New insight on tide-dominated estuary and delta in the Eocene-Miocene Mrayt Group, North-Western Rif, Morocco

Abstract

The sedimentary deposits of Eocene-Miocene Mrayt Group, North-Western Rif, Morocco, has been the subject of controversy by previous works regarding their depositional environments. Detailed sedimentological study based on petrographic study, and sedimentary facies and paleocurrent measurements analysis, leads to several results and new insights. Petrographic study provided the first evidence of mixed siliciclastic and carbonate sediments and their nomenclature: silty micrites, micritic siltstones, micritic sandstones, sandy micrite, and allochemic sandstones, as well as the nature of the sediment sources and their geological context. Twenty two sedimentary facies that have never been described before are identified, and based on their succession and association, a new interpretation of depositional processes and depositional systems is proposed. The paleoenvironments of the Mrayt Group are interpreted as littoral and shallow marine settings: tide-dominated estuary, tide-dominated delta systems and open coast tidal flat, under complex hydrodynamics strongly influenced by river discharge, tidal currents, waves, and storms action. Sedimentation occurred in “the Maghrebian basin” under the interplay of (i) tectonics related to the Cenozoic collision of the African and Eurasian continental plates, (ii) Cenozoic alternation of warm climate and cooling due to the increasing influence of Antarctica glaciation, (iii) sediments supplies induced by rejuvenation of sedimentary sources, and (iv) sea level fluctuation related to the advance and retreat of ice-sheet on Antarctica.