Written by Todd Bowers
Last update (9-20-05)
Introduction
This project has three goals, determine the electromagnetic properties of bones that have undergone permineralization, determine the location of bones within a jacket, and finally to find unobtrusive ways of collecting this data. The project will proceed by starting with the most unobtrusive survey and become more obtrusive while still keeping the sample safe.
Wyoming Survey Last update (9-20-05)
I'm not currently finished with my surveys on the jackets, but the oprotunity to tag along on a dig to Wyoming has presented itself, so I will be running a survey in wymoing for a week. I will be running a GPR survey over a dinosaur quarry which will help to determine the stratigraphy of the rock units and popssible locate more remains.
Wyoming Survey Last update (9-20-05)
Links contain raw data, header files, images, and data decriptions.
Selection of GPR survey parameters.
The goal of the 2-16-05 and 2-19-05 survey was to deteremine the suitability of a GPR survey on jacketed samples which contain bones. Here is a list of properties that are special to this survey.
- This is a small scale survey, which might require more precision than the GPR can provided
- The shallow target depth is a problem. A way to correctly target the sample will have to be determined. Target depth was a major problem in the 2-16-05 and 2-19-05 survey. I was more worried about the aluminium foil blocking the signal that I was not worried about the target depth.
- The target geometery is not a bunch of straight pipes, so determining what we are looking at in the data is harder.
Data for 2-19-05 Survey
Data for 7-6-05 Survey
Experiment Setup
A level platform has been built that the GPR will be placed on and the samples will be loaded beneath. This is the most unobtrusive method to survey the sample, because no contact in made with the sample. Energy lose and poor resolution will be major factors in this setup, but the degree to which this setup will affect data collected will be determined once the survey is run. The GPR will be moved across the platform on top of the 0.5 cm think piece of plywood. As suggested by George Tsoflias, the glue in the plywood might cause energy lose, so replacing the plywood with Plexiglas has been encouraged. The spacing for the survey has yet to be determined.
Variables
εr = Dielectric Constant
σ = Electrical Conductivity
v = Velocity
α = Attenuation
Dieletric Constants
Determination of target depth
Equation for depth relative to GPR range.
Depth (m, meters) = 35 / σ (mS/m, Miliseconds/Meter) = 30 / α (dB/m, decibel/meter)
Electrical properties of target and host material
Antenna separation (S)
The 1200mhz antenna which in used in these surveys has a set antenna spacing of 7.5 cm.
Transillumination Survey
Picture of platform over femur sample:
Picture of femur (thigh bone) sample:
Picture of tail sample:
Picture of tail and femur sample from dig site before removal:
Taphonomy is the study of how living organisms become fossilized (Prothero, 1998). Because GPR senses changes in the electromagnetic properties of material, taphonomy is important when understanding the composition of the mineral making of the fossil being imaged. Since fossils are rarely made of the same material as the original living organism, it is nessary to look for other materials which have taken place of the organism. The different chemical reactions that have taken place will have different electromagnetic properties which are detected by the GPR. There are five ways in which the remains of an organism can be preserved as unaltered remains, permineralization, dissolution and replacement, carbonization.
In the case where the original material of the organism is preserved as unaltered remains it is possible for the soft tissue to be preserved. It is unlikely that any large organism over 30,000 or 40,000 years old would be preserved in this manner. There are ammonites from the Cretaceous that have their orignal aragonite intact. This would be a more likely situation when running a GPR survey over recent remains of an organism, like in a survey involving a human grave.
Bones in animal are highly porous, so after soft parts decay material will enter these areas and form minerals. Permineralization results from new material being deposited in the void spaces in the organism, but the original material is not not removed. As example of this would be occur when the bone marrow from a leg bone decays and after the bone is buried. Ground water would carry dissolved calcium carbonate or silica into the void space and precipitate fill in up the space. Permineralization can be so complete that even the details of the cell structure are preserved.
Recrystallization occurs when mineral that are relatively unstable and reverts to a more stable form. This occurs when aragonite shells revert to the more stable form of calcium carbonate. This also occurs when smaller minerals recrystallize into larger crystals. Recrystallization will preserve the original shape of the fossil, but microscopic textures will be changed.
Dissolution and replacement occurs when the organism gets buried and the shape of the orangism gets preserved in the sediment even after the organism dissolves. The void space left behind is filled in with material which takes the shape of the void.
Carbonization occurs when a fossil is preserved as a thin film or carbon on the bedding planes of sandstones and shales. Carbonization produces a two dimensional outline of the organism which can sometimes show very detailed structures.
The dryosaous skeleton being used in this survey has undergone permineralization. I will have to get more information about the minerals which make up the skeleton, but this will be added as soon as I find out more information. All the taphonomy information in this section is taken from "Bring Fossils to life, an introduction to Paleobiology", by Donald R. Prothero 1998.
The following information was obtained from a GPR simulation run by Jasmin Talbert using GprMAX2D Version 1.5. GprMAX was created by Dr Antonis Giannopoulos
( http://www.civ.ed.ac.uk/~agianno) at the University of Edinburgh, Scotland.
GprMAX output from XXX mhz(I need to check with Jasmine about more details) wave reflecting off of tin foil:
As you can see from the picture above, the simulation shows the tin foil reflecting all the energy from the GPR. The objects placed under the foil in this simulation do not show up at all in the image. The reason for this simulation is to demonstrate the problems with trying to use GPR on a jacket which has a foil layer around the sample. A copy of the tinfoil.out file can be found here.
- Morrison Formation Diagenesis of host rock Sillinite
- Age and Location of Morrison Formation
- Lithology: very fine sand
Dryosaurus "Oak Lizard", named by Othinel C. Marsh in 1894, was first found at Como Bluff, Wyoming. The adult length is from 4 to 6 feet.
Reconstruction of skull of Dryosaurus altus, scan from Galton 1983
Skeletal reconstruction Dryosaurus lettowvorbecki from Tanazania, East Africa
Scale below reconstruction is 30 cm long, scan from Galton 1983, figure 7
Dryosaurus altus, from Morrison Formation of western USA.
Skull from Dinosaur National Monument, Utah.
No scale, scan from Galton 1983, plate 1, figure 1
Othniela rex, lateral view of articulated skeleton, from near Willow Springs, Utah
No scale, scan from Galton 1983, plate 4, figure 24
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(1981): Dryosaurus, a hypsilophodonitid dinosaur from the Jurassic of North America and Africa. Postcranial skeleton Palaont. Z. 55: 271-312, 20 abb.; 5 Anlag; Stuttgart. (1983): The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America. Geologica et Palaeontologica. 17: S. 207-243. Bringing Fossils To Life: An Introduction To Paleobiology by Donald R. Prothero |
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Some of the links below contain questionable sources for information, but are somewhat helpful.
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