Abstract We briefly outline the progressive development of approaches to both the characterization and simulation of the hydrogeology of northern European chalk aquifers, which were some of the first in the world to be studied. The volume's scope includes work on water resources and quality, chalk streams and wetland ecosystems, chalks as heat reservoirs for building temperature regulation, sources of groundwater flood risk and impacts of engineering on the subsurface, and diffuse and point-source pollution affecting these aquifers. It excludes hydrocarbon-related studies and those focused on offshore chalk sequences. We briefly outline the current state of knowledge of hydrogeological processes, characterization, assessment and modelling, and the increasingly recognized importance of karst features. The latter were little discussed 20 years ago and are still often neglected. There follows a brief quantitative analysis of publication topics relating to chalk hydrogeology in the scientific literature over the past three decades, which highlights key trends including both the purposes of studies and the methods employed. We present a summary of the topics and contributions within this volume, and conclude by identifying the key issues that need to be addressed in order to ensure the sustainability of our chalk aquifers for the future.

Abstract Chalk porosity plays a decisive role in the transport of solutes and heat in saturated chalk. From a geological point of view, there are at least two types of porosity: the porosity of pores corresponding to the micro-spaces between the fossil coccoliths that form the chalk matrix and the porosity owing to the micro- and macro-fractures (i.e. secondary porosity). For groundwater flow, the fracture porosity is a determining factor at the macroscopic scale. The multiscale heterogeneity of the porous/fractured chalk induces different effects on solute and heat transport. For solute transport considered at the macroscopic scale, tracer tests have shown that the ‘effective transport porosity’ is substantially lower than the ‘effective drainable porosity’. Moreover, breakthrough curves of tracer tests show an important influence of diffusion in a large portion of the ‘immobile water’ (‘matrix diffusion’) together with rapid preferential advection through the fractures. For heat transport, the matrix diffusion in the ‘immobile water’ of the chalk is hard to distinguish from conduction within the saturated chalk.

Abstract The historical view of an equable Jurassic greenhouse world has been challenged by recent studies documenting recurrent alternation between contrasting climate modes. Cooling of high-latitudinal areas may have been caused by orogenic processes at the northern margin of the Tethys Ocean that reduced heat transport towards the polar regions. Warm phases correlate to periods of intensified volcanism. The Jenkyns Event occurred during the transition from a late Pliensbachian icehouse into an early Toarcian greenhouse. Parallel evolution of different environmental processes, including sea level, climate and carbon cycle, indicate a causal mechanism tied to astronomical forcing. Insolation-controlled variations in the extent of the cryosphere (ice caps and permafrost) facilitated orbitally paced sea-level cycles via waxing and waning of the polar ice caps, and negative carbon isotope excursions via the release of cryosphere-bound 12 C-enriched carbon. This review and synthesis of sedimentological, geochemical and palaeontological palaeoenvironment indicators, and of simulations from climate models, aims to reconstruction, in particular, the high-latitudinal environmental conditions of late Pliensbachian–early Toarcian times. Focus is laid on the extent of the regions that were potentially suitable for hosting a cryosphere. An environmental response to cryosphere dynamics is considered to have been a key component of the Jenkyns Event.