Palynofacies patterns of the Devonian of the Parnaíba Basin, Brazil: Paleoenvironmental implications

Abstract

To help describe the paleoenvironmental interpretation of one the most extensive marine Devonian successions in Brazil, palynofacies analyses were conducted on 46 samples from the Itaim (Pragian–Givetian), Pimenteira (Givetian–Frasnian) and Cabeças (Famennian) formations of the Parnaíba Basin in north–central Brazil. For the palynofacies analyses, kerogen categories were counted and subjected to cluster analyses. Five palynofacies associations were identified for three studied sections: PseudoAOM palynofacies, which consists of amorphous organic matter (AOM), pseudoamorphous and coenobial algae Quadrisporites; Transl/Nbiostr. palynofacies, which consists of translucent non-biostructured phytoclasts (well-preserved and degraded), cuticles (well-preserved and degraded), Spongiophyton and Botryococcus; Marine microplankton palynofacies, which consists of acritarchs, prasinophytes and translucent biostructured phytoclasts; Opaque palynofacies, which consists of opaque phytoclasts (equidimensional and lath shaped); and Sporomorphs palynofacies, which consists of zoomorphs (e.g., Chitinozoa) and sporomorphs (e.g., spores). The stratigraphic distribution of the five palynofacies associations reflects a continuous terrestrial influx throughout marine succession. At the Pragian–Emsian age, the woody material of Transl/Nbioestr. palynofacies prevails, suggesting a marine depositional paleoenvironment (presence of marine palynomorphs), but under deltaic influence due to the input of terrigenous material. An increasing trend of marine elements of Marine microplankton palynofacies is recorded for the Givetian, which suggests a progressive marine influence. However, during the Frasnian, the highest abundance of marine elements was recorded (Marine microplankton palynofacies). Moreover, a bloom of Maranhites spp. and prasinophytes (e.g., Tasmanites and Cymatiosphaera) was also recorded. The abrupt increase of marine palynomorphs in the Frasnian – here termed the “Maranhites Event” – has been recorded by other authors. Finally, in the Famennian, woody material was most abundant in Transl/Nbiostr. palynofacies and Sporomorphs palynofacies, which reflects a depositional trend that is strongly controlled by fluvial input into a shallow marine environment.