New Ammonoid evidence for theJurassic/Cretaceous boundary in Kachchh Western India, and long distance correlation with Southern Europe

Abstract

The Jurassic/Cretaceous boundary in the ammonoid rich classic Jurassic region of Kachchh could not be precisedfor well over a century (1871–1991) due to the absence of ammonoids or other guide fossils of the Berriasian. Our present studies now firmly establish the basal Berriasian in Kachchh through close or identical ammonoids Aspidoceras cf. taverai Checa,, Argentiniceras loncochensis ( Steur)), Spiticeras cf. ducale ( Matheron)) and Berriasella sp. Relatively, among these, A. taverai Checa is considered a good marker of the basal Berriasian Jacobi Zone in the Subbetic Spain. Besides precising the Jurassic/Cretaceous boundary in Kachchh, A. cf. taverai Checa also allows long distance correlation to the precision of a single ammonoid zone across the Tethys between Kachchh (Indo-East-African province) on the south/east margin of the Tethys and Spain (Mediterranean province) on the north/west margin of the Tethys. The episodic presence of the ubiquitous Tethyan Aspidoceras in Kachchh during the Upper Kimmeridgian and basal Berriasian, interestingly, is found to correspond with phases of the eustatic rise of the Vail Cycles LZA 4.6 and LZB 1.4 which in turn suggests significant ammonoid faunal expansion events during the said intervals towards South and East from the Mediterranean to the Indo-East-African province.