Krishna J., Pandey B., Ojha J.R. (2009) Gregoryceras in the Oxfordian of Kachchh (India): diverse eventful implications // Geobios, doi:10.1016/j.geobios.2008.03.005 (in press)
The Kachchh Oxfordian ammonoid stratigraphic record for over 150 years remained restricted largely to Early Oxfordian condensed oolitic facies in the relatively distal Mainland Kachchh. Recently, it has been enlarged with the discovery in 1994 of over 200 m thick uncondensed Middle to Late Oxfordian succession at Kantkote in the proximal part of the basin. Apart from abundant Perisphinctinae and Mayaitinae, a 10 m thick sediment interval in the lower half of the above succession yielded a few examples of Gregoryceras. The specimens are here identified as G. gr. devauxi Bert and Enay and in view of their association with Larcheria subschilli (Lee) are assigned to the Middle Oxfordian Subschilli Horizon of Schilli Subzone. Gregoryceras distribution southern of the equator in Kachchh, Chile, Mexico and Madagascar all within 35° latitude marks the southern limit of its latitudinal expansion during the 1st order MFS (Maximum Flooding Surface) of the Schilli Subzone of the Kachchh Toarcian – Albian Sequence. The maximum ammonoid diversity, density and frequency of the Kachchh 1st order sequence coupled with dominance of mayaitins and perisphinctins suggest >20 m depth in the Gregoryceras interval. Distinctly greater bathymetry in the 200 km distally away basinal part causes sediment starved situation, and explains the Middle Oxfordian to early Early Kimmeridgian submarine non-depositional hiatus in the Mainland Kachchh.