Resume of facts and opinion on sedimentation in Gulf Coast Region of Texas and Louisiana

Beginning with a description of sedimentary processes now in operation, this paper contrasts the heterogeneous deposits of the Mississippi delta with the structure of top-sets, fore-sets, and bottom-sets which the term "delta structure" usually implies. It describes the landward parts of the Pleistocene beds along the Gulf Coast as the coalescing deltaic deposits of many streams, producing a deltaic coastal plain as defined by D. C. Barton. It suggests that such structure is a feature of the shoreward parts of many of the older beds. Proceeding to the offshore Recent and Pleistocene, the Ice age fall and rise of sea-level is discussed. It is stated that, beyond a certain distance from the present shore, deposition of sediments was continuous and that each interglacial rise of sea-level produced a tongue of deposits extending landward. This concept is extended to include the deposits of Tertiary time, during which there were changes of sea-level unrelated to the accumulation or melting of ice caps. A diagram is presented showing tongues of formation corresponding with incursions of the sea, while unconformities between the tongues, correspond with recessions of the sea. It is stated that offshore belts of sand deposition correspond in position with currents which flow parallel with the shore. Sand does not gradually give place to mud as deposition proceeds seaward; but, in this case, sands alternate with muds out to 40 or 50 miles from shore. Subsidence along with deposition is discussed as one of the most significant features of sedimentation in this region. It is suggested that loading by the sediments themselves may be an important cause of this subsidence. Offered in favor of this view is some of the evidence adduced by R. J. Russell and his associates of the Louisiana Geological Survey, but the scope of this paper is too limited to do full justice to those authorities. In this connection, the Gulf Coast geosyncline is illustrated and described with a reference to the views of Barton, for whom this feature is often called the "Barton geosyncline." Considerable space is used in describing the special characteristics of structure, especially of faults and salt domes, whose development went on contemporaneously with sedimentation over long periods of time. Throughout the article the point of view of a student is preserved since the paper results from an attempt by the writer to round out the work of a study group of which he was a member. It is suggested that this region affords exceptional data and facilities, perhaps the best in the world, for the study of clastic sedimentation. It is hoped that this article may direct attention to the Gulf Coast region for further study.