Earthen mound formation in the Uruguayan lowlands (South America): micromorphological analyses of the Pago Lindo archaeological complex

The stratigraphic excavation of the Pago Lindo archaeological complex, in central-eastern Uruguay (La Plata basin), helped to propose an alternative model for mound formation that expresses the intrinsic complexity of prehistoric earthen architecture. This model, known as the spatial–temporal discontinuous model, sees mound complexes as multi-functional areas, with diverse earth works occupied and abandoned intermittently. Since earthen mound sediments are homogeneous, resemble natural soils and show evidences of intense bioturbation, soil micromorphology was used to confirm, refute and further investigate issues raised during field work, related with the prime material used for mound construction, detection of major episodes of mound building, identification of activity areas and taphonomic processes. In this paper, we present the results of the micromorphological analyses of two different earth works from the Pago Lindo archaeological complex (a mound and a micro-relief). Analyses proved the recurrent use of surface horizons for mound and micro-relief building throughout the entire period of site occupation. It also demonstrated the difficulty in identifying discrete depositional episodes and occupation surfaces, because of the intense bioturbation. Two activity areas where recognized: a domestic hut built over a platform, ca. 1600 yrs. BP; and an area of plant residue accumulation over a platform, raised almost 800 hundred year after the domestic hut. The practice of cleaning the occupation surfaces was interpreted from the complete absence of bioarchaeological remains (bones and micro-charcoal). The use of micromorphology as a complementary tool in the stratigraphic excavation of Pago Lindo unraveled evidences that corroborate a newly proposed model for mound growth.