The Northwest European continental shelf has been subjected to repeated transgressive-regressive cycles as a function of fluctuating glacio-eustatic sea-level throughout the Quaternary. Numerical models incorporating both global eustatic and regional glacio-hydro-isostatic sea-level signals for the latest transgressive phase (20-5 ka BP) suggest extensive early subaerial shelf exposure, particularly in the Celtic Sea, with impounding of shallow freshwater bodies north of a terrestrial land-linkage between southwest Britain and southern Ireland. Whilst such models are well constrained by ¹⁴ C-calibrated index-points peripheral to the region, critical offshore evidence from the Celtic Sea constraining the early phases of transgression is lacking.
In this study, macrofossil-derived ¹⁴C-calibrated sea-level index-points from vibrocores between the shelf edge and St George's Channel are used to critically assess the accuracy of such models and to develop sea-level curves and palaeocoastline maps spanning the period of inundation. In addition, litho- and bio-stratigraphic techniques are employed to further elucidate the nature and timing of transgression across the shelf.
An extensive gravel lag possessing intertidal and subtidal taxa, representing initial inundation of subaerially exposed shelf and subsequent subtidal reworking is identified throughout the region. Evidence for the existence of a palaeolacustrine system within the present Celtic Deep basin subjected to marine incursion from the south is also described lending credence to published numerical models.
The accuracy of faunal-based index-points and resultant sea-level curves is, however, considered questionable, given the extensive taphonomic modification, time-averaging and condensation experienced by shell accumulations in such transgressive environments. Palaeo-water-depth estimates derived using sedimentological principles, whilst suggestive, do not provide the acuity necessary to confidently determine sea-level behaviour.
Whilst sea-level index-points are questioned, stratigraphic evidence for marine incursion into the Celtic Deep represents a critical constraint on palaeo-water-depth, exhibiting good agreement with published numerical models. High deglacial sea-level models, however, are not supported by the stratigraphic evidence.