Abstract
This work presents facies analysis of pyroclastic and effusive deposits present in areas of the Fernando de Noronha Archipelago (FNA), South Atlantic Ocean. A detailed stratigraphic study was carried out for the Remédios Formation at the Caieira beach and the Quixaba Formation at the Capim-Açu Edge, Americano, and Bode beaches. The lithofacies association for the deposits of the Remédios Formation characterizes non-welded ignimbrites of phonolitic composition generated by concentrated ground-hugging density currents originated from collapses of a buoyant eruption column. Possibly, this phase was followed by a caldera collapse and the exposition of a complex system of dikes at Caieira Beach. For the deposits of the Quixaba Formation, the lithofacies association characterizes scoria and ash flow/grain avalanching deposits, proximal fallout deposits, and Pahoehoe lava flows. The Quixaba volcanism shows evidence of pulses of Strombolian and possibly Violent Strombolian activity alternated with effusive Hawaiian activity. A later stage of magma-water interaction during the Quixaba volcanism led to the formation of a sustained eruption column and fallout deposits with ash aggregates formed through wet aggregation.
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