Gunver Krarup Pedersen

Thin, fine-grained storm layers in a muddy shelf sequence: an example from the Lower Jurassic in the Stenlille 1 well, Denmark

Thin storm-sand layers are a characteristic feature of many sandy shelf sequences, while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total. The present study shows that storm-generated depositional processes governed sedimentation in a muddy shelf environment. The studied sequence is dominated by blackish mudshale and silt-streaked mudshale with thinner intervals of pale, fine-grained heterolithic sandstone. It represents the Lower Jurassic Fjerritslev Formation in the eastern part of the Danish Basin and has been studied in four cores from the Stenlille 1 well. Within the muddy outer shelf association four sedimentary facies and 14 types of laminae, 0.5–10 mm thick, may be distinguished. Most of the laminae share the characteristics of graded bedding, erosive bases and occasional fading ripples with storm layers of sand grade. The structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm-generated currents. This kind of episodic deposition of fine-grained storm layers may be common, though rarely preserved, in outer shelf environments.

The nonmarine Cretaceous of the West Greenland Basin, onshore West Greenland

Abstract Nonmarine Cretaceous sediments crop out in West Greenland between 69° and 72°N. The outcrops are bounded to the east by Precambrian basement, against which the Cretaceous sediments have a faulted contact. To the west they disappear below a cover of Palaeocene sediments overlain by a thick sequence of Tertiary basalts. The nonmarine Cretaceous sediments are fluvial in the southern and eastern pans of the area; westwards and north-westwards there is both a lateral transition in space and an upwards transition in time, through delta plain deposits with coal into delta front deposits with horizons containing typical shallow marine trace fossils and occasional bivalves and ammonites. In the south and east the nonmarine sediments are of Albian-Cenomanian age (ages based on pollen), while to the west and north-west they are younger, in places possibly as young as early Campanian. Faults with downthrow to the west and south-west have contributed to this distribution.

Timing and duration of Early Tertiary volcanism in the North Atlantic: new evidence from West Greenland

Abstract Marine mudstones intercalated with Early Tertiary volcanic hyaloclastites in West Greenland contain dinoflagellate cyst assemblages corresponding to nanoplankton zones NP4-NP8 (Danian to Thanetian). Sediments correlated with NP3 are known from the bottom of the volcanic sequence, whereas the top of the sequence is non-marine. A horizon with normally-magnetized subaerial lavas correlates with hyaloclastites within the NP4 interval. This horizon must correspond to magnetic polarity zone 27N; the overlying reversely-magnetized lavas are assumed to belong to both polarity zones 26R and 25R. The main plateau-building volcanic phase in West Greenland is thereby constrained between ‘top polarity chron C28N’ and ‘top polarity chron C25R’, a time interval of 5–6 Ma. In comparison with other parts of the North Atlantic Tertiary Igneous Province, the volcanism in West Greenland started at an early stage, and the main plateau-building phase was finished before the volcanism in East Greenland started in the NP9 interval (C24R). Sea-floor formation and onshore picrite volcanism started almost simultaneously within a region; first along the West Greenland margin and later along the East Greenland margin. In terms of an impinging mantle plume in the North Atlantic, the volcanism started over the peripheral parts and not over the central part. The differences in timing and character of the volcanic products in the North Atlantic indicate a considerable lithospheric control. The early, picrite-dominated volcanism in West Greenland may be caused by channelling of hot material from the axial part of the plume, impinging on a thick Archaean lithosphere beneath central to eastern Greenland, towards the west into a pre-existing lithospheric ‘thinspot’. The switch of the onshore volcanism from West to East Greenland may be caused by a concomitant switch of the hot axial plume flow from west to east because of the westwards drift of the plate over the plume.

No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction

Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.

Fagaceae pollen from the early Cenozoic of West Greenland: revisiting Engler’s and Chaney’s Arcto-Tertiary hypotheses

In this paper we document Fagaceae pollen from the Eocene of western Greenland. The pollen record suggests a remarkable diversity of the family in the early Cenozoic of Greenland. Extinct Fagaceae pollen types include Eotrigonobalanus, which extends at least back to the Paleocene, and two ancestral pollen types with affinities to the Eurasian Quercus Group Ilex and the western North American Quercus Group Protobalanus. In addition, modern lineages of Fagaceae are unambiguously represented by pollen of Fagus, Quercus Group Lobatae/Quercus, and three Castaneoideae pollen types. These findings corroborate earlier findings from Axel Heiberg Island that Fagaceae were a dominant element at high latitudes during the early Cenozoic. Comparison with coeval or older mid-latitude records of modern lineages of Fagaceae shows that modern lineages found in western Greenland and Axel Heiberg likely originated at lower latitudes. Further examples comprise (possibly) Acer, Aesculus, Alnus, Ulmus, and others. Thus, before fossils belonging to modern northern temperate lineages will have been recovered from older (early Eocene, Paleocene) strata from high latitudes, Engler’s hypothesis of an Arctic origin of the modern temperate woody flora of Eurasia, termed ‘Arcto-Tertiary Element’, and later modification by R. W. Chaney and H. D. Mai (‘Arcto-Tertiary Geoflora’) needs to be modified.

Sedimentology, seismic facies and stratigraphy of a Holocene spit–platform complex interpreted from high-resolution shallow seismics, Lysegrund, southern Kattegat, Denmark

Abstract Eighty kilometres of high-resolution seismic profile data (8 km/km 2 ) were collected in the Lysegrund area, southern Kattegat, Denmark to reconstruct the seismic stratigraphy of a Holocene spit–platform complex. Comparison of two sets of seismic data shows a significant difference in reflection pattern. By using lap style analyses, four Holocene units were recognised in boomer profiles (0.8–2.0 kHz). They are closely examined in this paper and their geometry is illustrated in a series of isopach maps, drawn to understand the development of the deposit in time and space. Three vibra cores provide the stratigraphic control and demonstrate the presence of three lithofacies with gradational boundaries in the interval that correlates with the three upper boomer units. The three lithofacies are part of a single lithofacies succession. In contrast to the boomer profiles, the subbottom profiles (3.5 kHz) demonstrate continuous accretion surfaces within the lithofacies succession. Comparisons of the boomer and subbottom profile data therefore indicate that the three boomer units are genetically coupled and that there are no significant time gaps between units. The three boomer units are interpreted to represent a spit–platform complex that developed in three phases during a general rapid rise of relative sea-level (>10 mm/a) under conditions of excess sediment supply. The source materials were mobilised from glacial–fluvial sediments in a headland west of and close to the spit–platform. During phase 1, spit development occurred in shallow water. This acted as a core to the development of a spit–platform during phase 2 that consisted of three seismic facies identifiable on 3.5 kHz subbottom profiles. During phase 3, true foresets and bottomsets developed. Growth of the platform surface kept pace with sea-level rise and the entire spit–platform complex formed in less than a thousand years. Focusing on differences in the seismic data helps avoid pitfalls in choosing methods to interpret data. The closely spaced seismic line-net forms the basis of a 3D dynamic model of the spit–platform that resembles the model of Meistrell [Meistrell, F.J., 1972. The split–platform concept: laboratory observations of spit development. In: Schwartz, M.L. (Ed.), Spits and Bars, Dowden, Hutchinson and Ross, Stroudsberg, pp. 225–283.].

Intense and widespread seismicity during the end-Triassic mass extinction due to emplacement of a large igneous province

Multiple levels of earthquake-induced soft-sediment deformations (seismites) are concentrated in the end-Triassic mass extinction interval across Europe. The repetitive nature of the seismites rules out an origin by an extraterrestrial impact. Instead, this intense seismic activity is linked to the formation of the Central Atlantic magmatic province (CAMP). By the earliest Jurassic the seismic activity had ceased, while extrusive volcanism still continued and biotic recovery was on its way. This suggests that magmatic intrusions into sedimentary strata during early stages of CAMP formation caused emission of gases (SO 2 , halocarbons, polycyclic aromatic hydrocarbons) that may have played a major part in the biotic crisis.

Drowning of a nearshore peat-forming environment, Atane Formation (Cretaceous) at Asuk, West Greenland: sedimentology, organic petrography and geochemistry

Abstract The Cretaceous Atane Formation, Nuussuaq basin, West Greenland, is dominated by non-marine sandstones, shales, coals, and delta-front deposits. Marine incursions are frequent, however, and near Asuk, Disko, a coal seam is encased in shallow marine deposits. Notable changes in both petrography and geochemistry occur through the seam. At the base and top of the seam, the proportions of inertinite and liptinite increase at the expense of the huminite maceral group, and within all maceral groups proportions of detrital macerals increase. Geochemical changes include systematic variations in TOC, TS, n-alkane, acyclic isoprenoid, aromatic hydrocarbon, and di- and triterpenoid biomarkers, which include a number of rearranged hopanes and hopenes, and six isomers of 28,30-bisnorhopane. The variations reflect diagenetic changes related to the availability of clay, as well as changes in depositional environment going from shallow marine conditions, through fresh water mire back to open water conditions and to the eventual return of shallow marine conditions, shown by the occurrence of delta-front deposits containing Ophiomorpha nodosa trace fossils c. 50 cm above the top of the coal seam.

The syn-volcanic Naajaat lake, Paleocene of West Greenland

Abstract The Naajaat lake in the Nuussuaq Basin on Disko and Nuussuaq formed in a geological setting between cratonic crystalline Precambrian rocks overlain by Cretaceous sediments and an actively forming Paleocene volcanic province. The lacustrine deposits, shales as well as hyaloclastite breccias, accumulated in low-lying areas inundated by fresh water and sealed off from marine transgressions by a broad subaerial volcanic terrain. Foreset-bedded hyaloclastite breccias demonstrate water depths of up to 450 m, and the area of the lake was 2500 km2 at its maximum extent. The lake probably existed for less than 0.5 million years. The lake received clay and silt from two provenance areas. Quartz contents of more than 25% in the majority of the sediment samples indicate that large amounts of material were continuously supplied to the lake from the crystalline terrain, whereas the volcanic terrain supplied smectite and mixed-layer minerals to the lake. High kaolinite contents stem from the crystalline or both provenance areas. The shales are characterized by high TOC (up to 11%), lack of pyrite, presence of terrestrial spores and pollen and lack of marine dinoflagellates. The lacustrine sediments rest on an erosional unconformity and its correlative conformity. The unconformity developed during the latest Cretaceous and Early Paleocene. Five stages are recognized in the geological development of the lake. Stages 1–4 are characterized by accumulation of hyaloclastite breccias, rise in lake level, and eventual transgression of subaerial terrains. The rises in lake level were caused by stemming of fluvial run-off behind the aggrading volcanic pile. Stage 5 corresponds to cessation of volcanic activity, a stable lake level, and progradation of clastic sediments, resulting in infilling of the lake. During the lacustrine transgression only sediment in suspension was transported into the central parts of the lake.

Landslide and Tsunami 21 November 2000 in Paatuut, West Greenland

A large landslide occurred November 21, 2000 at Paatuut, facing the Vaigat Strait onthe west coast of Greenland. 90 million m3 (260 million tons) of mainly basalticmaterial slid very rapidly (average velocity 140 km/h) down from 1,000–1,400 maltitude. Approximately 30 million m3 (87 million tons) entered the sea, creatinga tsunami with an run-up height of 50 m close to the landslide and 28 m at Qullissat,an abandoned mining town opposite Paatuut across the 20 km wide Vaigat strait. Theevent was recorded seismically, allowing the duration of the slide to be estimated tocirca 80 s and also allowing an estimate of the surface-wave magnitude of the slideof 2.3. Terrain models based on stereographic photographs before and after the slidemade it possible to determine the amount of material removed, and the manner ofre-deposition. Simple calculations of the tsunami travel times are in good correspondencewith the reports from the closest populated village, Saqqaq, 40 km from Paatuut, whererefracted energy from the tsunami destroyed a number of boats. Landslides are notuncommon in the area, due to the geology with dense basaltic rocks overlying poorlyconsolidated sedimentary rocks, but the size of the Paatuut slide is unusual. Based onthe observations it is likely at least 500 years since an event with a tsunami of similarproportions occurred. The triggering of the Paatuut slide is interpreted to be caused byweather conditions in the days prior to the slide, where re-freezing melt water inpre-existing cracks could have caused failure of the steep mountain side.