The erosionally confined to emergent transition in a slope‐derived blocky mass‐transport deposit interacting with a turbidite substrate, Ventimiglia Flysch Formation (Grès d’Annot System, north‐west Italy)

Basal interaction beneath frontally-emergent mass-transport deposits has been widely documented in seismic data, but its effect on deposit heterogeneity not convincingly calibrated at outcrop. Several blocky occur as part of the Late Eocene Ventimiglia Flysch north-west Italy, comprising slope-derived marlstones, representing original slide, and turbidite material, entrained after erosion substrate sediments; this study reports best exposed. Correlation twenty-nine sedimentary logs tied to hosting stratigraphy allows thickness facies changes be tracked over an area ca 40 km2, spanning erosionally confined emergent transition. A basal >55 m deep several kilometres wide confines a marlstone megabreccia containing megaclasts up 1 km across, interpreted product submarine slide originated from sector collapse western basinal slope. Approaching downstream limit erosional confinement is replaced by highly deformed turbidites that, more distally, are turn superseded debrite composed dominantly material. Structural textural characteristics suggest that distally-extending was deposited forerunner debris flow formed sediments liquefied ahead advancing whereas were accumulated margins shortly before it came halt. Farther downstream, few metres thick sits onto undisturbed basin floor, indicating mass became sufficiently mobile (with estimated runout excess tens kilometres) redistribute material evacuated (>0.5 km3). The terminates upward into graded conglomerate late-stage multiphase flow. This provides rare insight variation deposit, showing how with poorly consolidated substrates can result significant transformation parental