Research paperEvaluation of pinnacle reef distribution at shallow subsurface using integrated geophysical methods: A case study from the upper Kimmeridgian (Spain)

- Usefulness of geophysical methods for the analysis of shallow-marine carbonate rocks.
- Facies heterogeneities and faults evaluated at shallow subsurface.
- Magnetometry and EM no useful for identification of facies heterogeneity and faults.
- Ground-penetrating radar allows 3D evaluation of pinnacle reefs and faults.

The well exposed outcrops of the upper Kimmeridgian shallow-marine carbonates at Jabaloyas (Iberian Chain, NE Spain) permit the evaluation of geophysical methods for the identification of sedimentary facies. Direct measurement of magnetic susceptibility in facies and detailed grids of magnetometry, electromagnetic multifrequency and ground-penetrating radar (50-500 MHz antennas) have been performed in two study areas where the upper Kimmeridgian rocks are nearly horizontal. Magnetometry indicates negative anomalies in residual magnetic field and vertical magnetic gradient related to reef pinnacles and faults. Electromagnetic data reveal that positive anomalies of apparent conductivity correlate with non-reefal facies. The areal distribution of magnetometry and EM data does not permit the unequivocal identification of pinnacles and faults at the studied area. By contrast, ground penetrating radar profiles and maps of relative reflectivity in two way travel time slices are useful for the identification of faults (hyperbolic anomalies) and reefal and non-reefal facies (radar facies A and B, respectively). The integration of geophysical data, mainly ground penetrating radar, has permitted the 3D reconstruction of reef pinnacles and its tectonic framework.