A Template for Other Extinction Events
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Global and Planetary Change 122 (2014) 29–49 Contents lists available at ScienceDirect Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha The global vegetation pattern across the Cretaceous–Paleogene mass extinction interval: A template for other extinction events Vivi Vajda ⁎, Antoine Bercovici Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden article info abstract Article history: Changes in pollen and spore assemblages across the Cretaceous–Paleogene (K–Pg) boundary elucidate the veg- Received 9 March 2013 etation response to a global environmental crisis triggered by an asteroid impact in Mexico 66 Ma. The Creta- Received in revised form 21 July 2014 ceous–Paleogene boundary clay, associated with the Chicxulub asteroid impact event, constitutes a unique, Accepted 30 July 2014 global marker bed enabling comparison of the world-wide palynological signal spanning the mass extinction Available online 7 August 2014 event. The data from both hemispheres are consistent, revealing diverse latest Cretaceous assemblages of pollen – Keywords: and spores that were affected by a major diversity loss as a consequence of the K Pg event. Here we combine new Biostratigraphy results with past studies to provide an integrated global perspective of the terrestrial vegetation record across the Palynology K–Pg boundary. We further apply the K–Pg event as a template to asses the causal mechanism behind other Asteroid major events in Earths history. The end-Permian, end-Triassic, and the K–Pg mass-extinctions were responses CAMP to different causal processes that resulted in essentially similar succession of decline and recovery phases, Siberian traps although expressed at different temporal scales. The events share a characteristic pattern of a bloom of opportu- End-Triassic nistic “crisis” tax followed by a pulse in pioneer communities, and finally a recovery in diversity including evolu- End-Permian tion of new taxa. P–Tboundary Based on their similar extinction and recovery patterns and the fact that the Last and First Appearance Datums Tr–J boundary associated with the extinctions are separated in time, we recommend using the K–Pg event as a model and to use relative abundance data for the stratigraphic definition of mass-extinction events and the placement of associated chronostratigraphic boundaries. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Contents 1. Introduction............................................................... 30 2. TheLateCretaceous........................................................... 30 2.1. Cretaceousclimateandsealevel.................................................. 30 2.2. FloristicprovincialityinthelatestCretaceous............................................ 32 2.3. ThelatestCretaceouspalynologicalrecordinNorthAmerica...................................... 33 2.4. Fossil macroflorasbeforetheendoftheCretaceous.......................................... 34 2.5. Non-marinevertebratesoftheend-Cretaceous............................................ 35 3. The global K–Pgboundaryinterval..................................................... 35 3.1. Theboundarylayer........................................................ 35 3.2. Palynostratigraphy of the K–Pgboundaryinterval.......................................... 35 3.3. Diversitytrends.......................................................... 36 3.4. Palynofloristicsignalintheaftermathoftheasteroidimpact...................................... 38 3.5. The K–Pg macrofloraturnover................................................... 39 3.6. K–PgfaunaturnoverinNorthAmerica............................................... 40 4. The K–Pgeventasatoolforassessingothermassextinctionevents...................................... 41 4.1. The definition of the K–Pgboundary................................................ 41 4.2. The definition of the Permian–Triassicboundary........................................... 41 ⁎ Corresponding author. Tel.: +46 46 222 4635. E-mail address: [email protected] (V. Vajda). http://dx.doi.org/10.1016/j.gloplacha.2014.07.014 0921-8181/© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). 30 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 4.3. The definition of the Triassic–Jurassicboundary............................................42 5. Summaryandconclusions.........................................................43 Acknowledgments...............................................................44 AppendixA. Supplementarydata.......................................................44 References..................................................................45 1. Introduction and the extinction of several key groups, such as the non-avian dino- saurs, pterosaurs, marine reptiles (Buffetaut, 1984, 1990; Jiang et al., As a consequence of an asteroid impact, 66 Ma ago, the biosphere ex- 2001; Fastovsky and Sheehan, 2005; Fastovsky and Weishampel, perienced a global extinction event so large that it defines the boundary 2005; Gallager et al., 2012), the ammonites and marine protists (Smit, between the Mesozoic and the Cenozoic eras (Alvarez et al., 1980; 2012). Major losses with widespread changes in terrestrial and marine Alvarez, 1983; Renne et al., 2013). It is now over 30 years since the hy- biotic representation were also recorded within groups that did not go pothesis of an asteroid impact forming the Cretaceous–Paleogene extinct such as the foraminifera, coccolithophorids, turtles, crocodilians (K–Pg) boundary was advocated by Walter and Luis Alvarez (Alvarez and mammals (Longrich et al., 2011, 2012; Smit, 2012 and references et al., 1980), based on anomalously high levels of iridium in the clay therein; O'Leary et al., 2013 and references therein). layer that forms the boundary between the Maastrichtian and the Thus far, about 350 K–Pg boundary sections have been described Danian—the so called boundary clay. The iridium anomaly was first globally, among which 105 are from terrestrial deposits (Fig. 2) based detected in marine deposits from the boundary clay in Denmark (Stevns on the compilation by Nichols and Johnson (2008). Different methods Klint; Fig. 1A–B) and Italy (Gubbio); (Alvarez et al., 1980). Iridium has can be applied for identifying the K–Pg boundary in these sections, the since been detected in association with the K–Pg boundary clay at most reliable being the identification of the geochemical and mineral- other marine sites worldwide (Bohor et al., 1987a,b; Lerbekmo et al., ogical signals outlined above that relate directly to the Chicxulub 1999; Eggert et al., 2009; Schulte et al., 2010), and also at some sites impact. This geochemically anomalous marker bed can be used as a that represented land during the end-Cretaceous event (Fig. 1C–F; unique and essentially instantaneous timeline for global correlation. Sweet et al., 1999; Sweet and Braman, 2001; Vajda et al., 2001, 2004; Biostratigraphy can also be useful in pinpointing the boundary, espe- Nichols and Johnson, 2008 and references therein; Ferrow et al., 2011). cially where complemented by radiometric dating and paleomagnetic Other anomalies corroborating an impact event have been detected evidence where suitable material is available. since those first observations, including high levels of the elements; A synthesis of the global data clearly shows that the terrestrial K–Pg nickel, chromium and iron, and the presence of quartz grains with planar boundary is currently best known from North America (Northern Great deformation features (PDFs) (Alvarez et al., 1995; Schulte et al., 2010). Plains of the United States and central Canada) for the Northern Hemi- During the final phase of the Cretaceous, the typical marine food sphere, and from New Zealand for the Southern Hemisphere (Fig. 2). web was founded on protists such as coccolithophorids and foraminif- Here we focus on the global record of terrestrial pollen and spore as- era, which occurred in such vast numbers that their tests provided the semblages across the K–Pg boundary with supporting data from the main components of the extensive Upper Cretaceous chalk deposits. macrofloral record. Studying the response of standing vegetation at the These protists mainly inhabited the photic zone, where most (but not time of the impact integrated with geochemical and sedimentological all) were directly dependent on sun-light for photosynthesis. Other pro- analysis, and calibrated with high resolution radiometric dates (Renne tists included dinoflagellates and radiolarians, the latter forming cherts et al., 2013), is key to understanding the extinction and recovery process. in deeper marine environments. The Cretaceous oceans also hosted a di- As primary producers, land plants underpin all terrestrial food chains and verse range of marine invertebrates; the most spectacular probably are a source of sustenance and shelter for numerous terrestrial faunal being the ammonites: cephalopods that reached large sizes and varied groups. The pollen and spore record is unique in that it does not repre- growth forms during the latest Cretaceous. The top predators in the sent individual organisms but rather reproductive cells produced in oceans were the vertebrates, such as sharks, mosasaurs and plesiosaurs high quantities by land plants. Being produced in