Aptian-Albian palynologic assemblages interbedded within salt deposits in the Espírito Santo Basin, eastern Brazil: Biostratigraphical and paleoenvironmental analysis

Abstract

The Espírito Santo Basin is a Cretaceous to Quaternary basin located on the eastern continental margin of Brazil and contains important oil and gas fields, most of which are actively being explored. However, few micropaleontological contributions are available, and most of the available information is contained in internal reports of oil and gas companies. This paper presents a biostratigraphical and paleoenvironmental analysis based on the palynology of an Aptian-Albian succession of the Mariricu (Itaúnas Member), São Mateus and Regência formations of Espírito Santo Basin. Samples were derived from two wells (BES-01 and BES-02) drilled in the onshore portion of the basin. Among the 24 samples, 18 revealed abundant and diverse assemblages of palynomorphs that included 51 taxa related to continental plants (23 taxa of fern spores and 28 of gymnosperm pollen grains), 4 algae (3 taxa of dinocysts and 1 chlorophicean), and not determined taxa of foraminifera linings, fungi, scolecodonts and acritarchs. Gymnosperm pollen grains are dominant in both wells and are mainly represented by abundance of Classopollis; other gymnosperm pollen grains and pteridophitic spores are subordinate. Biostratigraphic assignments were based on the ranges of guide species mainly in comparison with biozonations established for the Espírito Santo Basin, as well as to other marginal basins of Brazil. The samples of BES-01 were defined as early Albian age, whereas an age from late Aptian to early Albian (without distinction) is assigned for the samples in well BES-02. The dinocysts and foraminiferal linings are restricted to certain depths in well BES-01. A distinctive monospecific assemblage of Subtilisphaera in some samples represents the first identification of the Subtilisphaera Ecozone in the Espírito Santo Basin, which probably represent its southernmost occurrence in the Brazilian marginal basins. The depositional environment was interpreted as a coastal area that was episodically affected by epicontinental transgressions under shallow and restricted conditions. The palynofloral content of the assemblages represent the final presence of the Dicheiropollis etruscus/Afropollis Province, which is documented in several marginal basins of Brazil and Africa and is mainly defined by a gymnosperm paleoflora that was strongly adapted to warm and dry local climate conditions.