Data from marine sediment core GFL-CS05

The study of sedimentary core GFL-CS05, located on the eastern submarine upper slope of Mayotte, provides new insights into sedimentary and volcanic processes within a barrier reef carbonate steep-slope environment. The chronostratigraphic framework covers Late Quaternary sedimentation, primarily dominated by hemipelagic carbonate deposition, and includes significant reworked deposits. Facies analysis shows a predominance of mixed volcanoclastic–carbonate turbidites and two debrites, predominantly during sea-level lowstands, and calciturbidites deposited around during highstands. Sea-level fluctuations may influence the volcano-detrital component of the turbidites and their increased frequency during lowstands, while the source remains reef-sourced throughout most of the record. Geomorphological characterization indicates the area’s high susceptibility to slope failure, potentially increasing remobilization. Concurrent East Mayotte Volcanic Chain (EMVC) volcanic activity during deposition may have acted as an additional trigger. Volcanic layers within the core mainly display basanitic and tephritic, phono-tephritic, phonolitic, and trachytic compositions, providing new evidence for silica-rich and often highly alkaline magmas, so far poorly documented in the region’s submarine domain. The youngest tephra, around 7 ka cal BP, along with crypto-tephra, indicates recent Holocene volcanic eruptions in immediate vicinity of Mayotte. These findings stress the influence of volcanic activity, slope morphology, and sea-level changes on the distribution and occurrence of turbidites and gravity-driven deposits within a steep barrier-reef environment, revealing hazards and vulnerabilities for Mayotte Island.