Electron spin resonance characterization of calcretes from Thar desert fordating applications

Results of a study to characterize electron spin resonance (ESR) signals fr om naturally occurring carbonates from Thar desert are reported. Three radi ation induced signals at g = 2.0071 (signal A, very weak), g = 2.0012 (sign al B) and g = 2.0003 (signal C) with linewidths ranging from 0.5-2 G are se en. A broad signal (BL) with linewidth 7 G is also seen at 2,0038, Detailed ESR experiments involving (1) sensitivity of ESR signals to ionizing radia tion, (2) intensity variation of ESR signals with microwave power at differ ent temperatures, (3) analysis of acid insoluble residue to estimate the in terference from ESR signals of silicate fraction, and (4) X-ray diffraction analysis (to study possible phase changes on heating), led to the choice o f signal BL for dating. Experiments on acid insoluble residue revealed that signal C has a contribution from the E-1' centre of quartz and signal B is the parallel component (g(parallel to)) of the E-1' centre, Paleodose esti mates based on signal BL are stratigraphically consistent. (C) 2000 Elsevie r Science Ltd. All rights reserved.