Paper No. 173-3
Presentation Time: 8:30 AM
THE NORTHERN CALCAREOUS ALPS AND ALFRED FISCHER’S CONTRIBUTIONS TO CARBONATE SEDIMENTOLOGY
Extending from the suburbs of Vienna to the Swiss border, the Northern Calcareous Alps (NCA) consist largely of Mesozoic carbonate rocks varying from platform complexes to deep-water pelagic limestones. Having lived as a child with his German-American parents for a time in the midst of these rocks near Berchtesgaden, Al Fischer returned to this area in the late 1950s to conduct research on both the shallow- and deep-water facies. Using his paleontological expertise and inspired by his earlier meticulous research on the Permian Reef Complex in the SW U.S., Fischer applied similar exacting methods to the Triassic platform carbonates in the Lofer Steinberge and other nearby sites in central Austria. He identified numerous lagoonal cyclothems that he interpreted as records of astronomically moderated eustatic fluctuations. A key discovery was the recognition of a thin dessication facies at the base of the the individual cyclothems marking brief intervals of low sealevels and seafloor emergence. Integrating his estimates of the lengths of the cyclothems, their possible connection to the obliquity cycle, and his calculation of the magnitude of tectonic subsidence, he created a methodology that would be utilized by others and that he would refine in his future research.
Likewise, employing novel electron microscopic methods, his work identified widespread coccolith-rich Jurassic-Cretacous pelagic limestones, solidifiying the interpretation of their deep-water origin during seafloor spreading and rapid subsidence. Using petrographic studies of both NCA pelagic limestones and Holocene cemented slabs dredged from the modern seafloor, he showed that this sediment-starved environment in the NCA generated numerous hardgronds, products of condensed sedimentation and early diagenetic carbonate cementation at the sediment-water interface.
This focus on pelagic sediments led him to participate on two early DSDP cruises that shed light on the origins of both the Atlantic and Pacific Oceans. The Alpine research was also the springboard for his later groundbreaking work on paleoenvironmental patterns and cyclostratigraphy in other carbonate sections in Italy and elsewhere. It established his modus operandi of precise studies at all scales and guided his creative research on fundamental questions of the Earth’s past.