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Tectonic-Controlled Stratal Architecture and Decameter-Scale Cycle Variability of Shelf-Edge, Growth Faulted Deltaic Systems: A Case Study From the Frio Formation in Corpus Christi Bay, South Texas


Nearly 2,000 feet of continuous core, combined with well log and 3-D seismic data, provide an opportunity to document variations of stratal architecture and decameter-scale cycles of shelf-edge, growth faulted deltaic systems through active and inactive periods of growth faults at the scale of 4th-order sequences in the Frio Formation in Corpus Christi Bay. Varying subsidence rates serve as a dominant process in stratigraphic development of the Frio Formation, whereas sediment supply and eustatic sea-level changes are subordinate. The decameter-scale 4th-order sequences within the hanging wall section are grouped into two categories based on stratal architecture: (1) T-R cycles within rapid subsidence of growth faults and (2) R cycles within slow subsidence of growth faults. T-R cycles have complete transgressive and regressive intervals with similar thickness (R-T thickness ratio ∼ 1.7), created by a balance between abundant sediment supply and rapid accommodation rate caused by high subsidence and low sea-level drop rates. This balance controls preservation of both regressive and transgressive units and provides more time for modification of deltaic deposits by wave-storm processes. R cycles are dominated by regressive intervals with minor transgressive intervals (R-T thickness ratio >6). R cycles result from rapid progradation stacking that record abundantsediment supply, slow subsidence and rapid sea-level drop. Other factors such as topography, new created area by previous progradation, and variation of dominant process also influence the formation of T-R cycles and R cycles. T-R cycles have better reservoir quality than R cycles do as more sufficient modification of wave-dominated process during the interplay between deposition and subsidence. Integrated with higher sandstone proportion and thicker interval, T-R cycles have more potential to serve as great reservoirs.