Remains of a Cretaceous forest (fossil woods) in the Perito Moreno National Park, Santa Cruz Province, Argentina

COSME ROMBOLÁ; INÉS ARAMENDÍA; PUJANA, ROBERTO R.; GARCÍA MASSINI, JUAN

Serie Correlación Geológica

INSUGEO

Lugar: San Miguel de Tucumán; Año: 2023

1514-4186

An assemblage of 84 fossil woods from Aptian sediments of the lower member of the Río TardeFormation in the Perito Moreno National Park, Santa Cruz Province, Argentina, was recovered. This associa-tion is interpreted as a parautochthonous fossil forest based on the abundance, size, and distribution of thetrunks. Most of the specimens were collected as float wood (58%) in the field, whereas a smaller proportionwas found in situ (42%) embedded within the bearing sediments and parallel to the strata. Some fossil woodswere studied by means of standard thin sections. In general, the fossil woods are well-preserved anatomically.Based on the anatomical characteristics of the specimens analyzed, conifers dominate the association. This isconsistent with what has been observed in other Mesozoic fossil wood assemblages in southern Patagonia,which were mainly dominated by conifers. All the specimens observed by means of light microscopy showdistinct growth ring boundaries, delimited by a few rows of radially compressed tracheids. These characteris-tics of the rings indicate marked seasonality during the deposition of the Río Tarde Formation in the studyarea. The size of the specimens and the curvature of the rings are consistent with the presence of large trees.In addition, about 43% of the fossil woods studied show external evidence of biodeterioration by saproxylicarthropods (e.g., borings and coprolites) and by wood-degrading fungi (e.g., fungal degradation patterns). Thisevidence suggests that some of the fossil woods studied were in an advanced stage of decomposition beforetheir fossilization.