Abstract
This study reports an investigation of the structure and stratigraphy of the downdip Yegua sandstones at Edna Field, Jackson County, South Texas. The study is based on 22.9 square miles of three dimensional (3-D) seismic data, well-logs from 15 wells, 9 paleontologic reports, 3 check-shot velocity surveys and 2 synthetic seismograms. The seismic sequence stratigraphic approaches are used to infer structural and stratigraphic features that may have been overlooked from the previous interpretations. Four sequence boundaries or correlative paleohorizons are interpreted within the Yegua interval: Discorbis yegua (38.2 Ma), Nodosaria mexicana (38.8 Ma), Anomalina umbonatus (39.5 Ma), and one horizon denoted as Noforaminifera. Information generated from structure and isochron maps are used to delineate the depositional history of the downdip Yegua. Seismic data indicated that the study area is dominated by a long southwest northeast oriented normal growth fault. Several growth-fault-related antithetic faults developed on the downthrown side of the major fault, creating a series of subparallel fault system. Analysis of the time structure and-isochron maps suggests the growth fault plays an important role in providing sediment accomodation space. Sediments were accumulated in a number of small depocenters and were scattered largely along the downthrown side of the growth fault. The growth-fault-related antithetic faults are believed to control the sediment fairways and sediment thickness. Lack of good biostratigraphic control made it difficult to identify depositional sequences and system tracts in Yegua interval with confidence. On the basis of seismic data and well-log data, the Yegua sequences are interpreted as either lowstand basin floor fan or lowstand slope fan.This lowstand fan is deposited during the latest part of relative sea level fall and beginning of relative sea level rise,
Trikania, Andra (1996). Three-dimensional seismic stratigraphic study of downdip Yegua sandstones, Edna Field, Jackson County, Texas. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -T75.