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

SUMMARY Three up to 520-cm-long sediment cores from Hoya San Nicolas in Guanajuato, Mexico, were analysed for various magnetic properties in order to better define a palaeomagnetic 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−1 (interval 200–520 cm) and a basal age of about 11 600 calibrated years BP (cal. yr BP). We used magnetic susceptibility and natural remanent magnetization to correlate the three cores. A composite palaeomagnetic secular variation (SV) record was obtained from the cores with a stretching and stacking process, and a chronology established with accelerator mass spectrometer 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 9060 and 9810 cal. yr BP. The San Nicolas palaeomagnetic SV curve is similar to palaeomagnetic master curves from Europe and North America, in shape, occurrence and synchronicity of directional features, especially with respect to inclination.