3D Modeling of a foreland fold and thrust basin in the French sub-Alpine chains

Abstract

A three-dimensional geological model has been constructed of a 49 square km area in the sub-Alpine chains in the French Drôme department. The area was situated in the Vocontian Basin, which was an epicontinental sea situated at the western margin of the Alpine Tethys Ocean, between former continents of Gondwana and Laurasia. Formations of limestones and marls have been deposited over a time span of approximately 80 Ma from the Late Jurassic to the Early Cretaceous, which can be classified into eight distinct formations. This was followed by two phases of deformation. First, the counter-clockwise rotation of Iberia into Europe inducing S-N compression in this area. Second, the collision of Adria with the European continent inducing E-W compression. Both events uplifted the area by an estimated 2500 to 3000 m.
This thesis uses data collected during the second year fieldwork (course AESB2430) of the Applied Earth Sciences bachelor at Delft University of Technology. The cross sections and geological map from this fieldwork were revised where necessary. Three new cross-sections were constructed along the north, east, and west boundaries of the area for more coverage. All cross-sections were digitized using the Move software package. To check whether these were geologically feasible, they were restored to their pre-deformation state by removing the effect of faulting and folding. These cross-sections form the basis for a 1:25 000 scale three-dimensional model. Horizon surfaces were created between cross-section horizons using spline interpolation and fault surfaces using linear interpolation
Fauld displacements are removed and an unfolding is performed on the 3D model, in an attempt to reconstruct a balanced pre-deformational setting. The result is a viable model, with some inaccuracies such as gaps and overlaps between formation surfaces and slight variation s in layer thickness. The aim of this 3D model is to aid the understanding of the configuration of rocks and of the structural evolution of the area. The average shortening due to deformation for cross-sections was found to be 14.71 %. The surface reduction value of the area is found to be 8.2 푘푚 or 14.3 %.
The direction of shortening is primarily in the S-N, due to the Iberian collision, and to lesser extent in the E-W direction, due to the Adriatic collision.