Carbon-isotope stratigraphy of the Furongian Berry Head Formation (Port au Port Group) and Tremadocian Watts Bight Formation (St. George Group), western Newfoundland, and the correlative significance

Abstract

Carbon-isotope stratigraphy of the Furongian (stage 10; Upper Cambrian) and Tremadocian (lowermost Ordovician) reveals distinct variations from the carbonates of the Berry Head and Watts Bight formations of the East Isthmus Bay section that accumulated in a shallow-marine setting on the eastern Laurentian platform in a passive margin setting in western Newfoundland, Canada. The East Isthmus Bay δ13C values show insignificant correlation with their Sr (R2 = 0.04), Mn (R2 = 0.001) and Fe (R2 = 0.02) counterparts, implying preservation of at least near-primary C-isotope compositions. The investigated section is largely fossil poor, but the δ13C profile shows a pattern with distinct variations that can be matched with those of the western Laurentian Lawson Cove Auxiliary Boundary Stratigraphic Section and Point (ASSP) section, Utah, USA. Therefore, it was possible to reconstruct a conodont biozonal scheme by matching the δ13C profile with its counterpart from the Lawson Cove ASSP section. At the base of the East Isthmus Bay section, the δ13C profile exhibits a broad excursion (the top of the Herllnmaria – Red Tops Boundary), which can be matched with the base of the Eoconodontus Zone (mid-Furongian), followed by an enrichment trend through the Cordylodus intermedius Zone (top Furongian). A positive excursion (Hirsutodontus simplex spike) is recorded in the Cordylodus intermedius Zone (top Cambrian), and a prominent positive peak characteristic for the Cordylodus lindstromi Zone is recorded from the top of the investigated section. The δ13C values of the Newfoundland carbonates are generally ∼1‰ Vienna Pee Dee Belemnite lower than those of Lawson Cove, which is likely attributable to a relatively higher productivity and (or) organic burial in the Utah region.