Seismic Sedimentology and Depositional Systems in the Upper Cretaceous Olmos Formation, Gold River North Field, Webb County, South Texas

Seismic sedimentology is superior in mapping high-frequency sequences and depositional systems to standard seismic stratigraphic analysis. In the Olmos Formation of Gold River North field, Webb County, South Texas, we identified nine fourth-order sequences from sequence-stratigraphic correlations using 3D seismic and wireline-log data. Seismic amplitudes can be correlated to log lithologies using 90°-phased seismic data, and, consequently, seismic traces can be interpreted as wireline lithologic logs. Stratal slices made from the 3-D seismic volume reveal high-resolution sediment dispersal patterns and associated systems tracts on relative geologic time surfaces. The Olmos Formation in Gold River North field is characterized by two third-order, shelf-edge deltaic systems, from which five types of depositional systems were identified: (1) fluvial plain, which is characterized by fluvial channels, crevasse splays, and swales; (2) deltaic plain, which consists of distributary channels, levees, and crevasse splays; (3) deltaic-front mouth bars and sheet sands; (4) prodelta, which is composed of silty sediments; and (5) incised valleys, which were formed during subsequent lowstand erosion on exposed deltaic sediments. The Olmos Formation can be productive in Gold River North field because distributary-channel sandstones and incised-valley fills may form potentially important stratigraphic traps.