Application of Image-Logs to Tidal Ridges in the Offshore Cook Formation (E. Jurassic) North Sea.

Summary The Cook Formation (E. Jurassic) in the northern North Sea is interpreted as subaqueous tidal deltas capped by shelf tidal ridges. These shelf tidal ridges are up to 50 meters thick and consist of stacked dunes showing a coarsening upward trend in grainsize, accompanied with a winnowing effect of the fine-grained material content upward. This gives a tendency to weakly cross-bedded appearance in the cored material, masking and hampering the identification of the dunes and thus the internal architecture of the tidal ridges. The shelf tidal ridges of the Early Jurassic Cook Formation in the northern North Sea represents a case where the application of borehole image logs assisted in identifying the internal sedimentary strata in sections with poorly defined internal structures in addition to provide pale-current data.