Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

The geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

The Ammassalik Rifted Margin TSE, southern East and South-East Greenland margin

The Ammassalik Rifted Margin TSE comprises the Ammassalik and the Kangerlussuaq rift basins located on the southern East and South-East Greenland margin. The offshore Ammassalik Basin is one of the last virtually undescribed segments of the North Atlantic continental margins with a very sparse seismic coverage. The basin is compartmentalized into smaller sub-basins up to at least 4 km deep blanketed by Paleocene-Eocene basalt towards the east. Albian sediments cored in the basin suggest an at least partly Cretaceous age, making the Ammassalik Basin a likely analogue to basins on the conjugate outer British continental margin. However, the deeper, undated succession could include pre-Cretaceous strata. Located onshore southern East Greenland, the Kangerlussuaq Basin contains a Barremian/Aptian-Danian succession of estuarine-marine strata overlain by Paleocene fluvial sediments, basalts and thinner marine interludes. The sedimentary succession is less than 1 km thick. Cenozoic uplift and erosion affected both basins. Unlike the Kangerlussuaq Basin, the Ammassalik Basin may contain a working petroleum system. Together with the very large fault structures identified in the basin, this makes the Ammassalik Basin an interesting future exploration target, with the main challenge being to demonstrate a mature source rock, together with qualifying the effects of the Paleocene-Eocene magmatism and Cenozoic exhumation on the potential petroleum system.

The Scoresbysund rifted margin composite TSE offshore central East Greenland

The little explored central East Greenland margin contains thick sedimentary accumulations confined within the Scoresbysund Basin. The geological evolution of the area distinguishes from other parts of East Greenland. Even so, resemblances with the prospective basins onshore and offshore farther north probably exist, and the margin may hold a real petroleum potential. The Scoresbysund Rifted Margin Composite Tectonic-Sedimentary Element delineates the oldest part of the Scoresbysund Basin. It formed through multiple phases of rifting, volcanism, uplift and thermal subsidence between Devonian and Miocene time. The development of the composite tectonic-sedimentary element concluded with the latest Oligocene or early Miocene continental break-up of the Jan Mayen microcontinent and East Greenland. The Scoresbysund Rifted Margin Composite Tectonic-Sedimentary Element contains approximately 4 km of Eocene-lower Miocene fan-delta deposits that accumulated during down-faulting along the East Greenland Escarpment and farther seawards intercalate with basalts. The fan-delta deposits rest on Paleocene basalts that most likely cover Paleozoic-Mesozoic strata. Equivalent to onshore, the deeply buried section probably include source rock and reservoir intervals of Carboniferous, Permian and Mesozoic age. Together with the major fault structures existing in the western part of the area, this may form the basis for a working petroleum system.

Land-Ocean interactions at the southwest Greenland margin during the Holocene

<p>Palynomorph analysis of marine cores raised off Nuuk (southwestern Greenland) provided records of sea-surface conditions and climate-ocean-ice dynamics at centennial resolution over the last 12,000 years. Transfer functions using dinocyst assemblages provided information about the sea-ice cover, seasonal sea-surface temperature (SST) and salinity (SSS), as well as primary productivity. At about 10,000 cal. years ago, an increase in species diversity and the rapid increase of phototrophic taxa (light-dependent), marks the onset of interglacial conditions, with summer temperature increasing up to ~10°C during the Holocene Thermal Maximum (HTM). Low SSS and high productivity conditions are recorded during the interval, which we associate to increased meltwater and nutrient input from the Greenland Ice Sheet. After ~5000 cal. years BP, the decrease of phototrophic taxa marks a two-steps cooling associated with the Neoglacial trend. Since ~2000 cal. years BP, an increase in the high-frequency variability of sea surface conditions is noticeable. The second step change towards colder and more unstable conditions starting about 3000 cal. years BP coincides with the disappearance of the Saqqaq culture. The gap of human occupation in western Greenland, between the Dorset and the Norse settlements, i.e., from ca. 2000 to 1000 cal. years BP, may thus be linked to the highly unstable conditions in surface waters.</p>

Rift propagation north of Iceland: A case of asymmetric plume - rift interaction?

<p>Drilling by the Ocean drilling Program (ODP Legs 104, 152, 163) and geophysical studies have inferred a widespread and strong influence by the Iceland plume on the structure of the ~2500 km long volcanic rifted margins that formed between East Greenland and NW Europe during continental breakupat  ~56-54 Ma. A persistent, but spatially much reduced impact by the plume on crustal structure is evident along the ~250 km Greenland-Iceland-Faeroe ridge (GIFR). Spreading south of the GIFR has remained comparatively stable along the Reykjanes Ridge (RR). By contrast, spreading between the GIFR and northwards to the Jan Mayen Fracture Zone (JMFZ) involved northward rift propagation (~50-25 Ma) away from the Iceland plume and into the East Greenland margin. This was paired with a northward retreat of the initial spreading axis (Aegir ridge (AER)) further to the east. Slivers of the East Greenland continental crust topped by continental plateau basalts extruded during initial breakup were torn off by this northward rift propagation, and form segments of the Jan Mayen microcontinent (JMMC). Rift propagation resulted in the formation of the Iceland Plateau (IP) underlain by anomalously thick and shallow oceanic crust. The striking asymmetry in plate kinematics and crustal structures south and north of Iceland seems associated with a less enriched mantle source feeding the spreading system north of Iceland. This suggests a potentially long-lived north-south asymmetry in the composition and dynamics of the plume that, if confirmed, will favor the existence of distinctly different mantle reservoirs rather than a mixing (entrainment) process followed by a compositional de-convolution process during decompression melting and melt distribution. IODP proposal 976-Pre will address these topics by investigating the temporal and compositional development of the crust of the IP, as well as the transition from rift propagation by the IP rift (IPR) into the present day Kolbeinsey ridge (KR). Drilling will sample 2-3 stages of four IPR propagation stages we have mapped, the transition from the IPR to KR spreading, rifting and timing of transpressive movements along the pseudo-transform zone that linked the propagating IPR to the retreating AER. One drill site hopefully will establish the stratigraphic relationship between the JMMC basalts and the East Greenland plateau basalts. Sediment cover at the drill sites will constrain subsidence history and the paleo-environmental evolution of the high-latitude north-east Atlantic and its connectivity to the global ocean.The proposed drilling addresses long-standing ocean drilling themes of continental breakup, rift propagation, mantle plume reservoirs and structure, and north Atlantic paleoceanography.</p>

Submarine glacial landforms in Southeast Greenland fjords reveal contrasting outlet-glacier behaviour since the Last Glacial Maximum

<p>The Southeast (SE) Greenland margin, which includes the SE sector of the Greenland Ice Sheet (GIS) and the eastern Julianehåb Ice Cap (JIC), is drained by a number of fast‐flowing, marine‐terminating outlet glaciers. Although the SE Greenland margin is suggested to have been highly sensitive to past climatic changes, mountainous terrain and a lack of ice‐free areas have largely prevented analysis of the deglacial and Holocene behaviour of these outlet glaciers. Here we use bathymetric data, from multibeam echo-sounding acquired by NASA’s Earth Venture Sub‐orbital Oceans Melting Greenland (OMG) mission and from gravity inversion derived from Operation Icebridge (OIB) gravity data, from 36 fjords along the SE Greenland margin to map the distribution of more than 50 major submarine moraines. The moraines are up to 3 km long in the former ice‐flow direction, reach up to 150 m above the surrounding seafloor, and span the width of the fjord.</p><p>Inner‐fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords of the SE GIS and the JIC. Their locations beyond the oldest ice‐margin position where it is known from aerial photographs and correlation with prominent terrestrial moraines suggest that the inner‐fjord moraines were produced sometime during the Neoglacial (since approximately 4 ka).</p><p>Major moraine ridges are present in a midfjord setting in all of the nine fjords of the eastern JIC yet are generally absent from the deeper and wider fjords of the SE GIS. Given the distribution of published deglacial ages, we hypothesize that the midfjord moraines of the eastern JIC were formed during an ice‐margin still‐stand or advance that occurred during the early Holocene. It is possible that this still‐stand or advance had a climatic control, for example, the 8.2‐ka event that has been recorded from Greenland ice cores. The absence of midfjord moraines from the deeper and wider fjords of the SE GIS to the north suggests relatively rapid and continuous ice retreat occurred during the last deglaciation. The contrasting behaviour of the SE GIS and the eastern JIC during the last deglaciation probably reflects differences in fjord geometry and exposure to ocean heat.</p>

Seafloor sediment supply of nutrient silicon on the Greenland margin

<p>The biogeochemical cycling of nutrient silicon (Si) in the northern high latitudes has received increasing attention over recent years. This is in large part due to the discovery of silicon limitation of diatoms over seasonal timescales, the potential role of melting glaciers in supplying a significant amount of this nutrient to the coastal ocean, and the rapid environmental changes the polar ocean is experiencing as a result of global climate warming. However, our understanding of the nutrient Si in the polar ocean is severely restricted by the lack of knowledge of the benthic Si cycling and its controlling processes, which is due to the limited number of seafloor observations in the region. In this study, we address this knowledge gap through the acquisition of sediment pore water profiles and the execution of incubation experiments on sediment cores collected from the Greenland continental margin and the Labrador Sea.</p><p>Our results indicate a net (benthic) flux of dissolved silica (DSi) out of the sediment into the overlying seawater at the study sites. A new global compilation also reveals that benthic Si flux observed at our marginal sites are substantially higher than in the open ocean. This is likely because benthic flux in the open ocean is solely maintained by molecular diffusion along a concentration gradient, while there are additional processes: pore water advection and rapid dissolution of certain siliceous sponge groups, and other reactive silica phases, that contribute to the elevated benthic Si flux on the Greenland margin. This finding has important implications for existing evaluations of oceanic Si budgets, which have not accounted for any processes other than diffusion in the global estimation of benthic Si flux. Our results also suggest that strong benthic Si flux observed on the Greenland margin, combined with wind-driven coastal upwelling, could be a significant source of this nutrient to both the diverse (benthic) sponge communities and (planktonic) diatom productivity in the region. The magnitude of this benthic cycling could potentially rival the other continental inputs of Si in the northern high latitudes, as the first estimation of total benthic Si flux from the western Greenland shelf alone (0.04–0.27 Tmol year<sup>-1</sup>) is in the same order of magnitude as the total Si export from Greenland Ice Sheet (0.2 Tmol year<sup>-1</sup>) and the pan-Arctic rivers (0.35 Tmol year<sup>-1</sup>) respectively.</p>