Stratigraphic evolution of a spectacularly exposed turbidite channel belt from the Tachrift System (late Tortonian, north‐East Morocco)

Abstract

The sedimentary architecture of channelized turbidites can be highly complex as it reflects the response of submarine channels to several interplaying factors. Although intensively investigated through seismic imaging, turbidite channel fills are not convincingly calibrated for sedimentary facies at a sub‐seismic scale. This contribution addresses the sedimentary architecture and the controls on the evolution of a ca 20 m thick channel‐levee complex of the Tachrift turbidite subunit (Upper Miocene, the Melloulou Formation), which accumulated along the southern slope of the Neogene Taza‐Guercif Basin (Rifian Corridor of north‐east Morocco). Facies and architectural analyses indicate that the studied channel‐levee complex is the result of three‐fold evolution. From base to top, it is comprised of: (i) a ca 7 m thick lower mud‐prone interval containing relatively small and vertically stacked channel fills with poorly developed muddy levees; (ii) a ca 4 m thick and >1 km wide sandstone‐rich middle interval made of lateral accretion packages that become progressively less amalgamated and fine‐grained and is overlain by ca 5 m of thin‐bedded mud‐rich turbidites intercalated with hemiplegic marlstones; and (iii) an up to ca 9 m thick upper interval constituted by aggradational channel fills with well‐developed levees and variously directed lateral accretion packages. This organization suggests that, following a phase of inception (lower interval), the channel underwent extensive meandering with very minor vertical aggradation, prior to being blanketed by ‘retrogressive’ muddy lobes (middle interval) during a phase of reduced sediment input. In turn, the uppermost interval records a late phase of channel re‐establishment and aggradation that likely terminated as a result of up‐dip avulsion. It is suggested that the observed change of architectural style reflected the feedback of changing sediment input, slope equilibrium profile and channel morphodynamics.