Escarpment grit Fm
Type Locality and Naming
Mid-Zambezi Valley, Zimbabwe, Tuli Basin, Luangwa Basin (Zambia). This descriptive name was given by early geologists because this highly resistant, coarse-grained unit forms prominent, steep cliffs and escarpments throughout the Zambezi basin, creating a stark topographical contrast with the softer, underlying mudstones. Lowermost formation in Stormberg Gr in Mid-Zambezi Basin. Lower formation in Beaufort Gr in Tuli Basin
Synonym:
Lithology and Thickness
A massive, high-energy clastic sequence. It consists predominantly of very coarse-grained, gritty, pebbly feldspathic sandstones (arkose) and lenses of quartz-pebble conglomerate. It exhibits prominent, large-scale trough and planar cross-bedding. The sand grains are typically angular to sub-angular, indicating rapid transport and deposition.
Relationships and Distribution
Lower contact
Rests with a profound regional unconformity upon the fine-grained, greyish-green lacustrine beds of the Upper Madumabisa Mudstones Fm (Lower Karoo). Overlies with Fulton's Drift Mudstones Fm in Tuli Basin and Upper Madumabisa Mbr in Luangwa Basin (Zambia)
Upper contact
Conformably and transitionally overlain by the lower-energy, thinly bedded lacustrine/floodplain deposits of the Ripple marked Flagstone Fm. Overlain by the Red Beds Fm in Tuli Basin and Ntawere Fm in Luangwa Basin (Zambia)
Regional extent
Widespread and topographically prominent across the rift basins of northern and southern Zimbabwe, southern Zambia, and extending into parts of Mozambique. Basal unit of the Upper Karoo sequence (Zimbabwe). It broadly correlates chronostratigraphically with the Katberg Fm (Beaufort Gr) or with the Molteno Fm (lower Stormberg Gr) in the Main Karoo Basin of South Africa.
GeoJSON
Fossils
Age
Depositional setting
High-energy, continental braided river and alluvial fan environments. The Escarpment Grit represents a dramatic shift in basin dynamics. Following a long period of quiet, muddy lakes (Madumabisa Mudstone), massive regional tectonic uplift and faulting along the basin margins rejuvenated the landscape. This triggered vast, fast-flowing, gravel-choked braided river systems to sweep across the basin, carving into the older muds and dumping massive volumes of coarse sand and gravel.
Additional Information