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1.
Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite, gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a−1 for coastal diapirs and up to 120 mm a−1 for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached 3.5 mm a−1 on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a−1 based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge amounts of dissolved and clastic load, thus affecting the surrounding of the diapir.  相似文献   

2.
A foraminiferal transfer function for mean tide level (MTL) is used in combination with AMS radiocarbon dated material to construct a record of relative sea‐level (RSL) change from Poole Harbour, southern Britain. These new data, based on multiple cores from duplicate sites, indicate four phases of change during the last 5000 cal. (calendar) yr: (i) rising RSL between ca. 4700 cal. yr BP and ca. 2400 cal. yr BP; (ii) stable to falling RSL from ca. 2400 cal. yr BP until ca. 1200 cal. yr BP; (iii) a brief rise in RSL from ca. 1200 cal. yr BP to ca. 900 cal. yr BP, followed by a period of stability; (iv) a recent increase in the rate of RSL rise from ca. 400–200 cal. yr BP until the present day. In addition, they suggest that the region has experienced long‐term crustal subsidence at a rate of 0.5 mm C14 yr?1. Although this can account for the overall rise in MTL observed during the past 2500 yr, it fails to explain the changes in the rate of rise during this period. This implies that the phases of RSL change recorded in the marshes of Poole Harbour reflect tidal range variations or ‘eustatic’ fluctuations in sea‐level. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

3.
We report a new Holocene relative sea‐level curve based on the stratigraphy in five closely located isolation basins near Lista in southernmost Norway. The results detail the progress and timing of the mid‐Holocene Tapes transgression, the peak of which in this region represents the highest postglacial sea level, as well as the rate of land emergence since then. One additional cored basin is situated above the marine limit. All the basins have bedrock sills that were levelled using a differential GPS. Isolation and ingression boundaries were identified by macrofossil analysis and radiocarbon dated on terrestrial plant remains. In most cases several dates were obtained from each transition. Relative sea level rose with a mean rate of 7 mm a?1 during the last part of the Tapes transgression 8600?8200 cal. a BP and then gradually slowed to a mean rate of 1 mm a?1 from 8200?7000 cal. a BP. Mean sea level reached ～5 m higher than the present level when the transgression culminated. Land emergence took place after this, first slowly at a mean rate of 0.4 mm a?1 until ～3900 cal. a BP before it increased to 2.6 mm between 3900 and 3400 cal. a BP. Since then it has slowly decreased until today and has been ～0.2 mm a?1 for the last 2000 years. Based on the new curve we present updated Tapes isobases for the region that are displaced by ～20 km in relation to the existing model. From one basin we also report a 5–10 cm thick layer of sorted, sandy gravel, embedded in a more than 5‐m‐thick deposit of homogeneous shallow‐marine mud. The gravel was deposited ～5500 cal. a BP, which is the same age as a tsunami deposit previously mapped in Shetland. As several typical characteristics of tsunami facies deposits are lacking, the origin of the gravel layer remains inconclusive.  相似文献   

4.
Southwestern Finland was covered by the Weichselian ice sheet and experienced rapid glacio-isostatic rebound after early Holocene deglaciation. The present mean overall apparent uplift rate is of the order of 4-5 mm/yr, but immediately after deglaciation the rate of crustal rebound was several times higher. Concurrently with land uplift, relative sea level in the Baltic basin during the past more than 8000 years was also strongly affected by the eustatic changes in sea level. There is ample evidence from earlier studies that during the early Litorina Sea stage on the southeastern coast of Finland around 7000 yr BP (7800 cal. yr BP), the rise in sea level exceeded the rate of land uplift, resulting in a short-lived transgression. Because of a higher rate of uplift, the transgression was even more short-lived or of negligible magnitude in the southwestern part of coastal Finland, but even in this latter case a slowing down in the rate of regression can still be detected. We used evidence from isolation basins to obtain a set of 71 14C dates, and over 30 new sea-level index points. The age-elevation data, obtained from lakes in two different areas and located between c. 64 m and 1.5 m above present sea level, display a high degree of internal consistency. This suggests that the dates are reliable, even though most of them were based on bulk sediment samples. The two relative sea-level curves confirm the established model of relatively gradually decreasing rates of relative sea-level lowering since c. 6100 yr BP (7000 cal. yr BP) and clearly indicate that the more northerly of the two study areas experienced the higher rate of glacio-isostatic recovery. In the southerly study area, changes in diatom assemblages and lithostratigraphy suggest that during the early Litorina Sea stage (8300-7600 cal. yr BP) eustatic sea-level rise exceeded land uplift for hundreds of years. Evidence for this transgression was discovered in a lake with a basin threshold at an elevation of 41 m above sea level, which is markedly higher than any previously known site with evidence for the Litorina transgression in Finland. We also discuss evidence for subsequent short-term fluctuations superimposed on the main trends of relative sea-level changes.  相似文献   

5.
Shoreline displacement in the eastern part of the Gulf of Finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in Virolahti in southeastern Finland and on the Karelian Isthmus, and in Ingermanland in Russia. Study methods were diatom analyses, sediment lithostratigraphical interpretation and radiocarbon dating. In southeastern Finland, the marine (Litorina) transgression maximum occurred ca. 6500–6200 14C yr BP (7400–7100 cal. yr BP). In areas of the slower land uplift rate on the Karelian Isthmus and in Ingermanland, the transgression maximum occurred ca. 6400–6000 14C yr BP (7300–6800 cal. yr BP). The highest Litorina shoreline is located at ca. 23 m above present sea-level in southeastern Finland, whereas in the eastern part of the Karelian Isthmus, near St. Petersburg, it is located at ca. 8 m above present sea-level. The amplitude of the Litorina transgression in Virolahti area is ca. 4 m, whereas on the Karelian Isthmus and in Ingermanland the amplitude has varied between 5 and 7 m. The regional differences between areas are solely due to different glacio-isostatic land uplift rates. The seven basins studied in this research were connected to the Baltic Sea basin during the Litorina Sea stage and their diatom and lithostratigraphical records indicate a single, smooth Litorina transgression.  相似文献   

6.
Potash in a salt mushroom at Hormoz Island, Hormoz Strait, Iran   总被引：2，自引：0，他引：2  
Increasing volumes of potash are currently being discovered in a cluster of diapirs of Hormoz (formerly Hormuz) salt near Bandar Abbas, Iran. Most of the potash beds studied so far occur in complex recumbent folds in a salt mountain that would be difficult to exploit safely. However, Holocene marine erosion removed any salt mountains from a sub-group of near-shore Zagros diapirs and exposed their deeper structural levels. Even though these diapirs are still active, their potash deposits are likely more tractable to safe exploitation than in a salt mountain — as we make clear here for Hormoz Island.Geochemical surveys on Hormoz Island reveal two separate potash anomalies that are valuable pseudo-stratigraphic markers. Integrating field measurements of the attitudes of bedding with lineaments on air photos suggests that Hormoz Island consists of a mature bell- or plume-shaped mushroom diapir with potash beds wound around a toroidal axis of rotation near current exposure levels.2D numerical models simulate the salt mushroom on Hormoz Island and its internal circulation. They also suggest that the diapir has a wide overhand above a narrow stem in this gas-rich region. We use the mushroom diapir model to outline a regional exploration strategy that has the potential of influencing the world potash market thereafter.  相似文献   

7.
We present results from an investigation of relative sea-level changes in the Qaqortoq area in south Greenland from c. 11 000 cal. yr BP to the present. Isolation and transgression sequences from six lakes and two tidal basins have been identified using stratigraphical analyses, magnetic susceptibility, XRF and macrofossil analyses. Macrofossils and bulk sediments have been dated by AMS radiocarbon dating. Maximum and minimum altitudes for relative sea level are provided from two deglaciation and marine lagoon sequences. Initially, relative sea level fell rapidly and reached present-day level at ∼9000 cal. yr BP and continued falling until at least 8800 cal. yr BP. Between 8000 and 6000 cal. yr BP, sea level reached its lowest level of around 6-8 m below highest astronomical tide (h.a.t.). At around 3750 cal. yr BP, sea level has reached above 2.7 m below h.a.t. and continued to rise slowly, reaching the present-day level between ∼2000 cal. yr BP and the present. As in the Nanortalik area further south, initial isostatic rebound caused rapid isolation of low elevation basins in the Qaqortoq area. Distinct isolation contacts in the sediments are observed. The late Holocene transgression is less well defined and occurred over a longer time interval. The late Holocene sea-level rise implies reloading by advancing glaciers superimposed on the isostatic signal from the North American Ice Sheet. One consequence of this transgression is that settlements of Palaeo-Eskimo cultures from ∼4000 cal. yr BP may have been transgressed by the sea.  相似文献   

8.
The coastal zone of Norrbotten, northern Sweden, was gradually inundated by the Ancylus Lake following the retreating ice margin and forming a highest coastline approximately 210 m above the present sea level. The succeeding shore displacement is reconstructed based on lithological investigations and radiocarbon datings of identified isolation sequences from 12 cored lake basins. The highest lake basins, along with two basins above the highest shoreline, suggest ice-free conditions already at 10 500 cal. yr BP. This is at least 500 years earlier than previously thought and implies rapid ice-sheet break-up in the Gulf of Bothnia. The shore displacement (RSL) curve represents a forced regression of successively decreasing rate through the Holocene, from 9 m/100 yr to 0.8 m/100 yr. During the first 1000-1200 years, the isostatic uplift is exponentially declining, followed by a constant uplift rate from c. 9500 cal. yr BP to 5500-5000 cal. yr BP. The last 5000 years seem to be characterized by a low but constant rebound rate. The development of the Ancylus Lake stage of the Baltic may also be discerned in the Norrbotten RSL curve, suggesting that the chronology of the Ancylus Lake stages may have to be revised. The Littorina transgression is also reflected by the RSL curve shape. In addition, a series of early to mid-Holocene beach terraces were OSL-dated to allow for comparison with the 14C-dated shore displacement curve. Interpretations of these ages and their relation to former sea levels were clearly more problematic than the dating of the lake basin isolations.  相似文献   

9.
Multiple proxies from a 319-cm peat core collected from the Hudson Bay Lowlands, northern Ontario, Canada were analyzed to determine how carbon accumulation has varied as a function of paleohydrology and paleoclimate. Testate amoeba assemblages, analysis of peat composition and humification, and a pollen record from a nearby lake suggest that isostatic rebound and climate may have influenced peatland growth and carbon dynamics over the past 6700 cal yr BP. Long-term apparent rates of carbon accumulation ranged between 8.1 and 36.7 g C m? 2 yr? 1 (average = 18.9 g C m? 2 yr? 1). The highest carbon accumulation estimates were recorded prior to 5400 cal yr BP when a fen existed at this site, however following the fen-to-bog transition carbon accumulation stabilized. Carbon accumulation remained relatively constant through the Neoglacial period after 2400 cal yr BP when pollen-based paleoclimate reconstructions from a nearby lake (McAndrews et al., 1982) and reconstructions of the depth to the water table derived from testate amoeba data suggest a wetter climate. More carbon accumulated per unit time between 1000 and 600 cal yr BP, coinciding in part with the Medieval Climate Anomaly.  相似文献   

10.
Estuarine and beach deposits in the vicinity of the present coastline at Pakarae River record the infilling of an estuary and subsequent development of a sequence of seven marine terraces during Holocene time.

At the maximum of the last glaciation about 18,000 years ago the shoreline at the ancestral Pakarae River was approximately 20 km east of the present shoreline. By about 9000 years BP the sea had transgressed across most of that coastal plain to lie within a few hundred metres of the base of the present coastal hills. Seventeen radiocarbon ages from estuarine deposits record the overall rise in post-glacial sea level, but in the period c. 9500-7000 yrs BP there are reversals to the overall rising trend. Between 9500 and 8500 yrs BP there appears to have been a eustatic fall in sea level of at least 4 m. This observation is supported by data from several other localities around New Zealand. Maximum transgression occurred about 6500–7000 yrs BP when the sea reached the base of hillslopes and an extensive estuary existed behind a barrier bar.

Since that time the barrier bar disappeared, probably due to stranding in an uplift event, and the coastline advanced progressively outward toward its present position. Coastal progradation (sea level regression) and subsequent erosion have occurred in association with episodic large earthquakes at about 6700, 5400, 3910, 2450, 1570, 1000 and 600 yrs BP. The present distribution of terraces has been influenced by coastal erosion, which has removed all trace of some terraces from some areas, and river erosion has modified the marine terraces near the river.  相似文献   


11.
Bracketing ages on marine—freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about —15 m from 14000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 in a -1, similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a-1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet.  相似文献   

12.
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.  相似文献   

13.
A survey of raised coral reef terraces in locations along the southern coast of Iran was carried out with the aim of assessing regional Late Quaternary tectonic uplift rates influenced by salt doming. Two islands were studied: Kish, where no previous data were available, and Qeshm, where a previous survey had already attributed the lowest step in two sequences of raised marine terraces to the Last Interglacial.Twenty-five ESR and seven Th/U ages were obtained from Kish Island. The results show that this flat, about 32 m high, gently domed island was totally submerged during the last two interglacial periods. Corals ascribed to MIS 5 and MIS 7 have been dated at the same elevations, near the present sea level, and in the uppermost, inner part of the island, giving evidence of a polycyclic origin for the island surface deposits. Following a discussion on the possible position of eustatic peaks during MIS 7, a maximal average uplift rate of 0.20±0.02 mm/yr has been deduced from the above data.Furthermore, the survey obtained some new results from Qeshm, where seven ESR ages confirmed the MIS 5 age of the lowest raised marine terrace (that also corresponds to an uplift rate of about 0.2 mm/yr), failing, however, to date older steps, due to significant coral-sample re-crystallisation. In the western part of Qeshm, five new radiocarbon ages of elevated beach material demonstrated the variability of uplift rates even along short distances around an active salt dome.  相似文献   

14.
We reconstruct the Holocene shore displacement of the Västervik-Gamlebyviken area on the southeast coast of Sweden, characterised by a maritime cultural landscape and archaeological significance since the Mesolithic. Sediment cores were retrieved from four lake basins that have been raised above sea level due to the postglacial land uplift and eustatic sea level changes after the melting of the Fennoscandian Ice Sheet. The cores were radiocarbon dated and analysed for loss on ignition and diatoms. The isolation thresholds of the basins were determined using LiDAR data. The results provide evidence for the initiation of the first Littorina Sea transgression in this area at 8.5 thousand calibrated years before present (cal. ka BP). A relative sea level rise by ∼7 m a.s.l. is recorded between 8.0 and 7.5 cal. ka BP with a highstand at ∼22 m a.s.l. between 7.5 and 6.2 cal. ka BP. These phases coincide with the second and third Littorina Sea transgressions, respectively, in the Blekinge area, southern Sweden and are consistent with the final deglaciation of North America. After 6.2 cal. ka BP, the relative sea level dropped below 22 m a.s.l., and remained at ∼20 m a.s.l. until 4.6 cal. ka BP coinciding with the fourth Littorina Sea transgression in Blekinge. From 4.6 to 4.2 cal. ka BP, the shore displacement shows a regression rate of 10 mm a−1 followed by a slowdown with a mean value of 4.6 mm a−1 until 1.6 cal. ka BP, when the relative sea level dropped below 3.3 m a.s.l. The Middle to Late Holocene highstand and other periods of minor sea level transgressions and/or higher salinity between 6.2 and 1.7 cal. ka BP are attributed to a combination of warmer climate and higher inflow of saline waters in the southern Baltic Sea due to stronger westerlies, caused by variations in the North Atlantic atmospheric patterns.  相似文献   

15.
We present new results for relative sea‐level change for southern Greenland for the interval from 9000 cal. yr BP to the present. Together with earlier work from the same region this yields a nearly complete record from the time of deglaciation to the present. Isolation and/or transgression sequences in one lake and five tidal basins have been identified using lithostratigraphic analyses, sedimentary characteristics, magnetic susceptibility, saturated induced remanent magnetisation (SIRM), organic and carbonate content, and macrofossil analyses. AMS radiocarbon dating of macrofossils and bulk sediment samples provides the timescale. Relative sea level fell rapidly and reached present‐day level at ～9300 cal. yr BP and continued falling until at least 9000 cal. yr BP. Between 8000 and 6000 cal. yr BP sea level reached its lowest level of around ～10 m below highest astronomical tide. At around 5000 cal. yr BP, sea level had reached above 7.8 m below highest astronomical tide and slowly continued to rise, not reaching present‐day sea level until today. The isostatic rebound caused rapid isolation of the basins that are seen as distinct isolation contacts in the sediments. In contrast, the late Holocene transgressions are less well defined and occurred over longer time intervals. The late Holocene sea‐level rise may be a consequence of isostatic reloading by advancing glaciers and/or an effect of the delayed response to isostatic rebound of the Laurentide ice sheet. One consequence of this transgression is that settlements of Palaeo‐Eskimo cultures may be missing in southern Greenland. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

16.
The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates constrain their chronology. Here we present three Holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of Finnmark; located at the islands Sørøya and Rolvsøya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14,600 cal yr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. Also, the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor. After the Younger Dryas the coast emerged 1.6–1.0 cm per year until about 9500–9000 cal yr BP. Between 9000 and 7000 cal yr BP relative sea level rose 2–4 m and several of the studied lakes became submerged. At the outermost locality Rolvsøya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca 8200–8100 cal yr BP.  相似文献   

17.
Many coastal lakes were inundated by both the Storegga tsunami (7000 14C yr BP) and the mid-Holocene sea-level rise (the Tapes transgression) in western Norway. The tsunami eroded lake bottoms and deposited graded and/or massive beds of sand, rip-up clasts, and coarse plant material. By contrast, when the rising sea entered the lakes, it deposited only gyttja, silt and fine sand, without causing much erosion of the underlying lake sediments. Storegga tsunami deposits in some coastal lakes were interpreted previously as ordinary marine sediments from the Tapes transgression. Our reinterpretation of these deposits shows that the transgression maximum phase was reached after 6500 yr BP, more than 1000 yr later than previously inferred for the coast of Sunnmøre. The new data cannot be combined in a shoreline diagram without showing the 6000 yr BP and 7000 yr BP shorelines as slightly warped. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
A high-resolution, well-dated dinoflagellate cyst record from a lagoon of the southeastern Swedish Baltic Sea reveals climate and hydrological changes during the Holocene. Marine dinoflagellate cysts occurred initially at about 8600 cal yr BP, indicating the onset of the Littorina transgression in the southeastern Swedish lowland associated with global sea level rise, and thus the opening of the Danish straits. Both the species diversity and the total accumulation rates of dinoflagellate cysts continued to increase by 7000 cal yr BP and then decreased progressively. This pattern reveals the first-order change in local sea level as a function of ice-volume-equivalent sea level rise versus isostatic land uplift. Superimposed upon this local sea level trend, well-defined fluctuations of the total accumulation rates of dinoflagellate cysts occurred on quasi-1000- and 500-yr frequency bands particularly between 7500 and 4000 cal yr BP, when the connection between the Baltic basin and the North Atlantic was broader. A close correlation of the total accumulation rates of dinoflagellate cysts with GISP2 ice core sea-salt ions suggests that fluctuations of Baltic surface conditions during the middle Holocene might have been regulated by quasi-periodic variations of the prevailing southwesterly winds, most likely through a system similar to the dipole oscillation of the modern North Atlantic atmosphere.  相似文献   

19.
We estimated the long-term vertical velocity profile across the northeastern Japan forearc by using the height distribution of late Quaternary marine and fluvial terraces, and we correlated the ages of the two marine terraces with marine isotope stages (MIS) 5.5 and 5.3 or 5.1 by cryptotephra stratigraphy. The uplift rate, estimated as 0.11-0.19 m ka− 1 from the relative heights between the terrace surfaces and eustatic sea levels, was nearly equal to, or slightly slower than, the uplift rate farther inland (0.15-0.19 m ka− 1), as determined from the relative heights of fill terrace surfaces. In contrast, the short-term vertical velocity profile, obtained from GPS observations, showed that the forearc is currently subsiding at a maximum rate of 5.4 ± 0.4 mm yr− 1. Thus, the current short-term (geodetic) subsidence does not reflect long-term (geological) tectonic movement. Short-term vertical deformation is probably driven by subduction erosion or elastic deformation caused by interplate coupling, or both. However, long-term uplift is probably due not to moment release on the mega-thrust but to crustal thickening.  相似文献   

20.
Based on geological and archaeological proxies from NW Russia and NE Estonia and on GIS‐based modelling, shore displacement during the Stone Age in the Narva‐Luga Klint Bay area in the eastern Gulf of Finland was reconstructed. The reconstructed shore displacement curve displays three regressive phases in the Baltic Sea history, interrupted by the rapid Ancylus Lake and Litorina Sea transgressions c. 10.9–10.2 cal. ka BP and c. 8.5–7.3 cal. ka BP, respectively. During the Ancylus transgression the lake level rose 9 m at an average rate of about 13 mm per year, while during the Litorina transgression the sea level rose 8 m at an average rate of about 7 mm per year. The results show that the highest shoreline of Ancylus Lake at an altitude of 8–17 m a.s.l. was formed c. 10.2 cal. ka BP and that of the Litorina Sea at an altitude of 6–14 m a.s.l., c. 7.3 cal. ka BP. The oldest traces of human activity dated to 8.5–7.9 cal. ka BP are associated with the palaeo‐Narva River in the period of low water level in the Baltic basin at the beginning of the Litorina Sea transgression. The coastal settlement associated with the Litorina Sea lagoon, presently represented by 33 Stone Age sites, developed in the area c. 7.1 cal. ka BP and existed there for more than 2000 years. Transformation from the coastal settlement back to the river settlement indicates a change from a fishing‐and‐hunting economy to farming and animal husbandry c. 4.4 cal. ka BP, coinciding with the time of the overgrowing of the lagoon in the Narva‐Luga Klint Bay area.  相似文献   

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