Summary

Linear amplitude patterns on stratal slices in the Corpus Christi Bay area of Texas are important seismic geomorphological features that show sediment dispersal patterns. These amplitude patterns are oriented in both strike and dip directions. Some of the linear amplitude patterns are related to faults; however, most of them are not associated with faults but are related to sandstone bodies. Later faulting may make the depositional-related linear amplitude patterns more fragmented, but the faults will not change the overall orientation or the geomorphologic significance of the depositional-related linear amplitude patterns. In some cases the depositional-related linear amplitude patterns parallel the long axes of faults, which may have has come control on the depositional pattern. Amplitude patterns on stratal slices should be interpreted as non-biased, general sediments dispersal patterns unless the patterns can be directly ties to a structural feature. Indepth understanding of structural and depositional-related amplitude patterns leads to accurate stratal slicing interpretations. This is important because stratal slicing is a low cost and useful tool for facies/reservoir prediction with poststack 3-D seismic data.

Sequence-Stratigraphic and Depositional Model

The Oligocene (Frio) fault-controlled subbasins in the Corpus Christi Bay area were formed during third-order (1– 1.3 m.y.) Tertiary cycles in the GOM (Brown et al., 2004). Filled with third-order lowstand depositional systems, the subbasins are located on the basinward, downthrown side of regional growth-fault systems. Transgressive and highstand systems tracts formed above the subbasin and completed the third-order depositional sequence. The overall depositional history is a progradational succession from deep water, highly aggradational lowstand basin-floor and slope fans to shallow water, lowstand prograding wedge complexes, and terminally to on-shelf transgressive and highstand systems tracts (Brown et al., 2004; Zeng et al., in press). The sediments in the basin-floor fan are sandy whereas the slope-fan systems are predominately muddy and have thin intervals of sandstones and siltstones. The sandstones and siltstones in the slope fan are inferred to be turbidites deposited in submarine channels and levees on slope fans. The prograding deltaic complex is composed of interbedded sandstones and shales interpreted to have been deposited as overbank deposits along deltaic distributaries and at mouths of lowstand deltaic distributaries. The strong interaction between sea level cycle, sediment supply, and sediment ridge tectonics made sediment dispersal patterns that reflect an organized and relatively predictable pattern of basin fill. The model of the higher-order sequence development is a current subject of research.

Amplitude Patterns and Their Relationship to Faults

Because of the limit of seismic resolution and highly variable nature of Frio seismic events, high-resolution sequence stratigraphy and reservoir prediction from poststack 3-D seismic data have been a challenge. One of the alternative tools is stratal slicing to reveal horizontal amplitude patterns for high-resolution (10-m level) systems tracts (Zeng et al., in press). Depending on local structural and thickness trends, a stratal slice can be a time slice, horizon slice, or proportional slice. Proportional slices were used in this study to calibrate large thickness gradient in the subbasin.

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