Reflection of the mid-Ludfordian Lau Event in conodont faunas of Bohemia

Abstract

Conodont faunas of the Polygnathoides siluricus Zone (Ludfordian, Ludlow) from shallow-water environments of Bohemia are characterized by relatively high taxonomic diversity that reflects an interval with taxa thriving due to increased nutrient supply in rather stable environments during the pre-Lau Event time, as has been documented globally. Although the conodont faunas in strata with P. siluricus are more diversified and variable than those in the interval instantly following, the uninterrupted ranges of several taxa (of genera Wurmiella, Ozarkodina and Delotaxis) show that the change in conodont faunas in the sections is not as drastic in Bohemia as described on Gotland and that the extinction rate was rather moderate. A detailed correlation of conodont distribution in the sections indicates, however, that a large part of the Lau Event is not preserved in the shallow water environment of the former Řeporyje Volcanic Elevation. Accordingly, timing and spatial image of the conodont extinction are thus partly obscured. Only a short interval with considerably diminished conodont elements during the lower range of Ozarkodina? snajdri with random occurrences of Pedavis latialatus, corresponds to the part of the "Icriodontid Zone" on Gotland, i.e. the uppermost part of the Lau Event. This incompleteness in record confirms sedimentary starvation in the shallow environment on the former volcanic elevation in this part of the Prague Basin.•

A jawed polychaete fauna from the late Ludlow Kozlowskii event interval in the Prague Basin (Czech Republic)

“…Barrick et al (2010, p. 32), on the other hand, recorded "normal ecological adjustments to environmental changes" rather than major extinctions and ecosystem collapse, although, as noted by those authors, based on limited faunal data. Similarly Slavík et al (2010) recorded moderate changes in the conodont fauna of the Prague Basin, incomparable to those changes recorded in Gotland, Sweden, or Australia. According to Manda & Kříž (2006) also pelagic orthocerids and the nektonic Ceratiocaris passed unaffected through the critical interval.…”

At what stratigraphical level is the mid Ludfordian (Ludlow, Silurian) positive carbon isotope excursion in the type Ludlow area, Shropshire, England?

“…In Kosov Quarry, Bohemia (peri-Gondwanan Europe), graptolitic strata below the CIE indicating a 'deeper and less oxygenated' environment are overlain by shallower marine, thicker bedded limestones, in which the excursion is recorded (Lehnert et al 2007); in Požáry Quarry, Bohemia the excursion occurs in strata exhibiting 'rapid shallowing' with massive limestone beds with palaeokarst development (Lehnert et al 2007); a gap in the conodont record has recently been recognised at this level (Slavík et al 2010). Palaeokarst development at the same stratigraphical level was also recorded from Mušlovka Quarry by Lehnert et al (2007).…”

“…In Bohemia (peri-Gondwanan Europe) the beginning of the excursion has also been dated to the P. siluricus Biozone (Lehnert et al 2007, Slavík et al 2010 as it has also in the United States . In the latter no Icriodontid Biozone was recognizable.…”

“…Munnecke et al 2003, Jeppsson 2005, Stricanne et al 2006, Loydell 2007, Eriksson & Calner 2008 as it more accurately reflects the stratigraphical level of the excursion, as discussed below. Kaljo & Martma (2006), Barrick et al (2010), Slavík et al (2010) and Manda et al (in press) also refer to this excursion (and/or the penecontemporaneous Lau and Kozlowskii events) as mid Ludfordian.…”

The oldest evidence of non-coaxial shell heterostrophy in the Class Gastropoda

“…The oldest member of the Agnesiinae, Pernericirrus sinistorsus (Perner, 1907), was reported from Late Silurian strata of the Barrandian area (Frýda 1997). It occurs within the Prionopeltis archiaci-Atrypoidea modesta Community (Havlíček & Štorch 1990), which was the first highly diversified faunal community after the recovery following the midLudfordian positive carbon isotope excursion and LAU bioevent (Manda & Kříž 2006, Slavík et al 2010) and before Silurian-Devonian boundary bioevent (Manda & Frýda 2010). The Agnesiinae reached their highest diversity and morphological disparity during the Early and Middle Devonian; thus, during the time of major changes of the marine communities, and increasing predation pressure on the benthic as well as the planktic organisms (see Signor & Brett 1984, Brett 2003, Berkyová et al 2007, Klug et al 2010, which also influenced the ontogenetic strategies of gastropods , but see also Nützel et al 2006Nützel et al , 2007.…”