Fine Red Marly Sst Fm
Type Locality and Naming
Mid-Zambezi Basin. Mid-Zambezi Valley, Zimbabwe. This is a classic, descriptive stratigraphic name coined by early geologists (such as A.J.C. Molyneux and later formalized by G. Bond) during the 20th-century mapping of the Rhodesian (Zimbabwean) Karoo Supergroup. Middle formation in Stormberg Gr in Mid-Zambezi Basin.
Synonym:
Lithology and Thickness
A relatively fine-grained, highly oxidized "red bed" sequence. It consists predominantly of fine-grained, pink to deep red, calcareous (marly) sandstones, heavily intercalated with deep red, purple, and occasional greenish mudstones and siltstones. Calcareous nodules (calcrete) are frequently found throughout the mudstone horizons.
Relationships and Distribution
Lower contact
Conformably and transitionally overlies the shallow-water, often structurally distinct Ripple-Marked Flagstone Fm (which in turn overlie the coarse Escarpment grit Fm).
Upper contact
Unconformably to paraconformably overlain by the much coarser, high-energy, braided-river deposits of the Pebbly Arkose Fm.
Regional extent
Well-exposed in the Mid-Zambezi Basin of northern Zimbabwe and southern Zambia, often forming the lower, gentler slopes beneath the prominent ridges held up by the Pebbly Arkose Fm and Forest Sandstone Fm. Upper Karoo (Lower Stormberg Gr equivalent). It is often grouped stratigraphically with the underlying Ripple-Marked Flagstone Fm. Regionally; it roughly correlates with the uppermost Beaufort Gr (Burgersdorp Fm) or the lowermost Stormberg Gr in the Main Karoo Basin of South Africa.
GeoJSON
Fossils
Age
Depositional setting
Semi-arid continental floodplains and low-energy fluvial environments.
Additional Information
This formation records the transitional climatic phase of the Mid-Zambezi basin, marking the shift from the wet, high-energy braided streams of the Escarpment Grit to an increasingly dry, stable floodplain, before tectonic activity renewed the high-energy braided streams of the overlying Pebbly Arkose.