PRELIMINARY RESULTS IN ESTABLISHING A GEODIVERSITY INDEX FOR PUERTO RICO, USA

The quantification and mapping of geodiversity (i.e. geological, geomorphological, pedological, paleontological and hydrological features and assemblages) have practical applications in geoconservation and natural resource management.

The geological (G), pedological (P) and hydrological (H) indices for Puerto Rico were assessed and mapped. The method consists of several stages where a series of pre-existing maps is overlaid with a grid of a fixed cell size (e.g. 25x25) and where the number of units/cell (e.g. geological) is obtained following an automatic extraction algorithm.

The analysis was performed using Esri ArcGIS™ software. The G-index was based on lithostratigraphic formations. The P-index was obtained from soil orders. The H-index was generated upon deriving a channel network from a DEM and ordering streams as per Strahler’s system. The numerical values for all indices were mapped and reclassified on a low-high scale and regional correlations were observed.

The G-index reveals a number of hotspots (i.e. areas of high concentration of geological units) in the central and southwestern igneous sub-provinces: Cordillera Central consists of Cretaceous volcanic, plutonic and sedimentary rocks and Paleogene deposits; Sierra Bermeja contains a Jurassic-Cretaceous polymetamorphic complex of oceanic crust and island-arc origin and more recent Cretaceous-Neogene rocks. Low values are characteristic of both north and south Limestone provinces and coastal plains. The P-index has contrasting values among northern and southern coasts, with a high concentration of soil orders in the former and very few in the latter and the high mountains. The H-index reveals an abundant flow and a preference for the north-central coast. Underground drainage is inferred, which is responsible for a multitude of karst features.

The method depends on cartographic data in digital form, which in some countries may not always be available, and also has some procedural limitations. The advantage is that results are presented in a way that facilitates interpretation by a wide range of people besides geologists and geoscientists.

These preliminary results should be considered within the larger context of rapid urbanization of natural landscapes (e.g. north coast, Sierra Bermeja) and as a point of reference in decision-making concerning protection of geodiverse areas and efficient land-use planning.