SILURIAN ACRITARCHS FROM THE AMAZON BASIN, NORTHERN BRAZIL

This work is based on the palynological investigation of core samples from PETROBRAS deep well 1-AM-1-AM (Autás-Mirim) and ELETRONORTE shallow drills SM 1015, SM 1016, SM 1018, SM 1047 and SM 1048. The samples are from the Pitinga Formation and lower part of the overlying Manacapuru Formation, all within the Trombetas Group. Altogether forty-eight acritarch species were identified in this study. Their vertical distribution in every stratigraphic section was charted, and their geological age assessed in terms of the previous chitinozoan-based datings established by Y. Grahn and J.H.G. Melo in 1990. We maintain the twofold subdivision of the Pitinga Formation into a lower and an upper "member", with Telychian - Sheinwoodian and Homerian - Gorstian age spans respectively. These two sub-units are separated from each other by an intervening hiatus of late Wenlock - early Ludlow age. The main acritarch species from the lower Pitinga member include: Domasia limaciforme, Domasia canadensis, Domasia trispinosa, Domasia amphora, Domasia rochesterensis, Dateriocradus monterrosae and Salopidium granuliferum.The upper Pitinga member is better characterized palynologically, and includes: Deunffia furcata, Deunffia brevispinosa, Gorgonisphaeridium bringewoodense, Domasia bispinosa, Domasia trispinosa, Helios aranaides, Micrhystridium stellatum, Neoveryhachium carminae, Multiplicisphaeridium caperoradiola, Leiofusa kryanovii, Oppilatala insolita, Pterospermopsis marysae, Veryhachium rhomboidium, Cymbosphaeridium pilar, Multiplicisphaeridium fisheri, Dactylofusa striatifera and Veryhachium europaeum. The main acritarchs from the lower Manacapuru Formation includes Baltisphaeridium pilar, B. cariniosum, Multiplicisphaeridium saharicum, M. scaber, Domasia rochesterensis, Dateriocradus monterrosae, Neoveryhachium carminae and Perforela perforata. They possess a Ludfordian - Pridoli stratigraphic distribution, thus in agreement with Grahn and Melo's (1990) chitinozoan datings. Acritarch assemblages from the Trombetas Group show close similarity to coeval assemblages from the United States, Canada, Argentina, Spain, the British Isles, Norway, Sweden (Gotland), Belgium, Poland, Turkey, Libya, and Saudi Arabia.