Geological mapping for the urban area of Tarragona

Abstract

A detailed and systematic geological characterization of the urban area of Tarragona has been conducted under the project ‘1:5000 scale Urban geological map of Catalonia’ of the Institut Cartografic i Geologic de Catalunya. The results of this characterization are organized into: (1) a geological information system that includes all the information acquired; (2) a geological model focused on the identification, characterization and correlation of the geological materials and structures that are present in the area, and (3) a detailed geological map that represents the synthesis of all the collected information. The mapping project integrates in a GIS environment pre-existing cartographic documentation (geological and topographical), core data from compiled boreholes, descriptions of geological outcrops within the urban network and neighbouring areas, physico-chemical characterization of representative samples of geological materials, detailed geological mapping of Quaternary sediments, subsurface bedrock and artificial deposits, and 3D modelling of the main geological surfaces. The geological model is structured in a system of geological units that form a chronostratigraphic point of view are structured in Preneogene (from Mesozoic to Paleogene), Neogene, Quaternary and Anthropocene. The description of the geological units is guided by a systematic procedure. It includes the main lithological and structural features of the units that constitute the geological substratum and represents the conceptual base of the published map sheets of the urban geological map of the Tarragona metropolitan area. These map sheets are composed of a principal map, geological cross sections, and several complementary maps, charts and tables. Regardless of the geological map units, the principal map also represents the main artificial deposits, features related to the geohistorical processes, contours of outcrop areas, information obtained in stations, borehole data, and contour lines of the top of the pre-quaternary basement surface. The most representative complementary maps are the Quaternary map, the subsurface bedrock map, and the isopach map of thickness of superficial and anthropogenic deposits. The map also includes charts and tables of relevant physico-chemical parameters of the geological materials, harmonized downhole lithological columns from selected boreholes, stratigraphic columns, and photographs and figures illustrating the geology of the mapped area and how urbanization has changed the natural environment. The development of systematic urban geological mapping projects, such as the example of Tarragona’s case, which provides valuable resources to address targeted studies related to urban planning, geoengineering works, soil pollution and other important environmental issues that society should deal with in the future.