Gondwana Research 51 (2017) 272–288 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Integrated record of Ludlow (Upper Silurian) oceanic geobioevents – Coordination of changes in conodont, and brachiopod faunas, and stable isotopes Andrej Spiridonov a,⁎, Robertas Stankevič a,TomasGečas a,TomasŠilinskas a, Antanas Brazauskas a, Tõnu Meidla b, Leho Ainsaar b,PetrasMusteikisa, Sigitas Radzevičius a a Institute of Geosciences, Faculty of Chemistry and Geosciences, Vilnius University, M. K. Čiurlionio 21/27, LT-03101 Vilnius, Lithuania b Department of Geology, University of Tartu, Ravila 14a, 50411 Tartu, Estonia article info abstract Article history: The Ludlow Epoch (Silurian) was marked by several globally recognized but mechanistically poorly understood Received 16 May 2017 biotic events. The most pronounced of them was the Lau Event, which strongly decimated conodont, graptolite, Received in revised form 4 August 2017 and brachiopod faunas. Additionally, this event coincides with the largest positive stable carbon isotopic anomaly Accepted 7 August 2017 in the whole Phanerozoic, as well as the resurgence of the so-called “anachronistic” microbial facies that were fre- Available online 1 September 2017 quently encountered during survival episodes of the major mass extinction events. In this contribution, based on č Handling Editor: R.D. Nance the analysis of the outer shelf facies succession (Milai iai-103 core), from the Lithuanian part of the Silurian Baltic Basin, as integrated quantitative record of conodont, brachiopod and δ13C changes across most of the Ludlow is Keywords: presented. The succession was subdivided into four conodont zones that served as a stratigraphic framework Conodonts for analyzing the δ13C and palaeoecological trends. The depth constrained cluster analysis revealed successions Brachiopods of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each Stable carbon isotopes other near the change points in the stable carbon isotopic curve. The application of a newly developed mathemat- Lau event ical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts Time anomalous communities and brachiopods are represented by highly time specific assemblages in the aftermath of the Lau event (O. snajdri Joint recurrence analysis Interval Zone). The anomalous interval is confined to the transgressive and highstand phases of the 3rd order post-Lau transgression. The discussed interval is coeval with the extensive development of stromatolitic commu- nities in the nearshore environments around the world. The results allow for the first time to quantify the pro- found ecosystem-wide geobiological impact of the mid-Ludfordian event that lasted up to the latest Ludfordian. © 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction (the last one at the very end of the Epoch), based on the integrated strat- igraphical analysis of the distribution of conodont species, changes in sed- It is now widely recognized that the Silurian Period was a time of a re- imentary successions and stable carbon isotope trends in carbonates markable evolutionary turnover, extinction and biotic radiation events, (Jeppsson and Aldridge, 2000; Jeppsson et al., 2012; Melchin et al., accompanied by shifts in biogeochemical cycles of carbon and other nu- 2012). The Linde and Lau events most probably correspond closely to trients (Cooper et al., 2014; Crampton et al., 2016; Lenton et al., 2016). the leintwardinensis and kozlowski events, respectively (Jeppsson and The Ludlow epoch is characterized by up to five (Kaljo et al., 1996)glob- Aldridge, 2000; Jeppsson et al., 2012). Brachiopods experienced a signifi- ally recognized ecological and evolutionary perturbations of benthic, pe- cant drop in global genus level diversity in the mid-Ludfordian, an epi- lagic ecosystems (Talent et al., 1993; Urbanek, 1993; Jeppsson and sode of extinction called the “Pentamerid event” (Talent et al., 1993) Aldridge, 2000; Eriksson et al., 2009; Munnecke et al., 2012). Two major that is temporally equivalent to the Lau Event (Jeppsson and Aldridge, events are detected in the graptolite record of the Ludlow, namely the 2000). The data from the Prague Basin show that a significant reorganiza- early Ludfordian leintwardinensis Event and the mid-Ludfordian kozlowski tion of the benthic (trilobite, brachiopod and bivalve) communities took Event (Urbanek, 1993; Štorch, 1995; Štorch et al., 2014). Three oceanic place in mid-Ludfordian (Manda and Frýda, 2014). This all shows clearly events – the Linde, Lau and Klev events - are recognized in the Ludlow that the Ludlow Epoch was one of the most dramatic time intervals of the mid-Palaeozoic era (Calner, 2008). The most prominent geobiological turnover episode was the short- ⁎ Corresponding author. termed Lau Event (Jeppsson, 1998; Cramer et al., 2015). It was associated E-mail address: [email protected] (A. Spiridonov). with the largest positive stable carbon isotopic excursion of the whole http://dx.doi.org/10.1016/j.gr.2017.08.006 1342-937X/© 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. A. Spiridonov et al. / Gondwana Research 51 (2017) 272–288 273 Phanerozoic eon (Calner, 2008), as well as the global resurgence of 2. Geological setting microbially built structures (Calner, 2005a) and oceanic carbonate whit- ings due to the supersaturation of carbonates in the sea water The studied Milaičiai-103 core section is located in the western Lith- (Kozłowski, 2015). uanian part of the Baltic (or Baltoscandian) Silurian Basin, in the transi- The described patterns of community collapse and the tional zone between the shallow water carbonate facies mostly palaeoenvironmental change in Ludlow were explained by characterized by high abundance of shelly taxa and the deep water fa- interchanging oceanic and climatic states (humid vs. arid periods) cies characterized by high abundance of graptolites and dominance of that influenced the rates and modes of oceanic circulation regimes argillaceous sediments – mudstones and organic rich clays (Fig. 1). (Jeppsson, 1987; Samtleben et al., 1996; Jeppsson et al., 2012)oras The Silurian Baltic Basin was an epeiric sea deepening toward the mod- a result of effects of sudden, high magnitude sea level changes ern south-west direction and spanning the territories of southern Scan- (Loydell et al., 2001), most probably of glacioeustatic origin (Calner dinavia, Baltic countries, Kaliningrad District (Russia), eastern Poland and Eriksson, 2006; Lehnert et al., 2007). Better understanding on and westernmost part of the Ukraine (Einasto et al., 1986; Paškevičius, causes of the observed global perturbations is hampered by the 1997; Lazauskienė et al., 2003; Jeppsson et al., 2006; Koren' and lack of quantitative palaeoecological studies based on integrated Suyarkova, 2007; Kaljo et al., 2014). The greatest thickness of strata palaeontological and geochemical records. This contribution pre- and the most complete successions are found in the deeper part of the sents a high-resolution integrated stratigraphical–quantitative basin comprising Poland, western Lithuania, and the Kaliningrad Dis- palaeoecological study of conodonts, brachiopods, and stable carbon trict. Usually very good to excellent preservation of conodonts and isotopes of the Ludlow in the shelf succession of the Lithuanian part very low colour alteration index (≈1) (Männik and Malkowski, 1998) of the Baltic Silurian Basin. The main objective of this paper is to show that the Silurian strata of this basin are unaltered and therefore quantitatively test the influence of the oceanic events on the com- suitable for palaeoenvironmental and palaeobiological research. munity dynamics of conodonts and brachiopods using constructed The Dubysa, Mituva and Ventspils formations are distinguished in comprehensive stratigraphical framework. In order to achieve this the investigated interval of the Milaičiai-103 borehole (Paškevičius et goal, a new numerical technique that quantifies and tests the signif- al., 2012) and this lithostratigraphic subdivision is used in the present icance of temporal recurrence patterns of palaeocommunities was study (Fig. 2). The geological section of the investigated interval is main- developed and tested on the present data set. ly composed of dolomitized marlstones, nodular limestones and wavy- Fig. 1. Palaeogeographic map (Bassett et al., 1989) showing the location of the Milaičiai-103 borehole. 274 A. Spiridonov et al. / Gondwana Research 51 (2017) 272–288 Fig. 2. Distribution of graptolites, and conodonts, and δ13C trend. From left to right: series, stages, regional stages, formations and biozones. δ13C chemostratigraphical zones were named using nomenclature of Frýda and Manda (2013): R-Zone - the zone of the rising values; S-Zone - the zone of the stably high values; and F-Zone is the Zone of long exponentially falling values. bedded marlstones. There is a pervasive decreasing trend in clayey ma- Bohemograptus praecornutus Urbanek, B. cornutus Urbanek and long- terial content upward in the studied interval. ranging P. frequens, B. b. bohemicus, Pseudomonoclimacis tauragensis (Paškevičius), B. b. tenuis (Bouček) is interpreted as the leintwardinensis 3. Overview of graptolite biostratigraphy in the core Biozone. Previously this interval was