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The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped in four stratigraphic units: the basal, middle and upper units. and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial terrigenous elastic and chemical deposits of the upper unit. Evidence provided by primary sedimentary structures, palaeontological record, borehole data, palaeo-flow measurements and stratigraphic relations resulted in the palaeo-environmental reconstruction of the upper unit.

The dominant facies assemblages are represented by sandstones and finer-grained sediments, which both can be interbedded with subordinate intraformational coarser facies. The facies assemblages of the upper unit are interpreted as deposits of a low-sinuosity, ephemeral stream system with calcretes and silcretes in the dinosaur-inhabited overbank area. During the deposition of the upper unit, the climate was semi-arid with sparse precipitation resulting in high-magnitude, low-frequency devastating flash floods. The current indicators of the palaeo-drainage system suggest flow direction from northwest to southeast, in a dominantly extensional tectonic setting.

Based on sedimentologic and biostratigraphic evidence, the upper unit of the Tuli Basin correlates to the Elliot Formation in the main Karoo Basin to the south. (C) 2002 Elsevier Science Ltd. All rights reserved.