Ichnofabric variability and paleoenvironmental insights from the Middle Bhuban rocks of Aizawl, Mizoram, India

The Middle Bhuban succession of the Surma Group is extensively exposed in the Aizawl district of Mizoram, India; the study area predominantly features alternating intervals of shale, sandstone, and siltstone. The sediments exhibit significant bioturbation and host a diverse array of seventeen ichnofossils. Six ichnofabrics have been identified, including Cochlichnus, Funalichnus, Palaeophycus, Psilonichnus, Teredolites, and Thalassinoides. The bioturbational ichnofabrics are primarily composed of simple feeding traces (Cochlichnus, Funalichnus, Psilonichnus, and Thalassinoides) and the dwelling burrow (Skolithos) created by opportunistic organisms colonizing the foreshore/shoreface zone. In contrast, the bioerosional ichnofabric, characterized by the ichnogenera Teredolites, is confined to rippled sandstone deposits found in the foreshore/nearshore zone. The ichnofabrics display abrupt changes in colonization patterns (ichnofossils, ichnoassemblages, and tiering styles) throughout the succession, reflecting the benthic infaunal community responses to fluctuations in sedimentation rates and sea level dynamics. Sedimentological and ichnological analysis of the Middle Bhuban rocks in the study area suggests that the area was deposited under foreshore/shoreface environments, with a temporary sea-level rise indicated by the backshore environment marked by the Teredolites ichnofabric.