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.