Previous Next Tübinger Geowissenschaftliche Arbeiten, Series A, Vol. 52, pp. 95 – 104.
Abstracts of the 4th Workshop on Alpine Geological Studies, Tübingen 21-24 Sept. 1999

BLOCK PRESENTATION B087

 

Tectonostratigraphic concept for the Juvavic Domain

Hans-Jürgen Gawlick* 1, Leopold Krystyn 2, Richard Lein 3, Gerhard Walter Mandl 4


 1 

Montanuniversität Leoben, Institut für Geowissenschaften Prospektion und Angewandte Sedimentologie

 2 

Institut für Paläontologie, Geozentrum, Universität Wien

 3 

Institut für Geologie, Geozentrum, Universität Wien

 4 

Geologische Bundesanstalt, Austria

 * 

Correspondence:  Peter-Tunner-Straße 5, A-8700 Leoben, Austria (Hans-Juergen.Gawlick@unileoben.ac.at)

 

Viewed from its plate tectonic background the Permo-Triassic Tethys represents the transition phase from the Palaeotethys to the Neotethys Ocean. Its evolution is characterized by new seafloor spreading north of Gondwana with synchronous subduction along Eurasia (Fig.1). Two fundamentally different Triassic Tethys margins are the important result of this history, a narrow active Eurasian to the north resp. northeast and a wide passive Gondwanian along the southern and western shore. The turning point between active and passive margin was located close to the Tornquist line. From there the narrow eastern margin widened westward considerably and developed/opened into a broad shelf with its greatest width in the Dinaric and Hellenic sector (Fig.1). One argument for the palinspastic restoration of the presently completely dismembered "microplates" of the Alpin-Moesian segment is therefore the width and facial development of their respective shelves (Krystyn, this volume).

Austria´s Northern Calcareous Alps have formed together with the Carpathians, the Southern Alps and the Dinarids an up to 300 km wide and approximately 700 km long shelf strip at the western Tethys end (Fig. 1). Along this as well as other parts of the Tethyan passive margin, distinct belts of marine sedimentation have been arranged in a characteristic shore parallel fashion. They often have been illustrated by classical Upper Triassic Alpine sedimentary environments (Haas et al. 1995). The first and nearshore zone was the Keuper belt as deposition site of hypersaline or extreme shallow marine siliciclastics (Lower/Middle Austroalpine). Seaward followed broad Hauptdolomit and Dachstein carbonate platforms (Bajuvaricum, Tirolicum) flanked by reefs towards open shelfbasins. The Dachstein reefs (Juvavicum p.p.) produced large masses of skeletal and non-skeletal detritus which were deposited mostly along the platform margins and on the attached basin floors. Further offshore only a small amount of periplatform mud reached as reduced sediment supply the pelagic Hallstatt facies belt (Juvavicum p.p.). The later now is generally regarded as evidence for a contiguity of an oceanic realm and is used as a tool for delineating the Gondwanian margin towards the deep sea of Tethys.

The Jurassic opening of the Central Atlantic Ocean with its continuation into the Penninic Ocean leads to a new Mediterranean plate configuration. The Apulian plate is formed and its northern Alpine-Carpathian segment is initially dismembered by transform faults (Fig. 1) into several crustal blocks with strongly differing later tectonic history (e.g. Tisza, Moesia). Successive spreading of the Ligurian-Penninic Ocean is mirrored by the closure of parts of the Neotethys Ocean ("Pindos-Vardar-Meliata") resulting in an early deformation of the Juvavic shelf in Late Jurassic time (Fig. 3). The Iberia-Adria-Zone (IAZ - Fig. 1) characterizes a missing fragment between the Southern Alps and the Austroalpine. In late Upper Triassic and Jurassic times lateral movements may have started in the area between the IAZ and the AAT.

Compared with the simple palaeogeographical model, the present configuration of the tectonized fragments (Fig. 2) of this shelf is rather complicated and reason for many long lasting controversies. One of the crucial points in any palinspastic reconstruction of the Northern Calcareous Alps is the question of the original relationship between the Tirolic and the Juvavic domains. An original neighbourhood within one facies belt (Dachstein Facies) as suggested by Spengler (1951) and Tollmann (1985) is in discussion as well as a separation of Tirolicum and Juvavicum by a basinal zone like in the northern Dinarids, well-known there as Slovenian trough (Krystyn et al. 1994). Recently detected sequences of a peculiar Middle to Late Triassic basinal facies incorporated as small tectonic slices between the Tirolicum and the Juvavicum in the southeastern part of the Northern Calcareous Alps could be interpreted as remnants of such a basin (Lein, this volume). In any case, the Tirolicum and Juvavicum are part of one and the same shelf (one shelf model). Recently Neubauer (1994) and Schweigl and Neubauer, (1997) proposed the origin of the Juvavic nappes from a different (i. e. opposite) shelf with an ocean in between (dual shelf model). Neubauer´s view is in contradiction to the well known Triassic facies polarity of the Juvavic nappe system (Mandl, this volume), which is in general orientated toward the open Tethys in the "south". Therefore this model has to be rejected strictly.

In Early Jurassic times most of the NCA has formed a pelagic plateau ontop of the drowned Upper Triassic carbonate platform. Subsidence continued without significant sediment supply (Böhm 1992). The Middle Jurassic is a period of widespread omission, as shown by strongly condensed red limestone sequences and widespread ferromanganese crusts. Starting in late Early Jurassic times parts of the Alpine-Carpathian region have been affected by a transtensional tectonic regime related to the rifting in the Penninic realm. Horst/Graben-structures with associated breccias have been formed.

The sedimentation pattern in the Alpine-Carpathian region changed around the Middle/Late Jurassic boundary (Callovian-Oxfordian). The geodynamic history is characterized by a tectonic regime that differed from that of the Early to Middle Jurassic period, explained by Tollmann (1981) and Faupl (1997) in different ways. Significant sedimentation started with the deposition of radiolarian chert (Ruhpolding Formation) and the formation of new, elonate W-E striking, basins. The onset of radiolarien chert in this basins was generally attributed to Late Oxfordian, based mainly on ammonite biostratigraphy.

New investigations however are showing the existence of two radiolarite basin types partly formed in sequence indicating migration of tectonic activity: an older one (Lammer Basin and equivalents - Early Callovian to Middle/Late Oxfordian = Strubberg Formation) containing mass flows and slides originated from the former Juvavic shelf and a younger one (Tauglboden Basin and equivalents - Late Oxfordian to Early Tithonian = Tauglboden Formation) containing mass flows and slides originated from nearby (Tirolic) topographic rises. The basins may be interpreted as trenches in front of advancing nappes (= rises) as a result of the partially closure of the Tethys Ocean (Gawlick et al. 1999). By this the radiolarite succession (Ruhpolding Formation) in the southern and central parts of the Northern Calcareous Alps can be subdivided in an older (= Strubberg Formation - Callovian to Oxfordian; Gawlick and Suzuki 1999) and a youger (= Tauglboden Formation - Late Oxfordian to Early Tithonian, Gawlick et al., this volume) sedimentary succession.

Thrusting along the southern margins of the Lammer-/Strubberg Basin and the Tauglboden Basins occurred in sequence, i. e. respectively during the earlier and later times of radiolarian chert deposition. The consecutive destruction of the continental shelf and the thrust sequence indicates that tectonic movements have prograded from the oceanic Meliata realm and the Juvavic shelf area towards the interior of the NCA (Fig. 3, phase 1-3). The Juvavicum attains the overall structure of a tectonic melange formed originally by sedimentary processes which have been later overprinted by thrust tectonics. During the first displacement and a gravitative controlled lateral transport of Juvavic blocks and "nappes" some of these sliding masses (e.g. Ischl-Aussee Unit) have been rotated (visible in palaeomagnetic data, Gilder et al., this volume) and show an inverse facies polarity. Thrusting and subduction burial, which was predating the gravitational transport of Juvavic units, is interpreted as a reason for partly high pressure metamorphism in certain tectonic slices of the Juvavicum (Gawlick and Höpfer, this volume), whereas large parts near the southern rim of the Northern Calcareous Alps have been subjected to temperatures corresponding to low-grade metamorphism (Gawlick et al. 1994). Metamorphism occurred mainly contemporaneously with the deposition of the earlier radiolarian chert. The pressure conditions of this early metamorphism near the southern rim of the Northern Calcareous Alps are unknown because of a younger overprint (Gawlick et al., this volume).

The tectonic structures (basin and rise formation), which are related to the closure of the Tethys Ocean, are sealed by latest Jurassic pelagic and shallow-water carbonates representing a period of tectonic quiescence. The sedimentary sealing gives an upper time constraint for this tectonic event (Fig. 3). The higher parts of the Oberalm Formation (Late Tithonian) uniformly spread over the former basin-and-rise morphology. The latest Jurassic - Neocomian phase of tectonic quiescence was followed locally by additional thrusting and siliciclastic flysch sedimentation (Fig. 3: phase 4).

From a general point of view during Permotriassic to Early Jurassic times the Alpine-Carpathian region has been part of the Pangaean continental margin, which was flanked by the Tethys Ocean and which shows facies polarity orientated toward the southeast. The Penninic rifting/spreading and the subsequent closure of the Alpine-Carpathian sector of the Tethys ocean has changed this polarity completely. Beginning with the Upper Jurassic syntectonic clastics and the "neoautochthonous cover" the facies polarity is orientated toward northwest; e.g. Upper Jurassic reefs and platform carbonates are frequent above Juvavic units, whereas in the Tirolic, Bajuvaric and Central Alpine realms deepwater carbonates (Oberalm Lst., Aptychus Lst.) are prevailing. This new palaeoslope direction continues in principle during Cretaceous into Early Tertiary times.

 

 

Böhm, Florian , 1992,  Mikrofazies und Ablagerungsmilieu des Lias und Dogger der Nordöstlichen Kalkalpen. Erlanger geol. Abh., 121:55-217.

Faupl, P. , 1997,  Austria. in Moores, E.M. ,   Fairbridge, R.W., Encyclopedia of European and Asian Regional Geology, 51-63, Chapman and Hall, London.

Gawlick, Hans-Jürgen ,   Frisch, Wolfgang ,   Vecsei, Adam ,   Steiger, Torsten ,   Böhm, Florian , 1999,  The change from rifting to thrusting in the Northern Calcareous Alps as recorded in Jurassic sediments. Geol. Rdschau., 87:644-657.

Gawlick, Hans-Jürgen ,   Krystyn, Leopold ,   Lein, Richard , 1994,  CAI-Paleotemperatures and metamorphism in the Northern Calcareous Alps - a general view. Geol. Rdschau., 83: 660-664.

Haas, János ,   Kovács, Sándor ,   Krystyn, Leopold ,   Lein, Richard , 1995,  Significance of Late Permian - Triassic facies zones in terrane reconstructions in the Alpine - North Pannonian domain. Tectonophysics, 242:19-40.

Gawlick, Hans-Jürgen ,   Suzuki, Hisashi , 1999,  Zur stratigraphischen Stellung der Strubbergschichten in den Nördlichen Kalkalpen (Callovium – Oxfordium). N. Jb. Geol. Paläont. Abh., 211: 233-262.

Krystyn, Leopold ,   Lein, Richard ,   Schlaf, Jürgen ,   Bauer, Franz, K. , 1994,  Über ein neues obertriadisch-jurassisches Intraplattformbecken in den Südkarawanken. in Lobitzer, Harald ,   Császár, Géza ,   Daurer, Albert, eds., Jubiläumsschrift 20 Jahre Geologische Zusammenarbeit Österreich-Ungarn, 409-416, (Geol.B.-A.) Wien.

Neubauer, Franz , 1994,  Kontinentkollision in den Ostalpen. Geowissenschaften, 12: 136-140.

Schweigl, J. ,   Neubauer, Franz , 1997,  Structural evolution of the central Northern Calcareous Alps: Significance for the Jurassic to Tertiary geodynamics in the Alps. Eclogae geol. Helv., 90: 303-323.

Spengler, E. , 1951,  Die nördlichen Kalkalpen, die Flyschzone und die Helvetische Zone. in Schaffer, F.X., Hrsg., Geologie von Österreich, 302-413, Wien.

Tollmann, A. , 1981,  Oberjurassische Gleittektonik als Hauptformungsprozeß der Hallstätter Region und neue Daten zur Gesamttektonik der Nördlichen Kalkalpen in den Ostalpen. Mitt. österr. geol. Ges., 74/75:167-195.

Tollmann, A. , 1985,  Geologie von Österreich., Band 2.: 1-710, (Deuticke) Wien.

 

 

 

 

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Figure 1  

Paleogeography of the western Tethys in Late Triassic time (modified after Krystyn and Lein in Haas et al. 1995).

Fig. 1 - Paleogeography of the western Tethys in Late Triassic time

 

Fig. 2 - Geographic position of the juvavic nappe system

 

Figure 2  

Geographic position of the juvavic nappe system in the Upper Austroalpine and Southalpine

 

 

Fig. 3 - Principles of sedimentation and tectonics of the Northern Calcareous Alps

 

Figure 3  

Principles of sedimentation and tectonics of the Northern Calcareous Alps.

 

SUB-BLOCK S091

 

Diagenetic and metamorphic overprint of the Northern Calcareous Alps on the base of Conodont Colour Alteration Index (CAI) data

Hans-Jürgen Gawlick* 1, Leopold Krystyn 2, Richard Lein 3


 1 

Institut für Geowissenschaften, Prospektion und Angewandte Sedimentologie, Montanuniversität Leoben, Austria

 2 

Institut für Paläontologie, Universität Wien, Austria

 3 

Institut für Geologie, Geozentrum, Universität Wien, Austria

 * 

Correspondence:  Peter-Tunner-Str. 5, A-8700 Leoben, Austria (hans-juergen.gawlick@unileoben.ac.at)

 

By means of the conodont colour alteration studies the middle and eastern part of the Northern Calcareous Alps (Fig. 1) can be subdivided mainly into two distinct units with a lateral boundary marked by abrupt changes in the CAI values (Gawlick, Krystyn and Lein 1994): a northern unit (= Tirolicum) with a relatively homogeneous distribution of no or low grade conodont alteration (CAI 1.0-2.0 – the main body of the Northern Calcareous Alps; Fig. 1). The thermal overprint is thought to be relatively young and related to a heat flow from the Tauern crystallisation which influenced partly the southern parts (CAI 2.5-3.0; e. g. the area north of Saalfelden – Fig. 1A). The second part consists of the Juvavic nappe system (Juvavicum) which is distributed along the southern rim of the Northern Calcareous Alps but covers also some northern parts of the Tirolicum. With respect to its CAI distribution the Juvavicum is much more inhomogeneous on a regional as well as local scale with even local CAI inversions (e. g. Hochkönig nappe, Dachstein nappe). The Juvavicum additionally shows distinctly different sets of CAI values: one with weak (CAI 1.0-1.5 – parts of the Dachstein nappe, Berchtesgaden nappe, Proles nappe, Hohe Wand nappe, Hallstatt slides – Fig. 1), one with medium (CAI 4.0-5.0, partly CAI 3.0; e. g. parts of the Dachstein nappe, Schneeberg nappe – Fig. 1) and another with strong alteration (CAI 5.5-6.0, partly CAI 7.0; e. g. Hochkönig nappe, parts of the Dachstein nappe, Mandling unit, Mürzalpen nappe, some Hallstatt slides – Fig. 1) - the highest known thermal overprint measured in the Northern Calcareous Alps. The highest metamorphism (CAI 5.5) is relatively old and transported, since it predates the Upper Jurassic gravity tectonic emplacement of the Juvavicum onto the Tirolicum. The high CAI values of parts of the Juvavic nappe system are expected to be related to tectonic burial in an accretionary wedge formed parallel to the closure of the Tethys Ocean. The low CAI values of the Tirolicum apparently exclude a direct juxtaposition of the two units at time of this early metamorphism. The medium CAI values (CAI 3.0-5.0), especially in the Middle Triassic sediments, may be related to the Permian to Middle Triassic heat flow (Schuster et al., 1998) or to a heat flow from the Tauern crystallisation which influenced the southern parts with original low CAI values because of the continuous south to north and bottom to top decrease of the metamorphism in these nappes.

The otherwise described continuous south to north and bottom to top decrease of the metamorphism within the whole central and eastern part of the Northern Calcareous Alps (Kralik, Krumm and Schramm 1987, Frey, Desmons and Neubauer 1999) as a result of a metamorphic event penetrating the Northern Calcareous Alps from the south (affected by the Tauern crystallisation) cannot be confirmed by the CAI data. A result of the CAI investigations is the discovery of a regionally widely distributed metamorphism within parts of the Juvavicum. Besides areas without any thermal overprint corresponding mainly to the Hallstatt Salzberg-Facies we can distinguish regions with strongly different values - from low ones (CAI 1.0-1.5) to very high ones (CAI 5.5-6.0, partly 7.0). Especially the high thermal values with temperatures of more than 350 °C respectivly 490 °C (rare) cannot be explained solely by the overburden resulting from the known nappe stacking. It seems reasonable to explain this metamorphism as caused through crustal subduction induced by convergence of the Tethys Ocean. Following the present-day configuration, the latter seems to have been situated south of the Juvavicum. Parallel shortening and stacking of the sedimentary cover within an accretionary wedge could have resulted in strongly differing burial depth and heating conditions of the Juvavic domain leading to the extreme CAI values of 5.5-6.0, partly 7.0. Final closure of the Tethys Ocean and initial emplacement of the Juvavicum by gravity tectonics (Lein 1985) have both occured in Upper Jurassic time. The metamorphism therefore should predate the Hallstatt gravity tectonics. These interpretation is compatible with the radiometric ages of the eo-alpine metamorphic event dated by Kralik, Krumm and Schramm (1987) around ±135-150 My. The picture of a close paleogeographic interfingering between the Tirolicum and the Juvavicum as developed in the last decades by several authors cannot be confirmed in the light of the CAI data and its implications. The CAI data points to a much stronger lateral shortening than previously assumed and to an original paleogeographic width of the Juvavic domain of more than 100 km.

 

 

Frey, M. ,   Desmons, J. ,   Neubauer, F. , 1999,  Metamorphic maps of the Alps: Map of Alpine metamorphism.. Schweiz. Mineral. Petrogr. Mitt., 79/1

Gawlick, H.-J. ,   Krystyn, L. ,   Lein, R. , 1994,  CAI-Paleotemperatures and metamorphism in the Northern Calcareous Alps - a general view.. Geol. Rdschau., 83:

Kralik, M. ,   Krumm, H. ,   Schramm, J.M. , 1987,  Low grade and Very Low Grade Metamorphism in the Northern Calcareous Alps and in the Greywacke Zone: Illit-Crystallinity Data and Isotopic Ages.. in Flügel, H.W. ,   Faupl, P. (Eds.), Geodynamics of the Eastern Alps), 165-178

Lein, R. , 1985,  Das Mesozoikum der Nördlichen Kalkalpen als Beispiel eines gerichteten Sedimentationsverlaufes infolge fortschreitender Krustenausdünnung. Arch. f. Lagerstätterforschung. Geol. B.-A., 6: 117-128

Schuster, R. ,   Scharbert, S. ,   Frank, W. , 1998,  Permo-Triassic crustal extension during opening of the Neotethyan ocean in the Austroalpine-South Alpine realm.. J. Conf. Abs., 4: 297

 

Fig. 1 - CAI map of the middle sector of the NCA

 

Figure 1  

Simplified CAI map of the middle sector of the NCA. Partly modified after Gawlick, Krystyn and Lein (1994).

Fig. 2 - CAI map of the eastern sector of the NCA

 

Figure 2  

Simplified CAI map of the eastern sector of the NCA. Partly modified after Gawlick, Krystyn and Lein (1994).

SUB-BLOCK S088

 

Middle to Late Jurassic Basin and Rise formation due to the closure of the Tethys Ocean

Hans-Jürgen Gawlick* 1, Wolfgang Frisch 2, Adam Vecsei 3, Torsten Steiger 4, Florian Böhm 5


 1 

Institut für Geowissenschaften, Prospektion und Angewandte Sedimentologie, Montanuniversität Leoben, Austria

 2 

Institut für Geologie, Universität Tübingen, Germany

 3 

Geologisches Institut, Universität Freiburg, Germany

 4 

Institut für Geologie, TU Bergakademie Freiberg, Germany
 5  GEOMAR, Forschungszentrum für Marine Geowissenschaften, Kiel, Germany

 * 

Correspondence:  Peter Tunner Strasse 5, A-8700 Leoben, Austria (Hans-Juergen.Gawlick@unileoben.ac.at)

 

Basin and facies analysis, fossil dating, and the study of the metamorphism in the Middle to Late Jurassic sedimentary successions in the central part of the Northern Calcareous Alps allow to reconstruct the tectonic evolution in the area between the South Penninic Ocean in the northwest and the Tethys Ocean in the southeast. Several hypotheses have been proposed to explain the late Middle to early Late Jurassic tectonic phase, which was associated with the formation of asymmetric basins, large-scale sliding, halokinesis, and basin inversion by transtension-induced rifting due to the opening of the Penninic Ocean. In contrast to current models, which propose an extensional regime for the central and eastern Northern Calcareous Alps in the Late Jurassic, we propose a geodynamic model with a compressional regime related to the Kimmerian orogeny.

The Early and Middle Jurassic sediments were deposited in a rifted, transtensive continental margin setting. The sedimentation pattern dramatically changed around the Middle/Late Jurassic boundary. Significant sedimentation resumed with the deposition of radiolarian chert (Ruhpolding Fm.), present in all parts of the studied transect.

Around the Middle/Late Jurassic boundary two trenches in front of advancing nappes formed in sequence in the central part of the Northern Calcareous Alps. First several trenches formed in the south and then further trenches formed in the north. The southern trenches (Lammer Basin and equivalents - Callovian to Middle Oxfordian) accumulated a thick succession of gravitatively redeposited sediments (coarse breccias and slides) derived from the sedimentary sequences of the accreted Triassic-Liassic Hallstatt Zone (deposited on the outer shelf) and the margin of the Late Triassic carbonate platform. In an early stage, these sediments derived from sequences deposited on the more distal shelf (Salzberg facies zone of Hallstatt unit, Meliaticum), in a later stage from more proximal parts (Zlambach facies zone of Hallstatt unit, Late Triassic reef belt). Some Hallstatt limestone units, which experienced low temperature - high pressure metamorphism before redeposition, indicate deep burial by subduction in Late Jurassic times.

In the northern trenches (Tauglboden Basin and equivalents - Late Oxfordian to Early Tithonian) several hundred meter thick sediments accumulated, including redeposited material from a near-by topographic rise. This rise (Trattberg Rise) is interpreted as an advancing nappe front as a result of the subduction process. The basins and the rise, which are related to the closure of parts of the Tethys Ocean, are sealed by latest Jurassic pelagic and shallow-water carbonates representing a period of tectonic quiescence. The sealing by Tithonian sediments (Oberalm Fm.), gives an upper time constraint for the tectonic events.

Our conclusions appear to be of general validity for a large part of the Northern Calcareous Alps, although detailed investigation is still lacking in most of these basins. Our results show that an important orogenic event occurred in Late Jurassic time. In a greater geodynamic context, an important contractional event due to the closure of parts of the Tethys Ocean occurred in about Late Jurassic times in a vast region stretching from the European Alpides to southeast Asia. This event is known since long as the "Kimmerian orogeny" and infers a similar pattern of plate movements along the entire orogenic belt.

 

 

Gawlick, Hans-Jürgen , 1996,  Die früh-oberjurassischen Brekzien der Stubbergschichten im Lammertal - Analyse und tektonische Bedeutung (Nördliche Kalkalpen, Österreich). Mitt. Ges. Geol. Bergbaustud. Österr., 39/40: 119-186.

Gawlick, Hans-Jürgen ,   Frisch, Wolfgang ,   Vecsei, Adam ,   Steiger, Torsten ,   Böhm, Florian , 1999,  The change from rifting to thrusting in the Northern Calcareous Alps as recorded in Jurassic sediments.. Geol. Rdschau., 87: 644-657.

 

Fig. 1 - facies distribution of central NCA in Late Triassic

 

Figure 1  

Profiles showing facies distribution of central NCA in Late Triassic and tectonic destruction of Tethys continental margin by thrusting and redeposition in Late Jurassic times (Gawlick et al. 1999). Tectonic destruction occurred in a piggy-back manner, but a high-pressure - low-temperature metamorphic slab (4 LT-HP) became exposed by out-of-sequence thrusting. Sediments redeposited during an early stage were again reworked during later stages of the thrusting process.