DOI: 10.5176/2251-3361_GEOS12.14
Authors: Satish J. Patel and Jaquilin K. Joseph
Abstract:The Callovian-Oxfordian Gangta bet succession shows transgressive-regressive cycles of deposition that corresponds to the change in the relative sea level as well as regional factors. The succession of the Gangta bet member of the Khadir Formation comprises of lower siliciclastic and upper carbonate sequence representing eight facies association namely, ferruginous sandstone, shale, cross bedded sandstone, sandy shale, conglomerate, intercalated calcareous sandstone-siltstone-shale, ripple marked sandstone, intercalated limestone-shale facies. The calcareous sandstone-siltstone-shale, ripple marked sandstone and sandy shale are bioturbated and consists of 27 ichnospecies of 19 ichnogenera. These trace fossils show recurrent pattern of occurrence exhibiting Cruziana ichnofacies type condition. The intercalated sandstone-siltstone-shale and the limestone-shale facies consist of ammonites belonging to the Athleta, Maya and Kranaus-helenae zones suggesting Late Callovian to the Middle Oxfordian age. These sediments also represents three 3rd order transgression-regression cycles (RST-I and TST-II) in an overall transgressive phase of 2nd order. The trace fossils and sedimentary characteristics helped in delineating the stratigraphic surfaces representing the flooding and regressive surfaces. The present Callovian-Oxfordian sedimentation patterns with the ammonite zones across the world indicate that the global sea level and the regional factors were responsible for the changes in the paleo-depositional conditions in the Gangta bet.
Keywords:ichnology; lithofacies; sequence stratigraphy; Jurassic; Gangta Bet; Eastern Kachchh; India
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