The occurrence and role of microencruster frameworks in Late Jurassic to Early Cretaceous platform margin deposits of the Northern Calcareous Alps (Austria)

Late Jurassic reefs are generally assumed to lack “cement crusts”. In the present paper, microencruster frameworks with variable amounts of cement are described from Late Jurassic to Earliest Cretaceous shallow-water carbonates of the Northern Calcareous Alps of Austria. The boundstones are characterized by a specialized and highly diverse community of microencrusters, partly occupying cryptic habitats. Volumetrically of minor importance compared to similar Permo-Triassic examples, Late Jurassic to Earliest Cretaceous microframeworks here reported compare well with cement reefs or cement-supported counterparts of other time intervals. The assumed depositional setting is that of a fore-reef slope environment. Generally, this peculiar microfacies can be integrated in current concepts of Late Jurassic reef classifications. Although more details are still needed for comparison, Late Jurassic microencruster-cement frameworks seem to be typical, but not restricted to the margins of Neotethyan isolated platforms. This work is dedicated to Erik Flügel, former professor of the University of Erlangen, for his fundamental pioneer research on various aspects of microfacies, including poorly known phenomena of ancient cement reefs.     

Analysis of Late Jurassic to Early Cretaceous algal debris-facies of the Plassen carbonate platform in the Northern Calcareous Alps (Germany,Austria) and in the Kurbnesh area of the Mirdita zone (Albania): a tool to reconstruct tectonics and palaeogeography of eroded platforms

A characteristic microfacies of the Late Jurassic to Early Cretaceous allodapic Barmstein Limestone of the Northern Calcareous Alps are clasts of wackestones with numerous fragments of calcareous algae (“algal debris-facies”). According to dasycladale palaeocoenoses, several subtypes comprising different associations can be distinguished. One association is characterized by the debris of an unknown large dasycladalean alga reported as dasycladalean alga indet. sp. 1 from different localities in the Northern Calcareous Alps, typically forming a monospecific assemblage. Another microfacies type contains star-like calcitic bodies tentatively referred to the morphospecies Coptocampylodon pantici Ljubović-Obradović and Radoičić, originally described as being from the Turonian of NW-Serbia. Other Coptocampylodon-like bodies represent the calcified tufts of the laterals of Selliporella neocomiensis (Radoičić). The occurrence of Coptocampylodon pantici-like microfossils in the Late Tithonian to Early Berriasian, shows that obviously different species of dasycladaleans display identical to similar shaped tufts of laterals in transverse sections when becoming fragmented. Coptocampylodon pantici Ljubović-Obradović and Radoičić was observed only from different occurrences of Barmstein Limestone, but not from the autochthonous platform carbonates of the Plassen carbonate platform. The Coptocampylodon algal debris-facies is also reported from the Late Jurassic of Albania, Mirdita zone. Occurrences of different types of algal debris-facies in components of mass-flow deposits can be used as a tool to reconstruct eroded carbonate platforms and tectonics, as demonstrated in the Northern Calcareous Alps and the Albanides. Finally, the general occurrences of algal debris-facies in both settings—intra-Tethyan mostly isolated platforms (Alps, Albanides) vs. extended epeiric platforms (Middle East)—are compared and discussed.