Chapter Twenty Morphodynamics of muddy environments along the Atlantic coasts of North and South America

Abstract

Summary The Atlantic coast of the North and South American continents, including the Gulf of Mexico and the Caribbean, measures 37,000 km on a map of scale 1:5,000,000 (Figure 1). Portions of this coast are characterized by extensive regional mud deposits, especially where one or more rivers discharge significant quantities of suspended sediments to deltas and adjacent marginal estuaries, lagoons, chenier plains, and tidal flats. The delivery of terrigenous sediments by rivers is the main factor responsible for coastal mud deposits. Secondary factors favoring the development of muddy coastal deposits are a broad gently sloping coastal plain and adjacent shelf topography, macrotidal conditions, and the absence of energetic oceanic wind waves. Muddy coasts can equally well develop where relative sea level is rising or falling. Whereas large portions of the Atlantic and Gulf of Mexico coasts of the USA and Mexico are subject to rapidly rising relative sea level, the Atlantic coast of South America experiences falling relative sea level. We describe five major muddy coasts along the American Atlantic in terms of their morphodynamics. These systems include (i) the mesotidal lagoon-salt marsh coast of the South Atlantic Bight (southeastern USA), (ii) the microtidal Mississippi River delta and chenier plains (USA), (iii) the macrotidal Amazon chenier plain coast of the Guyanas, (iv) the macrotidal mangrove coast of Para and Maranhao (Brazil); and (v) the microtidal la Plata estuarine system (Argentina and Uruguay).