The combination of time-series analysis and sedimentological studies indicates that the upper part of the lower Jurassic Tilje Formation in the southern part of the Halten Terrace consists of tide-dominated deposits. Vertical tidal bundle sequences, showing a periodicity relatable to neap-spring variations in the tidal cycle, is the most prominent indicator of tidal activity. Vertical transitions between contrasting spring-tide sandstones and neap-tide mudstones occur on a metre scale, and are expected to have a significant influence on reservoir communication. The best connectivity between individual spring-tide sandstones is attained when the dimensions of the sandbeds are much larger than those of the mudbeds. Jf the two lithologies have approximately equal dimensions, the degree of sand connectivity will increase as the dimensions of the beds decrease. The large discrepancy between short-term and long-term sedimentation rates in the Tilje Formation is related to rapid infilling of accommodation increments in a setting characterized by limited long-term accommodation.
Tom Dreyer, Norsk Hydro Research Centre, P.O. Box 4313, 5028 Nygårdstangen, Bergen, Norway.