Evaluating bioturbation as an indicator of colonisation windows in deltaic systems, Kachchh Basin, India

The concept of colonisation windows—intervals during which benthic organisms can actively bioturbate before being interrupted by sedimentation or environmental shifts—offers a high-resolution tool for palaeoenvironmental reconstruction. The present study investigates the bioturbation patterns of the Lower Cretaceous, Ghuneri Member (Bhuj Formation) within the wave-dominated deltaic system of the Kachchh Basin. Through ichnofabric analysis, ichnodiversity indices, and ichnonetwork modelling across 26 stratigraphic sections, we delineate the spatial and temporal dynamics of trace fossil assemblages from proximal to distal settings. Results reveal a distinct asymmetrical bioturbation cyclicity, with higher diversity and prolonged colonisation windows concentrated in the distal, stable substrates, and reduced diversity in proximal, high-energy environments. Six ichnofabric types were documented, reflecting variability in sedimentation rates, storm influence, and substrate consistency. Network analysis identified core, bridging, and peripheral ichnotaxa, validating ecological structuring through metrics of centrality and co-occurrence. The lower Ghuneri Member is characterised by well-developed, multi-tiered ichnocoenoses with Glossifungites ichnofacies, while the upper part exhibits increased heterogeneity and ecological restructuring. These ichnological patterns, embedded within the broader deltaic progradation–transgression–regression cycle, underscore the utility of colonisation windows in deciphering facies transitions and depositional energy gradients in pericratonic rift basin settings.