Post-glacial sedimentary evolution and stratigraphy of the shallow offshore areas of the Shetland Islands (UK)

Rikza An Nahar , Maarten Van Daele, Pedro Costa, Max Engel, Sue Dawson, Juliane Scheder, Thomas Goovaerts, Vanessa Heyvaert, Marc De Batist

We present a high-resolution seismic–sedimentological reconstruction of post-glacial sedimentation in three shallow offshore basins around the Shetland Islands (Dury Voe, Colgrave Sound/Basta Voe, and Yell Sound), based on integrated multibeam bathymetry, sub-bottom profiler data, and 77 vibrocores supported by radiocarbon dating.
Sediment distribution is strongly controlled by inherited bedrock morphology, with post-glacial deposits preferentially accumulating in overdeepened sub-basins, while intervening highs remain sediment-starved. The stratigraphic successions consistently record four stages: (i) a pre-marine substrate of bedrock locally overlain by glacial or glaciofluvial deposits; (ii) early post-glacial infill formed under low-energy, restricted conditions (fluvial, lacustrine to estuarine/lagoonal); (iii) a transitional phase linked to early Holocene marine transgression and increasing hydrodynamic influence; and (iv) an upper unit dominated by sand-rich, current-influenced marine deposits forming laterally extensive mounded drift geometries.
High-amplitude, laterally continuous seismic units with sharp erosional bases and shell-rich, poorly sorted lithologies record regionally extensive extreme-wave events. Radiocarbon ages constrain the most prominent deposit to ca. 8.15 ka cal BP, enabling correlation with the Storegga Slide tsunami across offshore and nearshore settings. A younger event dated to ca. 1.5 ka cal BP is identified in Dury Voe and correlates with late Holocene onshore tsunami records in Shetland.
These results demonstrate that shallow voes preserve a coherent post-glacial stratigraphic framework, bridging offshore and onshore records, and provide new constraints on relative sea-level change and hydrodynamic reorganisation following marine transgression in formerly glaciated coastal systems.