Abstract
Large-scale magnetic susceptibility (MS) variations in ancient sediments are usually interpreted as related to sea-level and climate changes affecting the erosional regime and the amount of detrital input. To constrain such environmental changes during the Famennian, we compared MS records in representative sections of pelagic limestones of (1) the Avalonian margin of Laurussia [Sessacker (SES) and Beringhauser Tunnel (BHT), Rhenish Slate Mountains, Germany] and (2) in Gondwana related terranes [Erfoud (ERF), Tafilalt, Morocco; Col des Tribes (CT), Montagne Noire, France; Buschteich (BU), Thuringia, Germany; Corona Mizziu (CM I, II), Sardinia and Pizzul West (PZW) in the Carnic Alps, Italy]. Very low MS values throughout the Famennian characterize sections from Avalonia. In contrast, MS values are high and oscillating in Gondwana during the early Famennian; they drop significantly all together in the middle Famennian Palmatolepis marginifera marginifera Zone to match the pattern of low MS values of the Avalonian margin thereafter. To evaluate the importance of partial diagenetic overprint, MS data were compared to hysteresis parameters and geochemical proxies in sections BU, CM I, II and CT. The degree of thermal diagenesis is estimates taking into account the Color Alteration Indices (CAI) of conodonts. Striking dissimilarities in MS records between Laurussia and Gondwana are in favor for an existing remnant oceanic barrier between these continents during early Famennian times, when the amount of detrital supplies was obviously different. Uniformity is reached after the drop of MS values in N-Gondwana, when oceanic barriers could have vanished during the early middle Famennian T-R fluctuations of the sea-level. All sites remained under a rather similar regime of detrital supply through middle to uppermost Famennian. Comparison of MS trends with trends of conodont biofacies in five sections (CT, BU, CM I, II and SES) allows emphasizing the concordance of their relationship to sea level fluctuations.