84-1 Sediment compartmentalization as a function of stratigraphic and structural confinements in Indus offshore fan, Indus basin, Pakistan

Abstract:

The Indus Fan is one of the largest deep-marine sedimentary systems, where basin floor morphology, tectonic structures, and carbonate platform development exert a significant influence on sediment dispersal and turbidite deposition. This study investigates the impact of structural highs, volcanic basement topography, carbonate platforms, and specifically the Murray Ridge on the depositional architecture and evolution of the Indus Fan. Seismic stratigraphic analysis of regional seismic profiles was conducted to delineate morphological confinements and evaluate their influence on fan geometry, sediment distribution, and channel levee development. Variations in fan thickness were quantified across multiple seismic transects to assess the effects of frontal and marginal confinements on turbidite deposition. Structural highs, volcanic basement features, carbonate platforms, and channelized depositional systems were mapped and correlated throughout the study area. The results reveal two principal types of confinement: frontal confinements, formed by volcanic basement highs and overlying carbonate platforms, and marginal confinement, represented by the Cretaceous-aged Murray Ridge. Three major frontal confinements were identified downslope, where they exert a strong control on sediment routing and fan thickness distribution. Fan thickness reaches approximately 5.6 km immediately downslope of the shelf break but decreases abruptly to ~4 km and locally to 0.85 km over carbonate-platform capped structural highs, where carbonate buildups attain thicknesses of up to 1000 m. Further downslope, additional confinements partition sediment transport pathways and channelize fan deposits into multiple dispersal directions. Along the western margin, the Murray Ridge acts as a major topographic barrier, restricting fan expansion toward the Makran Basin and promoting asymmetric sediment accumulation, with fan thicknesses reaching up to 6.4 km adjacent to the ridge. The study demonstrates that structural and depositional confinements exert a fundamental control on fan morphology, sediment thickness distribution, channel evolution, and levee development throughout the Indus Fan. Frontal and marginal confinements promote sediment ponding, flow diversion, asymmetric levee growth, and localized channel modification, highlighting the critical role of tectonically inherited topography and carbonate platform development in governing the evolution of deep-water depositional systems.

Keywords: Sediment compartmentalization; Indus fan; restricted fan growth; Basement highs; Carbonate platforms

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