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Abstract
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Chapter 2
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Lateral Variability
of Sequence Stratigraphic Framework in the Campanian and Lower Maastrichtian
of the Western Interior Seaway
L. F. Krystinik
Union Pacific Resources
Co.
Fort Worth, Texas, U.S.A.
Beverly Blakeney DeJarnett
Consulting Geologist
Fort Worth, Texas, U.S.A.
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ABSTRACT
The Cretaceous Western Interior Seaway
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. We have
integrated biostratigraphic and litho-stratigraphic 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.
Basinwide progradational units occur at
the base of the Campanian and the lower Maastrichtian, but wide variability
in the stratal stacking patterns within time-equivalent deposits exists
along strike for most of the Campanian. Sequence boundaries and maximum
flooding surfaces have been documented by workers for local areas within
the Western Interior Seaway, but in most cases the regional extent and
significance of these surfaces have not been addressed. In addition, recently
published eustatic curves do not compare favorably with most of the lithostratigraphic/chronostratigraphic
profiles in this study. This suggests that tectonic activity during the
Campanian and early Maastrichtian probably played a major role in creating
the complex relationships observed in the Western Interior Seaway. Local
uplifts and basinal downwarps were a dominant control on relative sea level
histories for most of the western margin of the basin. Major sequence-bounding
unconformities, with hundreds of meters of erosion, are the direct time
equivalents of maximum flooding events in other parts of the basin, reflecting
the tectonic complexity typical of foreland basins.
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