Petrologic database to define the human-reworked, sediment-deficient plain of the Rio Grande Delta, Texas

Petrologic investigation of surficial samples collected on the Rio Grande delta plain in Texas in 1999 provides the record of a sediment cover resulting from interaction of natural transport processes and rapidly increased human activity. Numerous sediment samples collected in 10 different depositional environments identified on the plain are used to generate a database that includes information on grain size, total organic matter and composition of sand-size particles. Petrologic data record a less altered sediment cover than might have been expected, with little overall blurring of areal boundaries of depositional environments and obvious modification of original depositional facies. This apparent lack of sediment change has occurred in spite of markedly diminished discharge of water and sediment to the Rio Grande delta, and continued in situ anthropogenic reworking of the pre-dam (1916 and older) surficial cover. The most important influence on delta plain evolution since the latter half of the 1800s has been artificial subdivision of the former plain into hundreds of small, sediment-starved sections that are topographically and hydrographically isolated from each other by a dense network of irrigation canals, levees and roads. Human activity has artificially transformed the original Holocene Rio Grande delta to a destructional phase coastal plain that is no longer progradational, but rather undergoing substantial coastal erosion.