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Usili Formation

Usili Fm

Period: 
Permian

Age Interval: 
Late Permian (Wuchiapingian-Changhsingian)


Province: 
Tanzania

Type Locality and Naming

Ruhuhu Basin (Tanzania). Named after the Usili Mountain in the Ruhuhu Basin of southwestern Tanzania. Originally designated as the "Lower Bone Bed" or "K6" horizon by Stockley (1932) in his classic stratigraphic division, it was later formally renamed the Usili Formation by Wopfner (2002). Upper formation in Beaufort Gr in Ruhuhu Basin (Tanzania).

Synonym: Formerly known as the Kawinga Formation in older literature. K6 beds


Lithology and Thickness

Composed of a massive sequence (up to ~300 meters thick) of non-marine, fluvio-lacustrine sediments. It typically begins with a basal cross-bedded sandstone or conglomeratic unit that grades upward into a thick, monotonous succession of grey-green to purplish-red mudstones and siltstones. The mudstones are well known for containing abundant calcareous (calcrete/septarian) nodules.


Lithology Pattern: 
Siltstone


Relationships and Distribution

Lower contact

Conformably to transitionally overlies the calcareous and fine-grained Ruhuhu Fm

Upper contact

Unconformably overlain by the Triassic Manda Beds Fm

Regional extent

Geographically restricted to the Ruhuhu Basin in southwestern Tanzania. It directly correlates with the Beaufort Gr (specifically the Adelaide Subgroup / Dicynodon Assemblage Zone) in the Main Karoo Basin of South Africa, the Lower Sakamena Gr in Madagascar, and the Upper Madumabisa Mudstone Fm in Zambia.


GeoJSON

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Fossils


Age 

Late Permian (Wuchiapingian-Changhsingian)

Age Span: 

    Beginning stage: 
Wuchiapingian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
259.55

    Ending stage: 
Changhsingian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
251.90

Depositional setting

Terrestrial intracratonic rift basin.


Depositional pattern:  


Additional Information


Compiler:  

From the O. Catuneanu et al. The Karoo basins of south-central Africa, Journal of African Earth Sciences 43 (2005) 211–253; Stockley, G. M. (1932): The geology of the Ruhuhu Coalfields, Tanganyika Territory. Quarterly Journal of the Geological Society; Wopfner, H. (2002): Tectonic and climatic events controlling the deposition of the Karoo Supergroup in Tanzania. Journal of African Earth Sciences.