Greensand).
LOCATION:
Shanklin Chine to Luccombe Chine - Knock Cliff
(Details to be added)
.
LOCATION:
Luccombe Chine and Adjacent Cliffs
.
LOCATION:
Sandown - Dinosaur Museum
See the Dinosaur Isle Website.
For study of the dinosaurs of the Isle of Wight the key work is that of Martill and Naish (2001). This may be on sale at the Dinosaur Isle Museum. It is an excellent book, published by the Palaeontological Association.
Sandown Bay and Culver Cliff provide excellent sections through the Cretaceous strata at the eastern side of the Isle of Wight. These are comparable, but different in detail to the sections at Brighstone Bay and Compton Bay at the western side of the island. The cliff exposures are north-east of the Dinosaur Museum.
For more on Whitecliff Bay see the separate
Whitecliff Bay webpage.
LOCATION:
Hamstead Cliff and Hamstead Ledge
The geology of Hamstead Ledge and its vicinity is described in the Geologists' Association Guide, No. 60, The Isle of Wight, by Insole, Daley and Gale (1998) . This guide is essential for reference. It shows possible places to park a car and footpaths to the cliff. It then contains good descriptions of the Bembridge Marls Member and the Hamstead Member of the Bouldnor Formation.
Please go to Isle of Wight Bibliography .
I am particularly grateful to the Head of the School of Ocean and Earth Sciences for kindly facilitating the running of this website from Southampton University. Alan Holiday is acknowledged with thanks for providing excellent aerial photographs taken by him of the Isle of Wight (in turbulent conditions!). I am very grateful to the members of various field trips over the years to parts of the Isle of Wight who have cooperated with field discussion and photography.
Student parties from Southampton University and oil company groups have been particularly helpful. I am very much obliged to Mark Davies, who as an Environmental Science student in 1994 wrote an excellent project on landsliding at Blackgang Chine. I thank Sarah Glaccum for arranging a photograph to be taken of the specimen of Tempskya which she discovered. David Gaunt kindly provided a good photograph of the stacks at Freshwater Bay.
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Copyright
© 2013 Ian West, Catherine West, Tonya West and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity. A reasonable number of images and some text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing source is acknowledged.
Disclaimer:
Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancell part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.
Webpage - written and produced by:
.
Written and produced by:
Ian West, M.Sc. Ph.D. F.G.S.
Romsey, Hampshire
(including Shippards Chine SZ378841)
(West of Brook Village, SW coast of the Isle of Wight, Map Reference - SZ379836)
(southern Isle of Wight)
southeast of Blackgang)
(Dinosaur Isle)
|Solent Bibliography
Ian West, M.Sc. Ph.D. F.G.S.
