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, approximately south 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 '' 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, Požáry formation) and one formation of lower Devonian ( Lochkov formation named for the nearby ' Lochkov 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 '' 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,

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''. 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''), European ash (''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''), black locust (''Robinia pseudoaccacia'') and Norway spruce (''Picea abies''). The original community of oak-hornbeam forests ( sessile oak (''Quercus petraea''), common hornbeam (''Carpinus betulus''), field maple (''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'') and common dogwood (''Cornus sanguinea''), atop the hill we may find an area of xerothermic grasslands such as spotted knapweed (Centaurea stoebe) and hairy oxytropis (''Oxytropis pilosa''). Klonk is the nesting place for a number of birds, among others the grey wagtail (''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 (''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 (''Meles meles''), wood mouse (''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