Abstract

Ostracods are common and well preserved in the Frasnian Hay River Formation of the Great Slave Lake area and in the equivalent strata of northeastern Alberta. Five zones, with local divisions, are recognized and traced along a north-south line of section to relate the stratigraphy of these widely separated regions.

The type section of the Hay River Formation comprises all shales and limestones cropping out along Hay River from Great Slave Lake to the base of Alexandra Falls, in addition to the shales above the Middle Devonian carbonates penetrated in the adjacent Frobisher Hay River No. 4 well. These sequences carry all five ostracod zones, although much of the basal zone is missing due to onlap. Towards the northwest, west and southwest, the varied and rich benthonic ostracod faunas diminish drastically in a short distance; cricoconarids become dominant, and pelagic ostracods increase relatively in number and variety. These conspicuous faunal changes are to be related to environmental differences, resulting from increase in water depth and possibly changes in current pattern.

Correlative ostracod zones are recognized in the Waterways, Cooking Lake, and part of the Ireton Formations of northeastern Alberta. These Frasnian formations disconformably overlie the Givetian Slave Point Formation.

The ostracods compare closely with species recorded from the Frasnian Cerro Gordo Formation of Iowa and the Frasnian beds of the Russian platform.