Geochemistry of the Miocene Zoumi flysch thrust-top basin (External Rif, Morocco): new constraints on source area weathering, recycling processes, and paleoclimate conditions

This study focuses on the Lower-Middle Miocene syn-orogenic flysch deposits of the Zoumi basin to infer source area paleo-climatic conditions, the intensity of source rocks paleoweathering, and mechanical sorting and recycling effects. The mudrocks are enriched in Al2O3 , Fe2O3, CaO, and TiO2 relative to PAAS and depleted in the other mobile major elements. There are high positive correlations between SiO2, Al2O3, and TiO2 and negative correlations between SiO2 and CaO. Geochemically, the mudstones are mainly classified as shales, Fe-shales, and wackes. Various discriminant diagrams were used to reveal the inferred tectonics, source paleoweathering intensity, and paleoclimatic conditions. Chemical index of alteration (CIA) and chemical index of weathering (CIW) values for Lower-Middle Miocene vary from 50 to 80% indicating low to moderate degree of source area weathering compatible with non-steady-state weathering under wet and humid paleoclimatic conditions. Locally (Zoumi midsection) CIAvalues are higher (> 80) reflecting intense source area weathering, whichmay be attributed to high tectonic impulses and more humid conditions during deposition. The combination of ICV-CIA, Al2O3-Zr-TiO2, and Th/Sc-Zr/Sc values suggests the bulk rock is chemically immature and has experienced modest physical sorting and recycling reflecting little transportation until the final deposition.