Multi-proxy paleoenvironmental and paleoecological reconstruction of the Foremost Formation (Upper Cretaceous, Campanian) of Alberta

The Foremost Formation of southern Alberta, Canada, is the basal member of the Cretaceous (Campanian) Belly River Group and has been understudied relative to the overlying Oldman and Dinosaur Park formations of this group. Here we describe and analyze the sedimentology, foraminiferal micropaleontology, vertebrate microsite paleoecology, and paleoenvironmental conditions of the Foremost Formation. Outcrop of the Foremost Formation is characterized by estuarine and shallow marine facies that transition upward into coastal/fluvial facies that accumulated during the Claggett marine regression of the Western Interior Seaway (WIS). This is consistent with at least two rapid transgressive events driven by local subsidence interrupting the overall regressive phase of the Claggett marine cycle, creating the aggrading profile in the lower portion of the sections measured here, and suggesting that orogenic buildup in the Rocky Mountains and its associated basin subsidence were a controlling factor of local deposition in the WIS. A low abundance, low diversity agglutinated benthic foraminiferal fauna suggests frequently stressed oxygen and salinity conditions in marginal marine environments. Vertebrate microsite faunas display a mixed freshwater to brackish water environmental influence, with an increase in diversity upsection in conjunction with increased freshwater influence. Among dinosaurs, ceratopsids and ankylosaurs experience notable relative abundance decreases through the Foremost Formation and into the lower Oldman Formation, potentially reflecting preference for coastal habitats and/or plant resources relative to other terrestrial herbivores.