Evaluating late-Holocene relative sea-level change in the Somerset Levels, southwest Britain

Haslett, S.K, Davies, P, Curr, R.H.F, Davies, C.F.C, Kennington, K, King, C.P and Margetts, A.J (1998) 'Evaluating late-Holocene relative sea-level change in the Somerset Levels, southwest Britain.' The Holocene, 8 (2). pp. 197-207. ISSN 1477-0911

Official URL: https://doi.org/10.1191/09596839866949929


Holocene relative sea-level (RSL) change is investigated at Nyland Hill (Somerset Levels). The lithostratigraphy comprises turfa peat underlying marine clay, both onlapping a sloping Upper Palaeozoic basement. The altitude of the peat-clay contact ranges from 2.42 to 4.52 m OD, becoming lower down basement slope, yet 14C dates of three samples taken laterally along the contact at different altitudes yield similar ages (3640-3330, 3715-3460, 3725-3465 cal. yrs BP), suggesting either very rapid (‘instantaneous’) RSL rise or sediment compaction. Biostratigraphic data indicate a gradual transition to marine conditions across the peat-clay contact. Therefore, the height difference is interpreted as evidence for significant compaction. We consider 4.64 m OD the minimum pre-compaction altitude, indicating maximum observed compaction of 2.22 m. The clay surface, reclaimed during Roman occupation, represents an anthropogenically induced negative tendency and is dated chemostratigraphically to 1776 ± 46, using a datum related to the onset of local Roman lead mining AD 43-49. Sedimentation rates of the marine clay are established: 1.58-1.92 mm yr-1 and 0.8-0.96 mm yr-1 at sites of maximum and less severe compaction respectively. RSL continued to rise throughout the deposition of the clay unit at a rate of 0.41-0.82 mm yr-1, a view that disagrees with previous models that imply stabilised RSL by 3000 BP. These earlier studies underestimate compaction with implications for subsequent studies employing these sea-level data, particularly in crustal studies where the apparent trend of subsidence is overestimated/increased.

Item Type: Article
Keywords: Holocene, sea-level change, compaction, sedimentation, tectonics, Somerset Levels
Subjects: G Geography. Anthropology. Recreation > G Geography (General)
Divisions: Chancelry and Research Management
School of Sciences
Identification Number: https://doi.org/10.1191/095968398669499299
Date Deposited: 02 Sep 2014 16:45
Last Modified: 28 Nov 2023 17:55
URI / Page ID: https://researchspace.bathspa.ac.uk/id/eprint/4023
Request a change to this item or report an issue Request a change to this item or report an issue
Update item (repository staff only) Update item (repository staff only)