Radiocarbon Chronology of Paso Otero 1 in the Pampean Region of Argentina

JOHNSON, E.; POLITIS, G.; MARTÍNEZ, G; HARTWELL, W.; GUTIÉRREZ, M. A.; HASS, H.

Quaternary of Southamerica and Antarctic Peninsula

Balkema

Lugar: Washington; Año: 1998 vol. 11 p. 15 - 25

0168-6305

Paleosoils widely occur in the Pleistocene and Holocene sequence of the Pampean area of Argentina. During the last 30 years, Fidalgo and colaborators constructed a lithostratigraphic and pedostratigraphic scheme for the Pampean region from the latest Pleistocene to the present calibrated by means of many 14C dates (see Fidalgo 1992; Tonni et al. 1999; Table 1). The stratigraphic sequence relied in part on a former sequence by Ameghino (1889), modified by Frenguelli (1957) and others. The stratigraphic Holocene scheme of Fidalgo and others (see Fidalgo 1992) involved two paleosoils (Puesto Callejón Viejo Geosol, close to the Pleistocene-Holocene boundary, and the Puesto Berrondo Geosol, at about 2 ky B.P.), and the recent soil. Other workers (eg Iriondo and García 1993; Iriondo and Kröhling 1996; Carignano 1999) agreed only in the existence of a Holocene paleosoil and obviously, the present soil. In this later scheme, the Holocene pedogenetic event was considered long-lasting and assignable to the Hypsithermal (see Carignano 1999). Remarkably, there were no dates in the type area of the soil units of Fidalgo (1992; lower Río Salado basin). However, after the analysis of the numerous dates and additional field work in the Pampean area by workers of the Museo de La Plata, we consider that two Middle-Late Holocene pedogenetic events actually occurred: one at about 6-5 ky B.P. and the other about 2 ky B.P. The Aimaran "Stage" of Frenguelli (1957 and previous papers) corresponds to the 2 ky B.P. episode. Besides, according to recent dating (Figini et al. 1999), in Punta Hermengo (southeastern Buenos Aires Province), a paleosoil in the position of Puesto Callejón Viejo Geosol, which was assigned to the boundary Pleistocene-Holocene by Fidalgo (1992) and others, would be more modern and actually correspond to the Middle Holocene event. At the same pedogenetic event could correspond the paleosoils with dates of 6.5-4 ky B.P. in Paso Otero, La Horqueta II, Arroyo Tapalqué and Río Sauce Grande (see Table 1).