GLOBAL CLIMATE CHANGE AND PLANKTONIC FORAMINIFERAL RESPONSE – BIOSTRATIGRAPHIC MARKERS IN THE LATE CAMPANIAN - MAASTRICHTIAN OF THE TETHYS

The Late Campanian - Maastrichtian was a time of high climatic variability. The lengthy warm stable climate of the Cretaceous was replaced by warm-cool-warm-cool oscillations, with marked paleoceanographic changes in source and production of intermediate waters and consequent biotic response. Planktonic foraminiferal populations responded to these changes by evolution of new species, extinctions, innovations such as photosymbiosis, blooms and acmes.

Recent schemes for subdivision of the Late Campanian - Maastrichtian oceanic record reflect these changes. Li and Keller (1998; 1999) and Huber et al. (2008) improved upon the older three-fold zonal subdivision (G. falsostuarti-, G. gansseri- and A. mayaroensis- Zones), by emphasizing evolution and extinction events that emerged from high resolution studies of this time interval.

The first Cretaceous cooling in the Late Campanian resulted in a cool intermediate water mass in the tropical-subtropical realm, populated by evolving keeled globotruncanids. Subsequent warming at ~70 - 68 Ma led to significant reduction in cool deep water habitats and extinction of some of its more prominent inhabitants, e.g,, C. fornicata; C. plummerae; G. bulloides; G. linneiana; G. ventricosa. Cooling at ~68 - 65.78 Ma led to reestablishment of the cool intermediate water mass, provoking an acme response by the otherwise uncommon deep-intermediate dwelling species Gansserina gansseri. This cooling coincides also with the evolutionary innovation of photosymbiosis in planktonic foraminifera, namely in Racemiguembelina fructicosa. The short-lived warming event of the latest Maastrictian at 65.78--65.57 Ma caused the abrupt extinction of G. gansseri, while R. fructicosa survived.

The species used for the highly refined biostratigraphic zonation schemes are therefore part of the global biotic response to Late Cretaceous climate oscillations. They in fact track dramatic changes in the global environment as the Cretaceous drew to a close.