Bituminous shales can often be demonstrated to be relatively deep water deposits and tend to occur near the base of transgressive sequences, implying rather rapid rises of sea level, but they probably formed at a variety of depths controlled primarily by regional topographic restrictions on bottom water circulation. Oolitic ironstones, in contrast, frequently mark the late stages of regional regressions, with terrigenous input to the depositional area diminishing in many places as the sea shallowed. Many such regional changes in water depth can be related to eustatic rises and falls of sea level, not only for the NW European Jurassic, from which most examples are taken, but for rocks ranging widely through the Phanerozoic. The evidence from bituminous shales and ironstones supports a Jurassic eustatic model characterised by moderately rapid rises and falls of sea level, separated by longer phases of stillstand.

The interplay of regional or global sea-level changes and continuing crustal extension related to rifting in the North Atlantic and Tethyan megarifts dominated the palaeogeographical evolution of the area. The sea-level rise that commenced in the Rhaetian continued into the Jurassic to usher in a new phase of predominantly marine sedimentation across northwest Europe. The climate was warm and humid, the seas generally shallow. Land areas became well vegetated, as attested by the abundance of fossil driftwood in marine as well as non-marine sediments. The region probably lay about 10° south of present latitudes, in an area of overlap of Tethyan and Boreal marine realms. For much of the Jurassic, sea levels continued to rise but two major falls occurred, coinciding with accelerated extensional movements in the area. The first was during the mid-Jurassic ('mid-Cimmerian phase') when there was a major regional upwarp centred on the North Sea, and the second across the Jurassic/Cretaceous boundary ('late Cimmerian phase') when a global fall in sea level coincided with an important phase of rifting and block faulting. Major structural trends generally follow previously established lines. The basic structural framework for the Jurassic maps has been compiled from numerous sources, including Andrews &Brown (1987); Dunning (1985); Evans et al. (1982); Gardiner &Sheridan (1981); Van Hoorn (1987); Thomas et al. (1985); Whittaker (1985); Ziegler (1982, 1987); and papers in Brooks &Glennie (1987). Fault trends are generalized and selected to pick out the main structural features controlling the geography; their occurrence on

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SummaryA virtually complete Jurassic sequence recently drilled in north Lincolnshire is considered in a regional context. Liassic thicknesses and facies are largely unexceptional. The Frodingham and Pecten Ironstones are relatively thin and sandy, but the Marlstone Rock Bed is thicker and more ferruginous than elsewhere in the region. The Inferior Oolite is exceptionally thick and exhibits strong deltaic influence; equivalents of the Gristhorpe Member and Scarborough Formation of Yorkshire may be present. The Great Oolite was deposited in coastal-lacustrine-deltaic environments, more proximal than to the south or east. Thin Kellaways Clay separates the argillaceous Cornbrash from the Kellaways Sand. The organic-rich Lower Oxford Clay is thin owing to a basal non-sequence whilst the Upper Oxford Clay is condensed and less organic than in the East Midlands. The regressive West Walton Beds are followed by very thick Ampthill and Kimmeridge Clay sections beneath the Spilsby Sandstone. Regional thickness and facies analysis records the behaviour of the Market Weighton Block and reveals the influence of the Pennine High as both a positive tectonic feature and an occasionally active sediment source.