Magnetostratigraphy and environmental magnetism in a Pleistocene sedimentary sequence, Marcos Paz, Argentina

摘要

Late Cenozoic sediments exposed in a quarry in the locality of Marcos Paz (Buenos Aires province) were studied by applying paleomagnetism and environmental magnetism. The whole sequence, with the exception of the recent soil, belongs to the Pleistocene and is integrated by clayey silts (sandy) and also by a layer of fine sand. Eleven different depositional/postdepositional units, numbered in descending order from unit 1 to 11, were determined. The units 1, 2 and 3 in the upper portion of the geological section should be assigned to Brunhes (＜ 0.78 Ma). Below a depth of 6 m, the reverse polarity zone corresponds to Matuyama (＞0.78 Ma). Matuyama magnetozone includes some subzones of normal polarity that should be assigned to the subchron Jaramillo (0.99 Ma) and to the subchron Olduvai (1.9 Ma). The reverse polarity levels determined at the bottom of the profile should be assigned to the lower Matuyama (＞1.9 Ma). The highest volume susceptibility values are recorded in the less pedogenized sediments (400 x 10~(-5)), while the lowest values are always obtained in gleyed horizons (30 × 10~(-5)). The data support the wind-vigor magnetoclimatological model, although affected by different pedogenesis degrees and weathering as demonstrated by the behavioral pattern of chemical elements.