Late-Cenozoic Magnetostratigraphy: Comparisons with Bio-, Climato-, and Lithozones

Abstract

A workshop conference entitled “Late Cenozoic Magnetostratigraphy: Comparisons with Bio-, Climato-, and Lithozones” took place in Tokyo and Otsu, Japan, between October 28 and November 1, 1974. It was organized by G. J. Kukla and H. Nakagawa as an outcome of the PA-70-17 Project of the International Geological Correlation Programme, launched in 1970 by the International Union of Geological Sciences. The workshop was supported by the Japanese Society for the Promotion of Science, by IGCP, and the National Science Foundation (of the United States). Out of 70 participating geophysicists, geologists, and paleontologists, 37 attended in person, while the remaining 33 contributed by mail. 1 1 The participants (see Appendix) either attended the conference in person or contributed by mail. They also checked and corrected the draft version of the report, which was adjusted to meet their requirements; in this way it is co-authored by 70 scientists. Prior to the conference a questionnaire was distributed in order to collect opinions on several issues. The workshop's objective was to tackle problems in the recognition of depositional polarity and to review the relationship of magneto-stratigraphic units with radiometric data and with regional bio-, litho-, and climatostratigraphic systems of the Pliocene and Pleistocene. The principal conclusions of the conference were summarized as follows: 1. (1) The only practical (though not infallible) way of demonstrating the validity of interpreted depositional polarity and magnetostratigraphic zonation is to reproduce the results in parallel, widely separated sections with different lithology and sedimentation rates. 2. (2) The hazard of unrecognized postdepositional normal overprints must be recognized and considered in all attempted correlations. Multiple sampling of parallel sections and consistency checks of magnetic data are a prerequisite for correct results. 3. (3) Continuous sequences with high sedimentation rates, such as those which originated in subsiding basins, are viewed as prospective candidates for international stratotypes of the Pliocene and Pleistocene. The investigation of such deposits should be accelerated. 4. (4) Magnetostratigraphy must follow basic stratigraphic principles. Magnetic zones should be clearly defined and locally labeled, whether or not their correlation with paleomagnetic chronology appears possible. 5. (5) Improved data on absolute age of reversals are needed. For that purpose, multiple K Ar and fission-track analyses of key volcanic layers should be performed on a continuing basis.