Albian-Cenomanian foraminifera in northeastern British Columbia and western Alberta: Paleoecology and integration of biostratigraphy with allostratigraphy

The Rocky Mountain foredeep in northeastern British Columbia and northwestern Alberta preserves an expanded Albian to Cenomanian interval in outcrop and subsurface that documents a nearly complete sea-level record of the Western Interior Sea at that time. Current foraminiferal subzonations that were based on multiple short stratigraphic intervals and are linked to lithostratigraphic frameworks make correlations to areas of less accommodation space to the east and south problematic. An extensive subsurface and outcrop database based on sedimentology and wireline logs in this region resulted recently in a new allostratigraphic framework that forms the basis for new biostratigraphic correlations. Micropaleontological analysis of a complete section at Deadhorse Meadows has led to a new foraminiferal zonation where faunal changes are linked to allostratigraphic surfaces. This zonation was tested in previously used outcrops and lateral faunal distribution correlates remarkably well to the new allomember architecture. Latest Albian faunas represent highstand and falling stage systems tracts, where maximum abundances occur in the middle of the deposits associated with maximum flooding intervals. Cenomanian strata also represent transgressive system tracts associated with the Greenhorn transgression.; Latest Albian foraminiferal assemblages in this region consist almost entirely of benthic agglutinated species controlled by cool, low salinity waters of the Mowry Sea. Distribution of morphotypes, related to feeding strategies indicate lower shoreface to marginal marine environments confirming lower paleosalinities and paleoenvironmental and paleogeographic interpretations based on sediment facies. Lowest Cenomanian strata are barren of foraminifera due to bottom water anoxia. An increase in the oxygen minimum zone resulted in increased organic matter entering the water column during rapid transgression. As the basin deepened during continued Greenhorn transgression uncoiled and serial morphotypes began to colonize the mudstone dominated facies indicating normal marine paleosalinties and the return of bottom water oxygenation.