Late Ordovician brachiopods and biostratigraphy of the Hudson Bay Lowlands, northern Manitoba and Ontario

Abstract

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.

Late Ordovician brachiopods from eastern North Greenland: equatorial offshore migration of the Red River fauna

“…This confirms the correlation of the Centrum Sø succession with the D . occidentalis – H. capax biozone of Jin et al. (1997), although the current study suggests that H. gigas occurs stratigraphically above H. capax in North Greenland (Fig.…”

“…The present study had access to Troedsson’s original type material, which is reposited at the Natural History Museum of Denmark. Based on the measured parameters listed in Table 1 and those published by Jin et al. (1997) and Jin and Zhan (2001), I am confident that Troedsson’s (1928) type material indeed should be identified as H. capax (Conrad, 1842).…”

“…Following Jin and Zhan (2001), this further indicates that the upper part of the Børglum River Formation correlates with the D . occidentalis – H. capax biozone of the Churchill River Group of the Hudson Bay Basin (Jin et al. 1997).…”

TrueDalmanellaand taxonomic implications for some Late Ordovician dalmanellid brachiopods from North America

“…Examination of large populations from the Cincinnati type area, each comprising more than 100 well-preserved shells, indicates that this ribbing characteristic is basically invariable, making it reliable for taxonomic and phylogenetic interpretations. In the consistent development of a dorsal medial costa, the Cincinnatian 'Dalmanella' is more closely related to Paucicrura and Diceromyonia which are common in the Upper Ordovician of North America, especially in tropical epeiric sea settings (Wang 1949;Cooper 1956;Hall 1962;Walker 1982;Rice 1987;Jin & Norford 1996;Jin et al 1997;Jin & Zhan 2001. Their similarity is also indicated by the development of aditicules, strongly differentiated, twosized punctae, and a trilobate cardinal process, as will be discussed below.…”

Evolution of theRhynchotrema–Hiscobeccuslineage: implications for the diversification of the Late Ordovician epicontinental brachiopod fauna of Laurentia

“…With the wide dispersal of Hiscobeccus in Laurentia during Maysvillian-Richmondian time (Figs 1, 2), gigantism became evident in many species, characterized by increasingly larger, more globular shells with more pronounced, imbricated growth lamellae covering nearly the entire shell surface. The trend of gigantism seems to have been more pronounced in the palaeoequatorially located Williston and Hudson Bay basins than in the higherlatitude of the palaeotropics (Macomber 1970;Alberstadt 1973;Amsden 1983;Jin 1996Jin , 2001Jin et al 1997;Jin & Zhan 2001).…”