DINOFLAGELLATE EVIDENCE OF THE CRETACEOUS-PALEOGENE BOUNDARY IN ARGENTINA

Detailed studies of the Cretaceous-Paleogene boundary (KPB) interval are still scarce for Argentina. We report the dinoflagellate evidence of this interval in the Jaguel section from Neuquen Province, (38° 06' 25" S, 68° 23' 36" W) in a foreland basin approximately 100 km east of the cordillera. The boundary is biostratigraphically conformable, based on first occurrence datums of species ranging from latest Maastrichtian (Disphaerogena carposphaeropsis) to basal Danian (Senoniasphaera inornata) and on the worldwide record of the immediately subjacent spike of Manumiella seelandica.

The section consists mainly of massive and laminated mudstones and claystones above and below the KPB, which are distinguished primarily by change in color. A sandstone layer which ranges from 5cm to 10 cm in thickness coincides with the dinoflagellate definition of the KPB. It consists in part of well-preserved plagioclase feldspar. We suggest that this sand was deposited quickly and may be of tsunami origin. This conclusion is based on sudden change of grain size, and on the presence of well-preserved , nonbedded, plagioclase sand. The contact with the overlying clays is conformable. The lower contact of the sand is slightly undulatory on the underlying clays, which suggests a minor hiatus. We consider this to be further evidence of a tsunami origin.