Browsing by Author "Scourse, James D."

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    A critical review of the glaciomarine model for Irish Sea deglaciation; evidence from southern Britain, the Celtic shelf and adjacent continental slope
    (2001) Scourse, James D.; Furze, Mark F.A.
    In support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach-face gravels and sands around the shores of the Celtic Sea. Glacial and sea-level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south-central Celtic Sea. Relative sea-levels were lower, and therefore glacio-isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice-rafting at a time of high relative sea-levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation.
  • Thumbnail Image
    Item
    Deglacial to postglacial palaeoenvironments of the Celtic Sea; lacustrine conditions versus a continuous marine sequence
    (2014) Furze, Mark F.A.; Scourse, James D.; Pieńkowski, Anna J.; Marret, Fabienne; Hobbs, William O.; Carter, Rosemary A.; Long, Brian T.
    Recent work on the last glaciation of the British Isles has led to an improved understanding of the nature and timing of the retreat of the British−Irish Ice Sheet (BIIS) from its southern maximum (Isles of Scilly), northwards into the Celtic and Irish seas. However, the nature of the deglacial environments across the Celtic Sea shelf, the extent of subaerial exposure and the existence (or otherwise) of a contiguous terrestrial linkage between Britain and Ireland following ice retreat remains ambiguous. Multiproxy research, based on analysis of 12 BGS vibrocores from the Celtic Deep Basin (CDB), seeks to address these issues. CDB cores exhibit a shell-rich upward fining sequence of Holocene marine sand above an erosional contact cut in laminated muds with infrequent lonestones. Molluscs, in situ Foraminifera and marine diatoms are absent from the basal muds, but rare damaged freshwater diatoms and foraminiferal linings occur. Dinoflagellate cysts and other non-pollen palynomorphs evidence diverse, environmentally incompatible floras with temperate, boreal and Arctic glaciomarine taxa co-occurring. Such multiproxy records can be interpreted as representing a retreating ice margin, with reworking of marine sediments into a lacustrine basin. Equally, the same record may be interpreted as recording similar conditions within a semi-enclosed marine embayment dominated by meltwater export and deposition of reworked microfossils. As assemblages from these cores contrast markedly with proven glaciomarine sequences from outside the CDB, a glaciolacustrine interpretation is favoured for the laminated sequence, truncated by a Late Weichselian transgressive sequence fining upwards into fully marine conditions. Reworked rare intertidal molluscs from immediately above the regional unconformity provide a minimum date c. 13.9 cal. ka BP for commencement of widespread marine erosion. Although suggestive of glaciolacustrine conditions, the exact nature and timing of laminated sediment deposition within the CDB, and the implications this has on (pen)insularity of Ireland following deglaciation, remain elusive.
  • Thumbnail Image
    Item
    New evidence for a grounded Irish Sea glaciation of the Isles of Scilly, UK
    (2006) Hiemstra, John F.; Evans, David J. A.; Scourse, James D.; McCarroll, Danny; Furze, Mark F.A.; Rhodes, Ed
    New geomorphological and sedimentological data support previously published reconstructions of an Irish Sea Glacier advance as far south as the northern shores of the Isles of Scilly in the Celtic Sea (49°58′N). Offshore, boulder-covered bars with cores of diamicton are interpreted as moraines, which together with onshore moraine ridges and trimlines mark the maximal extent of the Irish Sea Glacier. At Bread and Cheese Cove, St. Martin's, a heterogeneous sediment unit, wedged between periglacial gelifluctates, is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills. Macrofabric signatures reflect a subglacial origin, but the whole unit has been subject to down-slope mass movement. Micromorphological analysis indicates highly variable response to deformation and glacitectonism, with most features relating to ductile behaviour and wet deformation. The characteristics suggest deposition during a short-lived advance of the Irish Sea Glacier over pre-existing marine and contemporaneous proglacial lacustrine sediments. Once blocks of stratified sediment and diamicton had been driven onshore, they were subject to paraglacial remobilization, resulting at most locations in complete disaggregation. The distribution of re-worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence.
  • Thumbnail Image
    Item
    Source, timing, frequency and flux of ice-rafted detritus to the Northeast Atlantic margin, 30-12 ka; testing the Heinrich precursor hypothesis
    (2010) Haapaniemi, Anna I.; Scourse, James D.; Peck, Victoria L.; Kennedy, Paul; Hemming, Sidney R.; Furze, Mark F.A.; Pieńkowski, Anna J.; Austin, William E. N.; Walden, John; Wadsworth, Emilie; Hall, Ian R.
    Alkane biomarker and pollen data were obtained from a 15-m-high and probably c. 240-kyr-old loess-like permafrost palaeosol sequence (‘Tumara Palaeosol Sequence’, TPS) in northeast Siberia. The alkane results were corrected for degradation effects by applying an end-member model and were evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian glaciation and finally reforestation during the Lateglacial and the early Holocene. For the lower part of the TPS, the palaeoclimatic interpretation according to modern analogue methods would indicate warm, interglacial conditions, but this is at odds with the climate chronostratigraphy based on a multi-proxy palaeopedological approach and numeric dating. Provided that the correlation of the discussed stratigraphic unit with the Late Saalian glaciation and the Marine Oxygen Isotope Stage 6 is correct, our results suggest that temperature was not a limiting factor for tree growth at that time. Furthermore, it seems very likely that it was not mainly temperature changes but rather increasing aridity and continentality during the course of the last glacial that favoured the expansion of the mammoth steppe.
  • Thumbnail Image
    Item
    The deglacial to postglacial marine environments of SE Barrow Strait, Canadian Arctic Archipelago
    (2012) Pieńkowski, Anna J.; England, John H.; Furze, Mark F.A.; Marret, Fabienne; Eynaud, Frederique; Vilks, Gustav; MacLean, Brian; Blasco, Steve; Scourse, James D.
    Core 86027-144 (74°15.56′N, 91°14.21′W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal δ18O and δ13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8 cal. ka BP) records deglaciation, ice-sheet destabilization, float-off and subsequent break-up. Zone II (c. 10.8–10.4 cal. ka BP) shows ice-proximal to ice-distal glaciomarine conditions, interrupted by pervasive land-fast sea-ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4–9.9 cal. ka BP), where planktonic foraminifera (Neogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW–SE; however, the deep-water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open-water season greater than present) in Zone IV (9.9–7.8 cal. ka BP) perhaps corresponds to the regional ‘Holocene Thermal Maximum’ previously proposed. A transitional period (Zone V; 7.8–6.7 cal. ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea-ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio-isostatic shallowing of inter-island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea-ice and modern microfossil assemblages, commence at c. 6.7 cal. ka BP (zones VI–VII). Although climate ultimately forces long-term environmental trends, core 86027-144 data imply that regional dynamics, especially changes in sea-level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago.