Foraminifers and Other Microfossils from the Early Cretaceous Mannville Group in Saskatchewan
Atkin, Kenneth Thomas James
Deposition of the basal Cretaceous Mannville Group in the Lloydminster area and in adjoining areas of Saskatchewan farther to the east was profoundly influenced by the Clearwater sea, which formed a gulf over what is now the western Prairie Provinces during Early Albian time. The presence of between twenty-five and thirty species of foraminifers, which are dominantly agglutinated but in part calcareous walled and which occur in diminishing variety and number through the Mannville sequence, provide the principal evidence of marine influence. The foraminifers belong to the assemblage diagnostic of the Marginulinopsis collinsi-Verneuilinoides cummingensis Zone. Alternation of beds containing foraminifers with those lacking foraminifers but containing numerous megaspores suggest alternation of marine and non-marine environments of deposition and, thus, repetition of transgression and regression over the Lloydminster and adjacent areas. Within the deposits of the Clearwater marine gulf as a whole, proportion calcareous-walled foraminifers form a greater of the foraminiferal fauna in the Rocky Mountain foothills than in Saskatchewan. The calcareous walled component also becomes more prevalent to the north northwest, the direction from which the sea advanced, and likely reflect increasingly open-marine (less restricted) environments of deposition. Be that as it may, the presence of marine foraminifers now establishes that marine conditions prevailed within Saskatchewan at least as far east as Prince Albert and as far south as Saskatoon. Pense sediments were deposited during the earliest temporary phase of marine transgression that led ultimately to deposition of the Late Albian Joli Fou sediments. Hence, the Pense Formation, upper of the two formations that constitute the Mannville Group across much of southern Saskatchewan, should be removed from the Mannville Group and classified with the Joli Fou FOrmation in the Oolorado Group.