Silurian and Lower Devonian chitinozoan taxonomy and biostratigraphy of the Trombetas Group, Amazonas Basin, northern Brazil


Authors: Grahn Y

Published in: Bulletin of Geosciences, volume 80, issue 4; pages: 245 - 276; Received 8 November 2004; Accepted in revised form 2 August 2005;

Keywords: Silurian, Devonian, Trombetas Group, Chitinozoa, biostratigraphy, zonation, Amazonas Basin, Brazil,

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Silurian and Devonian (Lower Lochkovian) chitinozoans from the Trombetas Group, and the basal Jatapu Member of the Maecuru Formation, have been studied in outcrops and shallow borings from the Amazonas Basin, northern Brazil. Outcrops were examined along the Trombetas River and its tributaries, the Cachorro and Mapuera rivers, situated on the northern margin of the Amazonas Basin, and from shallow borings in the Pitinga Formation along the Xingu River at Altamira and Belo Monte, together with outcrops along Igarapé da Rainha and Igarapé Ipiranga on the southern margin of the Amazonas Basin. In addition, nine deep borings in the central part of the Amazonas Basin were used as reference sections. The chitinozoans confirm a Llandovery (Late Rhuddanian-Late Telychian) to Early Wenlock (Sheinwoodian) age for the lower part of the Pitinga Formation, and a Ludlow to Early Pridoli age for the upper part of the Pitinga Formation. The overlying Manacapuru Formation is comprised of lower Pridoli rocks in the basal part, but middle and upper Pridoli strata are missing. The upper part of the formation and the basal part of the Jatapu Member of the Maecuru Formation consist of Lower Lochkovian rocks. Seven chitinozoan assemblages (designated in ascending stratigraphic order 1-7) can be distinguished. Of the 104 chitinozoan species encountered, 51 are left in open nomenclature, and three are newly described (Ancyrochitina pitingaense, Belonechitina? plumula and Linochitina penequadrata).