Danian ammonites - The present state of knowledge and perspectives for future research

To date, the strongest arguments for ammonite survival into the Danian (earliest Paleogene) are based on material from the lower Danian Cerithium Limestone at Stevns Klint (Denmark), where ammonites occur above a clay layer with impact products at its base, the latter defining the Cretaceous-Paleogene (K-Pg) boundary. The best-preserved specimen is filled with Danian sediment rather than with Maastrichtian chalk, which would be expected had this been reworked material. Arguments for ammonite survival into the Danian have also been provided by specimens from the sporomorph and calcareous nannoplankton-dated lowermost Danian strata of Meerssen Member unit IVf-7, the Netherlands. Their good preservation indicates that they were not subject to any significant transport or redeposition. However, there are no unequivocal impact-related signatures in unit IVf-7, except for rare shocked quartz grains, recorded from burrows at its base. Sections in the Manasquan Basin, New Jersey, USA, provide equivocal data as far as the problem of ammonite survival into the Danian is concerned. At the top of the Tinton Formation there is a Pinna layer replete with fossils, inclusive of ammonites. Their exquisite preservation and occurrence in monospecific clusters rule out redeposition. The Pinna layer contains exclusively late Maastrichtian microfossils. However, a clear iridium anomaly has been noted at its base. Either the New Jersey ammonites survived the K-Pg event for a short time or the iridium is not in situ due to post-depositional repositioning by percolating water. Planned work is to focus on: 1) a detailed centimetre by centimetre sampling of some Cerithium Limestone basins in Denmark in search of additional ammonite material, 2) palaeontological and taphonomic analysis of ammonites and search for impact signatures in unit IVf-7 in the Netherlands, and 3) geochemical study of the iridium anomaly in New Jersey in order to determine whether its position in respect to the ammonite-bed is original or secondary