314 Latest Ordovician solitary rugose corals of eastern North America

Latest Ordovician solitary rugose corals of eastern North America - BAP #314

This study comprises comprehensive taxonomic, paleoecologic, biostratigraphic, and paleobiogeographic analyses of latest Ordovician (Richmondian and Gamachian; Ashgill) solitary rugose corals in eastern North America. The corals are assigned to three provinces distinguished on the basis of assemblages and characteristic species. The distribution of these provinces, as well as taxa within them, was determined by regional environmental parameters related to paleogeography. During Richmondian time, the Richmond Province occupied a narrow belt extending northward from the Nashville Dome of Tennessee, along the Cincinnati Arch region of Kentucky, Indiana, and Ohio to northern Michigan, and eastward through southern Ontario and Quebec. It coincided with a carbonate platform at the margin of an epicontinental sea that was receiving clastic sediments from the Queenston delta (Ontario, New York, Pennsylvania, and Ohio). Solitary coral diversity was low, but variability within several species was high. The following taxa were present: Streptelasma divaricans (Nicholson, 1875b), Grewingkia canadensis (Billings, 1862), G. deltensis n. sp., and G. rustica (Billings, 1858a). This province was isolated by the positive Canadian Shield, Taconic Mountains, and Nashville Dome, and by deeper water in which the Maquoketa Group shale of the upper Mississippi valley was deposited.

Solitary corals in the Maquoketa Group and those at the eastern continental margin belonged to the Red River-Stony Mountain Province, which included most of the North America during the Late Ordovician. The vast continental interior portion was occupied by shallow, interconnected epicontinental seas, whereas normal open marine environments were present at the continental margins. The Maquoketa Subprovince was characterized by the paucity and very low diversity of solitary corals in carbonate beds within shales of the Maquoketa Group. The following taxa were present: Helicelasma randi Elias (1981) and Bighornia cf. B. patella (A. E. Wilson, 1926). The diverse assemblage associated with carbonate sequences in the Maritime Subprovince  (Anticosti Island and the Gaspe Peninsula of Quebec, and northern Maine) included typical continental interior species together with genera characteristic of North American continental margins and Baltoscandia. The following taxa were present: Streptelasma rankini n. sp., S. affine (Billings, 1865), Helicelasma selectum (Billings, 1865), Deiracorallium angulatum (Billings, 1862), Grewingkia penobscotensis n. sp., G. pulchella (Billings, 1865), Grewingkia sp., Lobocorallium trilobatum vaurealense (Twenhofel, 1928), Kenophyllum? Sp., Bodophyllum neumani n. sp., Bodophyllum? Sp., B. englishheadense n. sp., Bighornia cf. B. patella (A. E. Wilson, 1926), and Paliphyllum ellisense (Twenhofel, 1928).

At the end of Richmondian time, regression of the eastern North American epicontinental sea resulted in extinction of corals in the Richmond Province and Maquoketa Subprovince. The latest Ordovician (?Gamachian) Edgewood Province coincided with a carbonate sequence deposited in normal open marine environments during a transgression into the continental interior (upper Mississippi valley). The solitary corals resembled those previously restricted to continental margins, and foreshadowed the cosmopolitan Silurian fauna. The following taxa were present: Streptelasma leemonense n. sp., Streptelasma sp., S. subregulare (Savage, 1913), and Bodophyllum shorti n. sp.

R.J. Elias