In the downdip Gulf Coastal Plain tectonic forces produce the primary features: alternating deltaic and inter-deltaic regions. The latter consist of the coastal lake-and-bay regions such as extend from Matagorda Bay to the upper Laguna Madre between the Brazos-Colorado and the Rio Grande deltas.
The bays, lagoons, barriers, passes, and the sandsheet in southwest Texas are the secondary features. They reflect a delicate adjustment to the physicochemical environment.
The principal agent of the physical environment is the surface wind. In addition to normal wind-work it controls the nontidal currents, surface waves, and the coastal-drifting processes. These distribute the sediments and shape the secondary features. When analyzing the importance of the wind a distinction must be made between prevailing winds, which blow most of the time, and predominant winds, which expend a greater amount of energy and usually do the greater amount of geologic work.
There are three major environments: continental, transitional, and marine. They can be recognized in the subsurface if interpretative Stratigraphie methods are employed, utilizing lithology, paleontology and electric log data.
Figures & Tables
Finding Ancient Shorelines
For many years the primary function of the Research Committee of the Society of Economic Paleontologists and Minerologists was to organize a symposium concerned with the most pertinent problems in sedimentary geology. This year (1955) the main theme centered on the characteristics of near shore deposition, particularly aimed toward recognition of ancient shorelines. The chairman that year was Dr. Henry W. Menard of the Navy Electronics Laboratory. Committee members selected the topic for the symposium, aided in selection of the speakers, and often participated in the program. The plan was to ask each speaker to present his paper in twenty minutes. Following the formal presentation a discussant, who has had opportunity to examine certain parts of the paper, was asked to comment. This approach led to some lively and focussed comments which benefited the entire presentation and is very interesting to read in that context. Papers included: Continental terrace sediments in the northeastern Gulf of Mexico, Sediments of the eastern Mississippi Delta, Sandless coastal terrain of the Atchafalaya Bay area, Louisiana, Sediment zones bordering the barrier islands of central Texas coast, Dynamic geology of the modern coastal region, northwest Gulf of Mexico, Particle size distribution in nearshore sediments