ABSTRACT

Detailed correlation and study of approximately 500 well logs from the deep Wilcox trend of south Texas have shown the presence of at least three major deltaic complexes in the Rosita delta system. These sandstone-bearing units, previously considered to be a lower Wilcox strike-transported, shelf-edge sand facies, are reinterpreted as upper Wilcox deltas that prograded across a stable shelf to an unstabled shelf margin.

The Live Oak Delta complex, the youngest observed, comprises numerous lobes. The youngest of these, the Luling and Slick deltas, are both extensively growth faulted and show a downdip change from delta plain to prodelta facies. Areas of maximum net sandstone occur in the downdip part of the growth fault zone where rapid relative subsidence rates compensated for basinward decrease in sandstone percent. A Gulfward displacement of facies and associated growth faults occurred between deposition of the older Luling to deposition of the younger Slick delta. This suggests that the deltas prograded out to the shelf margin and that the associated growth faults reflect gravity instability related to the adjacent prodelta slope.