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 Monograptus uniformis.
The Klonk Section is about 35km southwest of Prague near the village of Suchomasty, in the southwestern part of the Barrandian area, Czech Republic.
The whole sequence of boundary beds consists of rhythmical alteration of limestone beds and calcareous shales.
First occurrence of Monograptus uniformis in Bed 20
The last occurrence of Monograptus transgrediens in Interbed 13/14, about 160-170cm below Bed 20.
The Lower Lochkovian index graptolites Monograptus uniformis uniformis and Monograptus uniformis angustidens appear suddenly and in great number in the upper part of Bed 20.
Bed 21 yields the trilobite species Walburgella rugulosa rugosa.
Graptolite FAD Monograptus uniformis
base-Devonian from scale in Cooper (GTS 2004), which is 1 myr younger than Tucker et al. (1998) estimate.
Chlupác, I. and Kukal, Z., 1977. The boundary stratotype at Klonk. The Silurian-Devonian Boundary. IUGS Series A, 5, p. 96 - 109.