Jurassic palynology from a borehole in the Champagne area, France-correlation of the lower Callovian-middle Oxfordian using sequence stratigraphy

Abstract

The cored borehole A901, drilled by the National Agency for the Management of Radioactive Waste at Montcornet, in Champagne, on the northeastern border of the Paris Basin, provided a continuous section from the Hettangian to the lower Kimmeridgian. Samples taken at regular intervals yielded marker dinoflagellate cysts of the northwest European domain that have been correlated with ammonite zones. The earliest dinoflagellate species appear in the upper Sinemurian (976 m, Obtusum zone), whereas the lowest intersected beds contain abundant conifer pollen and pteridophyte spores. The microplankton becomes diversified along the hole, in particular in the Callovian-Oxfordian beds; the Bathonian gravelly oolitic limestones are unfavourable for preservation of microflora. The sequence-stratigraphical interpretation was based on lithological, 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 lower Callovian to middle Oxfordian.