Palynomorphs abundance of the Jaciara section (Ponta Grossa Formation, Paraná Basin, Brazil), what does it tell us about the paleoenvironment?

GARCÍA MURO, VICTORIA J.; CLAUDIA VIVIANA RUBINSTEIN; PEREIRA, EGBERTO; PHILIPPE STEEMANS

London

Congreso; AASP-TPS 53rd Annual Meeting; 2021

Natural History Museum, London

Fourcoarsening upward depositional cycles (PS I-IV) can be observed in the Jaciara section,limited by flooding surfaces, corresponding to a ramp basin type. Palynomorphsfrom this section were preliminary studied and subsequently, in a later contributionfocused on terrestrial palynomorphs, the diversity of the spores in the sectionnotably increased. A late Pragian ? possibly middle Emsian age was previously suggestedfor the Ponta Grossa Formation, based on the spore assemblages. The marine componentsof the assemblage were recently broadly examined. A detailed counting of all palynomorphsreveals that the marine fraction represents, in most of the samples, more than50% of the assemblage, mainly coinciding with the flooding surfaces at the beginningof each cycle. PS I, PS II and the lower part of PS III, present majorabundance of acritarchs, followed by prasinophytes andphytoclasts. This portion also corresponds to the high values of δ13Corg, related to greater contributionfrom land plants. Besides, the sandier deposits of PS I andII are strongly related to the forced regressionepisodes during the Early Devonian transgression. Samples corresponding to the rest of the cycle PS III and PS IV, includingthe black shales flooding surface, contained higher abundance of acritarchs, followedby fluctuating abundance of trilete spores and phytoclasts. This matches with high values of TOC and negative δ13Corg values, associated with the flooding surfaces.Since the middle part of the PS III, the increase of phytoclasts and triletespores, might indicate a general shallowing trend towards the top of theJaciara section. Although, the presence of terrestrial organic material in relativelydistal marine facies could also be related to climatic conditions, such as humidperiods that increased nutrient input to the sea.