MUTTERLOSE, J., Institut fur Geologie, Universitat Hannover, Hannover, Germany; and E. ERBA, Dip. Scienze della Terra, Univ. Milano, Milano, Italy

ABSTRACT: Towards a World-Wide Applicable Biostratigraphy of Early Cretaceous Nannofloras

The nannofossil assemblages of the Early Cretaceous show a distinctive palaeobiogeographic distribution pattern for the intervals Berriasian-Barremian on one hand and for the Aptian-Albian on the other. The Berriasian-Barremian period is characterized by provinciality on the generic level. It is possible to differentiate in between a Boreal Realm and a Tethyan Realm. Different and independent biostratigraphic schemes were developed for the two areas using Tethyan and Boreal markers respectively. In the Tethyan Realm nannofossil events are calibrated to magnetostratigraphy, whereas in the Boreal Realm calibration to ammonite biostratigraphy is available. The orthostratigraphy is based on ammonites, which show a similar Tethyan-Boreal provincialism. Assemblages from the Indo-Pacific are show cosmopolitan elements and weak influences of tethyan floras. Therefore the Tethyan Realm is subdivided into a Mediterranean Province (Tethyan Realm sensu strictu) and an Indo-Pacific Province. While the Mediterranean Province is dominated by cosmopolitan and tethyan floras, the latter are absent from the Indo-Pacific Province. The Aptian-Albian period was marked by a floral (and faunal) turnover, causing major changes worldwide. The differences in between the Boreal Realm and the Tethyan Realm vanished, as well as the differences in between the two provinces within the Tethyan Realm. For this interval a new biozonation based on calcareous nannofossils is discussed and one scheme is proposed for world-wide correlation.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.