Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa

The Middle Permian Abrahamskraal Formation is the lowermost formation of the lower Beaufort Group (Adelaide Subgroup, Karoo Supergroup) in the main Karoo Basin. It has been amalgamated with the lithologically similar and age-equivalent Koonap Formation and now occupies the entire southern part of the main Karoo Basin. It consists of greenish-grey and less common reddish-brown mudrock and subordinate light grey fine-grained sandstone, arranged in fining-upward, 1st to 3rdorder cycles that range in thickness from a few metres to a few tens of metres. It reaches a maximum thickness in the southwest part of the basin (2200 to 2565 m) and thins northeastward with younging of the lower contact with the underlying Ecca Group and overlap of the overlying Middleton Formation onto the Ecca Group in the vicinity of Petrusville. The Abrahamskraal Formation contains several arenaceous zones in the southwest part of the basin, which increase in thickness towards a source area located along the southwest margin of the basin. The sedimentary facies represent deposition on a vast alluvial plain with lateral and downstream accretionary sand bodies in fluvial channels and floodbasin and subordinate lacustrine muds and silts in the extensive interchannel areas. Biostratigraphically, the Abrahamskraal Formation falls within the Tapinocephalus Assemblage Zone. However, along the southwestern margin of the basin, this zone is underlain by the Eodicynodon Assemblage Zone.