Abstract Chalk and limestone aquifers contribute one-third of the drinking water supply in Denmark, and one-sixth of that national groundwater resource is assessed as having a ‘Poor’ status in terms of the quantitative Water Framework Directive due to intensive abstraction. This paper describes the national groundwater level monitoring network with regard to the following three applications: (1) when used for the annual surveying and reporting of groundwater resources and impacts from climate and groundwater abstraction; (2) as part of real-time monitoring and modelling for daily and seasonal forecasting; and (3) for tracking long-term climate change impacts on groundwater levels. Groundwater level monitoring provides a particularly important indicator of abstraction pressure and sustainable balance compared with recharge. Many larger chalk and limestone groundwater bodies in Denmark are only monitored by local water companies and not represented in the national groundwater level network. This raises the concern that current national groundwater level monitoring does not fully support integrated modelling and assessment purposes for chalk and limestone groundwater bodies. This also implies that, for tracking long-term climate change and anthropogenic impacts on groundwater levels, the national groundwater monitoring network especially lacks long-term records with complete 30-year time-series for many intensively exploited large chalk and limestone aquifers.

Abstract Sequence stratigraphy has become a powerful tool in the basin analysis of the North Sea Basin, and will continue to be important in the maximization of the remaining hydrocarbon resources of Jurassic reservoirs in the region, whilst also moving through the energy transition. This chapter provides background to the main theme of this memoir, which is the description of a revised sequence stratigraphy scheme for the Jurassic–lowermost Cretaceous of the region, recognizing 39 stratigraphic sequences (‘J sequences’). The sequences are illustrated by 85 reference wells (56 UK wells, 22 Norway wells and seven Denmark wells), showing chronostratigraphy, lithostratigraphy, wireline logs and key biostratigraphic markers. The reference wells illustrate sequence development, together with their lower and upper boundaries. Comparisons of the North Sea Jurassic sequences with onshore outcrop sections, from the UK, demonstrate that many of the sequences can be recognized onshore. A comparison of the well sequences with seismic sequences is made in 17 illustrated seismic lines, demonstrating the seismic expression of many of the defined sequences. The recognition of a consistent set of stratigraphic sequences across the region allows a much better understanding of the development of the whole area during the Jurassic, which is currently hindered by the existence of multiple local and semi-regional lithostratigraphic schemes, in particular the differing notations that are utilized in the various international offshore jurisdictions that exist across the area.

Abstract This chapter describes Lower Jurassic second-order sequences J00 and J10, and their component third-order sequences J1–J6 and J12–J18. Two sequences (J1 and J3) are new, four sequences (J2, J4, J12 and J16) are amended and one sequence (J17) is renamed. A significant unconformity at the base of the J12 sequence (Upper Sinemurian) is present near the base of the Dunlin Group in the North Viking Graben–East Shetland Platform and in the Danish Central Graben, and correlates with an equivalent unconformity around the margins of the London Platform, onshore UK. A marked unconformity at the base of the J16 sequence is recognized in the North Viking Graben and onshore UK, where it is related to structural movements on the Market Weighton High, eastern England. Several levels of carbon enrichment (carbon isotope excursions (CIEs)) and associated geochemical changes tie to J sequences defining maximum flooding surfaces: the Upper Sinemurian CIE equates to the base J6 maximum flooding surface (MFS), the basal Pliensbachian CIE ties to the base J13 MFS, the basal Toarcian CIE relates to the base J17 MFS and the Toarcian Ocean Anoxic Event corresponds with the base J18 MFS.

Abstract The application of sequence stratigraphic concepts and methods augments the efficient development of North Sea hydrocarbon fields with Jurassic reservoirs. In particular, the approach provides enhancements to the development of robust reservoir zonations, more accurate assessments of the extent and continuity of reservoir zones and flow units, clearer identification and prediction of the most productive reservoir intervals, improved understanding of field-wide pressure barriers or baffles to fluid flow, and enhanced reservoir models. In addition, carbon capture and storage (CCS) projects in Jurassic rocks will benefit from the adoption of a sequence stratigraphic approach by enhancing the understanding of storage unit architecture, connectivity and top seals. In this chapter, these applications are discussed with reference to around 20 case studies from the North Sea Basin.

Abstract The most important North Sea Jurassic–lowermost Cretaceous lithostratigraphic units, as developed in the UK, Norway and Danish sectors, are summarized in this chapter (55 units from the UK, 25 from Norway and 10 from Denmark). Some significant issues remain with the use and application of lithostratigraphic terminology in the Jurassic of the North Sea Basin. In particular, there are inconsistencies in unit definition and nomenclature changes across country sector boundaries that obscure the recognition of regional stratigraphic patterns that exist across the region. To aid clarity and to overcome some issues of definition, some revisions are made to the existing lithostratigraphic schemes. Several informal lithostratigraphic units are described, a number of unit definitions are revised and various formerly informal units are formalized (Buzzard Sandstone Member, Ettrick Sandstone Member and Galley Sandstone Member). It is recommended that use of the Heno Formation in offshore Denmark is discontinued. In addition, four new lithostratigraphic member terms are introduced (Home Sandstone Member, North Ettrick Sandstone Member, Gyda Sandstone Member and Tambar Sandstone Member). All described units are placed into a sequence stratigraphic context. All significant lithostratigraphic boundaries conform with key sequence stratigraphic surfaces.

Abstract An updated, integrated biozonation scheme for the Jurassic (Hettangian)–lowermost Cretaceous (Upper Berriasian) of the North Sea Basin incorporates 49 palynology biozones plus subzones (based on dinocysts, spores and pollen) and 27 microfaunal zones plus subzones (based on foraminifera, radiolaria and ostracods) to provide the essential chronostratigraphic calibration of the defined sequences. The biozonation scheme is tied to standard ammonite zonal chronostratigraphy wherever possible. Parts of the biozonation scheme are also applicable to onshore UK (boreholes and outcrops), onshore Denmark (boreholes) and offshore Netherlands.

Abstract An updated sequence stratigraphic framework, comprising 39 third-order stratigraphic sequences, for the Jurassic–lowermost Cretaceous of the North Sea, is described by reference to key wells and seismic lines across the UK, Norway and Denmark sectors, and, where possible, to onshore UK outcrops. It appears evident that regional tectonics provided the main control on sequence development, particularly during the Late Jurassic. There is a close relationship between key sequence stratigraphic surfaces and many lithostratigraphic formation and member boundaries throughout the North Sea Jurassic. Four new sandstone members are defined. A biozonation scheme for the study interval is described that provides essential characterization of the defined sequences.