Late Neogene sequence stratigraphic evolution of the Foz do Amazonas Basin, Brazil

The margin of the Foz do Amazonas Basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late Miocene. By this time, the Amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor, thus confirming that the palaeo-Amazon fan had already initiated by that time (9.5-8.3Ma). Above this interval, during a prolonged lowstand, Messinian third-order sequences are preserved only in the incised-valley fills of the canyon with no equivalent strata on the shelf. Third- and fourth-order sequences younger than Messinian are preserved on the shelf after sea-level rise above the shelf by the early Pliocene. Sequences younger than 3.8Ma often show fourth-order cyclicity with an average duration of 400ka (larger scale eccentricity cycles) often preserved in high-sedimentation-rate areas of river deltas. Mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as the mid-Pliocene, after rapid progradation had produced steeper slopes more prone to failure.