Seismic Recognition of Salt Diapirs: GEOLOGIC NOTES

Abstract

Seismic recognition of a salt diapir is usually based on a combination of features such as shape, virtual absence of reflections from the interior, lateral-diffraction patterns, characteristic salt-base reflection, seismic-interval velocities, and halokinetic relation with surrounding sediments and adjoining diapirs. However, these well-known features do not always allow a distinction between salt and shale diapirs. Salt-dissolution phenomena (subrosion) are the only safe evidence for such distinction. Many of the so-called grabens on or near the crest of a salt diapir are due to salt dissolution. A profile across a sinkhole makes it appear as a graben and sink areas appear as local basins. On a seismic section, subrosional features commonly appear as concave reflection segments, in contrast to the major convex or downward shape of the diapir itself. By means of this concept, salt diapirs with dissolution features are identified off Nigeria, in the Canary basin, and in the Ecuadorian Oriente.