Calcareous nannofossil zonation of the Jurassic-Cretaceous boundary interval and correlation with the geomagnetic polarity timescale

Calcareous nannofossil stratigraphy has been investigated in six European land sections and at two Deep Sea Drilling Project Sites (391C and 534A) ranging from the Upper Kimmeridgian to the Lower Valanginian. Most of the sections contain a continuous record of the Jurassic-Cretaceous boundary interval, a time of rapid increase in nannofossil abundance and diversity and allow development of a revised nannofossil zonation scheme for this period. Numerous nannofossil lineages have been studied in detail and the results help to increase potential stratigraphic resolution in this interval. The proposed scheme consists of six zones which are units recognizable in all sections regardless of nannofossil preservation and eleven subzones determinable in all but the most poorly preserved material. Thirty-eight additional biohorizons are proposed based on the stratigraphy of the two DSDP sites. These can be accurately established only in moderately well-preserved material but spotty occurrences of these taxa in other sections may be stratigraphically useful. Most of the sections studied have been investigated magnetostratigraphically and the results of this study allow correlation between nannofossil zonation and the geomagnetic polarity time scale. Magnetostratigraphy indicates that many nannofossil events can be quite precisely determined and are not significantly time-transgressive. Finally, the magnetostratigraphic definitions of two stage boundaries are refined. The Kimmeridgian-Tithonian and Berriasian-Valanginian boundaries are placed within Chrons CM22n and CM15n respectively. Two new genera,Faviconus andUmbria, and seven new species are described:Umbria granulosa, Rhagodiscus nebulosus, Cretarhabdus octofenestratus, Faviconus multicolumnatus, Nannoconus infans, Nannoconus compressus andNannoconus wintereri. Eight subspecies and three taxonomic emendations are also described.