Browsing by Author "Kasanzu, Charles H."

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    Evidence for a record of possible Paleo-Tsunami or storm deposits in the fluviatile Neoproterozoic Malagarasi Supergroup of NorthWestern Tanzania
    (Tanzania Journal of Science, 2020-06-08) Kasanzu, Charles H.; Manya, Shukrani
    Two different localities within the fluviatile Neoproterozoic Malagarasi Supergroup of north-western Tanzania show striking evidence for tsunami related clastic sedimentary deposits. In each locality, the outcrops are characterised by the association of fine grained, thinly laminated shales at the bottom that are overlain by thick deposits of sandstones and conglomerates whose clasts and pebbles vary in size and angularity/roundness. In each case, the two rock units are separated by an erosional surface. The basal shale layers are consistent with deposition in deep shelf environments which are in stark contrast to the immediately overlying conglomerates/sandstones that suggest reworking under high energy conditions. The consistent association of erosional surfaces coupled with the deposition of adjacent low and high energy facies are interpreted as a result of an ancient earthquake triggered tsunami or storm that abruptly changed the depositional energy at the two localities. We propose that a backwash wave transported pebbles and sediments from the shore setting towards the basin interior depositing them on the shale units. Given the limited preservation of such unusual sedimentological deposits in ancient terranes, these two localities in the Neoproterozoic Malagarasi basin provide information on the effects of tsunami or storm impacts in Precambrian basins of Tanzania.
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    Geochemistry and Sm-Nd systematics of the 1.67 Ga Buanji Group of southwestern Tanzania: Paleo-weathering, provenance and paleo-tectonic setting implications
    (Elsevier, 2017-09) Kasanzu, Charles H.; Maboko, Makenya A. H.; Manya, Shukrani
    We present major and trace and Nd-isotopic data of the ∼1.67 Ga Buanji Group of southwestern Tanzania in order to constrain the nature of their protolith and the intensity of chemical weathering in the source terranes and make inferences on the nature of climatic conditions during the late Paleoproterozoic in the region. Major and trace element contents of the shales from three stratigraphic formations are comparable to those of the post-Archaean Australian Shale (PAAS) and the average Proterozoic Shale (PS). They are characterized by enrichments in LREE relative to HREE ((La/Yb)CN = 9.07–13.2; (Gd/Yb)CN = 1.51–1.85) and negative Eu anomalies (Eu/Eu* = 0.61–0.81); features which are comparable to those of PAAS and PS, indicating upper continental sources. Provenance proxy ratios, together with abundances of Cr, Ni, Co and V that increase up-stratigraphy suggest a decreasing input of felsic detritus up-stratigraphy. Chemical Indices of Alteration (CIA) for the lower, middle and upper Buanji formations are 81, 76 and 79, respectively. These indices largely indicate intermediate (ca. 60–80) to extreme (>80) weathering intensities of the precursor rocks. These observations may suggest the prevalence of warm, humid climates during the late Paleoproterozoic in the region.
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    Reconstruction of Pliocene-Pleistocene Sediment Sources and Weathering Intensity in the Paleo-Life Rich Olduvai and Laetoli Basins of Northern Tanzania Using Major and Trace Element Geochemistry and Sr Isotopic Data
    (Elsevier, 2016-07) Kasanzu, Charles H.; Maboko, Makenya A. H.; Manya, Shukrani
    Major and trace elements and Sr isotopic compositions were analyzed for samples from the Pliocene-Pleistocene to Recent Olduvai and Laetoli basins of northern Tanzania with the aim of constraining their provenance and paleo-climatic conditions. The Olduvai samples are characterised by La/Cr ratios of 0.69–3.73, Th/Sc = 1.12–24.6 and 87/Sr/86Sr = 0.70448–0.70563; features which suggest the volcanic facies of the nearby Olmoti as their possible source. The relatively lower values for the Laetoli basin (Th/Sc = 0.4–0.9 and 87/Sr/86Sr = 0.70412–0.70508) coupled with Zr/Nb, Nb/Ta ans Zr/Hf ratios are suggestive of a mafic protolith inferred to be the Sadiman lavas. The calculated Chemical Index of Alteration (CIA) values for the Laetoli samples are 58–78% (mean = 65%) indicating higher weathering intensities of the source compared to 45% in the Olduvai samples. The calculated Mean Annual Precipitation (MAP) values are higher at Laetoli (mean = 950 ± 181 mm/yr) relative to Olduvai (mean = 694 ± 181 mm/yr) consistent with increased rainfall in the Pliocene during the deposition of Laetoli strata when compared to the Pleistocene times when the Olduvai sediments were deposited. The CIA and MAP patterns observed at Laetoli and Olduvai can be related to temporal changes in weather conditions during the Pliocene and Pleistocene, respectively. The Lower CIA and MAP values at Olduvai imply the prevalence of arid to semi-arid climatic conditions during the Pleistocene whereas the higher values at Laetoli correspond with wetter conditions during the Pliocene times. This could have the potential for improved eutrophication at Laetoli. The climatic inferences drawn from CIA and MAP data may point to a more favourable habitat for life proliferation in the wetter environment of Laetoli compared to the drier Olduvai. This inference is consistent with archaeological evidence which indicates a greater abundance of hominin fossils including the well preserved footprints in Laetoli.