Recurrent volcanic activity recorded in araucarian wood from the Lower Cretaceous Springhill Formation, Patagonia, Argentina and its paleoenvironmental implication

DEL FUEYO GEORGINA M.; CARRIZO MARTIN A.; POIRE DANIEL G.; LAFUENTE DIAZ, MAITEN A.

Congreso; XIV International Palynological Congress and X International Organisation of Palaeobotany Conference; 2016

Periodic volcanic activity was one of the most stressful events that affected the plant assemblages inhabitingPatagonia during the Lower Cretaceous. Although recurrent eruptions are well recorded in this area, thisis the first time that they are registered in the coniferous wood described herein. The permineralized trunk was collected in a fine-grained gravel bed of the Springhill Formation, Berriasian-Valanginian in age, which outcrops at the El Álamo locality in Santa Cruz Province, Argentina. Its allochtonous preservationand subhorizontal position was probably due to fluvial remobilization in the alluvial plain. The trunk exhibits slightly marked growth rings and anatomical characters of Agathoxylon Hartig, Araucariaceae.Sedimentological and megafloristic based proxies of the Springhill Formation reveal that the araucariantree was growing under a warm and wet climate most probably reflecting a subtropical paleoenvironment.However, the occurrence of at least 5 subsequent frost rings in the earlywood of this araucarian woodsuggests recurrent disturbances at El Álamo locality, mainly caused by the regional continuous volcanicactivity originated in the not far volcanic arc nowadays located at west and coinciding with the Andeansouth?north oriented volcanoes Due to this activity, stratospheric winds could have promoted a rapiddrop in air temperatures, below freezing point, that results in stressing condition and in the preservationof multiple frost rings. A probable scenario showing pre-eruption, eruption and post-eruption successionoccurred at the El Álamo locality is here suggested. The presence of frost damages in the Agathoxylon wooddescribed herein would probably be a useful tool to search extreme climates back into the geological time,particularly during the Lower Cretaceous in Patagonia