Fluvial terrace mapping from ALOS-PALSAR data for archaeological prospection in the middle Uruguay River basin, Argentina

Abstract

Archaeological research carried out in the terminal section of the middle Uruguay River basin (Entre Ríos) since the end of the 19th century has made it possible to identify a complex network of human occupations that show differences in the settlement pattern and use of space. In the area between the Mocoretá River mouth and the Del Molino stream, located to the north of the city of Concepción del Uruguay, more than 68 archaeological sites are known. All of them are chronologically located within the Holocene and distributed in the adjacent plains, tributary courses and islands of the Argentine territory. As a result of the Pleistocene-Holocene fluvial dynamics and geological evolution, the geomorphological landscape of these banks displays three terraces in the middle course, between the cities of Federación and Concordia. The sedimentary deposits of the lower terrace, corresponding to the Holocene, are known as Concordia Formation. Previous research recorded sites distributed in different landscape units closely linked to river courses, in sectors with wide visibility (terraces, floodplains, sedimentary banks, erosion banks, dune fields and islands). Many of these sites were flooded by the Salto Grande dam, built in the 1970s. Since then, and despite the systematic archaeological research carried out in the region, the number of archaeological sites recorded is very low. This difficulty in locating the sites was the reason for the design of a prospecting model adjusted to this need. Based on known information, we designed a terrain prospection model using Geographic Information Systems. This model allowed us to identify the Holocene geoforms where it is most likely to find archaeological sites in the middle Uruguay River basin. This will enable the recording of archaeological sites to be expanded and their locations in the landscape to be characterised. This paper presents the results of geomorphometric analyses developed with a computer tool called Geomorphon, which recognises landform associations. A positive correlation was recorded between the location of the archaeological sites known to date and geomorphometric features interpreted as edges and top surfaces of the low terrace (ridges and shoulders associated with flat surfaces, from geomorph routine). This makes it possible to guide archaeological surveys towards the lower terrace (Concordia Formation) and test the model a priori.