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

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

Salvador

Congreso; XIV International Palynological Congress - X International Organization of Palaeobotany Conference; 2016

Universidade Estadual de Feira de Santana

Recurrent volcanic activity recorded in araucarian wood from the Lower Cretaceous Springhill Formation, Patagonia, Argentina. Paleoenvironmental interpretationsGeorgina M. Del Fueyo1, Martín A. Carrizo1, Daniel G. Poiré2, Maiten A. Lafuente Diaz11Museo Argentino de Ciencias Naturales ?Bernardino Rivadavia?-CONICET, Buenos Aires, Argentina, georgidf@yahoo.com.ar2Centro de Investigaciones Geológicas, UNLP-CONICET, La Plata, ArgentinaPeriodic volcanic activity was one of the most stressful events that affected the plant assemblages inhabiting Patagonia during the Lower Cretaceous. Although recurrent eruptions are well recorded in this area, this is 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 of Berriasian-Valanginian age outcropping at the El Álamo locality in Santa Cruz Province, Argentina. The fossil trunk was transported in an alluvial plain by fluvial agent and preserved in a subhorizontal position. 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 araucarian tree was growing under a warm and wet climate most probably reflecting a subtropical paleoenvironment. However, the occurrence of subsequent frost rings, at least 5, in the earlywood of this araucarian wood suggests that the paleoenvironment at El Álamo locality was subjected to recurrent disturbances most probably caused by the regional continuous volcanic activity originated by the volcanic arc located further away to the west where the Andean south?north oriented volcanoes exist nowadays. Because this activity would have produced a stratospheric veil promoting the surface air temperature drops precipitously below freezing point, the wood response to such stressful condition would have been the formation of multiple frost rings. Araucarian wood from Patagonia showing traumatic frost rings have been reported since the Triassic and were attributed to unpredictable frosts during the growing season. However, the finding of subsequent frost rings caused by regional recurrent volcanic eruptions is here recorded for the first time in a Lower Cretaceous araucarian wood from Patagonia; as well as in other Mesozoic coniferous woods from Western Gondwana. A probable scenario showing pre-eruption, eruption and post-eruption succession occurred at the El Álamo locality is here suggested. In the extant Araucaria araucana (Molina) K. Koch wood, endemic to temperate Subantarctic Patagonian forests, the record of frost rings for the last 600 years was used to build reliable frost ring chronologies to document past extreme climatic events in that area. Thus, the presence of frost damages in the Agathoxylon wood described herein would probably be a useful tool to trace solid frost ring chronologies for searching extreme climates back into the geological time, particularly during the Lower Cretaceous in Patagonia.Keywords: Volcanic eruptions, wood, Araucariaceae, Lower Cretaceous, Patagonia.It is a contribution to grants ANPCyT PICT 2012/528 and CONICET PIP 112-201201-00212, PIP 112-200901-01016.