The Archean Moodies Group (3.23–3.08 Ga), Barberton Greenstone Belt, South Africa, is the oldest known, well-preserved, quartz-rich sedimentary sequence on Earth. The Moodies Group is composed mainly of arkosic, lithic, and quartzose sandstones deposited in a range of terrestrial, marginal marine, and shallow-marine settings. Moodies strata are divided regionally into contrasting petrologic sequences by the Inyoka fault. North of the fault, Moodies strata include two petrofacies: the Oosterbeek and Elephant’s Head petrofacies. The Oosterbeek petrofacies, making up the lower two-thirds of the group, is characterized by a low proportion of unstable lithic grains and chert, common K-feldspar, a high proportion of monocrystalline quartz, and high percentage of framework grains. This petrofacies corresponds stratigraphically to an upward-fining and-deepening sequence representing strata deposited in alluvial to open-shelf facies. The overlying Elephant’s Head petrofacies is characterized by a variable but high proportion of chert, the near absence of feldspar, and a low abundance of matrix, monocrystalline quartz, and unstable lithic grains. This petrofacies corresponds to an overall upward-coarsening trend representing increasing uplift in the source area and southward progradation of syndeformational alluvial fans. All preserved Moodies strata south of the Inyoka fault are assigned to the Angle Station petrofacies, which is characterized by a lack of preserved feldspar. These southern strata were probably deposited in one or more basins that were separate from those to the north. Interpretation of sandstone provenance based on modal analysis is aided by studies of conglomerate-clast compositions, paleocurrents, shale geochemistry, and detailed stratigraphic and structural mapping. Monocrystalline quartz and K-feldspar were derived from intermediate and silicic plutonic rocks, probably located north or northwest of the present outcrops. All remaining grain types can be accounted for by rocks within the greenstone belt. Metamorphic source areas, such as the Ancient Gneiss Complex in Swaziland, probably did not contribute significantly to the Moodies Group. The petrofacies in the Moodies Group north of the Inyoka fault correspond to two distinct tectonic stages. The Oosterbeek petrofacies may have been related to subsidence and extension following orogeny during and immediately following deposition of the underlying Fig Tree Group. The Elephant’s Head petrofacies records uplift of source areas to the north, erosion, and southward transport of debris in late Moodies time. Late Moodies sedimentation occurred mainly within a foreland basin. South-facing alluvial fans near the top of the sequence record south-or southeastward-directed shortening and the start of the last major phase of greenstone belt deformation.