Magnetostratigraphy of the Ouarzazate Basin: Implications for the timing of deformation and mountain building in the High Atlas Mountains of Morocco.

Abstract

Two magnetostratigraphic profiles (450 samples) have been carried out to constrain the age of synorogenic formations in the southern foreland of the High Atlas of Morocco. The Amekchoud profile covers the Aït Ouglif and Aït Kandoula alluvial formations that form the bulk of the Ouarzazate basin fill, indicating an age between the upper Langhian and the Messinian (Miocene). Data obtained in the previously unexplored Hadida formation profile covers the oldest terms of the foreland basin succession, but the low quality of the magnetic record only allows proposing a tentative age between the middle Lutetian and an undetermined middle to late Eocene. The correlation of the Amekchoud profile is based on the recognition of the long C5n chron (Tortonian) in the middle part of the section studied and a new vertebrate locality of upper Tortonian age found in the upper part. These results indicate a discontinuous record of foreland basin development in the southern Atlas domain from mid Eocene to late Miocene times, punctuated by an intermediate large hiatus of 20-25 ma (late Eocene to mid Miocene). Thrusting in the Sub-Atlas frontal thrust belt began before the Aït Ouglif and Kandoula formations, probably during the Oligocene, and extends up to recent times. The alternation of periods of deposition with others of no sedimentary record, which does not coincide with specific tectonic events, results probably from the interference of orogenic deformation and the mantle-related thermal uplift events that have been described for the Moroccan Atlas.

The three main steps of the Marrakech High Atlas building in Morocco: Structural evidences from the southern foreland, Imini area

“…14, this study) Following the observations made in figure 4, this erosion phase must have occurred between the end of the deposition of marine Eocene and the base of palustrine-lacustrine Miocene-Pliocene deposits, i.e. before the Langhian-Early Serravallian (Tesón et al, 2010). On this site (Fig.…”

“…The first member of El Harfi et al, (2001) is classically attributed to the Upper Eocene, given its conformable position on the marine deposits. Paleontological data gives a Langhian-Early Serravallian age for the base of the Aït Kandoula member (Heldmach, 1988), whereas magnetostratigraphic data has given a similar age for the base of the Aït Ouglif member (Tesón et al, 2010). Magnetostratigraphy is not conclusive concerning the Aït Ouglif Formation, compared to the better dating for the Aït Kandoula Formation (Görler et al, 1988;Tesón et al, 2010).…”

“…Paleontological data gives a Langhian-Early Serravallian age for the base of the Aït Kandoula member (Heldmach, 1988), whereas magnetostratigraphic data has given a similar age for the base of the Aït Ouglif member (Tesón et al, 2010). Magnetostratigraphy is not conclusive concerning the Aït Ouglif Formation, compared to the better dating for the Aït Kandoula Formation (Görler et al, 1988;Tesón et al, 2010). El Harfi et al (2001 proposed no convincing arguments other than attributing this formation to Oligocene-Early Miocene times, given the ages of the Upper Eocene detrital member and the Aït Kandoula lacustro-palustrine member.…”

“…We favor the EarlyMiddle Miocene age for the Aït Ouglif Formation. The top of the Aït Kandoula member has been linked to a younger Messinian age by magnetostratigraphy (Tesón et al, 2010), and an Upper Pliocene age by El Harfi et al (2001), based on paleontological data.…”

Lartetium africanum (Lavocat, 1961) (Eulipotyphla · Soricidae) from Beni-Mellal (Morocco), the oldest African shrew: new descriptions, palaeoenvironment and comments on biochronological context

“…Finally, Tesón et al (2010) cited and figured the presence of an Oligosoricini shrew ('Lartetium-like') in Late Miocene sediments from Ouarzazate basin (Morocco). The m1 and the i illustrated by Tesón et al (2010) could also correspond to Lartetium but, as noticed by Engesser (2009), isolated teeth, especially in Lartetium, are often difficult to ascribe with certainty. In any case, reports on the occurrence of Lartetium in the Late Miocene of Morocco must be taken with caution.…”