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CONSERVATION ASSESSMENT AND EXPERIMENTAL MECHANICAL PINNING TREATMENT OF PETRIFIED SEQUOIA AFFINIS STUMPS AT FLORISSANT FOSSIL BEDS NATIONAL MONUMENT, COLORADO
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This research assesses the structural decay of nine silicified fossil stumps on the Petrified Forest Loop at Florissant Fossil Beds National Monument in central Colorado, and evaluates the use of mechanical pinning as a remedial conservation treatment. Condition assessment was established through an integrated review of archival documents related to the site’s excavation and display history, field examination, and petrographic analysis, among other laboratory characterizations. The story of this fossil forest begins with the violent burial of a Sequoia affinis paleo-forest from a volcanic mudflow (lahar) and subsequent cycles of lacustrine submerging and desiccation which likely caused organic materials to alternately rot and silicify. As part of the geological record, these stumps underwent immense pressure,mineralization, and seismic trauma. By the late-nineteenth century settlers and early paleontologists began to excavate the stumps, sometimes by dynamite, and pilfer wood alongside the area’s famous fossil-laden shale beds. A popular tourist site for collection and display, the site was ultimately acquired and protected by the National Park Service in xxxx, and today is one of the most important paleo-forest parks in the world. A highlight of visitation, many stumps are actively deteriorating as a result of complex mechanisms resulting in active detachment and loss. An experimental and reversible mechanical pinning assembly was explored to see if a viable method of remedial structural repair to the stumps’ delaminating lamellar fabric with minimal compromise to the their primary value as a significant paleontological resource is possible.
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Fossil forests have world-wide distribution, commonly preserving mineralized wood that displays vivid hues and complex color patterns. However, the origin of petrified color has received little scientific attention. Color of silicified wood may be influenced by the presence of relict organic matter, but the most significant contribution comes from trace metals. This study reports quantitative analysis of trace metals in 35 silicified wood samples, determined using LA-ICP-MS spectrometry. The most important of these metals is Fe, which can produce a rainbow of hues depending on its abundance and oxidation state. Cr is the dominant colorant for bright green fossil wood from Arizona, USA and Zimbabwe, Africa. Complex color patterns result from the progressive nature of the fossilization process, which causes wood to have varying degrees of permeability during successive episodes of permineralization. These processes include simple diffusion, chromatographic separation, infiltration of groundwater along fractures and void spaces, and oxidation/reduction.
Measuring density of silicified wood and determining weight loss after 450°C heating provides useful data for interpreting the process of permineralization. These simple gravimetric methods do not replace X-ray diffraction, electron microscopy, polarized light microscopy, Raman spectroscopy, and other specialized techniques for studying fossil wood, but they can be performed rapidly, and require minimal laboratory facilities. Woods mineralized with opal have densities of 1.9–2.1 g/cm3, compared to 2.3–2.6 g/cm3 for wood mineralized with chalcedony or quartz. Weight loss after 450°C heating, commonly described as “loss on ignition” can be used to roughly estimate the % of original organic matter that remains in chalcedony or quartz-mineralized wood, using the density of extant taxa for comparison. For opalized wood, 450°C weight loss mostly represents dehydration of the hydrous silica. Data from specimens from 20 localities reveal two characteristics: 1) silicified woods typically consist either of opal or chalcedony/quartz, not an intermediate mixture of the two silica polymorphs; 2) the percentage of organic matter that remains after petrifaction is usually very small.
The assessment, conservation, scientific research, and interpretation of palaeontological resources at Florissant Fossil Beds National Monument demonstrate a multifaceted approach to effective geoheritage management by the United States National Park Service. Assessment of palaeontological assets includes routine inventory and monitoring of fossil localities, and surveying Florissant publications and collections at other museums. Conservation activities involve maintaining fossil collections according to museum best practices and developing new methods to conserve fragile fossiliferous shale and large in situ petrified tree stumps. The monument actively supports ongoing scientific research, which in turn provides information for interpretive and educational media in a new exhibit hall. International collaboration enables sharing conservation methods with other petrified forest sites worldwide. Pursuit of geopark designation for the area is ongoing, but must garner better support from local communities, who stand to benefit economically from increased interest in the area.
Scientists are developing vital-sign indicators for evaluating the stability of in situ fossil resources.