Sedimentology and Geochemistry of Coal Deposit in Geba Basin, Illubabor,Western Ethiopia
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Date
2000-06
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Addis Ababa University
Abstract
The sedimentary succession exposed in a 386 sq. Ian Geba basin represents one of thick
accumulations of continental sediments that are commonly known to associate the Ethiopian
Tertiary volcanics. The succession is a coal and oilshale bearing, and comprises about 150m
Conglomerate, sandstone, siltstone, mudstone, reworked tuff, oilshale and coal sediments.
They are deposited in an east-west trending intracratonic rift basin, that may be evolved
locally, from other regional contemporaneous tectonic episodes between Middle Oligocene
and Early Miocene. The whole sedimentary sequence has been distinguished into five major
sedimentological units correlable with depositional environments ranging from fluviatiles to
lacustrine. Under fluvial conditions a number of coal seams are formed in flood plain. Under
lacustrine condition, several thick coal seams have been formed in marshy areas, developed at
the margin of the lakes.
Generally, the coal beds range in thickness from few tens of centimeters to about 4.0 meters.
Chemically, they are high ash and medium sulfur coals. The maceral study reveals that
huminite dominated the organic forms of Geba coals(>85%), with high proportion of
humocollinite and minor humodetrinite sub groups. Humotelinite sub group is markedly rare.
Low inertinite «7%) and considerable liptinite, as high as 23%, are main features of the
coals. The overall petrographic aspect of the coals suggests humic origin, possibly under
shallow water condition. Reflectances measured on the huminite range from 0.32-0.39%R.
This indicates an ASTM rank ranging from lignite to lower boundary of Sub bituminous.
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Geograpy