Conodont biostratigraphy of shallow marine Givetian deposits from the Radom-Lublin area, SE Poland

摘要

Detailed conodont data were obtained from 66 samples in 9 deep wells representative of three palaeogeographic regions of the Mid Devonian epicontinental basin of southeastern Poland: (1) the elevated part of the East European Platform representing the basin margin, (2) the Lublin Graben with a larger proportion of open marine systems, (3) the Radom Area characterized by more offshore, purely marine deposition and larger subsidence rates in the Radom Area. The 1344 specimens collected were assigned to 8 genera: Icriodus, Pofygnathus, Ancyrodella, Belodella, Mehlina, Neopanderodus, Pandorinellina and Skeletognathus, and 38 taxa of species or subspecies rank. The vertical distribution of the conodont assemblages studied in particular sections is highly irregular and discontinuous with many barren intervals controlled by less suitable palaeocological conditions, mostly representing restricted and/or very shallow-water facies. We found only a single index species characteristic of deeper marine facies, as applied in the standard conodont zonation. Therefore the biostratigraphic interpretation also takes into account the total range of all taxa found in particular samples, established after a critical analysis of adequately published total ranges of these taxa. The stratigraphic ranges of the following taxa were modified: Icriodus arkonensis arkonensis, I. a. walliserianus, I. eslaensis, I. platyobliquimarginatus, I. subterminus, I, aff. /. subterminus, Pofygnathus ansatus, P. latifossatus, P. linguiformis linguiformis, P. timorensis and P. varcus. As a result of the stratigraphic analysis of the conodont assemblages we distinguished five zones in the Givetian of the studied area, i.e. the rhenanus/varcus, ansatus, hermanni, norrisi (= lower part of Lower falsiovalis Zone) zones, and also two informal units, the subterminus and insita faunas. We documented the co-occurrence of I. subterminus and P. latifossatus which supports the earlier supposition of Rogers (1998) that the Lower subterminus Fauna may partly correspond to the Lower hermanni Zone.