On the basis of data from seven cruises in the Amazon River–Atlantic Ocean area, and with 14 anchored stations extending over complete tidal cycles, the currents, suspended sediment concentration, temperature, and salinity were measured at various depths. The physical circulation of water shows Amazon River water thrusting out across the continental shelf and over the sea water with some entrainment and mixing with the sea water. The brackish plume from the Amazon is then turned northwestward along the outer shelf by the Guiana current and longshore currents to parallel the coastline for 500 to 700 km. Sea water upwells and flows landward under this plume.
The sediments of the Amazon River are thrust out onto the outer shelf, where a gradual depositional process occurs: the sand is deposited first, followed by the silt, and most of the mud is carried shoreward by the landward-moving bottom waters. This combination of processes results in the existing depositional facies pattern; modern mud deposits along the shoreline grade outward into silt deposits and finally into modern sand. The depositional process occurring is contrary to the classic model with sand along the shoreline.