CALLOVIAN AMMONITES FROM A CONDENSED HORIZON IN THE KULDHAR MEMBER OF THE NORTHEASTERN JAISALMER BASIN (RAJASTHAN, INDIA) AND THEIR BIOSTRATIGRAPHIC IMPLICATIONS

Previously, Callovian ammonites in the Jaisalmer Basin of western India were mostly known from the type locality of the Kuldhar Member at the Kuldhar River Section in the southwestern part of the basin. At this locality, the succession can be subdivided into six ammonite zones and subzones. For the first time, the present article describes ammonites collected from a river section (N27 degrees 07'06.60 '', E71 degrees 05'24.72 ''), 1 km west of the village Kanod. In contrast to the type section, the Kuldhar Member in the northeastern Jaisalmer Basin is strongly condensed. Most of the ammonites occur within a 30-cm-thick bed of sandy, bioclastic siltstone with bored concretions. They belong to the genera Hecticoceras, Eucycloceras, Idiocycloceras, Sivajiceras, Obtusicostites, Kinkeliniceras and Hubertoceras. The assemblage is time-averaged ranging from the late Early Callovian to the early Late Callovian in age. The condensed nature of the sediment is also evident by abundant oysters and serpulids encrusting the ammonite shells. In total, twelve ammonite taxa are described and illustrated with a discussion on their biostratigraphic potential.