Abstract:
The Middle Ordovician Sunblood Formation in the South Nahanni River
area, District of Mackenzie, comprises mainly limestones and
dolostones of intertidal and shallow subtidal origin as indicated by the
presence of desiccation polygons, fenestral fabric, and oncolites.
The study of well preserved, silicified trilobites from low diversity,
Bathyurus-dominated, Nearshore Biofacies faunas of Whiterockian and
Chazyan age collected in six stratigraphic sections through the
Sunblood Formation permits the recognition of three new Whiterockian
zones, and two previously established Chazyan zones. The Bathyurus
mackenziensis, Bathyurus sunbloodensis, and Bathyurus margareti
zones (Whiterockian), together with the Bathyurus nevadensis and
Bathyurus granu/osus zones (Chazyan) represent the Nearshore
Biofacies components of a dual biostratigraphic scheme that considers
both temporal and spatial distribution patterns, and are
compositionally distinct from faunas in correlative strata around North
America that represent other biofacies.
Twenty-six species belonging to eighteen genera are described and
illustrated. Ludvigsenella ellipsepyga is established as a new
bathyurine genus, in addition to four new species of Bathyurus :
Bathyurus mackenziensis, Bathyurus sunbloodensis, Bathyurus
margareti and Bathyurus acanthopyga. Other genera present are:
Basilicus, Isote/us, ///aenus, Bumastoides, Fail/eana, Phorocepha/a,Ceraurinella, Acanthoparypha, Xystocrania, Cydonocephalus,
Ectenonotus, Pseudomera, Encrinuroides, Calyptaulax, Amphilichas and
Hemiarges.
