In the Late Pleistocene of northern coast of South America, sea level fluctuations, related to
climate variations and the sedimentary discharge of the Amazon River, have modified the
landscape of this region. Terraces of the Itaubal Formation previously considered as Miocene
Barreiras Formation, are part of the Amapá Coastal Plain, which covers the rocks of the
Guianas Shield. The geochronological analysis by Optically Stimulated Luminescence /
single and multiple aliquote regeneration (OSL/SAR-MAR) provided age around 120.600 (±
12.000) to 58.150 (±6.800) yrs BP and integrated with facies and stratigraphic analysis
allowed the identification of coastal deposits and put the Tartarugazliznho Formation in the
Upper Pleistocene. These up to 10 m thick, reddish tabular sediments have been divided into
two units separated by unconformity. The Lower Unit consists of subtidal plain deposits
(FA1), tidally influenced meandering stream deposits (FA2) and tidal plain deposits (FA3),
whereas the Upper Unit, containing a higher clay content tham the lower one, is composed of
braided stream deposits (FA4). The strata pattern of these units is progadational and takes part
in the regressive system tract. The Tartarugazinho Formation onlaps the basement of Guianas
Shield, weathered during Miocene-Pliocene and was exposed during the Last Glacial
Maximum, about 22.000 – 18.000 yrs BP. Finally fine graided deposits derived from the
Amazon River covered the Itaubal Formation and are responsible for the present shape of the
northern coastline of South America. For the first time, the Itaubal Formation defines the
Pleistocene sedimentary evolution of the Amapá coastal plain and the correlation with similar
sediments in Suriname and northeastern Pará expands the discussion about the evolution of
the coastal line in Northern South America during Pleistocene.
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