SILICEOUS PLANKTON BLOOM IN THE EARLIEST TERTIARY OF MARLBOROUGH, NEW-ZEALAND

In marked contrast to mass extinctions and productivity crises in much of the world's oceans at the Cretaceous-Tertiary boundary, siliceous plankton thrived in earliest Paleocene seas of Marlborough, New Zealan d. Five bathyal sections show no radiolarian mass extinction across a well-defined Cretaceous-Tertiary boundary but, instead, an abrupt incr ease of diatoms relative to radiolarians, a general increase in both g roups, acid an influx of spumellarians. A pronounced increase in modal quartz and SiO2 within a 9-25-m-thick basal Paleocene interval indica tes high biosiliceous productivity, the silica being derived primarily from diatoms, Enhanced upwelling in response to climatic cooling, or more efficient nutrient cycling related to sea-level changes, may expl ain this plankton bloom over the first 1 m.y. of the Tertiary.