Origins and Alteration of Ediacaran Carbonates Recording the Shuram Excursion in Oman

Abstract

The Shuram excursion is the largest known negative carbon isotope excursion in Earth's history.Recognized globally, it follows the Ediacaran Gaskiers glaciation and precedes a marked increase in thediversity and complexity of the earliest macroscopic multicellular organisms in the fossil record. A key questionis whether this excursion reflects a primary perturbation to the carbon cycle, which would provide crucialinsights into the environmental conditions shaping the earliest animals, or whether it is largely an artifact of laterdiagenetic alteration. To evaluate the extent of diagenesis in these rocks and constrain how much of theexcursion reflects a primary signal, we investigate the sedimentology and geochemistry of carbonate strata inOman using a variety of techniques spanning multiple spatial and temporal scales. Our multi‐faceted analysisidentifies and characterizes four modes of diagenetic alteration, with sediment‐buffered conditions andauthigenic carbonate precipitation as the dominant processes. However, the degree of alteration is insufficient toaccount for the range of marine sedimentologic and geochemical trends across the carbon isotope excursion.This suggests that, even with evidence of diagenesis, the rocks preserve a measurable record of changingconditions in both terrestrial and marine environments, offering unique insights into Earth's systems during apivotal time in early animal evolution.