WHERE SOUTH MEETS NORTH: A PALEOCEANOGRAPHIC FRONT IN THE WESTERN INTERIOR SEAWAY DURING OCEANIC ANOXIC EVENT 2
Billings was in a unique position in the seaway that at times shared foraminiferal traits similar to the southern US WIS, and at other times with the northern Canadian WIS. We attribute the changes in foraminiferal assemblages to shifting positions of an oceanographic front between Tethyan and Boreal waters as sea level changed. Prior to OAE2, the front was near Billings as the region was dominated by agglutinated taxa characteristic of Boreal waters. At the onset of OAE2, a brief pulse of calcareous benthic and planktic foraminifera correlative with the widespread “Benthonic Zone”, a time of increased benthic diversity associated with bottom water ventilation with the rapid incursion of Tethyan waters. At the peak of OAE2, the oceanic front moved northward as agglutinated taxa were again abruptly replaced by calcareous taxa signaling an expansion of Tethyan waters with continued transgression. TheHeterohelixshift, Gavelinella acme, and subsequent change to Neobulimina-dominance are also recognized at Billings, but are delayed relative to sections further south. Canadian sites, meanwhile, contain abundant planktic foraminifera, but are virtually absent of benthic taxa, signaling the most northern edge of the oceanic front. As sea level fell, the front shifted southward, and agglutinated taxa returned to Billings.