Downloaded from http://sp.lyellcollection.org/ by guest on October 4, 2021 Devonian climate, sea level and evolutionary events: an introduction R. T. BECKER1*, P. KO¨ NIGSHOF2 & C. E. BRETT3 1Institut fu¨r Geologie und Pala¨ontologie, Westfa¨lische Wilhelms-Universita¨t, Corrensstrasse 24, D-48149 Mu¨nster, Germany 2Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany 3Department of Geology, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221-0013, USA *Corresponding author (e-mail: [email protected]) Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. The face of Planet Earth has changed significantly Brett et al. 2009). The bounding events, even those through geological time. Dynamic processes active of lesser intensity, produced major re-structuring in today, such as plate tectonics and climate change, local to global ecosystems and are seen as critical have shaped the Earth’s surface and impacted bio- drivers of long-term evolutionary patterns (Brett diversity patterns from the beginning. Organisms, 2012). These linked abiotic and biotic events and on the other hand, have the capacity to significantly extinctions of different magnitude have been sum- alter Earth’s hydrological and geochemical cycles, marized by House (1983, 1985, 2002), Walliser its atmosphere and climate, sediments, and even (1984, 1996) and, more recently, by Becker et al. hard rocks deep down under the surface. Abiotic– (2012). The Devonian event succession is summa- biotic interactions characterize Earth’s system his- rized in Figure 1. Two first-order mass extinctions tory and, together with biotic competition and food at the Frasnian–Famennian boundary (Kellwasser webs, were the main trigger of evolutionary change, Crisis) and at the end of the Devonian (Hangenberg innovations and biodiversity fluctuations. Within Crisis), characterized by the loss of major fossil the Palaeozoic, the Devonian was an especially in- groups (classes and orders) and complete ecosys- teresting time interval as it was characterized by tems (e.g. metazoan reefs, early forests), have to be the ‘mid-Paleozoic predator revolution’ (Signor & viewed in the context of a complex global event Brett 1984; Brett 2003) and the related ‘nekton sequence. There are important similarities between revolution’ (Klug et al. 2010), characterized by discrete pulses/phases of the major biotic crises and the blooms of free-swimming cephalopods, includ- individual smaller-scale events. In our understand- ing the oldest ammonoids, and fish groups (e.g. ing, second-order global events are characterized toothed sharks and giant placoderms), the rise of by sudden extinctions in many groups and ecosys- more advanced vertebrates, including the oldest tems, including the complete disappearance of sev- tetrapods (e.g. Blieck et al. 2007, 2010; Niedz- eral widespread and diverse organism groups (orders wiedzki et al. 2010), the most extensive reef com- and families). Examples are the basal Emsian ato- plexes of the Phanerozoic (e.g. Kiessling 2008), pus Event, where the planktonic graptolites finally and the ‘greening of land’ by the diversification died out, the Taghanic Crisis, Frasnes events and and spread of land plants, including the oldest for- Lower Kellwasser Event. Third-order global events ests (e.g. Stein et al. 2012; Giesen & Berry 2013), show globally elevated extinction rates, often at which resulted in new soil types and changing lower taxonomic level (genera and species), but weathering. within many clades and in several ecosystems. These major evolutionary trends did not unfold Examples are the Silurian–Devonian boundary in a long interval of environmental stability, but in Klonk Event, and the Daleje, Choteˇc, Kacˇak, Con- times of numerous and repeated, geologically brief, droz and Annulata events. Fourth-order global global events that punctuated prolonged periods, extinctions refer to the sudden disappearance of up to several million years in duration, of relative relatively fewer but widespread groups, which im- stability, termed ecological-evolutionary subunits plies a global, not regional, trigger. This category (EE subunits: Boucot 1990; Brett & Baird 1995; may include the Lochkovian–Pragian boundary From:Becker, R. T., Ko¨nigshof,P.&Brett, C. E. (eds) Devonian Climate, Sea Level and Evolutionary Events. Geological Society, London, Special Publications, 423, http://doi.org/10.1144/SP423.15 # 2016 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on October 4, 2021 R. T. BECKER ET AL. Fig. 1. The succession of Devonian global events and crises (well-known examples in bold), including maxima of anoxic sedimentation (e.g. black shales), plotted against the chronostratigraphic scale, old and new conodont zonations (e.g. Klapper 1989; Yolkin et al. 1994; Klapper & Becker 1999; Aboussalam 2003; Slavı´k & Hladil 2004; Girard et al. 2005; Murphy 2005; Aboussalam & Becker 2007; Slavı´k et al. 2007, 2012; Kaiser et al. 2009; Hartenfels 2011; Corradini & Corriga 2012; Aboussalam et al. 2015; Spalletta et al. 2015; Valenzuela-Rı´os et al. 2015), and the zonal key for global ammonoid zones (Becker & House 2000). The substage levels shown here follow proposals to SDS but have only partly been ratified (Givetian, Frasnian) and not yet formally approved by the International Stratigraphic Commission. The given absolute age number for the base of each stage is adopted from the calibration and interpolation in Becker et al. (2012). Downloaded from http://sp.lyellcollection.org/ by guest on October 4, 2021 DEVONIAN EVENTS: INTRODUCTION event, and the Chebbi, Upper Zlı´chov, Middlesex 2011), and represent major abrupt faunal turnovers. and Dasberg events. Other intervals, such as the They have been recognized elsewhere (e.g. Spain) pumilio, Timan, Rhinestreet, semichatovae and but may not be as strong, making them third- or Nehden events, are better characterized as faunal fourth-order events. The ranking of the named indi- blooms, radiations and sudden organism spread with vidual events may change with continuing research transgression rather than as extinctions (Fig. 2). The and additional small-scale global extinctions will Bakoven and Stony Hollow events are strong in the probably be recognized in the future. Appalachian Basin, where their impact is locally far The widely known Devonian black shale events greater than the Choteˇc Event (DeSantis & Brett (Fig. 2) are linked with hypoxia/anoxia, rapid Fig. 2. Example of thin black shales interrupting a strongly cyclic middle–upper Famennian pelagic nodular limestone succession: the two Annulata Event beds (top lower third) and the Dasberg Black Shale (base of the upper third) at Effenberg Quarry, northern Rhenish Massif, Germany (photograph by S. Hartenfels). Downloaded from http://sp.lyellcollection.org/ by guest on October 4, 2021 R. T. BECKER ET AL. eustatic fluctuations, faunal blooms, geochemical understanding of mid-Palaeozoic events around anomalies, and stepped extinctions and survival. the eastern Proto- or Palaeotethys Ocean: for exam- But not all global events were associated with the ple, in Vietnam and Thailand. Combined biostratig- spread of anoxia in times of climatic warming raphy, sedimentology, physical stratigraphy and and eustatic rise, others correlate with sharp regres- isotope geochemistry in different facies settings sions and climate cooling. Clearly, multiple oceano- will be one of the future challenges in order to better graphic factors were involved. But sudden climate understand the evolution of ecosystems and climate change appears to have been the most important change. In this respect, and as an outlook, research common trigger, possibly linked with episodes of on varied and regionally distinctive shallow-water massive volcanism and times of significant draw- successions should be a focus in the near future. down of atmospheric CO2. Currently, there is no As mentioned earlier, the fruitful cooperation unequivocal example of bolide impact events as between IGCP and SDS produced a very large num- global extinction triggers in the Devonian, although ber of scientific papers and greatly increased knowl- some impacts are now well known, such as the edge in many respects. But there is still much work lower Frasnian Flynn Creek crater of Tennessee to be done in order to fully understand the complex- (Schieber & Over 2005) and the middle Frasnian ity of abiotic–biotic interactions. There will be key Alamo impact of Nevada (e.g. Warme & Sandberg roles for the integration of new and different tech- 1996; Poole & Sandberg 2015). niques, for an expansion into currently poorly Despite the summarized general patterns, knowl- known territory (new and neglected sections/ edge of many of the individual events and even regions), and, equally important, for a thorough inte- a deeper understanding of the two major crises is gration of the wealth of strongly dispersed data on still at an early stage, with more open questions different fossil groups and regions, both in datasets than answers (e.g. Racki 2005). For many of the and in models. second- or third-order global events there are no Some contributions of this volume were first summaries of their recognition in different regions presented at the 2013 meeting or subsequently, or of event patterns on different continents and for example at the IGCP 596–SDS