Palynology and geochemistry of the Frasnian global transgression in the Parnaiba Basin, Brazil

An integrated palynological and geochemical approach has been initiated to date and to precise the geochemical events of the Pimenteiras Formation, in the Late Devonian from the Parnaiba Basin, Brazil. Based on good biostratigraphic markers and presence of index species among miospores, acritarchs and chitinozoa, the investigated sequences are referred to the Middle to early Late Frasnian. Among Miospores, Chelinospora concinna and Verrucosisporites Witt-eras are likely to be from the BPi Interval Zone defined in the Amazon Basin. Chitinozoans of the Early to early Late Frasnian Angochitina (Lagenochitina) avelinoi zone of the Parnaiba Basin are present, and acritarch assemblages arc also consistent with a Middle to early Late Frasnian age, by comparison to assemblages previously described in other Brazilian basins. Some important accompanying species of palynomorphs are illustrated. In the studied outcrops, black shale intervals are referred to top of the Radioactive Sale B and Radioactive Shale C according to Rodrigues (1995) definitions. Top of Radioactive Shale B shows good concentration of terrestrial organic matter, but low potential source of gas. By comparison Radioactive Shale C of the upper part of the Pimenteiras Formation, with important concentration of marine organic matter have low to high potential as source of gas and condensate. This study shows that a progressive flooding took place during the Devonian period in the Parnaiba Basin with maximum marine transgression in the Frasnian. These global events of interest for hydrocarbon exploration, are regarded as markers for Gondwanan regional chronostratigraphic correlations. (C) 2020 Published by Elsevier B.V

Le Paléozoïque de la Presqu'île de Crozon, Massif Armoricain (France)

Geological outcrops are of good quality along the foreshore and cliffs in Crozon Peninsula allowing the study of Paleozoic series of the Armorican Massif. The sedimentary and faunal evolution of this area is part of the history of the Gondwana margin and records the opening of the Rhéic Ocean, eustatic variations and paleogeographic migration from high latitudes in the Ordovician to a sub-equatorial position in the Carboniferous. Geological outline of the Armorican Massif is briefly exposed and integrated in a climatic, eustatic and tectonic global framework. Afterwards, the second part deals with formations of the Crozon Peninsula since the Ordovician to Upper Devonian with their faunal and sedimentological characteristics. In the third part, the main outcrops visited during the fieldtrip of the Paleozoic French Group (GFP) during the Congress « Strati 2010 » are described; these outcrops illustrate some aspects of the armorican geological history