MICROTAPHOFACIES OF PALEOGENE LIMESTONES: THE ROLE OF TAPHONOMY IN SHAPING AND INTERPRETING CARBONATE FACIES ACROSS GEOGRAPHIC AND TEMPORAL BOUNDARIES

The taphonomic study of indurated carbonate rocks is often restricted to thin section analysis. Microtaphofacies analysis can provide for a wealth of information inherently different from the study of isolated fossils and has a high potential for the study of taphonomic processes in carbonates through time. Such an analysis can help to determine how our understanding of carbonate environments is dictated by changing taphonomic processes and bias. The study presented here is based on a taphonomic analysis of 14 major facies types within three time Paleogene time slices: 1) Middle Eocene 2) Late Eocene and 3) Early Oligocene) of the circum-alpine region. These facies are generally dominated by larger foraminifera and coralline algae, along with smaller benthic foraminifera, corals and bryozoans. The time period under study is especially interesting as it crosses two boundaries (Middle Eocene/Upper Eocene; Eocene/Oligocene) characterized by the extinction of dominating carbonate components (especially larger foraminifera). Changes in facies across the shelf gradient can be correlated to global extinction events, regional biogeographic patterns, local sedimentation patterns and the introduction of new growth strategies among biotic components. The semi-quantitative assessment of taphonomic features (including abrasion, fragmentation, bioerosion and encrustation) recognized within thin section has revealed important differences among dominant components (coralline algae vs. larger foraminifera) as well as between the different facies types. Complex taphonomic features including multiple encrusting and bioerosion sequences can be recognized and compared. In general, abrasion and fragmentation are more common in near shore environments; while encrustation and bioerosion are more common in deeper environments reflecting difference in sedimentation and disturbance rates. Differences in taphonomic patterns across stage boundaries are related to changes of respective biotic components.