K-Ar and Rb-Sr ages of Cretaceous glauconites from Jaisalmer basin, Rajasthan

The importance of dating glauconites is that they art: formed under low sed imentation rates connected with marine transgression and are commonly assoc iated with unconformities and other stratigraphic breaks. This paper presen ts the first quantitative age estimation of glauconite samples separated fr om subsurface cores of Goru and Pariwar Formations of Jaisalmer basin, Raja sthan, India. SEM studies, X-ray diffraction patterns and high K2O content (6.8 to 7.4%) of these samples indicate that they are highly evolved and ar e ideal for isotopic dating. The Rb-Sr age of 108+/-5 Ma and avenge K-Ar age of 103+/-3 Ma obtained for the glauconites from the Goru Formation are indistinguishable within error and agree with their biostratigraphic age. Glauconites from the upper most part of the Pariwar Formation give an avenge K-Ar age of 106+/-3 hla (early Albian), which is slightly lower than their biostratigraphic age.