Drowning of a barrier coastline under rapid rates of relative sea-level rise during the 8.2 ka cooling event: Cause or coincidence?
Abstract
Examples where barrier landforms and deposits are preserved offshore of a highstand shoreline are rare on contemporary continental shelves, and in the rock record. Therefore, understanding of the conditions required for preservation and the sedimentary processes-response to such factors is limited and heavily dependent on simulation models. Here, an integrated dataset of multibeam bathymetry and 2D seismic reflection profiles has uncovered an exceptionally well preserved drowned barrier complex at Hastings Bank, on the English Channel continental shelf, offshore of southeast England. Mapping of nine seismic stratigraphic units calibrated with lithological information from multiple vibrocores has enabled the interpretation of fluvial, shoreface, barrier, washover fan, back-barrier and tidal environments of deposition. Stratigraphic architecture is used as the basis for landscape evolution reconstructions that reveal phases of barrier progradation, degradation and retreat. Optical Stimulated Luminescence (OSL) dating of shoreface and beach deposits revealed ages in the range of 8.4 ± 0.2 ka and 7.8 ± 0.2 ka. These ages indicate the barrier developed under rapid rates of early Holocene sea-level rise and more specifically, correlate to the time period surrounding the 8.2 ka cooling event and associated sea-level 'jump'. To preserve a barrier beach including the barrier foreshore under such rapid rates of relative sea-level rise, sediment supply would have to be sufficient to keep pace to prevent the shoreline responding through continuous reworking, i.e. rollover. Further, the rate of transgression is conditioned by inherited topography with higher rates of retreat, and hence greater potential for drowning, expected across the shallowly dipping substrate. Using Hastings Bank as an example, it has also been demonstrated that the morphodynamic state of the barrier complex in terms of its ability to respond dynamically to relative sea-level rise, conditions its potential for drowning. Therefore, it is not possible to simply attribute drowning and preservation of a barrier coastline to a single forcing factor i.e. rate of sea-level rise. This research highlights the need for a highly resolved stratigraphic and chronological framework in order to fully examine the conditions under which a barrier complex is drowned and preserved.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS44A..04M
- Keywords:
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- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 4546 OCEANOGRAPHY: PHYSICAL / Nearshore processes