Magnetostratigraphy of the Zobzit and Koudiat Zarga sections (Taza-Guercif basin, Morocco): implications for the evolution of the Rifian Corridor

Abstract

Magnetostratigraphic analyses for two Neogene`post-nappes' successions of the Taza-Guercif basin enable a reliable correlation of the sedimentary sequence to the astronomical polarity time scale. Rock magnetic analyses indicate that hematite is the dominant carrier of the magnetisation in the marine marls of the Melloulou Formation, whereas both magnetite and hematite contribute to the NRM of the near-shore and continental sediments of the Kef Ed Deba and Bou Irhardaiene Formations. Anisotropy of magnetic susceptibility (AMS) measurements indicate that the maximum axes of the magnetic fabric are aligned in a direction SW±NE. This suggests that the AMS is tectonically induced, related to SE±NW compression, in agreement with the major fold and fault systems in the basin. Our magnetostratigraphic correlation shows that the oldest marine sediments in the basin, which are related to the development of the Ri®an Corridor, are dated at approximately 8 Ma. Between 7.2 and 7.1 Ma, just after the Tortonian/Messinian boundary, an important shallowing of the Taza-Guercif basin takes place. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. Our results indicate that at least the Taza-Guercif basin, and perhaps the entire Ri®an Corridor, became emerged at an age between 6.7 and 6.0 Ma. Continental deposits, separated from the underlying deposits by a considerable hiatus of 700 kyr, extend into the Pliocene (up to 4.7 Ma). #

Correlations and sequence stratigraphic model for Messinian carbonate platforms of the western and central Mediterranean

“…The deep parts of the basin suffered more restriction. Such a change in the Mediterranean paleo-oceanographic frame can be related to decreasing water exchanges between the Atlantic and the Mediterranean, which are documented from around 6.0 Ma (Krijgsman et al 2000). Recent Ar 39 /Ar 40 radiometric dating on volcanic rocks of the Alboran Sea area in the 8-to 3-Ma time-span and tectonic modeling conclude that such decreasing water exchanges resulted in the progressive closure of the Miocene marine gateway following a proposed 1-km uplift along the Iberian and African continental margins by Duggen et al (2003).…”

Extracting dynamic topography from river profiles and cosmogenic nuclide geochronology in the Middle Atlas and the High Plateaus of Morocco

“…The marine Messinian deposits dated by Krijgsman and Langereis (2000) in the center of the Guercif basin are significantly lower, at 450-650 m.a.s.l., and the resulting surface uplift rate here is of ~0.1 mm yr -1 . Hence, we retain the value of 0.1-0.2 mm yr -1 based on Messinian shallow marine deposits as an average long-term surface uplift in the study area during the late Pleistocene.…”

“…Paleomagnetic data reported by Krijgsman and Langereis (2000) suggest that the deposit of the Bou Irhardaiene Formation lasted till the lower Pliocene (Zanclean). Thrust-related folding occurs in the northwestern margin of the basin and deforms the Bou Irhardaiene Formation and Quaternary alluvial gravels; the gravels are unconformable in some places (Delcaillau et al, 2007).…”

“…These three basins are mostly filled with Miocene alluvial and lacustrine sediments. The sedimentary record has been described in detail by Bernini et al (1999;, Gomez et al (2000), Krijgsman et al (1999), Krijgsman and Langereis (2000) and Sani et al (2000) for the Guercif basin, by Beauchamp et al (1996) and Ellouz et al (2003) for the Missour basin, and by Dutour (1983) for the Arhbalou basin. Bouazza et al (2009) proposed that sedimentation in the Guercif basin ended at early Quaternary time when the basin probably have changed from endorheic to externally drained, connecting the Moulouya river to the Mediterranean Sea.…”

The Plio-Pleistocene evolution of the Southern Middle Atlas Fault Zone (SMAFZ) front of Morocco

“…This unit is dominated by fluvial deposits near to the frontal thrust of the SMAFZ and by interbedded finegrained lacustrine carbonates that were deposited distal to the active front thrust. Its base was dated at approximately 6.7 Ma (Krijgsman and Langereis 2000) and locally, it ends with Upper Pliocene lacustrine limestones (Martin 1981;Lefè vre 1985). To the South, the BI Fm outcrops continuously on the northern edge of the High Plateaux where it locally infilled NW-trending palaeotalwegs cut into Jurassic dolomites.…”