A candidate stratotype for the Precambrian–Cambrian boundary, Fortune Head, Burin Peninsula, southeastern Newfoundland

Abstract

The Burin Peninsula exhibits an exceptionally thick and essentially continuous succession of marine strata through the Precambrian-Cambrian transition. Fossils are abundant and include trace fossils, small shelly fossils, vendotaenid algae, soft-bodied megafossils, and microfossils. The Burin Peninsula is readily accessible and has long been considered a potential area for a Precambrian-Cambrian boundary stratotype. A continuous section through the upper part of member 1 and all of member 2 of the Chapel Island Formation is exposed at Fortune Head, and this section is herein proposed as a global stratotype for the Precambrian-Cambrian boundary. The boundary horizon is located 2.4 m above the base of member 2 of the Chapel Island Formation. This horizon marks the base of the basal Cambrian Phycodes pedium (ichnofossil) Zone and immediately overlies the top of the Late Precambrian Harlaniella podolica (ichnofossil) Zone. Shelly fossils (sabellitids) first appear a few metres below the proposed boundary. Soft-bodied megafossils, carbonaceous impressions of ventotaenid algae, and organic-walled microfossils occur both below and above this boundary and enhance global correlation with this section. Fossils of the Rusophycus avalonensis (ichnofossil) Zone first appear midway through member 2 (approximately 135 m above the proposed boundary) and occur commonly throughout the upper part of the Chapel Island Formation and the overlying Random Formation. Calcareous small shelly fossils (?Circotheca sp.) appear near the top of member 2 (approximately 400 m above the proposed boundary), and a more diverse Aldanella attleborensis small shelly fossil assemblage characterizes the uppermost strata of member 3 and all of member 4 of the Chapel Island Formation (approximately 550-650 m above the proposed boundary). The lowest trilobites, representatives of Callavia broeggeri Zone, first appear more than 1000 m above the proposed Precambrian-Cambrian boundary.