Publications
A cluster of the brachiopod Magas chitoniformis (von Schlotheim, 1813) represents settling of a single spatfall on a soft-bodied substrate, probably a sponge: instantaneous burial by a chalk ooze debris flow (Maastrichtian, Denmark).
A remarkable discovery at Stevns Klint, Denmark, reveals a monospecific cluster of the brachiopod Magas chitoniformis preserved in uppermost Maastrichtian chalk. The 53 well-preserved specimens, exhibiting a unimodal size-frequency distribution, indicate they represent a single successful spatfall likely attached to a soft-bodied sponge. The absence of transport or winnowing suggests instantaneous burial by a chalk ooze debris flow, potentially triggered by a major earthquake in the tectonically active Sorgenfrei-Tornquist Zone. This finding provides exceptional evidence of brachiopod attachment to a soft-bodied organism, offering insights into paleoecological dynamics and sedimentary processes during the Late Cretaceous.
A diminutive pterosaur from the uppermost Maastrichtian chalk of Denmark
A diminutive pterosaur, represented by a fragment of its finger bone, has been discovered in the uppermost Maastrichtian chalk at Stevns Klint, a UNESCO World Heritage site in Denmark. This finding marks the first record of a pterosaur from the chalk of Denmark and challenges previous hypotheses about Late Cretaceous niche partitioning between pterosaurs and birds. The specimen, identified as a proximal phalanx 1 of digit IV, indicates that small-bodied pterosaurs with wingspans under 50 cm persisted until the final 50,000–60,000 years of the Cretaceous period. Researchers compared the fragment to similar elements to determine its size and morphology, providing new insights into the evolutionary dynamics of these prehistoric creatures during a critical period of ecological transition.
Ammonite survival across the Cretaceous–Paleogene boundary confirmed by new data from Denmark
New evidence from Stevns Klint, Denmark, confirms that ammonites survived the Cretaceous–Paleogene extinction event. Researchers analyzed fossil specimens from the Cerithium Limestone Member, revealing that most ammonites in this unit are autochthonous Danian survivors, not redeposited Maastrichtian fossils. Only one specimen was identified as reworked from the Maastrichtian era. The study combines taphonomic and sedimentological analyses to support this conclusion, challenging previous assumptions about ammonite extinction. This finding raises questions about what ultimately caused the demise of the last surviving ammonites on Earth.
Carbonated Smart Water Injection for Optimized Oil Recovery in Chalk at High Temperature
Injecting carbonated seawater (CSW) slightly enhances oil recovery in chalk reservoirs at high temperatures, making it the most effective brine among tested options. This study, using Stevns Klint outcrop chalk as an analogue for North Sea chalk reservoirs, found that CSW outperformed other brines like formation water (FW), seawater (SW), and carbonated formation water (CFW) in both secondary and tertiary flooding modes. While oil swelling and viscosity reduction were initially hypothesized as key mechanisms, the research suggests wettability alteration is more likely responsible for the observed increase in oil recovery. The study also confirmed CO2 diffusion from the brine to the oil phase but noted that a significant amount of CO2 remained in the brine, with no notable mineral dissolution or changes in pore surface minerals. These findings highlight the potential of carbonated smart water injection as an environmentally friendly method to boost oil production while reducing greenhouse gas emissions.
Reaction Kinetics Determined from Core Flooding and Steady State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature
A novel methodology to determine reaction kinetics using core flooding and steady-state principles reveals that the dissolution of calcite and precipitation of magnesite in chalk reservoirs occur in a substitution-like manner, with calcium (Ca²⁺) production closely matching magnesium (Mg²⁺) loss. This approach, applied to Stevns Klint chalk from Denmark and Kansas chalk from the USA, demonstrates computationally efficient modeling that avoids complex spatial-temporal simulations. The study, conducted at reservoir temperatures of 100°C and 130°C, shows that injected MgCl₂ brine alters rock wettability and strength, with implications for oil recovery and reservoir management. By varying injection rates and using shut-in tests, the researchers accurately characterized reaction kinetics, providing insights into geochemical behavior under dynamic conditions.
Reaction Kinetics Determined from Coreflooding and Steady-State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature
Researchers have developed a novel methodology to determine reaction kinetics using coreflooding and steady-state principles, which efficiently characterizes chemical interactions in chalk reservoirs without requiring complex spatial modeling. The study, conducted on Stevns Klint (Denmark) and Kansas (USA) chalks at reservoir temperatures (100–130°C), demonstrated that Ca²⁺ ions were produced while Mg²⁺ ions were retained during injection with MgCl₂ brine, indicating calcite dissolution and magnesite precipitation. This substitution-like process was successfully modeled using a simple kinetic framework with three parameters, which accurately predicted chemical interactions in both oil-bearing chalk reservoirs and outcrop chalks. The methodology offers computational efficiency for reactive flow modeling, particularly for chemically sensitive reservoirs like those at UNESCO World Heritage Site Stevns Klint, where injected seawater can impact wettability and rock strength.
Adsorption of Crude Oil Components onto Carbonate and Sandstone Outcrop Rocks and Its Effect on Wettability
Research at Stevns Klint reveals that the mineral composition of rocks significantly influences how crude oil components adsorb onto their surfaces, thereby altering wettability—a critical factor for oil recovery. The study found that pure chalk preferentially adsorbs acidic components, while sandstone favors basic ones. Silica-containing chalk showed a reduced affinity for acids due to negatively charged minerals, highlighting the complex interplay between rock mineralogy and crude oil-brine interactions. Core flooding tests with light crude oils demonstrated that adsorption of polar organic components reduces water wetness across all tested cores (pure chalk, silica-containing chalk, and sandstone), emphasizing the profound impact of mineral composition on wettability dynamics. These findings underscore the importance of considering rock mineralogy when restoring core material wettability in laboratory settings.
Crude Oil–Brine–Rock Interactions in Tight Chalk Reservoirs: An Experimental Study
A systematic experimental study reveals that polar components in crude oil significantly alter wettability during ageing, directly influencing oil production behavior in tight chalk reservoirs. The research demonstrates that both formation water and ten-times-diluted seawater outperform seawater for enhanced oil recovery (EOR) in the Dan field. Additionally, the modified flow zone indicator, a measure of rock quality, is identified as the primary factor behind higher oil recoveries observed in Tor core samples. The study employed dynamic ageing methods on short chalk cores from Stevns Klint outcrops and reservoir plugs, using synthetic multicomponent brines under optimized capillary-dominant regimes. Fluid distribution and brine composition changes were analyzed via ion chromatography and X-ray computed tomography, providing critical insights into EOR strategies for tight chalk reservoirs.
Prognathodon (Squamata, Mosasauridae) from the Maastrichtian chalk of Denmark
Paleontologists have identified two mosasaur tooth crowns from the Maastrichtian chalk sequences of Stevns Klint and Møns Klint, Denmark, belonging to the genus Prognathodon. This discovery marks the first record of this mosasaur genus in Denmark, adding to the existing diversity documented by previous findings of Plioplatecarpus, Mosasaurus, and Carinodens. The study highlights the coexistence of four mosasaurid genera in Danish chalk, mirroring similar assemblages from the Maastrichtian type areas in the Netherlands and Belgium. By analyzing fossilized teeth, researchers reconstructed the paleobiodiversity of marine reptiles during the late Cretaceous period, providing new insights into the evolutionary history and ecological dynamics of these apex predators.
The K–T boundary strata north of Korsnæb, Stevns Klint, Denmark – evolution and geometry revealed in a long, horizontal profile
A 460-meter-long profile of the Cretaceous–Paleogene (K–T) boundary strata at Stevns Klint, Denmark, reveals unprecedented details about the stratigraphy, geometry, and paleotopography of this globally significant geological section. The profile, originally measured by Professor A. Rosenkrantz in 1944, was rediscovered in 2021 and provides critical insights into the boundary strata's evolution, which marks one of Earth's most profound mass extinctions. This coastal section, adjacent to a limestone quarry, showcases fine exposures of lower Danian bryozoan mounds and is partially covered by beach ridges composed of flint rubble. The study underscores the scientific and educational value of Stevns Klint while also highlighting its vulnerability to quarrying activities.
Enrichment of chalcophile elements in seawater accompanying the end-Cretaceous impact event
A new study reveals that chalcophile elements, such as copper (Cu), silver (Ag), and lead (Pb), were significantly enriched in seawater during the end-Cretaceous asteroid impact event. This enrichment is evidenced by their correlation with iridium (Ir) concentrations in Cretaceous–Paleogene (KPg) boundary clays from Stevns Klint, Denmark. Synchrotron X-ray fluorescence imaging showed that Cu and Ag were present as trace elements in pyrite grains or as discrete phases, suggesting different carrier materials transported these elements to the seafloor. The study proposes that iron oxides/hydroxides and organic matter acted as potential carriers for chalcophile elements, which were released during impact heating of target rocks. Intense acid rain following the impact may have further contributed to the enrichment of these elements, particularly those forming acid-soluble sulfides.
Kinetics of Calcite Dissolution and Ca–Mg Ion Exchange on the Surfaces of North Sea Chalk Powders
Research on Stevns Klint chalk reveals that Ca-Mg ion exchange, not calcite dissolution alone, is the dominant process in fluid-rock interactions during smart waterflooding in carbonate reservoirs. The study found two distinct kinetic phases: a rapid initial step within the first hour and a slower, prolonged second phase lasting beyond two weeks. A two-layer adsorption model successfully explained these kinetics, with findings suggesting that competitive cation adsorption controls the process at lower temperatures, while Ca-Mg exchange dominates at higher temperatures. These insights challenge the assumption that calcite dissolution alone accounts for enhanced oil recovery in reservoirs.
The role of polar organic components in dynamic crude oil adsorption on sandstones and carbonates
Crude oil injection shifts sandstone and carbonate cores to a mix-wet state, reducing capillary forces and moving them away from water-wet conditions. This effect is more pronounced with acidic polar components on carbonates than on sandstones, where basic polar components play a greater role in wettability changes. The study used outcrop materials—sandstone containing quartz, illite clay, and feldspars, and high-purity calcium carbonate from Stevns Klint—to analyze dynamic adsorption of low-asphaltene crude oils at 50°C. By measuring acid (AN) and base numbers (BN), researchers found that polar organic components (POCs) significantly influence reservoir wettability, offering insights to optimize waterflooding operations for enhanced oil recovery.
Diagenesis of Flint and Porcellanite in the Maastrichtian Chalk at Stevns Klint, Denmark
Flint nodules in the Maastrichtian chalk of Stevns Klint, Denmark, form through early diagenetic processes driven by microbial activity and low sedimentation rates. The study identifies four types of siliceous nodules—porcellanite, white flint, white flint with a dark core, and dark flint—composed primarily of microquartz, lutecite, chalcedony, megaquartz, and dolomite. Stable isotope analysis (δ18Osmow) indicates precipitation temperatures ranging from 15–17°C for microquartz and lutecite to up to 48°C for megaquartz, suggesting a transformation pathway from silica gel or opal-CT via dissolution-precipitation (Ostwald ripening). The research proposes that microbial decomposition of organic matter at the redox boundary below the seafloor initiated flint formation during periods of minimal sedimentation. This process implies that flint deposition reflects shallow-water conditions with high biosiliceous input and microbial activity, offering potential paleo-oceanographic insights for shallow carbonate systems.
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