A Template for Other Extinction Events

Global and Planetary Change 122 (2014) 29–49

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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 dinosaurs, 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 abundance, durable (e.g. Gallager et al., 2012). In non-marine environments, vertebrate and microscopic, they have the advantage of being preserved in great faunas were dominated by non-avian dinosaurs, together with crocodil- quantities in terrestrial sediments (with 104 to 106 specimens per gram ians, turtles, snakes and non-eutherian mammals (Buffetaut et al., 1999; of sediments being typical), thus providing large datasets with high sta- Russell and Manabe, 2002; O'Leary et al., 2013). tistic fidelity. Moreover, terrestrial spores and pollen are transported in The late Maastrichtian saw the initiation of a period of major volca- abundance into marine settings thus permitting correlation of terrestrial nic activity, the Deccan flood basalt volcanism (Traps) in what is today and oceanic events (Saito et al., 1986; Brinkhuis and Schiøler, 1996; western India. During the ~1-million-year-long main phase of eruption, Vajda and Raine, 2003; Molina et al., 2006; Willumsen and Vajda, 2010). ~80% of the Deccan activity occurred during two distinct intervals Our study integrates published palynological data from terrestrial (Chenet et al., 2009 and references therein): one during the late settings across the K–Pg boundary at a global scale, and provides new Maastrichtian starting 400 kyr before the K–Pg boundary (Ravizza and data on diversity trends related to the extinction event. This comple- Peucker-Ehrenbrink, 2003; Robinson et al., 2009) and during the early ments the comprehensive review of vegetation patterns across the K– Danian (Cripps et al., 2005). Some investigators have repeatedly advo- Pg boundary compiled by Nichols and Johnson (2008).Wealsocompare cated that Deccan volcanic activity was the primary cause behind the and contrast the event stratigraphy of the K–Pg with those of the Perm- K–Pg extinction (Keller, 2008; Keller et al., 2009) based on the argument ian–Triassic (P–Tr) and the Triassic–Jurassic (Tr–J) boundaries to assess that the extinction of species was gradual during the Maastrichtian the criteria for stratigraphically defining major geological events in (Clemens et al., 1981). Although the mass extinction seems to have Earth's history. been preceded by ~4 °C warming as a possible result of the Deccan volcanic activity (Wilf et al., 2003; Self et al., 2006), no major diversity loss 2. The Late Cretaceous within the Maastrichtian terrestrial biota has been noted. Instead, the North American fossil record documents an increase in plant diversity 2.1. Cretaceous climate and sea level associated to the end-Cretaceous warming event (Wilf et al., 2003). Recent radiometric dating (Renne et al., 2013) shows that the asteroid During the Early Cretaceous, the two supercontinents Gondwana impact was clearly coincident with abrupt global ecosystem disruption and Laurasia were almost entirely separated by the Tethys Ocean V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 31

Fig. 1. (A) View over the marine K–Pg succession at Rødvig, Stevns, Denmark. The carbonates below the K–Pg boundary are mainly coccolith chalk while the carbonates above the boundary comprise re-precipitated CaCO3 followed by bryozoan limestone. (B) The so called “ﬁsh-clay” or K–Pg boundary at Rødvig is a thin dark layer followed by the red iron- and sulfur-rich bed, succeeded in turn by light gray sediments. Photographs have been taken by the authors. (C) The K–Pg boundary in the badlands, of Marmarth, North Dakota USA. The K–Pg lies in close proximity of the Hell Creek–Fort Union Formation which is easily recognized by several features such as color change (especially from homogeneous darker gray to golden yellow and lighter banded units), break in slope, and the presence of modern vegetation just above the contact. (D) The K–Pg boundary layer at Mud Buttes. The sequence shows a 1-cm-thick pinkish clay layer (low angle ejecta), overlain by a 3-cm-thick orange layer containing altered spherules (high angle ejecta). The top part features shocked quartz and the maximum concentration of iridium. (E) Moody Creek Mine K–Pg boundary locality at Greymouth Coal ﬁeld, south island, New Zealand. (F) K–Pg boundary at Moody Creek Mine. The boundary itself is barely visible and lies within the top of the 12 cm dark coal. though each supercontinent was also undergoing internal fragmenta- the opening of new ocean basins, and formation of new mountain tion at this time (Fig. 3A; McLoughlin, 2001; Torsvik et al., 2001). The ranges (Miller et al., 2005). By the end of the Cretaceous, most of the tectonic activity was intense, leading to extensive continental rifting, modern continents had separated from each other and the North 32 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49

(1:4) Antarctica (3:26) New Zealand (1:5) India (1:7) Africa (3:12) Russia (2:8) China (1:5) Japan (2:5) Netherlands (2:3) France Williston Basin (3:9) Spain (17:142) SouthWestern ND Williston Basin (1:4) Alaska (11:15) Central ND (2:7) Eastern MT (20:191) Western Canada (11:142) Hell Creek MT N orth America

(6:73) Raton Basin, NM (1:2) Wasatch Plateau, UT (4:50) Powder River Basin, WY (4:39) Denver Basin, CO (8:101) Raton Basin, CO

Fig. 2. Compilation of 105 terrestrial K–Pg boundary sections, based on data from Nichols and Johnson (2008).Thefigures in parenthesis represent the number of sections from each area (in bold) and significance score based on the robustness of the identification of the K–Pg boundary as outlined by Nichols and Johnson (2008). The mineralogical and geochemical evidence is emphasized because of its decisive importance regarding the placement of the K–Pg boundary. Palynological analysis — 1 point; sedimentological analysis and sampling performed at less than decimeter resolution — 3 points; iridium anomaly present — 3 points; boundary claystone present — 3 points; shocked minerals present — 3 points; paleomagnetic analysis performed — 1 point; radiometric dating performed — 1 point; Cretaceous faunal assemblage recovered — 1 point; Paleocene faunal assemblage recovered — 1 point; Cretaceous macrofloral assemblage recovered — 1point;Paleocenemacrofloral assemblage recovered — 1 point; fern-spore spike identified — 1point.

Atlantic and South Atlantic were shaped (Torsvik et al., 2001). Although therein, Fig. 3B), largely based on distinctive angiosperm pollen and cool phases have been reported for the Early Cretaceous, the Late Creta- fern spores of restricted geographic and stratigraphic distribution. We ceous was a greenhouse world with high atmospheric CO2 levels have updated the boundaries of these provinces based on new palyno- (Beerling et al., 2001; Royer, 2003; Wang et al., 2014) and this is evident logical data, e.g., revealing that India included three provinces during both in the composition of the fossil biota containing thermophilic ele- the Maastrichtian (Fig. 3B). We outline the characteristics of the four ments in polar regions, and in the sedimentary record, expressed by main provinces below. widespread occurrences of coal, evaporites and laterites (Craggs et al., The Aquilapollenites Province had a northern circumpolar distribu- 2012). Polar ice caps were absent, or small in the Late Cretaceous tion extending to latitude 50° N but ranging to lower latitudes in (Kominz et al., 2008), resulting in high sea levels relative to present con- North America and Asia (Fig. 3B; Zaklinskaya, 1981; Herngreen et al., ditions (50–100 m higher: Miller et al., 2005;or75–100 m higher: 1996). This province is characterized by abundant and diverse represen- Kominz et al., 2008). A considerable portion of the areas that today are tatives of the morphologically distinctive Aquilapollenites pollen group land were covered by sea during the Cretaceous. This included large (triprojectate pollen, with three protruding pores). The affinity of parts of Western Europe, eastern South America, central Australia and Aquilapollenites–Triprojectacites complex have been discussed exten- northern parts of Africa (Scotese, 2001). Central North America was sively in the literature and it has been put forward that these pollen covered by the Western Interior Seaway, a shallow sea rich in marine are closely related to pollen produced by the modern Saantalales, life (Hoganson and Murphy, 2002; Murphy et al., 2002). more specifically to the Loranthaceae family (Funkhouser, 1961; Jarzen, 1977; Muller, 1984) Loranthaceae are woody plants of which 2.2. Floristic provinciality in the latest Cretaceous the majority are hemi-parasites, with mistletoe habit (Friis et al., 2011). Aquilapollenites Group pollen have been reported from numer- The Cretaceous is characterized by the appearance of a new ous Late Cretaceous northern high-latitude areas, including Greenland, plant group, the angiosperms (flowering plants), which by the mid- North America, northern and eastern Asia (Herngreen et al., 1996), Cretaceous had re-shaped global terrestrial ecosystems. The oldest re- but they also occur in relatively high abundance in Maastrichtian as- cords of angiosperms are represented by pollen grains in Hauterivian semblages from the Palmae Province of Bolivia (Pérez Leytón, 1987; and Barremian sediments from various, mostly low-paleolatitude Vajda-Santivanez, 1999) and Brazil (Regali et al., 1974; Herngreen, areas, from north-western Europe (Hughes et al., 1991)tocentral 1975). Aquilapollenites reached its maximum distribution and diversity and northern Africa (e.g. Doyle et al., 1977). The fossil record reveals during the Maastrichtian but most representatives become extinct at a remarkable increase in angiosperm diversity in the mid-Cretaceous the K–Pg boundary with rare occurrences up to the Oligocene; e.g. (Crane and Lidgard, 1989; Friis et al., 2001, 2006)andbytheLate Farabee (1991). The Khatanga–Lena subprovince is part of the Cretaceous, flowering plants began to dominate the global vegeta- Aquilapollenites Province and is distinguished by the absence of the tion supplanting ferns, conifer, Bennettitales and seed ferns that oculate pollen Wodehouseia (Zaklinskaya, 1977; Fig. 3B). had dominated earlier Mesozoic floras (Heimhofer et al., 2007; Friis The Normapolles Province extended from eastern North America, et al., 2011). through Europe and to western Siberia, the Middle East and Himalayas, Floristic provinciality reached its Mesozoic zenith during the (e.g. Herngreen and Chlonova, 1981; Song et al., 1995; Herngreen et al., Maastrichtian, probably as a consequence of habitat fragmentation 1996; Fig. 3B). The Normapolles Group is characterized by triaperturate caused by continental breakup and high sea-levels. The Late Cretaceous and oblate pollen and a systematic affinity to the Fagales has been pro- world has been divided into four major and two minor palynofloristic posed (Friis et al., 2006). This group reached its maximum geographic provinces (Zaklinskaya, 1981; Herngreen et al., 1996 and references distribution during the latest Cretaceous and constituted an important V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 33

A Western Canada Williston Basin Russia Powder River Basin Denver Basin Netherlands Raton Basin Japan Spain France

Chicxulub impact site El Kef China Upland / mountains Land Shallow seas Sea India

Deccan Traps

New Zealand Antarctica

Aquilapollenites Province Mixed Normapolles Province Mixed Palmae Province Mixed Proteacidites / Nothofagidites Schizaeoisporites Khatanga-Lena Subprovince

Fig. 3. (A) Paleogeographic map 66 Ma (Scotese, 2001). Location of the terrestrial K–Pg boundary section and the Global Boundary Stratotype Section and Point (GSSP) for the K–Pg in the shallow marine deposits of El Kef, Tunisia. (B) The main palynological provinces at the end of the Cretaceous (modiﬁed from Herngreen et al., 1996), with representative pollen morphologies.

and diverse element of many Late Cretaceous and early Cenozoic floras 2.3. The latest Cretaceous palynological record in North America of the Northern Hemisphere (Friis et al., 2006). The Palmae Province, characterized by the presence of palm pollen, The North American fossil record is probably the most suitable for extended through northern South America, central Africa and parts of documenting the evolution of the latest Cretaceous terrestrial ecosys- India, zones that represented low-latitude regions during the Late Cre- tems leading up to the K–Pg boundary. Excellent exposures of upper taceous (Fig. 3B, Pan et al., 2006). Palm pollen constitutes up to 50% of Maastrichtian to lower Danian strata spanning the K–Pg boundary the pollen grains within assemblages from these areas (Herngreen yield a diverse range of abundant fossils (vertebrates, invertebrates, and Chlonova, 1981; Herngreen et al., 1996) and probably reflects plant macrofossils and pollen) that can be studied with high strati- warm, ever-wet conditions. Palms are also represented by fossil flowers graphical resolution. Thus, the vast majority of high-resolution K–Pg and fruits in the Maastrichtian Deccan Intertrappean Beds of India (Friis palynological studies have been within the Aquilapollenites province of et al., 2011). central and northern North America. The Proteacidites/Nothofagidites Province was represented at high The best existing fossil record has been described from the Williston latitudes of the Southern Hemisphere including Australia, New Zealand, BasininNorthDakotaUSA(Johnson et al., 2002) which extends further Antarctica, and the southern part of South America (Srivastava, north into Canada (Saskatchewan and Alberta) up to the Canadian 1978, 1981; Herngreen et al., 1996). This province is typified by Northwest Territories (Sweet and Braman, 2001). The palynology of the abundant presence of Nothofagiidites (Nothofagus)andProteacidites the upper Maastrichtian successions is well-constrained; assemblages pollen (Herngreen et al., 1996). Palynological assemblages from South correspond to the Wodehouseia spinata Assemblage Zone, the first oc- Africa and Madagascar lack Nothofagiidites pollen, hence these areas currence of this species marking the base of the upper Maastrichtian do not strictly belong to this province (Nichols and Johnson, 2008). (Nichols, 1994; Bercovici et al., 2012a; Braman and Sweet, 2012). The Each of the major floristic provinces is bounded by zones of intermixed typical Wodehouseia spinata assemblage of North America features di- floras (Fig. 3B). verse and abundant fern spores and angiosperm pollen, among which 34 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 are several species of Aquilapollenites (Nichols and Johnson, 2008). Most rainforest-type plants, largely dominated by angiosperms, are associat- palynological studies have focused on the identification of the K–Pg ed with several ferns, some conifers (Taxodiaceae, Cupressaceae, boundary. Consequently, most high-resolution palynological studies Araucariaceae), cycads and ginkgoes (Johnson, 2002; Axsmith et al., have been limited to a few meters of stratigraphic interval spanning 2004; Axsmith and Jacobs, 2005). The environment was clearly forested the boundary. Nevertheless, several lower resolution studies of the pal- but the mix of deciduous and evergreen elements with palm trees and ynological record covering the entire Wodehouseia spinata Assemblage conifers, and extremely high diversity of angiosperms with lobed leaves Zone have been conducted, and the results from these show that there in the Hell Creek forest communities do not have any close modern an- is no major variation within the composition of the miospore assem- alog (Johnson, 2002; Raynolds and Johnson, 2003; Vajda et al., 2013a). blages (Nichols and Johnson, 2008). Floral changes are clearly visible within the stratigraphic succession of the Hell Creek Formation. Johnson and Hickey (1990) divided the 2.4. Fossil macrofloras before the end of the Cretaceous Hell Creek macroflora into three assemblages subsequently revised by Johnson (2002); and named HCI (a and b), HCII (a and b) and Assemblages from the topmost Cretaceous in the Hell Creek HCIII (Fig. 4). These Hell Creek assemblages are largely dominated by Formation have yielded the richest known Cretaceous macrofloral as- angiosperms with a few rare ferns, one cycad, one ginkgo, and conifers semblages in the world (Johnson, 2002). Multiple sites showing an representing the Taxodiaceae, Cupressaceae, and Araucariaceae exceptionally high abundance and diversity of leaf fossils have been de- (Nichols, 2002). A macroflora dominated by small leaved herbaceous scribed from various terrestrial depositional settings, such as flood and shrubby vegetation characterize the lower Hell Creek while the top- plains, ponds, crevasse splays, levees and within channels (Fastovsky, most macroflora is significantly more diverse (Fig. 4). The variations in 1987; Johnson, 2002). The fossil plant record leading up to the K–Pg floral composition reflect paleoclimatic changes with a significant boundary has been extensively sampled and documented in North Da- mean annual temperature increase at the end of the Cretaceous kota (Johnson, 1989; Johnson et al., 1989). Diverse assemblages of (Johnson and Hickey, 1990; Wilf et al., 2003).

Estimated mean annual temperature (°C) ? (Wilf et al., 2003; Wilf and Johnson, 2004) 25 4 8 12 16 20 Silt Sand Pebble 100 Formations

(m) P-mag

(+42 m) +10 (+30 m) 200 Pg FUI FORT UNION FORT 66.0 Ma 0 165

Chicxulub impact K 100 (Schulte et al., 2010) -10 HCIII 40 10 -20

C29r 150

-30 C30n 25 ~66.5 Ma 25 -40 HCII 1000 m 150 n = 75 -50 ? Emitted basalt HELL CREEK volume (x 10 3 km 3 ) -60

HCI ~67.0 Ma -70 Deccan activity (Self et al., 2006; Schulte et al., 2010) n = 200 -80

-90 n = 200 Best bins -100 67.4 Ma 10 20 30 0306090 105 15 20 25 Range-through (Hicks et al., 2002) Rarefied vertebrate diversity Macrofloral standing richness Categories of insect FOX HILLS (Pearson et al., 2002) and biozonation damage on leaves (Johnson, 2002) SUNSET BUTTE (Labandeira et al., 2002b) (Murphy et al., 2002)

Fig. 4. Compilation of vertebrate, macroﬂora and insect damage diversity trends over the last 1.3 Myr of the Cretaceous in the Marmarth area, North Dakota, USA. Mean annual paleo- temperatures are derived from leaf margin analysis, and further correlated to two global events: the Deccan volcanism and the Chicxulub impact. The Sunset Butte section is used as a baseline for the thickness of the Hell Creek Formation in North Dakota albeit paleontological data is compiled from a multitude of localities from within the Marmarth area. Dating based on Hicks et al. (2002). V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 35

Crossing the K–Pg boundary, the diverse angiosperm-rich few millimeters in antipodal regions such as New Zealand (Moody macroflora is replaced by a low diversity, angiosperm-dominated Creek Mine, Vajda et al., 2001). flora. In the lowermost Paleocene, local occurrence of specificmireveg- In Europe, mainly marine K–Pg boundary successions are preserved etation is thought to represent survival of Cretaceous swamp vegetation and no complete terrestrial K–Pg boundary section (with a diagnostic (Johnson, 2002). boundary clay including shocked quartz and a geochemical anomaly) New Zealand Upper Cretaceous and Paleogene non-marine sedi- has yet been identified there. ments host well-preserved macrofloras incorporating leaves, flowers In North American terrestrial successions, the K–Pg boundary is and seeds. These floras were first studied by von Ettingshausen (1887, commonly evidenced by a several centimeter thick boundary claystone 1891) who focused mainly on Late Cretaceous assemblages from the that can typically be subdivided into 2–3units(Sweet et al., 1999; Otago and Canterbury areas. Later, extensive work by Couper (1960) Sweet and Braman, 2001). At Mud Buttes (North Dakota, USA) the K– documented the palynological and the macrofossil record of the Pg boundary claystone contains a 1 cm thick white kaolinitic “bound- Maastrichtian, and the biogeography of the New Zealand vegetation ary” clay representing low-angle ejecta (Fig. 1C, D). This is overlain was presented in Mildenhall (1980). More recent works include, by an orange layer of millimeter-sized glass spherules altered to clays, e.g., those of Pole (1992, 1995, 2008), Pole and Douglas (1999), representing the high-angle ejecta (Sweet et al., 1999; Sweet and Kennedy (1993, 2003) and Kennedy et al. (2002). Generally, the Creta- Braman, 2001; Ocampo et al., 2006; Nichols and Johnson, 2008). ceous floras of New Zealand comprise Araucariaceae, Taxodiaceae, Above this occurs sub-millimetric quartz grains with planar deforma- Podocarpaceae and dicotyledonous angiosperms (Pole and Douglas, tion features typical of shock metamorphism (Izett, 1990; Nichols and 1999; Kennedy, 2003). The most striking transition in the macroflora Johnson, 2008), together with nickel-bearing spinels derived from the is the significant decrease of Araucariaceae across the K–Pg boundary impactor itself vaporizing on atmospheric entry (Robin et al., 1992; (Pole, 2008). Rocchia et al., 1996). The iridium anomaly varies considerably from High floral diversity in the upper Hell Creek Formation is correlated site to site and reaches maximum concentrations of around 56 ppb in to an episode of warming that occurred during the last 400 kyr of the North American boundary claystone (Izett, 1990) and 71 ppb in New Cretaceous. Leaf margin analysis (LMAT) based on North American Zealand where the boundary is within a coal seam (Vajda et al., 2001). leaf assemblages (Wilf et al., 2003; Fig. 4), shows an estimated The iridium anomaly co-occurs with high concentrations of other ele- ~4 °C warming on land at around 66.5 Ma, i.e. 500 kyr prior to the ments such as Fe, Cr, Ni and Au presumably derived from the asteroid K–Pg event. This warming event is also reflected in variations within (Schulte et al., 2010). The proximal ejecta deposits in northern Belize the marine record and lastedto100kyrbeforetheK–Pg event and southern Quintana Roo, Mexico, are characterized by two distinct (Thibault and Gardin, 2010). Wilf et al. (2003) suggested that the stratigraphical units; the lower spheroid bed and the upper diamictite temperature increase was driven by pCO2 rise from Deccan volcanic bed, both part of the Albion Formation (Pope et al., 1993; Ocampo activity (Fig. 4). et al., 1996; Wigforss-Lange et al., 2007; Vajda et al., 2014). These deposits are directly linked to the Chicxulub impact where the spheroid bed represents the initial vapor-plume deposits, and the overlying 2.5. Non-marine vertebrates of the end-Cretaceous diamictite bed constitutes a debris flow attributed to the collapse of the ejecta curtain (Ocampo et al., 1996) and the direct link to the The Hell Creek and contemporaneous formations in North America Chicxulub impact is further corroborated by geochemical analysis of (i.e. the Scollard, Willow Creek, North Horn, Frenchman, Lance Creek, these ejecta deposits (Wigforss-Lange et al., 2007). Radiometric dating Denver, and McRae formations) yield large quantities of latest Creta- of shocked zircons found in the boundary claystone in Haiti (Schulte ceous vertebrate fossils, including fish, amphibians (frogs and salaman- et al., 2010), Spain and Italy (Kamo et al., 2011) reveals a direct link to ders), turtles, lizards, crocodilians, champsosaurs, dinosaurs including the basement rocks of the Yucatan Peninsula. Additionally, 40Ar/39Ar birds, pterosaurs and early mammals. Though renowned for its dates of 66.032 ± 0.072 Ma obtained from impact glass (tektites) megaherbivores, such as Triceratops spp. and Edmontosaurus annectens, from Beloc, Haiti, derived from the Chicxulub impact, match 40Ar/39Ar together with large carnivores, such as Tyrannosaurus rex (Pearson et al., dates obtained for local volcanic ashes bracketing the K–Pg boundary 2001, 2002; Sampson and Loewen, 2005; Lyson and Longrich, 2011), layerinnorthernUSA(Renne et al., 2013). This synchronicity reaffirms the Hell Creek non-avian dinosaur fauna is of relatively low diversity the Chicxulub impact as the cause of the extinction at the K–Pg bound- (Vavrek and Larsson, 2010; Brusatte et al., 2012; Mitchell et al., 2012). ary (Renne et al., 2013). Despite previous claims of a latest Cretaceous gap, dinosaur fossils have been recovered up to the very top of the Hell Creek Formation. Ex- 3.2. Palynostratigraphy of the K–Pg boundary interval tensive sampling of the vertebrate content of the Hell Creek Formation has demonstrated that there is no significant decline in vertebrate di- Where the geochemical and mineralogical markers of the asteroid im- versity during the last 1.3 Myr of the Cretaceous (Fig. 4; Sheehan and pact are not present or ill-defined, high resolution palynostratigraphy is Fastovsky, 1992; Sheehan et al., 2000; Pearson et al., 2002; Fastovsky used as the main method for locating the K–Pg boundary. Flowering et al., 2004). This is in agreement with studies of marine reptiles from plants and especially dicotyledonous angiosperms were most affected New Jersey, USA, showing a sudden extinction of Mosasaurs (Gallager by the K–Pg extinction event, as evidenced in both the macrofloral and et al., 2012). palynofloral records of North America and in New Zealand (Nichols, 1990; Vajda et al., 2001, 2004; Nichols and Johnson, 2008; Pole, 2008). 3. The global K–Pg boundary interval In the Aquilapollenites Province of North America (Fig. 3B), a series of taxa become extinct at the K–Pg boundary and are commonly referred 3.1. The boundary layer to as “K-species” (Hotton, 1988, 2002)or“K-taxa” (Nichols, 2002), K signifying Cretaceous, (i.e. Cretaceous key-taxa), not to be confused Deposition associated with the Chicxulub impact is characterized by with K-strategy taxa of ecological studies (MacArthur and Wilson, ballistically and debris-flow transported material from the target rock in 1967). The stratigraphically important key species include most species Yucatan. This sequence thins with distance from the impact site (Bohor of Aquilapollenites, and several other morphologically distinctive angio- et al., 1984; Bohor and Izett, 1986; Ocampo et al., 2006; Schulte et al., sperm pollen taxa (Cranwellia edmontonensis, Erdtmanipollis cretaceus, 2010). Thus, the thickest deposits occur in Belize and southern Mexico Leptopecopites pocockii, Marsypiletes cretaceus, Tricolpites microreticulatus, proximal to the crater, where the successions reach up to 45 m in, e.g. Striatellipollis striatellus, Styxpollenites calamitas; Nichols, 2007; Bercovici Belize (Ocampo et al., 1996). The thinnest deposits constitute only a et al., 2012a). The Paleocene assemblages of North America are 36 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 characterized by a suite of Momipites and/or Caryapollenites (Nichols and Within the Palmae Province, the disappearance of the following Johnson, 2008 and references therein). key-taxa typifies the K–Pg boundary; Aquilapollenites magnus, Within the Proteacidites/Nothofagidites province, more specifically Crassitricolporites brasiliensis, Buttinia andreevi, Proteacidites in New Zealand K–Pg successions, a similar scenario is evident where dehaani and Gabonisporis vigourouxii (Vajda-Santivanez, 1999). typical end-Cretaceous key-species, mainly angiosperms, disappear Subsequent Paleocene assemblages include Mauritiidites franciscoi, at the boundary, including: Tricolpites lilliei, Quadraplanus brossus, and are dominated by periporate pollen (Muller et al., 1987; Nothofagidites kaitangata, a range of Proteaceae taxa (Wanntorp et al., Vajda-Santivanez, 1999). Groups such as Bombacaeae, Proxapertites 2011) and the water-fern Grapnelispora (Vajda and Raine, 2003). The and Mauritiidites dominate upper Paleocene assemblages from the Paleocene key-taxa are represented by Nothofagidites waipawaensis Cerrejón Formation, Colombia (Jaramillo et al., 2007). and Tricolpites phillipsii (Raine, 1984; Vajda and Raine, 2003). Changes in the palynological record occur at the K–Pg boundary in China (Nichols, 2003; Nichols et al., 2006). Data from the Songliao 3.3. Diversity trends Basin (Li et al., 2011) are consistent with the North American signal in revealing an extinction of several taxa at the K–Pg, including the The average extinction proportion of miospore taxa in North angiosperm pollen Aquilapollenites, Cranwellia, Wodehouseia and some America is around 30% (Nichols, 2002; Nichols and Johnson, 2008) Normapolles. Other studies include K–Pg successions at Jiaying in the andthisissynchronouswithasignificant drop in gross palynological Heilongjiang province, NE China (Sun et al., 2011), the Nanxiong site diversity (Fig. 5). An additional 20–30% of the miospore taxa in the Guangdong Province, Southern China (Zhao et al., 2002)and underwent a statistically significant decline in abundance (Hotton, the Dangyang site of the Hubei Province, Central China (Li et al., 2002). The extinction magnitude was apparently lower within New 2013). The K–Pg boundaries in these localities have been well studied Zealand assemblages where 15% of pollen and spores species disap- and new progress has been made in recent years. peared (Vajda and Raine, 2003) but this might be an underestimate

(cm) 300 Average composition for the Paleocene palynoflora K-taxa: 0 % 250 Dicots other than K-taxa: 15 % Gymnosperms: 20 % 200 Ferns: 40 %

150 Variegated beds

100 Fort Union Fm. Massive mudstone 50 sequence Shocked quartz Pg Ejecta layer Spherules Fern spike Boundary clay

Formation Ir anomaly (100x to 1000x above K contact lignite background level) -50 Formation contact Rooted mudstone -100 sequence

-150 Average composition for the Cretaceous palynoflora -200 K-taxa: 30 % Dicots other than K-taxa: 10 % Hell Creek Fm. Gymnosperms: 10 % -250 Ferns: 35 % n = 200 -300 0 10 20 30 40 10 20 30 40 K-taxa relative abundance (%) Rarefied palynological diversity

Fig. 5. Compilation of the average composition of the palynoflora derived from five K–Pg boundary sections in North Dakota, USA (PTRM 170/156, 166, 168, 171; Bercovici et al., 2009,and PRTM 191; Lyson et al., 2011). The relative abundance of K-taxa and rarefied palynological diversity at 200 specimens per sample are plotted on the right (with small dots representing individual samples, large dots representing averaged 20 cm stratigraphic bins and line representing sliding average). Stratigraphical alignment of the samples from the five sections is based on the point of major loss in K-taxa. The stratigraphic section represents a most common rock sequence spanning the K–Pg boundary in the Marmarth area. V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 37

Wood Mountain CCDP core Wood Mountain Creek WESTERN (Sweet et al., 1999) Section DB-89-84B (cm) (Sweet and Braman, 2001) + 20

Ir + 10 Ir Ir Ir Pg BC BC BC BC BC BC K

0 20 40 6080 100% 0 20 40 60 80% - 10 0 20 40 6080 100% 0 20 40 6080 100% 0 20 40 60 80% Wood Mountain Creek Rock Creek West E Frenchman Valley Section SLA-94-17 (Sweet et al., 1999) Rock Creek East A (Lerbekmo et al., 1987) 0 20 40 6080 100% (Sweet and Braman, 2001) (Lerbekmo et al., 1996) (Sweet and Braman, 1992) (Sweet and Braman, 1992)

(cm) WILLISTON BASIN POWDER RIVER BASIN (cm) + 50 + 50 + 10 + 10

Ir Ir Ir Ir Pg Qz Qz Pg Qz Qz BC BC BC BC BC K K 0 20 40 60 80% 0 20 40 60 80% - 50 - 10 Sussex Teapot Dome 0 20 40 60 80% 0 20 40 60 80% (Nichols et al., 1992) (Wolfe, 1991)

0 20 40 60 80% John’s Nose Brownie Butte (Bercovici et al., 2012) Mud Buttes (Tschudy, 1984) (Rook et al., 2010) (Nichols and Johnson, 2002) (Sweet et al., 1999)

RATON BASIN DENVER BASIN

(cm) Ir Ir (cm) Ir Ir + 10 + 10

Qz Qz Qz Qz Pg BC BC BC Pg BC

K K 0 20 40 60 80%

- 10

0 20 40 6080 100% New Zealand 0 20 40 6080 100% 0 20 40 60 80% Starkville North Sugarite West Bijou Creek (Pillmore et al., 1984) Starkville South (Pillmore et al., 1984) (Nichols and Fleming, 2002) (Tschudy et al., 1984) (Pillmore et al., 1984; 1999) (Nichols and Fleming, 1990) (Barclay et al., 2003)

Fig. 6. Selection of published global terrestrial and near-shore marine K–Pg boundary sites showing the occurrence of a fern spike immediately following the K–Pg boundary event, compilation based on studies referenced in the ﬁgure. Cumulative relative abundance of Cyathidites and Laevigatosporites is presented in those cases where the authors have separated the different fern spore components, otherwise the relative abundance of all fern spores as a group is presented. This ﬁgure is based on the following published literature: North America: Pillmore et al (1984, 1999), Tschudy (1984), Tschudy et al (1984), Lerbekmo et al. (1987, 1996), Nichols and Fleming (1990, 2002), Sweet et al. (1990, 1999), Wolfe (1991), Nichols et al. (1992),Sweet and Braman (1992, 2001), Nichols and Johnson (2002),.Barclay et al. (2003); Rook et al. (2010), Bercovici et al. (2012), Europe: Brinkhuis and Schiøler (1996);Japan: Saito et al (1986);NewZealand:Vajda et al (2001).

due to lower taxonomic differentiation of austral spore-pollen North American Late Cretaceous pollen assemblages have been groups. For example, many New Zealand angiosperm pollen types studied intensely taxonomically, which is probably the reason behind have been grouped within the broadly defined Tricolpites and the higher diversity numbers of angiosperm pollen, compared to Proteacidites genera, hence artificially reducing apparent diversity those of New Zealand. More recent taxonomic work on the Proteacidites compared to other floristic provinces. There is also a discrepancy be- group from uppermost Maastrichtian deposits of Campbell Island (New tween the diversity within the palynoflora and the macroflora seen Zealand) has shown that the proteacean pollen in the Nothofagus Prov- at e.g. Murderers Creek, New Zealand (Pole and Vajda, 2009)andat ince is represented by significantly higher diversity than previously Pakawau (Kennedy, 2003). Part of the reason is explained by differ- documented (Wanntorp et al., 2011). This could also explain the dis- ential preservation, e.g. Lauraceae produce pollen grains prone to crepancy in the diversity patterns when comparing the fossil macro- degradation which leads to higher preservation of macro remains. and palynofloras, showing much higher diversity for dicotyledonous Fern spores, at the other hand, are more resistant to degradation angiosperms in the macrofossil record (Kennedy, 2003; Pole and compared to parent plant. Vajda, 2009). 38 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49

CANADA NORTHERN NETHERLANDS JAPAN TERRITORIES (cm)

(cm) + 20 (cm)

+ 50 + 50 + 10 Ir Ir Qz Pg Pg BC Pg K K K

0 20 40 60 80% - 50 0 20 40 60% - 10 0 20 40 60 80% 0 20 40 60 80% Knudsen’s Coulee Police Island Geulhemmerberg Kawaruppu (Sweet and Braman, 1992) (Sweet et al., 1990; 1999) (Brinkhuis and Schiøler, 1996) (Saito et al., 1986)

Williston Basin Powder River B. Denver B. Raton B.

Chicxulub impact site

(cm) NEW ZEALAND + 20

+ 10

Ir Pg K

BC Boundary clay Cumulative spore relative abundance - 10 Qz Shocked quartz Cyathidites sp. 0 20 40 60 80% Ir Iridium anomaly - 20 Laevigatosporites sp. Reduced 0 20 40 60 80% Mid Waipara River Moody Creek Mine Maximun Bryophytes (Vajda et al., 2001) (Vajda et al., 2001)

Fig. 6 (continued).

Some of the K-taxa within the North American assemblages persist in taken place during a short time interval, possibly over the course of a low numbers up to a few meters above the K–Pg boundary (Hotton, few centuries to millennia (Vajda and McLoughlin, 2007) — atemporal 2002; Bercovici et al., 2009, 2012b) and this pattern of short-term surviv- scale now confirmed by radiometric dating of ash beds within North al/reworking is strikingly similar to the pattern described from Southern American strata hosting palynological evidence of the recovery succes- Hemisphere (New Zealand) K–Pg boundary sections (Vajda and Raine, sion (Renne et al., 2013). 2003; Ferrow et al., 2011). This observation warrants a discussion on In New Zealand, evidence of proliferation of fungi (a fungal-spike) the stratigraphical utility of Last Appearance Datums (LAD) of Cretaceous was identified from a few millimeter thick layer of fungal-spore-rich marker species to identify the position of the K–Pg boundary. coal indicating cessation of photosynthesis, where saprotrophs thrived on the abundant decomposing organic matter during a phase where 3.4. Palynofloristic signal in the aftermath of the asteroid impact sunlight was suppressed (Vajda and McLoughlin, 2004; Vajda, 2012). This is matched by increased microbial activity recorded from the The palynological record provides the best insights into ecosystem basal K–Pg boundary clay at Stevns Klint (Sepúlveda et al., 2009), fur- recovery in the immediate aftermath of the impact event from the ther supporting cessation of photosynthesis for a short period. first centimeters of sediments above the impact claystone. Initial recov- The subsequent resurgence of the light-dependent life is initially ery of the plant cover on the devastated landscape appears to have represented by an increase in spore abundance, or “spore spike”. This V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 39

Northern South America USA and Canada New Zealand Europe Patagonia (Venezuela, Brazil, Bolivia)

Gymnosperm/fern Gymnosperm dominance dominance (Phyllocladidites mawsonii) Diverse dinoflagellate Periporate angiosperm Classopollis spike Angiosperm spike Angiosperm spike assemblage pollen Kurtzipites/Ulmipollenites Triorites minor

Fern spike Fern spike Moss spore spike ? ? K–Pg boundary Diverse flora Diverse flora Diverse flora Diverse dinoflagellate Diverse flora Nothofagidites/Proteacidites Nothofagidites/Proteacidites Aquilapollenites Province assemblage Palmae Province Province Province

Fig. 7. Schematic illustration over the pre-impact palynological assemblages followed by the post-impact, long term recovery succession globally.

high abundance of spores, over a restricted stratigraphic interval corre- and pinaceae). These conifers represented climax vegetation, and were sponds to the re-establishment of the terrestrial herbaceous pioneer high pollen producers (Sweet and Braman, 2001; Bercovici et al., 2009). flora over the devastated landscape. The spore spike has been reported Long-term changes in the Southern Hemisphere floras are character- from multiple localities throughout North America (Figs. 6, 7; Fleming ized by substantially lower relative abundances of Araucariaceae pollen and Nichols, 1988, 1990; Sweet et al., 1999; Sweet and Braman, 2001; in the Paleocene compared to the Maastrichtian. Araucariaceae appears Nichols and Johnson, 2008; Bercovici et al., 2012b), from multiple sec- to have become supplanted from its habitat by podocarpacean conifers, tions (both marine and terrestrial) from New Zealand (Vajda et al., mainly Lagarostobos franklinii (Huon Pine) represented by the pollen 2001; Vajda and Raine, 2003; Vajda et al., 2004; Ferrow et al., 2011) Phyllocladidites mawsonii. This has previously been noted in the and from a Japanese marine K–Pg boundary succession (Saito et al., macrofloral record from New Zealand, where Araucariaceae macrofos- 1986). In these areas the spores mostly represent Cyathidites and sils are virtually ubiquitous in the Cretaceous assemblages but are ab- Laevigatosporites species and derive from ferns. The so called fern- sent or rare in Paleocene deposits (Pole, 2008). spike is matched by a corresponding drop in the relative abundance of This trend can further be traced into marine environments in angiosperm pollen in sections from both hemispheres (Sweet et al., European successions (e.g., Caravaca, Spain) where conifer biomarkers 1999; Sweet and Braman, 2001; Vajda et al., 2001; Nichols and drop in concentration at the boundary, only to recover 10 kyr after the Johnson, 2008). K–Pg event (Mizukami et al., 2013). Although the end-Cretaceous successions in Europe mainly repre- ThesamebroadpatternoccursinPatagoniawherethe sent marine depositional settings, the ecological collapse on land is Cheirolepidiaceae (represented by Classopollis pollen), which reflected in the marine sediments at several sites in the Netherlands played a subordinate role during the late Maastrichtian, proliferated in by a spore spike within the basal part of the boundary clay where the the Paleocene (Barreda et al., 2012). In that area they appear to have spore spike is represented in this case by bryophyte spores (Brinkhuis out-competed the Podocarpaceae in the basal Danian. A general pattern and Schiøler, 1996; Herngreen et al., 1998). Though representing a of post-catastrophe recovery is thus evident in both hemispheres. Initial different plant group, bryophytes are ecologically similar to ferns in vegetation collapse is followed by a brief proliferation of saprotrophs being opportunistic primary colonists of disturbed sites. More recent (observed at Moody Creek Mine site in New Zealand; Vajda and biomarker analyses at Caravaca revealed massive and sudden increase McLoughlin, 2004) followed by a resurgence of pioneer free-sporing in the supply of terrestrial organic matter represented by the presence plants, in turn succeeded by seed plants, with regional variations in of long-chain n-fatty acids (C20–C30) in the basal Danian (Mizukami the dominant taxa being controlled by the composition of the pre- et al., 2013), reflecting enhanced run-off following the vegetation die- existing vegetation and local environmental conditions. back. A study on sedimentary leaf wax n-alkanes across the K–Pg boundary at Loma Capiro, Central Cuba further supports vegetation 3.5. The K–Pg macroflora turnover turn over followed by recovery succession during warmer conditions during the Paleocene (Yamamoto et al., 2010). In North America, extinction among plants based on macrofloral Following the initial resurgence of spore-producing plants, an ex- evidence is striking, with 78% of the macrofloral species from the tended recovery succession of angiosperms initially represented by Hell Creek disappearing at the K–Pg boundary (Johnson, 2002; Wilf the pollen Ulmoideipites and Kurtzipites is seen in the North American and Johnson, 2004). The extinction rates are remarkably high and successions (Sweet and Braman, 1992). However, the apparent rise in concentrated at the K–Pg boundary itself, with extinction levels abundance of these angiosperm taxa is a function of the severe decrease variously calculated between 57 and 66% (Wilf and Johnson, 2004). in other angiosperms (i.e. this is an auto-correlation phenomenon) and The recovery flora, characterized by a low diversity assemblage the spike in these taxa is only evident when angiosperms are considered (Johnson, 2002; Bercovici et al., 2008), is dominated by angiosperms individually. (Wolfe, 1985). Amonospecific angiosperm pollen anomaly, or “angiosperm-spike”, Surviving taxa are not those that were dominant during the Creta- represented by high relative abundances of Triorites minor occurs direct- ceous. They represent species that were most common in Cretaceous ly above the fern spike in New Zealand successions (Vajda et al., 2004). mire facies (Johnson, 2002), hence there may be important local envi- In contrast to the Canadian “angiosperm-spike”, this is a genuine angio- ronmental or taphonomic biases in the data. The first occurrence of a sperm abundance anomaly where Triorites minor reaches up to 30% of typical Paleocene taxon is Paranymphaea crassifolia, which is recorded total miospores. This pollen type originated during the Cretaceous and a few meters above the K–Pg boundary (Johnson, 2002; Bercovici its resurgence in the early Paleocene is probably related to the parent et al., 2008). The distribution of major Paleogene vegetation types was plant being an opportunistic herbaceous early-successional colonist. also discussed by Macrofloristic diversity remained low in some North ThecomparableintervalinNorthAmericaistypified by a succession American ecosystems for several million years following the end- with increased relative abundance of conifer pollen (taxodiaceae Cretaceous event and did not reach end-Cretaceous values until the 40 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49

Eocene (Johnson and Ellis, 2002; Barclay et al., 2003; Barclay and from North Dakota reveal a stable range and quantity of insect damage Johnson, 2004; Peppe, 2010). However, the vegetation in other areas re- types throughout the end of the Cretaceous (Fig. 4, Labandeira et al., covered much faster and exceeded Cretaceous diversity levels, only 2002b). However, the data shows that insects suffered significant ex- 1 Ma after the K–Pg event. Sites showing this pattern, such as the tinction at the K–Pg boundary, as recorded by the disappearance of Castlerock flora in Colorado (Johnson and Ellis, 2002; Ellis et al., 2003), most specialized types of insect damage on leaves (Labandeira et al., may have experienced accelerated vegetation recovery due to their oc- 2002b; Wilf et al., 2006; Fig. 4). This is further supported by molecular currence in shelter zones such as intermontane basins. phylogenetic analyses indicating massive extinctions of bees linked to Some studies have also suggested that species able to produce the K–Pg extinction event (Rehan et al., 2013). polyploid forms were better adapted to dramatic ecosystem change Only two specimens of insect body fossils have been described from (Fawcett et al., 2009). As these are mainly represented amongst the an- Upper Cretaceous deposits of New Zealand, one from Canterbury giosperms, advantages such as altered gene expression would have (Harris and Raine, 2002) and another from Hawkes Bay (Craw and benefited this group in the longer-term recovery phase (Fawcett et al., Watt, 1987). However, arthropod mesofossils such as scale-insect 2009). shields have been encountered in abundance at some Upper Cretaceous A fluvial sequence near Cave Stream (north of Castle Hill Village, sites in Australia, the Chatham Islands and New Zealand (Tosolini and central Canterbury), New Zealand, is a classical site. A comparison be- Pole, 2010). Most scale-insects in modern ecosystems spend the major- tween the palynoflora and the macroflora across the K–Pg boundary ity of their life cycle as sedentary organisms on leaf surfaces under a showed a drop of c. 50% of Cretaceous macrofloral taxa at the boundary, waxy shield and extract sap directly from the plant's vascular system. the major change being the disappearance of the Araucariaceae both Interestingly, at the New Zealand Cave Stream site, (the only site within the macro- and palynoflora (Pole and Vajda, 2009). Paleocene where these fossils have been studied across the K–Pg boundary) the plant macro-assemblages contain new conifer genera and new angio- scale insects only occur below the K–Pg, and disappear at the boundary sperm taxa including Dryandra comptoniaefolia. The high abundance of ( Tosolini and Pole, 2010) suggesting that this specialist feeding guild Podocarpaceae (Pole and Vajda, 2009) suggests that these filled the was severely affected by the ecological crisis. The occurrence of leaves niches vacated by Araucariaceae. This process has been extensively with insect damage has also been reported from the Cretaceous of discussed in Jablonski (2008) showing that the post-extinction environ- New Zealand (e.g. Kennedy, 2003) although no quantitative studies of ments where formed by the survivors, and where the “winners” defined their abundance or diversity have been performed to our knowledge. the long-term evolution of individual clades. Raine (1984) and Sweet and Braman (2001) noted that pollen that Studies of a Late Cretaceous flora from Pakawau in northeastern disappeared at the K–Pg boundary are mostly represented by large an- south island New Zealand, revealed 58 angiosperm leaf-forms together giosperm grains with thick and complex surface structure (exine). with podocarp and araucarian leaves and some ferns (Kennedy, 1993; These taxa might be attributed to zoophilous; more specifically ento- Kennedy et al., 2002; Kennedy, 2003). The angiosperm leaves dominate mophilous (insect-pollinated) taxa, providing possible indirect support both in diversity and abundance and all but one of the 58 leaf-types for the extinction of certain insects. were dicotyledonous including representatives of the Nothofagaceae, The diversity of insect damage types on leaves was suppressed for an Lauraceae and Proteaceae (Kennedy, 2003). The depositional setting extended period in North America regaining pre-Pg levels only 10 Myr for the Cretaceous Pakawau site has been interpreted as dominantly la- later (Wilf et al., 2006). This possibly indicates that insect communities custrine with mire development at the lake margins, but there are also had a longer recovery time compared to plant communities. At the intervals interpreted as vegetated floodplains (Kennedy, 2003). Menat site in France, insect damage on Paleocene leaves deposited The Paleocene assemblages are also dominated by angiosperms with 5 Ma after the K–Pg event show “normal” pre-impact levels of insect only minor components of conifers and rare ferns. The Paleocene floras damage abundance (Wappler et al., 2009) tentatively indicating that in- from Ian's Tip and Pillar Point Track incorporate 23 and 28 dicotyledonous sect recovery was faster at this site compared to the US-sites. forms respectively, including Banksiaeformis and Dryandra (now considered a section within Banksia; Mast and Thiele, 2007). Compared to the 3.6. K–Pg fauna turnover in North America Cretaceous assemblage, the Paleocene flora shows a 50% drop in angiosperm taxa. Quantitative palaeoclimate estimates using both Leaf Margin Although several major Mesozoic groups such as the non-avian di- Analysis (LMA) and the Climate Leaf Analysis Multivariate Program nosaurs and pterosaurs went extinct at the K–Pg boundary, ecosystem (CLAMP) on New Zealand leaf assemblages consistently indicate cool- disruption also led to the disappearance of numerous species within temperate conditions for the Paleocene of New Zealand (Kennedy, 2003). groups that are still represented today. Within reptiles, a level of 83% In the New Zealand record, a 7 ± 0.8 °C decrease in mean annual species extinction has been documented together with a dramatic de- temperature over the K–Pg boundary is evident based on Leaf Margin crease in morphological diversity (Longrich et al., 2012). However, tur- Analysis (LMA). Based on data compiled by Kennedy (2003),the tles seem to have been relatively unaffected by the event and persisted mean annual temperature estimates from top-Maastrichtian leaf as- into the Paleogene without significant diversity loss (Lyson et al., 2011). semblages at Pakawau are 14.8 ± 0.8 °C for LMA, and 13.0 ± 1.2 °C Birds are the only group of dinosaurs that survived the K–Pg mass for CLAMP. The mean annual temperature estimates for Paleocene leaf extinction event. However, birds also suffered significant extinction at assemblages from three sites estimate temperatures at 7.5 ± 0.8 °C that time, since none of the “archaic” birds known from North for LMA and 10 ± 1.2 °C for CLAMP (Kennedy, 2003). America survived into the Paleocene (Longrich et al., 2011). Mammals This is consistent with data presented in Wilf and Johnson (2004), were also affected (Fox, 1989, 1997; Wilson, 2005; Meredith et al., based on LMAT on macroflora across the boundary in North Dakota, 2011; O'Leary et al., 2013) and in the Western Interior of North showing evidence for a dramatic cooling directly following the K–Pg America, communities dominated by marsupials and multituberculates event (Vellekoop et al., 2014). The data shows a 5 °C drop in the earliest in the Cretaceous were replaced by communities of diverse eutherians Paleocene correlated to the Chicxulub impact (Fig. 4). in the Paleocene (Archibald and Bryant, 1990; Eberle and Lillegraven, The plant record also provides insights into insect diversity across 1998; Hunter, 1999; Hunter and Archibald, 2002; O'Leary et al., 2013). the K–Pg boundary transition via the range of insect-induced damage Multituberculates seem to have recovered to some extent after the ex- types on leaves (Labandeira et al., 2002a). While only five undeter- tinction, probably due to their opportunistic lifestyle (Wilson et al., mined insect body fossils have been found throughout the Hell Creek 2012). Others groups, including sharks and rays, disappear regionally and Fort Union formations, the enormous leaf fossil database provides from the fossil record in North Dakota at the K–Pg boundary a unique opportunity for the examination of the response of insect her- (Archibald and Bryant, 1990; Sheehan and Fastovsky, 1992; Pearson bivores to the K–Pg event. The insect damage data for leaf assemblages et al., 2002). V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 41

4. The K–Pg event as a tool for assessing other mass extinction events drop in abundance of the Cathaysian cordaitalean and gigantopterid flora and the earliest Triassic is instead dominated by lycopsids 4.1. The definition of the K–Pg boundary (Annalepis)andpeltasperms(Yu et al., 2010). The global vegetation pattern is typified by an extinction of vegeta- Extinction of genera and species is a continuing process but the evo- tion predating the defined Permian–Triassic boundary, and diversity of lution of life on Earth has been disrupted several times by major, abrupt, some key groups declined throughout the Late Permian. Further, the global extinctions. Five large Phanerozoic extinction events have so far pattern of floristic turnover may have been diachronous across latitudes been identified in the paleontological record, but the causes of most ca- (McLoughlin et al., 1997; Coney et al., 2007; Lindström and McLoughlin, tastrophes remain hotly disputed. 2007; Retallack et al., 2007; Yu et al., 2007). Additionally, the timing of The detailed micropaleontological datasets from global K–Pg bound- the extinction of the terrestrial flora is still not well constrained and ary sites generated over decades, now provide excellent templates for the signals appear to differ between the Northern and Southern Hemi- assessing the various hypotheses explaining the patterns and causes be- spheres (McLoughlin et al., 1997; McElwain and Punyasena, 2007; hind other major global extinctions. The recognition of mass extinction Peng and Shi, 2009; Shi et al., 2010). events requires an understanding of the background rates of biological The sediments spanning the PTB in Central Europe are developed in turnover and needs specific criteria for recognizing stratigraphic bound- two major facies domains; the chiefly non-marine facies of the Germanic aries. The K–Pg boundary is unique in that a global timeline is provided realm and the mainly marine facies of the Alpine realm (Kürschner and by the boundary clay (Fig. 1). Biological extinction and recovery signals Herngreen, 2010; Bourquin et al., 2011). Miospore assemblages of latest both in the marine and terrestrial realms can be tied to this timeline. By Permian age from the Zechstein deposits (Germany) are characterized comparing and contrasting the paleontological signals with those of by diverse gymnosperm spore assemblages comprising alete pollen, other mass extinction events, causal mechanisms can be deduced both taeniate and non-taeniate bisaccate pollen, co-occurring with when relating to the fast impact triggered extinction at the K–Pg. diverse spore assemblages (Kürschner and Herngreen, 2010). The EPE At the official GSSP at El Kef in Tunisia, the base of the Danian stage is palynological record, in Central Europe is typified by a significant set to coincide with the base of the boundary claystone (Molina et al., turnover evident as a dramatic decrease in gymnosperm pollen 2006). This level is also characterized by the presence of the iridium resulting in an increase in relative abundance of spores (Visscher anomaly, recognized to have been generated by the impact process. and Brugman, 1988). The basal Triassic in this area is set at the Thus biostratigraphy plays a secondary role at sites where the K–Pg base of the Lundbladispora obsoleta–Protohaploxypinus pantii Zone boundary clay is present. In fact, the International Commission of Stra- characterized by typical Early Triassic spore taxa such as Aratrisporites, tigraphy (ICS) does not even mention the first occurrence of Paleocene Densoisporites playfordii,andKraeuselisporites produced by lycopsids fossils (the First Appearance Datum (FAD) of the P0 foraminiferal zone and invoked to mirror a herbaceous pioneer vegetation occupying in the marine sections) as a valid criterion for defining the K–Pg bound- well-drained floodplain and coastal environments (Retallack, 1977; ary, but mention the association of the extinction of several fossil taxa. van der Zwan and Spaar, 1992). Comparative studies across Gondwana reveal that the close of the 4.2. The definition of the Permian–Triassic boundary Permian was characterized by the extinction of glossopterid and cordaitalean gymnosperms, and these were replaced by peltasperms, The end-Permian Event (EPE) spans ~200 kyr, peaking at ~252.28 Ma scale-leafed conifers and lycophytes during the earliest Triassic as revealed by U–Pb dating of the marine Global Stratotype Section and (McLoughlin et al., 1997; Hill et al., 1999). On the other hand, there are Point (GSSP) at Meishan, China (Yin et al., 2001; Shen et al., 2011), also scattered reports of some typical Gondwanan Permian elements where the base of the Triassic is set at the First Appearance Datum of (e.g. Glossopteris) surviving into the earliest Triassic (McLoughlin, 2011). the conodont species Hindeodus parvus (Ogg et al., 2008; Peng and Shi, A similar scenario has been described from the Northern Hemisphere 2009). Over 90% of biota at species level got extinct at a global scale where gymnosperm-dominated Permian floras were replaced by a with extensive evidence suggesting the Siberian Traps as the main pioneer succession of mainly lycopsids and ferns in the earliest Triassic cause (e.g. Mundil et al., 2004; Schneebeli-Hermann et al., 2013;andref- (Fig. 8; Looy et al., 1999; Hochuli et al., 2010; Hermann et al., 2011). In erences therein). Photochemical model calculations have shown a de- some areas (e.g. Norway) palynological data reveals rapid recovery of crease in O2 that might have further contributed to the extinction gymnosperms following the spore-producing vegetation (Hochuli et al., (Kaiho and Koga, 2013). Ongoing debate surrounds the synchroneity of 2010). the extinction in the terrestrial and marine realms (Peng and Shi, 2009; Palynological sampling of beds in close vicinity to the PTB Shen et al., 2011) and the duration of the event, which has been estimated world-wide has additionally revealed anomalous percentages of to have spanned 40 kyr (Twitchett et al., 2001), 200 kyr (Shen et al., 2011) Reduviasporonites exemplifying a so-called “fungal-spike” (Eshet or 700 kyr (Huang et al., 2011). et al., 1995; Visscher et al., 2011, or alternatively interpreted as No standard reference section has been defined for the non-marine algae by Foster et al., 2002) signifying mass extinction both in Permo-Triassic transition, although the southern Karoo Basin, South land and in the sea and with a sharp increase in “disaster species” Africa, with its relatively complete continental section and well- (Visscher et al., 2011; Algeo et al., 2012 and references therein). constrained record of vertebrate fossils (Ward et al., 2005; Coney Importantly, in the context of this paper, is that the “fungal- et al., 2007) is a potential candidate. The Permian–Triassic Boundary spike” signaling altered ecological conditions, predated the PTB as (PTB) in the Karoo Basin is placed biostratigraphically at the Last Ap- defined by the FAD of H. parvus (Fig. 8)althoughinterrestrialsuc- pearance Datum of Dicynodon lacerticeps (Smith and Ward, 2001; cessions in Southern China fungi/Reduviasporonites have been Ward et al., 2005). identified within the boundary zone (Bercovici et al., in press). Similar successions have been proposed as non-marine global refer- The inhospitable ecological conditions of Early Triassic shallow marine ence sections in Guizhou and Yunnan, South China (Peng et al., 2005). environments are also expressed by a high abundance of cyanobacterial Furthermore, these sections feature several bentonite beds beneficial activity manifested by the presence of microbialites, such as wrinkle for correlation and accurate timing of the extinction event (Yu et al., structures and stromatolites on most continents (Kershaw et al., 2012). 2007; Shen et al., 2011). In South China, the EPE is associated with the This bloom of cyanobacteria is possibly linked to extreme environments, disappearance of coal-bearing and organic-rich sedimentary facies in which grazing organisms where not present, resulting in uncontrolled (Yu, 2008) and also characterized by a drop in abundance of plants growth of extremophiles. Interestingly, the microbial mats also seem to and pollen, co-occurring with a major facies change. Vegetation turn- have served as refuges for some organisms including ostracods (Forel over within end-Permian successions in South China included a major and Crasquin, 2011; Forel, 2012; Forel et al., 2013). 42 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49

EVENT Cretaceous–Paleogene Triassic–Jurassic Permian–Triassic GSSP reference El Kef, Tunisia Kuhjoch, Austria Meishan, China section Definition and integrated global response

Recovery flora of 1. Base of boundary clay Recovery flora of isoetales Iridium anomaly angiosperms and ( ) 2. Mass extinction of flora Pleuromeia gymnosperms and seed ferns and fauna Gymnosperm FAD of (Dicroidium) FAD of dominated flora Hindeodus Danian Psiloceras spelae parvus Induan Spore spike tirolicum Hettangian Pg Global spore spike J Tr 2 mainly lycophytes Fungal spike Ir 1 66.0 Ma 201.3 Ma Spore spike 252.2 Ma Reduviasporonites fungal spike Chicxulub K Tr in Northern P 1 Hemisphere impact Diverse and stable Riciisporites spike Siberian ecosystems in sea CAMP in Northern and on land Hemispere traps 1 Diverse and stable ecosystems in sea Diverse and stable Onset of mass extinctions and on land Floras dominated ecosystems in sea and on land Maastrichtian by angiospers, Floras dominated podocarps and Changxingian by glossopterids araucarian conifers Raethian Floras dominated by ferns, seedferns and cordaites Mass extinction(s) and gymnosperms

Fig. 8. Schematic illustration comparing the three events discussed in this paper. The ﬁgures have been correlated along the respective period boundaries. This emphasizes how these boundaries relate to different phases of the extinction process.

4.3. The definition of the Triassic–Jurassic boundary in the tropics and subtropics coincided with oldest CAMP flows. Nevertheless, the pattern of extinctions was significantly different in During the end-Triassic Event (ETE) the number of living families temperate northern and southern latitudes, although correlation is was reduced by around 35% (Raup and Sepkoski, 1982) and the extinc- hampered by these differences and as yet untested by independent tions punctuated the great wave of Late Triassic radiations amongst ter- geochrononological dating methods. restrial plants and vertebrates and led to the rise of radically different Although the CAMP is put forward as the main contributor to the ex- floras and faunas during the Jurassic. In the terrestrial realm, the basal tinction event, an impact of an extraterrestrial body has been invoked as archosaurs and a large percentage of the amphibians disappeared, pro- possible contributor to the event (Olsen et al., 2002; Tanner and Kyte, viding ecospace opportunities for the radiation of dinosaurs (Benton, 2005). The main candidate is the Rochechouart impact in France, 1995; Olsen et al., 2002; Ruhl et al., 2009). Ammonoids and bivalves dated at 201 ± 3 Ma by 40Ar/39Ar which renders an age coeval with were decimated and the conodonts were finally pushed to extinction the oldest CAMP lavas at the base of the ETE (Schmieder et al., 2010). (Benton, 1995). Although floras were less affected compared to the Anomalous concentrations of iridium from the USA (Olsen et al., faunas, clear changes occurred in the vegetation and the global carbon 2002) and Canadian Tr–J boundary successions (Tanner and Kyte, cycle across the Triassic–Jurassic boundary (TJB) (Hesselbo et al., 2002, 2005; Tanner, 2010) and the presence of shocked quartz in Tr–Jbound- 2007). ary layers in Italy (Bice et al., 1992) have been identified but more inves- The TJB is dated to 201.3 ± 0.2 Ma, based on the First Appearance tigations are required in order to tie these impact markers to the Datum of the ammonite Psiloceras spelae tirolicum in the marine realm, Rochechouart crater (Olsen et al., 2002; Tanner and Kyte, 2005). coinciding with the first occurrence of the gymnosperm pollen taxon Several studies have documented dramatic changes in the composi- Cerebropollenites thiergarthii in Northern Hemisphere terrestrial settings tion of the Late Triassic and Early Jurassic atmosphere, showing a two to

(Kürschner et al., 2007; Ogg et al., 2008; von Hillebrandt et al., 2008). fourfold increase in CO2, plausibly associated greenhouse warming of The Kuhjoch Section, Karwendel Mountains, Northern Calcareous Alps, 3–4 °C, based on plant stomatal data from Sweden, Greenland, UK Austria is the type section for the TJB where the boundary occurs 5.80 (McElwain et al., 1999; Steinthorsdottir et al., 2011) and Australia m above the base of the Tiefengraben Member of the Kendelbach (Steinthorsdottir and Vajda, in press). Although stratigraphical resolu- Formation (Ogg et al., 2008). tion of these studies are not the best being based on museum specimens The mass-extinction preceded the Triassic–Jurassic boundary by ap- with low stratigraphical control or, deriving from one single well-dated proximately 100,000 years and has been invoked as to have been bed as in Steinthorsdottir and Vajda (in press), the results reveal that caused by the massive outpourings of basalts and associated intrusions the end-Triassic and Early Jurassic atmospheric CO2 was significantly of the Central Atlantic Magmatic Province (CAMP) by many authors higher than present values. (e.g. McElwain et al., 1999; Hesselbo et al., 2002; Bonis et al., 2010; Even though floras were less affected compared to the faunas, clear Steinthorsdottir et al., 2011; Mander et al., 2013 and references therein). changes occurred in the vegetation during the ETE. In the Northern Hemi- U–Pb dates from the CAMP, exclusively based on samples from conti- sphere, the ETE is characterized by a macrofloral turnover evidenced by nental sequences of Morocco and Eastern North America, and further extinction of the peltasperm Lepidopteris and its replacement by the tied to palynological signals, show that the initiation of the extinctions dipteridacean fern Thaumatopteris, and a flora rich in ginkgoaleans, V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 43 conifers and bennettites (McElwain et al., 2007; Pott and McLoughlin, 5. Summary and conclusions 2009, 2011; Mander et al., 2013; Vajda et al., 2013b). In the pollen record, the ETE is met with major and dramatic changes. For example, Rhaetian We have outlined paleontological signatures of three major extinc- deposits at several European localities are typified by anomalous abun- tion events that profoundly affected the evolution of the Phanerozoic dances of the enigmatic gymnosperm pollen Ricciisporites tuberculatus biota: the end-Permian, end-Triassic and Cretaceous–Paleogene events. followed by a spore-spike (Götz et al., 2009; Larsson, 2009; van de We have focused on terrestrial environments, more precisely the paly- Schootbrugge et al., 2009; Mander et al., 2012; Vajda et al., 2013b and ref- nological and, to some extent, the paleobotanical records. erences therein). The Early Jurassic recovery floras include high percent- The end-Permian Event was the largest Phanerozoic extinction event ages of Classopollis (Cheirolepidiaceae) recorded e.g. from Sweden (Lund, and although exact numbers are difficult to deduce, the extinction affect- 1977; Guy-Ohlson, 1981; Vajda, 2001; Vajda et al., 2013b), Greenland ed over 90% of the biota at species level globally and the initial numbers (Pedersen and Lund, 1980)andBritain(Mander et al., 2013)andelse- put forward by Raup and Sepkoski (1982) are still generally valid. Recent where. During the Early Jurassic the Cheirolepidiaceae probably took high-resolution radiometric dating of Chinese PTB successions (including over the niche that was previously occupied by the seed-fern groups. Meishan) reveals that the major extinction interval occurred at ca. The high abundance of Classopollis is in Southern Hemisphere successions 252.3 Ma and that the anomalous environmental conditions persisted interpreted to mark the earliest Jurassic together with important for less than 200,000 years (Shen et al., 2011). The extinction can be sum- lycophyte key-species within the genus Retitriletes, including Retitriletes marized by the abrupt decline of the dominant woody gymnosperm veg- rosewoodensis and Retitriletes austroclavatidites (de Jersey and Raine, etation (cordaitaleans and glossopterids) and its replacement by spore- 1990; Zhang and Grant-Mackie, 2001; Akikuni et al., 2010; Bomfleur et producing plants (mainly lycophytes) before the typical Mesozoic al., 2014). woody vegetation evolved. The post-extinction Lower Triassic interval is China was located at higher latitudes during the ETE compared to represented by a coal- , chert- , and a coral-gap, i.e., deposits of these present and the ETE has been identified by palynology in fluvial and la- types do not occur in the geological record from this time interval, possi- custrine deposits in the southwestern Junggar Basin of Xinjiang Uygur bly implying that organisms producing these deposits were absent. In- Autonomous Region, northwestern based on FAD of lycophyte key- stead, ecosystems from this interval seem to have been dominated by taxa (Ashraf et al., 2010; Sha et al., 2011). These several 1000 m thick extremophiles, such as cyanobacteria forming microbialites (Kershaw deposits spanning the ETE need more studies in order to assess the et al., 2012). high resolution palynological signal related to the this extinction The end-Triassic event is the least well-studied of the three event. Recent progress on stratigraphy and biodiversity studies on suc- global crises outlined herein, with major data sets from Southern cessions spanning the end-Triassic and the Tr–J boundary in NW China Hemisphere lacking. The boundary between the Triassic and Juras- and in the Sichuan Basin in Southern China has emerged over the last sic occurs in strata dated at 201.3 Ma; the period boundary post- years (Wang et al., 2010a,b; Li et al., 2013). dates the major phase of the extinctions by approximately Also in Southern Hemisphere records, significant vegetation changes 100,000 years and is argued to have been caused by the outpouring occurred, where the Triassic seed-fern dominated floras (mainly of greenhouse gases produced by the Central Atlantic Magmatic corystosperms) were replaced by more complex associations of coni- Province (CAMP). Vegetation was affected to a minor degree compared fers, Bennettitales and new seed-fern groups during the Early Jurassic to the faunas, although major turnovers within palynofloras include an (Hill et al., 1999; Turner et al., 2009; de Jersey and McKellar, 2013 and interval dominated by the disaster taxon Ricciisporite tuberculatus references therein). These changes seen in the macroflora is however followed by a spore-spike in the earliest Triassic. Although this is true not easily detectable in the Southern Hemisphere palynological record, for Northern Hemisphere settings, a similar signal has yet not been possibly due to the fact that the new incoming seed fern groups pro- identified in Southern Hemisphere settings, where the vegetation turn- duced pollen grains with similar morphologies as the ones going extinct over instead is manifested by a shift from an Alisporites (corystosperm)- — usually grouped within the genus Alisporites.Theprominentandeas- dominated assemblage to a Classopollis (cheirolepidiacean)-dominated ily detectable Ricciisporites are lacking in Southern Hemisphere records. one. Instead the Triassic–Jurassic boundary is noticeable by the abundant oc- The best studied mass extinction is the K–Pg boundary event having currence of Classopollis and FAD of some species within the genus the benefit of an independent reference datum expressed by an iridium- Retitriletes. In New Zealand palynological assemblages, a turnover of enriched, globally distributed ejecta layer. The event occurred 66 Ma species is evidenced at one TJB where characteristic Triassic taxa such and ca. 75% of biota at species level perished. Our review has shown as Alisporites spp. and Densoisporites psilatus declined dramatically (de that the faunas were more severely affected by the Chicxulub impact, Jersey and Raine, 1990) but the turnover seems more gradual in coeval with greater losses in abundance and diversity, compared to the vegeta- Australian successions (de Jersey and McKellar, 2013). Interestingly, tion. This is explained by the short phase of anomalous post-impact con- prominent rise in the abundance of Classopollis is an Early Jurassic mark- ditions, e.g., with darkness, fires and reduced temperatures (Kring, er, comparable to that of the Northern Hemisphere. However, there is 2007). A time-span of a few years would have been sufficient for large an ongoing discussion whether this change may really be used as a animals to starve under such conditions. However, plants were able to marker for the boundary, or not. The general opinion is rather that recover owing to factors such as long-term germinule survival and the Classopollis pollen is a climate indicator and thus its appearance could potential for asexual reproduction, much the same as the dinoflagellates be diachronous across paleolatitudes. in the marine environments. Although the extinction in the end- Linking marine and terrestrial signals through the ETE has also Cretaceous palynological record is only moderate, a striking mass-kill proved to be difficult and debate continues as to whether the extinction of vegetation is evidenced by high-resolution sampling, which shows a on land precedes that in the oceans. High-resolution studies from New complete diversity loss across the boundary followed by a fungal/ Zealand have shown that the palynofloral turnover precedes the extinc- microbe-dominated interval, in turn followed by recovery of ferns, then tion in the marine realm (Akikuni et al., 2010). In contrast, correlations gymnosperms, and finally angiosperms. The development of the entire based on palynological assemblages from TJB sections in Greenland and pioneer succession probably spanned an interval of 100–1000 years, at the marine TJB succession at Audrey's Bay in the UK, (two areas that most, and a true extinction is detectable chiefly amongst angiosperms. were geographically much closer during the end Triassic) show evi- When analyzing at centimeter-scale resolution, data from both hemi- dence for synchronous disruption in the marine and terrestrial realms spheres reveal that the K–Pg crisis is most clearly detectable as a major (Mander et al., 2013). Clearly, further investigations are required to de- change in the abundance of plant groups and that defining the boundary velop a global integrated picture of the environmental changes across based on presence–absence data (FADs and LADs) is not reliable. the TJB. High-resolution palynological studies of both marine and terrestrial 44 V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49

% % synchroneity and extent of marine versus terrestrial extinctions; 3, comparison of patterns between the Southern and Northern hemispheres. When comparing the biotic signals expressed by terrestrial floras for the three extinction events, major differences, but also similarities are identified. All three events show the following signal: 1, an initial diverse flora; 2, extinction/mass-kill; 3, short term bloom of opportunistic “crisis” taxa proliferating in the devastated environment; 4, pulse in pioneer communities (spore spike); 5, recovery in plant diversity, with radiation and appearance of new taxa that may reach dominance in the long term. FAD Although the abrupt extinction and rapid recovery following the K– Pg event points to a single high-energy event, the earlier events have a more protracted signal. The EPE and ETE share a pattern of extinctions LAD that occur over a prolonged time, leading to successive pulses of diversity loss. The drawn-out signal of the EPE was likely caused by longer- term atmospheric changes driven by Siberian trap volcanism. The ETE shows a more ambiguous extinction pattern: CAMP volcanism is coeval with the onset of the event and consistent with some biotic and isotopic Event signals. However, an impact in the Northern Hemisphere of a medium- Interval of discussion sized asteroid may have exacerbated the crisis towards the end of the ETE, resulting in a synergy of processes. Further, comparison of the signals between the two hemispheres reveals a synchronous and similar extinction pattern for the K–Pg and the EPE, whereas the ETE seems to have affected the Northern Hemisphere biota more than its southern counterpart. Based on these observations, it is evident that the longer the extreme environmental conditions last, the greater is the extinction rate, and the Species A A Species B extinction patterns between autotrophs and heterotrophs, and between terrestrial and marine faunas become more similar. Employing the last and first appearances of individual taxa to define B major extinction-related boundaries is difficult because commonly there will be short-term survivors, reworked specimens, fossils repositioned by post-depositional bioturbation, or groups that survived Catastrophic event State A the event in extremely low numbers and appear as Lazarus taxa higher in the geological record. Such taxa can still be valuable subsidiary indices when applying the abundance approach. First appearance data are also inadequate for high-precision location of chronostratigraphic boundaries based on these events because a significant lag-time exists between the extinction event and the evolution of new taxa (Fig. 9). Despite having very different causes, the end-Permian, end-Triassic, and the K–Pg Response V(t) LAD events are consequences of dramatic environmental upheavals that gen- State B erated comparable extinction patterns, and similar phases of vegetation C Response time recovery but at different temporal scales. Based on the observed lag- timefortheFADsaftersuchbioticcrises, we recommend using relative abundance data for the stratigraphic definition of mass extinction events Fig. 9. (A) Theoretical section with relative abundance analysis of two taxa (A and B). The placement of three chronological events frames an interval of discussion for and the placement of chronostratigraphic boundaries. biostratigraphical correlation and event characterization. (B) Time constant equation used to model decay in relation to an abrupt change from equilibrium conditions. V0 is Acknowledgments the original state of the system, and system response is an exponential decay driven by τ its internal time constant . (C) Plot of the above equation, showing the response of an elastic V. Vajda acknowledges support from LUCCI (Lund University Centre system (plain line) to the abrupt change from state A to state B (dashed line). At 5τ,theex- ponential decay is equal to 1% of the original V0 state and can be approximated to the re- for Studies of Carbon Cycle and Climate Interactions), a Linnaeus centre sponse time which the system requires to operate the transition from state A to state B. funded by the Swedish Research Council (349-2007-8705), and from The Royal Swedish Academy of Sciences (2007/558). A. Bercovici is supported through the Swedish Research Council (VR) postdoctoral fellow- successions show that first appearances of Paleogene taxa typically occur ship grant 2011-7176. Dean Pearson and the Pioneer Trails Regional several centimeters to meters above the boundary clay. Therefore, we Museum are thanked for long term collaboration, discussions and assis- strongly recommend abundance data be used as criteria for defining the tance in the field. Reviewers Mikael Pole and Yongdong Wang are K–Pg boundary at sites where the boundary clay is not present. thanked for comments that greatly improved this paper. Three anony- With the large body of data now available, we can apply the paleon- mous reviewers are further thanked for providing constructive tological record spanning the K–Pg mass-extinction interval as a tem- criticism. plate for interpreting other extinction events. A model for biotic responses to extremely abrupt events (e.g., asteroid impact) can be de- Appendix A. Supplementary data rived from the K–Pg boundary record, and can be contrasted against the biotic signals and timing for other events with the aim of assessing their Supplementary data associated with this article can be found in the underlying causal mechanisms. online version, at http://dx.doi.org/10.1016/j.gloplacha.2014.07.014. Essential points in the evaluation of extinction patterns are 1, the These data include Google map of the most important areas described establishment of a high-resolution time frame; 2, comparison of the in this article. V. Vajda, A. Bercovici / Global and Planetary Change 122 (2014) 29–49 45

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