Upper Greensand Formation | |
---|---|
Stratigraphic range: Albian–Cenomanian | |
Type | Geological formation |
Unit of | Selborne Group |
Underlies | Chalk Group |
Overlies | Gault Clay |
Area | Wessex Basin, Weald Basin |
Thickness | 0–75 m |
Lithology | |
Primary | Sandstone |
Other | Siltstone |
Location | |
Country | England |
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. [1] It overlies the Gault Clay and underlies the Chalk Group. It varies in thickness from zero to 75 m. It is predominantly a glauconitic fine-grained sandstone, locally becoming silty. Fragmentary dinosaur remains, such as those assigned to Iuticosaurus , have been recovered from this formation. It has been quarried as a building stone from Roman times, and used in London and the area of its outcrop from Devon to East Sussex.
Sandstones from the Upper Greensand have been used as building stone since at least Roman times. [2] Reigate Stone was mined from the Upper Greensand in north east Surrey throughout the Middle Ages and early modern period, [3] forming the most important source of freestone in Medieval London. [2] In Dorset, the Shaftesbury Sandstone was quarried between Shaftesbury and Okeford Fitzpaine and used in the Shaftesbury area and along the Stour valley. In southeastern Devon, the Bindon Sandstone was quarried near Branscombe and used in buildings such as Exeter Cathedral. [4] Other building stones quarried from the Upper Greensand in the county include Salcombe Stone from near the border with Somerset, and the Green Glauconitic Sandstone from the western side of the Blackdown Hills. [5]
Hurdcott Stone was quarried in Wiltshire and used particularly in Mere and Shaftesbury. It is currently being produced from a quarry at Barford St Martin. Potterne Stone is quarried near Potterne and used there and in the Vale of Pewsey. [6] On the Isle of Wight the Upper Greensand has been quarried since Roman times, including Ventnor Stone near Ventnor, with varieties Green Ventnor Stone and Ventnor Foxstone, and Bonchurch Stone only found at Bonchurch. Chert from the top of the formation has also been used as a building stone since the 17th century. [7] In West Sussex and Hampshire, Malmstone was quarried and used in buildings such as Winchester Castle [8] and Amberley Castle. [9] In East Sussex, Eastbourne Sandstone was quarried from the foreshore at Eastbourne, and used in buildings in the town such as the church of St Mary the Virgin. [10]
Reigate is a town in Surrey, England, around 19 miles (30 km) south of central London. The settlement is recorded in Domesday Book in 1086 as Cherchefelle and first appears with its modern name in the 1190s. The earliest archaeological evidence for human activity is from the Paleolithic and Neolithic, and during the Roman period, tile-making took place to the north east of the modern centre.
Bargate stone is a highly durable form of sandstone. It owes its yellow, butter or honey colouring to a high iron content. In some contexts it may be considered to be a form of ironstone. However, in the context of stone buildings local to the extraction of Bargate Stone, the term 'ironstone' is often used to refer to a darker stone, also extracted from the Greensand, which rusts to a brown colour.
Greensand or green sand is a sand or sandstone which has a greenish color. This term is specifically applied to shallow marine sediment that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals, such as smectite and glauconite. Greensand is also loosely applied to any glauconitic sediment.
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color which is very friable and has very low weathering resistance.
Barford St Martin is a village and civil parish in Wiltshire, England, about 2.5 miles (4 km) west of Wilton, around the junction of the A30 and the B3089. Barford is known as one of the Nadder Valley villages, named for the River Nadder which flows through the parish.
Zeals is a village and civil parish in southwest Wiltshire, England. The village is about 2.2 miles (3.5 km) west of Mere, next to the A303 road towards Wincanton, and adjoins the villages of Bourton, Dorset and Penselwood, Somerset. Its name comes from the Old English sealh meaning a small willow or sallow.
Buckland is a village and civil parish in the Mole Valley district of Surrey, England, between Dorking and Reigate, its nearest towns. The civil parish is bordered by the North Downs escarpment in the north. The area contains a number of sand pits.
Somerset is a rural county in the southwest of England, covering 4,171 square kilometres (1,610 sq mi). It is bounded on the north-west by the Bristol Channel, on the north by Bristol and Gloucestershire, on the north-east by Wiltshire, on the south-east by Dorset, and on the south west and west by Devon. It has broad central plains with several ranges of low hills. The landscape divides into four main geological sections from the Silurian through the Devonian and Carboniferous to the Permian which influence the landscape, together with water-related features.
The Greensand Ridge, also known as the Wealden Greensand, is an extensive, prominent, often wooded, mixed greensand/sandstone escarpment in south-east England. Forming part of the Weald, a former dense forest in Sussex, Surrey and Kent, it runs to and from the East Sussex coast, wrapping around the High Weald and Low Weald. It reaches its highest elevation, 294 metres (965 ft), at Leith Hill in Surrey—the second highest point in south-east England, while another hill in its range, Blackdown, is the highest point in Sussex at 280 metres (919 ft). The eastern end of the ridge forms the northern boundary of Romney Marsh.
Kent is the south-easternmost county in England. It is bounded on the north by the River Thames and the North Sea, and on the south by the Straits of Dover and the English Channel. The continent of Europe is 21 miles across the straits.
Bonchurch Landslips is a 28.2-hectare (70-acre) site of special scientific interest which is located north-east of Ventnor, Isle of Wight. A wooded coastal landslip zone, the site was notified in 1977 for both its biological and geological features.
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 deposited in shallow marine conditions.
Chicksgrove Quarry is a 14 acres (5.7 ha) geological Site of Special Scientific Interest south of Upper Chicksgrove in Wiltshire, England notified in 1971.
Jacobsville Sandstone is a red sandstone formation, marked with light-colored streaks and spots, primarily found in northern Upper Michigan, portions of Ontario, and under much of Lake Superior. Desired for its durability and aesthetics, the sandstone was used as an architectural building stone in both Canada and the United States. The stone was extracted by thirty-two quarries throughout the Upper Peninsula of Michigan approximately between 1870 and 1915.
Kentish ragstone is a hard grey limestone in Kent, England, drawn from the geological sequence known as the Hythe Beds of the Lower Greensand. For millennia it has been quarried for use both locally and further afield.
The Portland Group is a Late Jurassic (Tithonian) lithostratigraphic group in South East England. The name is derived from the Isle of Portland in Dorset where the strata are exposed and have been extensively worked. Rocks of this age have in the past been called the Portlandian stage by geologists, which corresponds with the late Tithonian stage of the internationally used geological timescale.
The Undercliff, Isle of Wight, England is a tract of semi-rural land, around 5 miles (8.0 km) long by 0.25–0.5 miles (0.40–0.80 km) wide, skirting the southern coast of the island from Niton to Bonchurch. Named after its position below the escarpment that backs this coastal section, its undulating terrain comprises a mix of rough pasture, secondary woodland, parkland, grounds of large isolated houses, and suburban development. Its sheltered south-facing location gives rise to a microclimate considerably warmer than elsewhere on the island. Although inhabited, the Undercliff is an area prone to landslips and subsidence, with accompanying loss of property over time. Settlements along the Undercliff, from west to east, are: lower Niton, Puckaster, St Lawrence, Steephill, the town of Ventnor, and Bonchurch.
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.
Reigate Stone is a freestone that was mined from the Upper Greensand in north east Surrey. It was used in building work throughout the Middle Ages and early modern period. It is sometimes classified as a calcareous sandstone, although very little of the silica content is in the form of detrital sand grains. In addition to silicon dioxide, the stone also includes clay, fine-grained calcite, mica flakes and glauconite.
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.