Ammonite Biozonation of the Middle-Late Jurassic Sediments with Special Reference to Keera and Jara Dome, Kachchh District, Gujarat

A more refined ammonite biostratigraphy than hitherto proposed for the Middle to Late Jurassic sediments of Keera and Jara domes, Kachchh district, Gujarat is presented in this paper. Ammonite based six biozones (Triangularis, Formosus, Anceps, Athleta, Maya and Helenae) and thirteen subzones (Madagascariensis, Diadematus, Semilaevis, Anceps, Eucyclum, Singulare, Kleidos, Athleta, Lalandeanum, Semirugosus, Maya, Helenae and Kranaus) are distinguished in ascending oder for Pre-Callovian-Oxfordian rocks of Kachchh. The Triangularis Biozone is assigned to Pre-Callovian/Late Bathonian, the Formosus to Early Callovian, the Anceps to Middle Callovian, the Athleta to Late Callovian, the Maya to Early Oxfordian and the Helenae to Middle Oxfordian.