Shallow or deep? A reinterpretation of the Rifian Corridor’s unique sandy contourites

Daan Beelen, Lesli Joy Wood, Mohammed Najib Zaghloul, Michiel Arts, Fredrick Sarg

This study proposes that sandstone layers exposed in the Fez-Meknes region of Northern Morocco (Ben Allou (Sidi Chaded) and El Adergha localities), have been misinterpreted as unique examples of geostrophically-driven, deep marine (150 - 400 m water depth) sandy contourites. Instead, our independent paleontological, sedimentological, and stratigraphic analyses show that these sandstones represent more common, shallow marine (0 - 30 m water depth) tide-dominated deltas. Our findings imply that at least seven existing studies have based their interpretations on erroneous paleo water depth reconstructions. These have been derived from foraminiferal assemblages from siltstone and claystone layers that interbed the sandstones. Our foraminiferal data were obtained directly from all facies. These more complete data show that, while the siltstone and claystone layers can be considered deep marine, the sandstones are shallow marine, and previous studies did not account for major sea level fluctuations that occurred here during the late Miocene. Our reinterpretation has a defining impact on a wide scope of topics that have been covered by the existing body of work, which involves: the origin of global paleoclimate changes, sandy contourite facies models, conditions of bottom current controlled ecosystems and habitats, ichnofacies interpretations, changes in paleogeography, tectonics and reorganizations of global ocean currents and Mediterranean Outflow Water, and finally, geographic changes leading up to the disappearance of the Rifian Corridor and the associated Messinian salinity crisis. Using biostratigraphy and measurements of stratal thickness, we also establish that the successions here were responding to ± 70 - 80 m amplitude, 100 kyr period glacioeustatic fluctuations. These values represent hitherto unprecedented constraints on the nature of late Miocene climate fluctuations that were similar in period and intensity as Pleistocene glacial/interglacial cycles. Finally, we show that abundant authigenic sediment generation at the shallow marine fringes of the Rifian Corridor exacerbated its closure. This likely has significant, previously unrecognized implications to the onset of Mediterranean isolation and the associated Messinian salinity crisis.