Late Paleozoic Depositional Environments and Sediment Transport Directions of the Itararé Group Rocks From the State of São Paulo, Brazil, Determined From Rock Magnetism and Magnetic Anisotropy

Abstract

AbstractSedimentary rocks of the Itararé Group, deposited during the Late Paleozoic Ice Age in the Paraná Basin of South America, were collected throughout the state of São Paulo, Brazil, for an anisotropy of magnetic susceptibility (AMS) and rock‐magnetic study. A recent paleomagnetic study conducted on the same samples had determined that these rocks were largely remagnetized during the Cretaceous; however, rock‐magnetic experiments demonstrate that the AMS is dominantly carried by paramagnetic minerals and therefore is unaffected by the secondary magnetic overprints. AMS data are analyzed in terms of their shape and orientation, and according to the relationship between the q‐value (magnetic lineation/foliation) and the imbrication angle (β) of the minimum susceptibility axes with respect to bedding (q–β diagram). Using multiple lines of evidence, we demonstrate that AMS records primary sedimentary fabrics that reflect the depositional environments and paleocurrent conditions in which these rocks were deposited. The magnetic fabrics consistently record a SE‐NW paleocurrent orientation, with dominant direction of transport to the NW throughout the entire state of São Paulo, in agreement with ice flow and sediment transport directions reported from limited numbers of sites possessing sedimentary structures and ice‐kinematic indicators.