ABSTRACT
Geological events associated with the late Quaternary have controlled the origin and development of the Texas shoreline. Some features of the shoreline are of late Pleistocene age while others are definitely related to the Recent epoch. During the last Pleistocene glacial stage when sea-level was lowered approximately 450 feet, the coastal Texas streams deeply entrenched their valleys and the Gulf shoreline was probably 50-140 miles seaward of the present shoreline. With melting of the late Pleistocene glaciers and the accompanying rise in sea-level, Texas streams alluviated their entrenched valleys. Sedimentation in these valleys did not keep pace with rising sea-level and consequently the lower parts of the entrenched valleys were drowned to form a series of estuaries. The bay shoreline of Texas originated during this stage. During the standing sea-level stage, which began about 5,000 years ago, the large Texas rivers, such as the Rio Grande, Brazos, and Colorado, filled their former estuaries and constructed broad deltaic plains which protrude into the Gulf. The other smaller Texas rivers which carry smaller quantities of sediments are still in the process of filling their drowned valleys or estuaries. A series of barrier islands were formed along the coast between the Rio Grande and the Colorado-Brazos deltaic plain and east of the Colorado-Brazos deltaic plain, giving rise to the Gulf shoreline along these segments of the coast. The abandoned beach ridges and intervening low swales and mud flats, which are well preserved on these barrier islands, clearly demonstrate the seaward growth of the islands during the standing sea-level stage.
