Late Archaean foreland basin deposits, Belingwe greenstone belt, Zimbabwe

The c. 2.65 Ga old sedimentary Cheshire Formation of the Belingwe greenston e belt (BDB), central Zimbabwe, has been studied in detail for the first ti me to shed some light on the much debated evolution of this classical belt. The Cheshire Formation rests sharply on a mafic volcanic unit (Zeederbergs Formation) and comprises a basal, eastward-sloping carbonate ramp sequence built of shallowing-upward, metre-scale sedimentary cycles. The cycles str ongly resemble Proterozoic and Phanerozoic carbonate cycles and might have formed by small-scale eustatic sea level changes. The top of the carbonate ramp is represented by a karst surface. The carbonates are overlain by and grade laterally to the east into deeper water (sub-wave base) siliciclastic facies. Conglomerate, shale and minor sandstone were deposited by high- to low-density turbidity currents and were derived from the erosion of Zeeder bergs-like volcanic rocks from the east. Shortly after deposition, the Ches hire Formation and underlying volcanics were affected by a northwest-direct ed thrusting event. Thrusting gave rise to the deformation of semi-consolid ated sediments and resulted in the juxtaposition of a thrust slice of Zeede rbergs basalts onto Cheshire sediments. The stratigraphy, asymmetric facies and sediment thickness distribution, palaeogeographic constraints and evid ence for an early horizontal tectonic event suggest that the Cheshire Forma tion formed in a foreland-type sedimentary basin. (C) 2001 Elsevier Science B.V. All rights reserved.