Sediments of Laguna Madre, Texas1
Laguna Madre is a linear coastal lagoon, developed on the pre-Holocene3
Throughout the paper the age of transgressive de posits following the last glaciation is referred to as “Holocene,” in keeping with its generally accepted usage.
Source of the clay is unknown, but heavy and light mineral analyses of the sand fraction indicate locally reworked earlier deposits. The northern Laguna sediments are derived from the pre-Holocene sediments off the Nueces delta province and the southern Laguna sediments are derived from the Holocene and pre-Holocene deposits of the Rio Grande distributary province.
The immediate source of the lagoonal fill is the barrier island sand, which is believed to be derived from the earlier deposits of the nearshore gulf. During and after sea-level rise, the near-shore gulf floor was actively eroded by wave action to establish an equilibrium profile. The eroded material was sorted and the sand fraction was transported landward. Wind action piled the new beach sands into coastal dunes on the barrier. Where the earlier deposits were relatively un-consolidated, as offshore northern Padre Island, thick dune deposits could form because of large supply. Where the earlier deposits were more consolidated, and consequently less easily eroded, as in the vicinity of the Rio Grande delta, the dunes are lower and the barrier narrower.
Subsequent to the formation of the lagoon about 5,000 years ago, partial filling was accomplished by washover storm waves, wind transport, and tidal activity.
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.