Albian sedimentation in western Atlas, Morocco

Abstract

Detailed study of field sections and extensive ammonite collection allowed to specify the sedimentary evolution and age of the Albian series of the Western Atlas (Morocco). After a significant hiatus of earliest Albian age, the Albian transgression began in the late Douvilleiceras leightonense Zone with partly clastic deposits. A transgressive pulse gave way to clayey marl deposits (Douvilleiceras mammillatum Zone), which evolved upward to partly carbonate, laminated deposits of late early Albian to earliest middle Albian age (Lyelliceras pseudolyelli to early Lyelliceras lyelli zones). A major hiatus that encompassed most of the middle Albian, was followed by a new transgression marked first by sandy deposits (Dipoloceras cristatum and Pervinquiria pricei zones), and then by clayey marl and limestone nodules (Pervinquieria inflata Zone). A sharp sea level fall (late Pervinquieria inflata to early Pervinquieria fallax zones) led to the development of a shallow marine carbonate shelf (Kechoula Formation). A last transgressive pulse allowed deposition of outer shelf clayey marls (Pervinquieria rostrata to Arrhaphoceras briacensis (?) zones), interrupted near the Albian-Cenomanian boundary by a sea level fall and hiatus. Anoxic to disoxic conditions are recorded in the latest early Albian and the late Albian, which correlate with the Leenhardt and Breistroffer levels, respectively. Correlations with Albian successions in North Africa and southern Europe suggest a mainly eustatic origin for the most important sedimentary discontinuities, although the late Albian sea-level drop may be tectonically enhanced.