Klonk is a national nature monument in the Bohemian Karst Protected Landscape Area in the

Czech Republic The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...

. It lies in the northern part of the municipality of

Suchomasty Suchomasty is a municipality and village in Beroun District in the Central Bohemian Region of the Czech Republic. It has about 500 inhabitants. Administrative division Suchomasty consists of two municipal parts (in brackets population according to ...

, approximately south of

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. ...

. It is globally recognized as a geologically important location due to the presence of the

Global Boundary Stratotype Section and Point A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...

(GSSP) marking the boundary between

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

and

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

periods. The boundary was set based on the first appearance of the

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 ...

'' Monograptus uniformis'' in the bed number 20. The stratotype was ratified on 8 February 1972 by the

International Union of Geological Sciences The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to global cooperation in the field of geology. As of 2023, it represents more than 1 million geoscientists around the world. About Fo ...

Montreal Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...

as the first formally accepted GSSP.

History

The positioning of the boundary between Silurian and Devonian has been a matter of discussion since the 19th century. The so-called hercynian question was resolved only after the ratification of the GSSP in 1972. The monument was declared as a protected area in 1977.

IUGS geological heritage site

In respect of its being the location of the 'first global boundary stratotype section and point (GSSP)', Klonk Hill was included by the

(IUGS) in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as ''"a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history."''

Geology

Klonk is a rocky slope by the right bank of Suchomastský brook. It contains two formations of upper Silurian (

Kopanina formation Kopanina may refer to the following places in Poland: *Kopanina, part of the Poznań-Grunwald, Grunwald district of Poznań *Kopanina, Leszno County in Greater Poland Voivodeship (west-central Poland) *Kopanina, Szamotuły County in Greater Poland V ...

, Požáry formation) and one formation of lower Devonian (

Lochkov formation Lochkov is a municipal district (''městská část'') in Prague, Czech Republic. It has 874 inhabitants as of 2021, and is located in the southwestern part of the city. It is most notable for being the namesake of the Lochkovian The Lochkovian ...

named for the nearby '

Lochkov Lochkov is a municipal district (''městská část'') in Prague, Czech Republic. It has 874 inhabitants as of 2021, and is located in the southwestern part of the city. It is most notable for being the namesake of the Lochkovian The Lochkovian ...

profile'). Kopanina formation is represented by calcareous

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, Požáry formation by gray tabular

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) ...

s and bioclastic limestones can be found in Lochkov formation. The boundary beds are intact, without disturbance by tectonic processes, there are no facial changes and the profile is made of one continuous sequence. There are various paleontologically significant objects, apart from the already mentioned graptolites it is possible to find the

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 ...

'' Warburgella rugulosa'' typical for the base of Devonian period, the conodont '' Icriodus wolschmidti'' and the

chitinozoan Chitinozoa (singular: chitinozoan, plural: chitinozoans) are a group of flask-shaped, organic walled marine microfossils produced by an as yet unknown organism. Common from the Ordovician to Devonian periods (i.e. the mid-Paleozoic), the millimet ...

'' Agnochitina chlupaci''. Various other

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s can be found in the profile, such as

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

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

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 and

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s. Apart from animals, remains of terrestrial flora can also be found in the beds, namely the genus ''

Cooksonia ''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...

''. Soils are rather undeveloped, only close above the brook in the lower part of the slope clayey screes can be found. There is a unique monument representing the geological boundary set by international agreement. It was built in 1977 by academic sculptor Jiří Novotný.

Flora and fauna

Various plant communities can be found at Klonk. The vicinity of the brook is characterized by human planted vegetation, for example the

common alder ''Alnus glutinosa'', the common alder, black alder, European alder, European black alder, or just alder, is a species of tree in the family Betulaceae, native to most of Europe, southwest Asia and northern Africa. It thrives in wet locations whe ...

(''Alnus glutinosa''),

European ash ''Fraxinus excelsior'', known as the ash, or European ash or common ash to distinguish it from other types of Fraxinus, ash, is a flowering plant species in the olive family Oleaceae. It is native throughout mainland Europe east to the Caucasus ...

(''Fraxinus excelsior'') or Canadian poplar (''Populus x canadensis)'', in the lower parts of the slope are the remains of scree forests with dominant sycamore. Shady limestones by the brook are a favourable location for a number of rare bryophytes, such as the craven featherwort (''Pedinophyllum interruptu''m) or beech feather-moss (Eurhynchium crassinervum). Most of the slope is covered by vegetation which is not native to the location – black pine (''Pinus nigra)'',

European larch ''Larix decidua'', the European larch, is a species of larch native to the mountains of central Europe, in the Alps and Carpathian Mountains, with small disjunct lowland populations in northern Poland. Its life span has been confirmed to be clos ...

(''Larix decidua''),

black locust ''Robinia pseudoacacia'', commonly known as black locust, is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae of the legume family Fabaceae. It is native to a few small areas of the United States, but it has been widely pl ...

(''Robinia pseudoaccacia'') and

Norway spruce ''Picea abies'', the Norway spruce or European spruce, is a species of spruce native to Northern, Central and Eastern Europe. It has branchlets that typically hang downwards, and the largest cones of any spruce, 9–17 cm long. It is very clo ...

(''Picea abies''). The original community of oak-hornbeam forests (

sessile oak ''Quercus petraea'', commonly known as the sessile oak, Welsh oak, Cornish oak, Irish oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an unof ...

(''Quercus petraea''),

common hornbeam Common may refer to: As an Irish surname, it is anglicised from Irish Gaelic surname Ó Comáin. Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common, a central public park in Boston, Massachusetts * Cambridge Common, ...

(''Carpinus betulus''),

field maple ''Acer campestre'', known as the field maple, is a flowering plant species in the family Sapindaceae. It is native to much of continental Europe, Britain, southwest Asia from Turkey to the Caucasus, and north Africa in the Atlas Mountains. It has ...

(''Acer campestre'')) can only be found in the upper parts of the profile. The formerly woodless areas tend to be covered by bushes of dog-rose (''Rosa canina''),

blackthorn ''Prunus spinosa'', called blackthorn or sloe, is an Old World species of flowering plant in the rose family, Rosaceae. It is locally naturalized in parts of the New World. The fruits are used to make sloe gin in Britain and patxaran in Basq ...

(''Prunus spinosa'') and common dogwood (''Cornus sanguinea''), atop the hill we may find an area of xerothermic grasslands such as

spotted knapweed ''Centaurea stoebe'', the spotted knapweed or panicled knapweed, is a species of ''Centaurea'' native to eastern Europe, although it has spread to North America, where it is considered an invasive species. It forms a tumbleweed, helping to incre ...

(Centaurea stoebe) and hairy oxytropis (''Oxytropis pilosa''). Klonk is the nesting place for a number of birds, among others the

grey wagtail The grey wagtail (''Motacilla cinerea'') is a member of the wagtail family, Motacillidae, measuring around 18–19 cm overall length. The species looks somewhat similar to the yellow wagtail (disambiguation), yellow wagtail but has the yello ...

(''Motacilla cinerea''),

Eurasian sparrowhawk The Eurasian sparrowhawk (''Accipiter nisus''), also known as the northern sparrowhawk or simply the sparrowhawk, is a small bird of prey in the family Accipitridae. Adult male Eurasian sparrowhawks have bluish grey upperparts and orange-barred ...

(''Accipited nisus'') or the

common buzzard The common buzzard (''Buteo buteo'') is a medium-to-large bird of prey which has a large range. It is a member of the genus '' Buteo'' in the family Accipitridae. The species lives in most of Europe and extends its breeding range across much of ...

(''Buteo buteo''). Most of the fauna here is represented by invertebrates, however apart from other areas of the Bohemian karst it is somewhat poorer in

molluscs Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

. Vertebrate fauna is represented by

red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe and Asia, plus ...

(''Vulpes vulpes)'',

European badger The European badger (''Meles meles''), also known as the Eurasian badger, is a badger species in the family Mustelidae native to Europe and West Asia and parts of Central Asia. It is classified as least concern on the IUCN Red List, as it has a w ...

(''Meles meles''),

wood mouse The wood mouse (''Apodemus sylvaticus'') is a Muridae, murid rodent native to Europe and northwestern Africa. It is closely related to the yellow-necked mouse (''Apodemus flavicollis'') but differs in that it has no band of yellow fur around the ...

(''Apodemus sylvaticus'') and other, usually common species.

Protection plan

The goal of the protection plan is to secure the important geological profile and preserve it for future study. Klonk is mainly threatened by amateur palaeontologists who expect a rich locality, however the location is important mainly due to microfossils. Another threat is the overgrowing of vegetation, which has been successfully removed mechanically and by herbicides in the past. The removal of unwanted vegetation should also help the return of the original vegetation, which used to be strongly influenced by pasture. Plans for the future include marking of borders of the protected area in order to facilitate management, since it lies on parts of two private properties. The profile is currently closed to the public not only to protect it, but also to avoid injuries of visitors on the steep slope.

Educational trail

The location is a part of long geological educational trail, which also leads through adjacent areas of importance such as Lom na Kobyle, Zlatý kůň, Koda and others. Individual localities aren't necessarily related and it is thus possible to travel only through certain segments of the trail. The trail is suitable even for cyclists and the information boards are in Czech with English abstract.

References

* {{cite web, url=http://www.stratigraphy.org/sildev.htm , title=GSSP for the Silurian - Devonian Boundary , last=Ogg , first=James , access-date=2006-07-02 , archive-url=https://web.archive.org/web/20060618104054/http://www.stratigraphy.org/sildev.htm , archive-date=2006-06-18 , url-status=dead Geography of the Czech Republic Natural monuments in the Czech Republic Stratigraphy of Europe First 100 IUGS Geological Heritage Sites