Sedimentology, tectonic framework and economic potential of the Sinakumbe Group (? Ordovician to Devonian) and Karoo Supergroup (Permo-Carboniferous to Lower Jurassic) in the mid-Zambezi Valley Basin, southern Zambia.

• Main Author: Nyambe, Imasiku Anayawa.
• Other Authors: Dixon, O. A.
• Format: Others
• Published: University of Ottawa (Canada) 2009
• Subjects: Geology.
• Online Access: http://hdl.handle.net/10393/10370; http://dx.doi.org/10.20381/ruor-16795

Sediments of the Ordovician to Devonian Sinakumbe Group ($\sim$210 m thick) and overlying Late Carboniferous to Early Jurassic Karoo Supergroup ($\sim$4.5 km thick) were deposited in the mid-Zambezi Rift Valley Basin, southern Zambia. The Sinakumbe Group directly overlies the Precambrian Basement Complex, and Lower and Upper subgroups are recognised. The Karoo Supergroup unconformably overlies the Precambrian Basement or rests locally on the Sinakumbe Group. Lower and Upper groups are recognised in the Karoo, with their contact approximately at the Permian-Triassic boundary. From base to top, the Lower Karoo Group is subdivided into the Siankondobo Sandstone, Gwembe Coal, and Madumabisa Mudstone formations and the Upper Karoo Group into the Escarpment Grit, Interbedded Sandstone and Mudstone, Red Sandstone and Batoka Basalt formations. Limited palaeontological data from the mid-Zambezi Valley Basin suggest that the Siankondobo Sandstone is Late Carboniferous to Early Permian in age, the Gwembe Coal Formation is Early Permian, the Madumabisa Mudstone is late Permian, and the Interbedded Sandstone and Mudstone Formation is Early to Middle (?) Triassic. The Sinakumbe Group is recognised for the first time in outcrops. The Lower Sinakumbe Group ($\sim$60 m thick) is a coarsening-upward allocyclic sequence that represents progradation of an alluvial fan-lobe (conglomerate facies assemblage) down slope across mud flat and sand flat environments (mudrock facies assemblage) in response to tectonic uplift followed by waning subsidence. The disconformably overlying Upper Sinakumbe Group (over 150 m thick) consists predominantly of massive to stratified, medium-grained to pebbly quartz arenite lithofacies with subordinate mudclast breccia lithofacies. This quartz arenite facies assemblage is interpreted as braided-stream deposits in which the mudclast breccia lithofacies represents channel bank collapse. The Permo-Carboniferous Siankondobo Sandstone Formation (90 m thick) contains three facies assemblages. A diamictite facies assemblage is interpreted as subaqueous debris flow deposits from glacier melt-water. A succeeding siltstone facies assemblage is attributed to density underflows of sediment-laden meltwater flowing into a glacial lake, and sediment settling from suspension. A sandstone facies assemblage was emplaced by a variety of grain-support mechanisms, and the downstream accretion surfaces in the upper part of the assemblage indicate fluvial deposition in a deltaic setting. The Lower Permian Gwembe Coal Formation (280 m thick) represents deposition of sandstones, siltstones and mudstones in fluvial channels and on flood plains, and of coals in shallow swampy areas. Fourteen lithofacies in the formation are grouped into four facies assemblages. The Maamba Sandstone facies assemblage is probably a high-sinuosity meandering stream deposit. Accumulation of organic deposits (coal facies assemblage) in the swamps was interrupted by deposition of channel, crevasse channel and splay, levee (Interseam Sandstone) and overbank fine deposits. One sandstone body (Sandstone A facies assemblage) represents a change in fluvial style from proximal braided system to high-sinuosity meandering stream. The Triassic Escarpment Grit Formation (up to 500 m thick), consists of coarse to very coarse grained stratified sandstone (grit), with locally abundant conglomeratic sandstone lags, that grades into finer-grained sandstone and intercalated mudstone. This sandstone/mudrock facies assemblage occurs in poorly arranged fining-upward cycles interpreted as braided river deposits. The Middle (?) Triassic Interbedded Sandstone and Mudstone Formation (up to 2000 m thick), consists of a mudrock/sandstone facies assemblage arranged in fining-upwards cycles of sandstone (pebbly to very fine-grained, with basal lags and conglomerates), siltstone and mudstone. (Abstract shortened by UMI.)