The Triassic passive continental margin sedimentary evolution in the Western Tethyan realm,
very well preserved in the central Northern Calcareous Alps, is characterized by the demise
and aftermath of three main shallow-water carbonate ramp/platform cycles:
1) Late Early Triassic to Middle Anisian carbonate ramp evolution (upper Werfen,
Gutenstein and Steinalm carbonate ramp), deposited in an epicontinental sea (graben).
2) Latest Ladinian to earliest Carnian carbonate platform evolution (Wetterstein Carbonate
Platform), formed in a passive continental margin setting.
3) Late Triassic (Norian-Rhaetian) Hauptdolomit/Dachstein Carbonate Platform evolution,
and its Late Carnian carbonate ramp forerunner (passive continental margin).
The Northern Calcareous Alps as part of the Eastern Alps is one of the most prominent Alpine
areas. Together with the Western Carpathians, the Southern Alps and the Dinarides, they
constituted an up to 700 km wide and approximately 2000 km long shelf strip of the
northwestern Tethys margin. The Triassic sedimentation was controlled by Early to early
Middle Triassic extension, the break-up of the Neo-Tethys in the early Middle Triassic (Middle
Anisian) and the formation of huge carbonate platforms in the late Middle to Late Triassic.
After siliciclastic dominated (latest Permian to) Early Triassic sedimentation intense shallowwater
carbonate production started slightly before the Early/Middle Triassic boundary. After
deposition of more open marine influenced late Early Triassic limestones, in cases intercalated
with siliciclastic sedimentary rocks in the Early-Middle Anisian shallow-water carbonates were
deposited first under restricted and later under more open marine conditions (carbonate
ramps). The Late Anisian final break-up of the Neo-Tethys Ocean led to the drowning of this
shallow-water ramp deposits. In the frame of the final break-up of the Neo-Tethys
a horst-and-graben morphology formed and deep-water conditions prevail during Late Anisian
to Late Ladinian times. Only in short time spans during the latest Anisian
resp. the Anisian/Ladinian boundary some shallow-water carbonates were formed
on morphological highs, acting as nucleus for the later evolving Wetterstein Carbonate Platform.
This platform started to form in the Late Ladinian, and resulted in the complex latest Ladinian
to earliest Carnian platform - basin pattern (Wetterstein Carbonate Platform evolution).
After the demise of the Wetterstein Carbonate Platform and partial drowning of this platform
by siliciclastic input in the Middle Carnian again shallow-water carbonate production started
in the Late Carnian. These Late Carnian shallow-water carbonate ramp deposits (Waxeneck
ramp evolution) resulted in the evolution of the huge Norian Hauptdolomit/Dachstein
Limestone Carbonate Platform, with its classical lagoonal sediments - restricted lagoon
(Hauptdolomit), open lagoon (Dachstein Limestone with Lofer cycles) - the reefs belt and its
transition to the open shelf area (Hallstatt facies). In the Rhaetian the carbonate factories were
again influenced by siliciclastic input, and a deep lagoon (Kössen Basin) was formed.
At the Triassic/Jurassic boundary shallow-water carbonate production ended
and the Hauptdolomit/Dachstein Carbonate Platform drowned. Beside all sedimentological
features the controlling factors of ramp/platform evolution will be discussed as the role
of tectonics, ocean acidification, climate changes, stepwise mass extinctions and sea-level
fluctuations.