Paleomagnetic results from La Barrancosa Lake, Argentina

This study presents new paleomagnetic results from La Barrancosa Lake (37°19’ S, 60°06’ W), located in the Argentinian Pampean region. The region's sparse paleomagnetic studies and its location under the South Atlantic Anomaly (SAA) make it a key area to investigate past geomagnetic field behavior. A 1-meter-long sediment core (covering approximately the last 2500 years), the longest paleomagnetic record recovered from the lake to date, was collected and analyzed. This work aims to improve the understanding of paleosecular variations (PSV) and the geomagnetic field's non-dipole behavior in the Southern Hemisphere.

The magnetic susceptibility (k) profile was used to correlate this core with previous records from La Barrancosa. Standard paleomagnetic measurements were performed, including natural remanent magnetization (NRM) intensity and directions (declination D and inclination I). Stepwise alternating field (AF) demagnetization revealed a stable single-component NRM after removing a low-coercivity viscous component. Characteristic remanent magnetization (ChRM) directions were determined using principal component analysis. Additional rock magnetic experiments, such as anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM) until saturation (SIRM), thermomagnetic curves, hysteresis loops and First Order Reversal Curve (FORC) analysis provided insights into the concentration, coercivity and grain size of magnetic minerals. The measurements were carried out at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy.

Preliminary results demonstrate well-preserved paleomagnetic signals with inclinations ranging from -64° to -17°. MAD values lower than 5° in the samples indicate reliable ChRM directions. These data will be compared with global geomagnetic models to address potential discrepancies and explore the contributions of non-dipole features in the region, likely associated with the influence of the South Atlantic Anomaly (SAA).

The new paleomagnetic record from La Barrancosa Lake enhances the temporal resolution of paleomagnetic studies in the Pampean region and provides critical data to investigate geomagnetic field variations in the Southern Hemisphere. The results underscore the region’s potential for refining global and regional geomagnetic models and highlight the importance of further research to explore the implications of these deviations for understanding the evolution of the SAA.