Abstract: Structural Styles in the Espírito Santo - Mucuri Basin, Southeastern Brazil

Van der Ven, P. H.; Cunha, C. H. R.; Biassusi, A.S. - Petrobras/E&P

The Espírito Santo - Mucuri basin is a typical passive margin basin, developed over a 300km wide segment of continental crust. Local horst-and-graben structures capped by Aptian evaporites, Albian carbonate roll-overs structures related to salt withdrawal, and salt domes can be recognized along the basin. Sea level variations, especially during Cretaceous times formed at three major canyons. Turbidite sandstones are exploration targets within these paleocanyons, and in also offshore progradational marine sequences.

During the Tertiary, extensive volcanism played a significant role in changing basin configuration, and creating unique structural styles.

The first feature of notice, is the Abrolhos Complex, present in the eastern half of the offshore basin. Subaqueous volcanics intercalated by carbonates constructed an offshore platform, mainly mid-Eocene in age, which contributed to the basin fill by sedimentary aggradation and westward progradation as shown in figure A. Scarce seismic data and only two exploratory wells have investigated this area where deep reflectors show underlying Cretaceous and lower Tertiary structures. Regionally, the entire Abrolhos Complex seems to have been compressed into a basinwide subtle anticlinal feature as late as in the Oligocene.

Another structural element worthy of note is a very long compressional anticline feature which straddles the basin in a north-south direction between the Abrolhos Complex and nearshore (the Parcel das Paredes Anticline in the Mucuri basin). Locally (Fig. A) it sometimes underlies the Abrolhos platform and can be seismically interpreted as having associated backthrust elements. This feature is also present in shallow and deep water areas in the southernmost portion of the Espírito Santo basin (Fig. B), associated with but not genetically related to halokinesis. The salt dome seen in the same seismic example is independent of the anticlinal structure immediately to the west. Backthrusting in this structure is interpreted from seismic and corroborated by well data. Well penetrations of 800 and 200 meters show that the structure is composed by Cretaceous shales without any traces of evaporites. The absence of Eocene strata overlying the structure coincides with the peak of Abrolhos volcanism and platform development. This north to south basinal feature is interpreted as a middle Eocene to Oligocene back thrust of drift phase strata, caused by overloading of the eastern portion of the basin by the Abrolhos Complex.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil