Stable isotope and chemical stratigraphy of the Eocene Tambaba Formation: correlations with the Paleocene–Eocene Thermal Maximum event

Abstract

AbstractThe Paraíba Basin has a well-defined carbonate depositional sequence from the Upper Cretaceous (Campanian) to the Eocene. The carbonate sequence consists of the 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 rocks of this unit located in a representative geological section at the Tambaba Beach, northeastern Brazil, in order to elucidate 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 of the organisms that make up these reef limestones. These changes are also recorded in the behaviour of the major and trace elements – for example, the relationship between 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, palaeotemperature values (9–15°C, from δ18O data) obtained, 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 myr after the Paleocene–Eocene Thermal Maximum event.