The Barreiras Formation deposits, Miocene age, have a wide distribution in the
Brazilian coast. In the state of Para some of the best exposures of this unit are
located in the localities of Vila de Apeú (Castanhal) and Outeiro island (Belem). In
these area its was realized facies studies and the stratigraphic correlation between
the Barreiras Formation outcrops allowing to understand and interpret, through
different lithofacies, the likely depositional environment of the Barreiras Formation on
the northeastern Pará. Ten sedimentary facies was described composed
predominantly of siliciclastic rocks such as: claystone, sandstones and
conglomerates. These facies were grouped into two facies associations which
represent depositional environments of the fluvial channel and tidal flats. The
deposits of fluvial channels have a more restricted distribution compared to the tidal
flats. The tidal flats deposits are composed predominantly of clay facies. Locally
these clay deposits present mud cracks and bioturbation. Sandstones with crossbedding
and plane-parallel stratification are found intercalated with these clay
deposits. Heterolitics layers with tidal beddings (wavy) pass vertically to paleosoil
deposits that occur locally, and they are characterized by mottled appearance due to
bioturbation caused by root marks and worm tubes. The fluvial channel deposits are
characterized by the predominance of sandy and conglomeratic facies. Trough crossbedding
sandstone lags are the most common facies. These deposits partially erode
the tidal flat deposits, as evidenced by the presence of erosive truncations, fallen
land blocks and conglomeratic lags at the boundary between the two facies
associations. Ophiomorpha ichonofossils are abundant in fluvial channel deposits
and rarer in tidal flats. This ichnofossil usually represent dwelling builds of the
Callianassa decapod crustaceans in environments influenced by marine waters
similar to estuaries. The deposits studied in this work represent the record of
transitional environments characterized by tidal influences and continental influxes
made by fluvial channels.
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