Off-Shell Portion of Harris Delta: Reexamination of Downdip Woodbine-Eagle Ford

Mark H. Porter, Dewitt C. Van Siclen, Robert E. Sheriff

This study related the Eagle Ford equivalent Harris delta north of the Stuart City shelf edge with the downdip Woodbine-Eagle Ford section south of that shelf edge. Together, they comprised one large deltaic complex that divided into two major lobes at an avulsion site near Anderson County, Texas. One lobe prograded southwestward toward Kurten field in Brazos County, the other (now partly eroded) prograded southeastward beside the low-lying Sabine (uplift) landmass into Polk County. The Polk County lobe crossed the Stuart City shelf edge in the Seven Oaks-Hortense field area, and continued to prograde southward into deeper and higher energy water. Such an environment caused this "off-shelf Harris delta" to oversteepen, resulting in frequent slumps and gravity flows that d posited debris-flow and turbidite sands along with predominantly fine-grained prodelta sediments. More familiar deltaic facies (outer fringe) are present in the uppermost section.

Numerous structural and stratigraphic maps and cross sections illustrate the progradation of the downdip Harris delta and its features. The progradation was arrested for a time by deeper water at the older and more precipitous Sligo shelf edge. This progradational hiatus is recorded by a relatively strong reflection that separates two seismic sequences. The younger onlapping sequence appears to represent continued Harris delta sedimentation. Among the interesting features mapped seismically and/or geologically are: mounded reflections that represent the largest slumping events, thickness anomalies associated with the carbonate substrate, and erosional(?) channels at the section top. These off-shelf Harris delta deposits appear to interfinger laterally with a genetically different east rn (Tuscaloosa?) sequence in Tyler and Jasper Counties.

AAPG Search and Discovery Article #91029©1989 AAPG GCAGS and GC Section of SEPM Meeting, October 25-27, 1989, Corpus Christi, Texas.