Miocene geochronology: Methods, techniques, and results

Introduction. Prior to 1990, time scale syntheses for the Miocene Epoch were poorly documented with geochronological data. A few calibration points were obtained from glauconies and from a limited number of volcaniclastic layers found in sedimentary sequences. Often, these dated levels had scarce or imprecise stratigraphic attributions, and the resulting ages were more or less properly evaluated. However, in the past 10 years, geologists have shown that appropriate material for dating can be found in many areas worldwide in Alpine orogenic belts. This is one of the major reasons why the present research project has been undertaken, and this volume planned, when convincing results have begun to accumulate. In this paper, we shortly review the methods, techniques, and results obtained in the laboratories which contributed to this study. This technical text is also for the use of non-experts who may sometimes be confused by the variety and apparent complexity of the information given in geochronological studies but who may also wish to have some basic information for judgement about the significance and reliability of results quoted in the literature. We have used here and in the volume, a terminology adapted from the one recommended under the aegis of the Subcommission on Geochronology of IUGS (Odin, 1995).