Original paper
In search for the Basal Emsian GSSP in the Prague Synform: Mramorka – a possible candidate section
Weinerová, Hedvika; Slavík, Ladislav; Weiner, Tomáš; Hladil, Jindřich
Newsletters on Stratigraphy Volume 57 Number 2 (2024), p. 171 - 201
133 references
published: Apr 22, 2024
published online: Feb 1, 2024
manuscript accepted: Nov 7, 2023
manuscript revision received: Nov 2, 2023
manuscript revision requested: Aug 28, 2023
manuscript received: May 24, 2023
ArtNo. ESP026005702003, Price: 29.00 €
Abstract
The present GSSP for the basal Emsian boundary remains among the most problematic issues in the global Paleozoic stratigraphy as it is accented by the International Commission on Stratigraphy (ICS/IUGS). The former traditional Pragian Stage of the Lower Devonian that has been originally based on the Praha Formation in the Prague Synform was thus drastically reduced. Herein is presented a possible candidate section for the prospective basal GSSP redefinition – the Mramorka section near Chýnice, Prague Synform, Czech Republic. It has the typical varied development of the upper part of the Praha Formation including the Bohemian Graptolite Event (BGE), i.e. a prominent lithological marker in the NW flank of the Prague Synform. In order to provide a robust dataset for the rigorous evaluation of the GSSP potential of this candidate section, data from complex multiproxy studies including biostratigraphy, sedimentology, gamma-ray spectrometry, magnetic susceptibility, multi-element geochemistry (INAA, EDXRF), and stable isotopes (δ18O, δ13C) are presented. The boundary criterion is the gracilis Event that is close to the traditional boundary between the Pragian and Emsian stages. The event is characterized by a conodont Latericriodus bilatericrescens gracilis Bultynck, 1985, which widely occurs in NW part of Gondwana. The lowermost entry of the taxon within the Prague Synform has been recorded in the Mramorka section, 145 cm below the BGE interval. The sedimentology of the Mramorka section is characterized by grey nodular calcisiltites largely influenced by ichnofabric, but the BGE interval consists mostly of darker grey, ichnofossil-poor, platy limestones interbedded with black calcareous shales. The data obtained from multiproxy studies in the Mramorka section show a marked change in geochemical proxies within and above the BGE. The values of CGR and elements typical for terrigenous input show relatively higher values below the BGE interval and a gradual decrease above the BGE. The BGE interval is characterized by elevated paleoredox and paleoproductivity proxies. REEN values show mostly the MREE bulge pattern and are linked mainly to terrigenous (especially aeolian) supply. The MS is largely tied to the terrigenous input, but is also influenced by authigenic Fe minerals. δ13C values change markedly above the BGE. The sediments below the BGE interval are considered to record the culminating transgression and strata above the BGE interval the highstand. The BGE interval itself records the maximum flooding. If present, the BGE interval close above the gracilis Event may serve an independent marker for approximation of the prospective GSSP boundary.