Paper No. 7
Presentation Time: 8:00 AM-12:00 PM
ACRITARCHS AND PRASINOPHYTES FROM THE MANACAPURU FORMATION, LOWER DEVONIAN OF THE AMAZON BASIN, BRAZIL
The study succession refers to the upper portion of the Manacapuru Formation, Trombetas Group, Amazon Basin, assigned to the Lower Devonian based on chitonozoans. Samples were collected from six cored sections (SM 2001 to SM 2006), drilled at the margins of the Trombetas e Mapuera rivers, on the basin's northern flank. The Manacapuru Formation consists on its basal and middle portions of regressive sandstones interbedded with siltites and shales, and on its upper portion of a transgressive sequence with a higher clay content. The high magnitude hiatus that separates it from the underlying Pitinga Formation, coupled with more detailed sedimentological studies, could eventually justify placing the Manacapuru Formation as an autonomous depositional unity from the Lower Devonian of the Amazon Basin. Chitinozoans, achritarcs, prasinophytes and numerous spores, cryptospores, chlorofytes and scolecodonts were recorded in the sections. The following species were recorded by the palynological study: Cymatiosphaera winderi, Dactylofusa striatifera, Dictyotidium cohorum, Diexallophasis remotum, Duvernaysphaera angelae, Hapsodopalla chela, Leiofusa sp, Micrhystridium stellatum. Navifusa bacilla, Neoveryhachium carminae, Onondagella deunffii, Polyedryxium fragosulum, Pterospermella circumstriata, Tasmanites ferruginus Tyligmasoma alargadum, Veryhachium europaeum, Veryhachium lairdi, V. rhomboidium,V. trispinosum, V. trispinosoides. This acritarch and parinophyte association characterizes the Lower Devonian of the Amazon Basin, and is similar to the assemblages found in North Africa, South America and southern and western Europe. The achritarc species that present variation on their biochron (chronostratigraphic distribution) in different parts of the globe, are due, most likely, to varying paleobiogeographic and paleoenvironmental factors, which do not invalidate their local biostratigraphic application.