A Excursão do Laschamps registada em duas estalagmites da Gruta dos Morcegos, Portugal

Abstract

Stalagmites are potential candidates for high-resolution reconstruction of the Earth’s magnetic field and paleoclimatic variations. Here we provided a pristine record of the Laschamps geomagnetic excursion recorded in two stalagmites from the Bat Cave, Central Region of Portugal. SQUID microscopy reveals a high concentration of magnetic particles. FORC diagrams and hysteresis parameters point to non-interacting single-domain magnetite as the main magnetic carrier. Paleomagnetic data show a gradual variation of the magnetic declination and inclination from the normal component to an antipodal reverse component. Return to the normal component is abrupt and is not apparently associated with visible hiatus in the precipitation rate of the stalagmite. The stalagmite LM1 was dated based on U-Th and 14C methods. Owing to the speleothem’s high detrital content and low U concentration, U-Th age are not reliable in this case. 14C dating provided reliable age in stratigraphic order and with low uncertainties. The data provide one of the most robust highresolution continental records of the Laschamps, opening a new door to explore the behavior of the Earth’s Magnetic field during geomagnetic excursions.