CORRELATION OF LOWER PALEOZOIC K-BENTONITES: IMPLICATIONS FOR TECTONO-STRATIGRAPHIC CORRELATION IN EUROPE AND NORTH AMERICA

摘要

Continuing studies of Ordovician and Silurian K-bentonites in Europe and North America show that many of them are distributed regionally and thus can serve as important marker horizons for stratigraphic correlation. Two examples of projects underway are from the Carnic Alps in Austria and the North American midcontinent. Lower Paleozoic K-bentonites occur in a region of the Carnic Alps thatis characterized by a metamorphic overprint ranging from anchizone to epizone. As a consequence of this thermal history, the illite/smectite clay mineralogy that commonly characterizes such beds has been altered to illite and chlorite, similar to the clay minerals found in associated mudrocks. The volcanogenic origin of these beds is confirmed, however, by the presence of primary magmatic phenocrysts of biotite, apatite and zircon. In some samples the zircons show evidence of magmatic resorption.