Postęp w badaniach geochronologicznych

Abstract

ON THE DEVELOPMENTS IN GEOCHRONOLOGY Summary In 1982, the publishing house J. Wiley and Sons has published a monograph "Numerical Dating in Stratigraphy", edited by G.S. Odin. The monograph, published in two volumes, contains papers written by authors from 23 countries. It is mainly devoted to the use of minerals formed in sediments, especially glauconite, as chronometers, and the developments in this discipline are discussed in a number of papers. At the same time, several authors emphasize the use of various chronometers, often taken at points with imprecise or even debatable biostratigraphic datings; in the hitherto compiled radiometrie time scales. The cited examples include those of North American chronometers, dated on the basis of vertebrate remains found in neighbouring sedimentary rocks. There are also emphasized difficulties in biostratigraphic dating of igneous rocks of plutons. Because of the above difficulties there appeared a tendency to com pile numerical time tables on the basis of chronometers from stratotype sections, i.e. almost exclusively European ones. Up to the present there were put forward several serious objections in relation to the use of glauconite for datings made by the K/Ar method. The objections are carefully analysed in this monograph and the ways to eliminate the resulting errors are given. In concluding papers the authors formulate a principle according to which not the oldest but the youngest ages obtained on the basis of glauconite should be treated as reliable. In the past the former were treated as reliable and the latter questioned because of the possibility of easy escape of argon from this mineral (a phenomenon shown here to be rather rare). In turn, the oldest ages appeared to be influenced by some content of argon in parent matter, from which glauconite originated in marine environment. In the cited review of this monograph, W.B. Harland highly appreciated it as important contribution to the developments in geochronology.