Determining flow directions in turbidites: An integrated sedimentological and magnetic fabric study of the Miocene Marnoso Arenacea Formation (northern Apennines, Italy)

Abstract

Depositional models of turbidity flows require estimating paleocurrent directions using sedimentological indicators such as flute and ripple marks, but these are not always present in outcrop sections or drill cores. In this study, we apply the anisotropy of magnetic susceptibility (AMS) as an alternative tool to estimate paleocurrent directions in a case-study turbiditic system: the Marnoso Arenacea foredeep turbidites of Miocene age exposed in the northern Apennines of Italy. Different depositional facies have been sampled for AMS and additional rock-magnetic analyses. We observed a good agreement between paleocurrent directions from flute casts at the base of turbidite beds and mean directions of maximum magnetic susceptibility axes in organized facies such as massive and laminated sandstones, even if a relatively small but apparently consistent offset of ~15–20° seems to be present. Highly dispersed AMS fabrics were instead observed in disordered facies such as convoluted and undulated sandstones as well as debrites. This strong correlation between hydrodynamic regimes of depositional facies and AMS data represents a novel contribution and confirms the validity of the AMS method to estimate flow directions in the absence of sedimentological indicators. Finally, paleomagnetic analyses from the literature were used to reconstruct the paleogeography of the Marnoso Arenacea basin and make inferences about the origin and direction of transport of the sediments at the basin scale.