REVISED UPPER ALBIAN-LOWER CENOMANIAN CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE PROTO-NORTH ATLANTIC

Recent biostratigraphic analyses of upper Albian-lower Cenomanian nannofossil assemblages were used to test the fidelity of the CC and UC calcareous nannofossil biostratigraphic zonal schemes. These biostratigraphic zonation schemes use marker species from the Tethyan realm; however, other large oceans existed during this time. The proto-North Atlantic Ocean was a mid-latitude ocean that connected to the Tethys Ocean, but a widely used biostratigraphic framework does not exist for this region. This study identifies and assesses discrepancies between the two basins in order to refine current biostratigraphic frameworks.

Calcareous nannofossil assemblages were quantitatively analyzed from Deep Sea Drilling Project (DSDP) Sites 137 and 547. Existing datasets from Ocean Drilling Program (ODP) Holes 1050C and 1052E were also integrated into this study. These sites were chosen due to the presence of well-preserved nannofossil assemblages and stratigraphic coverage. Data were analyzed using probabilistic and deterministic biostratigraphic methods. Four biozones spanning the upper Albian through lower Cenomanian were determined using unitary associations (UA). Data were also used from these sequences to generate a ranking and scaling (RASC) optimum sequence from which three additional bioevents were shown to be reliable markers for lower Cenomanian biostratigraphy. In addition, the initial age model for Site 137 determined an age of Cenomanian, which is herein revised to upper Albian-middle Cenomanian.

The Albian and Cenomanian stages occurred during the Cretaceous paleomagnetic Normal Superchron (C34). As a result, biostratigraphy is an integral tool in correlation of marine strata of this age across different ocean basins due to the lack of paleomagnetic reversals. This study improves the ability to correlate across different ocean basins by increasing the resolution of the current biostratigraphic framework.