Bajuvarikum

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The Bajuvarikum is a tectonic unit of the Northern Limestone Alps .

etymology

The Bajuvarikum, also known as Bajuvarian blankets or Bajuvarisches blanketing system , is named after the Bavarian Alps - the Latin name for the tribe of the Bajuwars was Baiovarii .

Initial description

The term Bajuvarikum was first introduced into geoscientific literature in 1912 by FF Hahn.

introduction

The tectonic development of the Northern Limestone Alps took place in two main stages. In the period from the late Lower Cretaceous to the Upper Eocene , a north-west-Vergent nappes formed due to transpressive, right-handed shear movements in the orogenic collision wedge of the Eastern Alpine . In the Miocene , crust wedges were then pressed to the east in the central Eastern Alps, which turned the shear movements into their left-handed opposite. Within the nappe stack, three first-order thrust orbits can be distinguished, which use facial transitions in the sediment package and the resulting differences in competence. The interior design of the ceiling stack was mainly determined by existing disturbances .

definition

The Hochfelln is located on the northern forehead of the Lechtal ceiling. The view sweeps from the summit into the Alpine foothills with the Chiemsee .

In the Northern Limestone Alps, which are part of the Oberostalpin , a number of tectonic nappes can be distinguished, some of which also have certain strata sequences. Three main ceilings are separated - the Bajuvarikum in the north, followed by the Tirolikum and the Juvavikum further south.

The Bajuvarikum, for its part, is divided into two ceiling systems - the northern deep bayuvarikum in the lying wall and the southern high bayuvarikum in the hanging wall . The Tiefbajuvarikum is also known as the Allgäu blanket and the Hochbajuvarikum as the Lechtal blanket .

The individual nappes are separated from each other by tectonically incompetent shear horizons, which are mostly designed as ramp-flat structures ( ramp tectonics ). The Permo- Triassic Evaporites (such as the Hasel Mountains , the Alpine Buntsandstein and the Reichenhall Formation ) and rocks of the Werfen Formation act as shear horizons . But also the clays of the Partnach layers interlocking with the Wetterstein limestone , the gypsum- bearing Raibler layers and thin, clay-rich limestone layers in Jura / Chalk can represent mechanical discontinuities. The ramps usually penetrate competent lithologies. Overall, the three ceiling systems reveal an increasing deepening of their sedimentary facies - from the flatter Bajuvarikum to the Tirolikum to the deeper Juvavikum.

description

Cenomanian marginal scale

The Cenoman Randschuppe , also Randcenoman or Kalkalpen-Randschuppe , is wedged between the Allgäu blanket in the south and the flysch zone in the north. It is not included in the Bajuvarikum, but should be mentioned here for the sake of completeness. Although interrupted, but with a significant degree of constancy, the Cenoman edge scale runs along the entire northern edge of the Limestone Alps from Vienna to Bad Hindelang in the west. It represents its own large tectonic, calcareous frontal element under the Allgäu ceiling. This is shown by the fact that this narrow, mostly only several hundred meters wide edge zone is completely independent of the internal structure of the frontal edge of the rest of the deep bayu varicosum. For example, in the Tegernsee mountains and in the Schliersee mountains, one shed element after the other runs diagonally towards the front edge of the Allgäu ceiling. The sediments of the Cenomanian marginal scale cover the period Aptian to Coniacium and are built up from the Tannheim , Losenstein and Branderfleck formations .

Allgäu ceiling

The Allgäu Nappe forms the actual forehead of the Northern Limestone Alps and is pushed in a northerly direction onto the Cenoman marginal scale and the flysch zone of the Penninic . It is particularly strongly scaled or isoclinally folded . Its tectonic interface with the flysch zone is very steep north-verged and only turns into a flatter course at depth.

The Allgäu Nappe was formed about 97 million years ago during the Cenomanium as the deepest and last moving unit of the Bajuvian nappes. It then laid over the Cenomanian marginal scale to the north by 87 million years in the course of the Coniacium.

The Allgäu blanket starts in the west southwest of Oberstdorf and ends 15 kilometers west of Salzburg . After interruptions with smaller deposits near Salzburg, it reappears as Langbath plaice on the Traunsee and east of the Steyr as the Ternberg Nappe . From the Weyerer arches it stretches as the Frankenfelser blanket to the eastern edge of the Alpine Orogen north of Gießhübl .

Lechtal ceiling

Heiterwanger See (front) and Plansee. This is where the synclinory of the Lechtal ceiling begins .

The overlying Lechtal cover shows a more complete Mesozoic layer sequence than the Allgäu cover. Their older strata of the Permoskyth are only exposed at their southern edge. The landscape is dominated by the mighty Triassic carbonate complexes of the Ladinium ( Wetterstein Limestone ) and the Norium ( main dolomite ). In the west of the Lechtal ceiling, shed construction is predominant, but between Lech and east of the Inn there is a gentler hollow and saddle construction .

Most of the post-Triassic sediments, the so-called young layers , have been preserved in the troughs which traverse east-northeast . However, these are removed in axis accumulations by removal.

The Great Muldenzug appears on the northern edge of the Lechtal Nappe , which is in part considerably pushed over to the Allgäu Nappe . The Synklinorium runs to the south - a double hollow with an intermediate saddle that extends from the Plansee in the Ammer Mountains to Ruhpolding in the east. The Wamberger Sattel follows even further south from Garmisch-Partenkirchen to east of Kufstein . The Holzgauer Mulde runs west of the Zugspitze between Lech and Loisach and continues into the Puitental zone . To the east of the Isar , the Karwendel-Mulde appears, which extends through special folds into the Thierseer-Mulde , which is offset to the northeast . The Thierseer-Mulde then dips axially to the north of Kufstein under the Staufen-Höllengebirgs blanket of the Tirolikum, which extends to the northeast , or is crossed by the latter.

The Lechtal ceiling had already pushed itself over the later Allgäu ceiling during the Albium .

Sedimentary content

The Bajuvarikum is characterized by the following sequence of layers (from hanging to lying):

Occurrence

The Parseierspitze , at 3,036 meters the highest peak of the Bajuvarikum (Lechtal blanket)

The Bajuvarikum can be traced over 600 kilometers on the northern edge of the Alps from the Rätikon in the west (around 20 kilometers west of Bludenz , or immediately east of Vaduz ) to the Vienna Woods in the east. Between Salzburg and the Enns , the northern edge of the Bajuvarikum is largely suppressed by the advance of the Tirolikum or occurs only in narrow clods - for example as the Allgäu blanket at Mondsee , in the Langbath clod between Attersee and Traunsee (also Allgäu blanket) and in the form of the Ternberg ceiling on both sides of the Enns.

The Lechtal blanket is cut off about 20 kilometers west of Kufstein from the Staufen-Höllengebirgs blanket of the Tirolikum diagonally to the east-northeast and then disappears entirely at Ruhpolding. Only from Grünau does it start again with the Reichraminger blanket . After an interruption by the Weyerer arches, it then continues as the Lunzer ceiling as far as the eastern edge of the Alps (however, the Lunzer ceiling is covered by the Tirolikum between Kaumberg and Schwechat ).

The Bajuvarikum even appears - probably torn as clods and shearlings - under the Tirolikum of the Schafbergschuppe in the flysch window of Strobl .

Sedimentary development

The Bajuvarikum was an independent sedimentation area that came to lie north of the Tirolikum. Between the Permian and Paleogene he documented changes in sea ​​level , tectonic events (such as synsedimentary stretching tectonics in the Upper Norium and the rifting of the Lower Jurassic ) and paleogeographic developments . Above all, limestone , dolomite and marl from a passive continental margin were deposited.

Long-lasting subsidence movements during the Permian and Triassic periods accumulated up to 5,000 meters of sediments on the southeastern, passive continental margin of Eurasia. As a result of the rift process in the alpine Tethys in the Lower Jurassic, the Adriatic Plate , a spur of Africa protruding to the north , separated from Eurasia - which was reflected in the facies of the Central Jurassic . At the beginning of the Malm , a basin partly underlaid by oceanic crust - as a northern branch of the Pennine Ocean - was established between Eurasia and the Adriatic Plate. The sediments of the Upper Jurassic are already postrift and have been deposited on the Adriatic plate. From the Lower Cretaceous onwards, a diachronic synorogenic sedimentation took place in response to the onset of the Eoalpine orogeny , in the course of which the Pennine basin was closed and subducted under the Adriatic plate. The Adriatic Plate consequently moved closer to the southeastern continental margin of Eurasia, its own, tectonically stretched southeast margin, inverted sediments lying on top of it, were successively broken down into blankets, which, together with oceanic sequences originating from the Tethys area, advanced towards the northwest.

Geodynamics

The north face of the Zugspitze (2962 m), made up of Wetterstein limestone from the Lechtal cover

During the Upper Barremium around 125 million years ago, the northward movement of the Cretaceous ceiling was first felt in the Tirolean. Both the closure of the Meliata Vardar Ocean and a south / southeast directed subduction below the Adriatic Plate are assumed to be the cause of the ceiling movements . The subduction survived into the Upper Cretaceous and caused the oceanized Penninic basin to disappear along the southern Alpine continental margin. This was accompanied by a high pressure metamorphosis that is dated 80 million years ago ( Untercampan ). The result of the subduction was the successive spread to the north of four large ceiling complexes. The Meliatikum (with limestone, radiolarite and pebbly-detritic deep-water facies ) had already started in the Lower Oxfordian , followed immediately by the ceilings of the Juvavikum in the Upper Oxfordian. These early movements were directed towards the southeastern edge of the Adriatic Plate. In the Lower Barremium, already sedimented Juvavikum was remobilized again to the north. The Tirolean, for its part, began to migrate north on the Albium / Cenomanium border . The Bajuvarikum finally crossed the rhenodanubian flysch only in the Lutetian (Obereocene).

The pre-Gosau, eoalpine nappes can be divided into three pulses - with accents during the Albian (112 to 95 million years), the Cenomanian (100 to 93.5 million years) and the Turonian (93.5 to 89.3 million years) . After the end of the pre-Gosau movements, an isostatic uplift of the Eastern Alps occurred from the upper campan (around 75 million years ago) , which was preceded by widespread erosion and emergence, recognizable by karst bauxites , in the Middle Turon.

The Gosau sediments ( conglomerates , sandstones , marl and limestone) were deposited on the pile of nappes moving northwards in the period from the Turonian to the Eocene (around 90 to 40 million years before today). The northern part of the pile of nappes was then pushed in a north-westerly direction over the Rhenodanubian Flysch Zone and the Helvetic Region , and in places also onto the Subalpine Molasse . These post-Gosau movements caused another metamorphosis towards the end of the Eocene (around 38 million years, with cooling ages up to the Middle Miocene 16 million years ago), this time of the Barrow-type of a continental collision. From the Middle Oligocene 28 million years ago, the deformations had also reached the Helvetic Sea of ​​the European continental margin, which in turn was folded, scaled and shifted towards the Molasse.

In the Lower to Middle Miocene , 23 to 13 million years ago, the ore was extruded to the side , which made the Northern Limestone Alps take on their typical, east-north-easterly elongated shape. The east-west stretching resulted in a simultaneous north-south narrowing of 54 to 65 percent in the Eastern Alps. As a result, the Bajuvian nappes in the central Northern Limestone Alps were squeezed out in a kind of brittle mega-boudinage . On their migration from their ancestral Adriatic deposit area to their current position on the European continental margin, the cover systems of the Northern Limestone Alps must undoubtedly have achieved quite large thrust ranges in the hundreds of kilometers.

literature

  • Manfred P. Gwinner: Geology of the Alps . E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 1971, ISBN 3-510-65015-8 .
  • Dieter Richter: Outline of the geology of the Alps . Walter de Gruyter, 1974, ISBN 3-11-002101-3 .
  • Alexander Tollmann: Tectonic map of the Northern Limestone Alps 3rd part: The western section . In: Communications from the Geological Society in Vienna . 62nd Volume, 1969.

Individual evidence

  1. ^ FF Hahn: Attempt to structure the Austroalpine mass west of the Austrian Traun . In: Verh. Kk geol. Reichsanst. Vienna 1912, p. 337-344 .
  2. ↑ SM Schmid, B. Fügenschuh, E. Kissling and R. Schuster: Tectonic map and overall architecture of the Alpine orogen . In: Eclogae Geologicae Helvetiae . tape 97 (1) , 2004, p. 93-117 .
  3. ^ GW Mandl: The Alpine sector of the Tethyan shelf - Examples of Triassic to Jurassic sedimentation and deformation from the Northern Calcareous Alps . In: Communications from the Austrian Geological Society . v. 92, 2000, pp. 61-77 .
  4. ^ R. Huckriede: The chalk slate near Kaisers and Holzgau in the Lechtal Alps . In: Verh. Geol. Federal agency Vienna 1958.
  5. ↑ H. Miller: The tectonic relationships between the Wetterstein and Mieminger Mountains (Northern Limestone Alps) . In: N. Jb.Geol.Paleont. Depending on the band 118 . Stuttgart 1963.
  6. ↑ F. Trusheim: The Mittenwald Karwendel trough. Contributions to the lithogenesis and tectonics of the Northern Limestone Alps . In: Wiss. Publ. Dt. u. Austrian Alpine Association tape 7 . Innsbruck 1930.
  7. ↑ Patrick Oswald, Hugo Ortner and Alfred Gruber: Deformation around a detached half-graben shoulder during nappe stacking (Northern Calcareous Alps, Austria) . In: Swiss Journal of Geosciences . tape 112 , 2019, p. 23-37 .
  8. ↑ MR Handy, MS Schmid, R. Bousquet, E. Kissling and D. Bernoulli: Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological-geophysical record of spreading and subduction in the Alps . In: Earth Science Reviews . tape 102 (3–4) , 2010, pp. 121-158 .
  9. ^ R. Brandner: Sea level fluctuations and tectonics in the triad of the NW-Tethys . In: Yearbook of the Federal Geological Institute Vienna . tape 126 (4) , 1984, pp. 435-475 .
  10. ^ R. Lein: On the evolution of the austroalpine realm . In: HW Flügel and P. Faupl (eds.): Geodynamics of the Eastern Alps . Deuticke, Vienna 1987, p. 85-102 .
  11. ↑ N. Froitzheim and G. Manatschal: Kinematics of Jurassic rifting, mantle exhumation and passive-margin formation in the Austroalpine and Penninic nappes (eastern Switzerland) . In: Geological Society of America Bulletin . tape 108 (9) , 1996, pp. 1120-1133 .
  12. ↑ H. Ortner: Cretaceous thrusting in the western part of the Northern Calcareous Alps (Austria) - evidences from synorogenic sedimentation and structural data . In: Communications from the Austrian Geological Society . tape 94 , 2003, p. 63-77 .
  13. ↑ M. Thöni and M. Jagoutz: Isotopic constraints for Eo-Alpine high-P metamorphism in the Austroalpine nappes of the Eastern Alps: bearing on Alpine orogenesis . In: Switzerland. Mineral. Petrol. Mitt. Band 73 , 1993, pp. 177-189 .
  14. ↑ Jean Aubouin, J. and M. Latreille Debelmas: Geology of the Alpine chains born of the Tethys . In: Mémoire du BRGM n ° 115 . 1980, ISBN 2-7159-5019-5 .
  15. ↑ Wolfgang Frisch, Joachim Kuhlemann, Istvan Dunkl and Achim Brügel: Palinspastic reconstruction and topographic evolution of the Eastern Alps during late Tertiary tectonic extrusion . In: Tectonophysics . tape 297 , 1998, pp. 1-15 .
  16. ↑ K. Stüwe and R. Schuster, R .: Initiation of subduction in the Alps: Continent or ocean? In: Geology . v. 38, 2010, p. 175-178 .