Lochkovian (earliest Devonian) miospores from the Solimões Basin, northwestern Brazil

Abstract

Eighteen core samples from PETROBRAS well 1-JD-1-AM (Jandiatuba area, Solimões Basin, northwestern Brazil) have been studied for miospores. Fifty-three species are identified. This assemblage is tentatively correlated with the Z Phylozone of the BZ Oppel Zone ( Steemans, P., 1989. Palynostratigraphie de l'Eodévonien dans l'ouest de l'Europe. Professional Paper. Mémoires Explicatifs pour les Cartes Géologiques and Minéralogiques de la Belgique, 27, pp. 453.), dated late Lochkovian. This is in accordance with previous age determinations based on chitinozoans and acritarchs. Numerous representatives of the miospore genus Dictyotriletes are observed. These enable recognition of the Dictyotriletes emsiensis morphon, an informal classification unit which includes Dictyotriletes granulatus, D. emsiensis, Dictyotriletes cf. subgranifer, specimens previously misassigned to D. subgranifer and some Dictyotriletes spp. provisionally left in open nomenclature. Since all intermediate forms from typical D. granulatus to typical D. emsiensis coexist, it is currently difficult to determine the base of “E” Interval Biozone in South America as originally defined in Western Europe. It is suggested, therefore, that the base of the “Ems” Biozone defined in Brazil cannot be correlated with the base of the “E” Biozone. Instead, it should be included in an interval of uncertainty ranging from the European “Si” to “E” Biozones. Indeed, the underlying “NsZ” Biozone from South America contains species not known below the “Si” Biozone. Here, the D. emsiensis morphon Assemblage Zone is erected, which may be coeval with the “N” through “E” Biozones of Western Europe. The PISA palynoflora from the Paraná Basin is also attributed to this new biozone. However, in the absence of species observed in the “BZ” Biozone (and also in the Solimões Basin), the PISA assemblage could be somewhat older than that of well 1-JD-1-AM.