Abstract 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 hydro-isostasy 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 10 ka BP ; 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 BP ; and Dogger Bank as an island at high tide by 7.5 ka BP and totally submerged by 6 ka BP . 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 tidal-range 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.

Abstract The Carboniferous, as one of the three major productive intervals in the UK Southern North Sea, has considerable future potential, particularly as national demand for gas exceeds production. Almost 3 × 10 12 SCF are under development in the southern Quad 44 area, more than 600 × 10 9 SCF reserves discovered await development and the potential for yet-to-find reserves is recognized. Most of the undeveloped assets have transferred ownership a number of times and only now are operators and partner groups going ahead with development. The subsurface, engineering and commercial challenges that face those operators are outlined. The Carboniferous reservoir sandstones are relatively thin and cannot be mapped directly using 3D seismic data. Because they are separated by non-reservoir shales and siltstones, understanding the three-dimensional distribution of these sandstones is critical to ensure optimal well placement, maximum exposure to the reservoir and, ultimately, recovery of gas. Trap definition and size depend upon accurate seismic time-to-depth conversion of a complex overburden. Halokinesis, lateral velocity variations, erosional unconformities and wedges of low velocity sediments all need to be addressed in order to generate the best time-to-depth conversion. Gas in Carboniferous reservoirs is richer in inert gases, CO 2 and N 2 , than is gas from the Rotliegendes fields. These two gases contribute to reducing its calorific and commercial value, necessitating blending with higher quality gas or the removal of the inert gases before acceptence for entry into onshore distribution networks. This relies on the ability, willingness and capacity of host facility operators to accept this gas through their infrastructure. Negotiations to allow blending and acceptance of lower calorific value gas, to no detriment to the user, and the removal of inert gases will result in continued development of the Carboniferous fields. It may also encourage further exploration of the Carboniferous once a market and an off-take route to that market are established.