The Purbeck Group is an

Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geology, geological science associated with the study of stratum, strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

(a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) in south-east

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The name is derived from the district known as the

Isle of Purbeck The Isle of Purbeck is a peninsula in Dorset, England. It is bordered by water on three sides: the English Channel to the south and east, where steep cliffs fall to the sea; and by the marshy lands of the River Frome and Poole Harbour to the n ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset (unitary authority), Dors ...

where the

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

are exposed in the cliffs west of

Swanage Swanage () is a coastal town and civil parish in the south east of Dorset, England. It is at the eastern end of the Isle of Purbeck and one of its two towns, approximately south of Poole and east of Dorchester. In the 2011 census the civil ...

. The Purbeck Group is famous for its fossils of

reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...

and early

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

. This sequence of rocks has gone by various names in the past including amongst others the Purbeck Beds, Purbeck Formation, Purbeck Limestone Formation and Purbeck Stone. Rocks of this age have in the past been called the Purbeckian

stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...

by European geologists. The Purbeckian corresponds with the

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...

Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago) ...

stages of the internationally used

geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronol ...

Outcrops

Portland Limestone - Purbeck quarry - Southern England

The Purbeck Group outcrops follow the line of the Jurassic outcrop from Dorset, through the Vale of Wardour,

Swindon Swindon () is a town and unitary authority with Borough status in the United Kingdom, borough status in Wiltshire, England. As of the 2021 Census, the population of Swindon was 201,669, making it the largest town in the county. The Swindon un ...

Garsington Garsington is a village and civil parish about southeast of Oxford in Oxfordshire. "A History of the County of Oxfordshire" provides a detailed history of the parish from 1082. The 2011 Census recorded the parish's population as 1,689. The v ...

Brill Brill may refer to: Places * Brielle (sometimes "Den Briel"), a town in the western Netherlands * Brill, Buckinghamshire, a village in England * Brill, Cornwall, a small village to the west of Constantine, Cornwall, UK * Brill, Wisconsin, an un ...

and

Aylesbury Aylesbury ( ) is the county town of Buckinghamshire, South East England. It is home to the Roald Dahl Children's Gallery, David Tugwell`s house on Watermead and the Waterside Theatre. It is in central Buckinghamshire, midway between High Wy ...

. In East Sussex, the Purbeck Group outcrops at three locations north and northwest west of

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-east of London, east of Brighton and east of Lewes. Hastings is to the south-east and Bexhill-on-Sea to the south. Batt ...

and at Netherfield. They also occur at several other locations east of

Heathfield, East Sussex Heathfield is a market town in the Wealden District of East Sussex, England. The town had a population of 7,732 in 2011. With neighbouring Waldron, it forms the civil parish of the Heathfield and Waldron, which had a population of 11,913 in 2 ...

and at Beak's Wood near

Burwash Burwash, archaically known as Burghersh, is a rural village and civil parish in the Rother district of East Sussex, England. Situated in the High Weald of Sussex some 15 miles (24 km) inland from the port of Hastings, it is located five ...

. Deposits of evaporite minerals such as

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...

and

anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...

, within the Purbeck Group are mined and processed in

Mountfield, East Sussex Mountfield is a village and civil parish in the Rother district of East Sussex, England, and three miles (5 km) north-west of Battle. It is mentioned in the ''Domesday Book''. The parish church is dedicated to All Saints; Mountfield and ...

.Codd, J.W. (2007) ''Analysis of the distribution and characteristics of landslips in the Weald of East Sussex''. MSc dissertation, University of Brighton. In

Lincolnshire Lincolnshire (abbreviated Lincs.) is a county in the East Midlands of England, with a long coastline on the North Sea to the east. It borders Norfolk to the south-east, Cambridgeshire to the south, Rutland to the south-west, Leicestershire ...

they are represented in part by the Spilsby Sands and in

Yorkshire Yorkshire ( ; abbreviated Yorks), formally known as the County of York, is a Historic counties of England, historic county in northern England and by far the largest in the United Kingdom. Because of its large area in comparison with other Eng ...

by portions of the

Speeton Clay The Speeton Clay Formation (SpC)Speeton Clay Formation
- The rocks predominantly comprise calcareous mudstones though also include

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

s and

marl Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part o ...

s with

y, tuffaceous and shelly

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, occasional oolitic and sandy strata, and

evaporites An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...

. Nodules of

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

are present in some of the limestones. The thickness of the formation in Wiltshire is 80 to , but in Dorset it is typically between thick. In the

Weald The Weald () is an area of South East England between the parallel chalk escarpments of the North and the South Downs. It crosses the counties of Hampshire, Surrey, Sussex and Kent. It has three separate parts: the sandstone "High Weald" in the ...

East Sussex East Sussex is a ceremonial and non-metropolitan county in South East England on the English Channel coast. It is bordered by Kent to the north and east, West Sussex to the west, and Surrey to the north-west. The largest settlement in East Su ...

the Purbeck Group has a typical thickness of between . In most places the Purbeck Group rests conformably upon the Portland Group and it is conformably overlaid by the Wealden Group; but there are in some districts distinct indications that the Portland Group was uplifted and worn away to some extent prior to the deposition of the Purbeck Group.

Correlations

In the past, many geologists have ranged the Purbeck Group with the overlying Lower Cretaceous Wealden Group on account of the similarity of its fresh-water faunas; but the marine fossils, including the fishes, ally the Purbeck more closely with the Upper Jurassic rocks of other parts, and it may be regarded as the equivalent of the upper Volgian of

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. Contemporaneous rocks are also present in the neighbourhood of

Boulogne-sur-Mer Boulogne-sur-Mer (; pcd, Boulonne-su-Mér; nl, Bonen; la, Gesoriacum or ''Bononia''), often called just Boulogne (, ), is a coastal city in Northern France. It is a sub-prefecture of the department of Pas-de-Calais. Boulogne lies on the ...

, where they are characterized by thin limestones with ''Cyrena'' and gypsiferous marls. These French outcrops occur, just like those in England, in the core of the Weald-Artois anticline. Purbeckian aged deposits occur even further south in the

Charente Charente (; Saintongese: ''Chérente''; oc, Charanta ) is a department in the administrative region of Nouvelle-Aquitaine, south western France. It is named after the river Charente, the most important and longest river in the department, an ...

. In north-west

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

three subdivisions are recognized in strata of the same age: in descending order

Purbeck Kalk Purbeck may refer to: * Isle of Purbeck, a peninsula in the English county of Dorset ** Purbeck Mineral and Mining Museum * Purbeck District, a local government district in the English county of Dorset * Purbeck Hills, a range of hills in the Engl ...

, Serpulit and Münder Mergel.

Subdivisions

Modern

The Purbeck Group in

is now divided into three formations, the

Lulworth Formation The Lulworth Formation is a geologic formation in England. It dates from the late Tithonian to the mid Berriasian. It is a subunit of the Purbeck Group. In Dorset, it consists of three members, which are in ascending order, the Mupe Member, the ...

and the overlying

Durlston Formation The Durlston Formation is a geologic formation in England. Particularly in the Isle of Purbeck. It preserves fossils dating back to the Berriasian stage of the Lower Cretaceous. Vertebrate paleobiota Crocodyliformes See also * List of f ...

in the south (in the Vectian or

Wessex Basin The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the Englis ...

). A third underlying formation, the Haddenham Formation, is identified in Wiltshire, Oxfordshire and Buckinghamshire. Within the Vectian Basin, the Durlston Formation is further divided into a lower 'Stair Hole Member' and an upper 'Peveril Point Member'. Similarly the Lulworth Formation is divided in Dorset into a lower 'Mupe Member', a middle 'Ridgeway Member' and an upper 'Worbarrow Tout Member'. In

the Purbeck Group is formally subdivided into the Blues and Greys Limestones members

Traditional

The sequence was traditionally divided into three, though along different lines viz. Upper, Middle and Lower. The Upper Purbeck comprises . of fresh-water clays and shales with limestones, the

Purbeck marble Purbeck Marble is a fossiliferous limestone found in the Isle of Purbeck, a peninsula in south-east Dorset, England. It is a variety of Purbeck stone that has been quarried since at least Roman times as a decorative building stone. Geology Strat ...

and ''Unio''-bed, in the lower part. The Middle division (), mainly thin limestones with shaly partings, contains the principal building stones of the Swanage district; near the base of this subdivision there is a , bed from which an interesting suite of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

ian remains has been obtained; in this portion of the Purbeck Group there are some marine bands. The Lower Purbeck consists of fresh-water and terrestrial deposits, marls, and limestones (the famous

Portland limestone Portland stone is a limestone from the Tithonian stage of the Jurassic period quarried on the Isle of Portland, Dorset. The quarries are cut in beds of white-grey limestone separated by chert beds. It has been used extensively as a building sto ...

) with several fossil soils known as ''dirt beds''. This division is very extensively exposed on the

Isle of Portland An isle is an island, land surrounded by water. The term is very common in British English. However, there is no clear agreement on what makes an island an isle or its difference, so they are considered synonyms. Isle may refer to: Geography * Is ...

, where many of the individual beds are known by distinctive names. The chief building stones of Upwey belong to this part of the Purbeck Group.

Fossil content

No zonal

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

has been recognized for the British Purbeckian strata, but the horizon is approximately equivalent to that of '' Pensphinctes transilorius'' of the European continent. The Purbeckian equivalents of Spilsby and Speeton are in the zone of ''

Belemnites lateralis Belemnites may refer to: *Belemnitida Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. ...

''. Other marine fossils are '' Hemicidaris purbeckensis'' and '' Ostrea distonta'', the latter being abundant in the Cinder bed of the Middle Purbeck. The fresh-water mollusca include ''

Viviparus ''Viviparus'', common name the river snails, is a genus of large, freshwater snails with an operculum, aquatic gastropod mollusks.Bouchet, P. (2014). Viviparus Montfort, 1810. Accessed through: World Register of Marine Species at http://www ...

'' (''Paludina''), ''

Planorbis ''Planorbis'' is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids. All species in this genus have sinistral or left-coiling shells.Bouchet, P.; Rosen ...

'', ''

Melanopsis ''Melanopsis'' is a genus of freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Melanopsidae.Rosenberg, G. (2014). Melanopsis Férussac, 1807. Accessed through: World Register of Marine Species at http:/ ...

'', '' Unio'', '' Cyrena''. A large number of insect genera has been found in the Middle and Lower Purbeck Group.

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s (''

Owenodon ''Owenodon'' is a genus of iguanodontian dinosaur known from a partial lower jaw discovered in Early Cretaceous-age rocks of Durlston Bay, Dorset, United Kingdom. The specimen, NHM R2998, comes from the Purbeck Limestone, dating to the mid ...

'', ''

Echinodon ''Echinodon'' is a genus of heterodontosaurid dinosaur that lived during the earliest Cretaceous of southern England and possibly western France in the Berriasian epoch. The first specimens were jaw bones named ''Echinodon becklesii'' by Sir Ric ...

'' nown from "Isolated skull elements of at least [threeindividuals.""Table 18.1," in Weishampel, et al. (2004). Page 394.]), crocodylians (''Goniopholis'', ''Petrosuchus''), ''Cimoliosaurus'', the plesiosaurs and the Testudines, chelonians (''Chelone'', ''Pleurosternum'') are representative reptiles. The mammals, mostly determined from lower jaws, found in the beds mentioned above include ''

Plagiaulax ''Plagiaulax'' is a genus of mammal from the Lower Cretaceous of Europe. It was a member of the also extinct order Multituberculata, and shared the world with dinosaurs. It is of the suborder "Plagiaulacida" and family Plagiaulacidae. The genus ...

'', ''

Amblotherium ''Amblotherium'' is an extinct genus of Late Jurassic and Early Cretaceous mammal. The type species ''Amblotherium pusillum'' is from the Lulworth Formation of southern England, while the referred species ''Amblotherium gracile'' is from strati ...

'', '' Stylodon'', ''

Dorsetodon ''Dorsetodon'' is an extinct genus of mammal from the Early Cretaceous ( Berriasian) Purbeck Group of Britain. It is represented by isolated lower molars.P. C. Ensom and D. Sigogneau-Russell, 1998. New dryolestoid mammals from the basal Cretaceo ...

'', ''

Triconodon ''Triconodon'' ("three coned tooth") is a genus of extinct mammal from the Early Cretaceous of England and France with two known species: ''T. mordax'' and ''T. averianovi''. First described in 1859 by Richard Owen,R. Owen. 1859. Palaeontology ...

'', ''

Spalacotherium ''Spalacotherium'' is a genus of extinct mammal from the Early Cretaceous of Europe. The type species ''Spalacotherium tricuspidens'' was originally named by Richard Owen in 1854, and its material includes maxillary and dentary fragments and ...

'' and several others. The

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

'' Archaeoniscus brodiei'' is very common in the Purbeck of the

Vale of Wardour The Vale of Wardour encompasses the valley of the River Nadder in the county of Wiltshire, England. Geography Topography The Vale of Wardour lies east of the town of Shaftesbury and is a relatively small but varied landscape. Named after the ...

Reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

remains diagnostic to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

level (''Megalosaurus'' sp (theropod indet), ''

Opisthias ''Opisthias'' is a genus of sphenodont reptile. The type species, ''Opisthias rarus'', is known from the Late Jurassic (Kimmeridgian-Tithonian) Morrison Formation of western North America, present in stratigraphic zones 2 and 4–6. Distributi ...

'') are among the fossils that have been recovered from the formation.Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .

Fossil eggs Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of ...

referable to the

oogenus Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of ...

Mycomorphoolithus ''Mycomorphoolithus'' (meaning "fungus-shaped stone egg") is an oogenus of fossil eggs found in Spain and England. They possibly represent eggshells of non-eusuchian Crocodylomorpha, crocodylomorphs, and are similar to, but not part of, the Krokol ...

'' are also known from the Purbeck Group.Miguel Moreno-Azanza, Jose Ignacio Canudo, and Jose Manuel Gasca. (2015) "Enigmatic Early Cretaceous ootaxa from Western Europe with signals of extrinsic eggshell degradation" ''

Cretaceous Research ''Cretaceous Research'' is a bimonthly peer-reviewed scientific journal published by Elsevier. The journal focuses on topics dealing with the Cretaceous period and the Cretaceous–Paleogene boundary. Abstracting and indexing The journal is a ...

'' 56: 617-627. The

silicified In geology, petrifaction or petrification () is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. Petrified wood typifies this proce ...

stumps and trunks of

cycads Cycads are seed plants that typically have a stout and woody ( ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...

and

coniferous tree Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extant ...

s, often surrounded by great masses of calcareous

concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

s (''burrs''), are very noticeable in the dirt beds of Portland and near

Lulworth Lulworth is the popular name for an area on the coast of Dorset, South West England notable for its castle and cove. However, there is no actual place or feature called simply "Lulworth", the villages are East and West Lulworth and the coastal f ...

. '' Chara'' is found in the fresh-water cherts of the Middle Purbeck.

Use in construction

The building stones of the Purbeck Group have already been mentioned; the Purbeck or Paludina "

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or Dolomite (mineral), dolomite. Marble is typically not Foliation (geology), foliated (layered), although there are exceptions. In geology, the ...

", a grey or greenish limestone full of shells, was formerly extensively employed in cathedrals and churches. Stone tiles or slats were once used locally for roofing from the Lower Purbeck of Portland, Swanage and Swindon. Gypsum was formerly worked from the Lower Purbeck at Swanage.

References

{{EB1911 , wstitle=Purbeckian , volume=22 , pages=657–658 Geological groups of the United Kingdom Geologic formations of England Jurassic System of Europe Lower Cretaceous Series of Europe Cretaceous England Jurassic England Tithonian Stage Berriasian Stage Mudstone formations Limestone formations Marl formations Shale formations Ooliferous formations Geology of Dorset