Previous Next Tübinger Geowissenschaftliche Arbeiten, Series A, Vol. 52, pp. 86 - 92.
Abstracts of the 4th Workshop on Alpine Geological Studies, Tübingen 21-24 Sept. 1999

BLOCK PRESENTATION B025

 

 

The Alpine segment of the Triassic Tethys margin – a paleogeographic and geodynamic overview

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


 1 

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

 2 

Institut für Paläontologie, Universität Wien, Austria

 3 

Institut für Geologie, Universität Wien, Austria

 4 

Geologische Bundesanstalt, Austria

 * 

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

 

 

SUB-BLOCK S147

 

The northwestern margin of the Triassic Tethys – an overview

Leopold Krystyn* 1


 1 

Institut für Paläontologie, Universität Wien, Austria

 * 

Correspondence:  Geozentrum Althanstraße 14, A-1090 Wien, Austria (leopold.krystyn@univie.ac.at)

 

Parallel to the collision of the two landmasses of Gondwana and Laurussia in late Paleozoic time the Tethys was born as an elongated ocean of more than 10.000 km length and about 3.000 km width. The early (Permo-Triassic) evolution of the Tethys Ocean has a remarkable plate tectonic history. Within its proper limits a so-called Neotethys ocean (crust) was created on the expense of the Palaeotethyan one (Gawlick et al., this volume, fig. 1). New seafloor spreading south of the north drifting Gondwana-fragmented Cimmerian blocks have led to the subduction of the Palaeotethys Ocean beyond Laurasia (Sengör 1984, Stampfli et al. 1991). Two fundamentally different Triassic Tethyan margins are the important result of this tectonic history – a narrow active margin to the north resp. north-east (= A in Gawlick et al., this volume, fig. 1) and a wide passive one along the southern and western shore (= P in Gawlick et al., this volume, fig. 1).

During the Triassic sea level reaches an all time low and the earth is generally recognised as having a warm and extremely arid climate indicated by the extensive deposition of evaporites far from the equator (Habicht 1979). Uniform tropical condition have therefore prevailed in the Tethys ocean with 25-30°C sea surface temperatures. Bottom water temperatures must have been well above 10°C if the assumption of an island barrier diminishing bottom water exchange between Tethys and Panthalassa ocean is correct. All these points may explain the high degree of facies similarities as well as of lateral continuity of facies zones along the passive Tethys margin.

Austria’s Northern Alps formed together with the Carpathians, the Southern Alps and the northern Dinarids an up to 500 km wide and up to 700 km long shelf strip at the western Tethys end. Along this as well as other parts of the Tethyan passive margin belts of marine sedimentation were arranged in a characteristic shore parallel fashion. The first and near shore zone was the Keuper-belt as deposition site of hypersaline or extreme shallow marine siliciclastics. Seaward followed broad Dachstein carbonate platforms of flanked by reefs towards open shelf basins. The Dachstein reefs produced large masses of skeletal and non-skeletal carbonate 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. The latter now is generally regarded as evidence for the contiguity of an ocean and is used as tool for delineating the Gondwanian margin towards the deep sea of Tethys.

The eastern end of the Dinaric-Carpathian shelf was facing the current Moesian plate which on the other hand was at the transition from the passive to the active Triassic Tethys margin (Besse et al. 1998, Banks and Robinson 1997). My geodynamic argument for the palaeogeographic reconstruction of the Dinaric-Carpathian realm is therefore the width and facial differentiation of the respective shelf areas. Based on an Upper Triassic facies map (Gawlick et al., this volume, fig. 1) the western Tethys shelf is widest (at least 500 km) in the South Alpine-Dinaric transect due to an extreme wide shallow water carbonate platform (Dolomia principale/Dachsteinkalk). This shelf is considerable narrower but still wide (300 to 200 km from west to east) in the Austroalpine segment. The abrupt change in shelf width between Southern and Northern Alps is noteworthy and is a plausible argument for the assumption of a relatively broad missing zone between the two areas (see Gawlick et al., this volume, fig. 1). In the West Carpathians remnants of the outer shelf zone (Juvavicum) are very small and are characterized by a widespread Upper Triassic drowning phase. This is interpreted as major hint for a narrower shelf compared with the NCA. The Tethys margin of the Tisza block is recorded in the Apuseni mountains where unique Upper Triassic sequences demonstrate a still more reduced shelf area. In the Austroalpine the Keuper belt and the deeper marine Juvavic facies belt are well separated by the more than 100 km wide Hauptdolomit/Dachsteinkalk carbonate platform (Bajuvaricum/Tirolicum). On Tisza the later must have been considerable reduced because the proximal nappes show vertical successions of Upper Triassic basinal sequences at the base with Keuper on top and just a thin carbonate platform interval in between. The Tisza margin could therefore represent the transit stage to the active margin where there was no more space for a carbonate platform between coast and slope. The same is characteristic from Moesia eastwards and should not be climatically controlled because Upper Triassic reefs are known still in the Pamirs, well above 40° palaeonorth (Besse et al. 1998).

Another support for the palaeogeographic reconstruction may be found in palaeoclimate. The margin of the Dinaric-Carpathian segment was approximately SW-NE directed and covered a latitudinal range of about 20° to 30° north. This is well within the tropical belt but the region could have been sensitive to differences in the amount of precipitation and / or of monsoonal climate documented in the sedimentary record. This topic is presently not well understood and should become more important in the future. Some respective examples from carbonate as well as terrigenious facies environments will be discussed. They all demonstrate a sudden palaeoclimatic change from the Dinaric to the Austroalpine sector with a clear northern affinity of the Hungarian Mid-Transdanubian Range (Schwarzacher and Haas 1986). No convincing palaeoclimatic evidence is unfortunately present concerning the internal palaeogeographic architecture of the sector north of the Alpine-Dinaric lineament.

 

 

Banks, C.J. ,   Robinson, A.G. , 1997,  Mesozoic strike slip back-arc basins of the Western Black Sea region. in Banks, C.J. ,   Robinson, A.G., eds., Regional and petroleum geology of the Black Sea and surrounding region, AAPG Memoir, 58:53-62.

Besse, J. ,   Torq, F. ,   Gallet, Y. ,   Ricou, L. ,   Krystyn, L. ,   Saidi, A. , 1998,  Late Permian to Late Triassic palaeomagnetic data from Iran: Constraints on the migration of the Iranian block through the Tethys ocean. Geophys. Journ. Int., 135:77-92.

Bleahu, M. ,   Lupu, M. ,   Patrulius, D. ,   Bordea, S. ,   Stefan, A. ,   Panin, S. , 1981,  The structure of the Apuseni Mountains. XII Congress Carpatho-Balkan Geol. Ass. Guide book series, 23, 106 p.

Habicht, J.K.A. , 1979,  Paleoclimate, paleomagmatism, and continental drift. AAPG Studies in Geology, 9, 31 p.

Schwarzacher, W. ,   Haas, J. , 1986,  Comparative statistical analysis of some Hungarian and Austrian Upper Triassic Teritidal Carbonate sequences. Acta Geol. Hung., 29:175-196.

Sengör, A.M.C. , 1984,  The Cimmeride orogenic system and the tectonics of Eurasia. Geol. Soc. Amer. Spec. Pap., 195, 82 p.

Stampfli, G. ,   Marcoux, J. ,   Baud, A. , 1991,  Tethyan margins in space and time. Palaeogeography, Palaeoclimatology, Palaeoclimatology, 87:373-409.

Wilson, K.M. ,   Pollard, D. ,   Hay, W.W. ,   Thompson, S.L. ,   Wold, C.N. , 1994,  General circulation model simulations in Triassic climates: preliminary results. in Klein, G.D., ed., Pangea: Palaeoclimate, tectonics and sedimentation during acretion, zenith and breakup of a super continent, Geol. Soc. Amer. Spec. Pap., 288: 91-116.

 

 

SUB-BLOCK S092

 

Triassic depositional realms of the Juvavic domain (Northern Calcareous Alps, Austria)

Gerhard Walter Mandl


  

Geologische Bundesanstalt, Austria
  Correspondence:  Rasumofskygasse 23, A-1031 Wien, Austria (gmandl@cc.geolba.ac.at)

 

The Triassic sediments of the Northern Calcareous Alps have been deposited on a wide shelf area between the European hinterland and the Tethys ocean. This shelf has been destroyed by multiple nappe stacking during Alpine orogeny (Upper Jurassic to Tertiary). The uppermost tectonic unit - the Juvavic nappe system - exhibits sediments of various facies from the outer shallow shelf and adjacent deeper shelf areas:

"Middle Triassic": Wetterstein Interval (Upper Pelsonian - Lower Julian); platform, margins, intraplatform basin

1 Wetterstein Facies; interior of carbonate platform, lagoonal subfacies.

2 Wetterstein Facies; carbonate platform, marginal reef subfacies.

3 "Northern" slope facies; facing toward restricted intraplatform basin; reef debris.

4 Grafensteig Facies; restricted intraplatform basin; bedded black limestones, containing distal turbidites of platform origin; connecting seaways to open marine realm are not preserved; central parts of basin may persist into Upper Triassic (Carnian shales; Norian sediments are not preserved).

5 "Southern" slope facies; reef debris interfingering with open marine pelagic carbonate mud facies.

6 Distal "southern" slope facies; pelagic variegated carbonate mud facies mixed with finegrained platform derived debris.

7 Margin of basinal facies; grey limestones with chert nodules and intercalated carbonate turbidites.

Upper Triassic: Reingraben and Dachstein Interval (Upper Julian to Rhaetian); platform, margins, drowned platform

Middle- and Upper Triassic carbonate platforms are separated by the Reingraben event (sealevel fall). Platforms emerged; locally bypassing siliciclastics (mainly shales) reached the remaining basinal areas, onlapping the former Wetterstein platform slopes. Sealevel rise during Upper Carnian initiated a next platform growth:

8 Dachstein Facies; carbonate platform, cyclic bedded lagoonal subfacies; toward north transition into intertidal Hauptdolomit.

9 Dachstein Facies; carbonate platform, marginal reef subfacies situated above Wetterstein reef, facing toward Hallstatt deeper shelf.

10 Mitteralm Facies; Dachstein carbonate platform, backstepped margin above drowned interior of Wetterstein platform, facing toward Aflenz intraplatform basin.

11 Tonion Facies; backstepped platform like 10, separeted from drowned Wetterstein platform by pelagic Mürztal facies; platform progradation during Upper Norian, older parts of platform are not preserved.

12 Hohe Wand Facies; backstepped platform, prograding during Upper Norian over red Hallstatt limestone facies and reaching again a reef position above Middle Triassic platform margin.

13 Gosausee Facies; (distal) slope toward Hallstatt deeper shelf; carbonate turbidites of platform origin interfingering with pelagic grey mud facies (Pötschen facies).

14 Aflenz Facies; intraplatform basin over drowned Wetterstein platform; connection into a persisting depression above Middle Triassic intraplatform Grafensteig Facies questionable (sediments eroded).

15 Mürztal Facies; variegated pelagic limestones on "pelagic plateau" of drowned Wetterstein platform; transitions to Aflenz facies are not preserved (eroded).

Middle- and Upper Triassic (Upper Pelsonian to Rhaetian) in basinal facies, Hallstatt deeper shelf

16 Pötschen Facies; basinal realm of Hallstatt deep shelf,; bedded grey limestones with chert.

17 Siriuskogel Facies; few occurences of massive grey pelagic limestone, depositional site questionable.

18 Salzberg Facies; variegated Hallstatt limestones s. str.; intrabasinal rises due to synsedimentary diapirism of Permian evaporites and/or tectonics (mobile shelf margin) are the reason for reduced sedimentation, condensed sequences, block tilting and fissure fillings.

The Upper Triassic sedimentary history was terminated by increasing input of terrigenious material, in the Juvavic realm represented by the Zlambach Formation, covering the basinal areas as well as the platform slopes. In basinal areas the terrigenious input continued into the Jurassic (Allgäu Formation), drowned platforms became covered by pelagic red limestones (Hierlatz-, Adnet Formation).

 

 

 

Fig. 1 - Facies reconstruction of the Juvavic domain

 

Figure 1  

Middle- to Upper Triassic facies reconstruction of the Juvavic domain.

 

 

SUB-BLOCK S093

 

The Meliata Unit – a connecting link between the Eastern Alps and the Western Carpathians

Gerhard Walter Mandl


  

Geologische Bundesanstalt, Austria
   Correspondence:  Rasumofskygasse 23, Postfach 127, A-1031 Wien, Austria (gmandl@cc.geolba.ac.at)

 

The Northern Calcareous Alps (NCA) and the Inner Western Carpathians (IWC) are showing comparable features in stratigraphy and facies as well as in tectonic structures.

Recently the Meliata equivalents discovered in the NCA are palaeontologically proved only at two localities near the southeastern margin of the NCA - at the Florianikogel and within the Ödenhof window. Additional occurences are shown without explanation in Schweigl and Neubauer (1997), Fig.1. The sequence exhibits an association of Middle Jurassic terrigenious sediments and carbonatic to siliceouse rocks of Triassic age. The latter group is interpreted as various sized olistolites in a Jurassic matrix. The matrix consists of greenish-grey cherty shales changing upward into dark grey shales with increasing finegrained sandstone content. The olistolites contain large masses of crystalline white limestone (?Anisian; locally breccias within the Ladinian radiolarite contain cm-sized components of this limestone), pebbles of pelagic Lower and Middle Anisian limestones, blocks of Ladinian red radiolarite and silicified red filament limestone and a few Carnian dark cherty shales and Norian grey limestone - for stratigraphical and micropalaeontological details see Mandl and Ondrejickova , 1991, 1993, Kozur and Mostler, 1992. According to variability of Conodont Color Alteration Indices (CAI= 3 to 7) the Triassic olistolites underwent different thermal overprint before redeposition into their Jurassic matrix. The overall appearance corresponds very well with the current knowledge of the Meliaticum in the IWC - Kozur, Mock and Ozvoldova, 1996. Magmatic rocks within the sedimentary Meliata sequence of the NCA are known only as small fragments of serpentinites in thin sections. Meter-sized blocks of basic to ultrabasic rocks (alterated basalts, gabbros, serpentinites) occure within Upper Permian evaporites of the Juvavic nappes near to their basal tectonic plane. Due to missing geochronological and palaeontological data there is no common agreement about the origin of these rocks. Observations within the Hallstatt salt mine point at synsedimentary (Upper Permian) intercalations of basalts and tuffs within the evaporites. In contrast equivalents in Hungary are associated with Ladinian red radiolarite. Therefore they are interpreted as dismembered Triassic ophiolites tectonically incorporated into a salinar melange of Permian evaporites - e.g. Kozur and Mostler, 1992.

Although there exists no common agreement about the geodynamic models of the Western Carpathians, one of this models has been applied to the Eastern Alps - e.g. Schweigl and Neubauer, 1997. Decisive for their model is the tectonic position of the Meliaticum: The Grauwacke Zone (= Gemericum in IWC; Lower Palaeozoic to Carboniferous rocks) and its transgressive cover of Permoskythian siliziclastics is the tectonic deepest element of the Upper Austroalpine nappe pile. The upward following Tirolic unit is thought to be the normal stratigraphic Mesozoic envelope, with only minor tectonical detachment in the Middle and Eastern sector of NCA. In the IWC the Borka unit (exhibiting blueschist metamorphism) is thought by some authors to represent the remnant of the Mesozoic cover of the Gemericum. This basement has been overthrusted during Jurassic times by the Meliata unit and - as the uppermost nappes - by the Juvavicum (= Silicicum in IWC). The recent bottom to top succession of nappes is explained as a former (Triassic) arrangement of a Northern shelf (Tirolicum), an oceanic realm (Meliaticum and Lower Juvavicum) and a southern shelf (Upper Juvavicum). A crucial point, which is not taken into account enough in this model, is the well established facial zonation within the Mesozoic sedimentary sequence of the NCA. It demonstrates very clearly that a "southern" origin of the (Upper) Juvavic nappes is in contradiction to facies polarity especially of the Triassic rocks - e.g. Mandl, this volume.

The geodynamic history of the NCA as well as of the IWC seems to be much more complicate. Based on recent data we can shortly summarize some facts which have to match with a common NCA-IWC model, seen from a NCA point of view: The orientation of facies polarity indicates an origin of all NCA nappes (also including the Juvavic system) from a single "northern" shelf. Transitions to deeper open marine conditions are always facing toward "south". The tectonical detachment of the Triassic to Middle Jurassic shelf sediments from their basement has started about the end of Middle Jurassic. Jurassic syntectonic clastics (see Gawlick, this volume) as well as the sandwich of Juvavic units demonstrate a first displacement from Hallstatt deeper shelf (Pötschen- and Salzberg-Facies) and gravitative transport onto and across the drowned Triassic shallow shelf. Rocks derived from the Meliata oceanic realm should have been mobilized also before oder during this phase. With time the detachment encroached on the Triassic platform margins and at last on the platformes themselves - creating the large "Upper" Juvavic nappes like Dachstein- or Mürzalpen nappe. These large nappes carry tectonical outliers of Hallstatt facies on the one hand, on the other hand they have been transported onto similar Hallstatt outliers, resting in Jurassic basins of the future Tirolic nappes. Such a multiple stacking of triassic rocks of different depositional realms is a common feature of the Juvavicum, the time of stacking is restricted to the Ruhpolding Interval (Lowermost Upper Jurassic). After this first phase of intensive movements a periode of tectonic quiescence lasted until Lower Cretaceous. The Juvavic units became covered by marine Upper Jurassic to Lower Cretaceous carbonate sediments of platform- and basinal facies. A next phase of tectonics mobilized western parts of the Juvavicum again: the Dachstein nappe, the Reiteralm nappe and accompanied Hallstatt outliers have been transported onto the Upper Neocomian clastics of the Roßfeld trough, which contain also ophiolitic detritus (chromite). A subsequent uplift exposed large parts of the Eastern Alps to weathering and erosion before the Upper Cretaceous Gosau transgression. Intra- and Post-Gosau compressional tectonics and Miocene strike slip faults additionally affected the NCA nappe pile.

 

 

Kozur, Heinz ,   Mostler, H. , 1992,  Erster paläontologischer Nachweis von Meliaticum und Südrudabanyaicum in den Nördlichen Kalkalpen (Österreich) und ihre Beziehungen zu den Abfolgen in den Westkarpaten.. Geol. Paläont. Mitt. Innbruck, 18 (1991/92): 87-129.

Kozur, Heinz ,   Mock, R. ,   Ozvoldova, L. , 1996,  New biostratigraphic results in the Meliaticum in its type area around Meliata village (Slovakia) and their tectonic and palaeogeographic significance.. Geol. Palaeont. Mitt. Innbruck, 21:89-121.

Mandl, Gerhard Walter ,   Ondrejickova, A. , 1991,  Über eine triadische Tiefwasserfazies (Radiolarite, Tonschiefer) in den Nördlichen Kalkalpen - ein Vorbericht. Jb. Geol. B.-A., 143/2: 309-318.

Mandl, Gerhard Walter and Ondrejickova, A. , 1993,  Radiolarien und Conodonten aus dem Meliatikum im Ostabschnitt der Nördlichen Kalkalpen (Österreich). Jb. Geol. B.-A., 136/4: 841-871.

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

 

 

 

 

 

 

Fig. 1 - The position of the Meliata Unit

 

Figure 1  

The position of the Meliata Unit in the nappe pile of the Eastern Alps and the Western Carpathians (Slovakian part).