Climate, sediment supply and tectonics as controls on the deposition and preservation of the aeolian-fluvial Etjo Sandstone Formation, Namibia

Deposition and subsequent preservation of the Jurassic-Cretaceous Etjo Sand stone Formation of Namibia represents a complex interplay between climatic and tectonic factors and related variations in extrabasinal sediment supply . The aeolian and fluvial deposits indicate semi-arid to arid climatic cond itions throughout the deposition of four distinct sedimentary units. The su ccession records either an upward increase in aridity or an upward increase in aeolian sediment supply, represented by a transition from a fluvially d ominated basal unit, through a marginal fluvial-aeolian unit to an exclusiv ely aeolian unit. A combination of inherited palaeotopography and syndeposi tional extensional faulting provided the space necessary for the accumulati on of much of the succession. A basinwide unconformity (super surface) divi des the succession. This hiatus resulted partly from a lack of available pr eservation space and partly from a shutdown in aeolian activity related to a regional climatic reorganization. A subsequent shift in the palaeowind di rection from northwesterly to southwesterly exploited sand reserves in the Parana Basin of South America and led to the resumption of aeolian sediment ation across the region. Variations in preserved bedform thickness were dir ectly controlled by differential amounts of tectonic subsidence across the basin. A second major super surface towards the top of the succession resul ted from the regional shutdown of large tracts of the aeolian system follow ing the eruption of Etendeka hood basalts across the region.