Stratigraphic definitionsThe Cenomanian was introduced in scientific literature by French palaeontology, palaeontologist Alcide d'Orbigny in 1847. Its name comes from the New Latin name of the French city of Le Mans (département Sarthe), ''Cenomanum''. The base of the Cenomanian stage (which is also the base of the Upper Cretaceous series) is placed at the first appearance of foram species ''Rotalipora, Rotalipora globotruncanoides'' in the stratigraphic record. An official reference profile for the base of the Cenomanian (a GSSP) is located in an outcrop at the western flank of Mont Risou, near the village of Rosans in the French Alps (département Hautes-Alpes, coordinates: 44°23'33"N, 5°30'43"E). The base is, in the reference profile, located 36 meters below the top of the Marnes Bleues Formation. The top of the Cenomanian (the base of the Turonian) is at the first appearance of ammonite species ''Watinoceras, Watinoceras devonense''. Important index fossils for the Cenomanian are the ammonites ''Calycoceras, Calycoceras naviculare'', ''Acanthoceras (ammonite), Acanthoceras rhotomagense'', and ''Mantelliceras, Mantelliceras mantelli''.
Sequence stratigraphy and palaeoclimatologyThe late Cenomanian represents the highest mean sea level observed in the Phanerozoic Geologic time scale#Terminology, eon, the past 600 million years (about 150 meters above present-day sea levels). A corollary is that the highlands were at all time lows, so the landscape on Earth was one of warm broad shallow seas inundating low-lying land areas on the precursors to today's continents. What few lands rose above the waves were made of old mountains and hills, upland plateaus, all much weathered. Tectonic mountain building was minimal and most continents were isolated by large stretches of water. Without highlands to break winds, the climate would have been windy and waves large, adding to the weathering and fast rate of sediment deposition.
PalaeontologyThe crown group Crocodylia, the true crocodiles, first appear during the Cenomanian.Mateus, O., Callapez P. M., & Puértolas-Pascual E. (2017). The oldest Crocodylia? a new eusuchian from the Late Cretaceous (Cenomanian) of Portugal. Journal of Vertebrate Paleontology, Program and Abstracts. 2017, 160.
Further reading*Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: ''A Geologic Time Scale 2004'', Cambridge University Press. *Kennedy, W.J.; Gale, A.S.; Lees, J.A. & Caron, M.; 2004: ''The Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage, Mont Risou, Hautes-Alpes, France'', Episodes 27, pp. 21–32.