JURASSIC PALYNOLOGY FROM A BOREHOLE IN THE CHAMPAGNE AREA, FRANCE-CORRELATION OF THE LOWER CALLOVIAN-MIDDLE OXFORDIAN USING SEQUENCE STRATIGRAPHY

The cored borehole A901, drilled by the National Agency for the Manage ment of Radioactive Waste at Montcornet, in Champagne, on the northeas tern border of the Paris Basin, provided a continuous section from the Hettangian to the lower Kimmeridgian. Samples taken at regular interv als yielded marker dinoflagellate cysts of the northwest European doma in that have been correlated with ammonite zones. The earliest dinofla gellate species appear in the upper Sinemurian (976 m, Obtusum zone), whereas the lowest intersected beds contain abundant conifer pollen an d pteridophyte spores. The microplankton becomes diversified along the hole, in particular in the Callovian-Oxfordian beds; the Bathonian gr avelly oolitic limestones are unfavourable for preservation of microfl ora. The sequence-stratigraphical interpretation was based on litholog ical, sedimentological and biostratigraphical information and seismic profiles. A semi-quantitative estimation of the microplankton content and of the number of species per sample enabled identification of the main transgressive-regressive cycles and condensed sequences in the lo wer Callovian to middle Oxfordian.