The Early Cretaceous Moosebar Sea in Alberta

Abstract

ABSTRACT Marine mudstone deposited in the Early Albian Moosebar sea has been recognized in outcrop sections along the Alberta Foothills from Smoky River to Fall Creek, 160 km (100 mi) northwest of Calgary. The contact between the Moosebar Member of the Malcolm Creek Formation and the underlying Gladstone Formation is abrupt and disconformable, being marked by a thin bed of pebbles and glauconitic mudstone. The upper calcareous member of the Gladstone Formation yielded an interpreted brackish-water fauna in the central and northern Alberta Foothills but an entirely freshwater fauna in the southern Foothills. Equivalent beds in the Gething Formation between Smoky and Wolverine Rivers in the northern Alberta and northeastern British Columbia Foothills appear to be nonmarine, associated with a major deltaic complex. Marine influence again is present in upper beds of the Gething Formation north of the Wolverine River. The microfaunal assemblages in the Moosebar Member point to an open-marine environment in the Smoky River area changing progressively southward to a brackish-water environment in the central Foothills, and ultimately a freshwater environment at the southern extremity of the Moosebar Sea near Fall Creek. The Moosebar Sea transgressed southward along the Early Cretaceous drainage system, forming an extensive estuary during late Gladstone time. During deposition of the Moosebar sediments, the sea extended farther south, probably to about present-day latitude 52° in the Foothills, inundating most of the highlands adjacent to the estuary. Similar events and environments are interpreted for the Alberta Plains region where the Clearwater Formation is equivalent to the Moosebar Member.