THE GENUS ORBITOLINA D’ORBIGNY, 1850 (LARGER BENTHIC FORAMINIFERA) AND ITS CONSTITUENT SPECIES: NOTES ON IDENTITY AND STRATIGRAPHIC RANGES

Abstract

Following a literature review of the species of Orbitolina and its allies, the identity criteria and stratigraphic ranges of the six potential constituent species of the commonly encountered mid-Cretaceous foraminiferal genus Orbitolina d’Orbigny, 1850 (sensu stricto) are reviewed based on published material. It is noted that correct taxonomic assignment of Orbitolina species requires observation and measurement of both the embryonic apparatus in centred axial thin-sections and of the chamber passage shape in tangential sections. As a consequence, many illustrations purportedly of Orbitolina sensu stricto in the published literature cannot confidently be identified to species level, and such specimens (including new material) should be described or re-described as Orbitolina spp. The genus Orbitolina has a range of late Albian – middle Cenomanian. Species of Orbitolina, when identifiable, have shorter ranges. Orbitolina concava (Lamarck 1816) is restricted to the early – middle Cenomanian, and its inception thus forms a potential proxy for the base of the Cenomanian in carbonate platform settings, but care needs to be taken in its identification and separation from other species of Orbitolina that have at least partial late Albian ranges.