Volcanic stratigraphy offshore East Montserrat: Selective preservation and subaqueous remobilisation in marine records

Abstract In tectonically active regions, volcanic eruptions generate large volumes of material that are transported offshore through processes such as pyroclastic density currents, turbidity currents, and secondary sediment remobilisation. These deposits form key stratigraphic markers for reconstructing eruptive histories, yet their preservation, correlation with onshore events, and modification by mass wasting remain insufficiently understood. This study examines the effectiveness of marine sedimentary sequences in recording eruptive and mass-transport events from Soufrière Hills Volcano offshore Montserrat, in comparison to the monitoring record of its well-known last eruptive phase between 1995 and 2010. We focus on spatial and temporal variations in facies, evaluating how offshore deposits reflect transport mechanisms, depositional settings, and post-depositional reworking. Two gravity cores (~ 1.7 m in total) from the eastern offshore sector provide contrasting perspectives: one retrieved in a depression and close to a mass-transport deposit contains ~ 30 cm of volcaniclastic layers underlain by debrites, whereas the other, from a more stable setting higher at the slope, preserves only a thin (~ 1 cm) ash horizon. A multi-proxy approach, including X-ray fluorescence (XRF) geochemistry, multi-sensor core logging (MSCL), and computed tomography (CT) imaging, was applied to characterise volcanic facies, assess ash preservation, and evaluate the development of mechanically weak layers that may act as failure planes for eruption-induced remobilisation or slope instability. Results demonstrate significant challenges in correlating terrestrial and submarine records regarding smaller eruptive events and in the temporal order of years. Offshore sequences show selective preservation, with simple, thin ash deposits in undisturbed areas contrasting with complex, remobilised successions near disturbed settings. These findings underline the critical role of post-depositional processes in shaping proximal marine volcanic archives and highlight the value of integrated sedimentological and physical property analyses for reconstructing eruptive processes and improving hazard assessments in proximal volcanic island settings.