Detailed analysis of Oligocene Frio Formation intraslope, growth-faulted sub-basins in the Corpus Christi, Texas area indicates that deposition during relative lowstands of sea-level was the main cause or “trigger” of growth faulting. Lowstand depocenters on the low-gradient, upper continental slope comprising basinfloor- fan facies, slope-fan systems and prograding, lowstand delta systems exerted sufficient gravity stress to trigger major sections of outer shelf and upper slope strata to fail and move basinward. The faults sole out deep in the basin and rotation of hanging-wall blocks mobilized deep-water muds and forced the mud basinward and upward to form mud (shale) ridges that constitute the basinward flank of intraslope sub-basins overlying footwall fault blocks.

Lowstand sedimentation associated with third-order falls of relative sea-level produced load stress that triggered major regional syndepositional growth-fault systems. Sub-basins on the downthrown side of each arcuate fault segment composing a regional fault system were filled during a single lowstand of sea-level. Consequently genetically similar but diachronous lowstand depositional systems filled each successive growthfaulted sub-basin trend. Sub-basin development and fill extended the Frio shelf-edge stepwise into the Oligocene Gulf of Mexico Basin. Thus each successive, basinward sub-basin was younger than the previous landward sub-basin.

Lithostratigraphic Frio and Anahuac strata comprise six chronostratigraphic, third-order depositional sequences (~32.0–23.38 Ma) and myriad fourthand fifth-order sequences or parasequence sets. Except for incised valleyfills, lowstand tracts comprise off-shelf systems deposited within active, growthfaulted, intraslope sub-basins. Off-shelf and on-shelf deposition are temporally unique. Maximum Anahuac flooding (~24.57 Ma) provided a regional, dated marker to which latest published ages of sequence surfaces were calibrated. Maximum flooding surfaces and type 1

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unconformities are essentially isochronous, but sand-rich lith ofacies are mostly diachronous.

Sequence-stratigraphic analyses of Oligocene (Frio Formation) growth-faulted sub-basins in Corpus Christi Bay and offshore Mustang Island demonstrate that current exploration targets consist of sand-rich, proximal, deltaic, prograding wedge and incised-valley-fill sandstones, respectively. Postdepositional crestal faults on rollover anticlines provide reservoir trapping mechanisms. Wireline-log facies of productive reservoirs in the sub-basins are genetically similar, but more than 10 mi (> 15 km) apart, and several major faults separate successive sub-basins. A methodology is presented that incorporates the sequencestratigraphic interpretation of each sub-basin which improves correlations of systems tracts between the widely separated sub-basins. This methodology consists of composite wireline logs created by splicing unfaulted and relatively conformable log segments from the deepest wells in an area. The composite log provides a stratigraphic record that captures a complete succession of depositional and cyclic history. Site-specific sequencestratigraphic- section (S5) benchmark charts contain composite logs and additional data that summarize available geologic information for a specific sub-basin.

Growth-faulted sub-basins all along the Texas coast have been prolific petroleum targets for decades and are now the focus of prospecting for deep, on-shelf gas. Lowstand basin-floor and slope-fan sandstones are the principal gas targets. Understanding the origin of the growth-faulted sub-basins and their chrono stratigraphic relationships and depositional processes provides a perspective that can improve deep on-shelf exploration.

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