CEPHALOPOD ASSOCIATIONS, ALPHA DIVERSITY AND PALEOECOLOGY OF THE CRETACEOUS IN THE ALPSTEIN, SWITZERLAND

The Alpstein massif (northeastern Switzerland) has been of great interest for geologists over the last decades because of its excellent outcrops. Although rich and relatively high diverse associations of fossils have been sporadically reported, no comprehensive overview over the macro fossil associations has been available. Here, we report the cephalopod associations and discuss paleoecological changes from the Barremian to Cenomanian of the Alpstein.

Examined units include the Tierwis Formation consisting of the Altmann and Drusberg Members (latest Hauterivian–late Barremian), the Schrattenkalk Formation (late Barremian–Aptian), the Garschella Formation (Aptian–earliest Cenomanian) and the Seewen Formation (Cenomanian). We sampled macro fossils from highly fossiliferous layers of the Tierwis area of the Alpstein. Ecospace utilization, which was introduced by Bush et al. (2007), was investigated to quantitatively analyse paleoecological changes. Accordingly, all fossils were classified based on ecological parameters of tiering, motility and feeding mechanism and were subsequently plotted into the three-dimensional ecospace.

We documented 6 species (3 genera) of nautilids, 72 species (43 genera) of ammonites and other invertebrate fossils. The results of the paleoecological analyses demonstrated dynamic changes in ecospace utilization through time. The early Barremian faunule was dominated by nektoplanktonic organisms, followed by the early Aptian faunule lacking fossils of nektoplanktonic organisms. In the late Albian, the proportion of nektoplanktonic species surged again, resulting in a nektoplanktonic dominance during the early Cenomanian. Comparison of the results of our palaeoecological analyses and regional sea level fluctuations suggests that the dynamic palaeoecological shifts through time were affected by these sea level fluctuations.