Application of Thin-Bed Indicator and Sweetness Attribute in the Evaluation of Sediment Composition and Depositional Geometry in Coast-Perpendicular Subbasin, South Texas Gulf

Abstract

Studies of the few coast-perpendicular subbasins recognized to date have been on the mode of formation. The depositional geometry and possible sediment composition within these subbasins have not been fully examined. The focus of this paper is on the nature of sediments within late Eocene- to middle Oligocene-age, coast-perpendicular subbasins located on the SW side of the San Marcos Arch in Refugio County, near the South Texas Gulf Coast. Methods of investigation consist of 3D seismic interpretation, 3D visualization, seismic attribute extraction, and isochron mapping. Depositional geometry, inferred sediment composition, and bed-thickness data are examined by extracting amplitude envelope, sweetness, and thin-bed indicator attributes from 3D seismic volume. From 3D seismic interpretation, four subbasins, numbered SB1 through SB4 from NE to SW, are recognized. Three of these (SB2–SB4) are similar and oriented NW–SE, while SB1, nearest to the San Marcos Arch, is curvilinear in shape. Results from seismic interpretation also show that the tectonics within the subbasins are different. In SB1, structural features consist of synthetic faults and shale diapirs, whereas in SB2 and SB3, structural features consist of synthetic and antithetic faults featuring horst blocks; in SB4 they are mostly synthetic faults. Interpretation results from combined sweetness and thin-bed indicator attributes show that thickness of sand-prone beds varies from one subbasin to the other. Amplitude envelope results show that, although the distribution pattern of sand-prone sediments within each subbasin is mainly lobate in outlook and of sheet geometry, SB2 is less sand prone than the others. Its distribution pattern consists of short, narrow, linear features at the Eocene Jackson interval, suggesting a sediments provenance that is different from that of the other subbasins. Isochron mapping indicates that the basin-fill history of SB1 differs from the others. The depocenter in SB2–SB4 at the lower Vicksburg Formation occurs basinward at topographic low (ponded fill geometry), whereas in SB1, the depocenter occurs landward at topographic high (perched fill geometry). Because the basin-fill history and sediments composition within coast-perpendicular subbasins that developed at the same time may differ from one another, awareness of the foregoing will be useful in deep-water exploration.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016