Early Callovian Nannofossils from Jara Dome, Kachchh, Western India

A moderately preserved but diverse nannofossil assemblage comprising over twenty five species has been recovered from the calcareous mudstone of the basal part of Jara Dome in the northwestern part of Kachchh mainland. The assemblage contains Ansulasphaera helvetica, Axopodorhabdus cylindratus, Calohthus martelae, Crepidolithus crassus, Cyclagelosphaera margerelii, Watznaueria barnesae, W. fossacincta, W. manivitae, W. ovata, W. britannica, W. leucasii, Watznaueriasp.I, Watznaueriasp.2, Discorhabdussp., Ethmorhabdus gallicus, Faviconusmulticolumnatus, Hexapodorhabdus cuvillieri, Lotharingws crucicentralis, L.sigUlatus, Podorhabdus grassei, Podorhabdus sp., Stephanolithion bigotii bigotii, S. hexum, S. octum, S. speciosum, Thoracosphaera spp., Triscutum beaminsterensis, Timorella sp. and Zeugrhabdotus erectus and shows predominance of Watznaueria spp. The occurrence of the agediagnostic taxa A. helvetica, S. bigotii, and S. hexum in the assemblage allows correlation with Ansulasphaera helvetica zone (NJ 12) of Bown et al. (1988) of the Early Callovian age. The coeval nannofossil assemblage of A. helvetica zone has also been documented from the basal part of the Kuldhar section of the Jaisalmer area. The present findings are considered significant because of limited records of Jurassic nannofossils from the Indo-Pacific region.