Abstract

Detailed study of log markers (450 logs) and facies variations (80 cores) have revealed an erosional surface beginning along the southwestern margin of the Gilby A and B fields. This erosional surface is coincident with the sideritized muddy siltstone (with Skolithos) facies, or firmground, found to the south and along the southwestern margin of the fields, although the erosion has removed this facies to the northeast. The erosional surface has a general “trough-like” shape and a maximum relative relief of 9 m. Stratigraphically, this surface drops toward the northeast margin of the fields and gently rises approximately 6.4 to 9.7 km beyond the fields.

The erosional surface indicates that the Viking Formation coarse sediment package is not genetically related to the underlying offshore marine Viking Formation mudstones and siltstones and, consequently, probably did not form in an offshore position. It is suggested that this surface developed near the shoreline during a rapid lowering of sea level. The Viking Formation coarse sediment package was deposited during stillstand conditions.