Early Ordovician (early Arenig) radiolarians from the Cow Head Group and review of the Little Port Complex fauna, Western Newfoundland

Abstract

Radiolarians recovered from the lower Arenig strata in the Point of Head Section, Cow Head Group, include 5 families, 9 genera, and 21 species and subspecies. Among these, seven species are new: Antygopora littleportensis, Beothuka spongiosa, B. echinata, B.? concreta, Nyfrieslandia crassispinosa, Sphaeroentactinia? multiradiata, and Westernbrookia incohota. The red chert of the Little Port Complex also yielded five species of radiolarians. The two faunas share three dominant species: Antygopora ordovicica, Beothuka terranova, and B. aitchisoni. The extremely low diversity of the Little Port Complex fauna seems to be due to selective preservation.The isotopic age of the Little Port Complex is reported to be of the Middle Cambrian [508 and 505 (−2+3) Ma]. According to a previous radiolarian study on the red chert of the Complex, the fauna was assigned to the basal Tremadoc based on co-occurring conodonts. However, a recently recovered index fossil conodont from the Complex, Oepikodus evae, indicates that the fauna belongs to the O. evae conodont zone. The common three dominant species, as mentioned above, which make up more than 95% of the total individuals in the Little Port Complex and the strata assigned to O. evae conodont zone and Pendeograptus fruticosus graptolite zone of the Cow Head Group suggest that the two faunas are coeval in the lower Arenig.