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Phosphate Fractionation of Soils at Agroal, Portugal

Published online by Cambridge University Press:  20 January 2017

Katina T. Lillios*
Affiliation:
Department of Anthropology, Brandeis University, Waltham, MA 02254

Abstract

Eidt (1973, 1977, 1984a) suggested that the analysis of soil phosphate fractions (I-III) could be used to identify land-use areas on archaeological sites as well as serve as a relative-dating technique. He noted that the total inorganic phosphate value (I + II + III) reflects the type and intensity of land-use practice, and he hypothesized that the ratio of Fraction II/I correlates with the time elapsed since soil enrichment. A test of these propositions was carried out in conjunction with the excavations at the settlement of Agroal (Portugal), which was occupied during the Bronze Age (2000-1000 B.C.) and Middle Ages (A.D. 1300-1640). Samples were taken from all archaeological levels of the site as well from soils with known land-use histories in the area of Agroal. Results of this study support Eidt"s two principal hypotheses. First, there was a strong correspondence in the control soils between total phosphate values and the nature of land-use activities. Second, the ratio of Fraction II/I in the archaeological samples did, in fact, correlate with the relative age of the associated artifacts. A model of the site"s land-use history, based on the total inorganic phosphate and the Fraction II/I values, suggests a significant alteration and degradation of the soil landscape during the Bronze Age, as a consequence of agriculture, herding, and refuse disposal, followed by less-intensive use during the Middle Ages.

Resumen

Resumen

Eidt (1973, 1977, 1984a) ha sugerido que el análisis de las fracciones de fosfato en el suelo (I-III) podría ser utilizado como técnica para identificar áreas de uso en sitios arqueológicos y también como técnica de datación relativa. Este autor observó que el valor total de fosfatos inorgánicos (I + II + III) refleja el tipo e intensidad de uso de la tierra y propuso, a título hipotético, que la proportión Fractión II/I se encuentra correlacionada con el tiempo transcurrido desde el enriquecimiento del suelo. Se llevó a cabo una prueba de estas proposiciones durante las excavaciones en el sitio de Agroal (Portugal), un asentamiento que fue ocupado durante la Edad de Bronce (2000-1000 A.C.) y la Edad Media (1300-1640 D.C.). Se tomaron muestras de todos los niveles arqueológicos del sitio, así como de suelos en el área de Agroal, donde la historia de uso de la tierra es conocida. Los resultados de este estudio apoyan las dos hipótesis principales de Eidt. Primero, se observó una estrecha correspondencia en los suelos de control entre los valores globales de fosfato y la naturaleza de las actividades de uso de la tierra. Segundo, la proporción Fracción II/I en las muestras arqueológicas está correlacionada con la edad relativa de los artefactos asociados. Un modelo de la historia de uso de la tierra en el sitio basado en el contenido de fosfato inorgánico y en los valores de la proporción Fracción II/I indica una significativa alteratión y degradatión del suelo durante la Edad de Bronce, como consecuencia de la agricultura, el pastoreo y la deposición de residuos, y un uso menos intensivo durante la Edad Media.

Type
Reports
Copyright
Copyright © Society for American Archaeology 1992 

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