ABSTRACT: The Importance of Recognizing High-Frequency Sequences in Stratigraphic Correlations: A Stratigraphic Modeling Example from the Permian Basin

BORER, J. M., and P. M. HARRIS, Chevron Oil Field Research Company, La Habra, CA

Subsurface, outcrop, and stratigraphic modeling studies of the Upper Guadalupian Yates Formation and stratigraphic equivalent margin and basin deposits indicate that small-scale genetic units show many of the same attributes as seismic-scale sequences. These include critical surfaces (erosion, bypass, and flooding), dramatic spatial shifts in deposition through time, and internal facies stacking patterns. Failure to recognize the presence and importance of these high-frequency cycles precludes the accurate assessment of platform development and leads to erroneous shelf-to-basin correlations. For example, fourth-order lowstands occurring during a third-order highstand can introduce significant amounts of sediment into the basin. Conversely, fourth-order highstands during a third-order owstand can cause deposition on the shelf top and minor condensed intervals on the slope and basin floor.

Within a basin-margin context, flooding, aggradation, progradation, erosion, and bypassing should be considered high-frequency processes. Stratigraphic modeling studies illustrate how the efficiency and duration of these short-term processes vary with position in a third-order cycle. At some critical threshold, a surface is generated, which we will label a third-order surface; however, the surface is actually generated during a fourth- or fifth-order event when the rate of base-level change is maximized. Prior or subsequent high-frequency surfaces may be genetically just as important and make picking a single third-order surface difficult and misleading.

Whether fourth-order surfaces are amalgamated or separate entities is a function of the shape, magnitude, and duration of the third- and fourth-order sea-level events; the rates of sedimentation and subsidence; and the topographic profile of the shelf-to-basin transect. Stratigraphic models are excellent tools for investigating how each parameter varies the genetic importance of fourth-order cycles relative to third-order cycles. High-frequency sequences may or may not be important on an exploration scale; however, they are important when attempting to understand fine-scale geologic relations for development purposes.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)