High-resolution magnetostratigraphy in southern South America: results from the long sedimentary sequence of the maar lake Laguna Potrok Aike (ICDP-PASADO)

A. LISÉ-PRONOVOST; G. ST-ONGE; C. S. G. GOGORZA; P. KLIEM; B. ZOLITSCHKA; THE PASADO SCIENCE TEAM

Quebec

Conferencia; GeoHydro 2011. Water and earth: The junction of Quaternary Geoscience and Hydrogeology; 2011

The Canadian Quaternary Association (CANQUA) and the Canadian Chapter of the International Association of Hydrogeologists (IAH-CNC)

The maar lake Laguna Potrok Aike (52°S, 70°W) is located in the Patagonian steppe of southern Argentina, 80 km north of the Magellan´s Strait and 90 km from the coastal city Rio Gallegos. The Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) team drilled the lake in the austral spring 2008 in the framework of the International Continental scientific Drilling Program (ICDP). Here we present the full vector paleomagnetic reconstruction from the 106-meter long composite sequence from the lake center and discuss some of its characteristics and implications for both stratigraphy and paleomagnetism.The natural remanent magnetization (NRM) was step-wise demagnetized and measured on u-channel samples using a 2G cryogenic magnetometer at 1 cm interval and the paleomagnetic directions (inclination and declination) were calculated using principal component analysis (PCA). Afterward, the anhysteretic and the isothermal remanent magnetizations (ARM and IRM) were induced and measured using the same instrument in order to build a paleointensity proxy and to identify the magnetic carriers. To further define the magnetic assemblage, the hysteresis properties were measured using an alternating gradient force magnetometer at ca. 30 cm intervals and the high temperature dependence of magnetic susceptibility was measured from 50° to 700°C for all core catchers samples (ca. 3 m interval) using a Bartington system. The rock-magnetic results indicate that the magnetic assemblage of the background sediments is dominated by low coercivity mineral such as magnetite generally in the pseudo single-domain (PSD) range, which represents an optimal assemblage for a paleomagnetic study. The NRM is defined by a strong, stable, single component magnetization with maximum angular deviation (MAD) values are generally below 5° in background sediments. Altogether these results suggest a genuine recording of the geomagnetic field. Using the preliminary radiocarbon- and tephra-based chronology, the full paleomagnetic vector (inclination, declination and relative paleointensity) is compared with the closest available records from lake and marine sediments, lava flows, as well as with geomagnetic field models. These new high-resolution data reveal similarities with the other Holocene paleomagnetic records and suggest that the Laschamp geomagnetic excursion was recorded despite numerous rapidly deposited layers.