The Letná Formation is a Late Ordovician ( Sandbian, or in the regional stratigraphy Berounian) geologic formation of the Prague Basin,

Bohemian Massif The Bohemian Massif ( or ''Český masiv'', or ''Böhmisches Massiv'') is a geomorphological province in Central Europe. It is a large massif stretching over most of the Czech Republic, eastern Germany, southern Poland and northern Austria. Th ...

in the Czech Republic. The formation crops out in the Czech capital, more specifically at Letná Hill, after which the formation is named. The type locality is located at Malá Strana, Holešovice district.Kříž & Steinová, 2009 The more than thick formation comprises a rhythmic alternation of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s (

greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...

s and subgreywackes),

quartzite Quartzite is a hard, non- foliated metamorphic rock that 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 tecton ...

s, intercalated with

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. Although its permeabil ...

s and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

s deposited in marine

flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building ep ...

-like

environments Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...

. Because of the excellent preservation, including gut remains, of a wide assemblage of early Paleozoic taxa in which

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s dominate, the formation, which is lean in fossils in many areas but exceptionally rich in what has been interpreted as storm beds, has been designated a '' Konservat-Lagerstätte''.

Description

The Letná Formation was first formally defined in 1966 by Havlíček and Vaněk and crops out in the Prague Basin, a northeast–southwest trending minibasin stretching over between

Rokycany Rokycany (; ) is a town in the Plzeň Region of the Czech Republic. It has about 14,000 inhabitants. The historic town centre is well preserved and is protected as an Cultural monument (Czech Republic)#Monument zones, urban monument zone. Admini ...

in the southwest and

Úvaly Úvaly () is a town in Prague-East District in the Central Bohemian Region of the Czech Republic. It has about 7,500 inhabitants. Etymology The name means 'valleys' in Czech. It was originally used in the singular, but was gradually changed to th ...

in the northeast. The Prague Basin contains an Ordovician to Devonian succession in the larger

.Mikuláš, 1998b, p.143 The formation conformably overlies the Libeň Formation and is overlain by the Vinice Formation.Fatka et al., 2013, p.96 The Letná Formation is the thickest unit in the sedimentary sequence with a thickness of more than between

Beroun Beroun (; ) is a town in the Central Bohemian Region of the Czech Republic. It has about 22,000 inhabitants. It lies at the confluence of the Berounka and Litavka rivers. Beroun creates a conurbation with Králův Dvůr, former part of Beroun. ...

and

Prague Prague ( ; ) is the capital and List of cities and towns in the Czech Republic, largest city of the Czech Republic and the historical capital of Bohemia. Prague, located on the Vltava River, has a population of about 1.4 million, while its P ...

.Mikuláš, 1998a, p.5Fatka et al., 2013, p.97 The formation consists of a rhythmic alternation of

s (

s and subgreywackes),

s, intercalated with

s and

s with

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

lenses in the upper part of the succession, deposited in a shallow marine environment, representing a

deposition in the early Paleozoic. While in most of the layers fossils are absent, certain levels contain a rich assemblage of shallow marine fauna interpreted as storm-induced beds. The concentration of a wide variety of excellently conserved fossils of the Letná Formation has granted it the name of a '' Konservat-Lagerstätte'', giving insight into the diversification of marine ecosystems.Noheljová et al., 2019, p.69 A rather diverse fauna composed of brachiopods, trilobites, echinoderms, conularids, and non-trilobite arthropods has been found in outcrops located between Zdice and Chrustenice. This area probably represented a rather shallow environment in the northwestern part of the basin. The fossils are usually fragmentary and preserved as internal or external moulds associated with angular claystone fragments within quartzose sandstones to siltstones. Accumulations of these fossil remains are commonly found in thick-bedded quartzose sandstones of light-grey and yellow or grey-brown color, which might have been deposited in areas sheltered from wave activity by sand bars. Five communities of marine fauna were identified in the formation. The rich brachiopod dominated '' Drabovia'' Community is associated with shallow water, well-sorted quartzose sandstones. The '' Bicuspina'' Community, which probably represents a slightly deeper environment, is typically found in the poorly sorted greywackes of the higher horizons of the Letná Formation. These two communities constitute the '' Drabovia''-'' Aegiromena'' Fauna. In more proximal environments, this fauna is replaced by the trilobite-dominated ''

Dalmanitina ''Dalmanitina'' is an extinct genus of trilobite in the family Dalmanitidae. There are about seven described species in ''Dalmanitina''. Species These seven species belong to the genus ''Dalmanitina'': * † ''Dalmanitina acuta'' Hammann, 1971 ...

''-'' Deanaspis'' Association, which contains '' Birmanites ingens'' and '' Selenopeltis buchi''. The more distal, probably deeper parts of the basin are characterized by a poorly diversified assemblage of trilobites associated with rare

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

s. Lastly, trilobites of the so-called '' Cyclopygid'' Biofacies and brachiopods of the '' Paterula'' Association are typical for the deepest portions of the Prague Basin. Intertidal ('' Skolithos'' ichnofacies) and near-shore ('' Cruziana'' ichnofacies) environments are also evidenced by ichnofossils.Fatka et al., 2013, p.98 Fossilized gut remains have been observed in four of the about twenty trilobite species present in the Letná Formation: ''Birmanites ingens'', '' Dalmanitina socialis'', '' Deanaspis goldfussi'' and '' Selenopeltis buchi''. These four trilobites belong to the ''Dalmanitina''-''Deanaspis'' Association, characterizing rather proximal and shallow environments of the Letná Formation. Most of the non-trilobite arthropods discovered in this formation, including forms with non-mineralized exoskeletons, are also found associated with ''D. goldfussi'' and/or ''D. socialis''. This suggests that the development of conditions conducive to soft-tissue fossilization was not uncommon in the environment represented by the ''Dalmanitina''-''Deanaspis'' Association.Fatka et al., 2013, p.98

Fossil content

The following fossils were reported from the formation:Letná Formation
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org *

Trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s ** '' Actinopeltis completa'' ** '' Birmanites ingens''Fatka et al., 2013, p.99 ** '' Calymenella parvula'' ** '' Caryon bohemicus'' ** '' Cekovia transfuga'' ** '' Colpocoryphe grandis'' ** '' Dalmanitina socialis'' ** '' Deanaspis goldfussi'' ** '' Eudolatites dubia'' ** '' Eccoptochile (Eccoptochile) clavigera'' ** '' Eccoptochile (Eccoptochiloides) tumescens'' ** '' Kloucekia phillipsi'' ** '' Pharostoma pulchrum'' ** '' Placoparia (Hawleia) grandis'' ** '' Plaesiacomia rara'' ** '' Platycoryphe bohemica'' ** '' Primaspis (Primaspis) primordialis'' ** '' Selenopeltis buchi'' ** '' Stenopareia panderi'' ** '' Vysocania moraveci''Pereira et al., 2017, p.466 ** '' Zeliszkella (Zeliszkella) hawlei'' ** '' Girvanopyge sp.'' ** '' Heterocyclopyge sp.'' ** '' Prionocheilus sp.'' * Non-trilobite

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s ** '' Duslia insignis'' ** '' Quasicaris bohemica'' ** '' Furca bohemica'' ** '' Furca sp.'' ** '' Zonozoe drabowiensis'' *

Crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

s ** '' Caleidocrinus multiramus'' *

Lingulata Lingulata is a class of brachiopods, among the oldest of all brachiopods having existed since the Cambrian period (). They are also among the most morphologically conservative of the brachiopods, having lasted from their earliest appearance to the ...

** '' Lingula deleta'' ** '' Orbiculoidea grandis'' ** '' Schizocrania incola'' ** '' Schizotreta sp.'' *

Gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s ** '' Asinomphalus antiqua'' ** '' Bucania draboviensis'' ** '' Bucanopsina calypso'' ** '' Bucanopsis comata'' ** '' Cyrtodiscus procer'' ** '' Holopea antiquata'' ** '' Tritonophon bohemica'' ** '' T. peeli'' * Paragastropoda ** '' Antispira praecox'' *

Bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

s ** '' Astarte convergens'' ** '' Concavodonta ponderata'' ** '' Grammysia catilloides'' ** '' Leptodesma patricia'' ** '' Modiolopsis veterana'' ** '' Myoplusia bilunata'' ** '' Praenucula bohemica'' ** '' P. dispar'' ** '' Deceptrix sp.'' ** '' Palaeoneilo sp.'' ** '' Alena pustulosa'' *

Crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s ** '' Nothozoe pollens'' *

Ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

s ** '' Cerninella bohemica'' ** '' Crescentilla pugnax'' ** '' Cytheropsis testis'' ** '' Hastatellina sp.'' ** '' Trubinella latens'' *

Rostroconchia The Rostroconchia is a class of extinct molluscs dating from the early Cambrian to the Late Permian. They were initially thought to be bivalves, but were later given their own class. They have a single shell in their larval stage, and the adult ...

** '' Ribeiria apusoides'' *

Blastoidea Blastoids (class Blastoidea) are an extinct type of stemmed echinoderm, often referred to as sea buds. They first appear, along with many other echinoderm classes, in the Ordovician period, and reached their greatest diversity in the Mississi ...

** '' Mespilocystites bohemicus'' ** '' Anatifopsis sp.'' *

Rhynchonellata The Rhynchonellata is a class of Lower Cambrian to Holocene, Recent Articulata (Brachiopoda), articulate brachiopods that combines orders from within the Rhynchonelliformea (Articulata revised) with well developed pedicle attachment. Shell forms ...

** '' Svobodaina ellipsoides'' ** '' Jezercia chrustenicensis'' ** '' Drabovinella draboviensis'' ** '' Hirnantia ulrichi'' ** '' Drabovia asperula'' ** '' D. fascicostata'' ** '' D. redux'' ** '' Chrustenopora sp.'' ** '' Onniella sp.'' ** '' Saukrodictya sp.'' *

Craniata A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage. Living representatives are the Myxini (hagfishes), Hyperoartia (including lampreys), and the m ...

** '' Petrocrania obsoleta'' * Strophomenata ** '' Aegiromena aquila'' ** '' Bicuspina cava'' ** '' B. multicostellata'' ** '' Rafinesquina occulata'' * Tergomya ** '' Barrandicellopsis extenuata'' ** '' Cytherina graegaria'' ** '' Dactylogonia blyskavensis'' ** '' Sinuitopsis neglecta'' * Tentaculita ** '' Conchicolites confertus'' * Edrioasteroidea ** '' Hemicystites bohemicus'' ** '' H. velatus'' *

Eocrinoidea The Eocrinoidea were an extinct class of echinoderms that lived between the Early Cambrian and Late Silurian periods. They are the earliest known group of stalked, brachiole-bearing echinoderms, and were the most common echinoderms during the Cam ...

** '' Ascocystites drabowiensis'' ** '' A. cf. micraster'' ** '' Echinosphaerites infaustus'' ** '' Macrocystella bohemica'' ** '' Cystidea obscondita'' ** '' Rhombifera bohemica'' * Stylophora ** '' Mitrocystites mitra'' * Soluta ** '' Dendrocystites sedgwicki'' *

Scyphozoa The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word '' skyphos'' (), denoting a kind of drinking cup and alluding to the ...

** '' Anaconularia anomala'' ** '' Archaeoconularia fecunda'' ** '' A. insignis'' ** '' Conularia rugulosa'' ** '' Exoconularia exquisita'' ** '' Metaconularia pyramidata'' ** '' Pseudoconularia grandissima'' ** '' P. nobilis'' * Merostomata ** '' Triopus draboviensis'' * Polychaeta ** '' Serpulites sp.'' * Machaeridia ** '' Plumulites folliculum'' *

Algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

** '' Dendrocystis barrandei'' * Other ** '' Chasmatoporella havliceki'' ** '' Versispira contraria''

Gallery

Bicuspina multicostellata CRF.jpg, ''Bicuspina multicostellata'' Caleidocrinus multiramus CRF.jpg, ''Caleidocrinus multiramus'' Duslia insignis 34234.JPG, ''Duslia insignis'' Holopeidae - Holopea praestans.JPG, ''Holopea praestans''

References

Bibliography

* * * * * * {{citation , last=Mikuláš , first=Radek , year=1998b , title=Ordovician of the Barrandian area: Reconstruction of the sedimentary basin, its benthic communities and ichnoassemblages , url=http://www.jgeosci.org/content/Mikulas_1998.pdf , journal=

Journal of the Czech Geological Society ''Journal of Geosciences'' (1956-1992 ''Časopis pro mineralogii a geologii'', 1993-2006: ''Journal of the Czech Geological Society'') is a peer-reviewed scientific journal published by the Czech Geological Society and its predecessors since 1956. ...

, volume=43 , pages=143–159 , accessdate=2020-05-29

Description

Fossil content

Gallery

See also

References

Bibliography

Further reading