Integrated stratigraphic framework of the Upper Assam Basin, northeast India: tectonic evolution, sequence stratigraphy and future research directions

The Upper Assam Basin is one of India’s most prolific hydrocarbon provinces, yet its stratigraphic framework remains fragmented because of inconsistent lithostratigraphic nomenclature, incomplete chronostratigraphic calibration and the absence of an integrated basin-scale synthesis. This review critically compiles and evaluates published lithostratigraphic, palynostratigraphic, sedimentological, seismic, petrophysical, geophysical and tectonic studies to establish a comprehensive stratigraphic framework for the basin. The Cenozoic succession documents the transition from Paleogene shallow-marine carbonate and shelfal deposition through Oligocene deltaic progradation to Neogene fluvial foreland sedimentation in response to progressive India–Asia collision and Indo-Myanmar convergence. Basin architecture, sediment dispersal and depositional patterns are strongly controlled by tectonic segmentation associated with the Naga Thrust system, Kopili Fault Zone, basement-controlled structural highs and foreland flexure. Chronostratigraphic correlation relies predominantly on palynostratigraphic zonation because radiometric and magnetostratigraphic constraints remain scarce. Integration of sequence-stratigraphic studies identifies 10 tectonostratigraphic sequences bounded largely by tectonically generated unconformities, indicating that tectonic processes exerted a greater influence than eustatic sea-level fluctuations on basin evolution. Published petrophysical data reveal systematic variations in reservoir quality among the Lakadong–Therria, Barail and Tipam successions, reflecting contrasting depositional environments and diagenetic histories. Remaining uncertainties include inconsistent stratigraphic nomenclature, limited chronological calibration, incomplete structural characterisation and sparse basin-wide petrophysical datasets. Future progress requires integration of high-resolution geochronology, three-dimensional seismic stratigraphy, provenance analysis, palynofacies-organic geochemistry and digital basin-wide stratigraphic databases. This synthesis provides an updated geological framework for future investigations of hydrocarbon systems, geothermal resources, carbon storage and regional basin evolution in northeast India.