Terrestrial and marine palynomorphs from deposits of the pull-apart rift of West Gondwana (Parnaiba Basin, northern Brazil): Biostratigraphy and relation to tectonic events

摘要

The thick, predominantly siliciclastic deposits of the Itapecuru Formation cover a large geographical area. Their deposition was controlled by strong tectonism in the rift stage of the Gondwana separation and by the evolution of the Atlantic Ocean, with the Cretaceous section of the Parnaiba Basin being related to the development of the Equatorial Segment. The age assignment for the Itapecuru Formation is based on the chronostratigraphic positioning of its exposed deposits along the Itapecuru River, in the eastern area of the Parnaiba Basin. Due to their high biostratigraphic resolution in both continental and marine sections, palynomorphs were chosen to accurately assess relative age. Palynofloras are mixed and dominated by terrestrial palynomorphs and aquatic plant spores, with rare marine and Paleozoic reworked palynomorphs. Based on species of biostratigraphic value recorded in the palynological assemblages, the Complicatisaccus cearensis Zone was characterized, thus attributing the upper Aptian age to the deposits. The stratigraphic ranges of Elaterosporites protensus, Elaterosporites verrucatus, Elaterosporites klaszi and Elaterosporites spp. small forms, Cavamonocolpites punctatus, Quadricolpites reticulatus and Elaterocolpites castelainii (A and B forms) are here extended, invalidating the definition of the boundary between the Complicatisaccus cearensis and Elateropollenites jardinei zones. These results allowed the correlation of the studied deposits with depositional sequences. The compositional variation and abundance of Afropollis, Araucariacites and elaterate complex in the palynofloras allowed their correlation with three palynofloristic provinces: Afropollis, Lower Cretaceous Dicheiropollis/Afropollis and Albian-Cenomanian Elaterates, suggesting a wet equatorial climate near the paleo equator.