Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid- to late Holocene sea level change

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4.5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large-scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium- to small-scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo-) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years BP and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large-scale differences in barrier morphology.