Abstract A number of rock samples were collected from two dredge positions on the Lomonosov Ridge at water depths of 2–3.5 km. The dredge samples are dominated by sediments deformed and metamorphosed under greenschist-facies conditions 470 myr ago according to 40 Ar/ 39 Ar dating of metamorphic muscovite. This shows that the Lomonosov Ridge was involved in a major Mid-Ordovician orogenic event that correlates with early arc–terrane accretion observed in northern Ellesmere Island, Svalbard, and other parts of the Caledonian belt. Detrital zircon age spectra of these metasediments span the Mesoproterozoic–Palaeoproterozoic with a main peak at around 1.6 Ga, and a pattern similar to that known from Caledonian metasedimentary rocks in East Greenland and northern Norway, as well as from Cambrian sediments in Estonia and Palaeozoic sediments on Novaya Zemlya. A second population of dredge samples comprises undeformed, non-metamorphic sandstones and siltstones. Detrital zircons in these sediments span the Palaeoproterozoic with a few Archaean zircons. Both rock types are covered by an up to 8 Ma ferromanganese crust and are evaluated to represent outcrop, and apatite fission-track data from three of the rock samples indicate that exposure at the seabed corresponds to a regional event of uplift and erosion that affected the Arctic in the Late Miocene. The data from the Lomonosov Ridge suggest that the 470 Ma orogenic event extended from Scotland and northern Scandinavia into the Arctic, including Svalbard, the Pearya Terrane and the Chukchi Borderlands. Supplementary material: Detrital zircon age data and details of the thermal history constraints are available at: https://doi.org/10.6084/m9.figshare.c.3852151

Abstract Despite representing a widespread play in the Central North Sea, production from Lower Cretaceous chalks is currently confined to the Valdemar Field in the Danish Central Graben. The field comprises a heterogeneous reservoir succession, less than 100 m thick, consisting of hemipelagic chalks, marly chalks, and marlstones of Late Hauterivian-Early Aptian age. Although the field has in-place reserves in the order of 115 × 10 6 m 3 (725 × 10 6 BBL), the recovery from this complex reservoir was initially estimated to be only approximately 1%, primarily due to low permeability. The argillaceous chalks of the Lower Cretaceous reservoir are highly faulted and fractured, overpressured and undercompacted, giving rise to a complex distribution of hydrocarbons. Due to the lithological heterogeneity of the succession, internal stratigraphic barriers are common and result in stratigraphic compartmentalization. In addition, clay smearing in fault zones has created structural barriers and the development of structural compartments, as reflected by spatial differences in oil saturations, oil types and maturity, formation pressure and porosity distribution. Analysis of the reservoir properties and structural development of the Valdemar Field has provided data that can be extrapolated to the remainder of the Danish Central Graben, indicating that the Lower Cretaceous is most prospective in the central and southern Danish Central Graben.