Preserved cytoplasm in charred Agathoxylon-type wood from the Permian of Brazilian Paraná Basin

Abstract

The present study documents cytoplasm preserved by charring in parenchymatous cells of the wood rays of secondary xylem tissue in Agathoxylon-type wood from the Permian of the Brazilian Paraná Basin. Charred logs and bark fragments were collected from the upper coal seam of Sakmarian age (U-Pb dating 291±1.3 Ma) in the Faxinal Coalfield, Rio Grande do Sul, Brazil (Rio Bonito Formation, southern Paraná Basin). The material was examined under field emission gun-scanning electron microscopy. Results of energy dispersive spectroscopy are compatible with organic matter. Three types of cell contents preserved in parenchymatous tissue were observed in the charred samples: solidified, hydrolyzed and agglutinated. Lightning strikes are hypothesized as the likely fossilizing agent for plant cytoplasm, acting as killer and fixer and thus preventing the natural decay that ensues from plant death in the natural environment. The persistence of charcoalified plant tissues has been frequently documented since Paleozoic times, whereas preservation of cytoplasm is less common in wildfire settings since it likely involves a particular interaction of paleobotanic, cytological, physiological, taphonomic and paleoenvironmental factors. Nevertheless, preserved cytoplasm is probably ubiquitous in the fossil record and underreported.