Facies and evolution of the modern Brazos Delta, Texas: wave versus flood influence

In order to better define the facies architecture and processes controlling the evolution of wave-dominated deltas, a detailed sedimentary and geomorphologic study was undertaken on the Brazos Delta, Texas. The delta has formed since 1929, when the Brazos River was diverted by the U.S. Army Corps of Engineers. The Brazos Delta is composed primarily of fine-grained sediments. Prodelta clay constitutes more than half of the sediment volume. Thick sands are restricted to the narrow delta-front environment, whereas back-bar lagoonal clays are a significant component of the delta-plain sequence. The facies architecture is not representative of the classic strandplain model for wave-dominated deltas. This is due to the strong influence of floods on deltaic evolution. In early 1992, statewide flooding gave rise to a major constructional phase of the delta. Significant quantities of fine-grained sediments were deposited in the prodelta. One year after the onset of flooding, a channel mouth bar emerged offshore of the river mouth and enabled progradation of the delta. Similar flood events that occurred during 1941, 1957, and 1965 were recorded as ridge-trough pairs in the delta head-land. The Brazos delta is therefore fluvially influenced during hoods and wave influenced during intervening periods.