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Published July 16, 2022 | Submitted
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The Shuram excursion: A response to climate extremes at the dawn of animal life


The Ediacaran-aged Shuram excursion was the last and largest of the Neoproterozoic negative carbon isotope anomalies. Recognized in stratigraphic successions around the globe, it precedes diverse evidence for macroscopic, multicellular life, and follows the Cryogenian global glaciations and Ediacaran Gaskiers glaciation. Hypotheses for the cause of the Shuram excursion can be broadly grouped into those that argue for post-depositional diagenetic alteration of the carbon isotope record and those that argue the extremely low δ¹³C values reflect a primary perturbation to the carbon cycle. Given the timing and magnitude of this event, distinguishing between these disparate hypotheses, or combining them, is critical for reconstructing the environmental conditions under which complex life evolved on Earth. We test specific predictions of each model using a range of stratigraphic observations and micro- and macro-analytical techniques. We find that the type sections in Oman where the Shuram excursion was first described are well preserved and contain a range of features difficult to reconcile with a post-depositional origin. However, many salient features are consistent with an extreme warming event coupled to a carbon cycle perturbation, analogous to the Paleocene-Eocene Thermal Maximum (PETM), and increased middle Ediacaran volcanism. We propose that cooling associated with the recovery was critical for origination rates of macroscopic soft-bodied organisms.

Additional Information

CC_BY_NC_ND_4.0. K.D.B. thanks JC Creveling, Dave Johnston, and Andy Knoll for providing comments on early drafts of this work. C. Ma, J. Hurowitz, N. Kitchen, and Y. Guan provided assistance with analytical measurements. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the US Department of Energy Office of Science by Stanford University. S. Webb and J. Johnson helped with the XANES measurements at SLAC and provided standard data. We thank Petroleum Development Oman employees for helpful discussions, particularly Gideon Lopes Cardozo, Sven Scholten, and Irene Gomez Perez. Funding for analytical measurements was provided by the Agouron Institute and NASA Astrobiology Institute. We thank the Ministry of Oil and Gas, Sultanate of Oman for permission to publish this manuscript. Thure Cerling, Lou Derry, and an anonymous reviewer provided helpful criticism of an earlier verison of this manuscript. K.D.B. acknowledges funding from the Packard Foundation and NASA Exobiology Grant 80NSSC19K0464. M.D.C. was supported by a National Defense Science and Engineering Graduate Fellowship; K.D.B. and M.R.O. were supported by National Science Foundation Graduate Research Fellowships during their PhDs; Author Contributions: K.D.B. and W.F. conceptualized the study. K.D.B., M.R.O., and M.C. conducted field investigations. K.D.B. wrote the original draft. K.D.B contributed formal analysis, software, and visualization. All authors reviewed and edited the manuscript; Data and materials availability: All data are provided in the main text or in the supplementary materials. Data, figures, and code are available at Open Science Framework (link) for reviewers and will be made publicly available on manuscript acceptance.

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August 22, 2023
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