Tectonostratigraphic Evolution of the Guyana Basin: Implications for Sediment Routing and Slope Stability

ABSTRACT The Guyana Basin developed in an evolving tectonic setting, but a lack of subsurface data has limited understanding of its tectonic and sedimentary evolution through time. This study uses extensive, newly available 2D seismic reflection and exploration well data to develop a regional tectonostratigraphic framework, to reconstruct sediment accumulation and constrain sediment routing to the basin through time. Five megasequences (MS‐0 to MS‐4; oldest to youngest) are defined, each representing a distinct phase of basin fill. MS‐0 corresponds to the pre‐ and syn‐rift phases of the Central Atlantic rift, marked by folded volcano‐sedimentary units. MS‐1 (Middle Jurassic–Aptian) represents the post‐rift phase of the Central Atlantic, characterised by low sedimentation rates and isolated depocenters likely fed by nearby continental sources from the Guyana margin, and possibly adjacent conjugate margins in North America and Africa. MS‐2 (Aptian–Albian) represents the Equatorial Atlantic syn‐rift and transform phase, marked by the development of the Equatorial Atlantic Fracture Zone (EAFZ) and the emergence of a southeastern slope depocenter. MS‐3 (Albian–Middle Miocene) corresponds to the Equatorial Atlantic passive margin phase of the basin, with sediment transported through large canyon systems, likely indicating increased riverine flux from the Guyana margin. MS‐4 (Upper Miocene–Recent) reflects ongoing passive margin sedimentation and the development of a fold‐and‐thrust belt in the northwestern basin due to the collision between the Caribbean and South American plates. About 41% of the total sediments of the Guyana Basin were deposited in the last ~11.6 Myr, driven by a ~40 MTa −1 sediment flux primarily from the Amazon River–Guiana Current system. This order of magnitude increase in sedimentation rate in the Miocene corresponds with the onset of widespread mass transport deposits, indicating that rapid sedimentation and disequilibrium compaction preconditioned the continental slope for repeated failure. This has important implications for slope stability, with large‐volume submarine landslides forming a potentially significant landslide and tsunami hazard for subsea infrastructure and coastal populations.