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GEUS Bulletin, Volume 45; https://doi.org/10.34194/geusb.v45.5299
The geology of North-East Greenland (70–78°N) exposes unique evidence of the basin development between the Devonian collapse of the Caledonian Orogen and the extrusion of volcanics at the Paleocene–Eocene transition during break-up of the North-East Atlantic. Here we pay special attention to unconformities in the stratigraphic record – do they represent periods of stability and non-deposition or periods of subsidence and accumulation of rocks followed by episodes of uplift and erosion? To answer that and other questions, we used apatite fission-track analysis and vitrinite reflectance data together with stratigraphic landscape analysis and observations from the stratigraphic record to study the thermo-tectonic history of North-East Greenland. Our analysis reveals eight regional stages of post-Caledonian development: (1) Late Carboniferous uplift and erosion led to formation of a sub-Permian peneplain covered by coarse siliciclastic deposits. (2) Middle Triassic exhumation led to removal of a thick cover including a considerable thickness of upper Carboniferous – Middle Triassic rocks and produced thick siliciclastic deposits in the rift system. (3) Denudation at the transition between the Early and Middle Jurassic affected most of the study area outside the Jameson Land Basin and produced a weathered surface above which Middle–Upper Jurassic sediments accumulated. (4) Earliest Cretaceous uplift and erosion along the rifted margin and further inland accompanied the Mesozoic rift climax and produced coarse-grained sedimentary infill of the rift basins. (5) Mid-Cretaceous uplift and erosion initiated removal of Cretaceous post-rift sediments that had accumulated above the Mesozoic rifts and their hinterland, leading to cooling of Mesozoic sediments from maximum palaeotemperatures. (6) End-Eocene uplift was accompanied by faulting and intrusion of magmatic bodies and resulted in extensive mass wasting on the East Greenland shelf. This event initiated the removal of a thick post-rift succession that had accumulated after break-up and produced a peneplain near sea level, the Upper Planation Surface. (7) Late Miocene uplift and erosion, evidenced by massive progradation on the shelf, resulted in the formation of the Lower Planation Surface by incision below the uplifted Upper Planation Surface. (8) Early Pliocene uplift raised the Upper and the Lower Planation Surfaces to their present elevations of about 2 and 1 km above sea level, respectively, and initiated the formation of the present-day landscape through fluvial and glacial erosion. Additional cooling episodes of more local extent, related to igneous activity in the early Eocene and in the early Miocene, primarily affected parts of northern Jameson Land. The three earliest episodes had a profound impact beyond Greenland and accompanied the fragmentation of Pangaea. Younger episodes were controlled by plate-tectonic processes, possibly including dynamic support from the Iceland Plume. Our results emphasise that gaps in the stratigraphic record often reflect episodes of kilometre-scale vertical movements that may result from both lithospheric and sub-lithospheric processes.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.6519
A new inventory on onshore petroleum seeps and stains in Greenland has been released by the Geological Survey of Denmark and Greenland as a web-based GIS model on the Greenland Mineral Resources Portal: Petroleum Seeps and Stains in Greenland. Knowledge on oil and gas seeps, oil stains and solid bitumen occurrences provides key information on mineral and petroleum systems, especially in frontier basins. As the understanding of recent and previous migrations of fluids and gases is important for both mineral and petroleum explorations in Greenland, this new inventory has been developed to facilitate exploration and new activities. The classification includes the following types of occurrences: (1) oil seeps, (2) gas seeps, (3) mud diapirs, pingos and gas-rich springs, (4) oil stains in volcanics, carbonates and sandstones, (5) solid macroscopic bitumen and (6) fluid inclusions and other evidence of micro-seepage. The inventory comprises detailed information on localities, coordinates and sample numbers. It also includes descriptions of features and geology, references to data, reports and publications. All information is summarised in either a mineral or petroleum systems context. Petroleum seeps and stains have been reported from most Palaeozoic, Mesozoic and Cenozoic basins in Greenland where they add important information on petroleum systems, especially distribution and facies variation of source rocks, petroleum generation and later migration, accumulation, remigration, uplift and degradation. The inventory is designed to be updated with additional localities and descriptions and new organic geochemical data. This paper provides a general overview of classification, nomenclature, organisation and content of the inventory. We introduce the regional distribution of petroleum seeps and stains in Greenland and general interpretations in the context of mineral and petroleum systems.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.6530
We propose a new relative shore-level curve for the Aarhus Bugt area, an embayment in eastern Jylland, Denmark, based on a compilation of published and new radiocarbon ages of organic material. Lakes existed in the area during the Late Glacial and Early Holocene. Lake level rose gradually until the region was inundated by the sea at c. 9000 cal. years BP. The relative sea level reached a high stand at about 6000 cal. years BP, when the local relative sea level was c. 3 m above present-day mean sea level. The Aarhus Bugt area was inundated by the sea later than the Limfjord area in northern Jylland, but earlier than the Lillebælt region in southern Denmark. The shore-level curves for these areas differ partly because the glacio-isostatic uplift was more pronounced in the Limfjord area than farther south and partly because the northern regions were inundated by the sea earlier than the southern areas.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.5336
Salinity levels above the drinking water standard (>250 mg/l Cl–) are observed at shallow depth in a Maastrichtian chalk aquifer on the island of Falster, south-eastern Denmark. To understand the source of the salt, 63 samples from 12 individual, 1 m, screened intervals between 14 and 26 m b.s. were collected from 1 May to 4 June 2018. The samples were collected during a tracer test to estimate the dual porosity properties of the chalk and were analysed for a wide range of elements. Furthermore, samples from the Baltic Sea and from deeper saline aquifers in the area (40 and 85 m b.s.) were analysed for comparison. The geochemical data were analysed using an unsupervised machine-learning algorithm, self-organising maps, to fingerprint water sources. The water composition in the screened intervals at various stratigraphic levels has specific geochemical fingerprints that are maintained for the first days of pumping and are distinct amongst the different levels. This suggests an evolution in water composition because of reaction with the chalk. Water composition is distinct from both seawater from the nearby Baltic Sea and salty water from deeper levels of the reservoir. Thus, neither up-coning of salty water nor intrusion of seawater caused the elevated salinity levels in the area. The slightly saline composition of groundwater in the shallow aquifer (14–26 m b.s.) is more likely because of incomplete refreshing of the salty connate water in the chalk during the Pleistocene and Holocene. Furthermore, the geochemical fingerprint of salty water from the deeper aquifer at 40 m was similar to water from the Baltic Sea, suggesting a Baltic Sea source for salt in the aquifer at 40 m b.s., c. 100 m from the coast. Statistical analysis based on self-organising maps is an effective tool for interpreting a large number of variables to understand the compositional variation in an aquifer and a useful alternative to linear dimensionality-reduction methods such as principal component analysis. The approach using the multi-element analysis combined with the analysis of self-organising maps may be useful in future studies of groundwater quality.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.6523
Permian to Triassic outcrops in East Greenland diminish significantly northwards. Understanding the northward extent, and nature, of the Permian and Triassic successions has implications for regional palaeogeographic reconstructions and exploration in adjacent offshore basins. Examining the structural relationships between the basement, Permian, Triassic, Jurassic and Cretaceous successions can further our understanding of the tectonic evolution of the region. Here, we describe a hitherto overlooked section through the Permian to Cretaceous from central Wollaston Forland and consider its structural context. The western side of Permpasset forms the upthrown eroded crest of a horst block, which provides exposure of the earliest stratigraphic intervals in the region. The fractured Caledonian basement is overlain by evaporitic marine limestone facies of the Karstryggen Formation, which are succeeded by shallow marine sandstones assigned to the Schuchert Dal Formation, both Upper Permian. The overlying unit records a period of fluvial deposition and is not possible to date. However, an Early to Middle Triassic age (Pingo Dal Group) seems most likely, given regional eustatic considerations. This is, therefore, the most northerly record of Triassic strata in North–East Greenland. West of the horst structure, fine-grained sandstones and bioturbated siltstones of the Jurassic (Oxfordian) Jakobsstigen Formation are recorded. These were downfaulted prior to a prolonged hiatus after which both the Triassic and Jurassic strata were draped by Cretaceous shales of the Fosdalen Formation. The Cretaceous succession is overlain by a thick basalt pile of Eocene age, heralding the opening of the North-East Atlantic. Glendonites overlie Oxfordian siltstones at the base of the middle Albian Fosdalen Formation. These were likely winnowed from slightly older Cretaceous strata and overlie the hiatus surface between the Jurassic and Cretaceous. This is the first record of glendonites from the Cretaceous of East Greenland and they are interpreted to record the Circum–Arctic late Aptian – early Albian cooling event.
GEUS Bulletin, Volume 46; https://doi.org/10.34194/geusb.v46.6521
The East Greenland Rift Basin comprises a series of Jurassic subbasins with different crustal configurations, and somewhat different tectonic histories and styles. The roughly N–S elongated basin is exposed in central and northern East Greenland over a length of more than 600 km and a width of up to 250 km. The southernmost exposures are found in the largest subbasin in Jameson Land, while the northernmost exposures are on Store Koldewey and in Germania Land. The focus of the present revision is on the Jurassic, but the uppermost Triassic and lowermost Cretaceous successions are included as they are genetically related to the Jurassic succession. The whole succession forms an overall transgressive–regressive megacycle with the highest sea level and maximum transgression in the Kimmeridgian. The latest Triassic – Early Jurassic was a time of tectonic quiescence in East Greenland. Lower Jurassic deposits are up to about 950 m thick and are restricted to Jameson Land and a small down-faulted outlier in southernmost Liverpool Land. The Lower Jurassic succession forms an overall stratigraphic layer-cake package that records a shift from Rhaetian–Sinemurian fluvio-lacustrine to Pliensbachian – early Bajocian mainly shallow marine sedimentation. Onset of rifting in the late Bajocian resulted in complete reorganisation of basin configuration and drainage patterns, and the depositional basin expanded far towards the north. Post-lower Bajocian early-rift deposits are up to about 500–600 m thick and are exposed in Jameson Land, Liverpool Land, Milne Land, Traill Ø, Geographical Society Ø, Hold with Hope, Clavering Ø, Wollaston Forland, Kuhn Ø, Th. Thomsen Land, Hochstetter Forland, Store Koldewey and Germania Land. Upper Jurassic rift-climax strata reach thicknesses of several kilometres and are exposed in the same areas with the exception of Liverpool Land and Germania Land. In the southern part of the basin, the upper Bajocian – Kimmeridgian succession consists of stepwise backstepping units starting with shallow marine sandstones and ending with relatively deep marine mudstones in some places with sandy gravity-flow deposits and injectites. In the Jameson Land and Milne Land Subbasins, the uppermost Jurassic – lowermost Cretaceous (Volgian–Ryazanian) succession consists of forestepping stacked shelf-margin sandstone bodies with associated slope and basinal mudstones and mass-flow sandstones. North of Jameson Land, block-faulting and tilting began in the late Bajocian and culminated in the middle Volgian with formation of strongly tilted fault blocks, and the succession records continued stepwise deepening. In the Wollaston Forland – Kuhn Ø area, the Volgian is represented by a thick wedge of deep-water conglomerates and pebbly sandstones passing basinwards into mudstones deposited in fault-attached slope aprons and coalescent submarine fans. The lithostratigraphic scheme established mainly in the 1970s and early 1980s is here revised on the basis of work undertaken over subsequent years. The entire Jurassic succession, including the uppermost Triassic (Rhaetian) and lowermost Cretaceous (Ryazanian–Hauterivian), forms the Jameson Land Supergroup. The supergroup is subdivided into the Kap Stewart, Neill Klinter, Vardekløft, Hall Bredning, and Wollaston Forland Groups, which are subdivided into 25 formations and 48 members. Many of these are revised, and 3 new formations and 14 new members are introduced.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.6526
The Gardar Province of south Greenland is defined by the products of alkaline igneous magmatism during the Mesoproterozoic. The most laterally extensive Gardar intrusions are a series of giant dyke complexes best exposed on the Tuttutooq archipelago. We present new field observations and a geological map of north-east Tuttutooq island that provide fresh insights into the temporal evolution of the Younger giant dyke complex and two associated ultramafic lamprophyres. Our data demonstrate that distinctive crystallisation regimes occurred in different sectors of the dyke complex, leading to the formation of marginal gabbros and ovoid pod-like domains displaying lamination, modal layering and/or more evolved differentiates. We infer that at least two pulses of magma contributed to the formation of the Younger giant dyke complex. In addition, the relative ages of two ultramafic lamprophyre diatremes are constrained and attributed to two distinct phases of rifting in the Gardar Province.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.5369
The elevation of ice sheets response dynamically to climate change and satellite altimetry is the preferred tool for evaluating the ice sheet-wide changes. In-situ validation are needed to ensure the quality of the observed elevation changes, but the coast is most often the limiting factor for the amount of in-situ data available. As more and more tourists are accessing the ice sheets, citizen science might provide the needed in-situ data in an environmental and cost-efficient way. Here, we investigate opportunistic kinematic-GPS profiles across the Greenland ice sheet, collected the American-Icelandic Expedition on the Greenlandic icecap 2018. First, the collected GPS-data are tested against widely used NASA Operation IceBridge airborne lidar-scannings, and shows good agreement, with an accuracy of 11 cm. The main difference is attributed to changes in the compaction of the snow as encountered while driving, as well as changing tire pressures. The kinematic-GPS data is then used for satellite validation by inter-comparing it with data from ESA's CryoSat-2 mission. Here, a bias in the two records of 89 cm is observed, with the Cryosat-2 observation originating from the subsurface of the ice sheet. This points to surface penetration of Ku-band radar on the Greenland ice sheet, and the observed magnitude is in accordance with the literature. Finally, we assess the long-term durability of citizen science kinematic-GPS data, when compared to a profile obtained in 2005 near Kangerlussuaq, West Greenland. Here, the records show an average ice elevation decreased of 9 meters and with peaks at 25.7 meters. This result show how kinematic-GPS data can be used to see the full impact of climate change by repeat measurements. Thereby are citizen science kinematic-GPS data shown to be a highly versatile approach to acquire high-resolution validation data for satellite altimetry, with the added benefit of potentially direct sampling properties of the surface and firn, when applying traditional airborne platforms. Thereby linking up with citizen-science expeditions is truly a beneficial way of providing cost-efficient satellite validations and may also have a societal impact by involving more in the climate monitoring of ice sheets.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.5284
The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) provides surface meteorological and glaciological measurements from widespread on-ice automatic weather stations since mid-2007. In this study, we use 105 PROMICE ice-ablation time series to identify the timing of seasonal bare-ice onset preceded by snow cover conditions. From this collection, we find a bare-ice albedo at ice-ablation onset (here called bare-ice-onset albedo) of 0.565 ± 0.109 that has no apparent spatial dependence among 20 sites across Greenland. We then apply this snow-to-ice albedo transition value to measure the variations in daily Greenland bare-ice area in Sentinel-3 optical satellite imagery covering the extremely low and high respective melt years of 2018 and 2019. Daily Greenland bare-ice area peaked at 153 489 km² in 2019, 1.9 times larger than in 2018 (80 220 km²), equating to 9.0% (in 2019) and 4.7% (in 2018) of the ice sheet area.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.6090
Pesticide pollution has raised public concern in Denmark due to potential negative health impacts and frequent findings of new substances after a recent expansion of the groundwater monitoring programme. Danish drinking water comes entirely from groundwater. Both the raw groundwater and the treated drinking water are regularly monitored, and the chemical analyses are reported to a publicly available national database (Jupiter). Based on these data, in this study we (1) provide a status of pesticide content in drinking water supplied by public waterworks in Denmark and (2) assess the proportion of Danish households exposed to pesticides from drinking water. ‘Pesticides’ here refers also to their metabolites, degradation and reaction products. The cleaned dataset represents 3004 public waterworks distributed throughout the country and includes 39 798 samples of treated drinking water analysed for 449 pesticides (971 723 analyses total) for the period 2002–2019. Of all these chemical analyses, 0.5% (n = 4925) contained a quantified pesticide (>0.03 μg/l). Pesticides were found at least once in the treated drinking water at 29% of all sampled public waterworks for the period 2002–2019 and at 21% of the waterworks for the recent period 2015–2019. We estimate that 56% of all Danish households were potentially exposed at least once to pesticides in drinking water at concentrations of 0.03–4.00 μg/l between 2002 and 2019. However, in 2015–2019, the proportion of the Danish households exposed to pesticides (0.03–4.00 μg/l) was 41%. The proportion of Danish households potentially exposed at least once to pesticides above the maximum allowed concentration (0.1 μg/l) according to the EU Drinking Water Directive (and the Danish drinking water standard) was 19% for 2002–2019 and 11% for 2015–2019. However, the maximum concentrations were lower than the World Health Organization’s compound-specific guidelines. Lastly, we explore data complexity and discuss the limitations imposed by data heterogeneity to facilitate future epidemiological studies.
GEUS Bulletin, Volume 47; https://doi.org/10.34194/geusb.v47.5552
The large natural gas storage facility at Stenlille, Denmark, has been monitored to investigate the effect of pumping large amounts of gas into the subsurface. Here, we present a new dataset of microseismicity at Stenlille since 2018. We compare these data with methane in groundwater, which has been monitored since gas storage was established in 1989. Further, we conducted a controlled 172 day microcosm experiment of methane oxidation on an isolated microbial community under both aerobic and anaerobic conditions. For this experiment, water was filtered from a well at Stenlille with elevated levels of thermogenic methane and ethane. No microseismic activity was detected in the gas storage area above an estimated detection level of ML 0.0 for the established network. The long-term monitoring for methane in groundwater has still only detected one leak, in 1995, related to a technical problem during injection. The microcosm experiment revealed that oxidation of methane occurred only under aerobic conditions during the experiment, as compared to anaerobic conditions, even though the filtered water was anoxic
GEUS Bulletin, Volume 45; https://doi.org/10.34194/geusb.v45.5298
The Carboniferous–Palaeogene Wandel Sea Basin of eastern North Greenland (north of 80°N, east of 40°W) is an important piece in the puzzle of Arctic geology. It is particularly important for understanding how the Paleocene–Eocene convergence between Greenland, the Canadian Arctic and Svalbard relates to the compressional tectonics in the High Arctic, collectively known as the Eurekan Orogeny. In this study, we present apatite fission-track analysis (AFTA) data and review published vitrinite reflectance data combined with observations from the stratigraphic record to place firmer constraints on the timing of key tectonic events. This research study reveals a long history of episodic burial and exhumation since the collapse of the Palaeozoic fold belts in Greenland. Our results define pre-Cenozoic exhumation episodes in early Permian, Late Triassic, Late Jurassic and mid-Cretaceous times, each involving the removal of kilometre-scale sedimentary covers. Mid-Paleocene exhumation defines the timing of compression along the major fault zones during the first stage of the Eurekan Orogeny, after the onset of sea-floor spreading west of Greenland. Regional exhumation that began at the end of the Eocene led to the removal of most of a kilometre-thick cover that had accumulated during Eocene subsidence and involved a major reverse movement along the Harder Fjord Fault Zone, northern Peary Land. These events took place after the end of sea-floor spreading west of Greenland, and thus, represent post-Eurekan tectonics. Mid–late Miocene exhumation is most likely a consequence of uplift and incision across most of the Wandel Sea Basin study area. The preserved sedimentary sequences of the Wandel Sea Basin represent remnants of thicker strata that likely extended substantially beyond the present-day outline of the basin. We find that the present-day outline of the basin with scattered sedimentary outliers is primarily the result of fault inversion during Eurekan compression followed by deposition and removal of a kilometre-thick overburden.
GEUS Bulletin, Volume 45; https://doi.org/10.34194/geusb.v45.5297
Elevated plateaus with deeply incised valleys characterise elevated, passive continental margins (EPCMs) in all climate zones. These features are, however, a topic of debate regarding when and how the large-scale landscapes formed. We have investigated and mapped the partly glaciated landscape of North-East Greenland (70–78°N). The area consists of crystalline basement and Palaeozoic–Mesozoic rift basins, capped by Palaeogene basalts that erupted during the northeast Atlantic break-up. Our stratigraphic landscape analysis reveals a typical EPCM dominated by two elevated erosion surfaces, extending 200 km east–west and 900 km north–south. The low-relief Upper Planation Surface (UPS; c. 2 km above sea level) cuts across basement and Palaeogene basalts, indicating that it was graded to base level defined by the Atlantic Ocean in post-basalt times and subsequently uplifted. The UPS formed prior to the deposition of mid-Miocene lavas that rest on it, south of the study area. In the interior basement terrains, the Lower Planation Surface (LPS) forms fluvial valley benches at c. 1 km above sea level, incised below the UPS. The LPS is thus younger than the UPS, which implies that it formed post mid-Miocene. Towards the coast, the valley benches merge to form a coherent surface that defines flat-topped mountains. This shows that the LPS was graded to near sea level and was subsequently uplifted. Hence, both the UPS and the LPS formed as peneplains – erosion surfaces graded to base level. The fluvial valley benches associated with the LPS further indicates that full glacial conditions were only established after the uplift of the LPS in the early Pliocene (c. 5 Ma). The uplift of the LPS led to re-exposure of a Mesozoic etch surface. We conclude that episodes of late Neogene tectonic uplift shaped the stepped landscape and elevated topography in North-East Greenland.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.5342
Age assessments from both palynostratigraphy and macrofossil biostratigraphy of the sandstone-dominated Mågensfjeld Formation, Wandel Sea Basin, North Greenland were hitherto hampered by post-burial thermal degradation of dinoflagellate cysts and a lack of well-preserved macrofossils. The formation was previously assigned to the Upper Cretaceous based on erroneous fossil identifications. Finds of cardioceratid and kosmoceratid ammonites during recent field work now provide the first age control of the unit, demonstrating it to be of late Bajocian – late Bathonian and perhaps Callovian (Middle Jurassic) age. This makes it among the oldest Jurassic units, perhaps even Mesozoic units, recorded in Kilen, North Greenland and eastern North Greenland. Previously, the complex structural and tectonic evolution of the area was poorly understood, and the structural relation of the Mågensfjeld Formation to the surrounding Mesozoic units was a puzzle. The new age assessment simplifies the structural situation in the area significantly. Further, the inference of a large reverse fault previously required to explain the proximity of the Mågensfjeld Formation to neighbouring Jurassic units is now unnecessary. The data show that the Wandel Sea Basin was influenced by the Middle Jurassic transgression and had sufficient accommodation space for marine deposition earlier than previously thought. The unit serves as a key datapoint and analogue for possible Middle Jurassic units in adjacent offshore basins.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.4567
The Nuussuaq Basin in West Greenland has an obvious exploration potential. Most of the critical elements are well documented, including structures that could form traps, reservoir rocks, seals and oil and gas seepage that documents petroleum generation. And yet, we still lack a full understanding of the petroleum systems, especially the distribution of mature source rocks in the subsurface and the vertical and lateral migration of petroleum into traps. A recently proposed anticlinal structural model could be very interesting for exploration if evidence of source rocks and migration pathways can be found. In this paper, we review all existing, mostly unpublished, data on gas observations from Nuussuaq. Furthermore, we present new oil and gas seepage data from the vicinity of the anticline. Occurrence of gas within a few kilometres on both sides of the mapped anticline has a strong thermogenic fingerprint, suggesting an origin from oil-prone source rocks with a relatively low thermal maturity. Petroleum was extracted from an oil-stained hyaloclastite sample collected in the Aaffarsuaq valley in 2019, close to the anticline. Biomarker analyses revealed the oil to be a variety of the previously characterised “Niaqornaarsuk type,” reported to be formed from Campanian-age source rocks. Our new analysis places the “Niaqornaarsuk type” 10 km from previously documented occurrences and further supports the existence of Campanian age deposits developed in source rock facies in the region.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.5302
The process of coastal erosion is well known to the public and decision-makers in Denmark; however, there is little awareness of the risks posed by larger landslides. Only a few scientific studies investigate landslides in Denmark, and as a result, the country is underrepresented in international landslide inventories. Here, we present a systematically produced preliminary landslide inventory based on digital elevation models and high-resolution orthophotos. So far, the preliminary inventory documents 3026 morphological expressions of landslides close to the coast and inland, showing that landslides are more widespread in Denmark than previously recognised. A number of these landslides are near buildings and infrastructure. This paper therefore highlights the potential for geohazardous landslides to occur in Denmark on a national scale and discusses some of the implications. Two of the major questions arising from this study are (1) how to approach potential geohazards in a country with no framework or precedence for landslide hazard and risk management and (2) how landslides and associated risk in Denmark will evolve under a changing climate.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.4618
The early Miocene was an important period for the development of the eastern North Sea. Tectonism in North-West Europe resulted in uplift of the Scandinavian mountains, reactivation of salt structures, inversion of old graben structures and deposition of the most coarse-grained deposits in the Danish pre-Quaternary succession. Some of these deposits were later cemented into conglomerates. The deposits are common in the fluvial parts of the Billund Formation (Aquitanian) and the basal transgressive lag of the late Aquitanian – Burdigalian Klintinghoved Formation capping the Billund Formation. Questions remained as to the age of these deposits and what they infer about tectonic events in the region. This study reviews the geology of the flint-dominated conglomerates and presents the first dates for a sample of these unique deposits. We observe grain sizes up to 5 cm diameter. Palynological analyses place the sample as early Miocene. Some samples from the area have suggested a local source near active salt structures, associated with the uplift of the pre-Neogene sedimentary successions. We suggest that the common occurrences of flint clasts in the lower Miocene succession reveal significant erosion of Upper Cretaceous and Danian chalk, likely associated with the uplift of the Scandinavian lowlands during the Savian tectonic phase, early Miocene.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.4626
The Isortoq Giant Dykes in the Proterozoic Gardar Province, South Greenland, includes Isortoq South giant dyke and Isortoq North giant dyke. The fine-grained Fe-Ti-V deposit hosted by the Isortoq South giant dyke, referred to as the Isortoq Fe-Ti-V deposit, is considered a good test site for the use of magnetic susceptibility for the mapping of ore grades. Here, we test this and show that the Fe, Ti and V distribution is controlled by titanomagnetite disseminated throughout fine-grained troctolite. The deposit displays a clear correlation between magnetic susceptibility and Fe, Ti and V grades in bulk samples of consecutive 2 m sections from 11 drill cores, totalling 2671 m in length. We observe that Fe, Ti and V are almost entirely hosted in titanomagnetite, which controls the magnetic susceptibility. Field measurements of the magnetic susceptibility can thus be considered as a reliable exploration tool for this type of mineralisation. We further consider the origins of the deposit by reconnaissance petrography, mineral and bulk rock chemistry of the large mass of aphanitic Fe-rich troctolite in the Isortoq South giant dyke. We suggest that the deposit may represent the base of a basanitic to trachybasaltic magma chamber, in which Fe-rich immiscible melts accumulated, crystallised and fractionated. The processes suggested here may apply to other giant dykes and intrusions of the Gardar Province.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.5240
Geophysical methods have been widely used in recent decades to investigate and monitor landfill sites for environmental purposes. With the advent of the circular economy, waste contained in old landfills may be considered a resource that can be developed. Since the content of old landfills is largely unknown, the occurrence and quantity of valuable materials must be investigated before embarking on any development activity. Two landfills on Sjælland, Denmark (located at Hvalsø and Avedøre) were selected for a pilot study to characterise their content. At both locations, a set of geophysical surveys is underway. Here, we present the data obtained from magnetic and 2D seismic refraction surveys. Magnetic data show various anomalies that can be interpreted as caused by iron-rich waste. At both sites, the landfill material results in generally low P-wave velocity (550 m/s). We propose that seismic refraction can thus define the bottom of the landfill and possibly its internal structure, especially when combined with other methods.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.4630
Lammefjorden is a reclaimed fjord in north-west Sjælland, Denmark. Sediment cores from the area were collected to study its development after the last deglaciation, in particular the sea-level history. Late glacial and Early Holocene lake and bog deposits occur below marine deposits. Sparse late glacial fossil assemblages indicate tree-less environments with dwarf-shrub heaths. Early Holocene deposits contain remains of Betula sec. Albae sp. and Pinus sylvestris, which indicate open forests. The wetland flora comprised the calciphilous reed plant Cladium mariscus and the water plant Najas marina. Marine gyttja from basins is characterised by sparse benthic faunas, probably due to high sedimentation rates. In some areas, shell-rich deposits were found, with large shells of Ostrea edulis, indicative of high summer temperatures, high salinity and strong tidal currents. A marine shell dated to 6.7 cal. ka provides a minimum age for the marine transgression of Lammefjorden.
GEUS Bulletin; https://doi.org/10.34194/geusb.v44.4836
Play analysis has been widely used in hydrocarbon exploration for decades with great success. In recent years, progress has also been made to describe reservoir properties of very low permeability reservoirs. However, comparatively little research has been done into play analysis for such reservoirs, which may lead to misleading estimates of their hydrocarbon potential. Here, the concept of a semi-conventional play is defined and characterised as having a reservoir of such low permeability that a hydrocarbon column can form down-dip of an effective dry trap. A new exploration approach is proposed for such plays, using the Chalk Group Play in the Danish North Sea as an example. It is suggested that together with the usual risk elements, a more detailed analysis of ‘charge’ is necessary, paying particular attention to identifying possible hydrocarbon entry points, palaeostructures and the maximum distance from these entry points that the hydrocarbons may have reached since they first entered the reservoir. The application of this novel approach for semi-conventional plays in mature basins can help unlock further resources in proximity of existing fields, and reduce the risk of failure in frontier exploration.
GEUS Bulletin pp 57-60; https://doi.org/10.34194/geusb.v33.4498
The Greenland ice sheet is an excellent observatory for global climate change. Meltwater from the 1.8 million km2 large ice sheet infl uences oceanic temperature and salinity, nutrient fl uxes and global sea level (IPCC 2013). Surface refl ectivity is a key driver of surface melt rates (Box et al. 2012). Mapping of diff erent ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface refl ectivity are most prominent. Here, we present an updated version of a surface classifi cation algorithm that utilises NASA’s Moderateresolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite to systematically monitor ice-sheet surface melt (Fausto et al. 2007). Our aim is to determine the areal extent of three surface types over the 2000–2014 period: glacier ice, melting snow (including percolation areas) and dry snow (Cuff ey & Paterson 2010). Monthly 1 km2 resolution surface-type grids can be downloaded via the CryoClim internet portal (www.cryoclim.net). In this report, we briefl y describe the updated classifi cation algorithm, validation of surface types and inter-annual variability in surface types.
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-03-03
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-00-01
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-03-02
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-03
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-03-01
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-04
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-06
Ole Bennike* 1 , Jørn Bo Jensen 1 , Frederik Næsby Sukstorf 2 & Minik T
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-05
Sara Salehi* 1 , Christian Mielke 2 , Christian Brogaard Pedersen 1 , Simun Dalsenni Olsen 1 RESEARCH ARTICLE | OPEN ACCESS GEUS Bulletin Vol 43 |
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-04
Hanne D. Holmslykke* 1 , Niels H
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-03
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-01
William Colgan* 1 , Kenneth D. Mankoff 1 , Kristian K. Kjeldsen 1,2 , Anders A. Bjørk 2 , Jason E. Box 1 , Sebastian B. Simonsen 3 , Louise S
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-08
The landslide of 17 June 2017 at Karrat Fjord, central West Greenland, triggered a tsunami that caused four fatalities. The catastrophe highlighted the need for a better understanding of landslides in Greenland and initiated a recent nation-wide landslide screening project led by the Geological Survey of Denmark and Greenland (GEUS; see also Svennevig (2019) this volume). This paper describes an approach for compiling freely available data on landslides to improve GEUS’ capability to monitor active landslides in remote areas of the Arctic in near real time.
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-01
William Colgan* 1 , Jason E. Box 1 , Sofia Ribeiro 1 & Kristian K
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-02
Jonas K. Andersen 1 , Robert S. Fausto* 1 , Karina Hansen 1 , Jason E. Box 1 , Signe B. Andersen 1 , Andreas P
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-06
Ole Bennike* 1 , Niels Nørgaard-Pedersen 1 & Jørn Bo Jensen 1 GEUS Bulletin Vol 43 | e2019430106 | Published online: 24 June 2019 RESEARCH ARTICLE
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-02
Ernesto Pasten-Zapata* 1 , Torben O
GEUS Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-01-05
Niels H. Schovsbo* 1 & Finn Jakobsen 1 GEUS Bulletin Vol 43 | e2019430105 | Published online: 17 June 2019 https://doi.org/10
Published: 17 June 2019
Geological Survey of Denmark and Greenland Bulletin, Volume 43; https://doi.org/10.34194/geusb-201943-02-07
Kristian Svennevig* 1 GEUS Bulletin Vol 43 | e2019430207| Published online: 17 June 2019 https://doi.org/10
GEUS Bulletin pp 7-14; https://doi.org/10.34194/geusb.v42.4307
The Geological Survey of Denmark and Greenland (GEUS) successfully drilled the fully cored Blokelv-1 borehole in the central part of the Jameson Land Basin in East Greenland, targeting the Upper Jurassic, rich source-rock interval of the Hareelv Formation. The borehole achieved 100% core recovery from 1.72 m to a total depth of 233.8 m; the recovered Hareelv Formation section consists of interlayered black, laminated organic-rich mudstones, massive sandstones and heterolithic sandstone–mudstone intervals of the Katedralen Member, and amalgamated massive sandstones of the Sjællandselv Member. The core is of very high quality and has been subjected to an extensive sampling and analytical programme focused particularly on petroleum geological aspects, as presented in the following eight papers in this volume. This bulletin describes an important, previously poorly documented member of the ‘Kimmeridge Clay’ family of prolific petroleum source rocks in the North Atlantic area.
GEUS Bulletin pp 133-147; https://doi.org/10.34194/geusb.v42.4324
Apatite fission-track analysis (AFTA) data in two Upper Jurassic core samples from the 231 m deep Blokelv-1 borehole, Jameson Land, East Greenland, combined with vitrinite reflectance data and regional AFTA data, define three palaeo-thermal episodes. We interpret localised early Eocene (55– 50 Ma) palaeotemperatures as representing localised early Eocene heating related to intrusive activity whereas we interpret late Eocene (40–35 Ma) and late Miocene (c. 10 Ma) palaeotemperatures as representing deeper burial followed by successive episodes of exhumation. For a palaeogeothermal gradient of 30°C/km and likely palaeo-surface temperatures, the late Eocene palaeotemperatures require that the Upper Jurassic marine section in the borehole was buried below a 2750 m thick cover of Upper Jurassic – Eocene rocks prior to the onset of late Eocene exhumation. As these sediments are now near outcrop at c. 200 m above sea level, they have been uplifted by at least 3 km since maximum burial during post-rift thermal subsidence. The results are consistent with estimates of rock uplift on Milne Land since the late Eocene and with interpretation of Ocean Drilling Program (ODP) data off South-East Greenland suggesting that mid-Cenozoic uplift of the margin triggered the marked influx of coarse clastic turbidites during the late Oligocene above a middle Eocene to upper Oligocene hiatus.
Published: 28 December 2018
Geological Survey of Denmark and Greenland Map Series, Volume 8, pp 1-29; https://doi.org/10.34194/geusm.v8.4526
The geological map sheet of Kilen in 1:100 000 scale covers the south-eastern part of the Carboniferous–Palaeogene Wandel Sea Basin in eastern North Greenland. The map area is dominated by the Flade Isblink ice cap, which separates several minor isolated landmasses. On the semi-nunatak of Kilen, the map is mainly based on oblique photogrammetry and stratigraphical field work while in Erik S. Henius Land, Nordostrundingen and northern Amdrup Land the map is based on field data collected during previous, 1:500 000 scale regional mapping. Twenty-one Palaeozoic–Mesozoic mappable units were identified on Kilen, while the surrounding areas comprise the Late Cretaceous Nakkehoved Formation to the north-east and the Late Carboniferous Foldedal Formation to the south-west. On Kilen, the description of Jurassic–Cretaceous units follows a recently published lithostratigraphy. The Upper Palaeozoic–lowermost Cretaceous strata comprise seven formations and an informal mélange unit. The overlying Lower–Upper Cretaceous succession comprises the Galadriel Fjeld and Sølverbæk Formations, which are subdivided into six and five units, respectively. In addition, the Quaternary Ymer Formation was mapped on south-east Kilen. The Upper Palaeozoic to Mesozoic strata of Kilen are faulted and folded. Several post-Coniacian NNW–SSE-trending normal faults are identified and found to be passively folded by a later N–S compressional event. A prominent subhorizontal fault, the Central Detachment, separates two thrust sheets, the Kilen Thrust Sheet in the footwall and the Hondal Elv Thrust Sheet in the hanging wall. The style of deformation and the structures found on Kilen are caused by compressional tectonics resulting in post-extensional, presumably Early Eocene, folding and thrusting and basin inversion. The structural history of the surrounding areas and their relation to Kilen await further studies.
GEUS Bulletin pp 39-64; https://doi.org/10.34194/geusb.v42.4309
The fully cored Blokelv-1 borehole was drilled through Upper Jurassic strata in the central part of the Jameson Land Basin, central East Greenland. The borehole reached a total depth of 233.8 m with nearly 100% recovery of high-quality core. An extensive analytical programme was undertaken on the core; sedimentological interpretation and reservoir characterisation were based on facies analysis combined with conventional core analysis, bulk geochemistry and spectral gamma and density scanning of the core. The Upper Jurassic Hareelv Formation was deposited in relatively deep water in a slope-to-basin setting where background sedimentation was dominated by suspension settling of organic-rich mud in oxygen-depleted conditions. Low- and high-density gravity-flow sandstone interbeds occur throughout the cored succession. About two-thirds of the high-density turbidite sandstones were remobilised and injected into the surrounding mud-rock. The resulting succession comprises nearly equal amounts of mudstones and sandstones in geometrically complex bodies. Ankerite cementation occurs in 37% of the analysed sandstones in varying amounts from minor to pervasive. Such ankerite-cemented sandstones can be identified by their bulk geochemistry where Ca > 2 wt%, Mg > 1 wt% and C > 1 wt%. The analysed mudstones are rich in Al, Fe, Ti and P and poor in Ca, Mg, Na and Mn. The trace-metal content shows a general increase in the upper part of the core reflecting progressive oxygen depletion at the sea floor. The reservoir properties of the Blokelv-1 sandstones were evaluated by both conventional core analysis and using log-derived porosity and permeability curves. The high-density turbidite beds and injectite bodies are a few centimetres to several metres thick and show large variations in porosity and permeability, in the range of 6–26 % for porosity and 0.05–400 mD for permeability. Individual sandstone units that are 1–7 m thick yield a net vertical reservoir thickness of 40 m with porosities of 15–26% and permeabilities of 1–200 mD. Heterolithic sandstone–mudstone units are generally characterised by poor reservoir quality with porosities of 2–14% and permeabilities of 0.1–0.6 mD.
GEUS Bulletin pp 115-126; https://doi.org/10.34194/geusb.v42.4317
Zircon U–Pb geochronology and heavy mineral CCSEM analysis were used to interpret the provenance of Oxfordian–Volgian sandstones of the Hareelv Formation in East Greenland. Six samples were collected from the Blokelv-1 core drilled in southern Jameson Land, and the zircon age distributions and heavy-mineral assemblages are quite uniform. The samples contain a wide spectrum of Archaean to Palaeozoic zircon ages with peak ages at 2.71, 2.49, 1.95, 1.65, 1.49, 1.37, 1.10 and 0.43 Ga when combining all data. The heavy-mineral compositions show derivation from felsic source rocks, some of which were metamorphic. The results reveal that the sediment was derived from the Caledonides, and it is plausible that some or all of the material has experienced several cycles of sedimentation. Devonian and Carboniferous sediments preserved north of the area have zircon age distributions that correspond to those from the Hareelv Formation, and such rocks may have been reworked into the Jameson Land Basin. The provenance signature describes both the gravity-flow sandstones of the Hareelv Formation and the delta-edge sands that are inferred to have fed them. Lithological and provenance contrasts between the sandstones of the Sjællandselv Member and those of the Katedralen Member indicate a shorter transport distance, source to sink, suggestive of proximal topographic rejuvenation in the Volgian.
GEUS Bulletin pp 15-37; https://doi.org/10.34194/geusb.v42.4308
The Hareelv Formation in the Blokelv-1 core is biostratigraphically subdivided by means of ammonite and dinoflagellate cyst stratigraphy. The succession ranges from the Oxfordian C. densiplicatum Chronozone to the Volgian P. elegans Chronozone. The mudstones of the Blokelv-1 core are characterised by large amounts of amorphous organic matter. This hampers the preparation and identification of dinoflagellate cysts, which are also commonly degraded and corroded. Ammonites, on the other hand, are common and well-preserved in the core, contrasting with that observed in the equivalent facies and stratigraphic interval at outcrop. Integration of the ammonite and dinoflagellate cyst biostratigraphical data yields a robust chronostratigraphic subdivision of the middle Oxfordian – lowermost Volgian cored section.
GEUS Bulletin pp 65-84; https://doi.org/10.34194/geusb.v42.4310
Petrographic analysis combined with X-ray diffraction are used to identify the diagenetic changes that have affected the porosity and permeability of gravity-flow sandstones of the Oxfordian–Volgian Hareelv Formation in the cored Blokelv-1 borehole in Jameson Land. Kaolinite replacement of albite grains probably occurred early after deposition and microquartz coatings formed under shallow burial. At deeper burial, illite and quartz formed from kaolinite and K-feldspar. Pervasive ankerite cement formed in the finest grained sandstones and may have formed at the expense of early calcite cement. Quartz overgrowths are volumetrically small, partly due to inhibition by microquartz coatings and partly due to limited residence time during deep burial. The succession reached the maximum burial depth of c. 2.8 km during the late Eocene. Basaltic material was intruded into the sediments during the early Eocene and the enhanced heat flow accelerated diagenesis in the close vicinity of the intrusions, which have thicknesses of up to 2 m. Most of the sandstones have porosities between 14.4 and 25.7% and permeabilities between 0.4 and 411.9 mD; this variation resulted from a combination of microquartz coatings and clay minerals. However, the intrusion-influenced sandstones and the ankerite-cemented sandstones have lower porosity and permeability.
GEUS Bulletin pp 1-29; https://doi.org/10.34194/geusb.v8.4526
The geological map sheet of Kilen in 1:100 000 scale covers the south-eastern part of the Carboniferous– Palaeogene Wandel Sea Basin in eastern North Greenland. The map area is dominated by the Flade Isblink ice cap, which separates several minor isolated landmasses. On the semi-nunatak of Kilen, the map is mainly based on oblique photogrammetry and stratigraphical field work while in Erik S. Henius Land, Nordostrundingen and northern Amdrup Land the map is based on field data collected during previous, 1:500 000 scale regional mapping. Twenty-one Palaeozoic–Mesozoic mappable units were identified on Kilen, while the surrounding areas comprise the Late Cretaceous Nakkehoved Formation to the north-east and the Late Carboniferous Foldedal Formation to the south-west. On Kilen, the description of Jurassic–Cretaceous units follows a recently published lithostratigraphy. The Upper Palaeozoic–lowermost Cretaceous strata comprise seven formations and an informal mélange unit. The overlying Lower–Upper Cretaceous succession comprises the Galadriel Fjeld and Sølverbæk Formations, which are subdivided into six and five units, respectively. In addition, the Quaternary Ymer Formation was mapped on south-east Kilen. The Upper Palaeozoic to Mesozoic strata of Kilen are faulted and folded. Several post-Coniacian NNW–SSE-trending normal faults are identified and found to be passively folded by a later N–S compressional event. A prominent subhorizontal fault, the Central Detachment, separates two thrust sheets, the Kilen Thrust Sheet in the footwall and the Hondal Elv Thrust Sheet in the hanging wall. The style of deformation and the structures found on Kilen are caused by compressional tectonics resulting in post-extensional, presumably Early Eocene, folding and thrusting and basin inversion. The structural history of the surrounding areas and their relation to Kilen await further studies.
GEUS Bulletin pp 85-113; https://doi.org/10.34194/geusb.v42.4314
The marine, mudstone-dominated Hareelv Formation (Upper Jurassic) of Jameson Land, East Greenland is a representative of the widespread Kimmeridge Clay Formation equivalents, sensu lato, known from the greater North Atlantic region, western Siberia and basins off eastern Canada. These deposits constitute the most important petroleum source-rock succession of the region. The present study reports petroleum geochemical data from the 233.8 m thick succession penetrated by the fully cored Blokelv-1 borehole, and includes supplementary data from outcrop samples and other boreholes in Jameson Land. The succession consists of basinal mudstone intercalated with a significant proportion of gravity-flow sandstones, both in situ and remobilised as injectites. The mudstones are generally rich in organic carbon with values of TOC reaching nearly 19 wt% and high pyrolysis yields reaching values of S2 up to nearly 43 kg HC/ton. Hydrogen Indices are up to 363. The data presented herein demonstrate that weathering of abundant pyritic sulfur adversely affects the petroleum potential of the kerogen in outcrop samples. The succession is thermally immature to early mature, except where intrusions have locally heated adjacent mudstones. The documentation of rich gas/oil-prone Upper Jurassic successions in Jameson Land is important for the assessment of the regional petroleum potential, including the North-East Greenland continental shelf.
GEUS Bulletin pp 149-168; https://doi.org/10.34194/geusb.v42.4325
Data from the recently drilled, fully cored Blokelv-1 borehole and previous cored boreholes in the Upper Jurassic of Jameson Land, central East Greenland, are integrated with published field studies to address the depositional evolution of the Jameson Land Basin in the Oxfordian–Volgian. In Jameson Land, the succession represents a marine shelf-to-basin transect in a W–SW-dipping half-graben. Laminated organic-rich mudstones were deposited in the central deep parts of the basin and grade up-slope into bioturbated sandy mudstones. Extensive shallow marine – deltaic sand prograded from the western and northern basin margins and formed prominent sandy shelf-edge wedges. Sand-rich density flows initiated by periodic collapse of the shelf edge deposited massive sand bodies on the slope and basin floor; these sands were prone to post-burial remobilisation to form injectite bodies. Basin evolution was controlled both by relative sea-level changes, typically correlatable with regional and global sea-level curves, and by rift tectonics. During periods with high relative sea level, the organicrich muddy facies onlapped the sandy shelf environments; such periods of basinal expansion and onlap are recorded in the lower Oxfordian (Q. mariae Chronozone), the middle–upper Oxfordian (C. tenuiserratum – A. glosense Chronozones) and uppermost Oxfordian – upper Kimmeridgian (A. regulare – A. autissiodorensis Chronozones); the deepening, transgressive trend culminated in the mid-Kimmeridgian (A. eudoxus Chron). Marked progradation of the sandy shelf and associated deposition of gravity-flow sands on the slope and basin floor occurred in the early Oxfordian (C. cordatum Chron), the middle Oxfordian (C. densiplicatum Chron), the late Oxfordian (A. serratum Chron) and the early Volgian (P. elegans Chron). The basin architecture reflects periodic differential subsidence on the W- to SW-dipping fault block. The lower to middle Oxfordian is highly condensed in the east (300 m), reflecting accumulation during rift/fault-controlled block rotation. The upper Oxfordian – Kimmeridgian, in contrast, shows a broadly symmetrical distribution and records uniform regional subsidence.