Brachiopods and Their Response to the Early–Middle Frasnian Biogeochemical Perturbations on the South Polish Carbonate Shelf
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Brachiopods and their response to the Early–Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf ANDRZEJ BALIŃSKI Baliński, A. 2006. Brachiopods and their response to the Early–Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf. Acta Palaeontologica Polonica 51 (4): 647–678. The brachiopod faunas from deposits recording the Early–Middle Frasnian transition of Poland are poorly known. The present report describes these faunas that were recovered from Wietrznia and Kostomłoty (Holy Cross Moun− tains) and Dębnik (Silesian−Cracow Upland) regions positioned on the southern Polish carbonate shelf. The brachio− pod distribution was analysed relative to a significant d13C excursion, referred recently to as Palmatolepis punctata Event. The sporadic occurrence of brachiopods at Dębnik makes it difficult to analyse the biotic response to this geo− chemical anomaly. However, higher brachiopod frequency in the topmost part of the section coincides with a gradual decrease of d13C down to the Frasnian background values. At two studied sections at Wietrznia the greatest taxonomic diversity and abundance of brachiopods (Flabellulirostrum–Coeloterorhynchus assemblage) are confined to the Pal− matolepis transitans Zone. In the following Pa. punctata Zone brachiopods are rare (Biernatella lentiformis assem− blage) or absent, which suggests a serious deterioration of the environmental conditions linked probably with periods of benthic anoxia−dysoxia and oligotrophic conditions in the basin. In two Kostomłoty sections brachiopods faunas of this age are members of the mostly monospecific rhynchonellid−dominated Phlogoiderhynchus polonicus assem− blage which inhabited deeper−water environments characteristic of intrashelf oxygen−depleted basins of Łysogóry− Kostomłoty region. In some horizons large shells of P. polonicus were frequently colonised by discinoid Romerella? sp. Among 28 species described in this report new forms include: Flabellulirostrum kielcensis sp. nov., F. rackii sp. nov., and Thomasaria ventosa sp. nov. Key words: Brachiopoda, Flabellulirostrum, Thomasaria, carbon isotopes, diversity dynamic, Frasnian, Poland. Andrzej Baliński [[email protected]], Instytut Paleobiologii PAN, ul. Twarda 51/55, PL−00−818 Warszawa, Poland. Introduction Alamo Impact Event (Nevada, USA), massive dissociation of methane hydrate, and global warming (Yans et al. in This study is a contribution to the interdisciplinary project press). The present paper deals with brachiopod faunas and initiated by Grzegorz Racki (Faculty of Earth Sciences, Uni− their distribution patterns in the Early to Middle Frasnian versity of Silesia, and Institute of Paleobiology, Polish Acad− (Pa. transitans to Pa. punctata conodnt zonal interval) from emy of Sciences, Poland) to investigate the Early to Middle several outcrops in the Holy Cross Mountains (Wietrznia I, Frasnian biotic succession and events revealed in carbonate Kostomłoty II and V) and Silesian−Cracow Upland, southern sequence of the part of the Laurussian shelf in southern Po− Poland (Dębnik). This study contributes to the knowledge of land. It is noteworthy that this interval, which is correlated the faunal response and palaeoecologic impact of the “punc− with Palmatolepis transitans–Pa. punctata conodont zones, tata Event” (= Pa. punctata Event; as defined by Yans et al. has been recognised in recent literature as time of a major in press) on brachiopod faunas in southern Poland. global transgressive, anoxic and geochemical events (e.g., McGhee 2001; House 2002; Schieber 2003; Yans et al. in Institutional abbreviations.—GIUS, Department of Paleon− press). Recently published high−resolution carbon isotopic tology and Biostratigraphy of the University of Silesia, Sos− data from Ardennes and Poland (Racki et al. 2004; Pisa− nowiec, Poland; ZPAL, Institute of Paleobiology, Polish rzowska et al. 2006; Yans et al. in press), and other data from Academy of Sciences, Warsaw, Poland. China (Bai et al. 1994) and Moravia (Hladikova et al. 1997) show a global negative carbon isotope shift in the Pa. punctata conodont Zone. According to Yans et al. (in press) Geological setting these data document a worldwide perturbation in the earth– ocean system. As potential causes of this rapid (estimated Exposures of the Early–Middle Frasnian deposits of the Holy roughly at 0.1 My) changes in the carbon isotopic composi− Cross Mountains and the Cracow region have been studied tion of the oceanic reservoir the latter authors consider the since the 19th century (see overview in Szulczewski 1971). Acta Palaeontol. Pol. 51 (4): 647–678, 2006 http://app.pan.pl/acta51/app51−647.pdf 648 ACTA PALAEONTOLOGICA POLONICA 51 (4), 2006 Fig. 1. Location of collecting sites. A. General map of Poland. B. Geological sketch−map of the western part of the Holy Cross Mountains (after Racki et al. 2004; modified). C. Sketch map of Wietrznia quarries and location of the studied sections (after Makowski in Racki et al. 1993, simplified). D. Geological sketch−map of the Dębnik vicinity (after Szulczewski and Dvořák 1995; modified). The exposed strata form an elongate belt between the south− Wietrznia Ie section, set C is incompletely exposed (without western margin of the East European Craton and Variscan its basal 1.5 m part) and is ca. 7 m in thickness. The succession Deformation Front (Dadlez et al. 1994). They were deposited is composed mainly of rhythmically bedded, platy bituminous in the proximal part of an intracratonic basin up to 600 km in calcilutites and marly shales, with occasional thin calcirudites width, trending NW–NE, that extend from Western Europe and biorudites (for more details see Makowski in Racki et al. to the Ukraine (Narkiewicz 1985). Among exposures of the 1993: 81, figs. 9–10; Pisarzowska et al. 2006). Early–Middle Frasnian passage beds the Wietrznia Id−W and A few specimens of Roemerella? sp. and Phlogoiderhyn− Ie sections were analysed in detail (Figs. 1–3). These sec− chus polonicus (Roemer, 1866) were found at Kostomłoty V tions represent a continuous sedimentary succession which located ca. 3 km NNE of Kielce from exposures of dark includes a record of global and regional geochemical and bi− micrites with shaly and detrital intercalations. These strata otic events. For the purposes of the present study these sec− represent the middle part of the Szydłówek Beds (Racki and tions in the Holy Cross Mountains were sampled in detail to Bultynck 1993). Abundant collections of the same two spe− obtain high−resolution data on the conodont sequence (Pisa− cies mentioned above were recovered from Kostomłoty II rzowska et al. 2006) as well as the Frasnian brachiopod quarry where the same interval is well exposed (for more de− fauna. Supplementary brachiopod material was collected from tails on the outcrops see Racki et al. 2004). Kostomłoty Małe Górki (= Kostomłoty II; see Racki et al. A small brachiopod collection was recovered from a 2004: 269, figs. 2–4, 8) and Kostomłoty−Mogiłki (Kosto− quarry north of the village of Dębnik (= quarry above the młoty V; see Racki et al. 2004: 269, figs. 2, 8) quarries (Holy Rokiczany Dół ravine in Baliński 1979; Silesia−Cracow Up− Cross Mountains) as well as from Dębnik (Silesia−Cracow land, southern Poland). Rocks in the Dębnik area represent Upland, southern Poland; see Baliński 1979: fig. 1). the southern facies of the pericratonic basin located near the The Wietrznia I inactive quarry is situated in the southern stable, elevated Sub−Carpathian Arch (Narkiewicz 1985, part of Kielce, within the southern limb of Kielce Syncline 1988). Brachiopods recovered from this area were collected (Szulczewski 1971: 69, fig. 7; Fig. 1 herein). Five litho− in the western part of the quarry where the youngest layers stratigraphic sets (A through E) of the latest Givetian–Frasnian have been recently exposed. This section yields faunas of limestones that crop out in the area have been described earlier two local brachiopod zones: the older Cyrtospirifer bisel− by Szulczewski (1971). The brachiopod fauna described in latus Zone, and the lowermost part of the succeeding Pliono− this report comes from set C which represents the middle part ptycherhynchus cracoviensis Zone. The rocks yielding these of the Wietrznia Beds (= Phlogoiderhynchus Marly Level of faunas consist of a monotonous succession of interbeded thin Racki 1993a). At the Wietrznia Id−W section the set consists marly micrites and marls, sparse calcirudites, and intraclastic of about 8 m of thin−bedded bituminous micrites and inter− limestones (Nodular Limestone unit of Narkiewicz and bedded marly shales or calcirudites (see details in Makowski Racki 1984). It is noteworthy that the topmost layers of the in Racki et al. 1993: 81, figs. 9–10; Pisarzowska et al. 2006). section with assemblages of the Plionoptycherhynchus cra− Thin−bedded bituminous micrites with many fossiliferous coviensis brachiopod zone are the only known in situ occur− coarse−grained and graded biointrarudite intercalations are rence of faunas of the interval. Previously, it was known ex− characteristic for nearby Wietrznia Id−E section, where the set clusively from loose blocks found at the bottom of the nearby C is nearly 9.5 m in thickness (Pisarzowska et al. 2006). At Rokiczany Dół ravine (Baliński 1979). et al.(2006). Fig. 2. Distribution of brachiopod species in Wietrznia Id−W section. Lithology, stratigraphy, and stable carbon isotope geochemistry after Pisar BALIŃSKI—EARLY–MIDDLE FRASNIAN BRACHIOPODS 649 EARLY FRASNIAN