Paleocene Las Violetas Fossil Forest: Wood anatomy and paleoclimatology

摘要

Las Violetas Fossil Forest of the Salamanca Formation was a mixed forest of Paleocene age located in the Golfo San Jorge Basin, central Patagonia of Argentina, which includes conifers (previously studied), dicots and palms. In the present work, the dicot fossil woods outcropping in one of the fossiliferous levels (L3) of the Salamanca Formation are described, taxonomically assigned, and their affinities are discussed. They are three new species, including a new genus related to the Myrtaceae and Laurales. The complete fossiliferous assemblage is used to infer the climate and environment of the fossil forest. This assemblage represents a parautochtonous fossil plant association that lived either on the margins of channels or exposed bars in well-drained soils, probably tropical red-soils, close to their depositional setting (tidal channels and bars of an estuary). Warm and humid conditions and porous host-rocks favored the silicification of woods and pigmentation with Fe, resulting in yellow-orange and green fossil woods. We apply growth ring analysis to the conifer woods. For the dicots, wood anatomical characters influenced by the environment were analyzed, and the Vulnerability and Mesomorphy indices were used. These methods, comparisons with extant forests and the sedimentology, suggest that the Las Violetas Fossil Forest was an evergreen forest that developed under uniform growing seasons that ended abruptly, with an abundant water supply and high mean annual temperatures.