Neogene palynomorphs from the 2-CA-1-RS well, Pelotas Basin, Brazil: biostratigraphic and paleoecological significance

Abstract

There is information available on calcareous microfossils found in the pre-Quaternary section of the Pelotas Basin. However, there is relatively sparse palynological data, since palynological studies only started to be systematically conducted in the last years. This paper presents palynological results regarding 20 samples collected between depths of 262-145 m in the 2-CA-1-RS well, which is located in the onshore portion of this basin, in the Rio Grande do Sul state. Five samples showed rich and diverse associations of palynomorphs and fifteen samples showed a predominance of amorphous organic matter or phytoclasts. Species of spores, pollen grains, dinoflagellate cysts, as well as microforaminiferal linigs, scolecodonts, acritarchs, Chlorococcales algae (Botryococcus) and fungal spores were also identified in this study. Quantitative analysis on the distribution of particulate organic matter along the section allowed the identification of two palynological assemblages. The results indicate marine paleoenvironments, varying from the bottom to the top, for the studied section. Assemblage 1 (262 - 248 m) is interpreted as distal marine environment in open ocean, whereas Assemblage 2 (190 - 160 m) is associated with proximal marine environments. The stratigraphic range of certain species of dinoflagellate cysts indicates ages ranging from the Miocene to the Quaternary.