Revisão tectono-estratigráfica da seção cenozoica da porção emersa das bacias do Espírito Santo e Mucuri

Abstract

Part of the Cenozoic section of the Espírito Santo and Mucuri basins, particularly those related to the Barreiras and Rio Doce formations, was reinterpreted using the integration of sedimentological, geochemical, petrographic and seismic data. The seismic interpretation revealed the occurrence of pronounced volcanic features limited at the top by Pre-Upper Eocene Unconformity (DPES). Such surface was correlated to acidic volcanic rocks outcrops, which occur truncated at the top. These volcanic rocks are covered by a Neogene siliciclastic sequence. The facies analysis of such sediments revealed a fluvio-deltaic paleoenvironmental setting correlated to the Rio Doce Formation. The sequence begins with a facies association characteristic of river channels, which is followed by facies associations of delta front individualized by several load structures and fluid-escape features. Such system is capped by pyrite-rich black shales (Urucutuca Formation), which represent the distal pro-delta facies. The lithogeochemistry study performed in the volcanic (below the DPES) and in the sedimentary rocks (above DPES) showed high enrichment in rare-earth elements and a typical signature of acidic volcanic provenance. This characteristic, combined with petrographic results, allowed the interpretation of a fluvial-deltaic system associated with an explosive volcanic source area. Structural data (from both field and seismic interpretation) show that the current geomorphological configuration of the cliffs in southern Bahia may have been controlled by reactivated faults of the rift.