Disrupted Vegetation As a Response to Jurassic Volcanism in Southern Sweden

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Disrupted vegetation as a response to Jurassic volcanism in southern Sweden

VIVI VAJDA1*, HANS LINDERSON2 & STEPHEN MCLOUGHLIN1 1Department of Palaeobiology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden 2Laboratory for Wood Anatomy and Dendrochronology, Department of Geology, Lund University, So¨lvegatan 12, 223 62 Lund, Sweden *Corresponding author (e-mail: [email protected])

Abstract: Central Ska˚ne (Scania) in southern Sweden hosts evidence of extensive Jurassic volcanism in the form of mafic volcanic plugs and associated volcaniclastic deposits that entomb well- preserved macro-plant and spore–pollen assemblages. Palynological assemblages recovered from the Hoö¨r Sandstone are of Hettangian–Pliensbachian age and those from the overlying lahar deposits are dated as Pliensbachian–early Toarcian (?). Palynomorph assemblages from these units reveal significantly different ecosystems, particularly with respect to the gymnospermous components that represented the main canopy plants. Both palynofloras are dominated by osmundacean, marattiacean and cyatheacean fern spore taxa but, whereas the Hoö¨r Sandstone hosts abundant Chasmatosporites spp. pollen produced by plants related to cycadophytes, the volcanogenic deposits are dominated by cypress family pollen (Perinopollenites) with an understorey component rich in putative Erdtmanithecales (or possibly Gnetales), and collectively representing vegetation of disturbed habitats. Permineralized conifer wood attributed to Protophyllocladoxylon sp., belonging to plants that probably produced the abundant Perinopollenites grains, is abundant in the volcanigenic strata, and shows sporadic intraseasonal and multi-year episodes of growth disrup- tion. Together with the relatively narrow but marked annual growth rings, and the annual and mean sensitivity values that span the complacent–sensitive domains, these features suggest growth within Mediterranean-type biomes subject to episodic disturbance.

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Volcanic activity is one of Earth’s major natural historical times (Lawrence 2005; Arnalds 2013) hazards and the apparent driver of several Phan- including communities occupied by humans erozoic mass-extinction events. Large-scale vol- (Luongo et al. 2003). However, volcanic activity canism contributing to rapid increases of pCO2 may also lead to nutrient renewal in ecosystems at and other greenhouse gases has been implicated various scales (Frogner et al. 2001) and accelerated as a primary driving force behind the end-Permian recovery of ecosystems (del Moral & Grishin 1999). (e.g. Renne et al. 1995; Bond & Wignall 2014) Volcanic ash falls, lahars and associated hydrother- and end-Triassic mass-extinction events (Olsen mal systems, owing to their rapidity of deposition, 1999; Bond & Wignall 2014; Sha et al. 2015). Vol- liberation of mobile Si4+ and Ca2+ ions, and com- umetrically, water vapour (H2O), carbon dioxide mon association with hot-spring communities, also (CO2) and sulphur dioxide (SO2) are the most host some of the best Lagersta¨tten that facilitate important volcanic gases (e.g. Sigurdsson 1990). the reconstruction of ancient organisms and whole Whereas H2O and CO2 contribute to warming, SO2 ecosystems (Trewin 1996; Wang et al. 2012; forms aerosols that block sunlight, which leads McLoughlin & Bomfleur 2016). to long-term cooling (e.g. Sigurdsson 1990). Acid Over 100 volcanic plugs have been mapped rain and ozone depletion as a result of volcanic within the Central Ska˚ne Volcanic Province (CSVP), emissions of chlorine and fluorine (Thordarson & southern Sweden (Tappe 2004; Bergelin 2009; Self 2003) also impact on the health of global ter- Tappe et al. 2016) but there has been recent contro- restrial ecosystems. versy over the age and origin of this magmatism. Volcanism also disrupts ecosystems on a local Most recent data suggest that eruptive activity scale, with well-studied examples from the ancient occurred mainly during the late Early Jurassic on past (Cross & Taggart 1982; Taggart & Cross the flanks of the Sorgenfrei–Tornquist Zone – a 1990; Ro¨ßler et al. 2012; Oplusˇtil et al. 2014) to failed rift system linked to extension in the North

From:Kear, B. P., Lindgren, J., Hurum, J. H., Mila`n,J.&Vajda, V. (eds) Mesozoic Biotas of Scandinavia and its Arctic Territories. Geological Society, London, Special Publications, 434, http://doi.org/10.1144/SP434.17 # 2016 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

Sea and the opening of the North Atlantic (Tappe Geological setting and previous studies 2004; Bergelin 2009; Tappe et al. 2016). These volcanic plugs are locally associated with volcani- Mesozoic sedimentary deposits of Sweden are genic sediments (pyroclastic sheets and lahar restricted to the southernmost province, Ska˚ne flows) that have been the target of recent palaeon- (Scania: Fig. 1a–c), where Triassic and Jurassic tological interest owing to their entombment of strata accumulated mainly in non-marine environ- abundant permineralized plant fossils, one even with ments (Sivhed 1984; Pien´kowski 1991a, b; Ahlberg cellular preservation down to the level of organ- 1994) and the substantial Upper Cretaceous succes- elles and chromosomes (Bomfleur et al. 2014). sion was deposited mostly in marine settings. The Permineralized gymnosperm woods in these depos- oldest exposed Mesozoic rocks in the province com- its are also unique in being the only three- prise Upper Triassic strata that rest on deeply weath- dimensionally preserved axes yielding growth ring ered crystalline basement (Lidmar-Bergstro¨m data from the Early Jurassic of northern Europe 1997). The Triassic–Jurassic transition is seemingly and, thus, are of great significance for palaeocli- complete and the boundary is placed within the matic analysis. Ho¨gana¨s Formation in the NW part of the province Fossil pollen and wood represent important (Figs 1 & 2) (Sivhed 1984; Pien´kowski 1991a; Ahl- tools in palaeoclimate research because plants berg 1994; Lindstro¨m & Erlstro¨m 2006; Vajda & show rapid responses to climatic and other envi- Wigforss-Lange 2009). In southern Sweden, the ronmental changes. Quantitative changes between Triassic–Jurassic transition is characterized by a pollen taxa through geological successions can Transitional Spore-spike Interval (TSI) – an inter- reveal major extinctions or simply reorganization val with high fern spore abundance (Larsson 2009; within ecosystems, whereas tree growth rings can Vajda et al. 2013). This fern-dominated interval reveal detailed climatic or environmental changes has also been identified in the Danish Basin (van on annual or decennial scales. Another, relatively de Schootbrugge et al. 2009) and recently in the new technique is the stomatal proxy-based method, uppermost Rhaetian of Poland (Pien´kowski et al. whereby characters of leaf cuticle micromorphol- 2012). In the marine environment, fern spore repre- ogy are used to assess various palaeoenvironmental sentation is less pronounced and this interval is, parameters (for methods, see McElwain & Chal- instead, characterized by the presence of microbial oner 1995). This method has now been tested on mats in the subtidal zone, which suggests decreased a wide range of plant groups and has developed benthic biodiversity and suppressed grazing in inner into a robust technique: for example, for recording neritic environments in the early aftermath of the the palaeo-pCO2 through the geological record, end-Triassic mass-extinction event (Peterffy et al. although most studies derive from the Northern 2015; Ibarra et al. 2016). An extensive transgression Hemisphere (e.g. Woodward 1987; McElwain & affected southern Sweden following the Triassic– Chaloner 1995; Beerling et al. 1998; Steinthors- Jurassic transition and, in western Ska˚ne, Lower dottir et al. 2011). Scarce records exist from the Jurassic (Hettangian and Sinemurian) strata accu- Southern Hemisphere, although Steinthorsdottir & mulated in marginal- to shallow-marine environ- Vajda (2015), using the conifer Allocladus from ments (Pien´kowski 1991a, b; Peterffy et al. 2015) the Early Jurassic of Australia, and Passalia (2009), (Fig. 2). using conifer and Ginkgoales cuticles from the This study focuses on the Lower Jurassic Hoö¨r Early Cretaceous of Argentina, showed interpre- Sandstone and the overlying volcaniclastic deposits tations of pCO2 to be consistent with Northern of central Ska˚ne (Figs 1 & 2). The Hoö¨r Sandstone Hemisphere records. These records show that rests directly on weathered crystalline basement greenhouse conditions prevailed during the Early (Lidmar-Bergstro¨m 1997) and is represented by Jurassic, with pCO2 estimates of approximately isolated exposures through central Ska˚ne (Pien´kow- 1000 ppm based on Northern Hemisphere stomatal ski 2002). Traditionally, the Hoö¨r Sandstone has density proxies and calibrated pCO2 values of c. been subdivided into two units: the lower Stanstorp 900 ppm, based on Pliensbachian araucariacean Member, which reaches a thickness in excess of conifer leaf fossils from eastern Australia (Stein- 15 m (its base is not exposed); and the upper part thorsdottir & Vajda 2015). of the Stanstorps Member, which is exposed in Here, we explore the effects of volcanism on Stenskogen (the ‘stone forest’) in the abandoned the standing vegetation within the CSVP, and Stanstorp quarry and consists of sandstones interca- assess the broader environmental context of these lated with organic-rich mudstones, deposited in a deposits by palynological and fossil wood growth fluvial environment. Isolated beds within the Stan- ring analyses. This study also aims to clarify the storp Member host a rich macrofossil flora that ages of the wood-bearing volcaniclastic deposits has been described in most detail by Nathorst at Korsaro¨d and of the underlying siliciclastic Hoö¨r (1880), Antevs (1919) and Pott & McLoughlin Sandstone. (2009). The flora is dominated by Equisetales, Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN

Röstånga Djupadal Tjörnarp Skåne Volcanic Province

Rugerup Korsaröd Vittseröd

Höör Stenskogen Norway

Stanstorpsgraven (a) Sweden western Denmark Ringsjön A eastern Hörby SKÅNE Ringsjön N

Ängelholm Skåne Höganäs Volcanic Hässleholm 5km Province Helsingborg Kristianstad (c) Höör N Landskrona Volcano-sedimentary rocks Eslöv Lund Volcanic plugs

Urban areas/localities Malmö Ystad Lakes Trelleborg

20 km (b) Jurassic strata

Fig. 1. Maps of (a) southern Scandinavia, (b) Ska˚ne and (c) the Hoö¨r region of central Ska˚ne, showing the locations of the sampled deposits at Stenskogen (Hoö¨r Sandstone) and Korsaro¨d (volcaniclastic deposits). dipteridacean, matoniacean and osmundacean extensive volcanism, with over 100 volcanic plugs ferns, Bennettitales, Cycadales, Caytoniales, Gink- within a 1200 km2 area (Fig. 1). These volcanic goales, and various broad- to scale-leafed conifers features vary in size but several plugs exceed (Antevs 1919). 100 m in diameter (Tappe 2004; Bergelin 2006; The overlying Vittsero¨d Member reaches a max- Tappe et al. 2016). Most volcanic plugs have been imum thickness of 40 m (Pien´kowski 2002) and dif- dated in the range 191–178 Ma, according to Berge- fers from the Stanstorp Member in its composition lin et al. (2011), based on 40Ar/39Ar whole-rock of coarser, extensively silicified quartz arenites. Sil- ages for samples derived from eight basanite– icification is probably the result of hydrothermal nephelinite plugs. However, Tappe et al. (2016) fluids and thermal alteration from overlying volca- reported an age of 176.7 + 0.5 Ma based on high- nic extrusives and local intrusions that penetrated precision 40Ar/39Ar dating of one nephelinite plug the sandstones. Hadding (1929) and Troedsson near Lilla Hagstad in central Ska˚ne. Volcaniclastic (1940) identified marine–brackish-water bivalves sediments related to this Early Jurassic volcanism (Avicula inaequivalvis, Liostrea sp., Pecten sp., are preserved sporadically through the region and Cardinia follini), and Tullberg (1880) reported trace are indicative of Strombolian-type eruptions (Berge- fossils (Monocraterion sp.) in this member. lin et al. 2011). The volcaniclastic sediments host The Hoö¨r Sandstone is overlain by little-studied abundant plant macrofossils, most significantly a volcaniclastic deposits. These unnamed strata prob- calcite-permineralized osmundaceous fern rhi- ably correlate with the Rya Formation of NW zome (Bomfleur et al. 2015) and gymnosperm wood Ska˚ne (Fig. 2). Central Ska˚ne bears evidence of (described below). The permineralized fern has Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

NW Skåne Central Skåne System Stage Fm Member Fm Member Miospore Zone Toarcian Rydebäck Spheripollenites-Leptolepidites Volcaniclastic Katslösa sediments Pliensbachian Rya Chasmatosporites Fm Pankarp Cerebropollenites Lower Sinemurian Döshult Vittseröd Member Jurassic macroverrucosus Höör Sst. Pinuspollenites-Trachysporites Hettangian Helsingborg Stanstorp Member 201.6 Höganäs Transitional Spore-spike Interval Ma Fm Bjuv Hörby ? Corollina - Ricciisporites Rhaetian Vallåkra fm.

Upper Kågeröd Triassic Norian Fm Undefined

Fig. 2. Stratigraphic chart for the uppermost Triassic and Lower Jurassic of Ska˚ne. yielded exquisite anatomical details that have facil- a 2 m-thick profile. Samples from this section itated a re-evaluation of Osmundaceae systematics are listed here as Korsaro¨d 1–5 (Fig. 3: registered (Bomfleur et al. 2015). The well-resolved phyloge- as NRMS089756, NRMS089757, NRMS089758, netic relationships and the age of this fern have NRMS089759 and NRMS089760). also contributed to the testing of various methods Palynological samples were processed by stan- for the molecular-clock dating of ferns (Grimm dard methods at GeoLab Ltd, Canada. Counts of et al. 2015). The fern also hosts a range of epiphytes, 200 palynomorphs per sample were obtained for parasites, micro-herbivores and potential symbi- the abundance data (Table 1). onts that provide insights into biotic interactions within the Jurassic vegetation (McLoughlin & Bom- Tree ring analyses fleur 2016). Around 50 calcite-permineralized wood fragments were available for study in collections compiled Material and methods by Korsaro¨d farmer, Gustav Andersson, in 1973 Palynology and donated to the Swedish Museum of Natural His- tory (samples NRM S069604–S069642, S069647, Nine samples were analysed palynologically: four S069648, S069659 and S069709–S069720; pre- from the Hoö¨r Sandstone (H-1–H-4), and five pared thin-sections: S069604-01, S069620– from the volcaniclastic sediments overlying that S069622, S069623-01, S069624-01, S069636, unit (K-1–K-5: Fig. 3). The four Hoö¨r Sandstone S069638-01, S069639-01, S069639-02, S069641- samples derive from the Stanstorp Member exposed 01 and S069643-01). Two additional samples were in Stenskogen (Fig. 1). The samples were taken studied from the Tjo¨rnarp Sockengille (parish) col- from rock slabs hosting plant fossils that were stud- lections, and additional material was collected dur- ied by Nathorst (1880) and Antevs (1919), and ing re-excavation of the Korsaro¨d fossil site in held in the collections of the Swedish Museum of July 2014. Natural History under the registration numbers Analysis of the fossil wood anatomy and growth NRM S067097, NRM S067197, NRM S067279 patterns was based on standard methods in xylol- and NRM S067377, but listed here as H-1–H-4, ogy and dendochronology (e.g. see Fritts 1976; respectively, in tables and figures for compatibility Grissino-Mayer 2015). Annual rings were measured with the software that generated the palyno- (with 0.01 mm precision) along two radii for each abundance charts. The five samples from the volca- sample. Measurements were repeated for accuracy. niclastic sediments were collected during fieldwork Photographs of wood anatomy were taken with an in 2014 at a site near Korsaro¨dLake(558 58′ 54.48′′ Olympus DP71 digital camera attached to an Olym- N, 138 37′ 44.68′′ E), where a trench was excavated pus BX51 transmitted light microscope, and com- mechanically in poorly lithified strata to obtain piled using Cell-D software. Downloaded from

FERN SPORE TAXA GYMNOSPERM POLLEN TAXA http://sp.lyellcollection.org/ UASCVLAIMADVGTTO:SWEDEN VEGETATION: AND VOLCANISM JURASSIC

spp. sp. spp. es minimus ites spp. nites elatoides ollis classoides

Marattisporites scabratus AlisporitesClassop ChasmatosporitesEucommiidites troedssoniiPerinopolle PinuspollenitPodocarpiditesQuadraeculina anaellaeformis (m) TOTAL LYCOPHYTECyathidites SPORES OsmundaciditesTOTAL wellmanii FERN SPORESspp. SpheripollenTOTAL GYMNOSPERMTOTAL ALGAE 0.5 K-5 POLLEN K-4 1 K-3

1.5 K-2 byguestonSeptember27,2021

sediments 2 K-1

Volcaniclastic

Assemblage II Pliensbachian 2.5 3 H-4

3.5 H-3

Höör

Sandstone 4 H-2 Sinemurian Hettangian - Assemblage I 4.5 H-1 010050100 0 50 020 050100 0 10 0102005001002550 0 10 0 10 0 10 0 10 0 50 100 0 10 %

Fig. 3. Chart showing the relative abundance of selected pollen and spore taxa from the Ho¨o¨r Sandstone and from the overlying unnamed volcaniclastic sediments at Korsaro¨d. Downloaded from

Table 1. Relative abundance of palynomorph taxa in the studied assemblages based on counts of 200 specimens per sample

Sample NMRS NMRS NMRS NMRS NMRS NMRS NMRS NMRS NMRS 067279 067097 067197 067377 089756 089757 089758 089759 089760 Bed 1 (Black Bed 2 Bed 3 Bed 4 Bed 5 (white clay) clay) Unit Hoö¨r Hoö¨r Hoö¨r Hoö¨r Korsaro¨d Korsaro¨d Korsaro¨d Korsaro¨d Korsaro¨d http://sp.lyellcollection.org/ Sandstone Sandstone Sandstone Sandstone

Bryophytes Stereisporites antiquasporis 0.5 0.5 Stereisporites psilatus 1.5 Total bryophyte spores 0 0.5 0 0 2.0 .VAJDA V. Lycophytes Heliosporites sp. 0.5 0 Neoraistrickia sp. 0.5 3.4 1.0

Retitriletes 0.5 0 0.5 0.7 1.0 1.0 AL. ET austroclavatidites Retitriletes clavatoides 0.5 0 0.5 1.4 2.0 byguestonSeptember27,2021 Retitriletes semimuris 0.7 1.0 Total lycophyte spores 0 1.5 0 0 2 3 3 4 2 Ferns Apiculatisporis sp. 2.5 Calamospora tener 4.3 Cibotiumspora jurienensis 2.5 0.5 1.0 2.1 1.1 2.0 Cyathidites australis 2 1.5 3.5 5.9 1.0 Cyathidites minor 13 8 34 14.5 16.3 28.4 18.6 18.8 Conbaculatisporites 6 2.5 0.5 2.3 mesozoicus Deltoidospora toralis 3 14 7 19.5 12.8 6.8 9.8 11.5 Laevigatosporites ovatus 3 Laevigatosporites major 0.5 1 Marattisporites scabratus 38 41 10.5 12 14.2 10.2 2.9 9.4 Osmundacidites wellmanii 18.5 4 11.5 10.0 5.7 2.3 2.0 6.3 Polycingulatisporites sp. 1.1 Striatella seebergensis 1.5 0.5 0.5 1.5 Todisporites major 0.5 1.5 6.5 1.0 3.1 Todisporites minor 0.5 0.5 9

Total fern spores 80.5 65 65 51 47 55 52 42 50 Downloaded from Gymnosperms Alisporites grandis 3.5 3.0 1.5 10.0 10.0 0.7 Alisporites robustus 0.5 1.5 Araucariacites australis 1.5 Cedripites sp. 1.5 2.8 4.5 2.0 7.3 Cerebropollenites 0.5 1.5 2.1 macroverrucosus http://sp.lyellcollection.org/

Cerebropollenites 1.0 SWEDEN VEGETATION: AND VOLCANISM JURASSIC thiergartii Classopollis classoides 2.0 15.5 8.0 1.5 1.4 9.1 3.9 3.1 Chasmatosporites apertus 0.5 1.5 2.0 4.0 1.0 0.7 Chasmatosporites elegans 0.5 0.5 4.0 1.0 0.7 Chasmatosporites hians 3.0 7.5 6.0 12.5 2.0 Eucommiidites troedssonii 1.5 5.5 3.0 4.3 5.7 10.8 3.1 Ginkgoites nitidus 1.0 Monosaccate gymnosperm 0.5 0.5 Monosulcites punctatus 0.5 0.5 1.0 0.5 Perinopollenites elatoides 5.0 1.0 8.0 28.4 19.3 23.5 26.0 Pinuspollenites minimus 0.5 6.0 2.0 1.5 4.5 4.2

Podocarpidites sp. 1.0 5.0 1.0 byguestonSeptember27,2021 Quadraeculina 1.5 1.0 0.7 1.1 3.9 3.1 anaellaeformis Rugaletes sp. 7.5 Spheripollenites psilatus 4.0 1.0 4.0 1.5 Spheripollenites 1.5 1.0 3.5 2.9 subgranulatus Vitreisporites pallidus 4.0 1.5 0.5 1.0 Total gymnosperm pollen 19.5 33.0 35.0 49.0 48 42 44 51 47 Algae Botryococcus braunii 2.0 Lecaniella sp. 2.9 1.0 Pediastrum sp. 0.5 Total algae 2.5 2.9 1.0 Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

X-ray fluorescence spores, suggesting that they derive from the Transi- tional Spore-spike Interval and, thus, are of Hettan- Seven samples from the Korsaro¨d succession were gian age. The other samples correlate with the upper analysed for major and trace elements utilizing part of the Sinemurian–Pliensbachian Cerebropol- X-ray fluorescence (XRF). The five volcaniclastic lenites macroverrucosus Zone of Dybkjær (1991) rock samples (Korsaro¨d 1–5, the same as used for and with the Pliensbachian Chasmatosporites Zone palynology) and two permineralized wood samples of Koppelhus & Nielsen (1994) (Fig. 3). The assem- were studied using a Niton XL3t Goldd+ XRF blage in the younger samples is similar to those Analyzer at the Department of Geology, Lund Uni- recovered from the Sorthat Formation (also called versity. For calibration and detection of drift, stan- the ‘Sorthat beds’ within the Baga˚ Formation) and dard sample NIST 2709a with a known reference dated as Pliensbachian (Mehlqvist et al. 2009). value was analysed every tenth measurement. Palynology of the Korsaro¨d volcaniclastic Results deposits General palynology Apart from their excellent quality of spore/pollen/ The preservation of the pollen and spores varies charcoal preservation, all five samples from this unit between the assemblages from the two lithostrati- yielded assemblages that are remarkably free of graphic units. Although the recovery and preserva- other palynodebris. Gymnosperm pollen and fern tion of spores and pollen from the Hoö¨r Sandstone spores constitute roughly equal proportions of the samples is good, assemblages obtained from the assemblages. The dominant spores in most samples overlying volcaniclastic succession are of pristine are Cyathidites spp. (average 21%: Cyatheaceae) quality with no traces of modern contaminants followed by Marattisporites scabratus (3–14%: or reworking from older strata. The palynological Marattiaceae). The dominant gymnosperm pollen assemblages are represented mostly by pollen and in the volcaniclastic beds are Perinopollenties ela- spores but a few freshwater algae also occur in the toides (Fig. 4i) produced by gymnosperms related volcaniclastic deposits (Table 1). No marine palyno- to Taxodiaceae/Cupressaceae and Eucommiidites morphs were identified. The age assessment is based troedsonii (Fig. 4n) produced by plants probably on the presence/absence of key taxa in combination related to Erdtmanithecales or potentially Gnetales with abundance data compared with northern Euro- (e.g. Hughes 1961; Doyle et al. 1975; Trevisan pean palynostratigraphical schemes outlined by 1980; Friis & Pedersen 1996; Friis et al. 2011). Dybkjær (1991), Koppelhus & Nielsen (1994) and Taxa that are abundant in the underlying Hoö¨r Sand- Lund & Pedersen (1985). stone, such as Chasmatosporites (Fig. 4l, m; produced by cycadophytic plants) and Alisporites Palynology of the Hoö¨r Sandstone (probably produced by seed-ferns: Balme 1995), have significantly lower relative abundances. Only The assemblages from this unit are characterized by the basal sample within the volcaniclastic deposits typical Early Jurassic pollen and spore taxa. Most of differs in being more similar to the assemblages the 34 taxa identified are long ranging. The palyno- recovered from the Hoö¨r Sandstone. flora includes one bryophyte taxon, three lycophyte taxa, 13 fern spore taxa and 17 gymnosperm pollen Age. Pliensbachian–early Toarcian(?). The high rel- taxa (Table 1). Fern spores overwhelmingly domi- ative abundances of Perinopollenites elatoides and nate the basal sample, reaching a maximum relative Eucommiidites troedsonii, and the relatively low abundance of 80.5% in NRM S67279. proportions of Classopollis and Chasmatosporites The dominant spores are Marattisporites scabra- spp., markedly differentiate these assemblages tus (10–38%: Fig. 4g), Osmundacidites wellmanii from those of the underlying Hoö¨r Sandstone. The (12–19%: Fig. 4a) and Cyathidites spp. (average low relative abundance of Spheripollenites psilatus, 15%). Some Osmundacidites spores occur in clus- and the absence of Toarcian key taxa, such as Clav- ters (Fig. 4e), indicating minimal transport and pres- atipollenites hughesii and Callialasporites spp., ervation of the sporangial contents. Gymnosperm favours a late Pliensbachian to (questionably) an pollen of high relative abundances includes Chas- earliest Toarcian age (Fig. 3). The palynoflora is matosporites spp. (4–20.5%, with higher values in similar to the late Pliensbachian Assemblage A the younger samples: Fig. 4l, m), Classopollis spp., (A2) of Lund & Pedersen (1985) from Greenland. and Alisporites-type and Vitreisporites pallidus (Fig. 4j) bisaccate pollen. Geochemistry Age. Hettangian–earliest Pliensbachian. Two sam- Silica constitutes the most abundant element in all ples have very high relative abundances of fern five volcaniclastic samples (10.8–22.4%), followed Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN

Fig. 4. Light micrographs of representative spores and pollen grains from the Ho¨o¨r Sandstone and the Korsaro¨d volcaniclastic deposits. Taxon, sample number, England Finder Reference (EFR). (a) Osmundacidites wellmanii Couper, 1953, NRM S067377, EFR M 32; (b) Deltoidospora toralis (Leschik) Lund, 1977, NRM S067377, EFR-K44; (c) Retitriletes clavatoides Do¨ring (in Do¨ring et al. 1963), NRM S06730, EFR-37/2; (d) Striatella seebergensis Ma¨dler, 1964, NRM S7097, EFR-41/2; (e) cluster of Osmundacidites wellmanii;(f) Cibotiumspora jurienensis (Balme) Filatoff, 1975, NRM S067197, EFR-K23-4; (g) Marattisporites scabratus Couper, 1958, NRM S067377, EFR-N32; (h) Classopollis sp., NRM S067279, EFR-Q44; (i) Perinopollenites elatoides Couper, 1958, NRM S067279, EFR-W35/3; (j) Vitreisporites pallidus (Reissinger) Nilsson, 1958, NRM S7097, EFR-W43/3; (k) Pinuspollenites minimus (Couper) Kemp, 1970, NRM S067377, EFR-N22/4; (l) Chasmatosporites hians Nilsson, 1958, NRM S067377, EFR-P28/1; (m) Chasmatosporites apertus (Rogalska) Nilsson, 1958, NRM S067377, EFR-H32/2; (n) Eucommiidites troedssonii Erdtman, 1948, NRM S067279, EFR-K36/3; (o) Monosulcites punctatus Orłowska-Zwolin´ska, 1966, NRM 067197, EFR-G21; (p) Quadraeculina anaellaeformis Maljavkina, 1949, NRM S067377, EFR-P24/2. by Al (3.2–8.8%), Fe (1–12%), Ti (0.8–1.5) and (¼Balance) and make up major components of the Mg (0–1.1) (Fig. 5a; Table 2). Other elements rep- volcaniclastic sediments as constituents of silicate resent ,1% in any sample. However, light ele- minerals. The elemental percentages vary slightly ments, such as C and O, are grouped under Bal between the different beds (Fig. 5a): for example, Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

Table 2. The XRF data illustrated in the graphs below in Figure 5

Sample Si% Al% Fe% Ti% Mg% Ca% Bal%

Korsaro¨d-5 22.4 8.8 1.0 0.8 0 0.2 64 Korsaro¨d-4 17.2 5.4 10.2 1.2 0.8 0.4 63.7 Korsaro¨d-3 16.1 4.9 9.7 1.2 0.6 0.5 66 Korsaro¨d-2 15.9 5.3 11.7 1.5 1.1 0.6 63 Korsaro¨d-1 10.7 3.2 11.4 1.2 0.7 0.5 71.2 Wood 1 1.3 0.7 0.2 0.1 0 37 60.7 Wood 2 2 0.6 0.4 0.2 0 39 57.8

Note that Bal represents the aggregate percentage of elements with atomic numbers lower than Mg that are too light to be detected by the instrument. the topmost sample differs in its higher Si and Al content, and lower Fe. The composition of the volcaniclastic deposits is consistent with a source from the maﬁc alkaline magmatic plugs of the CSVP. Both analysed fossil wood samples are strongly dominated by Ca (bound in CaCO3), with only small amounts of Si and other elements (Fig. 5b). This suggests selective bonding of CaCO3 to buried organic matter during the fossilization process.

(a) 25 Korsaröd-5 % Korsaröd-4 Korsaröd-3 20 Korsaröd-2 Korsaröd-1 15

5 Fig. 6. Typical example of permineralized wood with a branch trace recovered from the volcaniclastic 0 sediments at Korsaro¨d, inset of cross cut with tree Si Al Fe Ti Mg Ca rings. The scale bar is 10 mm. (b) 40 Wood -2 Fossil wood % Wood -1 Wood preservation and stature. 30 The fossil wood occurs either as isolated fragments (Fig. 6) or as chaotic aggregations in a weathered volcaniclastic 20 agglomerate composed of ash to lapilli-sized maﬁc clasts, together with minor pebble- to cobble-sized 10 clasts of Mesozoic bedrock sandstones. The quality of wood permineralization in the samples is variable. Some specimens preserve excellent anatomi- 0 cal details but others have extensive zones of Si Al Fe Ti Mg Ca crushed tissue or cells dissociated by calcite inﬁltra- tion between the walls or calcite-veining transecting Fig. 5. Principal-element geochemical signatures cells. At least three phases of calcite mineralization determined by XRF and illustrated for (a) volcaniclastic sediment samples from Korsaro¨d are evident in the samples (Fig. 7k). An initial pulse (Korsaro¨d 1–5 in ascending stratigraphic order) and of mineralization deposited a very thin calcitic lin- (b) permineralized wood samples from the same site ing on the inner walls of cells. A second phase pro- (Wood 1 and 2). duced a thick coating of yellowish calcite on the Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN

Fig. 7. Anatomy of fossil wood (Protophyllocladoxylon sp.) from Korsaro¨d. (a) Transverse section through two typical growth rings: NRM S069604-01. (b) Narrow rings with minimal latewood: NRM S069604-01. (c) Rings with thick latewood: NRM S069604-01. (d) Wide growth ring with false ring in the earlywood: NRM S069638-01. (e) Radial longitudinal section showing low rays and uniseriate pitting on tracheids: NRM S069639-01. (f) Tangential longitudinal section showing uniseriate rays of two–five cells: NRM S069621. (g) Radial walls of tracheids with uniseriate, mostly contiguous, bordered pits: NRM S069639-01. (h) Radial longitudinal section showing cross-fields, each typically with one oblique elliptical pore: NRM S069622. (i) Tangential longitudinal section showing spiral fibrillar thickenings on tracheid walls: NRM S069639-02. (j) Damaged zone with possible fungal body in centre and indistinct septate hyphae (arrowed): NRM S069639-01. (k) Enlargement of tracheids in transverse section showing three phases of permineralization: thin wall coating (black arrow); thick yellowish calcite coating (white arrow); and late-stage calcitic lumen fill (cell centres): NRM S069604-01. (l) Possible fungal body within an earlywood tracheid: NRM S069639-01. Scale bars are 100 mm for (a)–(f), (i); 50 mm for (g)–(i); and 20 mm for (j)–(l). Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

‘inner’ surface of the first layer; in some cases, this radial diameters average c. 30 mm but are also var- phase fills the entire cell lumen. A third phase pre- iable within (Figs 7d & 8a) and between specimens, cipitated clear calcite that infilled any remaining in some cases reaching 60 mm. Tracheids are non- cell cavities. This final phase appears to be associ- septate and have gently tapered termini; radial ated with calcite veining that cuts across both the walls bear uniseriate bordered pits that are typically wood and surrounding volcanic ash and lapilli (see contiguous but sporadically separated (Fig. 7g). McLoughlin & Bomfleur 2016, fig. 2E). No pitting is evident on tangential tracheid walls. A few fossil wood specimens clearly represent Spiral fibrillar thickenings are common on tracheids portions of large trunks: one fragment is estimated (Fig. 7i). Rays are uniseriate, unornamented, typi- to derive from a trunk 1.68 m in diameter, equating cally two–five cells high and rarely up to eight to a circumference of c. 5.3 m. Most specimens are cells high (Fig. 7e, f). Cross-fields are occupied by small fragments (,10 cm long and 5 cm wide) that one, in some cases two, oblique pits with pointed might represent lateral branches or even roots. apices (Fig. 7h). Branch scars are evident on a few of the larger wood samples (Fig. 6). This variability in the quality Identification. We follow the key developed by Phi- of preservation, together with the small size and lippe & Bamford (2008) for the segregation of uncertain source (trunk v. branch v. root: cf Mos- Mesozoic homoxylous wood genera. Based on the brugger et al. 1994; Falcon-Lang 2005a) of many possession of uniseriate rays with smooth walls, samples, and problems with statistical standardiza- cross-fields bearing one or two large pointed oblique tion of measurements (cf. Poole & van Bergen oopores, the absence of axial parenchyma, and tra- 2006; Bunn et al. 2013), constrained the range of cheid radial walls with uniseriate, predominantly material that could be used for reliable taxonomic araucarioid pitting, we assign the Korsaro¨d woods and growth ring analysis. to Protophyllocladoxylon Kraüsel, 1939. However, we note that this genus might require subdivision Description. All of the studied material consists of in future to segregate Palaeozoic, Mesozoic and secondary homoxylous wood with distinct growth even Cenozoic forms from widely separated sources rings (Fig. 7a–c). Earlywood cells average c. and with different combinations of pitting architec- 30 mm in tangential diameter in most axes but tures that probably derive from unrelated plant reach 40 mm in some specimens. Earlywood cell groups (Pujana 2005; Pujana et al. 2014; Philippe

(a) 50 40 30 20

Cell radial width 10 µm 0 10 20 30 40 50 60 70 80 90 100 110 120 Cell number (b) Younging direction 5 µm 4 3 2 1

Cell wall thickness 0 10 20 30 40 50 60 70 80 90 100 110 120 Cell number (c)

13 17 12 17 19 17 23 >9 Cells/ring

Fig. 8. Plot of (a) cell radial width, (b) wall thickness and (c) cell number for a 7.5 year growth series in NRMS069604-01, showing mostly gradual transitions from earlywood to latewood. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN

& Bamford 2008). This task is beyond the scope Sensitivity analyses were conducted on two of the present study and requires reappraisal of the wood samples with .40 measurable rings (mea- type material from Egypt, which might have been sured along two radii). Annual sensitivities (AS) reworked into much younger (?)Late Cretace- vary markedly, especially between the two samples ous or Danian host sediments from its original (Fig. 9a–d). Mean sensitivity (MS) varies from source (Philippe & Bamford 2008). Similar woods 0.253 (complacent) to 0.412 (sensitive) between assigned to Protaxodioxylon Bamford & Philippe, the two samples. Median annual sensitivity values 2001 are distinguished by up to five oculipores in for each measured radius are lower than the mean the cross-fields, with horizontal or only slightly sensitivities (Table 3). oblique apertures. Importantly, assignment to Protophyllocladoxy- lon sp. does not imply a close relationship between Discussion these Mesozoic woods and modern Phyllocladus Geological context (Podocarpaceae). Based on the predominantly ‘taxodiaceous’ anatomical characters and the abun- The volcaniclastic deposit at Korsaro¨d is located dance of ‘taxodiaceous’ pollen from the volcaniclas- 380 m WNW of the nearest basaltic volcanic plug. tic host deposits, together with scale- or awl-leafed Abundant mafic clasts within the agglomerates sug- conifer foliage (attributed by Antevs (1919) to Ela- gest that the volcanigenic sediments derive from tocladus sp.) in the underlying Hoö¨r Sandstone this, or one of the many other nearby, eruptive cen- of central Ska˚ne, assignment of the woods to the tres of the CSVP. Clasts in the deposit are generally Cupressaceae (in its broad sense) is favoured. angular and poorly sorted (McLoughlin & Bomfleur 2016). There is some lithological heterogeneity Growth ring characteristics. Growth rings are dis- within the stratigraphic profile of the volcaniclastic tinct in all wood samples from Korsaro¨d (Fig. 7a– deposit but it is unclear whether the indistinct layers c). Ring widths vary considerably both within represent deposition during discrete episodes sepa- and between wood samples; they are typically nar- rated by intervals of non-deposition, or if the tex- row with average widths in the range of 0.49– tural differences simply represent weak variations 1.78 mm, although a few individual rings reach in sorting owing to a high-energy depositional set- 3.61 mm (Table 3). In some cases, rings consist of ting. The high ash/mud content of the deposit, as few as six cells with minimal latewood develop- poor bedding and the chaotic distribution of fossil ment (Fig. 7b). Other samples have c. 20 cells per wood favour interpretation as a lahar deposit, with ring, of which more than half represent latewood clasts representing mostly reworked pyroclastic (Figs 7c & 8a–c). Typical rings have about three– lapilli, but also incorporating some bedrock cobbles. seven latewood cells representing about 20–30% The similarity in geochemistry between the differ- of the growth ring width (Fig. 8a), but the boundar- ent layers also favours this depositional interpreta- ies between earlywood and latewood can be indis- tion. The fossil wood described herein is cemented tinct. A few rings have 25 or more cells. False by calcite, and the marked difference in composition rings are developed sporadically through the wood, between the fossils and the host volcaniclastic sedi- and are typically represented by one or two radially ments shows that calcite cement precipitated prefer- narrow and thickened cells within the earlywood entially within the plant remains, and/or has been (Fig. 7d). Cell wall thicknesses vary according to leached from the surrounding sediments. their position within the growth ring (Fig. 8b). The The underlying Hoö¨r Sandstone is a generally lumens of some latewood cells are almost entirely coarse, sandy (high-energy) fluvial–paralic deposit occluded by wall thickenings. with a scattered outcrop distribution of erosional

Table 3. Growth ring dimensions and sensitivity values for fossil wood specimens and radii analysed in this study

Dendrology Registration Afﬁnities Tree Number Tree ring width Annual sensitivity Mean Laboratory number part of years minimum minimum (median) sensitivity number (annual (average) maximum rings) maximum (mm)

OSF0246.1 TS1 Cupressaceae Stem 49 0.47 (1.46) 3.21 0.000 (0.334) 1.311 0.420 OSF0246.2 TS1 Cupressaceae Stem 51 0.77 (1.78) 3.61 0.005 (0.349) 1.053 0.369 OSF0247.1 NRM S069689 Cupressaceae Branch 62 0.24 (0.59) 1.14 0.016 (0.205) 0.695 0.254 OSF0247.2 NRM S069689 Cupressaceae Branch 70 0.12 (0.49) 1.02 0.000 (0.259) 0.841 0.292 Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

(a) OSF0246.1 1.4 Mean ring width = 1.46 mm 1.2 Standard deviation = 0.719 Total auto correlation = 0.387 Mean sensitivity = 0.420 1.0 Minimum annual sensitivity = 0 Maximum annual sensitivity = 1.311 0.8 Median annual sensitivity = 0.334

0.6

Annual Sensitivity 0.4

0.2

0 0 102030405060

(b) OSF0246.2 1.2 Mean ring width = 1.78 mm 1.0 Standard deviation = 0.648 Total auto correlation = 0.205 Mean sensitivity = 0.369 0.8 Minimum annual sensitivity = 0.005 Maximum annual sensitivity = 1.053 0.6 Median annual sensitivity = 0.349

0.4 Annual Sensitivity 0.2

0 0 10 20 30 40 50 60

Mean ring width = 0.59 mm Mean sensitivity = 0.254 Maximum annual sensitivity = 0.695 (c) OSF0247.1 Standard deviation = 0.20 Minimum annual sensitivity = 0.017 Median annual sensitivity = 0.205 0.8 Total auto correlation = 0.54 0.6

0.4

0.2

Annual Sensitivity Annual 0 0 10 20 30 40 50 60

(d) OSF0247.2 Mean ring width = 0.49 mm Minimum annual sensitivity = 0 Standard deviation = 0.21 Maximum annual sensitivity = 0.841 0.8 Total auto correlation = 0.57 Median annual sensitivity = 0.259 Mean sensitivity = 0.292 0.6

0.4

0.2 Annual Sensitivity 0 0 10203040506070 Growth ring series

Fig. 9. Plot of annual sensitivity values for two woods each measured along two radii in the Tjo¨rnarp Sockengille [(a) OSF0246.1 and (b) OSF0246.2 ¼ TS1] and Swedish Museum of Natural History collections [(c) OSF0247.1 and (d) OSF0247.2 ¼ NRM S069689]. Note that mean sensitivities are similar but not the same when calculated for each radius, and that the pattern of annual sensitivity trends vary notably both between and within woods from Korsaro¨d. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN remnants, but which once was probably distributed Patterns of wood growth extensively through central Ska˚ne. Volcaniclastic deposits, such as those at Korsaro¨d, appear to rest The consistently narrow growth rings in the Kor- directly on the Hoö¨r Sandstone, but the contacts saro¨d woods indicate growth under relatively are concealed in all cases. Given the interpretation adverse environmental conditions. This is supported of the volcaniclastic sediments as lahar deposits, by at least some wood radii that have mean sensitiv- they probably filled depressions in the landscape ity values within the sensitive field sensu Fritts and, consequently, are of greatly variable thickness (1976), and annual sensitivity values that reach over short distances. greater than 1.0 in some cases. These values imply considerable inter-annual variation in conditions for tree growth. Palaeovegetation False rings can be produced by trees enduring The palynological assemblages from the Hoö¨r short intraseasonal disturbances including drought, Sandstone and the overlying volcaniclastic deposits frost, herbivory, storm damage, ash fall and even reveal two significantly different ecosystems, par- earthquakes (Fritts 1976; Creber & Chaloner 1984; ticularly with respect to the gymnospermous com- Sheppard & Jacoby 1989; Filion & Quinty 1993; ponents that represented the main canopy plants Kurths et al. 1993). One Korsaro¨d specimen bears and, possibly, portions of the understorey. Fern evidence of charring without any healing response, spores and gymnosperm pollen are roughly of equal indicating death by the time of the fire. Earlier in abundance in the assemblages of both units. its development, this specimen shows an interval of The fern constituents are similar in both units with 5 years with greatly retarded growth, after which a Cyathidites/Deltoidospora, Marattisporites and few years of recovery is apparent. This single Osmundacidites dominating the palynofloras, re- extended phase of diminished growth within an flecting the Cyatheaceae/Dicksoniaceae, Marat- interval of 70 years, and the sporadic development tiaceae and Osmundaceae dominance of the of false rings in the Korsaro¨d woods, indicates understorey vegetation. By contrast, the gymnosper- an environment subject to episodic disturbance. mous component of the palynofloras differs between Although the precise cause(s) of these growth aber- the two units. A cheirolepid/cycadophyte/seed- rations cannot be identified, seismicity, episodic fern community expressed by assemblages in volcanic ash falls and drought in an edaphically the Hoö¨r Sandstone is replaced by a community dry landscape were all potential influences on plant strongly dominated by Taxodiaceae/Cupressaceae. growth in the CSVP during the Pliensbachian. This ‘taxodiaceous’ (cupressaceous) dominance is also reflected by the abundant fossil wood (Proto- Comparison of wood growth with other phyllocladoxylon) of this group. Eucommiidites- assemblages producing plants, possibly Erdtmanithecales or Gnetales, were also common during emplacement The Korsaro¨d fossil woods derive from a palaeolati- of the volcaniclastic sediments and might have tude of around 458 N (Scotese 2001; Blakey 2016). grown in the understorey. This major and abrupt Among other middle-latitude mid-Mesozoic assem- vegetational shift is difficult to attribute only to blages, the Middle Jurassic woods of the Cleveland the age difference between the two assemblages. Basin, UK, have a broad spectrum of mean sensitiv- Cross & Taggart (1982) noted that ash-covered ities (0.04–0.55) that encompass the range of the landscapes of volcanic terrains are inherently dry Korsaro¨d woods, although mean ring widths of the edaphically, and that opportunistic forbs, xerophytic former tend to be greater (up to 4.64 mm: Morgans woody shrubs and scale-leafed conifers play a key et al. 1999). The Late Jurassic Purbeck Formation of role in post-disturbance vegetation of such land- southern England hosts in situ permineralized coni- scapes. We interpret the palaeovegetational shift fer stumps with narrow (0.52–2.28 mm), but highly from the Hoö¨r Sandstone to the overlying volcani- variable, growth rings (mean sensitivities of 0.29– clastic strata to be, at least partly, a consequence 0.788) that were interpreted to reflect growth in a of the local ecosystem changes related to the volca- maritime Mediterranean climate (Francis 1984). nic activity in the area. The Korsaro¨d woods have similar ring characteris- The fact that the palynological assemblage in tics to the Purbeck woods, including the possession the lowermost volcaniclastic bed in the Korsaro¨d of intra-annual (false) rings that reflect growth succession is more similar to the Hoö¨r Sandstone within harsh and variable conditions. Middle–Late than higher samples possibly implies that some Jurassic mid-palaeolatitude woods from Liaoning, material from the underlying strata was incorpo- China, have generally broader growth rings (aver- rated into the volcaniclastic deposits. There is no age 2.24 mm) but mean sensitivity values (0.33) evidence of any reworking of more ancient palyno- within the range recorded from the Ska˚ne woods morph taxa. (Tian et al. 2015). Middle-latitude woods from the Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL.

Early Cretaceous of Western Australia have aver- but relatively few ring data appear to be available age ring widths of 0.177–9.390 mm and highly var- from warm and dry or winter-moist Mediterranean iable mean sensitivities (0.148–0.673), although climatic belts. A recent study by DeSoto et al. these samples preserved in nearshore marine depos- (2014) on the growth signatures of the western Med- its possibly derive from a broad range of hinter- iterranean Juniperus thurifera L. revealed generally land forest biomes (McLoughlin et al. 1995; narrow (0.67–1.71 mm) mean ring widths and var- McLoughlin 1996). iable (0.26–0.42) mean sensitivities, consistent with Cretaceous and Palaeogene woods from high values from both the Korsaro¨d fossils and those palaeolatitudes (e.g. from the Antarctic Peninsula) recorded by Francis (1984) from extant conifers of differ by having predominantly complacent ring Mediterranean biomes in both the Northern and sensitivities (average MS of 0.184 for the Creta- Southern hemispheres. ceous and 0.228 for the Palaeogene), some rings Philippe et al. (2004), in a survey of Mesozoic up to 9 mm wide, abrupt transitions to a narrow woods from the Southern Hemisphere, identified band of latewood, and no false rings (Francis Protophyllocladoxylon only from assemblages 1986; Falcon-Lang & Cantrill 2001). Similar differ- interpreted to represent the summer-wet palaeocli- ences are evident between the Korsaro¨d woods matic belt. However, it is unclear whether this and the high-latitude Mesozoic woods from Austra- holds true for the distribution of Northern Hemi- lia (Frakes & Francis 1990) and New Zealand sphere records or if wood of this fossil genus even (Pole 1999), and Eocene woods from the Canadian represents the same gymnosperm family across Arctic (Francis 1991), which have complacent its extensive geographical range. Although our mean sensitivities, at least some relatively broad studied sample is small, the growth ring patterns rings and abrupt latewood development. Permian (particularly complacent–sensitive MS values, rela- high-latitude Antarctic woods from the Gondwanan tively narrow growth rings composed of very few continental interior, by contrast, have wider aver- cells, diffuse transitions from earlywood to a gener- age growth rings (up to 3.87 mm) and more vari- ally large proportion of latewood, and a sporadic able mean sensitivities (0.190–0.475: Weaver representation of false rings) are broadly consis- et al. 1997). tent with growth features developed by modern Complacent mean sensitivities characterize the and ancient trees of middle-latitude Mediterranean wood of modern trees growing in moist, stable forest climates. interiors where no single environmental variable controls growth (Fritts 1976). Low growth rates (typified by narrow rings), combined with low Summary mean sensitivities, characterize trees of cool, consistently moist forests (e.g. the Magellanic forests The Hoö¨r Sandstone and overlying unnamed volca- of southern Chile: Francis 1986). The Korsaro¨d nigenic sediments in central Ska˚ne preserve key woods appear to have been subject to more varia- aspects of the Early Jurassic geological history of ble conditions, both within and between seasons. southern Sweden. Complementary spore–pollen Moreover, the variability in latewood development and fossil wood data, together with the characteris- contrasts with the consistently abrupt termination tics of the host strata, provide an integrated means of of the main growth season reflected in woods from interpreting the palaeoenvironment of central Ska˚ne high-latitude trees (Creber & Chaloner 1984). during the Early Jurassic. The chaotic distribution of Growth rings from trees of the Jurassic–Palaeogene wood and angular lapilli and basement clasts within palaeoequatorial belt of north Africa and SW USA the ash-rich agglomerate, the fine preservation of tend to have modest annual growth increments palynomorphs and some wood samples, and the (1–3 mm) but indistinct (or absent) ring boundaries occurrence of some spores in aggregates indicate (Creber & Chaloner 1985; Bamford et al. 2002; Par- an accumulation of the volcaniclastic sediments as rish & Falcon-Lang 2007). Some woods from Juras- a poorly sorted, short-transport, lahar deposit. More- sic warm middle latitudes (Neuquen, Argentina) over, the presence of pervasive calcitic and silice- have ill-defined growth rings (Morgans-Bell & ous cementation in the volcaniclastic deposits and McIlroy 2005). underlying Hoö¨r Sandstone, together with rapid Among modern trees, mean ring widths can have permineralization of woody remains, suggests that a wide range of values within any one climate zone, the vegetation grew in a hydrothermal region, with but there is a general trend of increasing width from major challenges for roots to cope with warm, boreal to moist temperate zones but a subsequent mineral-laden fluids percolating through the soil. slight decrease in the subtropical zone (Falcon-Lang The lahar sediments were also subject to the perco- 2005b). Mean sensitivity values are also highest in lation of hydrothermal fluids immediately after dep- forests of modern cool to cold, dry regions (high osition, as evidenced by pervasive calcite veining. altitudes or high latitudes: Falcon-Lang 2005b), We interpret the fossiliferous volcaniclastic strata Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

JURASSIC VOLCANISM AND VEGETATION: SWEDEN at Korsaro¨d to have been deposited in an active vol- shift in the dominance of gymnosperms towards canic landscape very close to the source of volcani- taxodiaceous conifers making up the canopy and genic material (Fig. 10). the enigmatic (possibly erdtmanithecalean or gneta- Spore–pollen data support a Hettangian–earli- lean) gymnosperms that produced Eucommiidites est Pliensbachian age for the fluvial–paralic Hoö¨r troedsonii pollen that possibly dominated the under- Sandstone. Palynostratigraphic dating of the overly- storey vegetation. The mix of typically water- ing continental volcaniclastic deposits to the Pliens- dependent (e.g. fern) and dry-climate (e.g. cheirole- bachian–early Toarcian(?) is broadly consistent pid) indices in these assemblages suggests a mosaic with, or signifies a slightly greater age than, radio- of habitats in the catchment area of the fossil as- metric dates obtained by previous workers (Bergelin semblages. The ring width characteristics of the 2009; Tappe et al. 2016) from alkaline mafic volca- cypress-related fossil wood in the volcanigenic sed- nic plugs in the CSVP. iments also suggest growth within environments The representation and abundance of palyno- subject to perturbations. We envisage that central morph groups in the Hoö¨r Sandstone suggests that Ska˚ne hosted a middle-latitude Mediterranean-type the earliest Jurassic vegetation of this region was biome in the late Early Jurassic, where rainfall was dominated by ferns (marattiacean, osmundacean relatively low and seasonal. Superimposed on this and cyatheacean), probably forming an understorey climate were the effects of active strombolian volca- or preferentially growing along water courses, nism and hydrothermal activity. There were peri- together with gymnosperms (cycadophytes, cheiro- odic eruptions of ash, lapilli and gas, and changing lepid conifers and pteridosperms) that constituted drainage patterns. Perhaps, most importantly, the shrub to tree-sized plants. Late Early Jurassic floras plants would have needed to cope with the stress preserved in the volcaniclastic deposits signify con- of growing in a substrate that was in some parts tinued strong representation of the same fern groups edaphically dry but locally permeated by hydrother- as in the underlying Hoö¨r Sandstone, but there was a mal fluids. All of these factors led to an unusual

Fig. 10. Reconstruction of a volcanic landscape in central Ska˚ne during the late Early Jurassic, with deposition of pyroclastic and lahar sediments and fossilization of autochthonous and allochthonous plant material. Illustration by Polyanna von Knorring based on photographs by V. Vajda taken in Rotorua, New Zealand. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

V. VAJDA ET AL. vegetation developed in an ecologically stressful sit- years of genomic stasis in Royal Ferns. Science, 343, uation (Fig. 10), which is reflected in the growth pat- 1376–1377 (+ online supplementary data pages 1– terns of the woods. 16; two video clips), http://doi.org/10.1126/science. 1249884 Financial support from the Swedish Research Council (VR Bomfleur, B., Grimm, G.W. & McLoughlin, S. 2015. grants 2015-04264 to V.V. and 2014-5234 to S.M.) is Osmunda pulchella sp. nov. from the Jurassic of Swe- gratefully acknowledged. Excavation at the Korsaro¨d fos- den – reconciling molecular and fossil evidence in the sil site in July 2014 was funded by the Crafoord Founda- phylogeny of modern royal ferns (Osmundaceae). tion, the Swedish Research Council (VR) and Lund BMC Evolutionary Biology, 15, 126, http://doi.org/ University Carbon Cycle Centre (LUCCI). Excavation at 10.1186/s12862-015-0400-7 the site was assisted by students from the Department of Bond, D.P.G. & Wignall, P.B. 2014. Large igneous Geology, University of Lund. The members of Tjo¨rnarps provinces and mass extinctions: an update. In: Keller, Sockengille are thanked for access to the fossil locality G. & Kerr, A.C. (eds) Volcanism, Impacts, and Mass and for their hospitality during excavation operations. Extinctions: Causes and Effects. Geological Society of We thank Pollyanna von Knorring for compiling the illus- America, Special Papers, 505, 29–55, http://doi.org/ tration in Figure 10. We thank two reviewers whose com- 10.1130/2014.2505(02) ments greatly improved the manuscript. Bunn, A.G., Jansma, E., Korpela, M., Westfall, R.D. & Baldwin, J. 2013. Using simulations and data to evaluate mean sensitivity (z) as a useful statistic in den- References drochronology. Dendrochronologia, 31, 250–254. Couper, R.A. 1953. Upper Mesozoic and Cainozoic spores Ahlberg, A. 1994. 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