University of Groningen Fish microfossils from the Upper Silurian Öved Sandstone Formation, Skåne, southern Sweden Vergoossen, Johannes Marie Josephus IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2003 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Vergoossen, J. M. J. (2003). Fish microfossils from the Upper Silurian Öved Sandstone Formation, Skåne, southern Sweden. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 23-09-2021 123 FISH MICROFOSSILS FROM THE UPPER SILURIAN ÖVED SANDSTONE FORMATION, SKÅNE, SOUTHERN SWEDEN. Chapter 6 Observations on the correlation of microvertebrate faunas from the Upper Silurian Öved Sandstone Formation. Published in: J. Satkunas, J., J. Lazauskiene (Eds.): “The Fifth Baltic Stratigraphic Conference, Basin Stratigraphy - Modern Methods and Problems”, September 22-27, 2002, Vilnius, Lithuania: Extended Abstracts: 222-224. Vilnius: Geological Survey of Lithuania. Note: Microvertebrate samples/ faunas from Scania referred to in the text below are samples /faunas examined in Chapters 1-5,7; unless stated otherwise. Rock, residue and slide samples from the Swedish Museum of Natural History (SNMH) from outcrops in the marine1, shallow water, regressive (shallowing upwards) Öved Sandstone (subunits 3 & 4 sensu Grönwall 1897 of the c.300-400m thick Öved-Ramsåsa Group) at Helvetesgraven, Klinta, Rinnebäcks, Ramsåsa sites C, D, E, H mostly yielded microvertebrate faunas that on the whole are typical of Thelodus sculptilis Zone assemblages (late Ludlow-early Pridoli), with the zonal thelodont in most faunas 2. Species were listed for each rock residue, plus some of the (published) form variants within the species, or new form variants. For residues from one Ramsåsa C and three Ramsåsa E pieces of rock such faunal lists were also made for size fractions 0.106, 0.212, 0.355, 0.425 and 0.5 mm mesh width; larger fractions are absent. Faunal lists are dominated by thelodont and acanthodian species and composed of different species and form variants per rock. Some form variants proved to be restricted to particular size fractions. Per rock residue, the most contrasting differences in faunal composition were observed in the 0.106-0.212 size fractions, the latter also yielded the greatest taxon diversity. Data on faunal composition, or on the morphology of species and their form variants, within such small size ranges are not available from the Late Silurian Microvertebrate Standard (the East Baltic sequence). Another correlational problem is that Scanian faunas with T. sculptilis Gross, 1967 and those from the Eke/Burgsvik Beds on Gotland could be older than the T. sculptilis Zone faunas of the East Baltic succession (see correlation charts; cf. Märss et al., 1995), where a hiatus exists before the first appearance of the zonal fossil (in Scania the Eke-Burgsvik boundary is found within the Bjärsjölagård Limestone, the upper unit of the Klinta Formation, Jeppsson pers. com.). When interpreted according to the concepts of Märss (1992), the ÖSF faunas from Helvetesgraven and Ramsåsa D (SW24) would represent such older (‘transitional’), late Whitcliffian/ lateLudlow faunas. Judging from recent time scales (Williams et al., 2000), the ÖSF faunas cover a time range of about 2-3 million years, which gives them a high biostratigraphical resolution potential. Some of the faunal differences can be attributed to (relatively small) differences in age within the T. sculptilis Zone. Other differences might be attributable to other, partly environmental, factors. Age-related differences can be associated with the presence of the older osteichthyan zonal fossil Andreolepis hedei Gross, 1968b (Helvetesgraven), with the presence of the thelodont and younger zonal equivalent Thelodus admirabilis Märss, 1982 and its formae: either in combination with A. hedei (Helvetesgraven) or Paralogania ludlowiensis (Gross, 1967) (Ramsåsa C), with the regular rather than incidental presence of P. ludlowiensis (Ramsåsa SMNH-Q 607). In the Baltic region the latter species is known from Whitcliffian levels both older and younger than the lowermost Tahula Beds, whereas in the Welsh Borderland it is also known from levels dated as Pridoli (Miller and Märss, 1999). Thelodus 124 carinatus sensu Märss, 1986b is as old as, or older than, A. hedei and the presence of T. carinatus (- like) scales (Ramsåsa D/SW24) might be age-related, although part of the scales figured in Chapter 4 (e.g., fig. 67) will probably have to be referred to a new Thelodus species. Among the thelodonts, other potential biostratigraphical markers are new form groups, also from the smallest size fractions, at first interpreted as form variants within known species (e.g., Chapter 2: fig. 49, forma subulata; Chapter 4: fig. 81, forma baltica) but the latter, and others (variant 1, Chapter 4: figs. 28-32) are now considered to represent new Thelodus species. Märss (2001) recently reviewed and revised “preliminary” identifications of Andreolepis hedei and placed the forms from the Tabuska Beds in a new species, A. petri. The age of the Tabuska Beds is said to be either late Ludlow or early Pridoli. As regards the occurrence of Andreolepis in the British Pridoli Long Quarry Beds (Andreolepis? and A. hedei), and in the Burgsvik Sandstone on Gotland (A. hedei), she stated that “more material is needed for exact identification of the species”. The Scanian occurrence (Helvetesgraven, Chapter 1) was not mentioned in her review; this material currently comprises 18 scale fragments from two samples, and with features of both taxa; if all these scales should prove to represent A. petri, the most important microvertebrate argument for one of my age interpretations of the Helvetesgraven faunas (late Whitcliffian transitional phase between A. hedei and T. sculptilis Zones, Chapter 1) would have been eliminated; in that case a late Ludlow or early Pridoli age will have to be considered. As things are, however, I see no reason to assign Helvetesgraven scale fragments to the new species. Among the acanthodians in the faunal assemblages no taxon can currently be linked up with age- related differences in the composition of the faunas because the species associated with T. sculptilis in the reference successions must be revised. The most important of these is ‘Poracanthodes porosus Brotzen’, presented as an acanthodian zonal fossil and deep shelf equivalent of T. sculptilis by Märss (1997, 2000), but ‘P. porosus’ in Märss’s sense comprises scales from several, histologically different taxa with different geographic distributions within Laurussia. The porosiform scales originally described as such were obtained from a Early Devonian erratic conglomerate. Radioporacanthodes porosus (Brotzen, 1934) s.s. as defined by Vergoossen (1999a) was not observed in the ÖSF faunas, but some of the form variants grouped together in the oldest (late Ludlow) occurrences of ‘P. porosus’ have been found and redescribed as R.. biblicus (Lehman, 1937) and ‘forma bifurcata’ (Table 2), partim a new Radioporacanthodes species (Chapter 5). It is likely that the zonal fossil ‘P. porosus’ also comprises eroded scales of the presumably punctatiform Poracanthodes? lehmani Vergoossen, 1999, which occurs both in the lowermost Tahula Beds and in at least some ÖSF faunas; its presence is, however, hard to establish under binoculars among small and poorly preserved scales. Punctatiform morphs, partim published as cf. Poracanthodes punctatus Brotzen, 1934, were also listed from ÖSF faunas, but have not yet been studied in detail, because in the pieces of rock from Ramsåsa their preservation is poor; the best material for such study appears to be present in the Helvetesgraven fauna, which needs to be described in detail. Gomphonchus volborthi (Rohon, 1893) is a potential biostratigraphic marker that disappears towards the mid-Pridoli. When G. volborthi and G. sandelensis (Pander, 1856) occur together in the Ramsåsa faunas, the first is predominant and present in all size ranges, whereas the second was chiefly collected from the smallest size ranges and difficult to identify, except in the fauna from Ramsåsa SMNH-Q607. The morphological analysis of trunk scales of Nostolepis striata Pander, 1856 and allied species (Chapters 3-5, 7) will contribute to the revision of N. striata, which in the ÖSF rock samples includes forms (esp. in the 0.106 and 0.212 fractions, and from Ramsåsa E) that show strong morphological resemblance to the Lochkovian acanthodian zonal fossil N. minima Valiukevicius, 1994 but may well be ‘specialised scales’ from a particular body region of a N. striata fish. Scales restricted to Ramsåsa C and described as acanthodian morph 5 (Chapter 5) might