Anatomy of a turbidite system along the shelf break-upper slope transition: stratigraphy, geometries, and facies distribution (Taza-Guercif Basin, Late Tortonian, NE Morocco)

Submarine channels act as a link for sediment delivery from coastal systems to the basin floor. Despite extensive research, field studies on the downstream evolution of channelized sandstones in upper slope settings remain limited. During the late Tortonian, a marine transgression drowned a mixed carbonate-siliciclastic coastal system, depositing marls in the Taza-Guercif Basin. This study focuses on the initiation of the Tachrift Turbidite System, which incised these marls. The exceptionally exposed outcrops offer a rare opportunity to study the 3D architecture from the shelf break to the downstream slope stratigraphy. The studied ~250 m thick succession is documented by field mapping, sedimentary logging, and facies analysis, recording >50 channel fills separated by meters-thick marlstones. The mostly fine- to medium-grained channel fills vary in width from 5 to 200 m, while the thickness of channel axis deposits ranges from 0.5 m to 8 m. Paleocurrent analysis and channel geometries distinguished five main flow pathways, enabling the reconstruction of upper-slope complex physiography. Four end-member depositional styles have been identified: 1) erosional channel fills, without overbank deposits; 2) laterally migrating channel fills, with overbank deposits; 3) vertically offset stacked channel fills, with poorly developed overbank deposits; 4) mixed vertically and laterally offset channel fills, with overbank deposits. Variability in depositional style is interpreted as a result of distance from the shelf break, suggesting that slope morphology influenced channel architecture and fill. These results could assist in the characterization of analogous channel fills in upper-slope settings in the subsurface.