Late Ordovician brachiopods and biostratigraphy of the Hudson Bay Lowlands, northern Manitoba and Ontario
Authors: Jin J , Caldwell W G E , Norford B S 
Published: November 2016

Brachiopods of the Upper Ordovician (Maysvillian- Richmondian) rocks of the Portage Chute, Surprise Creek, Caution Creek, and Chasm Creek formations and the undivided Bad Cache Rapids and Churchill River groups of the Hudson Bay Lowlands comprise 15 genera and 27
species of orthids, strophomenids, rhynchonellids, and atrypids, including one new species, Tetraphalerella churchillensis, an unusually large and flat strophomenid. Strophomenids are the dominant group, rhynchonellids and orthids are relatively common, and atrypids occur in small numbers at a few
localities. Pentamerid and athyrid brachiopods have not been found, and inarticulate brachiopods are known only in the Kaskattama Province No. 1 Well.
Two brachiopod assemblage zones are recognized, which correspond approximately to the Bad Cache Rapids and Churchill River groups, respectively. The lower Tetraphalerella churchillensis-Kjaerina hartae Zone contains 13 species, which indicate a Maysvillian age for the uppermost Portage Chute and
Surprise Creek formations. The basal Portage Chute Formation has sparse fossils and cannot be dated precisely. The boundary between the lower zone and the Dinorthis occidentalis- Hiscobeccus capax Zone is defined by the appearance of 11 species in the lower Caution Creek Formation. Twenty-one
species in the upper zone indicate a Richmondian age for the Caution Creek and Chasm Creek formations.
In composition, the brachiopod faunas of the Hudson Bay region are most closely related to those from the Upper Ordovician rocks of southern Manitoba. Many species in the T. churchillensis-K. hartae Zone are also present in the Selkirk Member of the Red River Formation, and those in the D.
occidentalis-H. capax Zone are characteristic of the Gunn and Penitentiary members of the Stony Mountain Formation. Although represented largely by fragmentary specimens, the T. churchillensis-K. hartae Zone can be recognized between depths of 873.8 and 746.6 m in the Kaskattama Province No. 1 Well,
extending into the Churchill River Group. Elements of the D. occidentalis-H. capax Zone are present at depths of 732.3 to 733.2 m, but the upper Churchill River Group and the Red Head Rapids Formation of the well have not yielded enough diagnostic brachiopods to allow the stratigraphic limits of the
zone to be determined.
Lithological and fossil evidence indicates that distribution of the brachiopod faunas in the Hudson Bay Basin was not as strongly controlled by sea-level fluctuations as it was in the northeastern Williston Basin (southern Manitoba). Some brachiopod and coral species show continuous ranges from the
Bad Cache Rapids Group to the Churchill River Group, which does not support the concept of a major hiatus between the groups, as advocated by several previous studies. The two brachiopod assemblages are characterized by large shell sizes and high diversity of species, which indicate a normal, open,
shallow- and warm-water, subtidal depositional environment for the Bad Cache Rapids and Churchill River sediments during Late Ordovician time.