CYCLOSTRATIGRAPHY lN THE INTRACRATONIC AMAZONAS BASIN ln thiswork the concepts ofmodem Sequence Stratigraphy are tentatively applied to an interior cratonic basin, while trying to refine the Early to Middle Devonian chronostratigraphy of the Amazonas Basin by using the Cyclostratigraphy techniques. The author employed the following techniques to interpret the data and elaborate a coherent geologic model for the sedimentary section studied: (a) analysis and reconstructions of Devonian features interpreted from the comparison ofbiotic, ichnologic and lithologic data to extensive reference checking; (b) study of the tectonic and climatic conditions that affected Gondwana Supercontinent during the Early and Middle Devonian; (c) facies analysis and paleoenvironment interpretations based on core and cuttings descriptions, considering the fauna, ichnotypes, sediment texture and rock structures; (d) definition of sequence stratigraphic key-surfaces by using welllogs, especially the gamma-ray log; and (e) orbital and climatic Cyclostratigraphy studies in order to check the influence ofEarth's short orbital cycles on the sedimentary record by comparing the gamma-ray log spectra of the section studied to cycles of the Milankovitch frequency bando The integration ofthese analyses allowed the construction of a chronostratigraphic framework for Early to Middle Devonian strata ofthe westem portion ofAmazonas Basin, comprising unit hierarchy, definition ofdepositional system tracts, sequence boundaries and other key-surfaces and the duration of events. The main contributions of this work include the successful application of Sequence Stratigraphy concepts to a cratonic interior basin and the chronostratigraphic refinement obtained from orbital Cyclostratigraphy data analysis, which increases the accuracy ofage estimates in at least one measurement order (from 10 6 to 10 5 years).

The sedimentary basins of the Amazonian region are the fundamental elements that dictate the present confi guration of what is generically known as Amazonia. The geological evolution of these basins established the landscape and the geomorphology of the rivers, lakes and marine systems that fi lled those depressions for the last 500 million years. The wide continental lowlands of Amazonia interacted dramatically with the uplift of the Andes during the last 23.5 million years (Neogene times), creating a special and unique region in terms of drainage, fauna and fl ora ('the Amazon rainforest'). In this chapter we review the genesis and evolution of the intracratonic Solimões and Amazonas basins and the Acre foreland basin, which together formed the framework for the Neogene sedimentary record that is the subject of this book.

The Paleozoic Parnaíba Basin has proven to be one of the most successful onshore gas basins in Brazil. Since 2010, seven gas fields have been declared as commercial. Conventional gas accumulations occur in the Devonian Cabeças Formation sandstone, Upper Devonian/Lower Carboniferous heterolitic sandstones of the Longá Formation, Carboniferous Poti Formation arkosic-sandstones and in the Upper Carboniferous Piauí Formation sandstones. The stacked geometry of an extensive Mesozoic igneous complex is responsible for the creation of several four-way structures and compartmentalization of both source rock and reservoirs. The dolerite sills intrude the organic-rich intervals of the Devonian Pimenteiras shale, triggering maturity and hydrocarbon generation, thus creating an atypical igneous–sedimentary petroleum system. Major seismic concerns are the complexity of imaging subigneous plays, the large areal extent of the basin, strong velocity heterogeneity and the difficulty of imaging high-angle or vertical sealing structures, critical to prospect success. The recognition and understanding of this atypical igneous–sedimentary petroleum system could be used to unlock the potential of analogue basins worldwide and also to expand the exploration successful cases in the Parnaíba Basin itself.