Relaxations in complex materials: thermally stimulated depolarization currents (TSDC) technique applied to a lithological problem

摘要

A lithological contact at the Pertigalete sedimentary sequence, Cretaceous Northeastern Venezuela, has been dielectric characterized by using Thermally Stimulated Depolarization Currents (TSDC) technique. The samples studied were collected near a contact identified as that between Chimana (CH) and Querecual (QC) formations. The complex spectra obtained in the temperature range from 77 K to 320 K indicate a remarkable difference between CH and QC series. Drying and rehydration treatments performed on these samples showed that the whole TSDC spectra could be associated to physisorbed moisture, trapped on different sites in the material. The Direct Signal Analysis (DSA) method was applied to find, for the low (from 77 K to 200 K) and high (from 200 K to 320 K) temperature zones of these spectra, the number of relaxation modes. As one approaches the contact, the variation in the mean energy values of these relaxations also testifies the existence of a transitional change of lithologies. In the same lithological zone where such variation was observed, Natural Remanent Magnetization (NRM) experiments, also performed to characterize lithologies in the sedimentary sequence, indicate significant changes. These results seem to point out at the potential of TSDC technique as an alternative means to characterize lithologies and stratigraphic discontinuities in a sedimentary sequence.