Foraminiferal response to Ecological perturbations along the eastern margin of the Canadian Western Interior seaway, Cenomanian-Turonian interval

Ecological perturbations during the Cenomanian-Turonian boundary interval along the eastern margin of the Canadian Western Interior Seaway (WIS) were investigated in a subsurface core from eastern Saskatchewan (distal) and outcrop at the Manitoba Escarpment (proximal). Paleoecological controls on biota included transgressive/regressive cyclicity, the Oceanic Anoxic Event 2, frequent ashfalls, and a stratified water column. Changes in foraminiferal assemblage composition, species richness, and abundance can be correlated between the core and outcrop. The lower Turonian biofacies at both sites is made up exclusively of planktic species, reflecting the persistent bottom water anoxia in the Canadian WIS. The low-diversity assemblage is nearly entirely composed of opportunistic, surface-dwelling species of the genera Muricohedbergella and Heterohelix, responding to water turbidity, reduced salinity, and shallow water depth. Abundances of planktic species are significantly higher in the distal core section. During the early Turonian, diversity slightly increased, with the presence of Whiteinella aprica reflecting periodic improvement of the water column conditions at both sites. The appearance of the clavate species, Clavihedbergella simplex, reflects an expanded oxygen minimum zone, also confirmed by biomarkers, particularly in outcrop. Dwarfing of foraminiferal tests is interpreted as a response to frequent ashfalls that affected the water column. Lowering of sea level during the middle Turonian allowed for seafloor winnowing and caused a brief disappearance of planktic foraminifera. The northsouth temperature gradient in the WIS resulted in a lower planktic foraminiferal diversity in what is now Canada compared to the waters that covered what is now the United States and the absence of benthic and deeper-dwelling, keeled planktic species can be attributed to an increasingly welldeveloped oxygen minimum zone or increasingly stratified water column. The appearance datum of planktic foraminifera is distinctly diachronous along a south to north transect

Early Pliocene fish remains from Arctic Canada support a pre-Pleistocene dispersal of percids (Teleostei: Perciformes)

Percid remains from Pliocene deposits on Ellesmere Island, Arctic Canada, are identified as a species of Sander, similar to the walleye and sauger of North America and the pike-perch of Europe and western Asia. They are named as a new species, Sander teneri. These remains are the most northerly percid elements found to date and suggest the palaeoenvironment was significantly warmer in the Pliocene than it is currently. The fossil remains show the presence in North America of the family Percidae as well as the genus Sander prior to the Pleistocene, indicating a previously proposed Pleistocene immigration from Europe or Asia can be discounted. These fossils contradict an earlier hypothesis that percids, in particular Sander, crossed from Eurasia to North America in the Pleistocene; instead, the fossils show percids were already in the area by the Pliocene

Late Cretaceous (Cenomanian to Campanian) paleoenvironmental history of the Eastern Canadian margin of the Western Interior Seaway: Bonebeds and anoxic events

Upper Cretaceous strata in the Pasquia Hills of the northern Manitoba Escarpment, eastern Saskatchewan, Canada provide a detailed paleoenvironmental and sea-level record of the eastern margin of the Western Interior Seaway. Sediments deposited during the Cenomanian/Turonian Greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column, with bottom-water anoxia recurrently reaching into the photic zone. A middle Cenomanian sea-level lowstand event followed by transgression left a series of bonebeds within the Belle Fourche Member of the Ashville Formation, indicating a sedimentary environment starved of coarse siliciclastics. Maximum sea level resulted in the formation of limestone beds within the Favel Formation, further favoured by reduced terrigenous sediment input compared to the western margin. Limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions, and reducing zoo- and phytoplankton diversities. During final Greenhorn regression, eastern Saskatchewan probably turned into a restricted basin severely limiting marine circulation. Poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the Cenomanian/Turonian transgressive/regressive cycle. This was caused either by a freshwater lid, stratification of Boreal and Tethyan-derived watermasses, or both, to various intensities affected by changing sea level. Basin oxygenation during Niobrara time varies between localities along the eastern margin as documented by presence/absence of benthic and planktic foraminifera