Abstract: Nonmarine Sequence Stratigraphy

J. C. Van Wagoner, R. W. Hill

Sequence stratigraphy predicts the effects of relative sea level changes on facies distribution and stratal stacking patterns. These effects have been well documented in paralic and shallow-marine strata. The influence of sea level or base-level changes on nonmarine strata have been more problematic. Recent studies of nonmarine rocks in the Book Cliffs of eastern Utah, and the Statfjord Formation, Statfjord field, Norwegian North Sea, have allowed us to refine a sequence-stratigraphic model to predict facies architecture in nonmarine rocks. This model is based on the response of nonmarine sediments to cycles of base-level change. During base-level lowering, fluvial systems incise and create paleovalleys. These valleys develop by upstream-migrating knickpoint erosion. Some valley syste s die out downdip before reaching the lowstand shoreline. Valleys fill with multistory braided-stream sandstones during base-level lowering and early base-level rise. During the middle part of base-level rise, deposition occurs in the upper parts of the valleys on the adjacent alluvial plain. Single-story channel fills, levee and crevasse deposits, and soil horizons are common. During the late part of base-level rise, deposition is dominated by muddier alluvial plain and lacustrine deposits. The cycle repeats with another drop in base level. This distribution of facies, tied to predictable changes in accommodation, is used to identify sequence boundaries and flooding surfaces and predict reservoir distribution in nonmarine rocks.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994