Abstract: Sequence Stratigraphy of Carbonate and Mixed Carbonate-Siliciclastic Depositional Systems: Some Considerations

P. M. Harris, J.M. Borer

Problems arise when a generalized sequence stratigraphy model is applied to carbonate or mixed carbonate-siliciclastic depositional systems.

1. Reefs and other carbonate environments aggrade quickly and can easily keep up with rising sea level, therefore transgressive systems tracts may not be dominated by retrogradational cycles.

2. Since carbonates maintain exceptionally steep slopes, highstand and lowstand deposits along a rimmed-margin are often decoupled and transgressive deposits are poorly represented.

3. Carbonate platforms shed fine debris during highstands, not lowstands; therefore, lowstand carbonate systems tracts, as a rule, should be poorly developed and condensed intervals may be related to lowstands not highstands.

4. Major bounding surfaces can be zones of amalgamated high-frequency surfaces that diverge updip in the case of flooding surfaces and downdip in the case of sequence boundaries.

5. Since the geometries of sediment packages that form the basis for a sequence stratigraphy interpretation are in themselves built by smaller-scale stratigraphic units, miscorrelations are probable when thick packages of basinal sediments are correlated to a single surface on the shelf.

Our model for the mixed carbonate-siliciclastic Yates Formation of the Permian basin illustrates how a conceptual sequence stratigraphic framework needs to be tailored for the intrinsic attributes of the depositional system. The Yates model includes high-frequency shelf bypass; multiple surfaces of stratigraphic discontinuity that occur in stratigraphic intervals rather than single surfaces of erosion or condensation; shelf progradation between the time of maximum rate of sea-level rise and maximum highstand related to "keep-up" carbonate deposition; and limited shelf progradation during relative sea-level fall due to a reduced carbonate factory, low accommodation, and the inability of siliciclastics to prograde across steeply dipping shelf margin carbonates.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994