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Abstract The Tonian–Ediacaran Hecla Hoek succession of Svalbard, Norway, represents one of the most complete and well-preserved Neoproterozoic sedimentary successions worldwide. With diverse fossil assemblages, an extensive carbonate δ13C record, and sedimentary evidence for two distinct Cryogenian glaciations, this succession will continue to yield insights into the Neoproterozoic Earth system; however, at present there are no direct radiometric age constraints for these strata. We present two new Re-Os ages and initial Os isotope data that constrain the timing of Neoproterozoic glaciation in Svalbard, providing further support for two globally synchronous Cryogenian glaciations and insight into pre- and post-snowball global weathering conditions. An age from the Russøya Member (Elbobreen Formation) facilitates correlation of the negative carbon isotope excursion recorded therein with the pre-glacial “Islay” excursion of the Callison Lake Formation of northwestern Canada and the Didikama and Matheos Formations of Ethiopia. We propose that this globally synchronous ca. 735 Ma carbon isotope excursion be referred to as the Russøya excursion with northeastern Svalbard as the type locality. This new age provides an opportunity to construct a time-calibrated geological framework in Svalbard to assess connections between biogeochemical cycling, evolutionary innovations within the eukaryotes, and the most extreme climatic changes in Earth history.
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An algorithm-guided Ediacaran global composite δ13Ccarb–Bayesian age model
While it remains uncertain whether excursions in the stable carbon isotopic composition of Ediacaran marine carbonate (δ13Ccarb) represent globally synchronous events (or a direct measure of ocean carbon cycling), the absence of widely distributed and readily preservable fauna, and the presence of several iconic carbon isotope excursions (CIEs), has sustained δ13Ccarb correlation as the primary means to establish relative time relationships for Ediacaran successions. Here we present an Ediacaran global δ13Ccarb composite built with a dynamic time warping (DTW) time-normalization algorithm that generates libraries of least-squares alignments between chemostratigraphic records of unequal length and distinct sediment accumulation rates. When developing a δ13Ccarb composite for each of 16 globally distributed Ediacaran paleo-depositional regions, we selected high Pearson r alignments that conformed with published geological guidance about the correlation of constituent sections. When applying DTW to align these regional algorithmic composites into one global δ13Ccarb stack, we selected alignments that allied the excursions that field workers have established (or speculated) are the Marinoan cap carbonate excursion, the Shuram excursion, and/or the basal Cambrian excursion. There are strengths and weaknesses to making explicit the temporal relationships (point-to-point correspondences) often left implicit in visual correlation. One strength is to extrapolate depositional ages by means of isotopic correlation, and here we explored this with a Bayesian Markov chain Monte Carlo age model that predicts a median age, and uncertainty, for every carbonate stratum in the global Ediacaran δ13Ccarb composite. Yet, one must caution against a false accuracy that can arise from selecting one alignment among many possibilities––the likelihood that time-uncertain time series can be stretched and squeezed into one unequivocal alignment is low. Thus, while these alignments are grounded in the expert assessment of the field worker, this global Ediacaran δ13Ccarb–Bayesian age model should be viewed as a working hypothesis to enrich, but not arbitrate, discussions of the correlation, synchrony, and completeness of Ediacaran successions.
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- Award ID(s):
- 2025735
- PAR ID:
- 10520572
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Palaeogeography palaeoclimatology palaeoecology
- ISSN:
- 0031-0182
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.palaeo.2024.112321
