Revised stratigraphy and age of the Red Sandstone Group in the Rukwa Rift Basin, Tanzania

The Red Sandstone Group comprises a succession of red sandstones and mudstones exposed in the Rukwa and Malawi rift basins of southwestern Tanzania and northern Malawi. Stratigraphic, sedimentologic, and paleontologic investigations of the Red Sandstone Group in the Songwe Basin (a sub-basin of the Rukwa Rift Basin) help clarify the age and depositional history of these strata, which have previously been assigned ages ranging from Middle Jurassic to late Miocene. These seemingly incompatible Mesozoic and Tertiary age assignments for the Red Sandstone Group are, in part, explained by our discovery of two distinct units (Units I and II) that are of different ages but composed of lithologically similar red sandstones and mudstones in the Songwe Basin. Based on distinct, temporally limited vertebrate fossil remains, a Cretaceous age is proposed for Unit I and a Paleogene age for Unit II. The identification of different-aged units in the Songwe Basin suggests a complex structural and stratigraphic history for the Red Sandstone Group in the context of East African Rift evolution.