Upper Oligocene-Miocene deposits of Eastern Amazonia: Implications for the collapse of Neogene carbonate platforms along the coast of northern Brazil

Abstract

Mixed carbonate-siliciclastic platforms developed in the onshore and offshore zones of several basins along the Amazonian coast starting in the Palaeocene. The shutdown of Miocene carbonate accumulation in distinct tectonic settings shows different evolutionary histories along the Eastern Amazonian coast. The shutdown has been attributed to the abundant siliciclastic fluvial inflow from the Andean Amazon River during the late Miocene. The combination of previously collected geological information and new stratigraphic data from the Oligocene-Miocene transgressive-regressive Pirabas-Barreiras sequence exposed on the Bragantina Platform of the Eastern Amazonian coast reveals the collapse of the carbonate platform by the Barreiras fan delta deposits during the middle Miocene. The development of the Barreiras fan delta, fed by a cratonic source exposed during the Langhian (15–10 Ma) sea-level fall, was concomitant with the so-called Cratonic Amazon River that preceded the transcontinental Andean Amazon River. The climax of sea-level fall caused the maximum expansion of the Barreiras fan delta, which reached the Marajó and Pará-Maranhão basins. The progressive denudation of the region, low fluvial inflow, and extensive Tortonian sea-level fall (11–8 Ma) resulted in the inactivity of the Barreiras Delta. Consequently, the exposure and subsequent intense lateritization of these degraded deposits generated an extensive unconformity that lasted until the deposition of Pleistocene Post-Barreiras sediments.