238-4 History and Formation of the NW Scottish Shelf Transgressive Sand Sheet

Session: Recent Advances and New Voices in Marine and Coastal Geoscience

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Transgressive sand sheets provide one of the few preserved records of shelf sedimentation during transgression. Thus, they can provide clues about the environmental conditions operating during times of sea-level rise, including constraining the rate of past sea-level rise. This study examines 63 sediment cores spanning the NW Scottish Shelf and Outer Hebrides slope in order to determine the mechanisms driving postglacial ravinement and sand sheet facies evolution over time. We identify two distinct processes controlling the formation and timing of the sand sheet’s ravinement surface, which vary by shelf position: (1) an offshore tidal ravinement surface (OTRS) that formed during peak tidal current velocities at ~15 ka, spanning both the inner and outer shelf as predicted by the PALTDE model (Scourse et al., 2024), and (2) a bottom-current-generated surface, likely linked to forebulge migration, active between ~12–8 ka across the mid shelf. The sand sheet’s ravinement surface is overlain by a transgressive lag (e.g., the muddy gravelly shell hash facies) that formed during a time of peak tidal current erosion, followed by overlying sand deposits (e.g., orange shell hash facies, shelly brown sand, and yellow scaphopod silt facies), which record tidal current waning during the early Holocene. These findings highlight the significance of tidal processes in shaping postglacial shelf stratigraphic architecture in a region that might otherwise appear as a wave-dominated system. In addition, this study offers an example of how glacial isostatic adjustment (GIA) and bottom currents influence the postglacial sedimentary record.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7646

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