MagNetZ With Romina Achaga (2025/07/25) - Paleomagnetic/-environmental Changes in La Barrancosa Lake

Paleomagnetic and Paleoenvironmental Changes in La Barrancosa Lake (Argentina) Over the Last Millennium The video is also available for download at: https://earthref.org/ERDA/2767/ and can be referenced with the doi: 10.7288/V4/ERDA/2767 Title: Paleomagnetic and Paleoenvironmental Changes in La Barrancosa Lake (Argentina) Over the Last Millennium Author: Romina Achaga from IPGP, France/ CONICET, Argentina La Barrancosa Lake (37°19’S, 60°06’W), located in the Argentine Pampas beneath the South Atlantic Anomaly (SAA), offers a valuable archive to explore past geomagnetic field behavior in a region with sparse paleomagnetic studies. In this talk, I will present new results from a 1 m-long sediment core, integrating paleomagnetic, rock magnetic, and geochemical analyses to reconstruct high-resolution paleosecular variation and environmental change over the last ~700 years. Initial studies in 2022, based on three ~60 cm-long cores, highlighted inconsistencies in the age-depth model. The 137Cs and 210Pb dates at the top, together with a radiocarbon date on bulk sediment at the base, suggested an abrupt change in the sedimentation rate. In addition, paleomagnetic inclination values were higher than expected for the inferred basal age when compared with global geomagnetic field models, suggesting that the base of the core might be younger than initially assumed. In 2024, a new 1 m-long core was recovered. Geochemical data revealed a distinct organic-rich, carbonate-poor layer that allowed targeted radiocarbon dating on bulk organic matter. The resulting younger age enabled us to revise the age-depth model. With this improved chronology, we reconstructed paleosecular variation from well-defined magnetic directions and interpreted geochemical shifts and changes in magnetic mineral concentration, grain size, and mineralogy in relation to past environmental changes. This work highlights how an interdisciplinary approach is essential to refine chronologies and enhance our ability to interpret past geomagnetic field behavior and environmental variability from lacustrine records. ----------------------------------------------------------- 00:00 - Intro 00:31 - Presentation 32:15 - Questions 42:35 - Announcements