Maastrichtian dinocyst floras from Maud Rise and Georgia Basin (Southern Ocean): Their stratigraphic and paleoenvironmental implications

Dinocyst assemblages from Ocean Drilling Project (ODP) Leg 113, sites 689 and 690, located at Maud Rise, and Leg 114, Site 698 at South Georgia Basin, are of medium diversity with close to 40 taxa. The floras are dominated by Isabelidinium pellucidum and Odontochitina porifera; common species are Batiacasphaera reticulata, Microdinium cassiculum, Leberidocysta sp. A, Nematosphaeropsis sp. and Valensiella reticulata. The age of these dinocyst-bearing sections has been determined, using paleomagnetics and biostratigraphy, as early Maastrichtian (Chron 32N), correlative to the uppermost part of the B. coronum to the lower part of the B. magnum nannofossil zones. Comparison with equally well-dated Kerguelen Plateau palynofloras indicates an age equivalent to the dinoflagellate Zone C2, and perhaps also Zone D of Mao and Mohr (1992). The precise age model for these dinocyst floras allows better calibration of other Antarctic shallow marine sections from the James Ross Basin. Decreasing species diversity and increasing endemism of these floras can be used to reconstruct environmental conditions. Decreasing diversity is interpreted as response to cooling of the Antarctic water masses, probably caused by the onset of a distinct proto-circum-Antarctic current during the latest Campanian and early Maastrichtian.