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 the diversity and complexity of the earliest macroscopic multicellular organisms in the fossil record. A key question is whether this excursion reflects a primary perturbation to the carbon cycle, which would provide crucial insights into the environmental conditions shaping the earliest animals, or whether it is largely an artifact of later diagenetic alteration. To evaluate the extent of diagenesis in these rocks and constrain how much of the excursion reflects a primary signal, we investigate the sedimentology and geochemistry of carbonate strata in Oman using a variety of techniques spanning multiple spatial and temporal scales. Our multi-faceted analysis identifies and characterizes four modes of diagenetic alteration, with sediment-buffered conditions and authigenic carbonate precipitation as the dominant processes. However, the degree of alteration is insufficient to account 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 changing conditions in both terrestrial and marine environments, offering unique insights into Earth's systems during a pivotal time in early animal evolution.