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The profound glaciations of the Neoproterozoic Cryogenian period (ca. 850–544 Ma) represent an extreme climatic mode when, it is claimed, Earth was fully or almost completely covered with ice for millions of years. We show that the geochemistry and mineralogy of fine-grained Neoproterozoic sedimentary rocks in Oman are best explained by climatic oscillations that drove variations in the intensity of chemical weathering on contemporary land surfaces. The cold climate modes of the Cryogenian were therefore cyclical, punctuated with well-defined warm-humid interglacial periods. The hydrological cycle and the routing of sediment were active throughout the glacial epoch, which requires substantial open ocean water. This reconstruction represents a significantly different target for numerical climate models at this critical time in the evolution of Earth's biosphere. [ABSTRACT FROM AUTHOR]

Although Earth is widely believed to have undergone a series of extreme low-latitude snowball glaciations during the Neoproterozoic (ca. 1000-543 Ma), only one reliable pa- leomagnetic result, from Elatina, South Australia, places glacial rocks close to the equator. We report new paleomagnetic data from the Neoproterozoic Huqf Supergroup of Oman that pass fold and reversal tests and yield a paleopole at 52.3°S, 074.4°E (N = 25 sites; α95 = 7.3°). This paleopole places the Muscat region of Oman at a latitude of 13° in the late Neoproterozoic and provides the first direct evidence that both glacial and overlying cap carbonate units were deposited in the tropics. The presence of glacial-interglacial cyclicity within the Huqf Supergroup indicates that areas close to the equator may have been largely free of ice at the time of deposition, a result that is inconsistent with the classic snowball Earth model. Our result precludes the possibility that contrasting lithologies mark a phase of rapid plate motion and provides the first evidence for low-latitude glaciation in Arabia. A series of magnetic reversals in the Fiq tillite and the overlying Had ash dolomite, in northern and central Oman, correlates well with a similar sequence in the Mirbat Formation in southern Oman and indicates that recovery from glacial conditions took place over long time scales (possibly >105_106 yr). [ABSTRACT FROM AUTHOR]