Pedosedimentary and palaeoenvironmental significance of a Holocene alluvial sequence in the southern Pampas, Argentina

A representative section of the Holocene alluvial record of the southern Pampas (Argentina) com prises a sequence of clastic sediments, a diatomite and two palaeosols. Detailed macro- and micromorphological descriptions provide the basis for the reconstruction of its pedosedimentary history. Combining the pedosedi mentary reconstruction with palaeoecological data allows a detailed overview of alluvial landscape development and associated palaeoenvironmental change in the region during the Holocene. The early-Holocene shift from a subhumid dry to humid climate was marked initially by a diminution in clastic sedimentation, the development of the Puesto Callejón Viejo Soil and then re-establishment of fluvial aggradation with a dominance of bioclastic sedimentation. Loess inputs increased during the mid-Holocene as the climate reverted to subhumid dry, and temporary subaerial exposure of the sediments led to the formation of the Puesto Berrondo Soil. More variable environmental conditions followed with natural fluvial aggradation ceasing in the late Holocene, though aeolian sedimentation has continued until the present day. The resultant surface accretionary soil has been modified by recent alluvial inputs from flood events linked to agricultural disturbance in adjacent catchments.