A new ichnospecies Nummipera saraswatii from the early Eocene (Ypresian) Assilina bank deposits of the Naredi Formation, Kutch Basin, India

Abstract

A new ichnospecies of the ichnogenus Nummipera Hölder, 1989 has been documented in the carbonate packstone and wackestone of the Ypresian (early Eocene) Naredi Formation from the western Kutch (Kachchh) Basin, India. This new ichnospecies is distinguished from Nummipera eocenica (the existing sole ichnospecies of ichnogenus Nummipera) on the basis of the burrow orientation, taxonomy and orientation of foraminifera lining the burrow walls, and burrow filling. Nummipera saraswatii isp. nov. represents the earliest occurrence of Nummipera. It is a horizontal to gently inclined, straight to feebly curved, intermittently vertically flattened tubular burrow closed at one end, displaying circular to elliptical cross-sections, and representing three-distinct morphotypes. The analyzed specimens are characterized by walls mostly lined with unbroken and well-sorted megalospheric tests of Assilina laxispira. Burrows are characterized by active massive fill akin to the host material consisting of organic-rich muddy material and bioclasts or active concentric fill displaying a distinct outer and inner lumen, filled with organic-rich materials of different grain-sizes varying from mud to sand. Crustaceans and vermiform animals can be envisaged as the probable producers based on the distinctive morphotypes and ethological affinity. The shallow-tier N. saraswatii shows association with the deep-tier Cylindrichnus concentricus. The association manifests key features of a stressed Cruziana Ichnofacies and characterizes an Assilina bank of a proximal carbonate open shelf setting.