PLEISTOCENE CALCAREOUS NANNOFOSSIL ASSEMBLAGES FROM THE MOZAMBIQUE CHANNEL

In October 2013, the RV Marion Dufresne collected piston cores in the Mozambique Channel offshore Madagascar for the South Atlantic Petroleum Company. Eighteen of the cores were donated to Sam Houston State University and we obtained samples from two of the cores collected from the Belo Profound locality (~19.5ºS, 42.2ºE): cores MD13-3504 and MD13-3506. The cores primarily consist of bioturbated calcareous ooze and clay varying in color between light tan, light brown, reddish brown, and olive gray. While some cores contain relatively frequent graded beds interpreted as turbidites, these beds are rare in core MD13-3506. Prior work used rock magnetic properties and paleomagnetic data to provide stratigraphic and chronologic constraints. Here we analyzed the calcareous nannofossil assemblages from these cores to provide biostratigraphic constraints to the age models for the cores. We also use variations in the assemblages and the abundance of the lower photic zone species Florisphaera profunda to infer changes in surface water conditions, including temperature, nutrient availability, and stratification. We prepared samples using the drop method to allow calculation of the total number of coccoliths per gram of sediments. We counted at least 500 specimens (excluding F. profunda) per sample using a Zeiss Axioscope 5 transmitted light microscope under cross-polarized and plane-transmitted light. The nannofossil assemblages are dominated by members of the family Noëlaerhabdaceae, including Emiliania huxleyi in the youngest part of the section and Gephyrocapsa spp. throughout both cores. In addition, F. profunda abundance varies significantly; intervals where this species is abundant experienced greater surface water stratification. Other taxa present in lower numbers include Calcidiscus leptoporus, Coccolithus pelagicus, Umbilicosphaera spp., Rhabdosphaera spp., and Syracosphaera spp. Reworking of older material is present in some of the samples. Our results will help to finalize the age model for the cores and to elucidate variations in surface water conditions between glacial and interglacial cycles recorded in the sediments.