The geological reference system: from the concept of an integrated geological knowledge management to cartographic representation.

Although digitized, geological maps have poorly evolved since their inception and still retain the constraints imposed by printing: heterogeneity between map sheets, limited point data, and challenging update procedure that remains essentially nonexistent.

The heterogeneity of geological maps also complicates their integration to Information System. Maps, based on rules and concepts that evolved over time, are no longer suited to the precision required by database structures. As concepts and models evolve in geology together with the scientific knowledge, the choice of the representation on the map also depends on the authors’ interpretations and the period of production. As a result, the mapped geological units reflect arbitrarily chosen characteristics of the rocks concerning either their protolith nature, their metamorphic characteristics or alteration transformations, considered as the most representative at the date of publication.

In France, 1:50,000 scale geological maps provide a full territory coverage but do not escape these heterogeneity issues. To address this problem, the BRGM (French Geological Survey) has implemented the RGF program (Référentiel Géologique de la France), which aims to develop a methodology to overcome these limitations and propose an innovative approach to represent the geological knowledge. In this research program new data are acquired by PhD students allowing to improve geological knowledge and to produce updated and harmonized information on geological maps and boreholes.

The tools developed and implemented over the past decade, based on the establishment of an Information System structured as a knowledge database called the Geological Reference System, now make it possible to offer a standardized representation of geological knowledge derived from traditional geological maps. This knowledge can be represented through different reference systems: lithostratigraphic unit, event (and thus the geological history), or domain and zone (e.g. lithotectonic units).

Here, we present some of the results obtained from works conducted in the Alps, the Pyrenees, and the Montagne Noire, illustrating how this structuring of geological knowledge into reference system enables the creation of new maps tailored to the geological information one wishes to represent and, consequently, to the scientific and societal challenges at hand.