Effect of volcanic ash-fall on a Permian peat-forming environment, on the basis of palynology, palynofacies and paleobotany (Faxinal Coalfield, Brazil)

Abstract

The aim of this paper was to assess, in a study case, whether ash-fall deposition influenced the character of the peat-forming vegetation in some coal beds in the southernmost Paraná Basin in Brazil, taking into consideration that records of tonstein levels are common in some coal bearing-strata. An investigation was made of the uppermost Faxinal coal seam (Coal Seam S), which displays two adjacent coal beds interbedded with a tonstein level. On the basis of the botanical affinity between the miospores and the parent plants as well as the relative abundance of the different plant groups, each coal plant assemblage was determined. Furthermore, previous paleobotanical data obtained on the tonstein level that identified a compressed Glossopteris flora were incorporated in the study. Palynofacies analyses performed on both coal and tonstein levels demonstrated good results for the recognition of preserved organic matter and changes in paleoenvironmental conditions along the coal sequence. The effect of volcanic ash-fall deposition was reflected by changes in the character of the vegetation associated with coal layers below and above the tonstein. Palynofacies results corroborated palynological and paleobotanical interpretation and contributed to the establishment of the floral succession deposited over a short time interval, under the effect of volcanic ash-fall deposition.