Sunday, August 1, 2010

The value of electron spin resonance (ESR) for probing impact markers in the stratigraphic record, as well as species extinctions and changes in geochemistry across such boundaries, is well proven and explained in the following three papers:

(1) "Electron spin resonance of 65-million-year-old glasses and rocks from the Cretaceous-Tertiary boundary,"  D.L. Griscom, V. Beltrán-López, C.I. Merzbacher, and E. Bolden, in Selected papers from the 18th International Congress on Glass, San Francisco, CA, July 10-15, 1998, R.A. Weeks, Ed., J. Non-Cryst. Solids 253 (1999) 1-22.

(2) “ESR Spectra of Limestones from the Cretaceous-Tertiary Boundary: Traces of a Catastrophe,” D.L. Griscom and V. Beltrán-López, Proc. International Symposium ESR Dosimetry and Dating, Osaka, Japan, October 2001. Advances in ESR Applications 8 (2002) 57-64.

(3) “New geochemical insights from electron-spin-resonance studies of Mn2+ and SO3- in calcites: Quantitative analyses of Chicxulub crater ejecta from Belize and southern México with comparisons to limestones from distal Cretaceous-Tertiary-boundary sites,” D.L. Griscom, V. Beltrán-López, K.O. Pope, and A.C. Ocampo, in Impact Markers in the Stratigraphic Record, Impact Studies, vol. 3, C. Koeberl and F. Martínez-Ruiz, Eds. (Springer Verlag, Heidelberg, 2003) pp. 229-270.

Often termed electron paramagnetic resonance (EPR), which is a more precise terminology when the measured spectra arise from weakly-interacting unpaired electrons, the ESR technique is also applicable to weakly interacting ferro- or ferri-magnetic minerals in small particle sizes.  In the latter case, the experiment is called ferromagnetic resonance (FMR) ...even though the spectra are recorded in the exact same way as EPR.  The following encyclopedia entry provides a short, but sufficiently technical, review of applications of ESR/EPR to paramagnetic species in crystals and glasses:

(4) “Amorphous materials: Electron spin resonance”, D.L. Griscom, in Encyclopedia of Materials: Science and Technology, (Elsevier Science Ltd., 2001) 179-186.

Application of ESR/FMR to ferro- and ferri-magnetic particles precipitated in natural glasses (and synthetic glasses modeling natural ones) is reviewed in the following article:

(5) "Ferromagnetic resonance of precipitated phases in natural glasses," D.L. Griscom, J. Non-Cryst. Solids 67 (1984) 81-118.

The slides below were adapted from work described in publications (2) and (3), which specifically treat the Cretaceous-Tertiary or K-T Boundary (recently changed to Cretaceous-Paleogene or K-Pg Boundary) corresponding to the impact of an asteroid about 66 million years ago that brought about the extinction of the dinosaurs and many other species.  The stratigraphic columns studied comprised limestones that were on the sea floor before, during, and after the time of the impact.  However, also examined were ejecta clasts and fire-ball accretionary lapilli created by explosive excavation of the 180-to-200 km-diameter crater buried beneath México’s Yucatán Peninsula.  See (6) for latest quasi-consensus on the bases for linking this impact to the mass extinction.

(6) “The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary,” Peter Schulte, Laia Alegret, Ignacio Arenillas, José A. Arz, Penny J. Barton, Paul R. Bown, Timothy J. Bralower, Gail L. Christeson, Philippe Claeys, Charles S. Cockell, Gareth S. Collins, Alexander Deutsch, Tamara J. Goldin, Kazuhisa Goto, José M. Grajales-Nishimura, Richard A. F. Grieve, Sean P. S. Gulick, Kirk R. Johnson, Wolfgang Kiessling, Christian Koeberl, David A. Kring, Kenneth G. MacLeod, Takafumi Matsui, Jay Melosh, Alessandro Montanari, Joanna V. Morgan, Clive R. Neal, Douglas J. Nichols, Richard D. Norris, Elisabetta Pierazzo, Greg Ravizza, Mario Rebolledo-Vieyra, Wolf Uwe Reimold, Eric Robin, Tobias Salge, Robert P. Speijer, Arthur R. Sweet, Jaime Urrutia-Fucugauchi, Vivi Vajda, Michael T. Whalen, and Pi S. Willumsen, Science 5 March 2010 327: 1214-1218 [DOI: 10.1126/science.1177265]