Correlation of Quaternary glaciations in the Northern Hemisphere

144

207

S. 2006. Relative sea-level changes, glacial isostatic modelling and ice-sheet reconstructions from the British Isles since the Last Glacial Maximum.ABSTRACT: While contributing <1 m equivalent eustatic sea-level rise the British Isles ice sheet produced glacio-isostatic rebound in northern Britain of similar magnitude to eustatic sea-level change, or global meltwater influx, over the last 18 000 years. The resulting spatially variable relative sea-level changes combine with observations from far-field locations to produce a rigorous test for quantitative models of glacial isostatic adjustment, local ice-sheet history and global meltwater influx. After a review of the attributes of relative sea-level observations significant for constraining large-scale models of the isostatic adjustment process we summarise long records of relative sea-level change from the British Isles and far-field locations. We give an overview of different global theoretical models of the isostatic adjustment process before presenting intercomparisons of observed and predicted relative sea levels at sites in the British Isles and far-field for a range of Earth and ice model parameters in order to demonstrate model sensitivity and the resolving power available from using evidence from the British Isles. For the first time we show a good degree of fit between relative sealevel observations and predictions that are based upon global Earth and ice model parameters, independently derived from analysis of far-field data, with a terrain-corrected model of the British Isles ice sheet that includes extensive glaciation of the North Sea and western continental shelf, that does not assume isostatic equilibrium at the Last Glacial Maximum and keeps to trimline constraints of ice surface elevation. We do not attempt to identify a unique solution for the model lithosphere thickness parameter or the local-scale detail of the ice model in order to provide a fit for all sites, but argue that the next stage should be to incorporate an ice-sheet model that is based on quantitative, glaciological model simulations. We hope that this paper will stimulate this debate and help to integrate research in glacial geomorphology, glaciology, sea-level change, Earth rheology and quantitative modelling.

Section: Creating a Revised Model For The British Isles And Ireland Imentioning

confidence: 99%

mentioning

confidence: 99%

Relative sea‐level changes, glacial isostatic modelling and ice‐sheet reconstructions from the British Isles since the Last Glacial Maximum

Shennan

Bradley

Milne

et al. 2006

144

207

“…This revised interpretation allowed Bridgland (1994) to attribute the Southend-Asheldham Channel deposits to the Hoxnian (sensu Swanscombe and Clacton), which he correlated with marine oxygen isotope stage (OIS) 11, and the Shoeburyness Channel deposits to the next interglacial cycle, equivalent to marine OIS 9 of the deep-marine sequence. These correlations are based on the assumption that the Anglian Stage, during which the most extensive of the British glaciations brought about the diversion of the Thames, equates with marine OIS 12 (Bowen et al, 1986;Bowen, 1999). Correlation of the Anglian with marine OIS 12 has received support recently from age estimates that imply a marine OIS 11 age for Hoxnian interglacial sediments overlying Anglian glacial deposits at Marks Tey (Rowe et al, 1999) and Hoxne (Grün and Schwarcz, 2000).…”

Section: Regional Geological Contextmentioning

confidence: 99%

Middle Pleistocene interglacial deposits at Barling, Essex, England: evidence for a longer chronology for the Thames terrace sequence

Bridgland

Preece

Roe

et al. 2001

Results are presented from a multidisciplinary study of fossiliferous interglacial deposits on the northern side of the Thames estuary. These fill a channel cut into London Clay bedrock and overlain by the Barling Gravel, a Thames-Medway deposit equivalent to the Lynch Hill and Corbets Tey Gravels of the Middle and Lower Thames, respectively. The channel sediments yielded diverse molluscan and ostracod assemblages, both implying fully interglacial conditions and a slight brackish influence. Pollen analysis has shown that the deposits accumulated during the early part of an interglacial. Plant macrofossils, particularly the abundance of Trapa natans, reinforce the interglacial character of the palaeontological evidence. A beetle fauna, which includes four taxa unknown in Britain at present, has allowed quantification of palaeotemperature using the mutual climatic range method (T max 17 to 26°C; T min −11 to 13°C). A few vertebrate remains have been recovered from the interglacial deposits, but a much larger fauna, as well as Palaeolithic artefacts, is known from the overlying Barling Gravel.The age of the interglacial deposits is inferential. The geological context suggests a late Middle Pleistocene interglacial, part of the post-diversion Thames system and therefore clearly post-Anglian. This conclusion is supported by amino acid ratios from the shells of freshwater molluscs. The correlation of the overlying Barling Gravel with the Lynch Hill/Corbets Tey aggradation of the Thames valley constrains the age of the Barling interglacial to marine oxygen isotope stages 11 or 9. The presence of Corbicula fluminalis and Pisidium clessini confirms a pre-Ipswichian (marine oxygen isotope substage 5e) age and their occurrence in the early part of the interglacial cycle at Barling precludes correlation with marine oxygen isotope stage 11, as these taxa occur only later in that interglacial at sites such as Swanscombe and Clacton. Thus by process of elimination a marine oxygen isotope stage 9 age would appear probable.

“…The western limits of the ice sheet during the last glacial maximum (LGM) are frequently depicted as being land-based on peninsulas in the northwest and west of Ireland (e.g. Bowen et al, 1986Bowen et al, , 2002. These areas are thus critical for testing the validity of the established view of LGM ice dimensions.…”

Section: Introductionmentioning

confidence: 99%

The Donegal ice dome, northwest Ireland: dimensions and chronology

Ballantyne

McCarroll

Stone

2007

Geomorphological evidence indicates that Donegal was formerly occupied by an ice dome that extended offshore to the west, northwest and north and was confluent with adjacent ice masses to the east and south. Erosive warm-based ice over-rode almost all the highest mountains, implying an ice-divide altitude greater than 700 m. Only six peripheral summits escaped glacial modification, implying either that they remained above the ice surface as nunataks or supported a thin cover of protective cold-based ice. Gibbsite, a pre-last glacial weathering product, is preferentially represented on summits that escaped glacial modification. Cosmogenic 10 Be exposure ages of 18.6 AE 1.4 to 15.9 AE 1.0 k yr for coastal sites confirm that Donegal ice extended offshore at the last glacial maximum. Reconstruction of the form of the Donegal ice dome suggests a former minimum ice thickness of $500 m close to the present coastline in the west and northwest, and $400 m near the coast of the Inishowen Peninsula in the north, with the ice extending at least 20 km across the adjacent shelf to the west and northwest.