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Basin Analysis with the New Stratigraphies: A Test Case Using Subsurface Data, Wilcox Group (Paleogene), South Texas

By

BELLAMY, JUSTIN B.

Pioneer Natural Resources USA, Irving, TX,

BREYER JOHN A.

Texas Christian University, Fort Worth, TX

 

Three schemes or methods of stratigraphic analysis have advocates today. Sequence stratigraphy, genetic stratigraphy and allostratigraphy all use physical discontinuities to subdivide the sedimentary record into repetitive sequences of strata for basin analysis and interregional correlation. This similarity aside, the schemes differ in important ways, most notably in the physical discontinuities used to subdivide the sedimentary record into units for stratigraphic analysis, but also in the duration and scale of the resulting units and in the fundamental nature of the units recognized. No one has applied all three schemes to the same set of strata and compared the results, and little consideration has been given to the relationship between the schemes or to the most appropriate use of each. Here the schemes are applied to the same set of stratigraphic data, providing results that are directly comparable and allowing the utility of all three schemes to be readily evaluated.

An interval approximately 1,000 ft thick in the Lower and Middle Wilcox in the subsurface beneath a 4,000-mi2 area in South Texas was subdivided into stratigraphic units corresponding to those used in each analytical scheme. Two depositional sequences, one genetic stratigraphic sequence and four allostratigraphic units were identified and mapped using well logs. Interval isopach maps, net sand maps and sand percent maps show the major sediment sources, the general sediment dispersal patterns and the depositional loci for each of the seven units. The vertical resolution of all of the units is too poor to depict individual depositional systems.