Publications
The last Mesozoic brachiopods
A remarkable discovery of the last Mesozoic brachiopods, dating to the topmost Maastrichtian chalk just below the Cretaceous–Paleogene (K–Pg) boundary clay at Stevns Klint, Denmark, sheds light on the climax of a specialized fauna that thrived in the Chalk Sea for 34 million years. This rich brachiopod assemblage, comprising 28 micromorphic species and 1967 individuals, represents the highest richness recorded from any Danish section at or near the K–Pg boundary, surpassing even the most benthos-rich parts of the Upper Cretaceous Chalk Group. The sample, derived from a 25 kg bulk chalk residue, showcases an extraordinary diversity and abundance, reflecting the full range of morphological adaptations to life on fine-grained seafloor. This finding underscores the unique macro-habitat of the Chalk Sea and provides critical insights into the evolutionary trajectory of its brachiopod fauna in the lead-up to the cataclysmic boundary event.
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.
Adsorption of Crude Oil Polar Components onto Silica-Rich Chalk and its Impact on Wetting
A comparative study of silica-rich Aalborg chalk and pure Stevns Klint chalk reveals that silica content significantly influences the adsorption of polar crude oil components, particularly basic compounds. While acidic component adsorption was less pronounced than in pure chalk, basic component adsorption was notably higher due to negatively charged silicate surfaces. This process instantaneously alters the water-wetness of Aalborg chalk, reducing its initial wettability after crude oil exposure. The findings provide critical insights for modeling initial reservoir wetting and understanding oil production dynamics in chalk reservoirs under normal water injection or Smart Water wettability alteration techniques.
Asteroidenedslag på Jorden og dinosaurernes endeligt – spor i Stevns Klint
A thin layer of clay at Stevns Klint, Denmark, contains extraterrestrial traces from the catastrophic asteroid impact that led to the extinction of dinosaurs and over half of Earth's life 66 million years ago. This Fiskeleret layer marks the end of the Cretaceous period and the beginning of a new era. The findings provide evidence of how the asteroid collision triggered one of the most significant mass extinctions in Earth's history, offering insights into the dramatic transition between geological epochs. Stevns Klint serves as a classic site for studying the Cretaceous-Paleogene boundary, making it an ideal location for educational fieldwork.
Bryozoan limestone experience—the case of Stevns Klint
Bryozoan limestone, a distinctive Danian formation underlying younger geological layers, exhibits unique mechanical properties influenced by its mineralogy and porosity. This study reveals that the similarity in mineral composition between Bryozoan limestone and Cretaceous chalk leads to comparable mechanical responses, despite variations in flint content and other materials. Investigations at Stevns Klint provide critical insights for infrastructure design, such as rock anchors. The research leverages an extensive database of geological data from major projects, including borehole registrations, wireline logging, and advanced laboratory tests, to interpret the mechanical behavior of Bryozoan limestone. This comprehensive approach enhances our understanding of this formation's structural characteristics and its implications for engineering applications.
Impact of Temperature on Wettability Alteration by Smart Water in Chalk
A significant temperature-dependent effect on wettability alteration by Smart Water (SW0Na) was observed, with the most pronounced change toward water-wet conditions occurring at 110 °C. This finding suggests that higher temperatures enhance the reactivity of potential determining ions in Smart Water, thereby improving oil recovery in chalk reservoirs. The study used outcrop Stevns Klint chalk cores and a model crude oil to evaluate spontaneous imbibition and calculate a modified Amott water index (Iw*). While no significant wettability alteration was detected at 70 °C or with standard formation water (FW) at 90 °C, SW0Na at 90 °C and above demonstrated substantial improvements. This insight could optimize Smart Water-based enhanced oil recovery (EOR) strategies in carbonate reservoirs.
Towards Identifying the Mechanisms of the Modified-Salinity Waterflooding by a Novel Combination of Core flooding and Mathematical Modeling
A novel approach to understanding modified-salinity waterflooding in carbonates, particularly in outcrop chalk like Stevns Klint, reveals that wettability changes driven by the adsorption of potential determining ions (PDIs), such as calcium, are critical to oil breakthrough times. Unlike traditional models focusing solely on recovery factors and pressure drops, this study prioritizes matching ion concentrations and oil breakthrough timings, identifying PDI adsorption as a key mechanism. By combining core flooding experiments with advanced mathematical modeling and optimization algorithms, researchers demonstrated that lower salinity brines can also induce wettability changes independently of ionic adsorption. While the approach remains semi-empirical, it provides a foundation for future fundamental studies to unravel the precise mechanisms underlying these processes.
XAFS study of Sb and As in Cretaceous–Tertiary boundary sediments: an index of soiling of the global environment with dust and ashes from impact ejecta falls
Research at Stevns Klint, Denmark, reveals that unusually high concentrations of pentavalent antimony (Sb5+) and arsenic (As5+) in Cretaceous–Tertiary boundary sediments serve as a global environmental indicator. These elements, coprecipitated with iron oxides like ferrihydrite (schwertmannite), suggest widespread contamination by dust and ashes from asteroid impact ejecta falls during this geological transition. The study employed X-ray absorption fine structure (XAFS) spectroscopy to analyze the chemical states and coordination environments of Sb and As, confirming their incorporation into low-crystalline ferrihydrite structures with an Sb–O interatomic distance of 1.99(1) Å. This finding highlights a unique environmental signature in these sediments, distinct from modern soil contamination.
Effect of Initial Wetting on Smart Water Potential in Carbonates
A significant discovery in carbonate reservoir engineering reveals that initial wettability in carbonates can be established almost instantly through the adsorption of polar components from crude oil, eliminating the need for prolonged aging. The study demonstrates that acidic polar components play a crucial role in altering wettability towards less water-wet conditions, with adsorption occurring most rapidly during the first pore volumes of oil injection. Increasing surface accessibility by reducing initial water saturation enhances this process, highlighting its strong influence on initial wettability. Unlike traditional methods relying solely on aging, this research shows that mixed wettability can be achieved efficiently through immediate adsorption, offering a more time-effective approach for laboratory experiments and potentially improving 'Smart Water' injection strategies in carbonates.
Evolution of contourite systems in the late Cretaceous Chalk Sea along the Tornquist Zone
Late Cretaceous bottom currents shaped the southern Baltic Sea's seafloor, creating two major contourite systems along the Tornquist Zone. Seismic and well data reveal that Turonian to Campanian tectonic uplift formed obstacles influencing these currents. A shallow, south-east directed flow generated contourite channels and drifts, including the system offshore Stevns Klint. A deeper, north-west current emerged later, forming a drift-moat system linked to the Alnarp Valley in Scania. This study integrates findings from the Kattegat and Stevns Klint, linking them to these inferred currents.
Shelf hypoxia in response to global warming after the Cretaceous-Paleogene boundary impact
Global warming following the Chicxulub asteroid impact at the Cretaceous-Paleogene (K-Pg) boundary triggered shelf hypoxia, offering a parallel to current climate change. The study, analyzing high-resolution geochemical and paleontological records from Stevns Klint (Denmark), Brazos-1 (Texas, USA), and Caravaca (Spain), reveals that rapid warming post-impact led to oxygen-depleted bottom waters due to reduced gas solubility, decreased ocean ventilation, and increased nutrient inputs. This hypoxia caused significant stress on benthic communities, highlighting the ecological consequences of abrupt climate shifts.
After the disaster: Bony fish remains (mostly otoliths) from the K/Pg boundary section at Stevns Klint, Denmark, reveal consistency with teleost faunas from later Danian and Selandian strata.
A groundbreaking analysis of bony fish remains, particularly otoliths, from the K/Pg boundary section at Stevns Klint, Denmark, reveals a striking consistency in teleost faunas across the Cretaceous-Paleogene (K/Pg) mass extinction event and into the Danian and Selandian stages. The study identified six otolith-based taxa from the uppermost Maastrichtian and three from the basal Danian, with notable overlaps such as Polymixia? harderi persisting through the boundary and Centroberyx sp. representing a common genus in both periods. Contrary to expectations, no evidence of phased extinction was found, suggesting remarkable resilience in early Paleocene fish faunas. The research relied on imprints from dissolved aragonitic otoliths and bone fragments, offering a unique window into post-disaster marine ecosystems.
First record of Carinodens (Squamata, Mosasauridae) from the uppermost Maastrichtian of Stevns Klint, Denmark
A significant discovery at the UNESCO World Heritage Site Stevns Klint, Denmark, reveals the first record of Carinodens minalmamar, a rare durophagous mosasaur, from the uppermost Maastrichtian strata. This tooth crown, found within 50,000 years of the K/Pg boundary, represents the northernmost occurrence of the genus and adds a new trophic niche to the Late Cretaceous marine reptile record in Denmark. Previous finds from the region were limited to hypercarnivorous mosasaurids like Mosasaurus hoffmannii and Plioplatecarpus sp., suggesting a more diverse food web during this period. The study, published in Alcheringa, highlights the importance of Stevns Klint as a key site for understanding Late Cretaceous biodiversity.
Review of the Danian vertebrate fauna of southern Scandinavia.
A diverse Danian vertebrate fauna, spanning four classes and 54 identifiable genera, has been documented from southern Scandinavia. The study reveals that while fish remains are common in Danian limestones, the Fiskeler Member at Stevns Klint (a UNESCO World Heritage Site) stands out for its significant shark teeth and bony fish fragments. Articulated fish remains are also noted in the Limhamn quarry and København Limestone Formation. The research identifies a range of taxa, including the gavialoid crocodylian Thoracosaurus, fragmentary turtle material, and bird remains exclusively from the Limhamn quarry. Despite the fragmentary nature of many findings, the study provides a comprehensive overview of the region's vertebrate diversity during the Danian age.
Thermodynamic Analysis of Chalk–Brine–Oil Interactions
A thermodynamic model initially developed for calcite-brine interactions fails to accurately predict reactive transport in natural carbonates, such as Stevns Klint chalk. Researchers found that ζ potential data alone is insufficient for optimizing surface complexation models (SCMs) for predicting ion breakthrough during core flooding experiments. By refining the SCM with coupled transport modeling and incorporating chromatographic data, they successfully correlated remaining oil saturation in spontaneous imbibition experiments to the bonding between amine/carboxylate groups on oil surfaces and carbonate/protonated calcium sites on chalk. This study advances understanding of chalk-oil-brine interactions, offering insights for enhanced oil recovery strategies.
An introduction to the Mesozoic biotas of Scandinavia and its Arctic territories
Scandinavia and its Arctic territories host some of the most significant Mesozoic fossil deposits globally, offering unparalleled insights into the region's rich biodiversity during this era. Notably, the UNESCO World Heritage Site at Stevns Klint in Denmark provides one of the most complete Cretaceous–Palaeogene boundary sections worldwide, while other key sites like Svalbard and the Kristianstad Basin in Sweden have revealed exceptional fossiliferous Lagerstätten. These deposits document diverse marine palaeocommunities, including benthic macroinvertebrates, pelagic cephalopods, chondrichthyans, actinopterygians, and aquatic amniotes such as ichthyopterygians and mosasauroids. Terrestrial plant remains, including exceptionally preserved carbonized flowers, further enrich the fossil record, occasionally accompanied by faunal traces like temnospondyl bones and dinosaur footprints. Despite substantial progress in research over the past 15 years, significant gaps remain, underscoring the potential for future discoveries that could deepen our understanding of Mesozoic life and environments.
Electrokinetics of Carbonate/Brine Interface in Low-Salinity Waterflooding: Effect of Brine Salinity, Composition, Rock Type, and pH on ?-Potential and a Surface-Complexation Model
A comparative study of carbonate rocks reveals that surface charge behavior is consistent across different rock types, with ζ-potential becoming more negative as brine salinity decreases. This finding suggests that low-salinity waterflooding can alter wettability in carbonate reservoirs, reducing oil-wetting tendencies. The research used Iceland spar calcite and three reservoir-related rocks—Middle Eastern limestone, Stevns Klint chalk, and Silurian dolomite—to measure ζ-potential across a range of salinities, brine compositions, and pH values. A new surface-complexation model (SCM) was developed to explain the observed increase in ζ-potential with pH, highlighting the influence of surface species like >CaSO4−, >CO3Ca+, and >CO3Mg+. Notably, chalk particles exhibited the most negative surface charges and highest reactivity to changes in pH and salinity, while dolomite showed the least.
Modeling Low-Salinity Waterflooding in Chalk and Limestone Reservoirs
Low-salinity waterflooding can significantly enhance oil recovery in carbonate reservoirs by altering rock wettability from oil-wet to water-wet. A new process-based model, incorporating geochemical interactions between crude oil, brine, and chalk surfaces, reveals that mineral dissolution reactions—particularly those involving anhydrite—play a critical role in improving oil recovery (IOR). Unlike previous empirical models, this approach dynamically adjusts relative permeability and residual oil saturation based on the concentration of oil acids attached to mineral surfaces. Core flooding experiments from Stevns Klint (SK) chalk and Middle Eastern limestone cores were used to validate the model, which predicts IOR ranging from 5% to 20% depending on aqueous chemistry and sweep efficiency. The findings underscore the importance of mineralogy in low-salinity waterflooding simulations.
Silver and silver microparticles of the Cretaceous-Paleogene boundary sediment of Fish Clay Højerup (Stevns Klint, Denmark)
A discovery of micrometer-sized silver particles, embedded within the calcite matrix of the Cretaceous-Paleogene boundary sediment at Stevns Klint, Denmark, suggests a link to the Chicxulub asteroid impact event. These pure silver microparticles (>99% weight) exhibit irregular, rounded, and dendritic shapes with rugged surfaces, as revealed by scanning electron microscopy and energy dispersive X-ray analysis. The findings imply these particles were dispersed globally during or immediately after the impact, offering new insights into the geochemical consequences of large-scale extraterrestrial events.
Weathering and precipitation after meteorite impact of Ni, Cr, Fe, Ca and Mn in K-T boundary clays from Stevns Klint
A study of K-T boundary clays from Stevns Klint, Denmark, reveals that elements such as Ni, Cr, and Fe in impact-related glasses undergo weathering and diagenesis to form stable hydrates and oxides. XANES and EXAFS analyses indicate that these elements adopt structures similar to Ni(OH)₂, Cr₂O₃, and FeOOH, respectively. Notably, Ca maintains a diopside-like structure, potentially retaining information about the meteorite impact conditions. Mn exhibits a divalent state akin to MnCO₃, with its scarcity in Fe-group elements attributed to consumption by life activity or diffusion. This research provides insights into the post-impact chemical transformations and environmental processes at this UNESCO World Heritage Site.
A Mechanistic Model for Wettability Alteration by Chemically Tuned Waterflooding in Carbonate Reservoirs
A novel mechanistic model demonstrates that chemically tuned waterflooding can enhance oil recovery by up to 40% original oil in place (OOIP) in carbonate reservoirs, such as Stevns Klint chalk. The model reveals that sulfate ions (SO₄²⁻) play a pivotal role in altering rock wettability from oil-wet or mixed-wet to more water-wet conditions by replacing adsorbed carboxylic groups on the rock surface, while cations like Ca²⁺ and Mg²⁺ have a minor effect. The study integrates multiphase flow, multicomponent surface complexation, and wettability alteration, showing that optimal brine formulations for chalk contain abundant sulfate (0.096 mol/kg water), moderate cation concentrations, and low salinity (<0.2 mol/kg water). This work provides the first mechanistic coupling of these processes to predict improved oil recovery under varying conditions, offering a powerful tool for optimizing chemically tuned waterflooding in carbonate reservoirs.
Digital models based on images taken with handheld cameras – examples on land, from the sea and on ice
Advancements in Structure from Motion (SfM) and photogrammetry enable the creation of detailed 3D digital outcrop models using images captured with handheld cameras, significantly reducing costs and effort. This study demonstrates the versatility of this approach by generating point clouds at varying scales—from metres to kilometres—across different environments: land (Faxe limestone quarry), sea (Stevns Klint coastal cliff), and ice (A.P. Olsen Land, Greenland). The models reveal outcrop topography or micro-topography with high precision, showcasing the method's potential for geological documentation in diverse and challenging settings.
Modeling Low Salinity Waterflooding in Mineralogically Different Carbonates
Low salinity waterflooding can significantly enhance oil recovery (IOR) in carbonate reservoirs by altering rock wettability from oil-wet to more water-wet. A novel mechanistic model, incorporating surface complexation and aqueous reactions, demonstrates that reducing sodium and chloride concentrations while maintaining sulfate in seawater can improve IOR by up to 6% OOIP in Stevns Klint (SK) chalk. The presence of anhydrite further boosts recovery due to its role as a natural sulfate source. This study extends previous work on spontaneous imbibition, using core flooding experiments and simulations with PennSim to dynamically adjust relative permeability and residual oil saturation based on mineralogy and chemical interactions. Results align closely with experimental data, highlighting the critical importance of aqueous chemistry and mineralogy in optimizing IOR strategies for carbonate reservoirs.
The Effect of Salinity, Rock Type and pH on the Electrokinetics of Carbonate-Brine Interface and Surface Complexation Modeling
Laboratory studies reveal that reducing brine salinity and altering pH can shift carbonate rock wettability toward a less oil-wetting state, driven by changes in surface charge. This effect is consistent across different carbonate rock types—including Stevns Klint chalk, limestone, and dolomite—though chalk exhibits the highest reactivity to pH and salinity changes, while dolomite shows the least. Surface complexation modeling suggests that surface species like >CaSO4-, >CO3Ca+, and >CO3Mg+ significantly influence total surface charge, with pH increasing the zeta-potential by converting negatively charged moieties into neutral ones. These findings provide insights into reservoir behavior under varying salinity and pH conditions, offering a tractable approach to predicting carbonate rock electrokinetic properties.
XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint
A groundbreaking study reveals that zirconium (Zr) in Cretaceous–Tertiary boundary clays from Stevns Klint, Denmark, retains structural signatures of thermal quenching linked to a meteorite impact. Using Zr K-edge X-ray absorption fine structure (XAFS), researchers found that the Zr-O bonding distance and coordination number closely resemble those in rhyolitic volcanic glass and tektites—materials formed during high-temperature, reductive conditions. Notably, the partial reduction of zirconium ions (Zr^3.8+–3.9+) suggests rapid cooling after formation, preserving unique chemical states absent in natural glasses. This discovery offers a novel method to identify sedimentary rocks deposited during extinction events by analyzing Zr's local structure, providing critical insights into the environmental conditions following catastrophic impacts.
A Mechanistic Model for Wettability Alteration by Chemically Tuned Water Flooding in Carbonate Reservoirs
Chemically tuned water flooding can significantly enhance oil recovery in carbonate reservoirs, with potential increases of up to 40% of original oil in place (OOIP). This finding stems from a mechanistic model that elucidates how sulfate ions (SO₄²⁻) replace adsorbed carboxylic groups on rock surfaces, altering wettability from oil-wet or mixed-wet to more water-wet conditions. The model, tuned using experimental data from Stevns Klint chalk, demonstrates that optimal brine formulations for chalk reservoirs contain abundant sulfate (0.096 mol/kg water), moderate cation concentrations, and low salinity (<0.2 mol/kg water). While cations like Ca²⁺ have a minor effect on recovery (~5% OOIP), physical parameters such as rock surface area and diffusion coefficient influence the rate but not the final oil recovery. This research provides a robust tool for predicting improved oil recovery (IOR) under varying conditions, offering practical insights for field applications in carbonate reservoirs.
Oil Recovery Mechanism(s) by Low Salinity Brines and Their Interaction with Chalk
Research demonstrates that low salinity brines (LSW) can significantly enhance oil recovery from chalk reservoirs, with the most effective dilution ratio found to be 1:10 seawater (SSW). The study, conducted using Stevns Klint chalk outcrops from Denmark, revealed that higher calcium ion concentrations in effluent and increased pH—particularly at pH 8—correlate with improved oil recovery. Dissolution and ion exchange processes, including the deficiency of magnesium ions, were identified as key mechanisms contributing to these effects. These processes may also impact chalk integrity, potentially leading to fine migration and reduced flow resistance, which further enhances oil displacement efficiency.
Crossing the boundary: an elasmobranch fauna from S tevns K lint, D enmark
A study of elasmobranch (shark and ray) fossils from Stevns Klint, Denmark, reveals that the fauna experienced only a 33% extinction rate during the Cretaceous-Paleogene (K/T) mass extinction event, contrasting sharply with the 96% extinction observed in Morocco. The research documents rapid recovery of diversity within millennia post-impact, attributing pre-boundary declines to sudden sea-level changes rather than the bolide impact itself. Precision sampling identified rare species like Parasquatina and Echinorhinus, including Europe's first Nebrius fossil, offering new insights into elasmobranch resilience during global crises.
Neoselachians from the Danian (Early Paleocene) of Denmark
A diverse elasmobranch fauna, including the earliest European records of Chlamydoselachus and Heptranchias howelli, was discovered in early to middle Danian deposits at Stevns Klint, Denmark. The study reveals that the K-T boundary did not mark the complete extinction of Cretaceous fauna; several species persisted into the early Paleogene. The research analyzed teeth from 27 shark species across three formations (Rødvig, Stevns Klint, and Faxe), highlighting a transition from an impoverished Maastrichtian fauna to a pronounced cold-water assemblage in slightly younger deposits. This provides critical insights into shark diversity and paleoecological shifts during the earliest Paleogene in the Boreal Sea.
Cliff collapse at Stevns Klint, south-east Denmark
Stevns Klint, a UNESCO World Heritage Site and renowned geological formation, experiences frequent cliff collapses due to the contrast between soft Cretaceous chalk and harder Tertiary bryozoan limestone. This study highlights how the erosion-resistant bryozoan limestone forms overhanging projections, leading to recurrent collapses, while the underlying chalk is eroded by storm waves and debris shedding. The research provides insights into the dynamic processes shaping this iconic coastal cliff, offering a deeper understanding of its geological evolution.
Local structure of Zn in Cretaceous-Tertiary boundary clay from Stevns Klint
Research at Stevns Klint, Denmark, reveals the unique local structure of zinc (Zn) atoms in Cretaceous-Tertiary boundary clay. Using Zn K-edge XAFS spectroscopy at KEK's Photon Factory, scientists found that Zn in this clay resembles the tetrahedral ZnO4 site of willemite, a zinc silicate, with first shell Zn-O and second shell Zn-cation distances of 1.953(3) Å and 3.51(2) Å, respectively. This structure differs from typical clay minerals and aligns with crystalline phases where Zn predominantly occupies tetrahedral sites. The study's findings, published in the Journal of Mineralogical and Petrological Sciences, provide insights into the atomic-scale behavior of Zn at a critical geological boundary.
Managing Injected Water Composition To Improve Oil Recovery: A Case Study of North Sea Chalk Reservoirs
A study on North Sea chalk reservoirs reveals that managing the composition of injected water can significantly enhance oil recovery. Unlike previous research primarily using outcrop chalk samples, this investigation utilized reservoir chalk samples and employed waterflooding techniques with various brines, including distilled water, sulfate-containing brine, and magnesium-ion brine. The findings indicate that while potential determining ions like SO4 2–, Ca 2+, and Mg 2+ play a role in improving oil recovery, their interaction with the rock is not solely temperature-dependent. Additionally, the composition of formation water also influences oil recovery at high temperatures, suggesting a more complex interplay between injected brine and reservoir conditions. This research provides new insights into optimizing waterflooding processes for enhanced oil recovery in chalk reservoirs.
The middle Danian Faxe Formation – new lithostratigraphic unit and a rare taphonomic window into the Danian of Denmark
A new lithostratigraphic unit, the middle Danian Faxe Formation, has been identified at Stevns Klint, Denmark, offering a rare taphonomic window into the Danian period's marine biodiversity. This formation, exposed in the Faxe quarry, transitions from coral and bryozoan limestone to bryozoan limestones of the Stevns Klint Formation. The Baunekule facies within this unit preserves a high-diversity invertebrate fauna with both calcite and originally aragonite-shelled species, many of which are unknown elsewhere in the Faxe Formation. Unlike the lithified parts of the formation, the Baunekule facies is weakly consolidated, allowing for easier fossil preparation and providing an unusually complete picture of cold-water coral mound ecosystems. This discovery sheds light on the diversity and density of shelly invertebrate fauna during this period.
Cosmic particles (micrometeorites) and nanospheres from the Cretaceous-Paleogene (K/T) boundary clay layer at the Stevns Klint Section, Denmark
A significant discovery of extraterrestrial metallic particles and nanospheres in the Cretaceous-Paleogene (K/T) boundary clay layer at Stevns Klint, Denmark, suggests that the asteroid impact 65 million years ago was accompanied by a substantial fall of finely dispersed cosmic matter. These particles, including iron, copper, Fe-Ni, Fe-Ni-Co, and Fe-Cr alloys, as well as magnetite and aluminosilicate balls, imply an intense supply of micrometeorites or asteroid fragments during the event. The findings challenge previous reconstructions by highlighting the need to account for this vast amount of cosmic dust in understanding the boundary events.
Iridium anomaly in the cretaceous-paleogene boundary at Højerup (Stevns Klint, Denmark) and Woodside Creek (New Zealand): The question of an enormous proportion of extraterrestrial component
A significant iridium anomaly, indicative of extraterrestrial material, has been identified at the Cretaceous-Paleogene boundary layers in Højerup (Stevns Klint, Denmark) and Woodside Creek (New Zealand). The study estimates that up to 26% and 65% of the carbonaceous chondritic component in these layers may originate from extraterrestrial sources, though this proportion is likely overestimated due to potential iridium influx from nearby marine or continental sites. The research utilizes integrated iridium fluencies to assess the extraterrestrial contribution, providing insights into the composition and origin of the boundary clays.
The Distribution of Benthic Foraminifera Across the Cretaceous–Paleogene Boundary in Texas (Brazos River) and Denmark (Stevns Klint)
A significant loss of benthic foraminifera diversity at the Cretaceous–Paleogene boundary is documented, with agglutinated taxa nearly disappearing and faunal changes suggesting shallowing events. Unlike Texas' Brazos River successions, Stevns Klint's chalk facies assemblages show distinct changes at hardground horizons, hinting at potential correlations between the two sites. The study uses micropaleontological analysis of samples from both locations to construct a sequence stratigraphy for this critical interval.
Calcareous nannofossils from the boreal Upper Campanian- Maastrichtian chalk of Denmark.
A comprehensive analysis of calcareous nannofossil assemblages from the boreal Upper Campanian to Upper Maastrichtian chalk of Denmark has uncovered 138 species, including several rarely documented and two newly described species: Prediscosphaera borealensis and Tranolithus stemmerikii, along with a new combination, Staurolithites dicandidula. The study, conducted across three sections—Stevns-1 borehole near Stevns Klint, Rordal-1 borehole, and Rordal quarry in North Jylland—reveals the diversity of these microscopic organisms during a critical period in Earth's history. The moderately preserved samples provide insights into the paleoenvironmental conditions of the time, contributing valuable data to our understanding of Cretaceous-Paleogene boundary dynamics.
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.
Sourcing flint from Sweden and Denmark. A pilot study employing non-destructive energy dispersive X-ray fluorescence spectrometry
A pilot study successfully demonstrated that non-destructive energy dispersive X-ray fluorescence (EDXRF) spectrometry can chemically distinguish flint samples from different geological formations across Sweden and Denmark. The analysis revealed that flint from Stevns Klint shares chemical signatures with samples from Södra Sallerup, Sweden, suggesting they may have originated from the same glacial-deposited formation despite visual and age differences. Similarly, flints from Klagshamn, Östra Torp, and Smygehuk exhibited identical chemical profiles, indicating a common geological source. The Common Kristianstad Flint (Hanaskog) stood out with a unique Ca/Fe signature, further validating the method's precision.
The cyclic Rørdal Member – a new lithostratigraphic unit of chronostratigraphic and palaeoclimatic importance in the upper Maastrichtian of Denmark
Researchers have identified the Rørdal Member, a new lithostratigraphic unit within the upper Maastrichtian chalk of Denmark, marking a significant early late Maastrichtian cooling event. This cyclic chalk-marl unit, approximately 10 meters thick, is distinct from surrounding pure white chalks and is recognized across multiple boreholes and outcrops, including Stevns Klint and the Rørdal quarry in Aalborg. The study leverages coccolith and brachiopod data to place the member within specific nannofossil and brachiopod zones, confirming its lower upper Maastrichtian age. Isotope analysis further supports its role as a basinwide isochronous marker, offering valuable insights into palaeoclimatic shifts during this period.
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