Abstract
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.