GSSP for Lochkovian Stage
Definition:
The base of the Devonian System and the Lochkovian Stage is defined in Bed 20, in the Klonk Section, Czech Republic, immediately below the first appearance of the graptolite species Uncinatograptus uniformis.
Location:
The Klonk Section is about 35km southwest of Prague near the village of Suchomasty, in the southwestern part of the Prague Synform, Czech Republic.
Sedimentology:
The whole sequence of boundary beds consists of rhythmical alteration of limestone beds and calcareous shales.
For detailed sedimentology see Hladil (1991 and 1992).
Primary Markers:
First occurrence of Uncinatograptus uniformis in Bed 20
Secondary Markers:
Graptolites:
The last occurrence of Istrograptus transgrediens in Interbed 13/14, about 160-170cm below Bed 20.
The Lower Lochkovian index graptolites Uncinatograptus uniformis uniformis and Uncinatograptus uniformis angustidens appear suddenly and in great number in the upper part of Bed 20.
Trilobites:
Bed 21 yields the trilobite species Walburgella rugulosa rugosa.
Correlation Events:
Graptolite FAD Uncinatograptus uniformis
Notes on Derivation of Age:
The accepted age for the Devonian base is 419 Ma as published in Becker et al. (GTS 2020), and is estimated from radioisotopic data combined with cyclostratigraphy and biostratigraphy.
References:
Becker, R.T.; Marshall, J.E.A.; Da Silva, A.-C., 2020. Chapter 22—The Devonian Period. In: The Geologic Time Scale 2020, Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M., Eds.; Elsevier: Boston, MA, USA, 2020; Volume 2, pp. 733–810. ISBN: 978-0-128-24361-9.Chlupáč, I., 1977. Barrandian. In: The Silurian-Devonian boundary: final report of the Committee of the Siluro-Devonian Boundary within IUGS Commission on Stratigraphy and a state of the art report for Project Ecostratigraphy, Martinsson, A., Ed.; International Union of Geological Sciences, Series A, No. 5: 84-95. ISBN: 978-3-510-56003-5.
Chlupáč, I. and Kukal, Z., 1977. The boundary stratotype at Klonk. The Silurian-Devonian Boundary. IUGS Series A, 5, p. 96 - 109. ISBN: 978-3-510-56003-5.
Hladil, J., 1991. Evaluation of the sedimentary record in the Silurian/Devonian boundarystratotype at Klonk (Barrandian area, Czechoslovakia). Newsletters on Stratigraphy 25, 115–125. DOI: 10.1127/nos/25/1991/115.
Hladil, J., 1992. Are there turbidites in the Silurian/Devonian boundary stratotype? (Klonk near Suchomasty, Barrandian, Czechoslovakia). Facies 26, 35–54. DOI: 10.1007/BF02539792.