OCORRÊNCIA DA FORMAÇÃO PIRABAS (MIOCENO INFERIOR) NA BACIA DE BARREIRINHAS, MARANHÃO

Resumo

A new outcrop of the Pirabas Formation was found in the right bank of the igarapé Marciano, 3.5 km south of Caeté, county of Pinheiro da Cruz. Field observations and examination of the collected samples lead the authors to describe a new geologic setting of the formation, inside the Barreirinhas basin. Moreover, the fossil content includes specimens of genus Orthaulax, a gastropod considered as a good index-fossil lor a great number of Lower Miocene formations of the Caribbean Province. A special kind of pyrite was found, probably biogenic, resulting from metasomatic processes affecting calcium carbonates.