Glacio-isostatic Uplift Research Articles

Accelerated uplift resulting from Anglian glacioisostatic rebound in the Middle Thames Valley, UK?: evidence from the river terrace record

A relatively simple analysis of the terraces of the Middle Thames valley reveals a complex sequence of responses to late-Anglian (late Middle Pleistocene) drainage disruption. A decrease in the amounts of vertical incision separating the later post-Anglian terraces strongly suggests a major change in the rate of incision in the Middle Thames area in the post-Anglian. A late Anglian and early post-Anglian incision rate of 1.45 m ka −1 was quickly replaced by incision at a rate of 0.089 m ka −1 in the later post-Anglian period. The lower incision rate of the later post-Anglian compares favourably with previous estimates of regional uplift. Two plausible explanations for the enhanced incision in the late Anglian and early post-Anglian are recognized, one related to ponding of the river by Anglian ice and the other to glacio-isostatic rebound. In the latter case, the mismatch between expected and actual heights of late-Anglian deposits would suggest glacio-isostatic uplift of the order of 22–25 m.

Late Devensian and Holocene relative sea level and environmental changes from an isolation basin in southern Skye

Synopsis Detailed lithostratigraphical and biostratigraphical studies from an isolation basin at Inver Aulavaig on the Sleat Peninsula, Isle of Skye, Scotland, disclose changing environmental conditions during the Late Devensian and Holocene. In particular, they reveal three marine transgressions at the site since the Late Devensian, when the sea crossed the rock threshold at +5.10 m od . The radiocarbon dates obtained may incorporate hard water errors, but are considered broadly indicative of the ages of these events. The earliest event recorded at Inver Aulavaig, took place prior to c . 12600 14 C bp and probably occurred soon after deglaciation as relative sea levels rose while the area was isostatically depressed. The second, which occurred between 8850±170 and 5440+50 14 C bp , is correlated with the Main Postglacial Transgression. The third, which briefly took place between the statistically indistinguishable dates of 3160±40 and 3070±60 14 C bp is believed to correlate with a widespread transgression recorded at several sites around the periphery of the Scottish glacio-isostatic uplift centre. The results would also appear to indicate that relative sea level in this area during the Younger Dryas did not exceed +5.10 m od .

Modelling the influence of glacial isostasy on Late Weichselian ice-sheet growth in the Barents Sea

A fully integrated ice-sheet and glacio-isostatic numerical model was run in order to investigate the crustal response to ice loading during the Late Weichselian glaciation of the Barents Sea. The model was used to examine the hypothesis that relative reductions in water depth, caused by glacio-isostatic uplift, may have aided ice growth from Scandinavia and High Arctic island archipelagos into the Barents Sea during the last glacial. Two experiments were designed in which the bedrock response to ice loading was examined: (i) complete and rapid glaciation of the Barents Sea when iceberg calving is curtailed except at the continental margin, and (ii) staged growth of ice in which ice sheets are allowed to ground at different water depths. Model results predict that glacially generated isostatic uplift, caused by an isostatic forebulge from loads on Scandinavia, Svalbard and other island archipelagos, affected the central Barents Sea during the early phase of glaciation. Isostatic uplift, combined with global sea-level fall, is predicted to have reduced sea level in parts of the central Barents Sea by up to 200 m. This reduction would have been sufficient to raise the sea floor of the Central Bank into a subaerial position. Such sea-floor emergence is conducive to the initiation of grounded ice growth in the central Barents Sea. The model indicates that, prior to its glaciation, the depth of the Central Deep would have been reduced from around 400 m to 200 m. Such uplift aided the migration of grounded ice from the central Barents Sea and Scandinavia into the Central Deep. We conclude that ice loading over Scandinavia and Arctic island archipelagos during the first stages of the Late Weichselian may have caused uplift within the central Barents Sea and aided the growth of ice across the entire Barents Shelf. Copyright © 2000 John Wiley & Sons, Ltd.

Material versus isobaric internal boundaries in the Earth and their influence on postglacial rebound

SUMMARY Most previous earth models used to calculate viscoelastic relaxation after the removal of the Late Pleistocene ice loads implicitly assume that there is no exchange of mass across the mantle density discontinuities on periods of tens of thousands of years (the material boundary formulation). In the present study, simple incompressible models are used to determine the Earth's behaviour in the case where the density discontinuity remains at a constant pressure rather than deforming with the material (the isobaric boundary formulation). The calculation of the movement of the boundary is more rigorous than in earlier studies and uses the local incremental pressure calculated at the depth of the boundary and allows for the vertical deformation caused by the change in volume as material changes phase. It is shown that the buoyancy modes associated with the density discontinuities decrease in strength and increase in relaxation time analogous to what results when the density contrast is reduced. Also, two viscoelastic modes arise from an isobaric boundary, which is also predicted when there is a contrast in rigidity or viscosity across a material boundary. The difference in predicted radial deformation between the isobaric boundary model and the material boundary model is largest for long-wavelength loads for which the material incremental pressure at depth is largest. If the isobaric boundary model is appropriate for the treatment of the mineral phase changes in the mantle on glacial rebound timescales, then previous inferences of the deep-mantle to shallow-mantle viscosity ratio based on large-scale deformation (spherical harmonic degree <lo) of the Earth and including data from the early part of the glacio-isostatic uplift are too small.

Formation of abandoned penguin rookery ecosystems in the maritime Antarctic

Due to regional glacio-isostatic uplift of land during the Holocene period, a large number of penguin populations from several rookeries began to nest on the newly formed beaches and emerged rocks, leaving previously colonized higher cliffs. Chronology and extent of raised beaches, lichenometric age estimation of Usnea antarctica and radiocarbon-dating of guano and subfossil penguin bones in the abandoned nesting sites suggest the progress of the downward movement of many rookeries about 2500 years ago, accelerated during the last millennium, when wide bands of 4 to 6 m raised beaches were formed. Patterns of relic ornithogenic soil formation in the abandoned rookeries (focussed on leaching, erosion processes and humus horizon creation), as well as the succession of vegetation in the age sequence of abandoned nesting sites, were investigated in detail at Stranger Point, King George Island. The chemical composition of Deschampsia antarctica growing in the area of active, abandoned rookeries and in control sites provides direct and indirect evidence of current and past ornithogenic manuring on nutrition of vegetation.

Strandflat development and Quaternary shorelines on Tiree and Coll, Scottish Hebrides

AbstractThe islands of Tiree and Coll in the Scottish Inner Hebrides are dominated by staircases of glaciated rock‐platform surfaces in Lewisian gneiss that are interpreted here as areas of strandflat. The rock platform surfaces exhibit differential glacio‐isostatic uplift from east to west and are considered to indicate at least four separate periods of strandflat formation during prolonged intervals of Quaternary cold climate. It is suggested that many of the well‐known areas of high rock platform located farther east in the Scottish Inner Hebrides represent eroded remnants of the strandflat surfaces described here. The existence of the Tiree and Coll strandflat surfaces in conjunction with their formation during periods of Quaternary glaciation implies that they were produced during periods when mainland Scotland was ice‐covered yet when the western margin of the ice sheet was normally located east of these islands. A prominent Late‐glacial raised shoreline also occurs on both islands and declines in altitude to the west, from 22 m in northeastern Coll to 9 m in western Tiree. It is believed that this shoreline, whose regional gradient is 0.39 m km−1, may represent part of the Main Wester Ross Shoreline that was formed in the Northwest Highlands of Scotland during a period of glacial advance that interrupted the decay of the last (Late Devensian) ice sheet. The general similarity in altitude between the Late‐glacial shoreline features and rock platform surfaces implies that during each period of Quaternary strandflat formation, relative sea‐level returned to the same approximate position. This would appear to indicate that the glacio‐isostatic and glacio‐eustatic components affecting the positions of relative sea level in Scotland have remained in approximate equilibrium throughout the duration of the Quaternary.

Emergence of the Varanger Peninsula, Arctic Norway, and climate changes since deglaciation

Fields of glacioisostatically uplifted beach ridges on the eastern Varanger Peninsula coast in northern Norway record the occurrence of major storms since deglaciation. More than 70 radiocarbon dates of palaeoshoreline indicators establish the Late Weichselian and Holocene history of beach-ridge building and relative sea-level change. Optimal ridge-building in the region requires sustained, strong easterlies driving high waves across the Barents Sea. Such winds occur when low pressure systems are forced across the North Sea and the Baltic landmass to the region of the Gulf of Bothnia and the Kola Peninsula. This situation probably frequently occurs during transition periods from milder to cooler climate in the region. The beach-ridge morphology reveals a fall of local sea level following the stormy episodes. Over the short term, this is related to the end of storm-induced set-up and the termination of mild-phase-related warm coastal currents. Over the long term, local sea-level falls with the onset of sustained calm winter-type conditions and continued glacioisostatic uplift. Pre- and early-Holocene changes in climate regime occurred with a frequency of several decades to several centuries. The mid- to late-Holocene records show increased climatic stability, transitions occurring with less frequency, and mild phases frequently lasting many hundreds of years.

Marine deposits of late glacial times exposed by tectonic uplift on the east coast of Taiwan

Marine sediments deposited some 14,000 years ago, when the sea level was between 80 and 100 m below the present sea level, have been found exposed at about 17 m in altitude near Tu-lan, on the east coast of Taiwan. This implies a minimum average uplift rate of 7.6 ± 0.9 mm/yr; similar values of tectonic uplift are not uncommon on the eastern Coastal Range of Taiwan. Such rates of tectonic uplift, among the highest reported in the literature, are of the same order as present-day maximum glacio-isostatic uplift rates.

Late quaternary crustal deformation and coastal changes in Finland

The crustal deformation which has been occurring in Finland since the last ice age is principally caused by glacio-isostatic uplift, as a result of which the highest postglacial shorelines in the country are located over 200 m above the present sea level. The uplift rate was well over ten times higher during and immediately after deglaciation in each region than it is today, so that numerous vertical faults were created in the northern part of Fennoscandia in the period 9000-8500 BP. In addition to this isostatic land uplift, the fluctuations in water level immediately after deglaciation were also affected by elastic rebound, geoid deformation and fluctuations occurring in the Baltic Sea basin independently of those taking place in the oceans in general. There was a marked decrease in the rate of uplift at 8500-8000 BP, and the highest rate recorded currently in Finland is just over 8 mm/year. This figure is estimated to include a 10–20% contribution from a tectonic component arising from the Mid-Atlantic ridge. Uplift has moved the shoreline outwards towards the sea, particularly on the flat west coast of Finland, which has a high rate of uplift. A large number of raised shorelines lie at different levels above sea level, and the effect of wave action is particularly evident in the glaciofluvial sand and gravel of eskers.

Petrogenesis and geological history of a uranium source rock: a case study in northeastern Washington, U.S.A.

A small (4 km 2) drainage basin in northeastern Washington contains highly uraniferous groundwater and highly uraniferous peaty sediments of Holocene age. The U is derived from granitic bedrock that underlies the entire drainage basin and that contains 9–16 ppm U. This local bedrock was studied by petrographic, chemical and isotopic methods to determine conditions of its petrogenesis and post-emplacement history that may have contributed to its present high U content and source-rock capability. The original magma was derived by anatexis of Precambrian continental crust of probable mixed metaigneous and metasedimentary character. Mineral-melt partitioning controlled the enrichment of U in chemically evolved phases of the crystallizing melt. Following emplacement in the upper crust at ∼100Ma, the pluton interacted with meteoric-hydrothermal water at ambient temperatures 300°C. Locally intense fracturing promoted alteration, and fracturing and alteration probably continued during later regional uplift in the Eocene. Regional uplift was followed by low-temperature alteration and weathering in the middle to late Tertiary. The combined result of hydrothermal alteration and low-temperature alteration and weathering was the redistribution of U from primary mineral hosts such as allanite to new sites on fracture surfaces and in secondary minerals such as hematite. Zones of highly fractured and altered rock show the most obvious evidence of this process. A model is proposed in which high-angle fractures beneath the drainage basin were the sites of Tertiary supergene enrichments of U. Recent glacio-isostatic uplift has elevated these older enriched zones to shallow levels where they are now being leached by oxidizing groundwater. The chemistry, mineralogy, texture and geological history of this U source-rock suggest criteria for locating other granitic terrane that may contain uraniferous waters and associated young surficial U deposits. The details of U distribution and mobility at this site also apply to the general topic of U mobility in granitic rocks.

Empirical estimation of isostatic uplift using the lake-tilting method at lake Fegen and lake S�ven, southwestern Sweden

A nonuniform glacio-isostatic uplift results in differential uplift for different parts of a lake. If the lake outlet is situated in the area with the greatest rate of uplift, then the lake will be continuously transgressed. Ancient lake levels can be estimated by dating transgressed peat at different depths in such a lake. Two lakes in southwestern Sweden have been investigated by this method and the course of glacio-isostatic uplift has been determined empirically. The uplift can be expressed by an exponential function through the following formula $$U = - \frac{{\upsilon _0 }}{{2.25 \times 10^{ - 4} }} + \frac{{\upsilon _0 }}{{2.25 \times 10^{ - 4} }}e^{2.25 \times 10^{ - 4} xt} $$ where U is land uplift inm, v0 is recent absolute uplift rate in m/year, andt is time in years BP. The recent absolute uplift rate is found to be somewhat faster than the relative rate established by earlier repeated precision levelings. This may be due to the present eustatic sea level rise on the order of 1.0 mm/year or possibly to irregularities in the glacio-isostatic uplift. By combining shore-level data with uplift data, some alternative eustatic curves have been calculated.

Geomorphological findings on the build-up of pleistocene glaciation in Southern Tibet and on the problem of inland ice ?

The last Ice Age (Wurm) glacier cover was reconstructed on the basis of standard geomorphological indicators in S Tibet between the S slope and N slope of the Himalaya by way of the Tibetan Himalaya to the Transhimalaya (28° – 29° 50' N/85° 40' – 91° 10' E). At the same time, though subject to varying density of data, the process of Late and Post-Glacial deglaciation to Neo-Galacial and Recent glacier cover was considered. Evidence of an almost total glaciation of S Tibet was found in indicators like glaciated knobs, trough valleys with pronounced flank polishings and limits of glacial scouring on nunataks, as well as in findings of erratics, lateral moraines, end moraines, and terraces of outwash plains. This total glaciation took the form of an ice-stream network and attained a thickness of at least 1200 m. Ice-free to about 87° – 86° E, the Tsangpo valley with its sander deposits occupied the gap between the glacier areas of the Tibetan and High Himalayas in the S (I 3) and those of the Transhimalaya in the N (I 2). In the light of recently glaciated Late Glacial terminal moraines and ice marginal rapms it has been possible to estimate a glacio-isostatic uplift of c. 400 m during 10 x 103 years (an average of 40 mm/year) following deglaciation. It is about 3 to 8 times greater than the tectonic uplift of the High Himalaya. The post-glacially intensified uplift of the S Tibetan Plateau by comparison with the High Himalaya is attributed to the much greater glacier burden during the Ice Age. In the area under investigation a High Glacial ELA depression (equilibrium line altitude depr.) of at least 1200 (1180) m was reconstructed for a mean altitude of about 4700 (4716) m asl. Assuming constant hygric conditions and a gradient of 0.7° C/100 m, the temperature drop at the time would have been 8.4° C. Since precipitation during the Ice Age must, if anything, have been less, a drop in summer temperature of about 10° C may be regarded as probable.

Quaternary sea-level changes in Western Scotland

In recent years, major advances have been made in our understanding of Late Quaternary sea-level changes in western Scotland. In particular, new hypotheses have been advanced to explain the ages and origins of high-level rock platform fragments and high-level marine shell beds. Certain raised shorelines in Islay and Jura, SW Argyll and Wester Ross have been related to former margins of the last ice sheet and are associated with drops in the Lateglacial marine limit. In some areas the decline in Lateglacial sea-level took place in association with a stationary ice margin while in others the fall in sea-level occurred in conjunction with considerable ice retreat. During the Lateglacial Interstadial, relative sea-level fell rapidly between ca. 13 and ca. 12 ka BP and thereafter more slowly until ca. 11 ka BP. Renewed marine erosion during the cold climate of the Loch Lomond (Younger Dryas) Stadial (ca. 11-10 ka BP) resulted in the production of the Main Lateglacial Shoreline, which declines in altitude to the W, SW and S away from the centre of glacio-isostatic uplift in the W Highlands. The shoreline has a maximum altitude of 10–11 m O.D. in the Oban area and passes below sea-level in NE Islay, Ardnamurchan, Colonsay, W Mull, Kintyre and Arran. During the early Holocene a pronounced marine transgression took place, probably culminating between 6.6 and 7.0 ka BP. The culmination of the transgression is represented by the Main Postglacial Shoreline that reaches a maximum altitude of ca. 14 m in the Oban area and declines gently in altitude away from the centre of glacio-isostatic uplift. Reconstruction of the uplift isobases for this shoreline appears to indicate a slight eastward migration of the uplift centre since the Younger Dryas. In peripheral areas of western Scotland the Main Postglacial Shoreline is not present owing to the effect of Holocene submergence.

Differential glacio-isostatic uplift of crustal blocks at Glen Roy, Scotland

Detailed measurements of the altitudes of the shorelines of former ice-dammed lakes in Glen Roy and vicinity in the Scottish Highlands prove erroneous the conventional view that former shorelines in areas affected by glacio-isostatic uplift are uniformly tilted and/or gently warped. The measurements demonstrate differential uplift of blocks of the earth's crust. The surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4.6 m/km and are tilted in different directions. In three areas 0.7–2.0 km long, shorelines are distorted by crustal movements; all these areas have landslides attributed to earthquakes that accompanied the release of stress. In the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area, and a fault scarp was produced. Possibly these local distortions accompanied catastrophic lake drainage by jökulhlaup, analogous to crustal movements associated with man-made lakes. A relationship between crustal movement and the limit of a glacial advance is demonstrated. These findings have implications for other parts of the world affected by glacioisostatic uplift.

Rapid localized glacio-isostatic uplift at Glen Roy, Scotland

Many studies involving measurement of the altitudes of fossil marine and lacustrine shorelines have demonstrated glacioisostatic tilting, particularly in North America, Fennoscandia and the British Isles. Such studies are normally illustrated by height–distance diagrams in which fossil shorelines are portrayed as straight lines. In some studies the shoreline-relation diagram is used to analyse and illustrate the altitudinal data1–3: before constructing such a diagram it is assumed that a simple pattern of glacioisostatic uplift has prevailed. Warping of shorelines, as opposed to uniform tilting, has been inferred in North America4–6. On the other hand, Harme7 envisaged block movements in Fennoscandia. Sauramo8 also proposed dislocations, but his interpretation was rejected by Hyyppa9. More recently the concept of the Scandinavian shield as a stable area has been dismissed10,11. Here we provide evidence from Scotland for shoreline dislocation by differential movement of blocks of the Earth's crust.

Faulting, fracturing, and seismicity as functions of glacio-isostasy in Fennoscandia

Recent studies in Fennoscandia have shown that the time at which the maximum rate of glacio-isostatic uplift occurs (usually about the time of deglaciation) is associated with intense faulting and fracturing of the bedrock, which, at least partly, implies corresponding seismic activity. This information improves the understanding of the process of glacio-isostasy and bears upon such problems as the storage of nuclear waste, the pathways for solutions giving rise to ore formation, and the interpretation (and nomenclature) of fractured bedrock and of certain bouldery deposits.

Isostasy and eustasy of Hudson Bay

In the eastern Hudson Bay area, a “staircase” of 185 Holocene strand-lines provides a continuous record of emergence from about 8,000 yr B.P. (sidereal) to the present. Ages were obtained from corrected radiocarbon analyses of shells and from application of a newly discovered 45-yr cycle in beach building that is presumed to be related to the “double Hale” solar cycle. Thus, we deduced a record of climatic storminess. The mean curve of emergence confirms Andrews9s model of glacio-isostatic uplift. Analysis of the residuals in the emergence curve can be transformed to an approximate eustatic curve, which shows some degree of coincidence with other sea-level curves derived from low latitudes as well as with several climatic indicators. The strandline analysis appears to be a powerful new tool for Holocene climate analysis and prediction.

Radiocarbon dated shell samples from Nordre Strømfjord, West Greenland, with comments on models of glacio-isostatic uplift

Shell-bearing marine sediments in the Nordre Strømfjord area belong to two lithofacies, calcareous sandy gravels and calcareous muddy sands, and to four biofacies comparable to modem communities and related to the sediment lithology: epifaunal benthic and infaunal benthic facies, a current reworked 'mixed' facies and a Portlandia - Propeamussium fades. Radiocarbon dates on nine samples provide a poorly defined model of the glacio-isostatic emergence of the region. The implications of such models and their physical validity are considered in the context of these and other data, and it is suggested that curves for uplift deceleration are a useful means of obtaining the exponential constant k.

Socioprofessional structure of the population of the USSR and its employment pattern

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.

Possible causes of the variability of postglacial uplift in North America

Postglacial uplift data from 33 sites in northeastern North America reveal that during the period from 11,000 years B.P. to 7000 years B.P., glacio-isostatic uplift rates varied in a consistent manner with distance from the former margin of the Laurentide Ice Sheet. The consistent trends of these uplift rate variations with distance from the former ice sheet margin suggest that they were not the result of changes in the rate of ice sheet retreat or local tectonic activity. They instead may have resulted from rebound affected significantly by the earth's viscosity at a depth approximately equal to the wavelength of isostatic deformation [McConnell, R.K., Jr., Journal of Geophysical Research 70, 5171 (1965)]. Extremely high viscosities below 600 km, however, probably provide the lower limit for this relationship.