Geochemistry Of Lower Sandstone In Blue Nile Gorge Mesozoic Sedimentary Sequences Implication For Provenance Composition And Paleoclimate

Mineralogy, major, traces, and rare earth elements geochemistry of Adigrat SandstonesrnFormation from the Blue Nile Basin (BNB), NW Ethiopian plateau have been analyzed torndetermine their provenance composition, paleoweathering and paleoclimaice scenarios. Samplesrnof this sandstone are slightly variable in composition. Mineralogically the framework grains arernquartz (Q), feldspar (F) and lithic fragments (L) and on QFL diagram; most o the samples arernplotted in subarkose and lithic subarkose fields. Geochemically, Adigrat sandstones arernclassified as arkose, subarkose, litharenite, and sublitharenite. The CIA, PIA and CIW values forrnthis sandstone and the A–CN–K diagram agreeably suggest that source rocks experiencedrnintense chemical weathering under hot and humid tropical to sub-tropical climate.rnMineralogical evidence suggests that plutonic and metamorphic rocks were major contributingrnsource rocks. Perhaps, multi-cyclic processes reworked the sediment. Relatively immobilernelements have been selected for provenance studies. Ratios and plots of relatively immobilernelements consistently suggest that the Adigrat Sandstone is derived from compositionally mixedrnsource between mafic and intermediate igneous rocks. Discriminant function diagramrnconstructed from major oxides, the Chondrite normalized REE plot, Cr/V vs. Y/Ni ratios, La vs.rnTh plot and Th-Hf-Co ternary diagram all suggest that the Adigrat Sandstone is derived fromrncompositionally mixed source. Significant contributions of intermediate supply are alsornconfirmed by Al2O3/TiO2 ratios and lower Eu/Eu* (0.552) values than that of PAAS (0.65).rnProvenance composition and degree of sorting between Adigrat Sandstone in BNB vs. MekelernBasin (MB) have been compared. The result shows that sediment of the former were highlyrnsorted and compositionally derived from mafic and intermediate input, where as that of the laterrnwas mainly derived from felsic rocks.rnKeywords: Adigrat sandstones, provenance, paleoweathering, paleoclimate and Discriminantrnfunction diagram

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