The Beothuka terranova (Radiolaria) assemblage and its importance for the understanding of early Ordovician radiolarian evolution

Abstract

The radiolarian Beothuka terranova occurs in the Arenigian Didymograptellus bifidus Biozone (uppermost Lower Ordovician) of Spitsbergen (Svalbard), associated with a diverse and wellpreserved radiolarian fauna. The presence of typical Cambrian spicular radiolarians associated with derived spherical forms shows a gradational faunal change from the Cambrian to the Ordovician. The genus and species Antygopora ordovicica n. gen. et n. sp. is described.

THE MIDDLE ORDOVICIANPROVENTOCITUM PROCERULUMRADIOLARIAN ASSEMBLAGE OF SPITSBERGEN AND ITS BIOSTRATIGRAPHIC CORRELATION

“…1). This level compares to the Yapeenian to Lower Darriwilian (Maletz and Bruton 2005) or the Upper Arenig to Lower Llanvirn as first suggested by Fortey and Holdsworth (1971). The authors reported radiolarians from three levels within an interval of five meters, but did not document these faunas separately.…”

“…It was interpreted to be of mid‐Arenig age based on the close proximity to levels with the Upper Bendigonian to Chewtonian graptolite fauna 5 of Stone and Smellie (1988). Maletz and Bruton (2005) referred the Proventocitum procerulum assemblage to the Lower to Middle Darriwilian, based on the observation that the assemblage differs considerably from Chewtonian to Castlemainian (Upper Floian to Lower Dapingian) assemblages of western Newfoundland and Spitsbergen. A comparison of radiolarian assemblages from the Lower to Middle Ordovician is here attempted to get a better idea on the exact biostratigraphic distribution of the Proventocitum procerulum assemblage and to understand its composition.…”

“…Diagnosis (emended from Maletz and Bruton 2005 ). Spherical spumellarians with one or more shells, formed by a thin layer pierced by round pores with elevated rims and ornamented on the surface with distinct connecting ridges forming a honeycomb pattern in some, but not all species; the internal microsphere may produce a variable number of external spines.…”

“…Remarks. The genus has been recognized in western Newfoundland and Spitsbergen (Maletz and Bruton 2005, 2007), but may be more widely distributed. Early species are spineless, but biostratigraphically younger species bear a variable number of outer spines, originating from a microsphere.…”

“…6U: Antygopora ordovicica ). The typical honeycomb pattern of the surface is easily recognizable under the SEM (Maletz and Bruton 2005, 2007), but impossible to see in transmitted light (Text‐fig. 6N, U, Y).…”