Abstract

Three major schemes of stratigraphic analysis are commonly employed in modern basin analysis: sequence stratigraphy, genetic stratigraphy, and allostratigraphy. All three use physical discontinuities to subdivide the sedimentary record into units for basin analysis and regional correlation. However, the criteria for defining and selecting physical boundaries used for subdivision varies greatly from one method to the next. There are also major differences in the duration and scale of the fundamental units recognized by each method. The primary objective of this research was to apply each stratigraphic method to the same set of strata and compare the relationship between the three schemes to consider the most appropriate use for each.

Two depositional sequences (A and B), one genetic stratigraphic sequence (GS-1), and four allostratigraphic units (AS-1 through 4) were identified on well logs in Lower and Middle Wilcox strata in South Texas. Depositional and genetic sequences correspond to full third-order RCSL cycles, and allostratigraphic units correspond to partial third-order RCSL cycles. Unconformable sequence boundaries previously identified by Smith (1986) and maximum flooding surfaces identified in this study were used as bounding surfaces.

Interval isopach and net sand maps prepared for each of the seven units show general sediment dispersal patterns and major sediment sources. The vertical resolution of units defined by each scheme is too poor to depict individual depositional systems but can be useful in interpreting large-scale paleogeomorphic features.

Maximum flooding surfaces and associated condensed sections proved to be easier to identify and correlate on well logs than unconformities. Given that maximum flooding surfaces and unconformities are of equivalent chronostratigraphic significance (Xue and Galloway, 1995), it is important to identify both when establishing a chronostratigraphic framework for basin analysis. The results of this study show that recognition of maximum flooding surfaces and subdivision into genetic stratigraphic sequences might be best utilized as a first step in basin analysis. Secondly, unconformity recognition and subsequent sequence stratigraphic subdivisions should be performed. Finally, allostratigraphic subdivisions should be implemented as they provide the highest chronostratigraphic resolution and most sedimentologically genetically-related subdivisions. The ability of the interpreter to apply these subdivisions is highly dependent on the data type and quantity available for study.