Mapping sediment-dispersal patterns and associated systems tracts in fourth- and fifth-order sequences using seismic sedimentology: Example from Corpus Christi Bay, Texas

摘要

A seismic-sedimentologic study was performed to map fourth- and fifth-order systems tracts in Oligocene (Frio) strata in Corpus Christi Bay, south Texas. Guided by third-order sequence-stratigraphic correlations from seismic and wire-line-log data, we prepared stratal slices from a three-dimensional seismic volume to reveal high-resolution (10-m [33-ft] levels) sediment dispersal patterns and associated systems tracts in a relative geologic-time domain. On average, 1200 m (3940 ft) of sediments were deposited in the third-order lowstand expansion cycle, and at least 16 higher order sequences (fourth- and fifth-order sequences) were recognized. Three types of depositional systems were identified in the Frio stratigraphic section: (1) offshelf lowstand slope fans that are best characterized by submarine channel and levee systems inside and outside incised submarine channels and by fan-shaped sand body geometry; (2) lowstand prograding deltaic systems that are composed of strike-oriented and lobate deltaic sand bodies; and (3) highstand systems that are represented by onshelf barrier, lagoon, and deltaic systems. Higher order sequence development was controlled by the interaction of relative sea level change, sediment supply, and gravity tectonics. The top of sediment ridges was eroded or decapitated during many of the higher order sequences. Sand dispersal patterns are primarily controlled by accommodation resulting from rollover topography associated with growth faulting. Between the boundary fault and the hinge line atop rollover structures, strike-oriented sandstone bodies dominate; within submarine channels and incised valleys and beyond the hinge line to the distal basin, dip-oriented sandstone bodies prevail. Sandstone thickness and dispersal patterns can be predicted by integrating wire-line-log measurements and seismic amplitude patterns.