ESR dating of a toxodon tooth from a Brazilian karstic cave

doi:10.1016/S0969-8043(00)00093-2

Applied Radiation and Isotopes

Volume 52, Issue 5, 15 May 2000, Pages 1345-1349

https://doi.org/10.1016/S0969-8043(00)00093-2 Get rights and content

Abstract

A pre-molar of a Toxodon platensis (sp), a large mammal that inhabited the forests of Southeast Brazil during quaternary times, was dated by electron spin resonance (ESR). Enamel and dentine were separated giving the following archeological doses (AD): (4.0 ± 0.8) and (11 ± 2) Gy, respectively. This difference was explained by the higher content of Uranium in dentine (25.1 ± 0.3) ppm as compared to enamel (0.37 ± 0.03) ppm. Taking account of the internal dose contribution to the AD, the age obtained is (6.7 ± 1.3) ky BP for dentine and (5.0 ± 1.6) ky BP for enamel.

Introduction

The study of stable paramagnetic centers created by radiation in solids has proved extremely useful for radiation dosimetry and dating. The subject of electron spin resonance (ESR) dosimetry and dating has been extensively reviewed in the proceedings of international conferences (Ikeya, 1985; Desrosiers et al., 1996), books (Ikeya, 1993, Leute, 1980) and articles (Ikeya, 1988, Mascarenhas et al., 1982). The dating technique is based on the fact that fossil material will receive radiation from uranium, thorium, potassium and their decay products plus cosmic radiation during the period it has been buried, leading to an absorbed dose. Several insulating materials, such as bone (Caracelli et al., 1986, Schramm and Rossi, 1996), teeth (Duran et al., 1985), shells (Baffa and Mascarenhas, 1985a, Baffa and Mascarenhas, 1985b), carbonates (Ikeya et al., 1984), aminoacids (Alexandre et al., 1992) and sugar (Silveira and Baffa, 1995), can be analyzed by ESR, and their spectra determined to assess the presence of paramagnetic centers. To summarize, the advantages of this technique are that it is relatively simple, requires a small quantity of material, has a wide range of applicability (from a few hundreds to million years). Another important feature of this dosimetric/dating technique is that the information is not destroyed during the measurement process and in situ measurements can also be performed with appropriate instrumentation (Furusawa and Ikeya, 1990).

A pre-molar of a Toxodon platensis (sp), a large mammal that inhabited the forests of Southeast Brazil during quaternary times, was found during paleontological and archeological excavations of the “Ponta de Flecha” cave, located at the Upper Ribeira Valley Karstic province, South of São Paulo State (24°38′38″S, 48°41′08″W). The cave is mainly of vertical development with morphology of a vadose canyon. Its entrance represents the sinkhole of an ancient polygonal karst depression. Along horizontal steps of the main vertical entrenchment clastic sediment has been trapped. This sediment is very unsorted and rich in organic debris, including bones of varied size. This material has been injected into the cave by the centripetal drainage of the closed polygonal depression. This centripetal drainage basin is not active due to its destruction by surface erosion. The ancient sinkhole of this basin is today on a hill crest position due to a topographic inversion process, as described in Karmann (1994). Together with the Toxodon teeth, bones and teeth of the Megatheroidea family have been identified. Our investigation of the age of the Toxodon tooth represents the first dating of an extinct Pleistocene fauna of Southeastern Brazil. This information will be important in paleoclimate studies in this region showing a new application of ESR dating applied to geological problems.

Section snippets

Materials and methods

The sample was cleaned from soil and calcite incrustations, and a block measuring (20 × 10 × 8) mm containing dentine and enamel was removed with a low speed refrigerated cutting disc. The enamel layer being approximately 1 mm thick was easily removed from dentine with a stainless steel scalpel. Attempts were made to use the sample in this form, but the inconvenience of reproducing sample orientation after each measurement to avoid error in the signal amplitude determination led us to crush it

Results and discussions

Fig. 1 shows the ESR signals from the enamel and dentine, before and after the irradiation. The ESR signal from both dentine and enamel had showed a signal with axial symmetry with $g_{⊥} =2.002$ and $g_{∥} =1.997$ , values typical of ESR signals produced in hydroxyapatite by irradiation. Previous studies indicate that this signal is due to the CO₂⁻ paramagnetic center created in hydroxyapatite (Schramm and Rossi, 1996). The signal growth as a function of artificial irradiation from ⁶⁰Co is shown in Fig. 2

Acknowledgments

The authors are indebted to Professor Shirley Schreier who made available the ESR spectrometer, to C.F.O. Graeff for the improvements in the spectrometer and discussions, A.M.O. Kinoshita for help with some measurements, the Radiotherapy Department of hospital das Clínicas-FMRP-USP for the irradiation of the samples, S.H Tatsumi for the the TLD dosimetry, and M. H. Kakazu and J.E.S. Sarquis from IPEN-CNEN for the Uranium content analysis. Partial financial support was provided by the Brazilian

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Citation Excerpt :
Holocene ages were identified by the ESR method for Toxodontinae fossils from Abismo Ponta da Flecha, a Kasrt deposit in the Ribeira Valley, Sao Paulo State, Brazil. The results obtained at 6700 ± 1300 and 5000 ± 1600 for Toxodon platensis teeth are the youngest ages of the extinct Quaternary megafauna (Baffa et al., 2000). However, they were dated by the 14C AMS method with ages of 13 ka BP and minimum Late Pleistocene age for these specimens (Neves et al., 2007).
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The present study reports the results of the first direct Electron Spin Resonance (ESR) dating study of Homo antecessor, the oldest known hominin species identified in Western Europe. The analysis of a tooth (ATD6-92) from TD6 unit of Atapuerca Gran Dolina (Spain) following a “semi non-destructive” procedure provides a final age estimate ranging from 624 to 949 ka, which covers all possible uranium uptake scenarios. Last, the additional magnetostratigraphic data collected within TD6 enables to further constrain the initial ESR chronology and to propose an age of between 772 and 949 ka for Homo antecessor, in agreement with previous dating works. Although our new results do not refine the existing chronology of TD6 unit, they nevertheless support the antiquity of H. antecessor, which pre-dates the estimated divergence age of modern and archaic human lineages based on genetic evidence.
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ESR dating of a toxodon tooth from a Brazilian karstic cave

Abstract

Introduction

Section snippets

Materials and methods

Results and discussions

Acknowledgments

Appl. Radiat. Isot.

Palaeogeography Palaeoclimatology Palaeoecology

Appl. Radiat. Isot.

ESR dating of fossil shells from Sambaquis (Brazilian shell mounds)

Radiation quality dependence of ESR dating of bones and shells

A high resolution Holocene pollen record from Lago Pires, SE Brazil: vegetation, climate and fire history

Journal of Paleolimnology

Evidence of dry and cold climatic conditions at glacial times in tropical Southeastern Brazil

Quaternary Research

Electron spin resonance dosimetric properties of bone

Health Phys.

Dosimetry of irradiated human teeth