2006 Philadelphia Annual Meeting (2225 October 2006)
Paper No. 90-11
Presentation Time: 4:15 PM-4:30 PM


BLACKWELL, Bonnie A.B.1, KHAN, Hermain S.2, HASAN, Maysun M.2, BLICKSTEIN, Joel I.B.2, SKINNER, Anne R.3, CHAUHAN, Parth R.4, and PATNAIK, Rajeev5, (1) Department of Chemistry, Williams College, Williams College, Williamstown, MA 01267, (2) R.F.K. Science Research Institute, 7640 Parsons Bvd, Flushing, NY 11367, hermain_khan@gmail.com, (3) Dept. of Chemistry, Williams College, Williamstown, MA 01267, (4) Stone Age Institute & CRAFT Research Center, Indiana University, 1392 W Dittemore Road, Gosport, IN 47433, (5) Geology Dept, Punjab University, Chandigarh, 160014, India

Crocodilians, including crocodiles, alligators, and gavials, are poikilothermic quadrupeds that evolved in the Triassic. Modern crocodilians' wide distribution across tropical and subtropical zones and their evolutionary stability make them valuable for dating large river systems and nearshore marine deposits. Reptilian tooth enamel has never been dated by ESR.

In the Siwalik Group, India, crocodylian and numerous other fossils have emerged from alluvial fan deposits. In central India, crocodylian teeth associated with hominid crania and Paleolithic tools also occur in the Narmada River system's deposits. Gavialis gengeticus, the gavial, typically prefers swift rivers in tropical woodlands, while Crocodylus palustris usually inhabits swamps. Although a strongly radiation-sensitive hydroxyapatite (HAP) signal was present in the crocodylian enamel, Fe3+ interference peaks reduced the accumulated dose and ESR age accuracy. Signal subtraction showed that underneath the Fe3+ signal, the HAP peak was growing in response to radiation. The crocodilians also had broader HAP peaks then typical in mammalian, which could indicate a fast relaxation time due to the Fe3+ interference. The Fe3+-induced baselines that exponentially decreased with added dose provided the first evidence that radiation may reduce Fe3+ to Fe2+. Other Fe-rich teeth must be analyzed further to see if this is a consistent tend with Fe3+ interference.

Modern alligator teeth show a strong ESR radiation-sensitive signal and do not contain significant Fe3+ to intefere with the ESR signal. Crocodylian teeth with low Fe3+ are datable using the same preparation protocol as that used for mammalian teeth. Therefore, dating crocodilians can provide detailed paleoecological data, to constrain the timing for paleoecological and sedimentological shifts as well as significant archaeological and paleontological sites.

2006 Philadelphia Annual Meeting (2225 October 2006)
General Information for this Meeting
Session No. 90
Archaeological Geology
Pennsylvania Convention Center: 109 AB
1:30 PM-5:30 PM, Monday, 23 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 235

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