The oldest (Early Ediacaran) Sr isotope record of mid-ocean surface seawater: Chemostratigraphic correlation of a paleo-atoll limestone in southern Siberia

Abstract

By examining Sr isotope stratigraphy of the Ediacaran paleo-atoll limestone in southern Siberia, we first demonstrated the surface seawater information from the lost Ediacaran (late Neoproterozoic) oceans. The Ediacaran Baratal limestone in the Gorny Altai Mountain in Siberia is a remnant of a mid-oceanic paleo-atoll complex developed on a paleo-seamount. Sr isotope ratios (87Sr/86Sr) from the basal 20m-thick interval of the Baratal limestone vary mostly by 0.7069–0.7079, and these show a generally increasing trend upsection. The relatively low Sr ratios indicate that mid-oceanic seawater, i.e. global seawater, was more influenced by hydrothermal activities along mid-oceanic ridges rather than continental erosion during the Ediacaran. A chemostratigraphical correlation with the hitherto known secular change in Sr isotope suggests that the basal Baratal limestone was deposited particularly in the Early Ediacaran. This timing corresponds to the immediate aftermath of the Neoproterozoic (Marinoan) snowball Earth event. The relatively low Sr isotope ratios and the increasing trend upsection are concordant with the onset of continental erosion during the deglaciation during the Early Ediacaran.