Stratigraphy and geochemistry of a ca 800 Ma negative carbon isotope interval in northeastern Svalbard
The Neoproterozoic Akademikerbreen Group in northeastern Svalbard comprises 2 km of nearly pure carbonate section. The carbonates are generally highly 13C-enriched (δ13C>5‰), but this trend is interrupted by an ∼325 m interval of low δ13C values (−4 to 0‰) in the upper Grusdievbreen and lower Svanbergfjellet formations. An abrupt negative isotopic shift at the onset of this low δ13C interval is reproduced in detail in multiple sections along the length of the outcrop belt (125 km) and everywhere coincides with a prominent sequence boundary and change in lithology. Likewise, the return to positive δ13C values coincides with a second exposure surface. Correlation of the lower Akademikerbreen Group δ13C record with a nearly identical isotopic profile in the Bitter Springs Formation of Central Australia suggests an age of ∼800 Ma for the low δ13C interval and confirms that it is a global seawater signal. The coincidence of the negative and positive δ13C shifts with major stratigraphic perturbations in the otherwise conformable succession suggests that both episodes of transient sea level change were related to global phenomena. 87Sr/86Sr ratios rise transiently from an average of 0.7063 to 0.7066 within this interval. Whereas large negative δ13C anomalies in the Neoproterozoic are commonly associated with episodes of widespread glaciation, the Akademikerbreen low δ13C interval precedes the oldest (Sturtian) of the known Neoproterozoic glacial events, and no other evidence suggests an ice age at this time. We propose instead that the negative δ13C interval is related to a pair of inertial interchange true polar wander (TPW) events.