Mapa de unidades geomorfológicas del Parque Nacional Bosques Petrificados de Jaramillo (Santa Cruz, Argentina) para su aplicación geoarqueológica

Abstract

Las investigaciones arqueológicas en el Macizo del Deseado (provincia de Santa Cruz, Argentina) han permitido registrar un gran volumen de evidencias de las sociedades cazadoras-recolectoras móviles que ocuparon el área desde tiempos prehispánicos. Para avanzar en estos estudios es necesario analizar la superficie del terreno y discriminar las diversas unidades geomorfológicas en donde se emplazan los restos arqueológicos. En este trabajo se utilizan técnicas geomáticas para generar una cartografía de detalle a partir de la hoja geológica existente para la región (escalas 1:250 000 y 1:100 000), imágenes satelitales de alta resolución e información planialtimétrica relevante. Como resultado se definieron nueve unidades geomorfológicas en las cuales se analizó la distribución de recursos que pudieron estar disponibles para las poblaciones en el pasado y se identificaron procesos naturales que afectan el registro arqueológico.

Archaeological investigations in Macizo del Deseado (province of Santa Cruz, Argentina) have allowed registering a large volume of evidence on nomad huntergatherers who lived in the area since pre-Columbian times. Specifically in the Bosques Petrificados de Jaramillo National Park (PNBPJ), an area where systematic surface records have been recorded, the current state of these studies require detailed geomorphological mapping to fulfill the needs of archaeological research. In this study, we analyzed the surface of the local terrain, seeking to identify the different geomorphological units where archaeological remains are located. A GIS (Geographic Information System) approach was applied, using geomatics techniques to relate different types of data, including remote sensing images and relevant altimetric information to elaborate the required maps. The baseline data used include the current geological chart for the region (4769-IV chart at 1:250000 scale); the geomorphological sketch of the Laguna Grande sector (1:100000 scale); the hydrographic network obtained from the Digital Elevation Model of the Republic of Argentina (MDE-Ar, 1 arc-second spatial resolution), and high-resolution satellite images available for the area (50 cm resolution Bing images). Geomorphological maps were elaborated through an analysis of the terrain using a non-automated landform recognition method. For the final characterization and differentiation, we used fieldwork information (photographs and descriptions). As a result, nine geomorphological units were identified. In each, the distribution of resources that might have been available for ancient populations was analyzed, and the natural processes affecting the differential preservation and visibility of the archaeological record were identified. These units are: 1. Mountain ranges, constituted by rocky outcrops of the oldest formations in the region, from the Jurassic period. 2. The basaltic-plateaux unit, formed by three massive lava flows dated between the Eocene and the Plio- Pleistocene. 3. The volcanic vent, comprising Cerro Madre and Daughter, a heavily eroded volcanic apparatus from the Mid-Miocene. 4. Pediments, deposits made of materials transported by gravity from across broad landscape sectors, accumulated at the bottom of basins and deposited at two different levels, some from the Early Pliocene and others during the Pleistocene. 5. Deposits of ancient lake beaches. 6. Lake littoral strips formed by sediments associated with water bodies that were larger during the Pleistocene. 7. Alluvial plains, with later Holocene-age deposits, distributed in several sectors across the study area, associated with lagoons and streams of the main intermittent watercourses. 8. Sediments in depressions and lagoons, also from the Holocene; these are deposited in endorheic basins that 9. Mass-displacement unit, consisting of materials from Holocene landslides. The analysis of geomorphological units and their concordance with geological information made it possible to delineate the structure of resources in the locality and generate expectations to be considered in the planning of further fieldwork. As regards the preservation of archaeological evidence, among the various units defined, basaltic plateaux, volcanic vents, and pediments are the sectors dominated by erosive factors or stability of the terrain surface. Archaeological visibility is high in those cases, and the most resistant materials are expected to continue being exposed on the terrain surface. In contrast, in deposits from beaches and lake littoral strips, alluvial plains, sediments in depressions and lagoons, and landslide deposits, the archaeological visibility on the surface is lower, dominated by optimal conditions for the burial of materials. This work is a contribution to the establishment of a geological, geomorphological, and geo-chronological contextual framework of the PNBPJ area. The earliest results derived from data gathering about the layers of archaeological data and the thematic cartography obtained have yielded information that constitutes a step forward in archaeological research, laying the foundations for the analysis of decisions on settlement in the landscape by ancient societies. In addition, the differential preservation processes and visibility across the geomorphological units identified represent key information for heritage management activities in this protected area.