SEISMIC FACIES, ARCHITECTURE, AND EVOLUTION OF THE BOLIVAR ROADS TIDAL INLET DELTA COMPLEX, EAST TEXAS GULF-COAST

The seismic facies, facies architecture, and stratigraphy of tidal-inl et and tidal-delta deposits and their relation to the development of a djacent coastal lithosomes are examined using high-resolution seismic profiles, vibracores, and borehole descriptions. The Bolivar Roads tid al inlet/delta complex, along the east Texas Gulf coast, was formed ap proximately 3.3 ka by spit accretion across a baymouth following a rap id sea-level rise approximately 4 ka. An increase in the tidal prism t hrough time and entrenchment of the tidal inlet over the Trinity River incised valley stabilized the inlet and intensified tidal processes o n the tidal inlet/delta complex. The tidal-inlet facies show channel s tacking and cut-and-fill structures. Stacked clinoforms dip westward a cross the inlet. The spit facies is characterized by oblique-tangentia l clinoforms that build outward and deepen from the edge toward the ce nter of the valley. The flood-tidal delta facies has a base that shall ows abruptly bayward. As the flood-tidal delta facies thins bayward, i t interfingers with bay sediments. Near the inlet the flood-tidal delt a shows channel cut-and-fill with an overall channel stacking pattern. On the seaward side the channels have a trough-like geometry. Bayward , the channels broaden and shallow. The channels show a prograded-fill pattern. The ebb-tidal delta facies exhibits gently inclined clinofor ms prograding over a ravinement surface. Tidal-inlet deposits are comp osed of sand, shell, and mud interbeds. Sand and clay interlaminae are ubiquitous in the tidal deltas, and sand and shell beds are common ne ar the inlet. Overall, the Bolivar Roads tidal inlet/delta complex is mud-dominated as a result of high influx of fine sediment into the bay .