The Bouldnor Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

in the

Hampshire Basin The Hampshire Basin is a geological basin of Palaeogene age in southern England, underlying parts of Hampshire, the Isle of Wight, Dorset, and Sussex. Like the London Basin to the northeast, it is filled with sands and clays of Paleocene and yo ...

of southern

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 ...

. It is the youngest formation of the Solent Group and was deposited during the uppermost

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

and lower

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 ...

Stratotype and occurrence

The Bouldnor Formation was named after

Bouldnor Bouldnor is a hamlet near Yarmouth on the west coast of the Isle of Wight in southern England. It is the location of Bouldnor Battery, a gun battery emplacement. Bouldnor is located on the A3054 road, and public transport is provided by buses ...

, a small hamlet east of

Yarmouth Yarmouth may refer to: Places Canada *Yarmouth County, Nova Scotia **Yarmouth, Nova Scotia **Municipality of the District of Yarmouth **Yarmouth (provincial electoral district) **Yarmouth (electoral district) * Yarmouth Township, Ontario *New ...

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...

. The formation is exposed along ''Bouldnor Cliff'' between Yarmouth and Hamstead occupying the core of the east-southeast-striking ''Bouldnor Syncline''. Yet the

stratotype A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...

of the formation is found at ''Whitecliff Bay'' on the east side of the Isle of Wight.

History

The Bouldnor Formation was scientifically established 1985 by A. Insole and B. Daly, who also defined its

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

. The

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 ...

strata on the Isle of Wight had already been described in 1853 by

Edward Forbes Edward Forbes FRS, FGS (12 February 1815 – 18 November 1854) was a Manx naturalist. In 1846, he proposed that the distributions of montane plants and animals had been compressed downslope, and some oceanic islands connected to the mainlan ...

. Forbes was followed in 1921 by H.J.O. White, a geologist from the Geological Survey.

Stratigraphy

The Bouldnor-Formation is the topmost formation of the Solent Group before the sea withdrew completely from the

. The thickness of the formation can vary between 45 and 115 metres. After a long

hiatus Hiatus may refer to: *Hiatus (anatomy), a natural fissure in a structure *Hiatus (stratigraphy), a discontinuity in the age of strata in stratigraphy *''Hiatus'', a genus of picture-winged flies with sole member species ''Hiatus fulvipes'' *Globa ...

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

and

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

sediments covered the formation discordantly. The Bouldnor Formation lies concordantly on desiccation cracks of the upper Bembridge Limestone (

Bembridge Limestone Formation Bembridge is a village and civil parish located on the easternmost point of the Isle of Wight. It had a population of 3,848 according to the 2001 census of the United Kingdom, leading to the implausible claim by some residents that Bembridge ...

), a freshwater deposit. The formation consists mainly of

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 ...

s with some intercalated

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

s which were sedimented along a coastal plain in

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

al and

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

palustrine Palustrine wetlands include any inland wetland that contains ocean-derived salts in concentrations of less than 0.5 parts per thousand, and is non-tidal. The word ''palustrine'' comes from the Latin word ''palus'' or marsh. Wetlands within this ca ...

facies judging by the enclosed freshwater, brackish and marine biota. Marine conditions were only rarely achieved, examples being the ''Bembridge Oyster Bed'', the ''Nematura Bed'' and sections of the upper Cranmore Member. A very diversified and well preserved biota can be found within the Bouldnor Formation comprising

molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil sp ...

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

(especially

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 ...

charophytes Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a phylum, division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly fro ...

and vascular

plants Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

. The nonmarine layers are characterized by

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...

like Australorbis,

Lymnaea ''Lymnaea'' is a genus of small to large-sized air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the subfamily Lymnaeinae ( of the family Lymnaeidae, the pond snails.Bouchet, P.; Rosenberg, G. (2013). Lymnaea Lamarck, 179 ...

/Galba and

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 ...

and

ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...

like Gandona,

Cypridopsis ''Cypridopsis'' is a genus of ostracods, belonging to the family Cyprididae. The genus was described in 1867 by George Stewardson Brady. The genus has cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the ...

and Moenocypris. In the middle section (i.e. in the Hamstead Member) the effects of the

Grande Coupure Grande means "large" or "great" in many of the Romance languages. It may also refer to: Places * Grande, Germany, a municipality in Germany *Grande Communications, a telecommunications firm based in Texas *Grande-Rivière (disambiguation) *Arroi ...

on the biota are clearly noticeable and follow immediately after the negative oxygen excursion Oi-1 at the beginning of the Oligocene. Stratigraphically the Bouldnor Formation is subdivided into three members (from top to bottom): * Cranmore Member * Hamstead Member * Bembridge Marls Member

Bembridge Marls Member

The basal, 20 to 23 metres, exceptionally-35 metres-thick Bembridge Marls Member is mainly composed of blueish to greenish-gray clays 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. Interlaced are several mollusc-bearing horizons. The clays show a rhythmical,

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (var ...

-like layering. The member overlies the summital mudcracks of the Bembridge Limestone Formation without any discontinuity. It correlates magnetostratigraphically with the upper part of chron C 13r and biostratigraphically with the calcareous nannoplanktonzone NP21. The member therefore belongs to the upper

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 ...

and has an absolute age of 34.0 to 33.75 million years BP. The Bembridge Marls Member was mainly sedimented in fresh or brackish water as indicated by

cirripedia A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...

and gastropods like Terebia. The lower section of the member is of

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

origin, whereas the upper section was laid down by rivers inhabited by prosobranchs like

. Relatively short-lived marine inraids are recognizable in horizons like the ''Bembridge Oyster Bed'' 1.5 metres above the base and a limestone band with bivalves like

Corbicula ''Corbicula'' is a genus of freshwater and brackish water clams, Aquatic animal, aquatic bivalve mollusks in the family Cyrenidae, the basket clams.Gofas, S. (2015). Cyrenidae Gray, 1847. In: MolluscaBase (2015). Accessed through: World Registe ...

and

Nucula ''Nucula'' is a genus of very small saltwater clams. They are part of the Family (biology), family Nuculidae. Fossil records This genus is very ancient. Fossils are known from the Arenig to the Quaternary (age range: from 478.6 to 0.0 million ye ...

. Amongst the

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

Amia sp. and other amiids have been found The fossil contents of the Bembridge Marls Member are quite varied, with freshwater species like

and Unio and marine taxa like

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:/ ...

Meretrix Prostitution in ancient Rome was legal and licensed. In ancient Rome, even Social class in ancient Rome, Roman men of the highest social status were free to engage prostitutes of either sex without incurring moral disapproval, as long as they dem ...

and

Ostrea ''Ostrea'' is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters. Fossil records This genus is very ancient. It is known in the fossil records from the Permian to the Quaternary (age range: from 259 to 0.0 ...

. The ''Bembridge Insect Bed'' at the base of the member is a marly sand layer with a very rich insect fauna and many

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

. This layer constitutes a

lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...

with very good preservation. Amongst the finds are

coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...

and

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

as for instance '' Aeschnophlebia andeasi'', '' Oligoaeschna anglica'' and '' Vectaraneus yulei''. Plant remains within the member include

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae **List of Arecaceae genera * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...

seeds and the

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

Acrostichum ''Acrostichum'' is a fern genus in the Parkerioideae subfamily of the Pteridaceae. It was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "ac ...

. Amongst the mammals are '' Anoplotherium latipes'', '' Bransatoglis bahloi'', '' Choeropotamus parisiensis'', '' Ectropomys exiguus'', '' Gesneropithex sp.'', '' Glamys devoogdi'', '' Haplomeryx zitteli'', '' Heterohyus'', '' Microchoerus edwardsi'', '' Palaeotherium medium'', '' Paroxacron sp.'', ''

Peratherium ''Peratherium'' is a genus of metatherian mammals in the family Herpetotheriidae that lived in Europe and Africa from the Early Eocene to the Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch ( ...

'', '' Plagiolophus major'', '' Plagiolophus minor'', '' Saturninia gracilis'', '' Suevosciurus ehingensis'', '' Tarnomys schmidtkittleri'', '' Theridomys bonduelli'' and '' Treposciurus''.

Hamstead Member

The 20 to 70 meter thick Hamstead Member is divided in two by the ''Nematura bed'' (rich in '' Nematura parvula'').

Lower Hamstead Member

The 10-meter-thick ''Lower Hamstead Member'' follows directly upon the Bembridge Marls Member with a 40-centimetre-thick olive to black seam, the ''Black Band''. This layer is very rich in organic matter and was deposited under freshwater conditions. At its base it carries

calcrete Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...

nodules and

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

lets. The Black Band is overlain by roughly 4 metres of a greenish-greyish clay-

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...

interlayering. This changes to 3 metres of blue to brown, finely laminated clays including some shelly horizons. These clays are capped by a 1-metre-thick, blueish-greyish, clayey sand layer with ball-and-pillow-structure, contorted bedding and

convolute bedding {{Short description, Geologic formation Soft-sediment deformation structures develop at deposition or shortly after, during the first stages of the sediment's consolidation. This is because the sediments need to be "liquid-like" or unsolidified ...

indicating dewatering of the sediment during

diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...

. This gravitationally unstable bed is known as the ''log bed'' for its up to 5-metre-long tree trunks. The log bed is clearly a freshwater deposit as it contains besides the tree trunks plenty of washed-up

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...

s of the species

Potamogeton ''Potamogeton'' is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed (''Elodea canadensis'' ...

and Stratiodes, and also the leaves of monocotyledon and dicotyledon plants. Its faunal remains attest the last pre-Grande Coupure assemblage (MP20). After a distinct hiatus follows

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

the ''Nematura bed'' which closes the Lower Hamstead Member. This bed is almost 1 meter thick and is characterized by chocolate-brown

ripple marks In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''unidi ...

enclosed in alternating clays and sands. It attests brackish conditions with a lot of reworked wood debris. Besides molluscs like ''Nematura'' (now Stenothyra) and Polymesoda there are also marine

dinoflagellates The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

and the ostracode Hemicyprideis. Within the basal shell layer traces of an eroded soil horizon (paleosoil) were found. The hiatus underneath is estimated to have lasted 350.000 years. The following mammal taxa were found in the Lower Hamstead Member: '' Amphidozotherium cayluxi'', '' Amphiperaterium exile'', '' Anoplotherium latipes'', '' Bransatoglis planus'', '' Butselia biveri'', '' Cryptopithecus'', '' Eotalpa anglica'', '' Glamys fordi'', '' Palaeotherium curtum'', '' Palaeotherium muehlbergi'', '' Paradoxonycteris tobieni'', '' Pseudoltinomys cuvieri'', '' Ronzotherium sp.'', '' Stehlinia minor'', '' Suevosciurus ehingensis'', '' Suevosciurus fraasi'', '' Theridomys bonduelli'' and '' Xiphodon gracilis''. Amongst plants

conifers 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 extan ...

start appearing, an example being '' Quasisequoia couttsiae'' and the

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

'' Inaperturopollenites magnus''.

Upper Hamstead Member

The Upper Hamstead Member can reach a thickness of 60 meters. It starts with a 3-meter thick interlayering of greenish-greyish clay and silt bearing decalcified Polymesoda shells. Roughly 10 metres above the base follows the ''Eomys bed'' and immediately above it the ''White Band'' also containing Polymesoda shells. After the ''Crocodile bed'' the member ends with 8 meters of turquoise, plastic clays with orange-red freckles. Intercalated are occasional brown,

slickenside In geology, a slickenside is a smoothly polished surface caused by frictional movement between rocks along a fault. This surface is typically striated with linear features, called slickenlines, in the direction of movement. Geometry of slickensi ...

d, laminated clays and some shell horizons. Worth mentioning is also the ''White lily bed'' in the upper third of the Upper Hamstead Member. Mammal remains were also found in the Upper Hamstead Member. They belong to the following species: '' Amphicynodon sp.'', '' Amphiperatherium exile'', '' Amphiperaterium minutum'', '' Asteneofiber'', '' Atavocricetodon atavus'', '' Bothriodon velaunus'', '' Butseloglis micio'', '' Cryptopithecus'', '' Elomeryx porcinus'', ''

Entelodon magnus ''Entelodon'' (meaning "complete teeth", from Ancient Greek ''entelēs'' "complete" and ''odōn'' "tooth", referring to its "complete" eutherian dentition), is an extinct genus of entelodont artiodactyl endemic to Eurasia. Fossils of species ar ...

'', ''

Eomys ''Eomys'' is an extinct genus of eomyid rodent from the late Oligocene of France, Germany, Spain, and possibly Turkey. The species ''Eomys quercyi'' is the earliest known gliding rodent. References External links ''Eomys''in the Paleobiology ...

'', '' Glamys fordi'', '' Hyaenodon dubius'', '' Isoptychus margaritae'', '' Leptadapis sp.'', '' Myxomygale antiqua'', '' Paradoxonycteris tobieni'', ''

Pecora Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, ''Hydropotes'' and ''Moschus''. The name “Pecor ...

'', '' Peratherium perriense'', '' Pseudoltinomys gaillardi'', '' Ronzotherium romani'', '' Stehlinia gracilis'', '' Tapirulus hyracinus'' and ''

Tetracus ''Tetracus'' is an extinct genus of gymnures. Species are from the Oligocene of Belgium and France. Fossils can also be found in the Bouldnor Formation in the Hampshire Basin of southern England. Species: * †''Tetracus nanus'' (Aymard, 1846) ...

''. Chronologically the Hamstead Member starts at the Priabonian/

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 ...

boundary and reaches into the upper Rupelian. It comprises the chrons C 13n and the lower part of C 12r. In absolute age it covers the time span 33.75 to 32.5 million years BP.

Cranmore Member

The Cranmore Member on top of the Bouldnor Formation is merely 5 to 9 meters thick and consists mainly of blueish-greenish clays. It starts off as a brackish facies (''Cerithium beds'' with

Cerithium ''Cerithium'' is a genus of small to medium-sized sea snails, marine gastropod molluscs in the family Cerithiidae, the ceriths.Gofas, S. (2011). Cerithium Bruguière, 1789. Accessed through: World Register of Marine Species at http://www.marinesp ...

) but changes to marine in the ''Corbula beds'' (with '' Corbula pisum'' and '' Corbula vectensis''). The marine character is also underlined by the gastropods '' Hydrobia sp.'', '' Pusillina turbinata'', '' Sandbergeria vectiana'', '' Strebloceras cornuides'', '' Syrnola sp.'' and '' Teinostoma decussatum''. Also present are '' Viviparus lentus'' shells. The Cranmore Member belongs biostratigraphically to the calcareous nannofossil

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties of ...

NP23. The sedimentation stopped at the end of the member and the sea withdrew completely from the Hampshire Basin.

Sequence stratigraphy

The Bouldnor-Formation consists of two second-order

sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is calle ...

s, the

sequence boundary In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called t ...

(SB) being situated right underneath the ''Nematura bed''. The first sequence already started at the base of the

. The marine intervals within the Bouldnor Formation are interpreted as

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

highstand A raised shoreline is an ancient shoreline exposed above current water level. These landforms are formed by a relative change in sea level due to global sea level rise, isostatic rebound, and/or tectonic uplift. These surfaces are usually expos ...

s. The ''log bed'' was formed during retreating sea levels and are part of a

falling stage systems tract Falling or fallin' may refer to: *Falling (physics), movement due to gravity *Falling (accident) *Falling (execution) *Falling (sensation) People *Christine Falling (born 1963), American serial killer who murdered six children Books *Falling ...

(FSST). It is plausible that this fall in sea level correlates with the onset of

glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

at the beginning of the Oligocene. The Eocene/Oligocene boundary most likely is situated below the sequence boundary in the Lower Hamstead Member or high in the upper Bembridge Marls Member. Remark: This interpretation proposed by Hooker et al. (2009) is not accepted by all geologists. Gale et al. (2006) for instance place the sequence boundary much lower in the Bembridge Limestone Formation and also further subdivide the lower sequence into three sequences.Gale, A.S. et al. (2006). Correlation of Eocene–Oligocene marine and continental records: orbital cyclicity, magnetostratigraphy and sequence stratigraphy of the Solent Group, Isle of Wight, UK. Journal of the Geological Society. London, 163, pp. 401–415

Grande Coupure

The

within the Bouldnor Formation can be characterized by the enclosed biota as follows: In the Upper Hamstead Member 16 new taxa appear for the first time and 11 disappear. Within the pre-Grand Coupure Lower Hamstead Member only 5 new appearances were registered, mainly European

rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are nat ...

like Butselia. Amongst the 16 newcomers at the Grande Coupure are 10 immigrant species from

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

. Noticeable is also a concurrent general reduction in diversity. Within the Bembridge Limestone Formation 47 taxa were present, whereas within the Upper Hamstead Member the number of species had reduced to 28. One should notice though that the minimum in diversity with 20 taxa was already reached within the Lower Hamstead Member. This argues for a much more drawn out process in the reduction of species setting in already before the Grande Coupure. The Grande Coupure itself is distinguished by the fairly rapid replacement of

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

species with immigrants from Asia.

References

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Bibliography

* Hooker, J.J. The Grande Coupure in the Hampshire Basin, UK: taxonomy and stratigraphy of the mammals on either side of this major Paleogene faunal turnover. Micropalaeontology, Sedimentary Environments and Stratigraphy. Edited by Wittaker, J.E. & Hart, M.B. * Hooker, J.J. et al.(2009). Refined correlation of the UK Late Eocene-Early Oligocene Solent Group and timing of its climate history. The Geological Society of America Special Paper 452. The late Eocene Earth: hothouse, icehouse and impacts. Edited by Christian Koeberl & Alessandro Montanari.

External links

Contribution by A.S. Gale et al.
Stratigraphy of the United Kingdom Geologic formations of England Eocene Series of Europe Oligocene Series of Europe Priabonian Stage Rupelian Stage Shale formations Paleontology in England Geology of the Isle of Wight Geology of Hampshire