Can the occurrence of the ammonite genus Hildoglochiceras Spath serve as an early Tithonian marker event?

• Published in: Palaeoworld Vol. 34; no. 5; p. 200945
• Main Author: Jain, Sreepat
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2025
• Subjects: Hildoglochiceras; Himalayites; Jaisalmer Basin; Late Jurassic; western India; Himalayites; Jaisalmer Basin; western India; Hildoglochiceras; Late Jurassic
• ISSN: 1871-174X
• DOI: 10.1016/j.palwor.2025.200945

The 20–40° southern latitude-delimited Hildoglochiceras fauna enables correlation of South Tethyan early Tithonian rocks along the northwestern peri-Gondwana margin stretching from Madagascar to Nepal. Herein, a new assemblage of the ammonite genus Hildoglochiceras Spath is recorded from the Rupsi Shale Member of the Baisakhi Formation in the Jaisalmer Basin, western India, and consists of H. cf. latistrigatum (Uhlig), H. cf. kobelliforme (Bonarelli), H. cf. nodosum Prasad, and Hildoglochiceras sp. A. On its base, it is delimited by the occurrence of the early Tithonian Aulacosphinctoides cf. mayeri (Uhlig), A. perrinsmithi Uhlig, A. cf. tardissimus Enay, A. infundibulum (Uhlig) and A. cf. infundibulum (Uhlig) and, on its top, by the late Tithonian index Himalayites aff. seideli (Oppel). Based on the present and previous records from western India (i.e., from Kachchh and Jaisalmer basins), the occurrence of Hildoglochiceras Spath is correlated with the Standard Tethyan Darwini Zone of early Tithonian. It is plausible, and with more precise sampling from other western Gondwana margin localities, that the occurrence of Hildoglochiceras Spath may suggest an early Tithonian (Darwini to Semiforme zones) event, facilitating improved large-scale biostratigraphic correlations.