Paleomagnetism of glacial varves from the last glaciation maximum in Patagonia at Lago Blanco

Abstract

Paleomagnetic measurements have been carried out from a sequence of 178 glacial varves from Lago Blanco, west Patagonia, Argentina. The deposition of the glaciolacustrine sediments has been determined as associated with the last glaciation maximum, occurring either at around 20 000–19 000 or at around 14 500–14 000 years BP. The magnetic mineral composition was determined by the Simplex method. Both haematite (0.16%) and magnetite (0.1%) were identified. The intensities have in general high values and vary in agreement with the susceptibility. After demagnetization at 20 mT, the general trend of declination shifts from about 15°W at the bottom to 5°E at the top, and swings markedly to the east between varves 59 and 93. The general trend of inclination shifts from about −30° at the bottom to about −20° at the top. Extremely low inclinations are recorded at around varve 70. Virtual geomagnetic pole (VGP) positions are generally located in northern Canada with a short and rapid swing down to central Africa. Neither sedimentological changes nor anomalies in the anisotropy of the magnetic susceptibility that might be responsible for this swing have been observed.