Mineralogical and Biogenic Composition of the Zanzibar Channel Sediments, Tanzania
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Date
2000
Authors
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Publisher
Estuarine, Coastal and Shelf Science
Abstract
Sediments from the Zanzibar Channel have been analysed for mineralogical and biogenic composition. The main
objective of the study was to describe the depositional environment of the sediments based on these parameters. The
study was also conducted to give an insight into sediment provenance of the sediments. Quartz, feldspar (both microcline
and plagioclase) and hornblende are the main mineralogical components, while zircon, muscovite, biotite and augite
occur as accessory minerals. The quartz grains are generally angular to sub-angular and highly strained, indicative of
immature sediments, probably derived from highly metamorphosed rocks. The presence of hornblende also supports the
conclusion that the sediments are immature. A possible source is the metamorphic rocks of the Mozambique belt, located
about 25–50 km from the coastline. Benthic foraminifera are the dominant biogenic constituents. Other common
biogenic constituents are molluscs (pelecypods and gastropods) and corals. Bryozoans and ostracods are relatively less
common, while sea urchins are accessory biogenic components. The composition and abundance of these biogenic
components and morphological, sedimentological and mineralogical data permit construction of a simple model which
distinguishes between three bio-physiographic settings in the Zanzibar Channel using depth contours: (1) the coastal zone
(0–10 m depth); (2) the reef platform/patch reefs zone (10–20 m depth) and (3) the central channel zone (>20 cm depth).
In the coastal zone, the sediments are dominated by fine sand, sized with a very prominent fine sand mode. The
proportion of benthic foraminifera is lower than in the other two zones (<45%) as is the biogenic:quartz ratio (<2), but
the lithogenic concentration is highest (>25%). Two lithogenic mineral components (quartz and feldspar) occur in
significant proportions. In the reef platform/patch reefs zone, the sediments are coarse to medium sand sized with no
distinct mode. the proportion of benthic foraminifera is highest (80–85%) there, and so is the biogenic:quartz ratio (>10)
but that of lithogenic components is lowest (<5%). In the central channel zone, the sediments are medium to fine sand
sized and often bimodal, with a prominent fine mode and a less prominent coarse mode. The proportion of benthic
foraminifera (70–75%) is also higher than in the coastal zone but slightly lower than in the reef zone. The proportion of
lithogenic components (5–20%) is higher than in the reef zone but lower than in the coastal zone and the biogenic:quartz
ratios is intermediate.
Description
http://linkinghub.elsevier.com/retrieve/pii/S0272771400906863
Keywords
Benthic foraminifera, Sediment sources, Mineralogy, Composition
Citation
Shaghude, Y.W. and Wannäs, K.O., 2000. Mineralogical and biogenic composition of the Zanzibar Channel sediments, Tanzania. Estuarine, Coastal and Shelf Science, 51(4), pp.477-489.