Geodiversity is a recent concept that refers to the abiotic variety of nature. It is defined as the range of geological (rocks, minerals, fossils), geomorphological (landforms, processes) and soil features, including their assemblages, relationships, properties, interpretation and systems. In this work, a method of quantitative assessment of geodiversity was applied to the Xingu drainage basin (Amazônia -Brazil). The method is based on the quantification and integration of abiotic features represented on thematic maps at scales ranging from 1:250,000 to 1:2,500,000, overlaid by a 1:25,000 systematic grid. In order to calculate the final geodiversity index, five partial numerical indices representing the main components of geodiversity were drawn compiled: geology, geomorphology, soil, palaeontology and mineral occurrences. The resulting Geodiversity Index map is presented in the form of five isoline classes. The objective of this method is to present such a mapping technique as a tool for environmental planning, particularly for the identification and definition of priority areas for conservation.
From the 1990s, geodiversity studies have been widely carried out in order to understand, describe and preserve the natural heritage of the abiotic environment. Geodiversity assessments have principally been conducted using geological (minerals, rocks and fossils), geomorphological (landforms and processes) and pedological variables. This concept has been widespread and consolidated in scientific circles, where early studies focused on methods that assessed the spatial variability of the geodiversity, with a particular focus on quantitative aspects. In this study, a geodiversity quantification methodology (Pereira et al. 2013) has been applied to the Xingu River basin (Amazônia, Brazil), which covers approximately 51 million hectares. This methodology is based on measuring and integrating abiotic elements, which are spatialised using thematic maps at scales varying between 1:250,000 and 1:1,000,000 and using a 1:25,000 systematic linkage grid. This methodology was adapted for the Amazonian environment by including parameters related to river channel patterns, as approximately 12.6 % of the area is a fluvial environment (channels and floodplains). After applying the methodology, geodiversity indices varying between 4 and 32 were obtained, and a geodiversity hot spot in the basin was identified in the region known as "Volta Grande do Xingu" (The Great Bend of the Xingu). The results of the study highlight the fragility of legal tools for environmental protection of the area, primarily those related to aspects of the physical environment. Although large portions of the basin are partially or fully protected (as indigenous lands and conservation units), the area with the greatest geodiversity is precisely the one which has fewer legal protection devices and is where the Belo Monte hydroelectric power plant is being built.
Research related to geodiversity aim at valuing abiotic aspects as inseparable components of natural heritage and, thus, as well as biodiversity, must be understood and valued through the ordering of their use and geoconservation. Geodiversity studies are developed based on several approaches, from the broadest ones, which contemplate the measurement of abiotic elements fully, to those that assess geoheritage through geodiversity values. The present research follows the broader approach of evaluating and analysing the entire geodiversity, applying the measurement of abiotic elements without their valuation, and spatialising areas with a greater and lesser density of the selected elements related in this research lithology, relief, and soil. For this purpose, bases produced by systematic surveys of Brazilian research institutions were used. As a result, the mapping of the subindexes obtained pointing from the division into 5 classes, the areas which present greater and lesser diversity of each element, as well as the synthesis map for the indexes of geodiversity elements in Brazil, considering the three elements selected for this mapping. The analysis of the indexes' spatialisation was carried out from a descriptive and genetic perspective, aiming to explain the causes of the distribution of the abiotic elements in the Brazilian territory, providing subindexes for studies in the scope of environmental services, nature, and territory conservation planning. A spatial analysis was also carried out between the Geodiversity Index Map and the Brazilian conservation units and the areas where geopark projects are being developed.
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