Postglacial Isostatic Rebound Research Articles

Marine deposits of the Chuy Formation (Late Pleistocene) and isostatic readjustments in the area of Laguna de Rocha (Uruguay)

The Chuy Formation is characterized by up to 135 m of an alternation of green pelites and fine to coarse sandstones with sparse invertebrate fossils. The marine deposits are interbedded with continental, loessic deposits of the Libertad Formation and overlain by the Dolores Formation, made up of mudstones with calcareous concretions. The results of the radiocarbon dating showed calibrated ages of 13.9±0.2, 41.5±1.9 and 50±3 ka BP on bioclasts of marine fossils at an elevation (above sea level, asl) of -2.8, -6.13 and -8 m respectively. Such ages and elevations are in disagreement with the sea-level evolution inferred for the Late Pleistocene. Two possible explanations are: (a) the ages represent minimum ages and deposition took place during the last interglacial at 115-130 ka (Marine Isotope Stage MIS 5e), or (b) they represent depositional ages but the area experimented large isostatic readjustments during and after the last glaciation. Several lines of evidence suggest a Late Pleistocene age for the upper Chuy Formation, including the d18O curve obtained from invertebrate shells, which shows large secular variations consistent with MIS 1 to 7. The proposed scenario envisages significant subsidence between 50-20 ka due to the far-field effects of glacial load in the Andes/Patagonia. At 20 ka the eustatic regression outpaced subsidence, leading to continentalization of the Laguna de Rocha area. Marine conditions returned at 15 ka and into the Holocene, except for continental deposits (Dolores Formation) at ca. 11-10 ka (Younger Dryas). An uplift of 115 m took place between 15 and 9 ka in the area, which is interpreted as post-glacial rebound. In the Holocene, moderate subsidence was further recorded. A regional trend is observed, with uplift of marine deposits increasing towards the W-SW, which is consistent with an explanation as post-glacial isostatic rebound.

10Be chronology of deglaciation and ice-dammed lake regression in the vicinity of the Mylodon Cave (Cerro Benítez, Patagonia, Chile)

Located 51.5°S in the vicinity of the Southern Patagonian Ice Field, Cerro Benítez and the glacial valley of Lago Sofía host several caves and rock shelters that were occupied by megafauna and humans during the Late Pleistocene, including the Mylodon Cave and two of the oldest archaeological sites in Patagonia. During the last glaciation, Cerro Benítez was alternately covered by the Patagonian Ice Sheet and surrounded by an ice-dammed lake which restricted the access to the caves and rock shelters located under its uppermost level, 155 m a.s.l. This study aims to provide a detailed chronology of the deglaciation and lake regression in Cerro Benítez. The glacial fluctuations and the variations of lake level were reconstructed from multi-scale, remote-sensing data and field geomorphological mapping. In addition, we calculated the surface exposure age of 11 erratic blocks located above and on the lacustrine erosional platform using terrestrial cosmogenic 10Be in order to date ice downwasting and lake regression, respectively. Dates of ice downwasting and lake regression events were modelled from prior surface exposure ages using Bayesian statistics. The results suggest that the Patagonian Ice Sheet locally thinned by at least 300 m during MIS 3 in the aftermath of a major glacial advance. Following deglaciation, the ice-dammed lake experienced a slow local regression (ca. 2.5 mm. a−1) until 16.9 ka B2k, interpreted as the result of lake basin tilting due to differential post-glacial isostatic rebound. This initial phase of lake regression was followed by a faster regression caused by the reversal of the lake drainage between 16.9 and 15.4 ka B2k. We assess the chronological model by comparison with uplift and lakeshore erosion rates from the literature and eventually discuss the implications for megafaunal colonisation of the area.

Hammerfest Basin Composite Tectono-Sedimentary Element, Barents Sea

Abstract The Hammerfest Basin is an east–west-trending graben located between the Loppa High and the Finnmark Platform in the southern part of the Norwegian Barents Sea. Mainly siliciclastic strata of Carboniferous–Cenozoic age cover the Caledonian basement and have a total estimated thickness of 5–8 km. The basin evolved through several tectonic phases: Carboniferous rifting, Late Jurassic rifting, opening of the Atlantic Ocean, Oligocene reorganization of plate movements and post-glacial isostatic rebound. An east–west-trending dome in the centre of the basin developed during the main extensional tectonic event in the Late Jurassic. Horst structures represent the main hydrocarbon traps. Erosional channels on the flanks of the basin represent entry points for Lower Cretaceous sands. For the rest of the Cretaceous and Cenozoic intervals, no significant reservoir sands are expected. The first exploration well in the Barents Sea in 1980 was located in the Hammerfest Basin and by 2019 a total of 45 wells had been drilled in the basin, with 34 classified as exploration wells. The result is 18 oil and gas discoveries, which gives a discovery rate of 53%. Two fields are now in production: the Snøhvit gas-condensate fields and the Goliat oilfield. A total of 340 Msm 3 (2140 Mbbl) recoverable oil equivalents have been discovered. For the middle Jurassic play, the yet-to-find potential may be around 50 Msm 3 , distributed in several small structures in the basin. Following the oil discovery in the Middle Triassic interval in the Goliat structure, and because several of the previously drilled structures only penetrated the Jurassic and the uppermost Triassic section, considerable exploration potential may exist in the deeper Triassic interval in structures with the best reservoir facies. Stratigraphic traps of Cretaceous age may have a moderate petroleum potential, with excellent reservoirs encountered along the flank of the basin. Exploration potential may also exist in Upper Permian sandstones along the southern and eastern flanks of the basin. However, in large parts of the basin, the remaining potential is in the deep structures and, hence, is gas prone.

Local and regional controls on Holocene sea ice dynamics and oceanography in Nares Strait, Northwest Greenland

Nares Strait is one of three channels that connect the Arctic Ocean to Baffin Bay. Unique sea-ice conditions in the strait lead to the formation of landfast ice arches at its northern and southern ends. These ice arches regulate Arctic sea-ice and freshwater export through the strait and promote the opening of the North Water polynya. The present study addresses the paucity of pre-satellite records of environmental conditions in the Nares Strait area, and aims at reconstructing Holocene sea-ice conditions and ocean circulation in the strait. The investigation is based on a marine sediment core strategically retrieved from under the current ice arch in Kane Basin to the south of Nares Strait, and provides a continuous record spanning the past ca 9 kyrs. We use benthic foraminiferal assemblages and sea-ice biomarkers to infer changes in Holocene ocean circulation and sea-ice conditions in Kane Basin. The establishment of the modern ocean circulation in Kane Basin is related to ice sheet retreat and postglacial rebound, while changes in sea-ice cover concur with major shifts in the Arctic Oscillation (AO). Our results suggest that sea-ice cover in Kane Basin was highly variable between ca 9.0 and 8.3 cal. ka BP, before increasing, probably in link with the 8.2 cold event and the opening of Nares Strait. A short period of minimum sea-ice cover and maximum Atlantic bottom water influence occurred between ca 8.1 and 7.5 cal. ka BP, when Kane Basin was deeper than for the remaining of the Holocene. As atmospheric temperatures dropped, sea-ice cover intensified in Kane Basin between ca 7.5 and 5.5 cal. ka BP, but strong winds under prevailing positive-like AO conditions likely prevented the formation of ice arches in Nares Strait. During this time, our micropaleontological data show that Atlantic water was progressively excluded from Kane Basin by the postglacial isostatic rebound. Increasingly cooler atmospheric temperatures and a shift towards more negative phases of the AO may have promoted the establishment of ice arches in Nares Strait between ca 5.5 and 3.0 cal. ka BP. Instabilities in the Kane Basin ice arch ca 3.0 cal. ka BP coincide with a shift towards prevailing positive phases of the AO, while a brief recovery of the ice arch occurred during more negative-like AO conditions between ca 1.2 and 0.2 cal. ka BP.

Identifying sites of high geoarchaeological potential using aerial LIDAR and GIS on Quadra Island, Canada

The dynamic environmental history and relative sea level (RSL) changes experienced on the Northwest Coast of North America during the early post-glacial period and the early Holocene resulted in significant archaeological visibility challenges for prospection of early coastal archaeological sites. This study offers an integrated methodological approach in support of locating palaeo-coastal sites by combining: (1) geomorphic interpretation of landscape attributes captured by LIDAR (Light Detection and Ranging) mapping; (2) GIS-based archaeological site potential mapping; and (3) local RSL history. The RSL history for the study site (Quadra Island, British Columbia, Canada) shows notable regression over the past 14,300 years from a highstand of at least 197 m resulting from post-glacial isostatic rebound. Late Pleistocene and early Holocene palaeo-shorelines are found inland from, and elevated above, modern sea level and represent key areas for archaeological prospecting. Bare-earth Digital Terrain Models (DTMs) derived from the LIDAR dataset were interpreted to identify palaeo-shorelines at 10 m and 30 m above mean sea level. A GIS-derived map was created to identify regions of high archaeological potential. Field validation suggests that this integrated methodology provides a promising approach for archaeological prospection that could be applied to other post-glacial coastal settings.

Temporal evolution of magma and crystal mush storage conditions in the Bárðarbunga-Veiðivötn volcanic system, Iceland

The depth(s) of magma storage reservoirs beneath active volcanic regions may change with time. Determining the rates and causes of millennial-scale changes in magmatic system architecture is critical for the development of realistic time-integrated models of crustal evolution. Here we examine a suite of samples from the exceptionally well-exposed Bárðarbunga-Veiðivötn volcanic system in central Iceland in order to resolve the temporal evolution of magma storage conditions within one of Iceland’s most productive volcanic systems. We have measured the major and minor elemental composition of glass, mineral and melt inclusion from five erupted units that span a full glacial cycle, from a <100 ka subglacial eruption to a historical eruption in 1477 AD. All samples contain macrocrysts (>500 μm), polymineralic clots and high-crystallinity nodules, consistent with derivation from crystal mush bodies. Macrocryst rims are in chemical equilibrium with their respective carrier melts, while macrocrysts cores are too primitive to have crystallized from these melts. Each sample records a distinct range of macrocryst compositions, indicating that the composition and/or eruptibility of stored crystal mush has changed with time. Macrocrysts from the oldest units are the most primitive, and the macrocryst compositional range becomes wider and, on average, more evolved, with time. Clinopyroxene-melt and melt-based (OPAM) geobarometers reveal temporally invariant crystallization conditions of 1.9–2.2 ± 0.7 (1σ) kbar pressure, corresponding to depths around 6.8–7.8 ± 2.5 km. All the samples also contain melt inclusions trapped at mid-crustal pressures of ∼2.6 kbar (9.6 km). In addition, melt inclusions hosted in most primitive olivines and plagioclases from subglacial and early Holocene eruptions preserve evidence of crystallization in a lower-crustal storage level(s) located at 17.5 km (4.9 kbar). This petrological record of deep crystallization may be linked to a surge in eruption rates, tapping of lower-crustal magma reservoirs, consistent with a crustal response associated with postglacial isostatic rebound. In contrast, the absence of a deep crystallization signature in the younger eruptive units may reflect lower magma production rates under steady-state conditions of the crust, and new magma pathways favouring melt storage in the mid-crust.

Tracing sea-level changes during the mid-Holocene in the southern Mediterranean coast: An example from the Gulf of Gabes

Mid-Holocene sea-level emergence was recorded along a mid-latitude coastal site in the Gulf of Gabes, Tunisia, in beach rock deposits. However, the post-emergence sea-level curve and associated hydro-sedimentary processes have rarely been documented. This study presents new records of sea-level changes along the Tunisian coast since the mid-Holocene. Each phase of the sea-level curve was evidenced and supported by lithostratigraphic, morphological and archaeologic markers. Post-emergence sea-level fall due to postglacial isostatic rebound was recognized in regressive sequences which vary depending on available accommodation space, from a small pocket beach to a well developed dune system. Sea-level stabilization following isostatic rebound has promoted the end phase deposits of the regressive sequences. However, this stability was interrupted during the late Holocene by a high-energy storm event that accumulated a transgressive boulder unit at 2 m above present. Shape and disposition of the boulder ridge behind a prograding modern shoreline suggests that sea level has not changed during the late Holocene. The existence of a Roman fish pond on the upper foreshore confirms stability of sea level during the last two millennia. The combination of lithostratigraphic, morphological and archaeologic markers represents a tool for improving the accuracy of dating of erosional and depositional periods in mid-coastal sections.

Gas hydrate dissociation off Svalbard induced by isostatic rebound rather than global warming

Methane seepage from the upper continental slopes of Western Svalbard has previously been attributed to gas hydrate dissociation induced by anthropogenic warming of ambient bottom waters. Here we show that sediment cores drilled off Prins Karls Foreland contain freshwater from dissociating hydrates. However, our modeling indicates that the observed pore water freshening began around 8 ka BP when the rate of isostatic uplift outpaced eustatic sea-level rise. The resultant local shallowing and lowering of hydrostatic pressure forced gas hydrate dissociation and dissolved chloride depletions consistent with our geochemical analysis. Hence, we propose that hydrate dissociation was triggered by postglacial isostatic rebound rather than anthropogenic warming. Furthermore, we show that methane fluxes from dissociating hydrates were considerably smaller than present methane seepage rates implying that gas hydrates were not a major source of methane to the oceans, but rather acted as a dynamic seal, regulating methane release from deep geological reservoirs.

A ubiquitous hydrothermal episode recorded in the sheet-crack cements of a Marinoan cap dolostone of South China: Implication for the origin of the extremely 13C-depleted calcite cement

Sheet-crack – primarily filled with chalcedony, quartz and calcite – is a type of significant sedimentary structure in almost all documented cap carbonates in platform-to-slope settings, which sharply overlie the global Marinoan (∼635Ma) glacial tillite. The Jiulongwan section, located in the Yangtze Gorges areas, South China, is significant for the first discovery of extremely 13C-depleted (δ13C down to −41‰) calcite cements in sheet-crack structure (Jiang et al., 2003a), which provides direct evidence for the methane seep hypothesis (Kennedy et al., 2001). Focusing on the calcite cements in the same section, Bristow et al. (2011) proposed a hydrothermal origin based on high temperatures (378°C) determined by carbonate clumped isotope thermometry (CCIT). In this study, we provide evidence for the hydrothermal model using fluid inclusion technology (FIT) to quartz cements in the Jiulongwan section. The widespread sheet-crack structures in South China have uniformmineralparageneticassemblages, which apparently reflect three stages of a hydrothermal fluid activity, including dolomitization at the early stage, silicification comprising chalcedony and quartz at the middle stage, and calcitization characterized by carbonaceous calcite filling preexisting voids at the late stage. Primary aqueous fluid inclusions from quartz crystals have homogenization temperatures of approximately 160–220°C (mean, 192°C, n=31), while the salinity histogram contains two peaks at low salinity (6.3–8.3wt.% NaCl equiv.) and high salinity (18.0–20.8wt.% NaCl equiv.), reflecting precipitation caused by mixing of high- and low-salinity fluids. A modified and detailed hydrothermal model is proposed indicating that the sheet-crack structure resulted from successive thermal fluid activity after karstic dissolution due to postglacial isostatic rebound. This model is compatible with the unified sequence of glacio-eustatic events after the termination of Marinoan glaciation (Zhou et al., 2010) and the temperature results determined by CCIT (Bristow et al., 2011).

Subaqueous rock-avalanche deposits exposed by post-glacial isostatic rebound, Innfjorddalen, Western Norway

This paper presents a detailed description of deposits and landforms of multiple rock avalanches in Western Norway, one of which fell onto water-saturated sediments in Innfjorddalen below the former water level. Deposits of the latter are now exposed on the valley floor due to post-glacial isostatic rebound. At least three rock avalanches from the same source at Gråfonnfjellet Mountain have occurred during late glacial and post-glacial time, and their deposits are distributed over an area of 1.44km2 in the valley. These rock avalanches have volumes of 15.1×106m3, 5.4×106m3 and 0.3×106m3 and yielded cosmogenic radionuclide 10Be ages of 14.3±1.4ka, 8.79±0.94ka and 1.028±0.380ka, respectively. The youngest event dates, within uncertainty limits to a historic rock avalanche in the year 1611–12 CE. The rock avalanches formed a stratified succession of deposits. The rock-avalanche deposits (1.38m2) have lobate forms, have frontal rims and parallel ridges, extend across the valley floor and up the opposite slope, and form dams on the valley floor. Isolated hills comprised of rock boulders (0.61km2), interpreted to be ‘toma hills’, are disconnected from the main rock-avalanche deposits by a 520-m-wide zone of deformed, valley-fill sediments. Trenches and a ground penetrating radar survey of these deposits indicate large-scale deformation or liquefaction. Numerical runout modeling of the rock avalanches with the code DAN3D supports the interpretation of their landforms and sources, and highlights their runout behavior.

Postglacial tectonic structures and mass wasting in Lake Vättern, southern Sweden

Deformation of the Earth's crust by glacial loading and unloading was first recognized more than a century ago (De Geer 1888). This deformation is expressed by postglacial isostatic rebound and is ongoing in large parts of glaciated regions. It is typically a process with uplift rates of millimetres per year (Johansson et al. 2002). The crustal rebound which initially followed deglaciation was, however, faster and therefore caused large earthquakes under certain conditions (Lundqvist & Lagerback 1976; Steffen et al. 2014). In Lake Vattern, southern Sweden, mass wasting and deformation structures have been mapped in the sediment accumulated on the lake floor (Jakobsson et al. 2014). Along an 80 km stretch of the lake, deformation structures seen in sediments reveal up to 13 m of vertical displacement in the underlying bedrock. From this displacement, an earthquake with seismic magnitude up to 7.5 was interpreted to have occurred in Lake Vattern shortly after the Scandinavian Ice Sheet had retreated …

Kettle holes, ‘dead-ice’ topography and eskers on a lake floor in Telemark, southern Norway

Hummocky terrain in deglaciated areas is often attributed to ‘dead-ice’ activity, that is, a depositional environment produced by the presence and melt-out of large blocks of stagnant ice (Gravenor & Kupsch 1959; Eyles et al. 1999). Morphologically similar dead-ice terrain is found on the floor of Lake Bandak in southern Norway, a former fjord now isolated from the sea, where a stagnant glacier terminated during the Late Weichselian deglaciation. Lake Bandak is an east–west-orientated lake with a length of c. 26 km, an average width of c. 1 km, and an area of 26.4 km2 (Fig. 1). It is situated 72 m above sea level some 85 km inland from the outer coast (Fig. 1b). The marine limit is 120–130 m above present sea level due to postglacial isostatic rebound (Bergstrom 1999), implying that the glacier which filled the valley at the Last Glacial Maximum terminated in a fjord during deglaciation. Both the glacial ice divide and present watershed lie west of the lake, indicating flow from west–east. The lake is deepest (200–300 m) and relatively flat from Lardal and eastwards with steep lateral slopes (Fig. 1a), whereas the western part is shallower (typically <100 m deep). Seismic and backscatter data suggest that …

Compositional dependence of lower crustal viscosity

We calculate the viscosity structure of the lower continental crust as a function of its bulk composition using multiphase mixing theory. We use the Gibbs free-energy minimization routine Perple_X to calculate mineral assemblages for different crustal compositions under pressure and temperature conditions appropriate for the lower continental crust. The effective aggregate viscosities are then calculated using a rheologic mixing model and flow laws for the major crust-forming minerals. We investigate the viscosity of two lower crustal compositions: (i) basaltic (53 wt % SiO2) and (ii) andesitic (64 wt % SiO2). The andesitic model predicts aggregate viscosities similar to feldspar and approximately 1 order of magnitude greater than that of wet quartz. The viscosity range calculated for the andesitic crustal composition (particularly when hydrous phases are stable) is most similar to independent estimates of lower crust viscosity in actively deforming regions based on postglacial isostatic rebound, postseismic relaxation, and paleolake shoreline deflection.

Glacial legacy effects on river landforms of the southern Laurentian Great Lakes

Abstract Stream and river drainage networks are fundamental in watershed science, but the low-relief river catchments of the southern Laurentian Great Lakes do not easily conform with traditional ideas in fluvial geomorphology. The effects of Pleistocene glaciation and post-glacial isostatic rebound require an adapted fluvial landscape model in order to understand the organization of river landforms. Advancing our understanding of glacial legacy effects in low-relief river catchments is important for the effective management of aquatic ecosystems and water resources in these environments. Based on a classification framework for alluvial floodplains, the spatial arrangements of river landforms are presented for three catchments in southern Ontario, Canada. The typical Holocene response of southern Ontario rivers is confounded by numerous distinct glacial landform assemblages and dynamic baselevel histories. Mapping of river landforms provides an interpretive framework to explain glacial legacy effects in the context of local sources of glacial sediment and patterns of fluvial sediment flux over the Holocene. A number of general glacial–fluvial landform relationships are identified and can be broadly clustered into three themes: 1) topographic and sedimentological glacial legacy effects; 2) landforms resulting from isostatic and lake baselevel change, and 3) superimposed patterns of Holocene fluvial sediment supply. Geochronological evidence is assessed for floodplain landform ages, but radiocarbon methods are limited in many floodplain types due to slow vertical accretion processes. Laterally active meandering channels with well-developed point-bar deposits tend to rework the alluvium every few centuries in smaller channels and every few millennium in larger channels.

The impact of low and intermediate-level radioactive waste on humans and the environment over the next one hundred thousand years

In order to assess the potential radiological risk to humans and the environment from a geological repository for radioactive waste, a safety assessment must be performed. This implies that the release and transfer of radionuclides from the repository into the surface environment are calculated and that the effects in the biosphere are evaluated for an assessment period up to one hundred thousand years according to Swedish regulations. This paper discusses the challenges associated with the modelling of surface ecosystems over such long time scales, using the recently completed assessment for the extension of the existing repository for the low- and intermediate-level nuclear waste (called SFR) in Forsmark, Sweden as an applied example.In the assessment, natural variation and uncertainties in climate during the assessment period were captured by using a set of climate cases, primarily reflecting different expectations on the effects of global warming. Development of the landscape at the site, due to post-glacial isostatic rebound, was modelled, and areas where modelling indicated that radionuclides could discharge into the biosphere were identified. Transfers of surface water and groundwater were described with spatially distributed hydrological models. The projected release of radionuclides from the bedrock was then fed into a biosphere radionuclide transport model, simulating the transport and fate of radionuclides within and between ecosystems in the landscape. Annual doses for human inhabitants were calculated by combining activity concentrations in environmental media (soil, water, air and plants) with assumptions on habits and land-use of future human inhabitants. Similarly, dose rates to representative organisms of non-human biota were calculated from activity concentrations in relevant habitats, following the ERICA methodology.In the main scenario, the calculated risk for humans did not exceed the risk criteria or the screening dose rate for non-human biota, indicating that the repository design is sufficient to protect future populations and the environment. Although the combination of radionuclides, land-uses/habitats, type of most exposed population and area of exposure that contribute most to the total dose shifts over time, the total calculated dose shows limited variability. Significant reductions in the dose only occur during submerged periods and under periglacial climate conditions. As several different water and food pathways were equally important for endpoint results, it is concluded that it would be difficult to represent the biosphere with one or a set of simplified models. Instead, we found that it is important to maintain a diversity of food and water pathways, as key pathways for radionuclide accumulation and exposure partly worked in parallel.

Fluvio-deltaic avulsions during relative sea-level fall

Understanding river response to changes in relative sea level (RSL) is essential for predicting fluvial stratigraphy and source-to-sink dynamics. Recent theoretical work has suggested that rivers can remain aggradational during RSL fall, but field data are needed to verify this response and investigate sediment deposition processes. We show with field work and modeling that fluvio-deltaic systems can remain aggradational or at grade during RSL fall, leading to superelevation and continuation of delta lobe avulsions. The field site is the Goose River, Newfoundland-Labrador, Canada, which has experienced steady RSL fall of around 3–4 mm yr –1 in the past 5 k.y. from post-glacial isostatic rebound. Elevation analysis and optically stimulated luminescence dating suggest that the Goose River avulsed and deposited three delta lobes during RSL fall. Simulation results from Delft3D software show that if the characteristic fluvial response time is longer than the duration of RSL fall, then fluvial systems remain aggradational or at grade, and continue to avulse during RSL fall due to superelevation. Intriguingly, we find that avulsions become more frequent at faster rates of RSL fall, provided the system response time remains longer than the duration of RSL fall. This work suggests that RSL fall rate may influence the architecture of falling-stage or forced regression deposits by controlling the number of deposited delta lobes.

Investigation of crustal motion in Europe by analysing the European VLBI sessions

Since 1990 the International VLBI Service for Geodesy and Astrometry (IVS) has been performing geodetic Very Long Baseline Interferometry (VLBI) observations within the European geodetic VLBI network. In this work, 114 European VLBI sessions from January 1990 to September 2011 are analysed using the Vienna VLBI Software (VieVS). A total of 58 baselines with lengths ranging from 59 m to 4581 km are investigated and the lengths of most of them indicate repeatabilities at the sub-centimetre level. The horizontal station motions which describe the motion of the Eurasian plate are compared to the NUVEL-1A and MORVEL tectonic plate models. Intraplate crustal motions are investigated by estimating the station velocities with respect to Wettzell (Germany), a station on the geodynamically stable part of Eurasia. The northern part of Europe is dominated by the postglacial isostatic rebound, confirmed by four VLBI sites in this region with an uplift from 2.89±0.71 mm/yr (Svetloe, Russia) to 7.23±1.00 mm/yr (Ny-Alesund, Norway) with respect to the central part of the European plate. Besides the vertical uplift, these radio telescopes evidence a horizontal motion from the centre of the former ice sheet towards its border. In the southern part of Europe the motion of the VLBI sites is caused by the collision of the African plate with the Eurasian plate, while the stations on the stable part of Europe do not present any significant relative motions. Our results are compared against those by Haas et al. (J. Geodyn. 35:391–414, 2003) and with velocities of the current reference frame of the International Global Navigation Satellite Systems Service.

The birth and death of lakes on young landscapes

AbstractOngoing land uplift caused by postglacial isostatic rebound creates strong landscape‐age gradients alongside the Gulf of Bothnia, northern Scandinavia. Lakes are continuously generated on this dynamic landscape as the uplift isolates bays from sea inundation. However, concomitant with this process older lakes are lost as the basins are filled with sediments, creating a continuum of lake ages on the landscape. We studied the lake size and depth distributions and lake densities, along an age gradient covering 0–4500 years. Map data on the density, area, and elevation of lakes were combined with field‐based measurements of maximum basin depth. We find that young lake populations are densely distributed and dominated by small and shallow lakes. Over time, small and shallow lakes are lost by complete sediment filling, resulting in lower lake density and a shift in size and depth distributions towards larger, deeper lakes. Since lake filling is a universal process, we propose that these findings can be generalized to other gradients in landscape age.

The Grosmont: the world's largest unconventional oil reservoir hosted in carbonate rocks

AbstractThe Upper Devonian Grosmont platform in Alberta, Canada, is the world's largest heavy oil reservoir hosted in carbonates, with 400–500 bbbl of initial oil in place at an average depth of about 250–400 m. Past pilot activity between 1975 and 1987, mainly with ‘huff and puff’ technology, had variable results and the reservoir was deemed uneconomical at the time. More advanced thermal recovery technologies, such as steam assisted gravity drive and electrical in-situ retorting, much higher world market prices for oil and certain political pressures have led to a flurry of activity in the Grosmont since 2006. To be successful, all these schemes require a solid geological, geophysical and petrophysical reservoir evaluation. Our study, which aims to aid in thermal recovery of this reservoir, shows that the current reservoir characteristics were created by a succession of five major factors and/or processes: sedimentary stratigraphy, dolomitization, polyphase and polygenetic fracturing, polyphase and polygenetic karstification, and biodegradation. Most of the present porosity and permeability is due to fracturing and karstification.The sedimentary stratigraphy of the Grosmont reservoir consists of six stacked carbonate units interbedded with marls and some evaporites. The latter two originally acted as aquitards during diagenesis but are breached or missing in parts of the area today. Dolomitization by density-driven reflux was the first pervasive diagenetic process. Most dolostones are fine-crystalline and tight, however, and the only notable porosity caused by and/or related to dolomitization is scattered molds and vugs.A dense fracture network was created in three or four phases. Most fractures probably originated from collapse following subsurface salt dissolution and/or from Laramide tectonics far to the west, whereby pulsed crustal loading in the fold-and-thrust belt created a dynamic forebulge in the Grosmont region via multiple pulses of basin-wide crustal flexing, each followed by relaxation. The fracture network probably was reactivated and/or expanded by glacial loading and post-glacial isostatic rebound in the Pleistocene and Holocene, respectively.The region experienced three or four prolonged periods of epigene (top-down) karstification, although there is tangible evidence for only two of them in the Grosmont platform. The first of these episodes was a ‘warm epigene karstification’ during the Jurassic–Cretaceous, and the second was/is a ‘cold epigene karstification’ that started sometime in the Cenozoic and is continuing to this day. In addition, there is circumstantial evidence for hypogene (bottom-up) ‘karstification’ (=dissolution) throughout much of the geological history of the Grosmont since the Late Devonian, with two possible maxima around the time of hydrocarbon emplacement, that is Early–Middle Cretaceous and Early Cenozoic, respectively. Epigene karstification was accompanied and/or followed by extensive biodegradation. Present bitumen in-situ viscosities are &gt;1 million cP and API gravities range from 5 to 9°. Taken together, these conditions pose considerable challenges for any type of thermal recovery scheme.

Youth Environmental Science Outreach in the Mushkegowuk Territory of Subarctic Ontario, Canada

We connected youth of the Mushkegowuk Territory (specifically Fort Albany First Nation) with environmental science and technology mentors in an outreach program contextualized to subarctic Ontario that addressed some of the environmental concerns identified by members of Fort Albany First Nation. Most activities were community-based centering on the general theme of understanding a changing environment (e.g., long range transport of contaminants, global warming, and postglacial isostatic rebound); however, our initiative also included an annual trip for Grade 8 students to the Ontario Science Centre and the Royal Ontario Museum in Toronto, Ontario, to expose students to science in an interactive, fun setting. We found that informal educational settings, resources that relied on spatial/visual cues, group activities, and hands-on and experiential teaching were effective in engaging the schoolchildren. Our hope is that some of the students that attend our community-based camp will pursue a postsecondary education in the environmental sciences.