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Geological Society, London, Special Publications; 2007; v. 278; p. 197-217;
DOI: 10.1144/SP278.9
© 2007 Geological Society of London

Articles

Environmental changes at the Frasnian–Famennian boundary in Central Morocco (Northern Gondwana): integrated rock-magnetic and geochemical studies

L. Riquier1, O. Averbuch1, N. Tribovillard1, A. E. Albani2, N. Lazreq3 & S. Chakiri4

1 UMR 8110, Processus et Bilans en Domaines Sédimentaires, Bâtiment SN5, Université de Lille 1, F-59655 Villeneuve d'Ascq cedex, France (e-mail: Laurent.Riquier{at}univ-lille1.fr)
2 UMR 6532, Hydrogéologie, Argiles, Sols et Altérations, Bâtiment Sciences Naturelles, Université de Poitiers, 40 Avenue du recteur Pineau, F-86088 Poitiers cedex, France
3 Université Cadi Ayyad de Marrakech, Faculté des Sciences Semlalia, Département de Géologie, Avenue du Prince Moulay Abdellah, BP 2390, 40001 Marrakech, Morocco
4 Université Ibn Tofail, Faculté des Sciences, Laboratoire de Géologie dynamique et appliquée, BP 133, 14000 Kénitra, Morocco

Rock magnetic (magnetic susceptibility and hysteresis parameters) and geochemical analyses (major and trace elements) were carried out on whole rock samples of two Frasnian–Famennian boundary sections, Anajdam and Bou-Ounebdou in the Central Morocco (Western Meseta). During the Frasnian, the decreasing trend of the magnetic susceptibility signal, mainly carried by low-coercivity magnetite grains, indicates a gradual reduction of detrital influx. This decrease in detrital input parallels a Frasnian long-term sea-level rise. In the Late Frasnian Kellwasser Horizons, that are classically considered to represent highstand deposits, the magnetic signal exhibits the lowest intensities in connection with maximum diamagnetic contribution of the carbonate fraction. With respect to geochemical data, the two black carbonate-rich Kellwasser Horizons are characterized by noticeable positive anomalies of bottom-water dysoxic proxies and of marine primary productivity markers. Our data thus suggest that in Central Morocco, the Late Frasnian marine environments were marked by a relatively important biogenic productivity favouring the onset of oxygen-depleted conditions during periods of maximum transgression on the continental platforms.