Taphonomic experiments on marginal marine foraminiferal assemblages: how much ecological information is preserved?

The most important taphonomic processes affecting the composition of benthic foraminiferal assemblages are transport and destruction of tests. The latter includes dissolution of calcareous tests. We have previously simulated nature experimentally by dissolving mainly shelf to deep sea samples in weak acid to give acid-treated assemblages (ATA). In this study we sampled the marginal marine environments of the Skagerrak/Kattegat and found that the main taphonomic process there is dissolution of calcareous tests. Consequently, the taphonomic processes occurring in this area represents a perfect natural analogue of what we suspect to be the main mechanism for the formation of some fossil agglutinated assemblages. The evidence for this is that some living assemblages dominated by calcareous forms become original dead assemblages (ODA) often consisting entirely of agglutinated species and equivalent to ATAs. The principal ATA is dominated by Miliammina fusca and this ATA can be derived from 10 different types of ODA including those that are strongly dominated by various calcareous taxa. This residual M. fusca assemblage represents a broad range of intertidal to shallow subtidal environments. On the other hand, marsh living assemblages are completely agglutinated and obviously give rise to agglutinated ODA/ATAs but not necessarily dominated by the same taxa. All the ATAs faithfully record the low species diversity characteristic of marginal marine environments. The principal conclusion is that in spite of the severe taphonomic loss, the preserved assemblages record much ecological detail. This is in accordance with similar investigations of deeper water assemblages and has important consequences for palaeoecology. This study demonstrates unequivocally that it is always essential to compare data on living and dead assemblages in order to determine the pathways to fossilisation. The use of total (living plus dead) assemblages in this area would give unrepresentative and misleading results.