TECTONIC EFFECTS ON COASTAL LANDFORMS: NORTHERN GULF OF MEXICO

Coastal landforms are sculptured by ongoing interplay between processes of deposition, erosion, tectonic movement and sea level fluctuation. Tectonic processes have been given little consideration by coastal researchers in the northern Gulf region.

A tectonic framework made up of linked systems and subsystems lies within the northern Gulf. Each component has an assemblage of structural elements including faults, salt domes, fractures and fissures. The structural components underlie both onshore and offshore areas. In the western and central Gulf movement along growth faults that are sub-parallel to the shore is a primary cause of subsidence and tilting of the surface. Geofractures with northeast-southwest and northwest-southeast strikes, form a rectilinear grid pattern, segment blocks between growth faults, and have a strong influence on stream trends and configuration of coastal bays.

There is pronounced variation in neotectonic activity across the region. The eastern (Florida Platform) and western areas (south Texas) are relatively stable at present, but the central region (southeast Texas and south Louisiana) has been subject to active movement throughout the Late Quaternary.

Earthquakes occur along faults and fractures in the central region. Some result from spontaneous release of stress, while others are triggered by shock waves from remote earthquakes. All earthquakes are indicators of active fault movement.

The Comanchean Shelf Edge – Florida Escarpment constitutes a sharp boundary between the active central and relatively stable eastern Gulf areas. In the Mississippi-Alabama area the Gulf shore crosses the structural strike at near right angles where an old structural system reaches the coast. The Florida Platform is relatively stable with broad arches and basins and corresponding gently uplifted and submerged coastal features.

The trends and geometry of coastal bays, lagoons, barrier islands, beaches, submerged lands, headlands and streams are structurally influenced and reflect the relationship between depositional trend and structural strike. Process-response models will be used to illustrate the process interactions and resulting landforms.