NEWFOUNDLAND: A KEY AREA FOR ORDOVICIAN RADIOLARIAN BIOSTRATIGRAPHY

Paleozoic radiolarians have been discovered in rocks as old as Middle Cambrian and are often abundant and well preserved. Their fast faunal turnover makes them perfect candidates for biostratigraphic purposes in deep water sediments, but they also occur associated with diverse macrofaunas in more shallow water sediments. Radiolarians are common in early Paleozoic successions of western Newfoundland, especially in the Cow Head and Table Head Groups of the Humber Arm Allochthon.

The oldest faunas in the Cow Head Group are from the Upper Cambrian Martin Point Member, in which graptolite faunas are not present. The Upper Cambrian to Tremadoc radiolarians represent the order Archaeospicularia and a number of poorly understood groups like the Aspiculuminidae and early Entactinaria. A number of diverse radiolarian faunas from Tremadoc and Arenig rocks of the Broom Point and St. Pauls Member are associated with common graptolites allowing a precise dating of these levels. The Arenig radiolarian faunas from the St. Pauls Member are dominated by spumellarian radiolarians showing various types of their shell development. Antygopora species with their unique sheet-like surfaces bearing pores with raised rims, are common from the Didymograptellus bifidus zone (Chewtonian) on and diversify in the Isograptus victoriae lunatus Zone (Castlemainian 1). Nyfrieslandia species with one or more spheres constructed of round bars are abundant in the D. bifidus zone. Typical labyrinthine shells representing early Haplotaeniatumidae are moderately common in the Castlemainian, but may be lacking in the Chewtonian. Sphaeroentactiniidae appear for the first time in the D. bifidus zone, but their ranges are not further constraint.

Radiolarians are also common in the Table Head Group, where they have been found associated with graptolites of the Nicholsonograptus fasciculatus to Pterograptus elegans graptolite zones. These faunas are highly distinct form older faunas, dominated by inanniguttids with a variable number of spherical shells. Species of Nyfrieslandia and Antygopora are lacking altogether. The Haplotaeniatuminidae are rare, possibly due to ecological factors.