Palaeomagnetic secular variation and rock-magnetic studies of Holocene sediments from a maar lake (Hoya de San Nicolas) in Central Mexico

MARCOS A.E. CHAPARRO; HARALD N. BÖHNEL; NORBERT R. NOWACZYK; ROBERTO S. MOLINA-GARZA; JUNGJAE PARK; JÖRG F.W. NEGENDANK

GEOPHYSICAL JOURNAL INTERNATIONAL

Wiley-Blackwell Publishing

Lugar: Edinburgh; Año: 2008 vol. 175 p. 462 - 476

0956-540X

Three up to 520 cm long sediment cores from Hoya San Nicolas in Guanajuato, Mexico, were analyzed for various magnetic properties in order to better define a paleomagnetic secular curve for Central Mexico. The results –magnetic susceptibility, hysteresis cycles, anhysteretic and isothermal remanent magnetization– suggest that the remanent magnetization of the sediments is controlled by ferrimagnetic minerals (pseudo-single domain magnetite), which are suitable recorders of the geomagnetic field. The age-depth model indicates average deposition rates of 0.32 (interval 146-198 cm) and 0.45 mm/yr (interval 200-520 cm) and a basal age of about 11,600 cal. years BP. We used magnetic susceptibility and natural remanent magnetization to correlate the three cores. A composite paleomagnetic secular variation record was obtained from the cores with a stretching and stacking process, and a chronology established with AMS dates on microscopic charcoal and stratigraphic correlations with other well dated Holocene records from Mexico and Guatemala. The declination and inclination results show oscillatory behaviour varying in a narrow range, although a distinctive directional swing is evident between 9,060 and 9,810 cal. years BP. The San Nicolas paleomagnetic secular variation curve is similar to paleomagnetic master curves from Europe and North America, in shape, occurrence and synchronicity of directional features, especially with respect to inclination.