Biostratigraphy of Lower Cretaceous microfossils from the Araripe basin, northeastern Brazil Biostratigraphie (microfossiles) du Crétacé inférieur du Bassin de Araripe, nord-est du Brésil João Carlos Coimbra a, *, Mitsuru Arai b , Ana Luisa Carreño c a Departamento de paleontología e estratigrafia, instituto de geociências, universidade federal do Rio Grande do Sul, Cx.P. 15001, CEP. 91501–970, Porto Alegre, RS, Brazil b Petróleo Brasileiro S.A./CENPES/PDEP/BPA, Ilha do Fundão-Quadra 7, CEP. 21949–900, Rio de Janeiro, RJ, Brazil c Instituto de geología, circuito exterior, C.U., delegación de Coyoacán, 04510 D. F. , Mexico Received 4 September 2001; accepted 8 April 2002 Abstract A biostratigraphic study was carried out in the Lower Cretaceous Araripe basin, northeastern Brazil, allowing the recognition of several chronostratigraphic units: the Dom João (Jurassic?–Lower Cretaceous?), the Rio da Serra (Neocomian) and the Alagoas (Aptian/Albian) local stages. For the first time a large hiatus between the Rio da Serra and Alagoas local stages is carefully documented. The palynomorphs and the ostracode associations throughout the Jurassic?–Aptian/Albian sequence allow the interpretation of the paleoenvironmental evolution of the Araripe basin which otherwise confirms that a polycyclical sedimentation occurred in the basin, being one of the controlling factors on the distribution of ostracodes and palynomorphes. © 2002 E ´ ditions scientifiques et médicales Elsevier SAS. All rights reserved. Résumé L’analyse biostratigraphique dans le Crétacé Inférieur du Bassin d’Araripe, au nord-est du Brésil, a permis la reconnaissance de plusieurs unités chronostratigraphiques : l’étage Dom João (Jurassique ?-Crétacé inférieur ?), l’étage Rio da Serra (Néocomien) et l’étage Alagoas (Aptien/Albien) et la mise en évidence d’un considérable hiatus entre les étages des Rio da Serra et Alagoas. La répartition du Jurassique jusqu’à l’Albien/Aptien des ensembles des palynomorphes et ostracodes a permis de montrer l’évolution des paléomilieux, laquelle confirme de plus qu’une sédimentation polycyclique arrive dans le bassin, celle-ci étant un des facteurs déterminants de la distribution des ostracodes et palynomorphes. © 2002 E ´ ditions scientifiques et médicales Elsevier SAS. Tous droits réservés. Keywords: Ostracoda; Palynomorphs; Lower Cretaceous; Araripe basin; Biostratigraphy; Northeastern Brazil Mots clés: Ostracoda; Palynomorphes; Crétacé inférieur; Bassin d’Araripe; Biostratigraphie; Nord-est du Brésil 1. Introduction The Araripe basin occupies an area of 8000 km 2 and is located on the crossing of the co-ordinates 7°02'–7°49' S and 38°30'–40°55' W (Fig. 1), in the border region between the Ceará, Pernambuco and Piauí states, northeastern Brazil. This basin includes the world famous Lower Cretaceous Santana lagerstätten that contains an excellently preserved diverse fossil assemblage, such as ostracods with preserved appendages and eggs (Smith, 1999, 2000). Besides the importance of the taxonomic study of the entire biota, this mother lode is one of the most beautiful and complicated puzzles to resolve, and for this reason it is also important to locate these deposits in a lithological and chronostrati- graphic regional context. As a part of a long-term project conducted by CENPES (Centro de Pesquisas Leopoldo Miguez de Mello, at PETROBRAS), which includes an * Corresponding author. E-mail address: coimbra@if.ufrgs.br (J. Carlos Coimbra). Geobios 35 (2002) 687–698 www.elsevier.com/locate/geobio © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 0 0 1 6 - 6 9 9 5 ( 0 2 ) 0 0 0 8 2 - 7