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 pedum (ichnofossil) Zone and immediately overlies the top of the Late Precambrian Harlaniella podolica (ichnofossil) Zone. Shelly fossils (sabelliditids) first appear a few metres below the proposed boundary. Soft-bodied megafossils, carbonaceous impressions of vendotaenid 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 the Callavia broeggeri Zone, first appear more than 1000 m above the proposed Precambrian–Cambrian boundary.

Ediacaran matground ecology persisted into the earliest Cambrian

“…Basal Fortunian strata in Burin Peninsula of southeast Newfoundland are represented by Member 2 of the Chapel Island Formation 5 . These deposits dominantly record sedimentation in shallow marine and deltaic settings under storm influence, as indicated by the abundance of combined-flow and wave-generated sedimentary structures, such as symmetrical to quasi-symmetrical ripples, and hummocky cross-stratification, graded tempestites, and pot and gutter casts [9][10][11][12] .…”

“…This event is thought to have taken place at the beginning of the Phanerozoic, signalling the establishment of modern-style ecosystems after 3 billion years of mostly microbial evolution 4 . On the basis of detailed analysis of the type section of the Fortunian (lowermost Cambrian) at the Global Stratotype (GSSP) for the Cambrian System in Fortune Head, southeast Newfoundland, Canada 5,6 , we document widespread microbially induced sedimentary structures (MISSs 7 ) and associated trace fossils, indicating that a microbial matground-based ecology actually persisted well into the early Cambrian. This study has significant implications with respect to the evolutionary history of the Ediacara biota because it shows a continuity of the Ediacaran taphonomic window into the early Cambrian, implying that the disappearance of this biota cannot be attributed solely to the lack of adequate preservational conditions 8 .…”

Pistas fósiles y dubiofósiles del Ediacárico y Cámbrico del Anticlinal de Alcudia, España

“…The Cambrian traces here described could belong to the lowermost Cambrian ichnozone (that is, the Treptichnus pedum + Monomorphichnus lineatus Zone in Spain, and the global and probably equivalent Treptichnus pedum Zone, see Narbonne et al, 1987;Gámez-Vintaned & Liñán, 2007). However, the time spans of these traces extend into younger zones, and so they could as well represent the second Cambrian ichnozone (the global Rusophycus avalonensis Zone and the very similar Spanish Rusophycus avalonensis + Rusophycus bonnarensis Zone; Narbonne et al, 1987;Gámez-Vintaned and Liñán, 2007).…”

“…• The FAD of spreiten-burrows in Newfoundland and Spain (Teichichnus in both cases) is in the second Cambrian ichnozone (Narbonne et al,1987;Gámez-Vintaned & Liñán, 2007). However, burrows with spreite of upper Ediacaran age have been found in the Nama Group (MacDonald et al, 2014).…”

“…However, the time spans of these traces extend into younger zones, and so they could as well represent the second Cambrian ichnozone (the global Rusophycus avalonensis Zone and the very similar Spanish Rusophycus avalonensis + Rusophycus bonnarensis Zone; Narbonne et al, 1987;Gámez-Vintaned and Liñán, 2007). This is the ichnozone information provided by the Cambrian traces: • Monomorphichnus lineatus first appear in the lowermost Cambrian ichnozone (Liñán et al, 1984;Narbonne et al, 1987;Gámez-Vintaned & Liñán, 2007). …”