Abstract:
Paleozoic sedimentary rocks in the Blue Nile of central Ethiopia are related to two major
Gondwana glaciations: namely, the Late Ordovician- Silurian and the Carboniferous- Permian
glaciation. The present study investigates sandstone sections cropping out in the BokotaboSentom and Daguja town, both of which are found around the Kuch area, in the western parts of
Blue Nile basin, central Ethiopia. The upper Paleozoic sandstones are composed of mudstones,
siltstones, and sandstones in the Bokotabo-Sentom area and deposited as sandstone-siltstoneand
tillite in the Daguja area. The present study is aimed at investigating the petrography and
geochemistry of these sandstones to evaluate the provenance, the tectonic setting, and the
paleoclimate conditions under which the upper Paleozoic sandstones were deposited. The study
was conducted using a transmitted microscope, inductively coupled plasma mass spectrometry
(ICP-MS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Based on
major, trace and rare earth element analysis and petrographic data, the upper Paleozoic
sandstones are dominated by Quartz (on average of 64.5% in Bokotabo-Sentom area and 58.4%
in Daguja area) and followed by feldspars (on average of 31.0% in Bokotabo-Sentom area and
36.6% in Daguja area) and rock fragment (on average of 3.2% in Bokotabo-Sentom area and
4.9% in Daguja area). The sandstone is medium- to coarse-grained, texturally immature to submature, and poorly to moderately sorted. The sandstone was derived from transitional continental
and basement uplift rocks. The sandstone could be classified as arkosic and lithicarenite. The
chemical index of alteration, plagioclase index of alteration, and chemical index of weathering
values identifythe upper Paleozoic sandstone has moderate to high weathering history in the
Bokotabo-Sentom area and low to moderate in the Daguja area. Based on trace and rare earth
element concentrations, its sources possibly are juvenile material, the basement nearby.
Keywords: upperPaleozoic, Sandstone, Blue Nile basin, Petrography, Geochemistry, Provenance