LATE CRETACEOUS INTEGRATED STRATIGRAPHY BASED ON FORAMINIFERA, CALCAREOUS NANNOFOSSILS AND CARBON ISOTOPE AT SOUTHERN HIGH LATITUDES: SEARCHING FOR PRECISION IN GLOBAL CORRELATIONS

An integrated bio- chemostratigraphic framework of the Turonian-Santonian interval at southern high latitudes is presented based on the distribution of planktonic and benthic foraminifera, calcareous nannofossils and carbon isotope data. Data are from Integrated Ocean Discovery Program (IODP) Sites U1513 and U1516 drilled in the Mentelle Basin (Indian Ocean, offshore SW Australia) during Expedition 369. The sites were located at 57°- 62°S paleolatitudes during the Late Cretaceous.

Across the Cenomanian-Turonian boundary interval calcareous plankton bioevents, combined with carbon isotope data, are correlated with records at low latitudes in the Tethys and Western Interior Seaway. They provide a good chronostratigraphic and integrated stratigraphy framework that represents one of the best documented records for southern high latitudes. Among calcareous nannofossils Helenea chiastia and Quadrum gartneri are confirmed to be reliable bioevents. Benthic foraminiferal markers in the southern high latitudes include Gavelinella intermedia and Gavelinella vesca, also documented from middle Cretaceous Tethyan settings

The calcareous plankton assemblages from the Turonian to the Santonian interval reveal a Tethyan affinity. The Turonian/Coniacian boundary is inferred to fall within Zone CC13 and between the last occurrences of the planktonic foraminifera Falsotruncana maslakovae and the calcareous nannofossils Micula staurophora in agreement with mid- to low latitude records (NW Australia, Tanzania and Tethyan localities). The Coniacian/Santonian boundary lies within Zone CC16 and is placed at the last occurrence of the planktonic foraminifera Globotruncana linneiana, according to the definition of the Santonian Global Stratotype Sections and Points (GSSP). The benthic foraminiferal assemblages show high similarities with the South American records, and only rare taxa, including Gavelinella berthelini and Notoplanulina rakauroana, can be used for worldwide correlations.

We discuss and compare the foraminifera and calcareous nannofossils bioevents observed in the Mentelle Basin with the records reported from other stratigraphic sections, and provide an integrated bio- chemostratigraphic scheme highlighting the synchronicity of marker species and their reliability for global correlations from low- to high southern latitudes.