Ammonite bio-horizons in the alpine Lower Cretaceous

Lower Cretaceous (144.2 - 98.9 my) sediments of the Tethyan Realm represent a major part of the northern tectonic units of the Northern Calcareous Alps (e.g. Ternberg-, Reichraming-, Frankenfels-, and Lunz Nappes) covering wide areas in large synclines with sediment thicknesses up to 250 metres (e.g. Rossfeld-, Losenstein-, Schneeberg-, Anzenbach-, Ebenforst-, and Flössel Synclines); they are also present in various other European areas (e.g. Vocontian Trough, Dolomites, Umbria, Outer Carpathians, Gerecse and Mecsek Mountains). The exceptionally high dispersal potential of ammonites (cephalopods) via planktonic larvae makes them better stratigraphic tools as index fossils than other invertebrates. The main topic of the submitted project will be the paleoecological and paleobiogeographic investigation of several Lower Cretaceous ammonite-marker-beds. The objective is to gain additional data useful for stratigraphic correlation between occurrences in the Northern Calcareous Alps and comparable sections in Central- and Western-Europe (e.g. Spain, France, Switzerland, Italy, Hungary, Czech Republic). Fieldwork in co-operation with colleagues in the above-mentioned areas and excursions should provide local information. Another topic of the proposed project will be the environmental conditions and the original local position of the sedimentation area with regard to post-sedimentary mass-transport controlled by gravity and/or tectonics. New facts on the relative autochthonous or allochthonous nature of the ammonite levels should help to clarify geodynamic processes and the paleooceanographic configuration in the Lower Cretaceous of Central and Western Europe and provide paleobiological data on the investigated ammonite groups. Promising results of the FWF-Project P13641-Geo will no doubt provide additional results on the already investigated mass-occurrences as well as results on newly found, additional levels with ammonite mass- occurrences. A precondition for paleobiological, paleogeographic and biostratigraphic conclusions and/or correlations is the comprehensive taxonomic study of the new material gathered in detailed, bed-by-bed collections in the field. This should ultimately lead to the designation of new ammonite-marker-beds useful for correlation within the whole Tethyan Realm.

Bio-events manifested in ammonite bio-horizons and ammonite-levels characterized by abundance or mass- occurrence of ammonites could be detected in Lower Cretaceous sediments of the Northern Calcareous Alps. The age of the ammonite horizons could be classified by the ammonite themselves and by the correlation with other important fossil groups (e.g. microfossils). Ammonite levels traced during the project P16100-N06 clarified the history of environmental and sedimentary conditions at the time of deposition and constitution of such bio-events, manifested in ammonite mass-occurrences. Taphonomic and post mortem conditions in addition with processes during the formation of these levels (autochthonous versus allochthonous) were investigated. These fields have been combined with investigations of supraregional (Dolomites) and local paleogeography and geodynamics. Valanginian, Hauterivian, Barremian and Aptian sediments have been investigated to detect intervals of ammonite abundances or its manifested horizons in different time slabs. It could be shown that there are several ammonite levels (favoured intervals) in the Lower Cretaceous which can be traced over the whole Northern Calcareous Alps region. Upper Valaninian, Upper Hauterivian and Lower Berremian times are three of the most important and significant intervals in the Lower Cretaceous within the Northern Calcareous Alps concerning ammonite distribution and evolution. Studies included geochemical analyses (e.g. sulphur, oxygen, carbonate), paleotemperature analyses (oxygen isotopes in well-preserved shells of ammonites), as well as directions of bottom or surface currents by measuring sedimentary marks on bedding planes in the field (alignments). Detailed taxonomic analyses were the basic requirement for assessing the identity and contemporaneity of ammonite mass-occurrences. Another topic of this project: was to demonstrate that macrofossil distribution (e.g. ammonites), together with parallel investigation of microfacies appearances and lithological changes, can serve as a tool for a more detailed biostratigraphy of pelagic carbonate sequences as well as for the interpretation of paleoenvironmental conditions. New results were extracted from the analysis of Aptian sediments which generated new insights on the geodynamical and sedimentological development of this region in the Lower Cretaceous. The project impacted the interpretation of the geologic history of Alps. Hence the beginning oceanic subduction of the Panninic Ocean beneath the Alpidic Microcontinent could be very preciselly dated to 123 m.y. After finishing the project, more than 15 national and international publications under the financial support of the FWF have been published in the last 4 years. More than 15 posters have been made and talks have been held over the last 4 years at international and national symposia to present the results carried out within this project.