AGNOSTID TRILOBITES AND SMALL SHELLY FOSSILS (SSFS) FROM THE DRUMIAN (MIDDLE CAMBRIAN) MANUELS RIVER FORMATION, CONCEPTION BAY SOUTH, NEWFOUNDLAND, CANADA - IMPLICATIONS FOR BIOSTRATIGRAPHY, PALEOBIOGEOGRAPHY AND PALEOGEOGRAPHY

The Drumian (middle Cambrian, Series 3) Manuels River Formation exposed along Manuels River at Conception Bay South, Newfoundland, Canada, consists of fossiliferous grey to black shales with limestone interbeds and concretions. The rock succession is interpreted as having been deposited in a shallow-marine, oxygen-depleted environment. Agnostid trilobites collected from the shales and determined by use of modern systematic concepts are assigned to the species Peronopsis fallax (Linnarsson, 1869), Peronopsis scutalis (Hicks, 1872), Hypagnostus parvifrons (Linnarsson, 1869), Ptychagnostus punctuosus (Angelin, 1851), Ptychagnostus affinis (Brøgger, 1879), Ptychagnostus atavus (Tullberg, 1880), Tomagnostus fissus (Lundgren in Linnarsson, 1879), Tomagnostus perrugatus (Grönwall, 1902), Pleuroctenium granulatum (Barrande, 1846) and Eodiscus punctatus (Salter, 1864).

The phosphatized small shelly fossils (SSFs), preserved in calcareous concretions of the formation, comprise a fairly low-diversity assemblage of brachiopods, hexactinellid sponge spicules and fragments of trilobites and indeterminate taxa. As a result of the early-diagenetic formation of the concretions, the SSFs are generally well preserved in three dimensions, in contrast to the more flattened specimens found in the surrounding shales.

The agnostid biozones of the Manuels River Formation can be correlated regionally and globally. The composition of the fauna and the resulting biostratigraphy are useful instruments for reconstructing the position and movements of the early Paleozoic microcontinent Avalonia within the paleobiogeograpic framework of the surrounding continents. The results challenge parts of the previous concepts of Avalonian biostratigraphy, agnostid faunal provinces and the paleogeographic position within the peri-Gondwanan realm.

Financial support by the Klaus Tschira Foundation (KTS 00.195.2011 and 00.272.2015) is gratefully acknowledged.