Palynology of the Toarcian–Aalenian Global Boundary Stratotype Section and Point (GSSP) at Fuentelsaz (Lower–Middle Jurassic, Iberian Range, Spain)

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    Article history:Received 13 July 2009Received in revised form 15 March 2010Accepted 11 April 2010Available online 24 April 2010

    Keywords:ToarcianAalenian stratotypepalynology

    Review of Palaeobotany and Palynology 162 (2010) 1128

    Contents lists available at ScienceDirect

    Review of Palaeobota

    l se1. Introduction

    The Jurassic palynology of the Iberian Peninsula is little known.The rst information was provided by Doubinguer et al. (1970) whomade a reconnaissance study of the Lower Mesozoic of Europe,including the Lias of Portugal. Studies of the Portuguese Lias werecontinued by Adloff et al. (1974), Adloff and Doubinguer (1978),Davies (1985) and Veiga de Oliveira et al. (2007). Palynologicalstudies of the Lusitanian Basin, however, have mainly focused on theMiddle and Upper Jurassic (Riley, 1974; Boland, 1986; Van Erve andMohr, 1988; Mohr and Schmidt, 1988; Mohr, 1989; Smelror et al.,

    1991) during this period is almost completely unknown, eventhough a large number of sections have been well studied fromsedimentological, stratigraphic and palaeontological points of view(Vera, 2004; Gmez and Goy, 2005). The palynological study of theSpanish Lias has recently begun in sections in Asturias, the BasqueCantabrian Basin and the Iberian Range (Barrn et al., 1999a, b,2006; Gmez et al., 2007). The few studies that exist on MiddleJurassic palynomorphs from Spain were performed by Fenton andFisher (1978) and Smelror et al. (1991), and focus on Bathonian toCallovian dinoagellate cyst assemblages from northeastern Spainand the Iberian Range.1991; Mohr and Schultka, 2000; Barrn andLittle palynological information exists o

    Spain. Indeed, the plant life that reigned in tEuropean Province of the Eurosinian Regi

    Corresponding author. Fax: +34 91 349 5830.E-mail address: e.barron@igme.es (E. Barrn).

    0034-6667/$ see front matter 2010 Elsevier B.V. Aldoi:10.1016/j.revpalbo.2010.04.003 2010 Elsevier B.V. All rights reserved.biostratigraphyenvironmental conditionspalaeoecologyThe Fuentelsaz Section is located in the Castilian Branch of the Iberian Range (Guadalajara, Spain). Itsexceptional LowerMiddle Jurassic transition outcrops led to its designation as the Global BoundaryStratotype Section and Point for the base of the Aalenian. The sediments of the ToarcianAalenian transitionat Fuentelsaz are composed of marls with interbedded limestones in rhythmic alternation. Marls aredominant in the Toarcian and the Opalinum Zone up to the middle part of the Comptum Subzone. In theremaining Comptum Subzone, marly materials are scarce and limestones predominate. Sedimentation atFuentelsaz took place over an extensive marine epeiric carbonate platform that was well connected with theopen sea. In the Fuentelsaz Section, a total of 43 palynomorph taxa were recorded: 23 spore taxa, 13 pollentaxa, 4 acritarchs, 2 prasinophytes and 1 dinoagellate cyst. The studied sediment samples were alwaysdominated by terrestrial allochthonous miospores. In general, miospore assemblages are biased due to thetransport of pollen from land or islands to the continental platform. Spheripollenites, Classopollis or indeedboth pollens numerically dominate the assemblages. Other miospores appear in low numbers. Aquaticpalynomorphs are also scarce; Micrhystridium lymensis is the most common. Five palynological assemblages(PA) were distinguished: PA1, PA2 and PA3 are Toarcian in age, PA4 is located at the boundary between theToarcian and the Aalenian and PA5. This latter palynological assemblage which is lower Aalenian in ageshows a strong reduction in palynomorph diversity and preservation in the Comptum Subzone.Palaeoecological analysis of the palynomorphs indicated the presence of calm, oligotrophic sea water. Thepalaeooral communities of gymnosperms and vascular cryptogamswhich grew in subtropical aridconditionswere poorly diversied.Azerdo, 2003).n the Lower Jurassic ofhe west of the Southernon (sensu Vakhrameev,

    The sectionBoundary StratoAalenian stage inJaneiro, Brazil, 2phy. It has beenlogical, stratiggeochemical, migical studies in

    l rights reserved.a r t i c l e i n f o a b s t r a c tPalynology of the ToarcianAalenian Glob(GSSP) at Fuentelsaz (LowerMiddle Jura

    Eduardo Barrn a,, Soledad Ureta b, Antonio Goy b, La Instituto Geolgico y Minero de Espaa (IGME), Ros Rosas 23, 28003 Madrid, Spainb Departamento and UEI de Paleontologa (UCMCSIC), Facultad de Ciencias Geolgicas, Jc Departamento Interuniversitario de Ecologa, Facultad de Ciencias Biolgicas, Universidad Departamento de Ecologa, Universidad de Alcal, 28871 Alcal de Henares, Spain

    j ourna l homepage: www.el Boundary Stratotype Section and Pointic, Iberian Range, Spain)

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    ntonio Novis 2, 28040 Madrid, Spainmplutense de Madrid, Jos Antonio Novis 2, 28040 Madrid, Spain

    ny and Palynology

    v ie r.com/ locate / revpa lboof Fuentelsaz was formally stablished as Globaltype Section and Point (GSSP) for the base of thethe 31st International Geological Congress (Rio de

    000) by the International Commission on Stratigra-exhaustively studied from lithological, sedimento-

    raphic, palaeontological, magnetostratigraphic,neralogical and isotopic points of view. Palaeontolo-clude groups such as ammonites, brachiopods,

  • ostracods, nannofossils, foraminifers and palynomorphs (Goy andUreta, 1987, 1991; Martnez, 1992; Garca-Joral and Goy, 1994; Goy

    NWSE trending Iberian Range which is an intracontinental Alpinebelt with Variscan basement and Mesozoic and Cenozoic cover. The

    3. Materials and methods

    anA

    12 E. Barrn et al. / Review of Palaeobotany and Palynology 162 (2010) 1128section is located at about 0.5 km north of the Fuentelsaz village,Guadalajara province (Fig. 1A). It has previously been describedby Comas-Rengifo and Goy (1983), Goy and Ureta (1987, 1991),Garca-Joral and Goy (1994), Goy et al. (1994, 1996) and Cresta et al.(2001).

    At Fuentelsaz the Upper Toarcian (Mactra, Aalensis and Buck-mani subzones of the Aalensis Zone) and Lower Aalenian (Opalinumand Comptum subzones of the Opalinum Zone) (Fig. 1B,C) are re-presented by a (41.5 m of thick) complete succession of alternatinglimestones (mudstones and bioclastic wackestones, occasionallypackstones) and marls. The lower and middle parts of the section,which are markedly marly (levels 1 to 153), correspond to the upperpart of the Turmiel Formation (Goy et al., 1976), whereas the upperpart, which is predominantly calcareous (levels 154 to 205), belongsto the lower part of Casinos Formation (Gmez et al., 2003)(Fig. 1B).

    The depositional environment at this time correspond to a fault-bounded subsiding block, within in a NS trending marine epeiriccarbonate platform well connected with the open sea until the lateComptum Biochrone (Fig. 2B). Facies pattern and vertical evolutionobserved in the Fuentelsaz section reveal a striking similarity to manyothers outcrops in the Iberian Range where an important episode ofextensional faulting has been recognized in the late Early Aalenian.Synsedimentary extensional tectonic activity is documented by adrastic increase in the net accumulation rate (12 m/Ma) during thelatest Comptum Biochrone, and is especially well recorded at theFuentelsaz section (see Garca-Frank et al. 2008).

    Fig. 1. (A) Geological and geographical setting of the Fuentelsaz section; (B) Upper Toarciet al., 1994, 1996; Herrero and Canales, 1997; Perilli, 1999; Crestaet al., 2001). The richness of successive ammonoid assemblagesallowed a high resolution biostratigraphic scale to be established,which permits detailed correlations be made with other Jurassicsections (Goy and Ureta, 1987, 1991; Goy et al., 1994, 1996, 1999;Cresta et al., 2001). Biostratigraphic event based in the ammoniteevolution (the rst appearance of the graphoceratid genus Leioceras)marks the LowerMiddle Jurassic boundary at the base of levelFZ107 in Fuentelsaz (Goy and Ureta, 1987, 1991; Goy et al., 1994,1996, 1999; Cresta et al., 2001).

    To date, only a few short palynological contributions regardingFuentelsaz have been published (Goy et al., 1996, 1999; Cresta et al.,2001), focusing on assemblages from a few levels near the ToarcianAalenian transition. These assemblages, which are dominated by thepollen grains of gymnosperms, contain conspicuous amounts ofacritarchs. Spores of vascular cryptogams and the phycomes ofprasinophytes are scarce. More recently, Peyrot et al. (2007a) usedconfocal microscopy to study Classopollis in the Fuentelsaz Section.The present paper reports a complete study of the palynologicalcontent of the Late ToarcianEarly Aalenian rocks outcropping in theFuentelsaz Section. Qualitative and quantitative analyses wereperformed in order to identify palynological assemblages, whichwere calibrated using the above ammonoid-based biostratigraphicscale. These analyses also allowed the inferred assemblages to becompared with contemporaneous counterparts in other parts ofEurope and North Africa. The palaeoenvironmental conditionsreected by the section were also analysed.

    2. Geological setting

    The Fuentelsaz section is situated in the central sector of thetransition at Fuentelsaz and details of the ToarcianAalenian boundary.One hundred and two sediment samples from the FuentelsazSection were examined. All samples were prepared following thestandard palynological technique (Batten, 1999; Peyrot et al., 2007a).Sixty nine samples yielded palynological contents: 66 from theTurmiel Formation (from the Insigne to Comptum p.p. Subzones) andthree from the Casinos Formation (in the Comptum Subzone)(Figs. 1B, 34).

    To determine the oral turnover in response to palaeoenviron-mental changes, the palynomorphs were organised according to theirbotanical afnities in accordance with the data of Harris (1974),Balme (1995), Batten and Dutta (1997) and Abbink (1