Absolute dating of igneous rocks of Crimea as reference formations for Bajocian

Because of the fairly homogeneous petrographic and chemical character of the assemblages of the Crimean igneous rocks (plutons), they can be used for an accurate geochronological correlation of the Middle Jurassic. Potassium-argon ages have established the ages of many of the Crimean intrusives as averaging 159 ± 3 m.y. Hypabyssal and effusive rocks (the Bajocian formations) genetically associated with the Crimean intrusives can therefore also be dated as 159 ± 3 m.y. Limits of the Triassic Period should be left at 135 and 180 (perhaps 185) m.y. Younger age determinations of 106 ± 5 m. y. suggest a regional rejuvenation of some of the Crimean intrusives in connection with low temperature hydrothermal metamorphism. Additional work should be carried out to further elucidate this fact. — R.M. Hutchinson.