Foraminiferal-ostracod late jurassic biozonation of the Scotian shelf

The writer's 1977 foraminiferal and ostracod biozonation of the Scotian Shelf has been updated and refined for the Late Jurassic interval and extended to the East Newfoundland Bason of the Grand Banks. The use of four categories of microfossils (planktonic Foraminifera, calcareous benthonic Foraminifera, arenaceous benthonic Foraminifera and Ostracoda) makes possible the correlaation of coeval deposits of widely differend facies (littoral-inner neritic, outer neritic and bathyal). Planktonic Foraminifera provide one assemblage zone, of Callovian-Oxfordian age; calcareous benthonic Foraminifera three zones, of Oxfordian, Kimmeridgian and Tithonian age; arenaceous benthonic Foraminifera two zones, of Oxfordian-Early Kimmeridgian and Late Kimmeridgian-Tithonian age, and Ostracoda three zones, of Oxfordian, Kimmeridgian and Tithonian age. The combined use of these different zones has effected food stratigraphic correlation between 19 wells of the Scotian Shelf and one well of the East Newfoundland Basin (Mobil-Gul Bonnition H-32), even when dealing with poor foraminiferal and ostracod assemblages. Calpionellid assemblages have been studied in detail in Shell Mohican I-100 (Scotian Shelf) and in Bonnition H-32 and have allowed spearation of the Late Tithonian from the Early Berriasian and a precise definition of the Jurassic-Cretaceous boudary in the latter well. The established calpionellid biozonation - identical to the "standard biozonation" of the Mediterranean area - permitted calibration of the stratigraphic ranges of foraminiferal and ostracod marker species at and near the Jurassic-Cretaceous boundary. The top of the Tithonian has been placed at the highest stratigraphic occurrence of Anchispirocyclina lusitanica (Egger), which in Bonnition H-32 corresponds to the lower part of calpionellid Zone "B". The combined use of foraminiferal, ostracod and calpionellid biozonations has been found to provide excellent stratigraphic definition across the Jurassic-Cretaceous boundary, from the East Newfoundlant Basin to the Georges Bank area. This definition is undoubtedly better than that attainable by using one category of microfossils alone.