Journal of
Geology and Mining Research

  • Abbreviation: J. Geol. Min. Res.
  • Language: English
  • ISSN: 2006-9766
  • DOI: 10.5897/JGMR
  • Start Year: 2009
  • Published Articles: 169

Article in Press

Sedimentary facies analysis and depositional environments of the Buanji Group, Chimala (East), SW Tanzania

Godson Godfray and Joshua J. Mahwa

  •  Received: 07 May 2019
  •  Accepted: 18 September 2019
This work presents a facies analysis of Buanji Group based on field data. The succession is divided into two depositional sequences which are lower siliciclastic units (ranging between 600 – 750 m thickness) of the lower and middle Buanji and upper non-clastic – clastic strata (600 ± 20 m thickness) of the middle and Upper Buanji Units. Six lithofacies (conglomerate (F1), sandstone (F2), siltstone/mudstone (F3), shale (F4), dolomite (F5) and chert (F6)) are identified within the lower, middle and upper units. The major facies of the Buanji Group are also characterized by numerous sub-lithofacies such as massive sandstone (Sm), trough and planar cross-stratified sandstone (St, Sp), parallel laminated sandstone – siltstone (Sh), massive to parallel laminated mudstone – shale (Fl, Fsc1 – 3), dolomite(D1) to dolomitic chert (D2), chert (C1) and thin beds of ortho- and para-conglomerate (Gmm, Gcm) interbedded with reddish brown shales (Fsc2) of the lower Buanji Group, where the sequence shows a fining-upward trend with a minor coarsening-upward trend in some sandstone facies. The facies associations characterize numerous repetitive fining-upward units and cycles, indicating various sub-environments (channel, floodplain, overbank or waning flood, restricted basin with moderate depth setting) in the fluvial regime. The conglomerates (Gcm, Gmm) might have been deposited as debris flow or channel lag deposits. The sandstones (Sm, Sp, Sh and Fl) were deposited mainly as a multistoried channel in ascetically braided and sinuous streams. The red shales (Fsc1) interbedded with conglomerate and sandstone lithofacies show floodplain to flood basin environments and the greenish-greyish shales (Fsc3), dolomite (D1, D2) and chert (C1) were deposited in a complex moderately depth lake/pond setting environment. The lower part of a succession of the lower and middle Buanji strata suggests that the facies were deposited in a fluvial environment where the depositional basin has more braided channels and sinuous stream setting. The upper cycle where deposited in a flooded basin environment forming reducing moderately depth lake/pond setting.

Keywords: Lithofacies, Depositional sequence, Buanji Group, Vertical profile, Depositional environments, fluvial, moderate depth setting