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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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http://hdl.handle.net/123456789/3447
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| Title: | Geochemistry of lower sandstone in Blue Nile Gorge Mesozoic sedimentary sequences: Implication for provenance composition and paleoclimate |
| Authors: | Barsisa, Bekele |
| Advisors: | Balemwal Atnafu(Dr.)
Dereje Ayalew(Dr) |
| Keywords: | Adigrat sandstones
provenance
paleoweathering
paleoclimate and Discriminant function diagram |
| Copyright: | Jun-2011 |
| Date Added: | 20-Jul-2012 |
| Publisher: | Addis Ababa University |
| Abstract: | Mineralogy, major, traces, and rare earth elements geochemistry of Adigrat Sandstones
Formation from the Blue Nile Basin (BNB), NW Ethiopian plateau have been analyzed to
determine their provenance composition, paleoweathering and paleoclimaice scenarios. Samples
of this sandstone are slightly variable in composition. Mineralogically the framework grains are
quartz (Q), feldspar (F) and lithic fragments (L) and on QFL diagram; most o the samples are
plotted in subarkose and lithic subarkose fields. Geochemically, Adigrat sandstones are
classified as arkose, subarkose, litharenite, and sublitharenite. The CIA, PIA and CIW values for
this sandstone and the A–CN–K diagram agreeably suggest that source rocks experienced
intense chemical weathering under hot and humid tropical to sub-tropical climate.
Mineralogical evidence suggests that plutonic and metamorphic rocks were major contributing
source rocks. Perhaps, multi-cyclic processes reworked the sediment. Relatively immobile
elements have been selected for provenance studies. Ratios and plots of relatively immobile
elements consistently suggest that the Adigrat Sandstone is derived from compositionally mixed
source between mafic and intermediate igneous rocks. Discriminant function diagram
constructed from major oxides, the Chondrite normalized REE plot, Cr/V vs. Y/Ni ratios, La vs.
Th plot and Th-Hf-Co ternary diagram all suggest that the Adigrat Sandstone is derived from
compositionally mixed source. Significant contributions of intermediate supply are also
confirmed by Al2O3/TiO2 ratios and lower Eu/Eu* (0.552) values than that of PAAS (0.65).
Provenance composition and degree of sorting between Adigrat Sandstone in BNB vs. Mekele
Basin (MB) have been compared. The result shows that sediment of the former were highly
sorted and compositionally derived from mafic and intermediate input, where as that of the later
was mainly derived from felsic rocks. |
| Description: | A thesis submitted to school of graduate studies of Addis Ababa
University in partial fulfillment of the requirements for the Degree
Of Master of Science in Geo-Chemistry |
| URI: | http://hdl.handle.net/123456789/3447 |
| Appears in: | Thesis - Earth Sciences
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