Ichnofabric Analysis of the Jumara Formation, Jara Dome, Western Kachchh, India

The Jara dome in the western part of the Kachchh basin is the distal-most exposure of the Callovian to Aptian age sediments of the Kachchh stratigraphy. These outcrops are represented by three formations, namely, the Jumara, Jhuran, and Bhuj formations. The central part of this dome is represented by the entire succession of the Jumara Formation (Member-I to IV). This paper aims to document ichnofabric changes in the distal part of the basin during a basinal-scale transgression. The Jumara succession at the Jara dome is represented by finer sediments compared with the other coeval sediments across the basin. Ichnofabric analysis of the Jumara Formation at the Jara dome implies 21 ichnospecies from 12 ichnogenera with the reconstruction of ichnofabric constituent analysis for all four members. Member-I implies low diversity-low density trace fossils with a simple tiering profile. Member II is two thick bands of marls rich with high diversity and density occurrence of Zoophycos. Ichnofabric analysis suggests slow sedimentation in the shelf environment below the Storm wave base under dysoxic conditions. Ichnofabric analysis of overlying Member III suggests deposition below the fairweather wave base with well-oxygenated, shifting substrate-type environments. Ichnological analysis of Member IV (Dhosa oolite Member) suggests that a transgression event was inferred at Jumara Dome. Thus, the ichnofabric analysis of the Jumara Formation suggests an increase in ichnodiversity steadily from member-I to III and then a decline. A comparison of the Jara dome ichnology data with other coeval sediments of the Kachchh basin suggests high diversity in the Jara dome area.