New U-Pb zircon dates for the Neoproterozoic Ghubrah glaciation and for the top of the Huqf Supergroup, Oman

The Huqf Supergroup, Oman, contains volcanic horizons with the potential to calibrate Neoproterozoic events and chemostratigraphy using U-Pb zircon ge ochronology, A tuffaceous bed near the base, within the lower (Ghubrah) dia mictite and beneath a lower cap carbonate, provides the first C-Pb zircon d ate obtained from within a Neoproterozoic glacial deposit, This date of 723 +16/-10 Ma suggests a Sturtian age. Diamictites about 1 km higher in the s ection are overlain by the Hadash cap dolomite, which compares with cap dol omites above Marinoan glacial units elsewhere. A U-Pb zircon age of 544.5 /- 3.3 Ma from ignimbrites in the Fara Formation, near the top of the super group, is just beneath that of the Precambrian-Cambrian boundary (ca, 543 M a), consistent with the presence of the Neoproterozoic skeletal-fossil Clou dina in correlative subsurface rocks, This revised chronology confirms the existence of four negative delta(13)C excursions between ca, 723 and 543 Ma , the lower two of which are clearly associated with glaciations.