Paleosecular variation 12-20 kyr. as recorded by sediments from Lake Moreno (southern Argentina)

MARIA A. IRURZUN; CLAUDIA S. G. GOGORZA; ANA M. SINITO; MARCOS A. E. CHAPARRO; HECTOR NUÑEZ; JUAN M. LIRIO

Studia geophysica et geodaetica

StudiaGeo s.r.o.

Lugar: Praga; Año: 2008 vol. 52 p. 157 - 172

0039-3169

            We describe paleomagnetic and sedimentological studies carried out on three cores Lmor1, Lmo98-1, Lmor98-2 from bottom sediments of Lake Moreno (south-western Argentina), and integrate our results with data from Gogorza et al. (2000a).             The cores were collected (371 samples in all), with lengths varying from 2.5 to 4 m. Measurements of directions (declination and inclination, D and I) and mass specific intensity of natural remanent magnetization (NRM intensity), magnetic susceptibility (specific, X and volumetric, k), isothermal remanent magnetization (IRM), saturation of isothermal remanent magnetization (SIRM), and back field remanent coercivity (B0CR) were performed. The stability of the NRM was investigated using alternating-field demagnetization. The results show that these sediments meet the criteria required to construct a reliable paleomagnetic record             The cores were correlated very well based on magnetic parameters, such as X and NRM intensity, as well as with lithological features. Tephra layers were identified from the lithological profiles and magnetic susceptibility logs.             We obtained the D and I logs of the characteristic remanent magnetization for the cores as a function of shortened depth. The data from the three cores were combined to form a composite record using the Fisher method.             A comparison between stacked inclination and declination records of Lake Moreno and results obtained in previous works, Lake Escondido (Gogorza et al., 1999) and Lake El Trébol (Irurzun et al., 2006), shows good agreement. This agreement made it possible for us to transform the stacked curves into time series spanning the interval 12-20 kyr. The results obtained improved our knowledge of SV and the behaviour of the geomagnetic field and also allowed us to determine the range of past inclination variations (-70o - -45o) for the southern hemisphere, where data are scarce.