Controls on Quaternary coastal evolution of the east-northeastern coast of Brazil: roles of sea-level history, trade winds and climate

Abstract

East-northeastern Brazil has a wave-dominated, micro-to meso-tidal coast, lying entirely within the southern Atlantic trade wind belt. Integration of geologic mapping, radiocarbon dating and vibracoring data shows that the Quaternary coastal evolution of this area was controlled by three major factors: (1) sea-level history; (2) trade winds; and (3) climate change. Sea-level history. Along the east-northeastern coast of Brazil, relative sea level has fallen approximately 5 m during the last 5000 y. Correlation of this sea-level history with the evolution of beach-ridge, lagoonal and coastal plain deposits shows that: (1) sea-level rise favours the formation of barrier island-lagoonal systems and the construction of intralagoonal deltas; (2) sea-level lowering is not conducive to barrier island formation. Rather, lagoons and bays become emergent and beach-ridge plains rapidly prograde. Trade winds. Sediment dispersal systems along the coastal zone of east-northeastern Brazil have been highly persistent since Pleistocene time, as deduced from beach-ridge orientation. This persistence results from the fact that sediment dispersal in wave-dominated settings is ultimately controlled by atmospheric circulation which, for the east-northeastern coast of Brazil is associated with the South Atlantic high-pressure cell. The remarkable stability of this cell through time, has allowed the accumulation of extensive beach-ridge plains at the longshore drift sinks located along the coast. Climate change. Effects of Quaternary climate changes on coastal sedimentation are twofold. Climate changes may affect rainfall patterns, thus exerting an important control on coastal dune development. Along the coast of northeastern Brazil, active coastal dunes are only present in those areas in which at least four consecutive dry months occur during the year. Mapping of these areas has shown that dune development during the Hoiocene has been episodic, these episodes being probably controlled by variations in rainfall patterns associated with climate changes. Secondly, despite its overall stability, the position of the high-pressure cell has experienced small shifts in position during the Holocene in response to climate changes. Changes in wind direction associated with these shifts have induced modifications in the coastal dispersion system, which are recorded in the strandplains as small truncations in the beach-ridge alignments. These results have important implications in understanding accumulation of ancient sandstone shoreline sequences.

Quantitative seismic geomorphology of a submarine channel system in SE Brazil (Espírito Santo Basin): Scale comparison with other submarine channel systems

“…The sediment source of this canyon system is affected by longshore drifts, which play an important role in distributing sediment on the continental shelf and slope of SE Brazil (Dominguez et al, 1992;Martin and Suguio, 1992). At least three major channel events have been identified within the Rio Doce Canyon system (Fig.…”

A significant longshore transport divergence zone at the Northeastern Brazilian coast: implications on coastal Quaternary evolution

“…Because of the remarkable stability observed in the high pressure cell of the South Atlantic, trade winds generated in this cell are expected to show a remarkable persistence during the Quaternary (Dominguez et al 1992). Consequently, these authors conclude to be logical to expect that the patterns of sediment dispersion along the coastal stretch analyzed herein have maintained themselves also persistent during the Quaternary.…”

“…Consequently, these authors conclude to be logical to expect that the patterns of sediment dispersion along the coastal stretch analyzed herein have maintained themselves also persistent during the Quaternary. In this sense, using the paleogeographic reconstructions obtained in different coastal plains along the Brazilian East-Northeast coast, Dominguez et al (1992) have shown that, in general, such patterns remained the same since the Pleistocene. In relation to the studied coastal stretch a significant example may be observed in the coastal plain of beach-ridges terraces between the Real and Vaza-Barris rivers, in Sector I (Figs.…”

“…In this region, there may be clearly seen that the geometry of the Pleistocene beach-ridge terraces display a remarkable correspondence with those of Holocene beach-ridges terraces and with the present coastline. As considered by Dominguez et al (1992), although other regions of the world present evidences of this persistence in the dispersion patterns (e.g. Cape Kennedy, NE of Florida, delta of the Apalachicola river, NW of Florida), this phenomenon is accentuated along Brazil's East-Northeast coastline because of its location in relation to the trade winds belt.…”

“…As the studied coastal stretch is entirely located within the trade winds belt, the waves generated by these winds, of extremely constant velocity and direction, exerts a strong influence on the coastal processes (Dominguez et al 1992). Martin et al (1998), based on a detailed analysis of the atmospheric circulation system, presented a conceptual model for the wave regime affecting the study area.…”