Soil Formation and Site Formation at Archaeological Sites in the Río Quequén Grande Valley (Southeastern Pampas), Argentina: The Paso Otero 4 Site

For more than 15 years, archaeological investigations have continued at the Paso Otero locality of the southeastern Pampas of Argentina. Evidence from four archaeological sites buried in the ancient floodplain of the Middle Río Quequén Grande have led to the development of a high resolution stratigraphic and chronological framework for a segment of the valley for the Holocene (ca. 9000-2700 radiocarbon years BP). Sites dating to the Middle Holocene have been difficult to detect throughout the southeastern Pampas. However, in early 2008, excavations at the Paso Otero 4 site have begun to demonstrate that Middle Holocene sites do exist as the site is located within a regionally defined Middle Holocene geological deposit. As a rare archaeological site for this region, geoarchaeological investigations carefully examined this site in order to define the local site stratigraphy, site formation processes, and regional correlation. Disagreement exists regarding the extent of regional soil formation within this Middle Holocene deposit since structural development and pedogenic features are not clearly evident at the macro-scale of field analysis. Some believe that this unit is composed of multiple soil horizons and others define it as a cumulic soil with localized expressions of pond or eolian deposition that can not be regionally correlated beyond the scale of the geological unit. Therefore, in addition to detailed stratigraphic recording, particle-size analysis and micromorphology were conducted in order to define the deposit with greater detail and evaluate the extent of pedogenesis. It is necessary to define the nature of pedogenesis within the unit because different soil formation processes have various effects on the preservation of the archaeological record. This paper presents new evidence on the extent of soil formation within the Middle Holocene deposit and its impact on the archaeological record at the Paso Otero 4 site.