For this project I made thin-sections and then examined them using various types of microscopy including; plane light, polarized light, and cathode-luminescence. By using a variety of methods to view the thin sections I was able to identify the minerals in the samples as well as their relative timing relationships. On a hand specimen scale, I used a technique called phosphor imaging which shows where the radio-atoms in a sample are concentrated. Additionally, I observed my samples with a SEM (scanning electron microscope), which allowed magnification of 15000X. The purpose of my research is to petrographically analyze permineralized fossils and petrified wood for uranium (U) concentrations in order to understand how the uptake of U is related to the mineralization. Ultimately, I would like to prove that preserved organic materials in fossils are directly related to U concentrations in samples. Many gaps exist in the sedimentary rock record and understanding the correlation between the marine and terrestrial record is hampered by poor time resolution. It is hoped that this research will facilitate efforts to use fossils for U-Pb (uranium-lead) dating of terrestrial sections. This research will also provide important insight to research on ESR (electron spin resonance), a technique for dating young fossils that requires modeling for U uptake. For this project, I used two groups of permineralized bone and one group of petrified wood. The samples used in this project are all from the Mesozoic Era. One group of bones are from the Morrison Formation, which is known for its economic U ore deposits and was formed sometime around the Jurassic/Cretaceous boundary. Less is known about the U content of the Cretaceous Formation from Madagascar from which the second group of bones was collected. In my first test, I left my samples on the phosphor imager plate for 4 days. These initial results show high U concentrations in the bones from the Morrison Formation and much lower U concentrations in the Cretaceous bones from Madagascar. These observations are consistent with the color of the bones, which most likely reflects the presence or absence of organic material. Although the bones from both formations are phoshatic, the ones from the Morrison Formation are bluish black, indicating organics are preserved while the ones from Madagascar are light brown. The Petrified wood is from Arizona and formed during the Triassic period. While a petrographic analysis shows beautiful preservation of cellular structures, results from the phosphor imaging did not look promising. The petrified wood is silicified and samples range in color from red to white. Thus the color suggests that although the textures are well preserved, the organic matter has been removed. Funding for this project was provided by Simons Grant 265210 and by NSF EAR Grant No. 0096103.

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