This work presents the data obtained from the analysis of calcareous microfossils in samples collected in CIMPOR quarry,town of São Miguel dos Campos, State of Alagoas, Morro do Chaves Formation in the Sergipe-Alagoas Basin, in order to investigate the presence of the marine environment or marine influence in the Lower Aptian of this lithoestratigraphic unit. The samples were collected in the pit south, San Miguel (Atol Quarry), and were investigated 23 levels of pelites, interbedded with 13 packages coquina and sandstones, totaling 76 m exposure. The treatment of samples followed the usual methods for calcareous microfossils analysis. The paleontology and fossil content of the Morro do Chaves Formation include mainly fishes associated with bivalvs, gastropods, ostracods, palynomorphs and tetrapods. The Morro do Chaves paleolake was a carbonate platform generated in lacustrine environment, characterized by accumulation of coquina during the rift stage of evolution of the brazilian continental margin, deposited in unstable tectonic. Were recovered and recognized five microfossilíferous taxa, including the Ammonia and Cibicides- foraminifera, Cypridea and Darwinula- ostracods, zoarial fragments of bryozoans scheilostomes, spicules of sponges and an undetermined microbivalve. The taxonomic composition and taphonomic preservational signatures suggest that foraminifera, bryozoans, sponges and microbivalve typically marine suffered short-distance transport, characterizing a allochthonous fossiliferous concentration and the ostracofauna is tipically and is lacustrine is autochthonous. This mixture living forms in different environments have occurred during positive oscillations in the lake Morro do Chaves caused by monsoon rains, common during the Early Cretaceous. The data collected in this study suggest that there not existed the marine environment nor with marine influence in the Morro do Chaves Formation.
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