MAGNETOSTRATIGRAPHY OF THE TYPE-MARINOAN SUCCESSION AND CORRELATIVES THROUGHOUT AUSTRALIA

High-resolution magnetostratigraphy through the type-Marinoan deglacial succession documents as many as 5 geomagnetic reversals in a putatively conformable succession, including at least three geomagnetic reversals intimately associated with the Nuccaleena cap dolostone. These reversals, correlatable over 50 km between three sections, offer a fingerprint for calibrating carbon and other stable isotopic excursions across the Australian continent at the beginning of Ediacaran time, during the transition from Snowball Earth to a less severe climatic mode.

Using duration-of-reversal statistics, it appears likely that deglaciation of Snowball Earth lasted some ten times longer (ca. 100,000 years) than Pleistocene deglaciation, with onset of cap carbonate deposition diachrononous to not more than ca. 3,000 years. Cessation of cap carbonate deposition may be considerably more diachronous, influenced by various, specific basinal dynamics. These timescales imply that methane clathrates likely contribute only a part of the negative isotopic signal of cap carbonates; and that upwelling of stratified bottom water appears likely but must be matched by enhanced alkalinity flux from continental runoff over a prolonged interval.