187 Paleontology/Paleobotany (Posters) II

DEVELOPING ESR DATING FOR SHARKS' TEETH: TOWARDS A NEW GEOCHRONOLOGICAL METHOD FOR SEDIMENTOLOGICAL AND PALEONTOLOGICAL ANALYSIS

Paper number: 187-13
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Enameloid from three species of fossil sharks was examined for its suitability for ESR dating analysis. Similar in structure and geochemistry to mammalian enamel, shark enameloid contains a mineral matrix of hydroxyapatite. The characteristic radiation-sensitive hydroxyapatite signal occurs in the shark enameloid centred at g=2.0018. The three species all showed similar ESR signals that grew consistently with added radiation dose. A low-intensity narrow interference peak occurs consistently for enameloid in all three species at g ~ 2.006, while a much broader peak appears at g ~ 2.056. Neither affect the measurement of ESR signal intensity for the hydroxyapatite dating peak at g=2.0018. Side-band peaks, attrributed to organic radicals, also occur on either side of the dating peak. The differences between the enameloid signal in the shark and the enamel signal in mammalian enamel suggest that shark enameloid contains more organic matter and may be formed differently in the developing embryo from mammalian enamel.

Both Carcharodon megalodon (great white shark) and Isurus hastalis (mako shark) teeth contained enough enameloid per tooth to provide one to two subsamples with 10-15 aliquots. Tiger shark teeth (Galeocerdo aduncus) were too small to provide sufficient enameloid for a growth curve to be constructed. Preparing sharks' teeth for dating required total preparation times averaging less than 2 hours per subsample, making it an inexpensive technique.

Radiation-sensitivity for the ESR signal is similar in all three species, with saturation occurring after 3-4 Mrad of total radiation dose. Growth curves provided accumulated doses with precisions ranging from 3% to 8% after 12-15 added doses. Tests for dating accuracy now need to be completed.