Analysis of cores collected from Late Devensian (Weichselian) and Holocene sediments on the floor of the North Sea provides evidence of the transgression of freshwater environments during relative sea-level rise. Although many cores show truncated sequences, examples from the Dogger Bank, Well Bank and 5 km offshore of north Norfolk reveal transitional sequences and reliable indicators of past shoreline positions. Together with radiocarbon-dated sea-level index points collected from the Holocene sediments of the estuaries and coastal lowlands of eastern England these data enable the development and testing of models of the palaeogeographies of coastlines in the western North Sea and models of tidal range changes through the Holocene epoch. Geophysical models that incorporate ice-sheet reconstructions, earth rheology, eustasy, and glacio-and hydroisostasy provide predictions of sea-level relative to the present for the last 10 ka at 1-ka intervals. These predictions, added to a model of present-day bathymetry, produce palaeogeographic reconstructions for each time period. The palaeogeographic maps reveal the transgression of the North Sea continental shelf. Key stages include a western embayment off northeast England as early as 10kaBl~; the evolution of a large tidal embayment between eastern England and the Dogger Bank before 9 ka BP with connection to the English Channel prior to 8 ka Bl'; and Dogger Bank as an island at high tide by 7.5 kaBP and totally submerged by 6kaBP. Analysis of core data shows that coastal and saltmarsh environments could adapt to rapid rates of sea-level rise and coastline retreat. After 6 ka Bp the major changes in palaeogeography occurred inland of the present coast of eastern England. The palaeogeographic models provide the coastline positions and bathymetries for modelling tidal ranges at each 1-ka interval. A nested hierarchy of models, from the scale of the northeast Atlantic to the east coast of England, uses 26 tidal harmonics to reconstruct tidal regimes. Predictions consistently show tidal ranges smaller than present in the early Holocene, with only minor changes since 6 ka BP. Recalibration of previously available sea-level index points using the model results rather than present tidalrange parameters increases the difference between observations and predictions of relative sea-levels from the glacio-hydro-isostatic models and reinforces the need to search for better ice-sheet reconstructions.
The distribution of large channel-like features, comprising Weichselian/Devensian incisions, in the western North Sea provides evidence for a much larger extension of the last ice sheet than currently assumed. Morphological comparison of the incisions with those in North Germany and Poland reveals a striking similarity in shape and distribution. The features on the North Sea floor are interpreted as being formed by meltwater erosion within the margin of the ice sheet, The widespread absence of Weichselian/Devensian till in the area under consideration may be attributed to later erosion. Large-scale reworking and redistribution of sediments is indicated by the complete sediment infill of the majority of the incisions. Journalof Quaternary Science
From the recognition that major incisions formed at lowland or tidewater ice sheet margins during each of the last three glacial stages, it is assumed that a standard Quaternary stratigraphy is applicable to the deposits geophysically profiled on the continental shelf off Britain. Ice limits for each glacial stadia1 can be mapped from the geographical distribution of the incisions.During the next glacial stage major incisions will be downcut on the present continental shelf or coastal lowlands to some 350 m below the ambient surface. This will have important environmental consequences regarding the long-term burial of hazardous wastes. Terra Nova, 1, 538-548
A macroscale model is attempted to accommodate offshore observations indicative of former sea-levels in the Irish and Celtic seas. The indications considered here are those that appear to post-date 12 ka bp . Raised beaches at about present sea-level, and formed in the Last Interglacial, are found about these seas. This shows that controls to produce the later sea-level changes have acted to return to about their conditions in the Last Interglacial, and that later permanent tectonic displacements have not been significant. A simple, geometrically based model is developed of the interaction of: glacio-eustasy, from graphs based on coral-reef studies; glacio-isostatic depression with an annular forebulge of equal volume, both contracting through the interval considered; and hydro-isostasy, as an enhancement of the other effects by up to 20%. The best fit of the empirical submarine data suggests that from 12 to 9 ka bp relative sea-levels varied from 80 m above, and 160 m below present mean sea-level in the two seas. The resultant sea-level graphs for points from Scotland to Ushant compare with published graphs from eastern North America and northern Europe. Derived maps of palaeocoasts show land-bridges from Britain to Ireland and later to the Isle of Man after 11.35 ka bp .
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