The geology of the Isle of Wight is dominated by

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s of

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

and

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

age. This sequence was affected by the late stages of the Alpine Orogeny, forming the Isle of Wight

monocline A monocline (or, rarely, a monoform) is a step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence. Formation Monoclines may be formed in several different ways (see diagram) * ...

, the cause of the steeply-dipping outcrops of the Chalk Group and overlying Paleogene strata seen at

The Needles The Needles is a row of three stacks of chalk that rise about out of the sea off the western extremity of the Isle of Wight in the English Channel, United Kingdom, close to Alum Bay and Scratchell's Bay, and part of Totland, the westernmo ...

Alum Bay Alum Bay is a bay near the westernmost point of the Isle of Wight, England, within close sight of the Needles rock formation. Of geological interest and a tourist attraction, the bay is noted for its multi-coloured sand cliffs. The waters and adj ...

and

Whitecliff Bay Whitecliff Bay is a sandy bay near Foreland which is the easternmost point of the Isle of Wight, England, about two miles south-west of Bembridge and just to the north of Culver Down. The bay has a shoreline of around and has a popular sandy ...

Pre-Cretaceous

Rocks of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

and

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

age are known to be present in the subsurface of the island from boreholes and interpreted

seismic reflection Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismi ...

profiles. Up to 389 m of presumed Devonian sedimentary rocks been proved by six boreholes drilled on the island, consisting of

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

, similar in type to other dated Devonian sequences. A nearly full Triassic succession has been drilled, reaching a maximum thickness of 450 m. Sandstones of the

Sherwood Sandstone Group The Sherwood Sandstone Group is a Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands. The name is derived from Sherwood Forest in Nottinghamshire which is underlain by r ...

are overlain by claystones and siltstones of the

Mercia Mudstone Group The Mercia Mudstone Group is an early Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands – the name is derived from the ancient kingdom of Mercia which corresponds to t ...

and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s of the

Penarth Group The Penarth Group is a Rhaetian age (Triassic) lithostratigraphic group (a sequence of rock strata) which is widespread in Britain. It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed ...

. A complete Jurassic succession is shown by the boreholes at Arreton, reaching over 1400 m in thickness, comprising mainly mudstones of the

Lias Group The Lias Group or Lias is a lithostratigraphic unit (a sequence of rock strata) found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, sh ...

, oolitic limestones of the Inferior and

Great Oolite Group The Great Oolite Group is a Middle Jurassic stratigraphic unit that outcrops in southern England. It consists of a complex set of marine deposits primarily mudstone and bioclastic ooidal and fine grained limestone, deposited in nearshore to shel ...

, claystones of the Kellaways and

Oxford Clay Formation The Oxford Clay (or Oxford Clay Formation) is a Jurassic marine sedimentary rock formation underlying much of southeast England, from as far west as Dorset and as far north as Yorkshire. The Oxford Clay Formation dates to the Jurassic, specifica ...

s, bioclastic limestones of the Corallian Group, organic-rich mudstones of the

Kimmeridge Clay Formation The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea. This rock formation is the major source rock for North ...

, limestones of the Portland Group and the lower part of the

Purbeck Group The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group (a sequence of rock strata) in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the ...

. The entire sequence presents sedimentation in a shallow water environment.

Cretaceous

Wealden Group

A complete section is found in the subsurface, but only the upper part of the succession is exposed from

Compton Bay Compton Bay is a bay located on the southwest section of the Isle of Wight, England. Its northwestern edge is defined by the distinctive white chalk cliff In geography and geology, a cliff is an area of rock which has a general a ...

Brighstone Bay Brighstone Bay is a bay on the south west coast of the Isle of Wight, England. It lies to the south and west of the village of Brighstone from which it takes its name. It faces south west towards the English Channel, its shoreline is 7 km ...

and at

Sandown Bay Sandown Bay is a broad open bay which stretches for much of the length of the Isle of Wight's southeastern coast. It extends from Culver Down, near Yaverland in the northeast of the Island, to just south of Shanklin, near the village of Lucc ...

, in the core of two broad

anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

s. In the Arreton boreholes the

Wealden Group The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (a sequence of rock strata) in the lithostratigraphy of southern England. The Wealden group consists of paralic to continental (freshwater) facies sedimentary ...

reaches a total of 620 m. The exposed sequence comprises the upper part of the

Wessex Formation The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages (about 145–125 million years ago) of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vecti ...

and the overlying

Vectis Formation The Vectis Formation is a geological formation on the Isle of Wight and Swanage, England whose strata were formed in the lowermost Aptian, approximately 125 million years ago."Magnetostratigraphy of the Lower Cretaceous Vectis Formation (Wealden ...

. The Wessex Formation consists of red mudstones with some interbedded sandstones laid down in a freshwater and floodplain environment. The Vectis Formation consists of grey mudstones, deposited in a shallow water lacustrine to lagoonal setting, with some evidence of marine influence. The type section for the formation is in Brighstone Bay.

Lower Greensand Group

The

Lower Greensand Group The Lower Greensand Group is a geological unit present across large areas of Southern England. It was deposited during the Aptian and Albian stages of the Early Cretaceous. It predominantly consists of sandstone and unconsolidated sand that were ...

marks the return to fully marine conditions in this area.

Selborne Group

The Selborne Group comprises claystones of the

Gault Formation The Gault Formation is a geological formation of stiff blue clay deposited in a calm, fairly deep-water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). It is well exposed in the coastal cliffs at Copt Point in Fol ...

and sandstones of the overlying

Upper Greensand Formation The Upper Greensand Formation is a Cretaceous formation of Albian to Cenomanian in age, found within the Wessex Basin and parts of the Weald Basin in southern England. It overlies the Gault Clay and underlies the Chalk Group. It varies in thick ...

Chalk Group

The

Chalk Group The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur acr ...

consists of a sequence of chalky limestones with some interbedded marls. The age of the sequence ranges from Cenomanian through to Campanian, The upper boundary is an unconformity across which rocks of

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

age are missing.

Palaeogene

Rocks of Palaeogene age rest unconformably on the Upper Cretaceous sequence on the Isle of Wight. Most of the Palaeocene is missing, in common with all of onshore UK. The Palaeogene strata were deposited in a shallow water marine environment, which was affected by repeated changes in relative sea level, causing cycles of transgression and regression.

Lambeth Group

The

Lambeth Group The Lambeth Group is a stratigraphic group, a set of geological rock strata in the London and Hampshire Basins of southern England. It comprises a complex of vertically and laterally varying gravels, sands, silts and clays deposited between 56-55 ...

is well exposed at the southern end of Alum Bay and Whitecliff Bay at the western and eastern ends of the island. This

Thanetian The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

(Upper Palaeocene) sequence is represented by the

Reading Formation The Reading Formation is a geologic formation in southern England. It dates to the Paleocene period, and is part of the Lambeth Group. It overlies the London Basin and is below the Harwich Formation. The formation is composed of "a series of lent ...

, a thin sequence of mainly claystones with variable amounts of sands, varying from 25 – 40 m in thickness.

Thames Group

On the Isle of Wight this group comprises the

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

(lowermost Eocene) London Clay Formation, which reaches up to 160 m in thickness. The formation is a sequence of mainly claystones, although to the east of the island the formation contains sandstones of the Whitecliff and Portsmouth Sand Members.

Bracklesham Group

The

Bracklesham Group The Bracklesham Group (formerly Bracklesham Beds), in geology, is a series of clays and marls, with sandy and lignite, lignitic beds, in the middle Eocene of the Hampshire Basin and London Basin of England. The type section of the Bracklesham Gro ...

is of Ypresian to

Lutetian The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Midd ...

in age. Its type section is along the cliffs in Whitecliff Bay.

Barton Group

This sequence is of Lutetian to

Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage of t ...

(uppermost Eocene) in age. It comprises a mixture of clays, fine sands, sandy clays and clayey sands. The stratigraphy exposed at the two ends of the island are somewhat different.

Solent Group

The Solent Group is Priabonian to

Rupelian The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene Epoch/Series. It spans the time between . It is preceded by the Priabonian Stage (part of the Eocene) and is followed by the Chattian ...

(early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

) in age. It comprises the Headon Formation, the Bembridge Limestone Formation and the

Bouldnor Formation The Bouldnor Formation is a geological formation in the Hampshire Basin of southern England. It is the youngest formation of the Solent Group and was deposited during the uppermost Eocene and lower Oligocene. Stratotype and occurrence The Boul ...

Quaternary

The outcrops of Quaternary age are relatively poorly understood.

Structure

Deposition of the Triassic, Jurassic and lowermost Cretaceous sequences was controlled by two large west–east trending, south- dipping normal faults, the Needles Fault and the Sandown Fault, which have an overlapping en-echelon geometry. Reactivation of these faults over part of their lengths during the Paleogene inversion event produced the structures that control the current outcrop patterns. The two main structures are the Brighstone and Sandown Anticlines, which relate to reactivation of the Needles and Sandown Faults respectively. These anticlines have steep, locally vertical northern limbs, forming the monoclinal structures seen at The Needles, Alum Bay and Whitecliff Bay. In the centre of the island the shortening is transferred between the fault zones, forming the zone of lower dips and north–south strike between

Calbourne Calbourne is a village in the civil parish of Calbourne, Newtown and Porchfield, on the Isle of Wight, England. It is located 5 miles (8 km) from Newport in the west of the island. The village takes its name from the stream that passes th ...

and Garston's Down. To the north of the monoclines the Paleogene sequence is deformed into a gentle syncline, the Bouldnor Syncline.

References

{{Geology of England , state=expanded