Geology of East Sussex
Encyclopedia
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
to Upper Jurassic Stratigraphy. East Sussex, geologically is best known for the identification of the first dinosaur
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
by Gideon Mantell
Gideon Mantell
Gideon Algernon Mantell MRCS FRS was an English obstetrician, geologist and palaeontologist...
, near Cuckfield
Cuckfield
Cuckfield is a large village and civil parish in the Mid Sussex District of West Sussex, England, on the southern slopes of the Weald. It lies south of London, north of Brighton, and east northeast of the county town of Chichester. Nearby towns include Haywards Heath to the southeast and Burgess...
, to the famous hoax of the Piltdown man
Piltdown Man
The Piltdown Man was a hoax in which bone fragments were presented as the fossilised remains of a previously unknown early human. These fragments consisted of parts of a skull and jawbone, said to have been collected in 1912 from a gravel pit at Piltdown, East Sussex, England...
near Uckfield
Uckfield
-Development:The local Tesco has proposed the redevelopment of the central town area as has the town council. The Hub has recently been completed, having been acquired for an unknown figure, presumed to be about half a million pounds...
.
The county’s chalk has provided a world-class stratigraphic marker giving a great deal of detail in Cretaceous Chalk Paleoecology and Palaeontology while in the east of the county on the Kentish border the Dungeness Foreland is important for the study of Geomorphology and Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
sea level fluctuations.
Geological history
The geological history of East Sussex commenced during CarboniferousCarboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, with the rocks which are today basement deposited within a low swamp providing coals which were exploited to the north and east in Kent
Kent coalfield
The Kent Coalfield was a coalfield located in the eastern part of the English county of Kent.Coal was discovered in the area in 1890 while borings for an early Channel Tunnel project were taking place and the resultant Shakespeare colliery lasted until 1915...
, but boreholes drilled in the 19th century failed to find this deposit in Sussex. The Carboniferous coals are overlain by Permian and Triassic sediments. The sediments where uplifted and faulted within the Variscan Orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
, with the land now occupied by East Sussex being a low external fold belt to the main orogeny, which was located within the present day English Channel, the remnants of the mountain belt can be seen today in Devon and Cornwall in what is known as the Cornubian Massif. Although unlike in Devon and Cornwall, there was little or no metamorphism.
The mountain belt collapsed soon after the orogeny leading to the former northward thrusts to be reactivated as normal faults and lead to the formation of the Weald basin which developed as an extension of the considerably larger Wessex Basin. The northern margin of the basin was formed by a series of normal faults, against what was then an area of land, known to geologists as the London-Brabant Massif. The Weald basin gently subsided throughout the Jurassic, Cretaceous and Early Tertiary leading to a thick succession of sedimentary rocks being deposited.
Purbeck Beds
The oldest rocks in the county are the Purbeck beds of JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
age which crop out in small localities north west of Battle
Battle
Generally, a battle is a conceptual component in the hierarchy of combat in warfare between two or more armed forces, or combatants. In a battle, each combatant will seek to defeat the others, with defeat determined by the conditions of a military campaign...
they have a thickness of 77 to 186m in the Weald and are composed of Interbedded mudstones, limestones and evaporates (such as gypsum) of marginal freshwater, brackish and marine origin with detrital
Detrital
Detritus is a geological term used to describe particles of rock derived from pre-existing rock through processes of weathering and erosion. Detrital particles can consist of lithic fragments , or of monomineralic fragments...
quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
. These rocks were deposited in an environment of braided rivers and muddy lagoons, which periodically dried out, resulting in economic deposits of gypsum being deposited in this area, The same beds crop out in Dorset. but there are difficulties in correlating the two beds which has led to increased study on these rocks. During the deposition of these rocks they were at 30°N and thus experienced a tropical climate, which has led to the Purbeck Beds host the economic supplies of 21m thick beds of gypsum in the Robertsbridge area
Ashdown Beds and Wadhurst Clay
Ashdown Forest
Ashdown Forest is an ancient area of tranquil open heathland occupying the highest sandy ridge-top of the High Weald Area of Outstanding Natural Beauty. It is situated some south of London in the county of East Sussex, England...
.
The Ashdown Beds are predominantly siltstones and silty fine-grained sandstones with small amounts of finely-bedded mudstone and mudstone arranged in rhythmic units ("cyclothems
Cyclothems
In geology, cyclothems are alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists that worked in coal basins formed during the Carboniferous and earliest Permian periods...
") commonly divided by thin pebble beds. as described by the British Geological Survey
British Geological Survey
The British Geological Survey is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...
who also describe the Wadhurst Clay as made of soft, dark grey thinly-bedded mudstones ("shales") and mudstones with subordinate beds of pale grey siltstone, fine-grained sandstone, shelly limestone, clay ironstone and rare pebble beds, which shows evidence of unconformable weathering at the top of the bed. The Wadhurst clay hosted the small nodules of iron ore which was the very foundation of the Wealden Iron Industry. The ore was deposited in a tropical environment within which iron brought in from the eroding mountains in the west was altered into small nodules of ilmenite
Ilmenite
Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
. A succession of clays and sands was deposited into the subsiding basin, with much of the source material also being delivered from the north and east as well as the west.
Greensands and Gault
The Greensands and Gault ClayGault Clay
Gault is a clay formation of stiff blue clay deposited in a calm, fairly deep water marine environment during the Lower Cretaceous Period...
best defines the Wealden Anticline, running in a broad horseshoe from Folkestone in the East, to Petersfield in Hampshire in the West and back to Eastbourne. The Greensands are divided into two units, the Lower and Upper Greensands, which sandwich the Gault. The three units outcrop in East Sussex along the bottom of the Downs and northward into the Vale of the Weald. Although named as such the lower Greensands are rarely sand and rarely green; the name was applied by mistake by 19th century geologists mistakenly thinking that the mineral glauconite
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
would be found in the seams of sandstone both above and below the gaunt clay.
The Gault clay is one of the most fossil rich horizons in the UK; yielding plentiful bivalves, cephalopod (including ammonites) and gastropods. This has allowed for a tight correlation of the age of the gault with other geological units in Europe, under the science of biostratigraphy
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
. At its maximum the Gault clay sea grew to cover the northern landmass which had supplied the sediment for the lower sandstones; by this time Britain was at 35°N and the land and sea teemed with dinosaurs and marine reptiles, the remains of which have been found in the Gault.
Chalk
Seven Sisters
-Astronomy and mythology:*Pleiades , seven sisters who are companions of Artemis in Greek mythology*Pleiades , a star cluster named for the mythological characters...
and geologically and biologically rich cliffs from Brighton to Newhaven
Brighton to Newhaven Cliffs
Brighton to Newhaven Cliffs is a biological and geological Site of Special Scientific Interest in East Sussex, England. The site was notified in 1986 under the Wildlife and Countryside Act 1981...
. The Chalk formed in a warm, clear sea which stretched from Texas to Poland (prior to the opening of the Atlantic) and is subdivided into three units, the Lower, Middle and Upper Chalk.
Tertiary
After the end of the Cretaceous deposition continued, with the Reading and London Beds (clays and sandstones) being deposited during the Tertiary, these are no longer exposed in East Sussex, but can be seen in London and North Kent. The older Shelly clays of the Woolwich Beds at Newhaven; with gypsum to be found within the beds.The structural reversal of the basin
For much of its history the Weald had been slowly subsiding basin, but the growth of the Alpine ChainAlpide belt
The Alpide belt is a mountain range which extends along the southern margin of Eurasia. Stretching from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic, it includes the Alps, the Carpathians, the mountains of Asia Minor and Iran, the Hindu Kush, the Himalayas,...
to the south during the Tertiary caused a reactivation of the Variscan basement
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
basin-bounding faults, the rocks were arched into a broad anticline
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
which stretched across the English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
to Northern France, the Weald–Artois anticline. Inversion
Inversion (geology)
In structural geology inversion or basin inversion relates to the relative uplift of a sedimentary basin or similar structure as a result of crustal shortening. This normally excludes uplift developed in the footwalls of later extensional faults, or uplift caused by mantle plumes...
of the basin is closely correlated to compressional events within the Alps and occurred alongside deformation in Hampshire, Dorset and northern France. The basin was compressed between two 'blocks' of basement rocks, with the northward movement of the block against the London Platform; the areas of land that earlier in the Weald's history supplied the sediments. The Anticline has since been eroded down to reveal the pattern of stratigraphy with the oldest rocks in the centre of the anticline forming a low ridge which runs roughly from Crowborough
Crowborough
The highest point in the town is 242 metres above sea level. This summit is the highest point of the High Weald and second highest point in East Sussex . Its relative height is 159 m, meaning Crowborough qualifies as one of England's Marilyns...
to Battle
Battle, East Sussex
Battle is a small town and civil parish in the local government district of Rother in East Sussex, England. It lies south southeast of London, east of Brighton and east of the county town of Lewes...
and onto Boulogne
Boulogne-sur-Mer
-Road:* Metropolitan bus services are operated by the TCRB* Coach services to Calais and Dunkerque* A16 motorway-Rail:* The main railway station is Gare de Boulogne-Ville and located in the south of the city....
.
Economic Resources
The Geology of East Sussex includes a number of natural resources, at Mountfield, Robertsbridge there is a gypsumGypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
mine which produces significant quantities of gypsum extracted from the Purbeck Beds. As previously mentioned the Wadhurst Clay holds ferrous ore which was extracted up to the 17th century. Although source rock
Source rock
In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...
s for oil underlie East Sussex and the major geologic structure in the area is an anticline, petroleum is not considered to be hosted below East Sussex. However while drilling for water at Heathfield railway station
Heathfield (Sussex) railway station
Heathfield railway station was on the Cuckoo Line between Horam and Mayfield, serving the market town of Heathfield.It was built in 1880 by London, Brighton and South Coast Railway on the line extension from Hailsham to Eridge.- Present day :...
, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
was discovered, which was utilised to provide the first gas lighting in the UK, however it was recognised that economic oil reserves where not accessible. Ongoing exploration for petroleum is active in West Sussex
West Sussex
West Sussex is a county in the south of England, bordering onto East Sussex , Hampshire and Surrey. The county of Sussex has been divided into East and West since the 12th century, and obtained separate county councils in 1888, but it remained a single ceremonial county until 1974 and the coming...
however.
The large amount of clay extraction occurs within the low Weald, with brickworks
Brickworks
A brickworks also known as a brick factory, is a factory for the manufacturing of bricks, from clay or shale. Usually a brickworks is located on a clay bedrock often with a quarry for clay on site....
extracting the Weald and Wadhurst clay. Chalk is also extracted in the south of the county, with commercial extraction ongoing near Lewes
Lewes
Lewes is the county town of East Sussex, England and historically of all of Sussex. It is a civil parish and is the centre of the Lewes local government district. The settlement has a history as a bridging point and as a market town, and today as a communications hub and tourist-oriented town...
and a number of chalk extraction pits lie disused.
