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Early Seed Plants from Western Gondwana: Paleobiogeographical and Ecological Implications Based on Tournaisian (Lower Carboniferous) Records from Argentina

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Early Seed Plants from Western Gondwana: Paleobiogeographical and Ecological Implications Based on Tournaisian (Lower Carboniferous) Records from Argentina Palaeogeography, Palaeoclimatology, Palaeoecology 417 (2015) 210–219 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Early seed plants from Western Gondwana: Paleobiogeographical and ecological implications based on Tournaisian (Lower Carboniferous) records from Argentina C. Prestianni a,⁎, J.J. Rustán b,d, D. Balseiro b,c,E.Vaccarib,d, A.F. Sterren b,c, P. Steemans e, C. Rubinstein f,R.A.Astinib a Paleontology Department, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, 1000 Brussels, Belgium b Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), CONICET-Universidad Nacional de Córdoba, Edificio CICTERRA Av. Vélez Sarsfield 1611, X5016GCA, Ciudad Universitaria, Córdoba, Argentina c Centro de Investigaciones Paleobiológicas (CIPAL), FCEFyN, Universidad Nacional de Córdoba, Av. Velez Sarsfield 299, 5000, Córdoba, Argentina d Universidad Nacional de La Rioja, Av. René Favaloro s/n 5300, La Rioja, Argentina e Unité de Paléobiogéologie, Paléopalynologie et Paléobotanique, Dpt. de Géologie, Université de Liege, B18/P40 Boulevard du Rectorat, 4000 Liege, Belgium f Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA): CCT CONICET-Mendoza, Av. Ruiz Leal s/n, Parque General San Martín M5502IRA, Mendoza, Argentina article info abstract Article history: The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic section located Received 28 May 2014 in Western Argentina (Precordillera Basin). Palynological evidence indicates an Early Mississippian (probably Received in revised form 21 October 2014 Tournaisian) age for this new succession. The two identified early seeds generas, Pseudosporogonites cf. hallei Accepted 29 October 2014 and Warsteinia sancheziae n. sp. were up to now considered as restricted to the Devonian of Laurussia. This find- Available online 6 November 2014 ing suggests a dispersal of earliest spermatophytes between Laurussia and Gondwana during Devonian/ Tournaisian times, thus accounting for the Rheic Ocean as a surmountable biogeographic barrier for continental Keywords: Spermatophytes biotas. Alternatively, contrasting biogeographic hypotheses dealing with early spermatophytes rising in Carboniferous paleotropics and then displacing herbaceous communities of non-spermatophytes typical from cool high latitu- Gondwana dinal regions, are explored for explaining the recognized paleobiogeographical pattern. The new information Argentina supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Based on pre- Paleogeography liminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and more similar to those reported from Laurussia. In addition, their discovery in a sedimentary envi- ronment associated to glacigenic deposits, show that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Although for the past twenty years our knowledge of the earliest origin of seed plants has been greatly increased, their origin and earliest Seed plants (or spermatophytes) are the most successful modern diversification have been exclusively reconstructed based on informa- group of plants. The seed habit is one of the key evolutionary acquisi- tion coming from paleotropical records from Laurussia (Prestianni and tions that allowed them to colonize new habitats and to reproduce Gerrienne, 2010). Seed plants seem to have colonized all latitudes by without available free water (Chaloner and Hemsley, 1991; Bateman the Tournaisian (359–346 Ma), yet the understanding of their dispersal, and DiMichele, 1994; Prestianni and Gerrienne, 2010). The most primi- a critical paleobiogeographical event taking into account the major tive seeds evolved during the Devonian, a time of rapid and important barrier of the Rheic Ocean, remains obscure and strongly biased by the modifications in both the biosphere and the geosphere that completely lack of Late Devonian–earliest Mississippian data from the Southern transformed continental ecosystems throughout a long and complex Hemisphere. geobiotic process known as terrestrialization (Algeo and Scheckler, In this paper, report is made of the earliest occurrences of seed plants 1998; Meyer-Berthaud and Decombeix, 2007; Mintz et al., 2010). in western Gondwana, based on ovules from Tournaisian strata of a new glacial-linked stratigraphic succession of Western Argentina. They have fi ⁎ Corresponding author. Tel.: +32 2 627 44 83. been identi ed as Pseudosporogonites cf. hallei and Warsteinia sancheziae E-mail address: [email protected] (C. Prestianni). sp. nov., up to now two strictly Devonian genera from Laurussia. http://dx.doi.org/10.1016/j.palaeo.2014.10.039 0031-0182/© 2014 Elsevier B.V. All rights reserved. C. Prestianni et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 417 (2015) 210–219 211 A discussion is proposed about the paleogeographical as well as Precordillera separates the Devonian from the Carboniferous. This set biostratigraphical implications and major ecological evolutionary signif- of strongly folded, faulted and intruded stratigraphic units, underlie icances of this discovery. the uncontroversial Pennsylvanian glacial rocks of the base of the Río del Peñón Formation (Fauqué and Limarino, 1991), thus allowing the interpretation of a complex story of uplift, erosion and onlapping for 2. Geological and stratigraphic settings the region. Prior to the early Pennsylvannian, at least one important folding episode took place forming an angular unconformity named The study area is part of the Sierra de Las Minitas, a set of low moun- “Agua de Carlos unconformity” (see Fig. 1). A number of glacial tains located in the north of the La Rioja Province, Western Argentina diamictites can be recognized underlying this unconformity (Astini (Fig. 1). The Sierra de Las Minitas is located approximately 30 km to and Ezpeleta, 2008; Ezpeleta and Astini, 2009). Geochronological the southwest of the small town of Jagüé, and it is considered as the (Coughlin, 2000), and paleontological data (Vaccari et al., 2008; northern reach of the Argentine Precordillera in the context of the Rubinstein et al, 2010; Sterren et al., 2010; Prestianni et al., 2011, Central Andean foreland basin (Caminos et al., 1993). 2012) seemed to point these glaciomarine deposits being Devonian to The areas next to Sierra de Las Minitas were originally surveyed by Mississippian, and thus different from the Pennsylvanian Río del Aceñolaza (1971) and Caminos et al. (1993), yet the studied area was Peñón glacial record (Astini and Ezpeleta, 2008). mapped in detail by Coughlin (2000). The structure of the region is complex as the folded bedding was later faulted and intruded by igne- ous bodies. Except for certain Lower Devonian trilobite-bearing units 2.1. Studied stratigraphic section cropping out to the north of the Sierra de Las Minitas (Rubinstein et al., 2010; Rustán et al., 2011; Holloway and Rustán, 2012), the bulk A new stratigraphic section (Fig. 2), devoid of structural complexity of the stratigraphic record of the region has been preliminarily assigned and including glacial diamictites, was surveyed in the eastern flank of a to the poorly defined Jagüel Formation (González and Bossi, 1986). This major syncline structure located to the southern area of the Sierra de Las formation is characterized by a wide range of sedimentary siliciclastic Minitas (about 28° 48′ 35″ S/68° 45′ 04″). Without exposed contact with lithotypes, and might partially involve several other units recognized the ancient most Lower Devonian trilobite-bearing units, this section in the area (Fauqué and Limarino, 1991; Azcuy and Carrizo, 1995; embraces the upper interval of the set of stratigraphic units underlying Carrizo and Azcuy, 1998; Limarino et al., 2006; Rustán et al., 2011). It the Pennsylvanian Río del Peñón Formation. has been interpreted to include stratigraphic intervals that may, in The stratigraphic column exposed at this new section is very thick part, fill in the regional gap that elsewhere in the Argentine and only its lowermost third was surveyed. The measured interval is Fig. 1. Simplified map of the Sierra de Las Minitas and location of the studied stratigraphical section (A). Modified from Coughlin, 2000. 212 C. Prestianni et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 417 (2015) 210–219 Fig. 2. Stratigraphical log of the here studied interval with localization of plant beds and palynological samples. nearly 300 m thick (Fig. 1), with the base covered by modern deposits. and massive beds of medium to coarse scarcely fossiliferous sandstones. The lowermost part of the section starts with massive and laminated Above, another thickening–coarsening upward interval of nearly 80 m dark mudstones with dropstones. It continues with a nearly 12 m occurs, mainly composed of greenish to blackish green siltstones with thick dark gray to black, stratified, matrix-supported polimictic relatively scarce interbedded fine-grained sandstones, which contains diamictite, with stratified pebbly mudstones and thick beds of fine the sampled plant bearing levels (AQ-365 and AQ-380). grained sandstones in its upper portion. Boulders in the diamictite are The upper part
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