Patagonia, South America

Introduction

Patagonia, a large plateau in southern Argentina, is home to vast expanses of Jurassic, Cretaceous, and Tertiary-aged fossil deposits (Derbach, 1996). Time and again large, forested, areas were overwhelmed by volcanic tuff, which entombed trees and cones. The volcanic tuff acted as a silica source helping to create beautifully preserved permineralized wood and cones. Two sites, Santa Cruz and Chubut, are particularly important to both scientists and collectors interested in well-preserved conifer cones.

In the province of Santa Cruz the Cerro Cuadrado Petrified Forest produces various coniferous woods with Araucaria-like being most common, Araucaria mirabilis conifer cones and Pararaucaria patagonica cones associated with the extinct coniferous family Cheirolepidaceae are also found at this location (Calder, 1953; Escapa, Rothwell, Stockey, and Ruben-Cuneo, 2012).

The petrified forest of Cerro Cuadrado is underlaid by an Upper Triassic rock unit and overlaid by Upper Cretaceous strata. Sediments that seem to be associated with the tuffs that contain the wood and cones possess Jurassic aged vegetation. This geologic evidence suggests that the wood and cones from this forest grew during the Middle to Upper Jurassic period (Dernbach, 1992). Many of the Araucaria mirabilis cones exhibit excellent cellular detail with embryos visible in some of the seeds. Scientific studies of tissue organization in the seeds and embroys of Araucaria mirabilis cones indicate a close affinity with present day Araucaria bidwillii (Stockey, 1975; Derbach, 2002).

You can explore how a multifaceted approach to studying Araucaria mirabilis can provide insights into phylogeny, biogeography, and plate tectonics by reading the article Patagonia's Jurassic-Aged Conifer Cones: Keys to a Botanic and Geologic Past in March/April 2017 issue of Rocks and Minerals.

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Bibliography