Abstract

Sequences in the Mid-Continent tend to be abbreviated because of limited accommodation space. Some sequence components (e.g., systems tracts) present on continental margins are either absent or merged with other elements. Nevertheless, sequence boundaries are rather easily distinguished because of the associated unconformity. The boundary commonly corresponds to the base of channelized sandstones or to regional unconformities, where the difference in ages of the strata above and below it is readily apparent. Some regional unconformities are recognizable because of convergent strata, but they are actually less than spectacular on a local scale. Other less prominent sequence boundaries are associated with paleosols. Transgressive units have been recognized and have been effectively used in dividing strata into mappable units for delineation, not only of local structure but also delineation of sandstone reservoirs.These units not only include transgressive surfaces, but they may coincide with or approximate marine-flooding surfaces, condensed sections, or parasequence boundaries, or a combination.