Gravity modelling to assess salt tectonics in the western end of the South Pyrenean Central Unit

Abstract

A new gravity survey (almost 900 new sites and more than 4000 sites from previous studies) reveals the existence of Pyrenean-oriented long-wavelength residual gravity anomalies ranging from −18 to 28 mGal, associated with frontal structures, and short-wavelength gravity lows (up to −16 mGal) distributed along an oblique zone in the western sector of the South Pyrenean Central Unit of the Spanish Pyrenees. These clearly correlate with the occurrence of several bodies and diapirs of Triassic evaporites and mudstones. The subsurface geometry and regional location of these evaporitic bodies is derived from four 2.5D gravity models that tie data from field geology, rock density analysis, seismic reflection profiles, boreholes and our gravity survey. Gravity-constrained cross-sections allow us to distinguish between vertically well-developed and poorly developed diapirs that belong to the Sierras Marginales Unit, and to characterize the relationships between thrusting and diapirism during Eocene–Oligocene time.