Can magnetic fabric indicate the direction of a glacier movement? An example from Itarare Group and Aquidauana Formation, Parana Basin, Brazil

摘要

Magnetic fabrics was determined on Late Paleozoic sedimentary rocks from Aquidauna Formation (50 sites) and Itarare Group (71 sites) that outcrop in Parana Basin, applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence magnetization (AARM). Rock magnetism analyses reveal that magnetite, hematite, and paramagnetic matrix minerals are responsible for the magnetic susceptibility and AMS, while the magnetite is the carrier AARM. The AARM tensor is coaxial with AMS fabric. The analysis at the individual-site scale defines two AMS fabric types (A and B). The type A shows vertical AMS foliation pole (K-min perpendicular to the bedding plane), while K-max and K-int are scattered within the bedding plane itself. This fabric is usually interpreted as sedimentary-compactional. Type B shows the three well-clustered AMS axes with Kmin off-vertical, this fabric is the most important since it was found in the majority of the sites. This fabric is interpreted as indicative of sediment transport that could be inferred by the imbrication of AMS foliation (Kmin). The comparison of magnetic lineation (K-max) for both Aquidauana Formation and Itarare Group with their respective glacial striae allow inferring that K-max can be used as an indicator of glacier movement that was from SE towards NW, even though some variation or changes in the movement orientation could happen as found in the Itarare Group (from Sao Paulo and Parana states), probably related to glacier advance and retreat or different glacier lobes.