Conservation of an Eocene petrified forest at Florissant Fossil Beds National Monument: Investigation of strategies and techniques for stabilizing in situ fossil stumps

Abstract

Silicified stumps at Florissant Fossil Beds National Monument are subject to degradation from a variety of causes including freeze-thaw weathering. In the past, noninvasive measures have been taken to conserve selected fossils, including use of metal bands for reinforcement and construction of shelters. Our study had two goals. The first was to document the temperature and relative humidity to which petrified stumps are exposed at Florissant. The second was to conduct a preliminary examination of the feasibility of using consolidants and adhesives to reinforce fossil wood and reduce its susceptibility to weathering. Electronic data loggers were used to monitor temperature and relative humidity both internally and externally for one exposed and one sheltered fossil stump, and results indicated that over 289 days of the cold season there were 119 freeze-thaw events for the surface of the exposed stump and 95 events for the surface of the stump protected by a roof. Temperature and humidity variations were markedly lower for the subsurface sensors. Seven organosilicate formulations were field tested as consolidants on samples of petrified wood. Adhesives used to repair fractures included two polyvinyl butyral (PVB) formulations, two casein adhesives, and one epoxy. After eight months of exposure, fractures repaired with epoxy remained well bonded. Specimens repaired with PVB remained intact, but outer regions were visibly damaged, presumably from UV radiation. Of the two casein products that were tested, one had poor bond strength and the other was difficult to apply because of its low viscosity. Evaluating the effectiveness of organosilicate emulsions as consolidants to reduce weathering rates will