T260 Cambrian–Ordovician Faunas and Events: A Session in Honor of John F. Taylor and John E. Repetski

Wednesday, 12 October 2022
1:30 PM - 5:30 PM
Mile High Ballroom 4A

FORTUNE HEAD AND THE CAMBRIAN GSSP AT BURIN PENINSULA, SOUTHEASTERN NEWFOUNDLAND, EASTERN CANADA: REVISITING AN EXCEPTIONAL ICHNOLOGIC AND STRATIGRAPHIC SUCCESSION

Paper number: T260-6
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM

Authors

Abstract

In 1992, the Cambrian GSSP was placed at the first appearance of the trace fossil Treptichnus pedum at Fortune Head, Burin Peninsula, southeastern Newfoundland, eastern Canada. Fortune Head hosts a remarkable 450 m-thick, continuous siliciclastic succession encompassing upper Ediacaran to Fortunian strata. Although the quality of the section was noted in the 1980s, current debates surrounding the decision on the GSSP have not always given proper consideration to its excellent sedimentology, stratigraphy, and evolutionary significance. Here, we present new datasets from Fortune Head focussing on bioturbation intensities (Bioturbation Index or BI, and Bedding Plane Bioturbation Index or BPBI), burrow width and depth, trace fossil composition and stratigraphic appearance, ichnodiversity and ichnodisparity, as well as a revision of the sedimentology and depositional environment interpretation. The Fortune Head succession demonstrates a significant increase in trace fossil abundance, diversity, and disparity within a 14.0 m interval across the Ediacaran-Cambrian boundary interval. Late Ediacaran trace fossils are usually simple and horizontal (e.g. Archaeonassa fossulata) (BPBI = 2-3), whereas vertical bioturbation is incipient (e.g. Treptichnus isp.) (BI = 0-1). The depth (up to 0.8 cm) and width of burrows (up to 0.3 cm) are also limited. Conversely, the Fortunian is marked by a slight increase in vertical bioturbation (BI = 1-2) in concordance with marked increases in burrow width (up to 1.0 cm) and depth (up to 3.5 cm). Evolutionary changes across the Ediacaran-Cambrian boundary interval took place in offshore and shelf environments. Following upward in the succession, the Fortune Head succession demonstrates an increase in bioturbation intensities (BI = 1-4, BPBI = 2-5) associated with the emergence of larger sediment bulldozers (e.g. producer of Psammichnites gigas circularis) in lower shoreface, offshore, and shelf environments that aided in the development of a sediment mixed layer by the Cambrian Age 2. Therefore, excellent outcrop quality, stratal continuity, recurrence of depositional environments, and evolutionary signal as depicted at Fortune Head are instrumental in understanding early steps in animal evolution prior to the body fossil diversification of the Cambrian Explosion.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379857

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