Upper Anisian to Lower Carnian magnetostratigraphy from the Northern Calcareous Alps (Austria) Yves Gallet, Leopold Krystyn, Jean Besse To cite this version: Yves Gallet, Leopold Krystyn, Jean Besse. Upper Anisian to Lower Carnian magnetostratigraphy from the Northern Calcareous Alps (Austria). Journal of Geophysical Research : Solid Earth, American Geophysical Union, 1998, 103 (B1), pp.605-621. insu-01863517 HAL Id: insu-01863517 https://hal-insu.archives-ouvertes.fr/insu-01863517 Submitted on 28 Aug 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNALOF GEOPHYSiC• RESEARCH,VOL 103,NO. B1, PAGES 605-621, JANUARY 10, 1998 UpperAnisian to Lower Carnianmagnetostratigraphy from the Northern CalcareousAlps (Austria) Yves Gallet Laboratoirede Pa16omagn6tisme, URA 729, Institutde Physique du Globede Paris, France LeopoldKrystyn Institutefor Paleontology,Vienna, Austria Jean Besse Laboratoirede Pa16omagn6tisme, URA 729, Institutde Physiquedu Globede Paris, France Abstract. We presenta magnetostratigraphicstudy of threepelagic limestone sections (Gamsstein,Mendlingbach and Mayerling) from the eastern part of theNorthern Calcareous Alps.Together these sections, which contain a richconodont fauna, yield a sedimentaryrecord encompassingthe uppermost Anisian, the Ladinian and the Lower Carnian. Thermal demagnetizationand isothermal remanent magnetization experiments indicate that the magnetizationis essentiallycarried by a mineralof themagnetite family. The high unblockingtemperature components isolated from thethree sections provide clear magnetic polarityzonations. Correlations between these results, based on the biostratigraphic data and tephrochronology,allow the construction of a compositemagnetic polarity sequence from the Illyriansubstage (Upper Anisian) to theJulian 2 zone(Lower Carnian). This sequence contains17 well-definedpolarity reversals, and eight more poorly defined intervals. Correlationscan be suggestedbetween the new dataand other magnetostratigraphic results previouslyobtained from marine sections. We estimatethat the magnetic reversal frequency was2.5 to 3.6 reversalsper million yearsduring the Ladinian. Introduction reliable compositemagnetic polarity sequencefrom these latter resultsis problematic,they shouldbe constrainedby additionalmagnetostratigraphic data from well-datedmarine The Triassic magnetostratigraphy has been recently sections. improved by several studies both on marine and continental In this study we report the magnetostratigraphyof three sedimentarysections [e.g., Steiner et aI., 1989; Ogg and pelagiclimestone sections from the NorthernCalcareous Alps Steiner, 1991; Gallet et aI., 1992, 1993a, 1994, 1996; (NCA; Austria). Correlationsbetween these sections based on Muttoni and Kent, 1994; Muttoni et al., 1994, 1995, 1996, conodontsand taphrostratigraphyallow the constructionof a 1997; Kent et al., 1995; Molina-Garza et al., 1991, !993, magneticpolarity sequencefrom the UppermostAnisian to 1996]. However, these data concentrateon the magnetic the Lower Carnian. reversalchronology during the Late and Early Triassic.For the Middle Triassic, magnetostratigraphicresults obtained from marine sedimentsare available only for the Lower and Middle Anisian [Muttoni et al., 1995, 1996] and from the Ladinian Biochronologyand Chronostratigraphy UppermostAnisian to the Lower Ladinian[Muttoni and Kent, !994; Muttoni et al., 1994]. Other studies that provide Several recent studies that focused on the Ladinian informationabout Middle Triassicmagnetostratigraphy come biochronology[e.g., Brack and Rieber, 1993, !994; Kovacs from the southwestern United States (upper Moenkopi et al., 1994; Mietto and Manfrin, 1995] show differences formation[e.g., Helsley and Steiner,1974; Baag and Helsley, both in the content and scope of the recognized 1974;Elston and Purucker,1979; Lienert and Helsley, 1980; biostratigraphiczones. Consequently,the Ladinian may Puruckeret al., 1980; Molina-Garza et al., 1991, 1996]) and either contain six ammonoid zones (with the inclusion of the from Spain[Turner et al., 1989]. Thesedata were obtained Reitzi zone [Kozur, !995]), five zones (beginningwith the from continentalsediments (red beds)where biostratigraphic Nevaditeszone [Krystyn, 1983]) or four zones (beginning controlis generallypoor. And becausethe constructionof a with the Curionii zone [Brack and Rieber, 1994; Bucher and Orchard, 1995]). In this study we will use the secondvariant which correspondsto possibilityB suggestedby Brack and Copyright1998 by the American Geophysical Union. Rieber(1994). In this way, the baseof the Ladinianis marked Papernumber 97JB02155. by the onset of the Nevadites secedensiszone and 0!48.0227/98/97JB.02155509.00 approximatesclosely to the appearanceof the conodont 605 606 GALLET ET AL.: MAGNETOSTRATIGRAPHY FROM NORTHERN CALCAREOUS ALPS Paragondolellatram/neri [see Krystytz, 1983; Nicora and modified by introducing the Secedensis zone, and also Brack, 1995; Muttoni et al., 1997]. The Lower Ladinian stratigraphically by shifting beds 10 and 11 from the contains two ammonoid zones (the Fassanian1 and 2 zones) Archelauszone downwards to the Gredlerizone (Figure 1). The andthe UpperLadinian three zones (the Longobardian 1 to 3 reasonfor this revisionis the discoveryof a Protrachyceras zones). gredleri specimenin bed 10. Bed 11 lacks diagnostic The three Ladinian sectionsanalyzed in this study come ammonoids but it has identical lithology and microfaciesas from the Reifling formationwhich is apparentlydevoid of the underlying levels 10 and 9. The other changesin ammonoids but contains rich conodont faunas. The latter have conodont faunas concern Paragondolella excelsa (Last been grouped into six intervals and have been OccurrenceDatum [LOD] in bed 6/3), P. inclinata (First chronostratigraphicallyfixed by conodont-basedcorrelations Occurrence Datum [FOD] in bed 7), the introduction of with the ammonoid-rich sections of Epidaurus (Greece) and Budurovignathus longobardicus from beds 13 to 17 andthe Bagolino(Northern Italy). However,the chronostratigraphy removal of Gondolalla cf bakalovi (see commentof Kovacs of the Epidaurussection needs to be reconsideredbecause [1994]). Within the Upper Fassanian,the former Hungatica additional ammonoid and conodont faunal data collected in zonehas been renamed for P. excelsain orderto avoidany 1994 provided new stratigraphic constraints (Figure 1) furtherconfusion with the originalscope of this zone[Kozur, [Krystyn, 1983]. The ammonoid zonation is nomina!y •980]. FASSANIAN LONGOBARDIAN • • ! ß • , • • • , •" z z •' • ' • • i • m o I • • • ½ • • m m • • % • • • • • • g • bed hr. I I• I ., i..... I .....III I I , 1"1 tramtoefl excelsa incl. mung. Iongobard. diebell ................. • P, trammeri •i I P, excelsa • • P. Iiebermanni • P. inclinata -- . • B. /apontcus• B, Iongobardicus I i i • • •B. mungoensis I I ' II IIIIiIII II II I I I I • • • B. diebeli I I ! • • • B. mostleri I I i ! .............. I ,, I ......... I ,, ! .... P. excelsa !• I• M. .....t=dp ole N. pseudoionga • P. inclinata I ! i • B. hungaricus • N. transira • • B. m ungoensis m I• N. praehungarica• B. Iongobardicus • I • • Z i• •i i• B. diebell i P, trammeri i mostleri iI I! iI G. malayensis I I I I I I IIIIIII II I I ! I I ß ,,,,i .................... I ,,, i .......... pseud, transita incl. mung. Iongobard. diebeli ......................... Figure 1. Ladinian biochronologyused in this study. GALLlETET AL.: MAGNETOSTRaTIGRAPHYFROM NORTHERN CALCAREOUS ALPS 607 Many sectionsof the Reifiing basincontain three distinct three major tuffaceous intervals which are located in the well- tuffaceouslayers with a light grey to greenishprimary and known Bagolinosection at 61 m, between70 and 75 m and 84- .,,ellowishweathering secondary color. These layers probably 88 m, respectively[Bracl, et al., 1995]. Accordingto Nicora representaltered pietra verde. They have been numbered as T1, and Brack [1995], these intervals fit closely in age •ith the T2 and T3 in our sectionsand are interpretedas geologically three Reifling basin layers. isochronousand therefore chronostratigraphic marker beds. Tephrochronologythus provides an independenttool to constrainthe adopted correlationsbased on conodontsand to GeologicalSetting, Lithology and Sampling establish long-distance time relationships with other tuff- bearingLadinian sections of the Alpine region.In particular, Kozttr and Mostlet' [1971] described a section from the The studied sections are located in the eastern part of the Nemesvamos formation (Koeveskal, Balaton Highland, Northern Calcareous Alps, within the so-called Bajuvaricum Hungary)with two distincttuffaceous intervals at 7.5 and 11.5 mega-unit. This unit consists of a series of north vergent m which may correspond to the T2 and T3 layers of the nappesstacked between the Cretaceousand the early Cenozoic Reifling basinaccording to the conodontdata. The T2 and T3 [e.g., Tollmann, 1976]. Two of the sampling sites, the layersmay be also identifiablein Reifiinglimestones from the Mendlingbachand Gamssteinsections, are