K-Ar and Rb-Sr Ages of Cretaceous Glauconites from Jaisalmer Basin, Rajasthan

The importance of dating glauconites is that they are formed under low sedimentation rates connected with marine transgression and are commonly associated with unconformities and other stratigraphic breaks. This paper presents the first quantitative age estimation of glauconite samples separated from subsurface cores of Goru and Pariwar Formations of Jaisalmer basin, Rajasthan, India. SEM studies, X-ray diffraction patterns and high K 2 O content (6.8 to 7.4%) of these samples indicate that they are highly evolved and are ideal for isotopic dating. The Rb-Sr age of 108 ± 5 Ma and average K-Ar age of 103 ± 3 Ma obtained for the gtauconites 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 average K-Ar age of 106 ± 3 Ma (early Albian), which is slightly lower than their biostratigraphic age.