Browsing by Author "Kaaya, Charles"

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    The quaternary stratigraphy, tectonics and sea level fluctuations in Northern Dar es Salaam area- Tanzania
    (University of Dar es Salaam, 1984) Kaaya, Charles
    A detailed geomorphological and geological study on a 75km2 coastal strip of Dar es Salaam has been carried out. The area comprises three main morphological units trending more or less parallel to the present coast. The highest Inland plateau lies between 4o and 9om above sea level. It consists of Mio - Pliocene, fluviatile, deltaic to estuarine claybound sands. In two places it is overlain unconformably by Lower Pleistocene Wazo Hill and Kunduchi reef limestones. The next morphological unit, the Coastal plain or Tangs terrace, represents a meridional down faulted and down warped block against the Inland plateau. It lies between 7.5 and 30m above sea level and consists of reef limestones and loose, poorly sorted elastics. Together they overlie the claybound sands. The grain size analysis and sedimentary structures of the elastics indicate that they are terrestrial flash flood deposits, although occasional mollusca shells on the surface and 5 minor terraces indicate an erosive marine incursion on top. The lowest morphological unit, Mtoni terrace, lies between 0 and 5m above sea level. It consists of Holocene to recent beach sands, lagoonal and salt marsh deposits. The spectrum of heavy mineral assemblage in all clastic sediments is nearly similar. Hydrodynamic segregation accounts for areal and vertical variation rather than difference in source area or chemical weathering. Montmorillonite and illite are the main clay minerals indicate that they are weathering products of Mg-rich metamorphic rocks of the Usagaran system and were deposited in a poorly drained, alkaline environment. E.S.R. and 234Th / 230u dating have been unsuccessful due to technical problems. Thick lamellibranchia shells are suitable and recommended for future dating. A tentative geological history is reconstructed. The area is a typical tectonic coast where both sea level fluctuations and tectonics are responsible for the terrace morphology.