Book Description

The largest coastal alluvial-plain in Mexico lies along the southern Gulf Coast, almost entirely within the state of Tabasco. This plain is principally of fluvial origin, associated with the Mezcalapa and Usumacinta river systems. These two rivers, whose previous channel migrations have directly or indirectly produced most of the lowland landforms, currently share the major outlet to the Gulf, the Grijalva River. Skirting the gulfward edge of the Tabasco Plain is a narrow zone of coastal landforms comprised primarily of beach ridges plus a few groups of sand dunes. Systematic investigation of beach ridges includes profiles noting general configuration and dimension. Beaches are profiled to record sediment removal, migration, and accumulation over various time periods. Trenches and pits dug in accretionary portions of the beach profile reveal stratification sequences of inland-dipping foreset units. These deposits correlate with frequent winter-season storms, nortes, which raise Gulf levels and wave heights to construct a beach crest upon the winter beach. Intermittent washover deposition contributes sediment to the upper surface and lee side of the ridge to heighten and broaden it while producing a slow migration inland. Subsequent calm-weather accretion gradually widens the beach and eventually strands the beach ridge. Beach ridges are most numerous and the coastal zone widest where river channels course through the coastal topography and discharge into the Gulf. Adjacent to these channels, the ridge trends collectively arch seaward, fan-like, to produce a cuspate delta projecting into the Gulf. (Author).