Volcanic flows and tuffs interbedded with ammonite-bearing sediments
directly correlatable with the stratotype section of the Bajocian stage
have been dated for the first time within the Caucasus area. Three
samples, each from a different section, allowed separation of
well-preserved brown hornblende; these are considered reliable
geochronometers in a region where subsequent volcanic activity occurred.
The dated separates are V139: a volcanic layer probably near the base,
V142 another layer near the top of the Lower Bajocian substage; V141 a
boulder from a latest Bajocian volcanic conglomerate. From bottom to
top, apparent ages at 173.5 +/- 2.6, 164.8 +/- 2.5 and 167.1 +/- 1.9 Ma
(analytical uncertainty, 95% confidence level) respectively, can be
calculated. The consistency of the results is obtained if the dated
boulder is interpreted as derived from an underlying layer, The
Bajocian-Bathonian boundary is much younger than commonly accepted and
younger than 164 Ma.