An alternate perspective on the opening and closing of the intracratonic Purana basins in peninsular India

Abstract

absolutely unaffected and found as ‘fresh limestones’ as is directly evident from their micritic nature with clayey intercalations under microscope and the laminations/bandings visible even on a handspecimen scale besides their geochemical attributes (lack of influence of kimberlite bulk-geochemistry). Such limestone xenoliths must have been incorporated into the kimberlite magma at a much shallower depths (close to the surface), thereby necessitating their survival and non-reactiveness, and certainly not ‘exhumed’ being entrapped in the kimberlite as expressed by Prof Kale. We also wish to point out that the presence of ‘fresh limestones’ in a kimberlite is not a ‘remarkable’, aspect but in fact has been well-documented and quite familiar to those involved in research on kimberlites. For example, ‘fresh limestone xenoliths (some of them with profuse conodont fossils) have been recovered from the kimberlites occuring in the Slave (Cookenboo et al. 1998; Geology, v.26, n.5, pp. 391-394) and Saskatchewan (Lefebvre and Kurszlaukis, 2008; Journal of Volcanology and Geothermal Research v.174, pp. 171-185) cratons of Canada and constitute the only solid evidence that sea water inundated, in the geological past, in the now exposed cratons. Likewise, fossiliferous limestone xenoliths derived from the kimberlites of the Baffin Island, Nunavut, Canada (Zhand and Pell, 2014; Canadian Journal of Earth Sciences v.51, pp. 142-155) confirm the Paleozoic cover in this domain. We do agree with Prof. Kale that despite more than a century of study many apects of the Purana basins still remain open to debate. We also deeply appreciate the remarkable efforts made in recent years by Prof Abhijit Basu and his co-workers for reviving interest in these fascinating basins.