RECORD OF EARLY BATHONIAN AMMONOIDS FROM KACHCHH, INDIA: BIOSTRATIGRAPHIC AND PALAEOBIOGEOGRAPHIC IMPLICATIONS

We present here the significance of the Early Bathonian (Middle Jurassic) ammonoid record on the South Tethyan Margin through discovery of the genera Zigzagiceras Buckman, Procerozigzag Arkell, Siemiradzkia Hyatt, Berbericeras Roman, Parkinsonia Bayle, Ebrayiceras Buckman, Micromphalites Buckman and ?Telermoceras Arkell, in association with Prohecticoceras Spath, Procerites Siemiradzki, Cadomites Munier-Chalmas, Oecotraustes Waagen and Phylloceras Suess from Kachchh, western India. The exposed similar to 24 m thick sedimentary succession is predominantly composed of whitish grey limestone with shale/silt/marl interbeds exposed in the Nara Dome, Mainland Kachchh. This interval has been earlier considered to be the part of hiatus or ammonoid devoid on the entire South Tethyan Margin including the Kachchh Basin. The preliminary generic level taxonomic determination, their stratigraphic ranges and dominance of individual taxon allow the formulation of Siemiradzkia Procerozigzag assemblage. Most of the genera of this assemblage are well known from Zigzag Zone of Early Bathonian age in the Submediterranean province, which facilitates the precise dating of the studied succession. The presence of diverse Submediterranean ammonoid fauna in Kachchh locality of the Indian subcontinent is probably due to the expansion event during the eustatic rise in Early Bathonian. The contribution would prove a milestone for the workers on the marine Jurassic System by way of (1) filling the gap of knowledge about Early Bathonian interval for dating and intrabasinal correlation on the South Tethyan Margin, (2) its long distance correlation with Submediterranean and NW European counterparts and (3) differentiation of Early Bathonian transgressive event with a deepening phase in the Kachchh basin already recognized within the Early Bathonian Zigzag Zone, most probably in the Macrescens Subzone of the Submediterranean realm and NW European standard bio-chronostratigraphic scheme.