Thursday, April 25, 2013

Highlights—Marine Mudstone: Neither Homogeneous nor Isotropic

Mudstone-dominated marine successions are common in the geological record, but a full understanding of their depositional processes commonly is hampered by a lack of generally accepted diagnostic criteria to distinguish between hemipelagic settling and deposition from a flowing medium.  In this paper, Dall’olio et al. integrate sedimentologic observations with analyses of the anisotropy of magnetic susceptibility (AMS) in the Miocene Marnoso Arenacea Formation of Italy to explore the utility of this technique for evaluating depositional processes.  The results reveal that maximum susceptibility axes clustered within the depositional plane along the average palaeoflow direction inferred from flute casts at the base of the nearest turbidite beds. This fabric is interpreted as largely sedimentary in origin, due to the alignment within the bedding plane of paramagnetic/ferromagnetic grains; this result contrasts with the hemipelagic settling interpretation that is commonly invoked for this unit.  Collectively, the results illustrate the value of AMS analysis in study of depositional processes.

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