Stable Isotopes and Trace Elements in Tooth Enamel Bioapatite: Effects of Diagenesis and Pretreatment on Primary Paleoecological Information

Author

Jessica Norman Wilson, University of South FloridaFollow

Graduation Year

2013

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Jonathan G. Wynn

Keywords

barium, carbon, oxygen, paleodiet, strontium

Abstract

The geochemical analysis of bioapatite in vertebrate skeletal tissues is an important tool used to obtain ecological information from fossil animals. An important consideration when conducting stable isotope and trace element analyses is obtaining biogenic information that has been unaffected by diagenetic processes.

A two-step pretreatment procedure is commonly used remove diagenetically altered material by removing organic material, via an oxidation reaction with H2O2 or NaOCl, and secondary carbonate, via dissolution in dilute acetic acid, from bioapatite. While much work has been done to determine the efficacy of the pretreatment process, little research has been conducted to determine the potential effects of this process on the oxygen isotope composition of enamel bioapatite. A comparison between δ¹⁸O values of fossil enamel treated with ¹⁸O-depleted (δ¹⁸O = -10.0 / V-SMOW) and ¹⁸O-enriched solutions (δ¹⁸O = +16.4 / V-SMOW). On average, samples treated with 18O-enriched solutions had δ¹⁸O values at least 0.4 / V-PDB more positive than samples treated with ¹⁸O-depleted solutions. These results suggest that the isotopic composition of solutions used in the pretreatment process can significantly affect the δ¹⁸O values of fossil enamel prior to isotopic analysis.

Diagenetic alteration can potentially be assessed using the linear relationship between δ¹⁸O values of the carbonate and phosphate components of bioapatite, as any deviation from a slope of 1 suggests alteration. Comparing the relationship between δ¹⁸Op and δ¹⁸Oc for fossil mammals from the Hadar Formation suggests that this method is successful at identifying samples that are significantly different from the remaining samples due to diagenetic alteration. The relationship between δ¹⁸Oc and δ¹⁸Op for the majority of sampled fossils from the Hadar Formation has a slope very close to 1 with an average offset, and apparent fractionation factor, between δ¹⁸Oc and δ¹⁸Op consistent with modern mammals. Therefore, it is likely that many of the fossil mammals sampled from the Hadar Formation retain in vivo δ¹⁸O values relating to the δ¹⁸O value of the water they consumed.

The reliability of paleodietary reconstructions using trace element ratios (notably Sr/Ca and Ba/Ca) is strongly dependent on the preservation of biogenic trace element concentrations. Although most trace element ratio research relies on bone bioapatite, enamel has a better preservation potential and may successfully preserve biogenic trace element relationships. An analysis of Sr/Ca, Ba/Ca, and Zn/Ca ratios indicates that, despite rare earth element concentrations greater than the 1ppm observed in modern enamel, mammals from the Hadar and Busidima formations potentially reflect feeding strategies observed in modern counterparts, i.e. grazers have higher Sr/Ca and Ba/Ca ratios than browsers and omnivores

Scholar Commons Citation

Wilson, Jessica Norman, "Stable Isotopes and Trace Elements in Tooth Enamel Bioapatite: Effects of Diagenesis and Pretreatment on Primary Paleoecological Information" (2013). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/4965