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

Sedimentary rocks of the Itarare Group, deposited during the Late Paleozoic Ice Age in the Parana Basin of South America, were collected throughout the state of Sao 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 (beta) of the minimum susceptibility axes with respect to bedding (q-beta 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 Sao Paulo, in agreement with ice flow and sediment transport directions reported from limited numbers of sites possessing sedimentary structures and ice-kinematic indicators.

Automated summary

The study conducted magnetic and rock-magnetic research on sedimentary rocks in the state of Sao Paulo, Brazil, confirming the rocks were largely remagnetized during the Cretaceous. Analysis of AMS showed that it records primary sedimentary fabrics reflecting depositional environments and paleocurrent conditions of the rocks.