Sedimentology and magneto-biostratigraphy of the channelised turbidites of the El Rhirane System (Upper Miocene; Taza-Guercif Basin, NE Morocco)

The Taza-Guercif Basin (TGB) of Northern Morocco represents the Mediterranean part of the Rifian Corridor, a seaway that in the Late Miocene connected the Atlantic Ocean to the Mediterranean Sea. Current paleogeography models indicate TGB was located immediately to the east of a structural sill that was key in regulating the Mediterranean Sea dynamics. Two turbidite systems with a common southerly sediment source are documented in the southern TGB, namely the Tachrift System (TS) and the El Rhirane System (ERS), which crop out 1.5 Km apart to the east and to the west of the Zobzit River, respectively. While TS, late Tortonian-early Messinian in age, was the subject of magneto-biostratigraphic studies in the late ’90s (Krijgsman & Langereis, 2000) and is currently being investigated for its exceptionally exposed slope channel complexes (Felletti et al., 2020), ERS has received little attention to date. The relationship between the two systems is unclear, with earlier works interpreting ERS as non-channelised and relatively older and thinner than TS, implying a complex and potentially dynamic palaeobathymetry. This contribution reports on the sedimentology, magnetostratigraphy, and foraminiferal and nannofossil biostratigraphy from a composite section of the El Rhirane System, aiming at clarifying its relationship with TS and better defining the complexity of the southern edge of the TGB. Sedimentary logging and facies analyses suggest that, albeit comparatively thinner, ERS stratigraphy is similar to that of TS, with several superimposed leveed channel-fills, each up to a few tens of m-thick, encased in hemipelagic marlstones. Stratigraphic changes in the orientation of palaeocurrent indicators suggest local palaeoflow evolved from north-eastward to northward and parallel to mean TS paleoflow. Paleomagnetic analyses allowed defining a magnetic polarity stratigraphy comprising several reversals. Based on identification of key planktonic foraminifera (FO G. suturae, FCO of G. miotumida) and nannofossil (FO of A. primus and N. amplificus) bioevents, the magnetic polarity stratigraphy was correlated with the Chrons C4r.1n-C3Ar of the Geomagnetic Polarity Time Scale (Ogg, 2020), suggesting ERS was largely coeval to TS. All in all, the channelised nature of ERS and correlation with TS indicate the southern slope of the TGB hosted a multilateral slope channel system, whose depositional pattern was, at least upon inception, conditioned by a complex slope morphology