LIGHT-SENSITIVE ELECTRON SPIN RESONANCE DATING OF QUARTZ SEDIMENT

Electron Spin Resonance dating of quartz is a technique that allows for burial-time age determination on sediments that have received very long light exposure. Its accuracy has been verified through comparison with radioisotopic and palaeomagnetic methods in coastal settings (lacustrine and marine) (Rink et al., 2007). A secure age range of 1 to 1.4 million years ago was established. More recently sediments from ancient coastal settings in Florida were studied with the method, yielding ages ranging from 0.4 to 2.3 million years ago, and these were concordant with expectation based on the geomorphological settings within the state (Burdette, 2010, Burdette et al., 2011). Two radiation defects in quartz yield the light-sensitive, radiation sensitive signals: a titanium atom on a silicon site and an aluminum atom on a silicon site. Internal concordance of equivalent dose results from these two centers assures the long bleaching time was attained at the time of last light exposure (titanium site: about 10-20 days of sunlight, aluminum site: about 100 days of sunlight). An unbleachable residual signal on the aluminum site must be subtracted to obtain the equivalent dose, and this value is obtained by laboratory light exposures. Zero-age titanium signals, and residual-size aluminum signals were found for modern beach sediments. This method allows for long-range dating of coastal sediments into the Lower Pleistocene and into the Pliocene with a current precision of about 15-20%.

References:

Burdette, K.E. (2010) Pleistocene Stratigraphy and Optical Dating of Surficial Sands in Florida’s Coastal Plain and Central Highlands: Implications for Sea-Level and Shoreline Ages. Ph.D. Thesis, McMaster University, Hamilton, Ontario, Canada.

Burdette, K.E., Rink, W.J., Mallinson, D.J., Means, G.H., Parham, P.R. (2011, in revision) Electron spin resonance dating of marine, estuarine and aeolian sediments in Florida, USA. Quaternary Geochronology

Rink, W.J., Bartoll, J., Schwarcz, H.P., Shane, P. and Bar-Yosef, O. (2007) Testing the reliability of ESR dating of optically exposed buried quartz sediments. Radiation Measurements 42, 1618-1626.