The Camborygma Ichnofacies in a high-resolution sequence-stratigraphic framework for the Eocene palustrine-alluvial depositional interval of the Kutch Basin, India

Abstract

The non-marine strata of the Ypresian Naredi Formation have been deposited and intermittently pedogenized after the culmination of the Early Eocene Climatic Optimum (EECO). This continental interval comprises intercalation of laterite and palaeosol horizons developed by cyclic episodes of erosion, subaerial exposure, and deposition. The palaeopedological analyses investigate the morphological and micromorphological features evidencing repeated subaerial exposure and consequently moderate to well-developed palaeosol horizons. The topmost laterite bed records an intensely bioturbated ichnofabric (consisting of the root traces and the composite ichnotaxa of lungfish aestivation burrows, Macanopsis (possible arachnid burrows), and Skolithos. The pedogenized shale horizons contain the paucispecific Camborygma-root trace ichnofabric with highly localized patchy preservation of Camborygma symplokonomos, Camborygma eumekenomos, and rhizoturbation. The ichnospecies variation of Camborygma along with the ichnofabric analyses led to the demarcation of stratigraphic horizons and evaluation of the palaeowater-table fluctuations vis-à-vis the low-order allocyclicity, the ethology of producers, and the depositional setting. The paucispecific suite of trace fossils refers to the Camborygma Ichnofacies, where the substrate is intermittently pedogenized and lateritized with upward increasing thickness of beds and intensity of pedogenesis, lateritization, ichnodiversity, and ichnoabundance. Hence, as an expression of high-frequency (interpreted as 5th-order) stratigraphic fluctuations within an early Falling Stage Systems Tract (FSST), a hot palaeoclimate with seasonality varying between humid inundated to dry desiccated conditions is interpreted with the palaeowater table being the base-level control. It culminates with the driest condition at the top with the thickest laterite development associated with the RAeMaS ichnofabric. With the onset of early transgression as documented in the overlying marine deposits of the Bartonian Harudi Formation, the top of the studied interval marks an induced subaerial unconformity.