Reef Development in the Middle Triassic (Ladinian and Cordevolian) of the Northern Limestone Alps Near Innsbruck, Austria
Rainer Bradner, Werner Resch, 1981. "Reef Development in the Middle Triassic (Ladinian and Cordevolian) of the Northern Limestone Alps Near Innsbruck, Austria", European Fossil Reef Models, Donald Francis Toomey
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The Middle Triassic Wetterstein Limestone platform north of Innsbruck, Austria, forms a gently dipping platform that contains various organic buildups. The upper part of this platform is dominated by a massive reef laid down in shallow water (Hafelekar Reef complex), whereas the lower portion of the Wetterstein Limestone contains conspicuous patch-reefs.
The massive shallow water reef in the upper part of the Wetterstein Limestone shows a distinct biotic zonation. This zonation reflects a rather simple pattern of ecological zones attesting to a smooth transition of biological adaptation by various reef organisms.
Reef growth in the patch-reef sequence appears to have been influenced by subsidence associated with sea level changes, and a gradual increase of skeletal debris derived from actively accreting shallow water reefs. It is throught that a sea level rise in excess of 10 meters would prove sufficient to obstruct patch-reef growth. Sea level rise activated short lived basinal sedimentation adjacent to the reef area. Basinal sediments are characterized by radiolarian-bearing limestones. This same event however, initiated a revival of rapid reef growth on the platform. Here reefs are composed of calcisponges, Tubiphytes, and tubular foraminifers. Reef and lagoonal areas are separated by a barrier of skeletal sand shoals.
Large scale syngenetic submarine cementation of the reefs was followed by early diagnetic dolomitization. Subsequent sedimentation and cementation produced conspicuous thick coatings of fibrous spar (?aragonite), and these are interpreted as diagenetic fabrics that formed during an early burial stage.
Synsedimentary tectonics was especially active along the rim of the Wetterstein carbonate platform, as part of a much broader tectonic phase that was active and affected the Middle Triassic Tethys. In general, development of the Wetterstein carbonate platform was a regressive phase frequently disrupted by disturbances caused by continued subsidence in association with block-faulting tectonics.
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European Fossil Reef Models
The voluminous amount of information presented in this Special Publication not only fills a gap in understanding the European approach to reef studies but also provides the necessary data base to allow us (in particular the North American geologist) to incorporate this information in our overall interpretive studies. These studies should serve as an impetus for new investigations and will broaden our understanding of the complex interrelationships that operate in the reef environment.