Construction of accurate geological cross-sections along trenches, cliffs and mountain slopes using photogrammetry

This paper discusses the application of close range photogrammetry for the construction of geological cross-sections from outcrops located on trenches, cliffs and mountain slopes. Our methodology is based on stereoscopic pairs of photographs of the outcrops on which geological interpretations may be carried out directly using a digital stereo viewer. It is also possible to automatically obtain point clouds. Through control points of known coordinates taken on the field and located in the photographs, the three-dimensional model recovered is correctly geo-referenced and the residual error is minimized. Layers and tectonic structures recognized in the photographs can be easily projected in any desired direction, as, for example, in the direction of the fold axes to obtain a proper view of the geometry of the structures, or in one direction parallel to the tectonic transport vector if a restoration is demanded. The application of this methodology is shown by constructing a detailed geological cross-section at the cliffs of La Conejera Inlet (Asturias, Spain). The studied structures, involving Jurassic rocks, are located in a Permian-Mesozoic extensional basin called Asturian Basin (NW Iberian Peninsula). This basin was partially formed during the opening of the Bay of Biscay and partially inverted during a Cenozoic contraction responsible for the Pyrenees and its western prolongation along the north margin of the Iberian Peninsula.

► We present a methodology for the construction of geological cross-sections.
► This methodology is based on the interpretation of stereoscopic pairs of photographs.
► It allows the creation of distortion-free geological cross-sections.
► It may be applied to cliffs, mountains slopes, trenches or similar outcrops.
► It has been successfully employed to a natural example of inversion tectonics.