The Fish River Subgroup in Namibia: Stratigraphy, Depositional Environments and the Proterozoic–Cambrian Boundary Problem Revisited
Geol. Mag. 142 (5), 2005, pp. 465–498. c 2005 Cambridge University Press 465 doi:10.1017/S0016756805000956 Printed in the United Kingdom The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic–Cambrian boundary problem revisited G. GEYER* Institut fur¨ Palaontologie,¨ Bayerische Julius-Maximilians-Universitat¨ Wurzburg,¨ Pleicherwall 1, D-97070 Wurzburg,¨ Germany (Received 16 October 2003; accepted 15 March 2005) Abstract – The Fish River Subgroup of the Nama Group, southern Namibia, is restudied in terms of lithostratigraphy and depositional environment. The study is based on partly fine-scaled sections, particularly of the Nababis and Gross Aub Formation. The results are generally in accordance with earlier studies. However, braided river deposits appear to be less widely distributed in the studied area, and a considerable part of the formations of the middle and upper subgroup apparently were deposited under shallowest marine conditions including upper shore-face. Evidence comes partly from sedimentary features and facies distribution, and partly from trace fossils, particularly Skolithos and the characteristic Trichophycus pedum. Environmental conditions represented by layers with T. pedum suggest that the producer favoured shallow marine habitats and transgressive regimes. The successions represent two deepening-upward sequences, both starting as fluvial (braided river) systems and ending as shallow marine tidally dominated environments. The first sequence includes the traditional Stockdale, Breckhorn and lower Nababis formations (Zamnarib Member). The second sequence includes the upper Nababis (Haribes Member) and Gross Aub formations. As a result, the Nababis and Gross Aub formations require emendation: a new formation including the Haribes and Rosenhof and possibly also the Deurstamp members.
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