Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Benito Moreno, María Isabel

Fernández Barrenechea, José María

Galán Abellán, Ana Belén

Lago San José, Marceliano

López Gómez, José

Docta Complutense

  105 macla nº 9.  septiembre ‘08 revista de la sociedad española de mineralogía Early Triassic-Anisian Continental Sediments from SE Iberian Ranges: Sedimentological and Mineralogical Features /ANA BELÉN GALÁN ABELLÁN (1, *), JOSÉ FERNÁNDEZ BARRENECHEA  (2), JOSÉ LÓPEZ GÓMEZ  (1), MARCELIANO LAGO SAN JOSE (3), MARÍA ISABEL BENITO MORENO (1)  (1) Dpto. Estratigrafía. Universidad Complutense Madrid. Instituto de Geología Económica. C.S.I.C. José Antonio Novais 2. 28040 Madrid (Spain) (2) Dpto. Cristalografía y Mineralogía, Facultad de Geología, Universidad Complutense de Madrid.José Antonio Novais 2. 28040 Madrid (Spain) (3) Dpto. Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, Pedro Cerbuna 12, 50.009 Zaragoza (Spain) INTRODUCTION.  The present work is part of amultidisciplinary study focused on thereconstruction of the environmentalconditions that prevailed during thelarge biotic crisis at the Permian-Triassic transition and the subsequent EarlyTriassic recovery, in the SE IberianRanges. The causes that promoted suchcrisis include meteoritic impact, sealevel fluctuation, changes in sea waterchemistry and volcanic activity related tothe Siberian continental flood basalt province (see Erwin et al. (2002) for a critical examination of these extinctionmechanisms). The environmental crisispersisted during Early Triassic times,and leaded to a slow recovery of bothbiological diversity and size of theorganisms (Twichett et al., 2004). Thisperiod has received growing attention inrecent years. The data available are stillcontroversial, especially in continentalsediments, where dating and correlationbetween different areas is hampered bythe scarce presence of fossils. The aim of this work is to perform asedimentological and mineralogicalcharacterization of the Cañizar andEslida Formations, of Early  Triassic-Anisian age (Doubinger et al., 1990), intwo stratigraphic cross-sections locatedin different sub-basins within the SEIberian Ranges: one section inTalayuelas (Cuenca province), and theother in Gátova (NE of Valenciaprovince). This is an indispensablepreliminary step for the multidisciplinaryapproach.  GEOLOGICAL SETTING.  The Permian-Triassic sediments of this area can be defined in a general way bythe classic german trilogy:  Buntsandstein, Muschelkalk andKeuper. The sedimentary record hasbeen subdivided into nine tectono-sedimentary cycles, separated byangular unconformities and hiatuses(Arche and López-Gómez, 2005), but only the third and fourth ones are ofinterest in this work.   The Cañizar Fm. is part of the thirdsedimentary cycle and consists of redsandstones which unconformablyoverlay the Late Permian rocks of theAlcotas Fm. The field study has allowed discriminate six members within theCañizar Fm., in both the Talayuelas andthe Gátova sections. These membersshow specific sedimentological featuresand are limited by major boundarysurfaces (MBS). Sedimentologically, theCañizar Formation represents the evolution of sandy braided fluvialsequences with a paleocurrent trendpointing to S and SE (Arche and López-Gómez, 2005). In the Talayuelas section,sandstones of the Cañizar Fm. aredirectly overlain by dolostones(Muschelkalk facies). Thus, the Eslida Fm. is not represented in this section.  Conversely, in the Gátova section theEslida Fm., that constitutes the fourthsedimentary cycle, overlays the CañizarFm. It is formed by lutites andsandstones. Carbonate nodules arefrequently observed in the lutitic layers. These rocks are interpreted as part of abraided fluvial system, with a betterdevelopment of flood plain deposits,which include paleosol profiles.  MATERIALS AND METHODS  Seventy two samples corresponding tosandstone, siltstone and lutite layers were collected along both sections. Bulkmineralogy was obtained by combiningX-ray diffraction (XRD) and petrographicobservations. Clay composition wasdetermined by XRD analysis performedon oriented aggregates. Detailedtextural features were obtained fromback scattered electron  microscope(BSEM) images during the microprobe study and from scanning electron microscope (SEM). The composition of the mineral phases was determined by microprobe analysis (EMPA).  RESULTS.  Samples from the Cañizar Fm. containdetrital mica, quartz, K-feldspar and hematite. The clay fraction is composed of illite and minor hematite, together with traces of kaolinite in a few samples. Accessory minerals include zircon, monazite, ilmenite, rutile, tourmaline and apatite.  In addition, small amounts of strontium-rich aluminium phosphate sulphate minerals (APS minerals) are detected on XRD patterns of some samples from both sections (Talayuelas and Gátova). These minerals are members of the alunite-jarosite group. BSEM images reveal that they occur as irregular polycrystalline aggregates (up to 120 µm large), surrounded by detrital mica plates and quartz. Small hematite patches are frequently associated with the APS minerals (Figure 1a). Quartz and illite adapt to the shape of idiomorphic APS minerals in the borders of the polycrystalline aggregates (Figure 1a and 1b), evidencing that the precipitation of the APS minerals predates the quartz and illite cements, The average structural formula for these phases can be expressed as a solid solution between goyazite, svanbergite, crandallite and woodhouseite:  Sr0.49Ca0.31(Al2.85)(P1.61S0.57O4)2(OH)6  Detrital biotite and muscovite are present as elongated and platy crystals (60 to 150 µm large) that may show preferred orientation. Representative structural formulae of detrital biotite and muscovite determined by EMPA can be written as:  palabras clave: Pérmico-Triásico, recuperación, minerales APS, Cordillera Ibérica key words: Permian-Triassic, recovery, APS minerals, Iberian Range  resumen SEM/SEA 2008 * corresponding author: galanabellan@geo.ucm.es   106 (K1.57Na0.07Ca0.02) (Fe2.20 Mg1.41Al(VI)1.29Ti0.36) (Al(IV)2.21 Si5.79) O20 (OH)4 and (K1.71Na0.11 Ca0.01) (Fe0.16 Mg0.20 Al(VI)3.62 Ti0.05) (Al(IV)1.61 Si6.39) O20 (OH)4, respectively.  20 µm 20 µm fig 1. BSEM images of Sr-rich APS minerals fromsamples of the Cañizar Fm. in the Gátova section, a)intergrown with hematite patches and b) surroundedby quartz and detrital mica.  BSEM images show that detrital zircon,monazite and apatite grains (up to 50µm large) are rather frequent in thesesamples. Rutile occurs as stronglycorroded sub-idiomorphic crystals (30 to40 µm). In addition, analysis of detritaltourmaline allows differentiate bothdravite Na0.63Ca0.12 (Mg1.39Fe0.94Al0.7Ti0.14) Al6Si6 O18 (BO3)3 (OH)4 and schorl Na0.65Ca0.04 (Mg0.42Fe1.76Al0.76Ti0.03) Al6Si6 O18 (BO3)3compositions within the accessoryminerals.  Compared with the Cañizar Fm.,samples from the Eslida Fm. show ahigher proportion of phyllosilicates andfeldspar, and a progressive increase inthe presence of calcite and dolomitefrom base to top of the unit.   DISCUSSION.  The comparative study of stratigraphic features points to an enhancedsubsidence rate for the eastern sub-basin (Gátova section). Moreover,sediments from the Eslida Fm. areindicative of a significant change in thedepositional regime, towards low energysystems in a more open sub-basin.  The presence of the APS minerals canbe very important, since they canprovide information on the physical-chemical formation conditions (Eh, pH)(Dill, 2001). First of all, there seems tobe a stratigraphic control, since thesephases had been previously reported in another section of the Cañizar Fm.(Benito et al., 2005). Textural relationships indicate that theprecipitation of the APS mineralspredates the formation of illitic andquartz cements. Therefore, we can arguethat the APS minerals formation occurred shortly after the sedimentation,and most probably were related to thecirculation of acidic meteoricgroundwater, since low pH environmentsand oxidising conditions at shallowdepths are a common feature to mostAPS occurrences in different geologic settings (Dill, 2001). This is in goodagreement with the origin proposed bySpötl (1990) and Pe-Piper and Dolansky (2005) for APS minerals of similarchemical composition (compoundphosphate-sulphate) in terrestrial sandstones in Austrian Alps and Nova Scotia (Canada) respectively. Oxidisingand acidic conditions thus, prevailedduring the first stages of recovering afterthe Permian-Triassic crisis in the Iberian Ranges. These conditions wereprogressively decreasing from the Earlyto the Middle Triassic, that is, from the Cañizar Fm. to the Eslida Fm.  The increase in the proportion of calciteand dolomite from base to top of theEslida Fm. in the Gátova section isrelated to the development of paleosolswithin the flood plain lutitic deposits, and probably reflect a growing marineinfluence to the top of this unit.  RESULTS. Arche, A., López-Gómez, J. (2005): Sudden changes in fluvial style across the Permian-Triassic boundary in the eastern IberianRanges, Spain: Analysis of possible causes.Palaeogeography, Palaeoclimatology,Palaeoecology, 229, 104-126.  Benito, M. I., de la Horra, R., Barrenechea, J. F., López-Gómez, J., Rodas M., Alonso-Azcárate, J.;  Arche , A., Luque , F. J.,(2005):Late Permian continental sediments in the SE Iberian Ranges, eastern Spain: Petrological and mineralogical characteristics and palaeoenvironmental significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 229, 24-39. Dill, H.G. (2001): The geology of aluminium phosphates and sulphates of the alunite group minerals: a review. Earth Science Reviews, 53, 35-93.  Doubinger, J., López-Gómez, J., Arche, A., (1990): Pollen and spores from thePermian and Triassic sediments of the southeastern Iberian Ranges, Cueva de Hierro (Cuenca) to Chelva-Manzanera (Valencia-Teruel) region, Spain. Reviews of Paleobotany and Palynology, 66, 25-45. Erwin, D.H., Bowring, S.A., Yugan, J. (2002):End Permian mass extinction : A review. Geological Society of America Special Paper, 356, 363-383. Pe-Piper, G., Dolansky, L.M. (2005): Early diagenetic origin of Al phosphate-sulphate minerals (woodhouseite and crandallite series) in terrestrial sandstones, Nova Scotia, Canada. American Mineralogist, 90, 1434-1441. Spötl, C. (1990): Authigenic aluminium phosphate-sulphates in sandstones of the Mitterberg Formation, Northern Calcareous Alps, Austria. Sedimentology, 37, 837-845. Twitchett, R. J., L. Krystyn, A. Baud, J. R. Wheeley, and S. Richoz. (2004) Rapid marine recovery after the end-Permian mass-extinction event in the absence ofmarine anoxia. Geology 32, 805-08. , geology, and mineral analysis. Baldwin & Cradock. London, 725 p. Tornos, F. (1989): Los skarns y mineralizaciones asociadas del Sistema Central Español. Modelo de caracterización petrológica, geoquímica y metalogénica. Tesis Doctoral, Universidad Complutense de Madrid. 

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Early Triassic-Anisian continental sediments from SE Iberian ranges: sedimentological and mineralogical features

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Early Triassic-Anisian continental sediments from SE Iberian ranges: sedimentological and mineralogical features

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