Lower Madumabisa Mudstones Fm
Type Locality and Naming
Mid-Zambezi Basin (Zimbabwe and southern Zambia). Named after Madumabisa Hill near Hwange (formerly Wankie) in northwestern Zimbabwe. It represents the basal unit of the thick, tripartite Madumabisa Mudstone succession, originally subdivided and formally defined by Geoffrey Bond in the mid-20th century. Uppermost formation in Ecca Gr in Mid-Zambezi Basin. Lower formation in Beaufort Gr in Luangwa Basin (Zambia)
Synonym:
Lithology and Thickness
A heavily carbonaceous and organic-rich argillaceous sequence. It is composed primarily of dark grey to black carbonaceous shales and mudstones. Unlike the middle and upper divisions, it frequently contains distinct beds of ironstone (siderite nodules), thin lenses of micaceous sandstone at its base, and highly coaly shale horizons, though it generally lacks the thick, minable coal seams found in the underlying units.
Relationships and Distribution
Lower contact
Conformably and abruptly overlies the coarse-grained Upper Wankie Sandstone Fm (or directly overlies the Black Shale and Coal Gr in areas where the sandstone is absent).
Upper contact
Conformably and transitionally overlain by the dark, but slightly less coaly, carbonaceous shales of the Middle Madumabisa Mudstones Fm.
Regional extent
Widespread across the Mid-Zambezi Basin in Zimbabwe (especially well-documented in the Hwange coalfield region) and extending across the Zambezi River into the southern basins of Zambia. Upper Ecca Gr equivalent. It closely correlates chronostratigraphically and environmentally with the upper portions of the Vryheid Fm or the Volksrust Fm in the Main Karoo Basin of South Africa.
GeoJSON
Fossils
Age
Depositional setting
Paludal (swamp), distal deltaic, and restricted shallow lacustrine environments.
Additional Information
The Lower Madumabisa is an important stratigraphic marker because its transition from the underlying coal measures represents a basin-wide sequence boundary (a major flooding surface) in the Zambezi region.