Lithostratigraphy of the Pietermaritzburg Formation (Ecca Group, Karoo Supergroup), South Africa

Abstract

Abstract The Lower Permian Pietermaritzburg Formation is a mudrock-dominated, upward-coarsening stratigraphic unit in the lower Ecca Group (Karoo Supergroup) in the northeastern part of the main Karoo Basin of South Africa. The formation extends over most of the KwaZulu-Natal Province, and due to its lithology and the local climate, it is usually poorly exposed; hence the description is mainly based on borehole records. From a measured thickness of about 430 m south of the type area around Pietermaritzburg, the formation thins progressively northwards and pinches out against the Dwyka Group and pre-Karoo basement north of latitude 26° 30' S. This Lower Permian formation is considered a stratigraphic equivalent of the Prince Albert Formation in the southern part of the main Karoo Basin. The Pietermaritzburg Formation only preserves scattered, fragmentary plant fossil and invertebrate trace fossils, which are diagnostic of marine conditions (e.g. Helminthopsis). Based on its sedimentary facies characteristics and ichnofossil assemblages, the unit was probably deposited under low energy conditions on a northerly shallowing marine shelf that initially experienced deepening (during a major Artinskian transgression) and then shallowing in the early Kungurian.