Abstract
The Global Stratotype Section and Point (GSSP) of the Silurian/Devonian boundary, Lower Devonian Series and Lochkovian Stage was formally placed in 1977 at Klonk, in the Czech Republic, at the first appearance of the graptolite Uncinatograptus uniformis uniformis (Přibyl). However, since then, correlation of this limit has been often hampered in carbonate facies where graptolites are uncommon or totally absent. A large calcareous deposition occurred at the Silurian/Devonian boundary along the northern and peri-Gondwana margin, thus representing an ideal location to select and test a possible additional biostratigraphic marker of the limit among conodonts. The first appearance of Caudicriodus hesperius almost simultaneously at the base of the Devonian in Bohemia, the Carnic Alps, Sardinia, Morocco and elsewhere indicates that this taxon is the conodont that best approximates the beginning of the Period. The first or last appearance of other species (e.g., Ozarkodina confluens, Zieglerodina klonkensis, Z. remscheidensis and Caudicriodus woschmidti) may help to recognise the boundary as well.
Highlights
Academic Editors: EmanuelaGraptolites and conodonts represent the best biostratigraphical tools for the Silurian and the Devonian, and most of the Stage limits of both Periods have been traditionally placed referring just to those fossil groups
The former documents the Devonian resting unconformably on the Lower Ordovician, whereas only in the latter a composite section has recorded in continuity an Upper Ordovician to Devonian sequence, including the recognition of the Silurian/Devonian boundary in marine Bohemian facies within a sandy limestone series yielding conodonts and chitinozoans [113,114,115,116]
Ozarkodina confluens is in general limited to the Silurian, and has its last occurrence in the uppermost Přídolí strata, but in Bohemia it occurs just above the boundary
Summary
Graptolites and conodonts represent the best biostratigraphical tools for the Silurian and the Devonian, and most of the Stage limits of both Periods have been traditionally placed referring just to those fossil groups. Most of the sectors comprising peri-Gondwana and northern Gondwana are included in South-Central Europe (Czech Republic, South Germany, Spain, Portugal, France, Austria, Italy and probably Romania), North Africa (Morocco, Algeria, Tunisia, Libya, Niger and Egypt), the Middle East (Turkey, Syria, Jordan, Iraq and Saudi Arabia), Florida and parts of southeastern USA [27]. The palaeogeographical configuration adopted in this study (Figure 3) follows Scotese (2014) [54] in placing all areas of northern Gondwana along a continuous margin at high latitudes, with the Prague Synform (Barrandian area, Czech Republic), where the GSSP for the Silurian/Devonian boundary has been selected [16], at lowermost latitudes and in a promontory position. The name of the original Silurian/Devonian Boundary Event by Walliser in relation to the CIE is preferred and recommended in this paper
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