Bays of Central Texas Coast1
Approximately 1,000 samples have been obtained from the bays of the centra! Texas coast. Their size parameters, constituents, and organisms have been studied in relation to salinity, depth of water, and relations to entering rivers and to inlets. All of these bays are cut off from free connection with the gulf by barrier islands, although widely-spaced inlets allow some exchange with gulf waters.
Among the bay facies are (1) bays near stream mouths which have alternating silty clays and sands, commonly laminated and containing abundant plant fibers and aggregates, along with abundant ostracods in some localities; (2) shallow bays not related to stream mouths, which have an abundance of marine plants, a large number of gastropods, and higher sand content than most other bay environments; (3) deep central bays which have unstratified silty clay sediments commonly with a high content of benthonic Foraminifera in the coarse fraction; (4) central bays with oyster reefs which have been built up above the surrounding bay surfaces, and (5) bays near inlets or narrows where the currents have introduced considerable sand, and the sediment is a bimodal sandy clay with relatively small silt content.
Borings into the bays and into the deltas recently built over their northern ends show that as much as 80 feet of bay sediment has accumulated during the past 9,000 years, since the ocean first came up into the valleys eroded during glacial stages, in what is now the bay area. The samples from the borings along most of San Antonio Bay show a remarkable constancy of sediment types with the only significant changes being from central bay facies to oyster-reef facies. The faunas, however, indicate salinity changes. No lamination and little stratification were found in the borings except near or under the delta at the head of the bay.
Figures & Tables
All but one of the papers contained in this volume represent a symposium summarizing the results of work carried on in Project 51 of the American Petroleum Institute. This study of modern sediments along the northwest margin of the Gulf of Mexico contains 14 papers plus a consolidated bibliography. Paper titles are: Geologic framework of Gulf coastal province of United States; Sources and dispersion of Holocene sediments; Mississippi delta; Delta building and the deltaic sequence; Phytoplankton production in the Mississippi delta; Bays of central Texas coast; Sediments of Laguna Madre; Gulf Coast barriers; Sediments and history of Holocene transgression; Sedimentary patterns of microfaunas; Ecology and distributional patterns of marine macro-invertebrates; Rise of see level; Regional aspects of modern sedimentation; and Recent sedimentology.