Palynology of carcinolites and limestones from the Baunilha Grande Ecofacies of the Pirabas Formation (Miocene of Pará state, northeastern Brazil)

Abstract

The Pirabas Formation records important transgressive/regressive marine events in northern Brazil during the Miocene. Here, we present the results of a palynological analysis of four samples from finely stratified gray limestone and associated carbonate concretions bearing decapod crustacean remains. These sampled strata are representatives of the Baunilha Grande Ecofacies, and our analysis enhances the knowledge of local biostratigraphy and paleoecology.The palynoflora is dominated by taxa typical of Neogene tropical areas, such as Zonocostites ramonae (the most common species), together with Retitricolpites and Retitricolporites genera. Commonly represented are the smooth and apiculate trilete/monolete spores (Polypodiisporites, Verrucosisporites, Magnastriatites, and Deltoidospora), in conjunction with some freshwater algae (Ovoidites and Botryococcus). Gymnosperm pollen grains were absent. Marine microplankton (dinoflagellate cysts, acritarchs and foraminiferal test linings) are scarce, although present in all samples.The presence of the index species, Malvacipolloides maristellae and Pachydermites diederixii, co-occurring with Zonocostites ramonae and Lanagiopollis crassa, suggests that these sediments and concretions belong to the “T-13 Malvacipolloides maristellae” palynozone (Jaramillo et al., 2011), considered as late-Early Miocene in age. Palynological and sedimentological evidence further points to a predominantly continental depositional environment with a weak marine influence, as indicated by the persistent presence of sparse dinoflagellate cysts, acritarchs and foraminiferal test linings, typical of a mangrove environment.