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This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: B26359.1v1 121/7-8/1172    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Woodcock, D. Articles by Morales, G. GeoRef GeoRef Citation

Geologic and taphonomic context of El Bosque Petrificado Piedra Chamana (Cajamarca, Peru)

Deborah Woodcock^1,, Herbert Meyer², Nelia Dunbar³, William McIntosh³, Isabel Prado⁴ and Guillermo Morales⁴

¹ Marsh Institute of Clark University, 950 Main Street, Worcester, Massachusetts 01610, USA
² U.S. National Park Service, Florissant Fossil Beds National Monument, P.O. Box 185, Florissant, Colorado 80816, USA
³ New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA
⁴ Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Av. Arenales 1256, Lima 14 Peru

Correspondence: E-mail: dwoodcock{at}clarku.edu

Volcanic and volcaniclastic rocks in the northern Peruvian Andes (central Cajamarca, 79°10'W, 6°35'S) contain a diverse assemblage of permineralized woods known as El Bosque Petrificado Piedra Chamana. The fossil forest and associated paleosol are preserved in ash-fall and lahar deposits of the Huambos Formation. Dating of plagioclase from the ash-fall deposit using ⁴⁰Ar/³⁹Ar methods yields a middle Eocene age of 39.35 ± 0.21 Ma. Accuracy of this age determination is supported by a more robust sanidine age of 39.52 ± 0.11 Ma from an underlying welded ignimbrite. Fossil wood and leaves associated with the ash-fall deposit include vertical trees rooted in the paleosol and buried in situ by the ash. Fossil wood is also present in high abundance and diversity in the overlying lahar. The fossils are significant as a low-latitude assemblage including a diversity of both monocots and dicots and in having fossil leaves occurring in close proximity to fossil woods. Preliminary analyses of wood and leaf characters suggest a megathermal climate with some limitations on plant growth associated with limited (seasonal) moisture availability. The assemblage represents lowland tropical forest that was probably growing near sea level and subsequently uplifted to the current elevation at the site (~2400–2600 m).