Models of submarine channel–levee transitions: Spatiotemporal constraints from the Tachrift system, late Tortonian, Morocco

Characterization of turbidite channel–levee deposits enhances subsurface modelling, where data are restricted to borehole sections or seismic images. As with the areas of discontinuous outcrop, interpretation of the temporal relationship of channel–levee systems and hence the evolution of turbidite sedimentation is largely inferred. This work presents an outcrop study of Complex 6, a turbidite channel–levee complex belonging to the Upper Miocene Tachrift system in Taza–Guercif Basin, Morocco, and it aims to document its 3D architecture, facies assemblages and evolution. The method integrates geological mapping, facies analysis of 46 logs and physical stratigraphic correlations. Statistical analyses on sedimentological variables support quantitative comparison among depositional elements and their lateral transitions. Complex 6 is 13 m thick and consists of three sandstone-rich Units labelled A, B and C from older to younger, which progressively increase in grain size and are laterally stacked towards the south-east. The tabular, fining-upwards sandy bedsets with concave-upwards erosional surfaces in Unit A suggest a system of small sinuous and ephemeral distributary channels. Upwards, Units B and C display channel-fill deposits and genetically linked levees with different crossflow facies tracts recording changes in flow parameters and morphodynamics of the parent channel: Unit B was built by sinuous low aggradational meandering channels, dominated by lateral accretion packages that transition to levees at the accreting inner bank, showing complex lateral relationships with the outer bank levee; Unit C is characterized by aggradational channels where amalgamated sandstones of channel axis laterally pass into sandy inner levee, then to mud-prone outer levee heterolithics. The stratigraphic architecture of Complex 6 reveals an eastward channel belt migration with a progressive flow energy/density increase. Owing to magnificent 3D exposures, the study provides sedimentological characterization of contrasting channel–levee transitions, insights into the evolution of their parent channel from inception to abandonment and predisposes sub-seismic lithological calibration of subsurface analogues.