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Florissant Survey

Archival research and site survey were conducted by the ACL on 4-7 November 2016. Stump assessment has been significantly informed by Young et. al. (2008), where temperature and humidity data were recorded over a winter and microporosity between tracheids was first noted. A glossary of conditions, specimen survey, and a conditions matrix were compiled. Archival research was performed after site familiarisation to inform the survey. The results of this survey, site research, and material characterisation led to the design of the mechanical pinning treatment testing program to follow.

Archival Research
FLFO archives revealed critical information about the internal composition and physical integrity of the stumps. In her Drilling Report, Kate Gregory describes the process of obtaining two cores from P46 as being very difficult because of the lamellar nature of stump fabric. Gregory accompanied her report with a separate letter, again highlighting the fractured nature of the stumps as:

"The first few inches of drilling water pumped into the core hole to cool the drill flowed back out the core hole. However, the drill soon encountered fractured zones filled with soil, or zones of wood fibre which had negligible hardness. Once these fracture zones were encountered, all water disappeared into the stump, indicating the zones were pervasive. In fact, fracture zones were so numerous that the core came out in 1-2 inch pieces instead of one continuous sequence. Thus, the stump is a ring of petrified wood that surrounds a fractured and intensely decayed center."

Tiffany View 2
Planes of secondary mineral infill on P47. Note on left that material has preferentially exfoliated at this interface.
Park personnel quickly named these rediscovered documents the “Dead Tree Scrolls.” Gregory’s discovery brought about many questions about the integrity of the stump core, and mused that coring effluent might be “mudflow,” meaning lahar. It is very common for mature Sequoia trunks to have hollow centres near their base. Nevertheless, more research is needed to determine if a stump core is hollow and what it might be filled with. Differential hygroscopic coefficients of expansion and discontinuities in thermal conductivity could cause pathologies of differential movement and result in further fracturing.

The most significant intrinsic reason for material decay is as a direct result of silicification processes and blasting. Stump jointing, a geological term for planes of weakness or preferential cleavage, is a significant reason for deterioration. Site survey and analysis demonstrated that the interface of secondary or tertiary mineralisations of cracks determine areas of tabular detachment. Field microscopy with a hand held digital microscope following visual identification of botryoidal deposition determined that these lines of later mineralisation become the boundaries of material detachment.

Stump Conditions & Deterioration Systems
Geoengineers have developed the term Rock Quality Designation (RQD) through core analysis as a method of in situ evaluation of the quality of a rock mass determined by fractures and jointing. RQD appraisals can be complicated, being tailored to the geotechnical requirements of the mining industry. In her letters, Gregory mentions that the drill operators found it very difficult to core into stump P46. How sensitive the operators were is significant, because any fractures caused by either handling, or the drilling process must be discounted. The RQD of P46 directly relates to a combination of factors including the material's fossilized origins, its silicification, the likely excavation by dynamite, and subsequent weathering. While geotechnical assessment may be of use, its conventional use for situations such as faceplate pinning, webbing, and shotcrete are not compatible with preservation intent, site value, or touristic display of the stumps.

stump junk

Large excavated FLFO stumps such as P16, P20, P31, P46, & P47 have deterioration patterning that can be grouped in three zones:

1)    Zone of Fragmentation- The upper-most area of the stump exhibits splintering, fibrous disintegration, vegetative growth, fractures, animal burrowing, and is subjected to the most water from direct precipitation: snow, ice, and rain, more constant loading from thermal radiation, and mechanical interventions such as metal strapping bound to halt fragmentation and sectional loss. This area has the worst material integrity.

2)    Zone of Exfoliation- The middle area of a stump suffers from dimensional loss due to secondary mineralisations, fractures, lamellar exfoliation, and can have discolorations due to corrosive metals or biocolonisation. This area has the best material integrity.

3)    Zone of Rising Damp- Stump base absorbs water through capillary flow and snow piling. The resultant undercutting, buttress root fracturing, or basal deterioration is the result. There is no evidence of salt efflorescence.

This project examines the feasibility of stabilizing the large petrified stumps at FLFO. These petrified stumps constitute one of the major natural resources of the park. Of the nine stumps currently exhibited on the Petrified Forest Loop several of these are visibly deteriorating due to cracking, spalling and the loss of large fragments of petrified wood. This project addresses an urgent need for conservation. While the research focuses on remedial methods of stabilization, the overall goal is to create a stable environment for the long-term preservation of the stumps in situ. This thesis develops site-based methods for the conservation of petrified trees in order to benefit the park’s mission to conserve its fossil forest. The monument is interactive with other petrified forest sites internationally, thus enabling broad sharing of methodologies for the conservation of petrified trees.
Material Characterization
The purpose of these measurements was to understand the material properties of FLFO silicified wood behaviour in order to influence the decision-making process of mechanical pinning treatment design. Samples available for destructive analysis were procured from FLFO during a site visit in November 2016. Samples were sourced from material found during excavations for a new visitors centre in 2011, or came from FLFO stump P-47.

Material characterisation tests performed included:

1)    Gross Physical Characteristics: Bulk Density, Specific Gravity, and Colour
2)    Water Absorption
3)    Reflected and Stereoscope, Polarised Light Microscopy, and Scanning Electron Microscopy
4)    Thermal Linear Coefficient of Expansion
5)    Mechanical Properties

flfo survey-3
Transverse view of detail of microcrack occurring at late to early wood, the annual ring. Anomalous birefringence of quartz or quartz polymorphs, such as chalcedony can be accounted for thickness of section preparation. Paleontologists who view petrified wood often use thicker sections for anatomy details, around 50 microns. Sample P55a, George Mustoe collection. Viewed at 100x in Plane Polarized Light top and Cross Polarized Light bottom.
Wood cellular density changes radically at the latewood to spring wood boundary. There is a concentration of what might be relict organics or iron oxides at the interface of this crack. Textural density and mineralogy may help explain why exfoliation or tabular detachment often occurs along annual rings. Radial section anatomy can be seen to correspond to annual rings. The same cracks exhibited in transverse grain can be confirmed as planar fissures when viewed along the radial grain.

Sub-micro porosity was visible with Scanning Electron Microscopy (SEM) at the boundaries between tracheids, probably as a result of silicate inaccessibility.

A three dimensional model of stump p-47. To rotate the model place the mouse over the image and, while left clicking, move the mouse. Click on each of the numbers to read more information about that location. To view the model in full frame mode, place the mouse cursor over the view and then click on the small double-ended arrow icon which appears in the bottom right corner of the view.

flfo survey-1

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