Integrated Albian-Cenomanian calcareous nannofossil and planktic foraminiferal biostratigraphy and paleoceanography of southern high latitude IODP sites drilled on Naturaliste Plateau (southeast Indian Ocean)

Albian–Cenomanian calcareous claystone sequences drilled in the Mentelle Basin (MB) offshore southwest Australia at International Ocean Discovery Program sites U1513, U1514, and U1516 yield mostly well preserved but highly fluctuating populations of planktic foraminifera and calcareous nannofossils. The sites were deposited at a high paleolatitude (60–61°S) in the southeast Indian Ocean. The chronostratigraphic framework for the recovered sequences is primarily based on biostratigraphically important calcareous nannofossil species with 25 Albian and 15 Cenomanian nannofossil bioevents correlated to Boreal or low to mid-latitude zonations, providing reliable datums for the age-depth curves at each of the sites. The low diversity, high dominance planktic foraminiferal assemblages generally lack age diagnostic species and are assigned to a southern high latitude zonal framework. The planktonic foraminifer species, Planohedbergella antescheri Huber and Petrizzo and Praeglobotruncana praedelrioensis Huber and Petrizzo, are described as new, ranging within the Albian at all three MB sites. Onset of open marine conditions in the Mentelle Basin occurred by ∼112 Ma based on age determination of the oldest Albian sample yielding calcareous microplankton. The composition and structure of the calcareous nannofossil assemblages indicate the Albian and Cenomanian surface waters were generally of low fertility and supported relatively low carbonate productivity, punctuated by four episodes of enhanced fertility correlated directly to Oceanic Anoxic Events. The fertility episodes were coeval with significant increases in the rate of sediment accumulation, suggesting the enhanced nutrient availability promoted increased biogenic carbonate production in an otherwise sediment- and nutrient-starved paleoenvironment. Upper Albian–middle Cenomanian intervals with abundant clinoptilolite pseudomorphs of calcisphere and radiolarian shells formed during periods of low foraminiferal abundance and enhanced biosiliceous productivity.