Marine evaporites from an oceanic island in the Neoproterozoic Adamastor ocean

We report a hitherto unknown occurrence of ancient Neoproterozoic evaporite deposits from an allochthonous terrane in the Pan-African Gariep belt in Namibia. Low contents of Rb, Cs, Ba, Zr, Hf, Th, and U, flat chondrite-normalised rare earth element (REE) patterns, Sr/Sr ratios as low as 0.7075, Na–Cl–Br systematics of fluid inclusion leachates, and high dB values for stratiform tourmalinites, together with geologic evidence, such as association with oceanic basalt, gabbro, and stromatolitic dolomite, point to a marine evaporitic origin. An atoll environment on an oceanic island is envisaged as a likely depositional setting. In the associated mafic sequence we found a diamictite with metre-sized ice rafted detritus, suggesting the presence of sea ice cover at relatively low latitude around the time of evaporite deposition. Based on chemostratigraphic (Sr/Sr, dC) comparison with passive continental margin sediments in the para-autochthonous external part of the Gariep belt, a correlation of the mafic diamicitite with the global Varangian (590–560 Ma) glaciation is proposed. © 2001 Elsevier Science B.V. All rights reserved.