KRYSTINIK, LEE F., Krystinik Litho-Logic, Fort Worth, TX, and BEVERLY BLAKENEY DEJARNETT

ABSTRACT: Sequence Stratigraphic Variability in Foreland Basins: An Example from the Cretaceous Western Interior Seaway of North America

Foreland basins are important petroleum provinces throughout the world, but are known for their complex stratigraphic records. A diverse range of deformation occurs in foreland basins and may change character significantly through the filling history of a basin. Complexity is compounded by variable sediment supply rates, producing a sequence stratigraphic architecture that is difficult to predict along strike.

The Cretaceous Western Interior Basin of North America is the focus of many sequence stratigraphic analyses because of extensive outcrops and abundant subsurface data. Although most of these studies are local in scope, some workers have been tempted to correlate stratal stacking patterns and bounding surfaces across large areas, based on lithostratigraphic similarities rather than age equivalence. This study integrates biostratigraphic and lithostratigraphic data to create a chronostratigraphic framework for the Campanian and lower Maastrichtian of the Western Interior Seaway. This chronostratigraphic framework allows comparison of coeval stratal stacking patterns and key surfaces along the western margin of the basin and documents some of the complex sequence stratigraphic relationships that can occur within foreland basins.

Sequence boundaries and maximum flooding surfaces, key to sequence stratigraphic interpretation occur throughout the basin fill. Unfortunately, linking these surfaces regionally is complicated by tectonic uplifts that may cause local unconformities, subsiding areas that may cause local transgressions, and variable sediment supply rates that may cause local shoreline progradation or retreat during stable sea level.

As a result, stratal stacking patterns may be the opposite of that predicted by global sea level curves and maximum flooding surfaces can be directly coeval with sequence bounding unconformities.

Although working with detailed correlations in this type of basin fill can be challenging, the basin fill is responding to the delicate balance of sediment supply, sea level, and subsidence rate. Once an understanding of the local balance of these factors has been reached, sequence stratigraphic analysis, especially in the down-dip orientation can be highly predictive.

AAPG Search and Discovery Article #90910©2000-2001 AAPG Distinguished Lectures