Foraminiferal record in a condensed marine succession: a case study from the Albian and Cenomanian (mid-Cretaceous) of Annopol, Poland

Abstract

AbstractA condensed succession at Annopol is of key importance for the mid-Cretaceous palaeontology and palaeobiogeography in Poland. Here, the planktonic and benthic foraminifera from the Albian and Cenomanian intervals are studied. The local foraminiferal record is strongly influenced by burrowers. On the one hand, piping down of the foraminiferal tests through burrows disturbed the original succession, for example by introduction of the Cenomanian foraminifera into the Albian phosphorite horizon. On the other hand, the foraminifera in the burrow fills near the base of the Cenomanian provide the sole piece of evidence of a lower upper Cenomanian unit lost from the record by erosion. Changes in foraminiferal assemblages allow for the interpretation of the succession in terms of bathymetry and biological productivity. The highest rate of primary production is deduced for the Albian phosphorite horizon. Integration of foraminiferal and ammonite biostratigraphy with sedimentology allows for the comparison of a pattern of sea-level oscillations recorded at Annopol with the relevant portion of the classic graph of sea-level changes for the British Isles. It turns out that all important elements of the British curve, that is, transgressive peaks and regressive troughs or lows, left their distinctive, albeit highly residual, record in the Annopol succession. This study demonstrates that even extremely condensed marine deposits, such as those at Annopol, may provide a foraminiferal record of better quality, order and resolution than conventionally anticipated.