Anisotropy of magnetic susceptibility analysis in Tunas Formation cores (Permian), Claromecó Basin, Buenos Aires, Argentina: Its relation to depositional and post-depositional conditions

Abstract Anisotropy of magnetic susceptibility (AMS) has been used as an important tool to study magnetic fabrics and as a basis of interpretation of depositional conditions and post-depositional processes in sedimentary successions. This contribution presents results of standard AMS and magnetic mineralogy analysis performed in core samples from the PANG 0003 well, located at the Claromeco Basin, Buenos Aires province, Argentina. The sedimentary sequence analyzed has been assigned to the Tunas Formation (Permian), upper Pillahuinco Group, southwestern of the Gondwana boundary. Additionally, obtained results were compared with previous Tunas Formation outcrop data at the Sierras Australes and Claromeco Basin area. Measured AMS parameters vary with depth, reflecting changes in postdepositional conditions such as mechanical compaction and the influence of tectonic stress. Analyses of the mean magnetic susceptibility, thermomagnetic properties and petrographic studies indicate that paramagnetic minerals as Fe-phyllosilicates are the main contributors for the AMS of this sequence. Obtained AMS parameters are mainly characterized by triaxial to oblate AMS ellipsoids and shortening directions (Kmin) with a tendency to cluster in vertical positions, parallel to the bedding plane poles, assigned to sedimentary or weak deformed magnetic fabrics. By contrast, toward the base of the sequence, strongly oblate AMS ellipsoid shapes and Kmin axes that migrate to horizontal positions indicate a high deformation degree product of tectonic stress. The presented results are consistent with geological, AMS and paleomagnetic data from Tunas Formation outcrops and confirm that deformation degree was gradually attenuated upwards in the sequence, to the younger strata and toward the foreland Claromeco basin. The study of AMS parameters and magnetic mineralogy have proven to be important tools to interpret the processes that acted during the burial history of Tunas Formation, increasing the knowledge about the evolution of the Claromeco Basin.