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

ROMBOLA, COSME F.; ARAMENDÍA, INÉS; PUJANA, ROBERTO ROMÁN; GARCÍA MASSINI, JUAN LEANDRO

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 ofthe Río Tarde Formation in the Perito Moreno National Park, Santa Cruz Province, Argentina,was recovered. This association is interpreted as a parautochthonous fossil forest based on theabundance, size, and distribution of the trunks. Most of the specimens were collected as floatwood (65%) in the field, whereas a smaller proportion was found in situ (35%) embeddedwithin the bearing sediments and parallel to the strata. Some fossil woods were studied bymeans of standard thin sections. In general, the fossil woods are well-preserved anatomically.Based on the anatomical characteristics of the specimens analyzed, conifers dominate theassociation. This is consistent with what has been observed in other Mesozoic fossil woodassemblages in southern Patagonia that were mainly dominated by conifers. All the specimensobserved by means of light microscopy show distinct growth ring boundaries, delimited by afew rows of radially compressed tracheids. These characteristics of the rings indicate markedseasonality during the deposition of the Río Tarde Formation in the study area. The size of thespecimens and the curvature of the rings are consistent with the presence of large trees. Inaddition, about 43% of the fossil woods studied show external evidence of biodeterioration bysaproxylic arthropods (e.g., borings and coprolites) and by wood-degrading fungi (e.g., fungaldegradation patterns). This evidence suggests that some of the fossil woods studied were in anadvanced stage of decomposition before their fossilization.