José Diego Dias Veras
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João Adauto de Souza Neto
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Alcides Nóbrega Sial
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Valderez Pinto Ferreira
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Virgínio Henrique de Miranda Lopes Neumann
AbstractThe Paraíba Basin has a well-defined carbonate depositional sequence from the Upper Cretaceous (Campanian) to the Eocene. The carbonate sequence consists of Itamaracá, Gramame, Maria Farinha and Tambaba formations, which mainly contain calcareous sandstones and carbonates with siliciclastics, limestone-marl alternations, limestones and marls, and limestones, respectively. The Tambaba Formation is composed of reef limestones, ranging from fossil- and ichnofossil-rich calcilutite to calcarenite. We investigated the rocks of this unit located on a representative geological section in the Tambaba Beach, Northeastern Brazil, in order to elucidated the environmental responses recorded in geochemical proxies (C and O isotopic composition, and distribution of major and trace elements). The δ13C and δ18O values ranged from 1.0 to 2.7‰ VPDB and from -1.3 to 1.1‰ VPDB, respectively. The interpretation of this response suggests environmental changes, such as an increase or decrease in bioproductivity from the organisms that build these reef limestones. These changes are also recorded in the behavior of the major and trace elements, for example, the relationship among SiO2, Al2O3, MgO and CaO, characterizing two different cycles during the deposition of these limestones: the first one characterized by a predominantly carbonate deposition, and the second one presenting a pulse of siliciclastic content. In addition, the palaeotemperature values (9 to 15°C, obtained by δ18O data) found together with chemostratigraphic profiles of previous studies (e.g. δ13C, CaO, MgO, SiO2, Al2O3) indicate that the reef limestones of the Tambaba Formation were probably deposited about 5 Ma after the Palaeocene-Eocene Thermal Maximum event.
The Relationship Between Chemical Index of Alteration andSome Major and Trace Elements Content in Rocksof Injana Formation of Northern Iraq