Publications

The Trombetas Group in the Amazonas Basin has been dated with the help of chitinozoans. These indicates an age range from late Caradoc? to early Lochkovian. Major hiatuses comprise middle Wenlock, middle Ludlow and the late Pridoli gap. The Trombetas Group is divided into four formations (from base to top): Autás-Mirim, Nhamundá, Pitinga and Manacapuru. The basal Autás-Mirim Formation is of late Caradoc? – Ashgill age, and the Ordovician – Silurian boundary lies approximately at the top of this formation. The upper sandstones of the overlying Nhamundá Formation constitute a lateral facies to the Pitinga shales, and are of Llandovery to earliest Wenlock age. Three diamictite horizons present in the Nhamundá Formation suggest glaciations during middle and late Llandovery. The graptolitic lower Pitinga Formation is of middle Llandovery (gregarius graptolite Zone) to earliest Wenlock age, and interfingers with, or overlies the Nhamundá sandstones. The upper Pitinga Formation bears a chitinozoan fauna characteristic of the late Wenlock – early Ludlow. The Manacapuru Formation can be divided into two units. The lower unit comprises a diagnostic late Ludlow – earliest Pridoli chitinozoan fauna, and the upper unit contains early Lochkovian chitinozoans. A hiatus corresponding to late Lochkovian – middle or late Emsian separates the Trombetas Group from the overlying Maecuru Formation. The Silurian chitinozoan assemblages from Brazil show affinities with the Guinean ones.