Geochemistry and lithostratigraphy of the mugher mudstone: Insights into the late jurassic-early cretaceous clastic sedimentation in Ethiopia and its surroundings

Abstract

Deposition of clastic rocks during the Jurassic -Cretaceous periods in Ethiopia are sources of vital information on the nature and timing of the withdrawal of the Tethyan Sea from Northeast Africa. The Mugher Mudstone is one of these clastic rocks in Ethiopia.Lithostratigraphic, mineralogical and geochemical studies were conducted on the Mugher Mudstone to constrain the sedimentation history, provenance and tectonic setting of the basin. Mapping of the northern part of the Abay Basin showed that the Mugher Mudstone extends up to 10°51'20'' N. The formation is constituted by sandstones, mudstones, siltstones and claystones. The sandstones and mudstones constitute more than 95% of the formation. Quartz is dominant with accessories of K-feldspar, muscovite, zircon and sphene. The Mugher Mudstone is highly depleted in Na2O, K2O,CaO, MgO, Rb, Sc, Ni, and Co while it is enriched in SiO2, Ta, Zr, Nb, and Hf. Elemental distribution shows significant variation among the different size classes. Siltstones and mudstones are enriched in Zr and Hf while clays are highly enriched in REE. These features together with calculated indices and ratios demonstrate high degree of weathering, recycling and sorting. Triangular and bi-variant discrimination diagrams of trace elements suggest mixed source rocks of mafic metavolcanics, metaultramafics and recycled metasedimentary rocks deposited in a passive margin setting. Finally, the high degree of recycling, textural and compositional maturity may indicate the Early Cretaceous had humid paleoclimate and stable uplifted source area in the region favoring a prolonged weathering, recycling and sorting.