Znaczenie konodontów dla biostratygrafii wapieni stromatopoidowo-koralowcowych dewonu Gór Świętokrzyskich
Abstract
SIGNIFICANCE OF CONODONTS FOR BIOSTRATIGRAPHY OF STROMATOPOROID-CORAL LIMESTONES OF THE HOLY CROSS MTS.
Summary
In the last years, the use of conodonts resulted in marked developments in biostratigraphy of Upper Devonian rocks of the Holy Cross Mts whereas all the attempts to establish zonation of stromatoporoidcoral limestones, widely distributed in this region and usually assigned to the Givetian, appeared unsuccessful. The latter may be explained in terms of paleoecology of conodonts. The environment of stromatoporoid-coral facies, extremely shallow-water and generally isolated from open sea influences, was unfavourable for Conodontomorphida, especially those of stratigraphic importance (Fig. 1). These theoretical premises were supported by the studies carried out in the western Holy Cross Mts. The studies showed that in the case of this facies the occurrence of conodonts is almost exclusively limited to lithological types characterized by open sea fauna, mainly of echinoderms (especially crinoids), brachiopods, sponges, fishes, nautiloids, trilobites and ostracodes (Fig.
2 A-D). The conodont assemblage comprises both the species typical of widely interpreted Middle-Upper Devonian boundary beds (e.g. Polygnathus xylus Stauffer, P. dubius Hinde, P. varcus Stauffer, P.
latifossatus Wirth, P. ovatinodosus Ziegler and Klapper, P. linguiformis linguiformis Hinde, Ozarkodina brevis (Bischoff and Ziegler) and O. semialternans (Wirth)) and forms typical of the Upper Devonian (e.g. Polygnathus pollocki Druce, P. incompletus Uyeno, P. cf. dengleri Bischoff and Ziegler, P. aff. timanicus Ovnatanova and Pandorinellina aff. insita Stauffer). It seems that this fauna is not older than the upper Schmidtagnathus hermanii-Polygnathus cristatus zone (tab.), which implicates that Givetian limestones may be younger than it was assumed. However, this problem will not be definitely solved until the Givetian/Frasnian boundary s defined by the IUGS Subcommission on Devonian Stratigraphy.
Summary
In the last years, the use of conodonts resulted in marked developments in biostratigraphy of Upper Devonian rocks of the Holy Cross Mts whereas all the attempts to establish zonation of stromatoporoidcoral limestones, widely distributed in this region and usually assigned to the Givetian, appeared unsuccessful. The latter may be explained in terms of paleoecology of conodonts. The environment of stromatoporoid-coral facies, extremely shallow-water and generally isolated from open sea influences, was unfavourable for Conodontomorphida, especially those of stratigraphic importance (Fig. 1). These theoretical premises were supported by the studies carried out in the western Holy Cross Mts. The studies showed that in the case of this facies the occurrence of conodonts is almost exclusively limited to lithological types characterized by open sea fauna, mainly of echinoderms (especially crinoids), brachiopods, sponges, fishes, nautiloids, trilobites and ostracodes (Fig.
2 A-D). The conodont assemblage comprises both the species typical of widely interpreted Middle-Upper Devonian boundary beds (e.g. Polygnathus xylus Stauffer, P. dubius Hinde, P. varcus Stauffer, P.
latifossatus Wirth, P. ovatinodosus Ziegler and Klapper, P. linguiformis linguiformis Hinde, Ozarkodina brevis (Bischoff and Ziegler) and O. semialternans (Wirth)) and forms typical of the Upper Devonian (e.g. Polygnathus pollocki Druce, P. incompletus Uyeno, P. cf. dengleri Bischoff and Ziegler, P. aff. timanicus Ovnatanova and Pandorinellina aff. insita Stauffer). It seems that this fauna is not older than the upper Schmidtagnathus hermanii-Polygnathus cristatus zone (tab.), which implicates that Givetian limestones may be younger than it was assumed. However, this problem will not be definitely solved until the Givetian/Frasnian boundary s defined by the IUGS Subcommission on Devonian Stratigraphy.