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1.
The Gurvan Bogd mountain range is a fault system characterized by strong earthquakes (M ∼ 8) separated by long periods of quiescence. Further to the previous works in the area, our study provides new data concerning the tectonic and climatic processes in the Gobi-Altay. To quantify the slip rates along the faults, we dated offset alluvial fans analysing the in situ produced 10Be along profiles at depth. The slip rates along the Bogd strike–slip fault and its associated thrust faults over the Upper Pleistocene–Holocene period are 0.95 ± 0.29 mm yr−1 and comprised between 0.12 ± 0.02 and 0.13 ± 0.02 mm yr−1, respectively. The surfaces ages account for a cyclic formation of the fans over the past ∼360 ka, in correlation with the terminations of the marine isotope stages 2, 6, 8 and 10.  相似文献   

2.
Timpanogos Cave, located near the Wasatch fault, is about 357 m above the American Fork River. Fluvial cave sediments and an interbedded carbonate flowstone yield a paleomagnetic and U–Th depositional age of 350 to 780 ka. Fault vertical slip rates, inferred from calculated river downcutting rates, range between 1.02 and 0.46 mm yr− 1. These slip rates are in the range of the 0–12 Ma Wasatch Range exhumation rate ( 0.5–0.7 mm yr− 1), suggesting that the long-term vertical slip rate remained stable through mid-Pleistocene time. However, the late Pleistocene (0–250 ka) decelerated slip rate ( 0.2–0.3 mm yr− 1) and the accelerated Holocene slip rate ( 1.2 mm yr− 1) are consistent with episodic fault activity. Assuming that the late Pleistocene vertical slip rate represents an episodic slowing of fault movement and the long-term (0–12 Ma) average vertical slip rate, including the late Pleistocene and Holocene, should be  0.6 mm yr− 1, there is a net late Pleistocene vertical slip deficit of  50–75 m. The Holocene and late Pleistocene slip rates may be typical for episodes of accelerated and slowed fault movement, respectively. The calculated late Pleistocene slip deficit may mean that the current accelerated Wasatch fault slip rate will extend well into the future.  相似文献   

3.
R. Hinsch  K. Decker 《地学学报》2003,15(5):343-349
Seismic slip rates of about 0.2 mm yr?1 calculated from cumulative seismic moments of earthquakes along the Vienna Basin Transfer Fault (VBTF) between the Alps and the Carpathians are very low compared to geologically and geodetically determined slip rates of 1–2 mm yr?1, proving a significant seismic slip deficit. Additional seismic slip calculations for arbitrarily selected fault sectors reveal large differences along strike ranging from c. 0.02 to 0.5 mm slip yr?1. As the earthquake frequency distribution suggests seismically coupled deformation, these variations might indicate locked fault segments. Results suggest that (1) the seismic cycle of the VBTF exceeds the length of available seismological observation, and (2) larger earthquakes than those recorded may occur along the fault. Thus, current local seismic hazard estimates, which are solely based on this historical database, probably underestimate the earthquake potential of the fault system.  相似文献   

4.
Reliable dating is an essential element of palaeoseismological studies, yet whilst a suite of geochronological methods can now provide late Quaternary age control it remains very difficult to date modern events (i.e., those occurring within the last 150 years). This is significant because the starting point for many palaeoseismological investigations is a modern surface-rupturing event, whose geological effects need to be disentangled in trench stratigraphies from palaeoseismic ruptures. Two dating methods which, in combination, can provide robust dating control in recently deposited sediments are the 210Pb and 137Cs dating methods. Here, we test the applicability of using 210Pb and 137Cs to date colluvial sediments exposed in three trenches excavated across an earthquake fault—the Eliki fault, Gulf of Corinth, Greece—which ruptured in an earthquake in 1861. The 210Pb and 137Cs profiles observed in these colluvial sequences are relatively erratic due to the mixed nature of the sediments, i.e., their deposition in an environment where the supply of slope sediments is driven by seasonal rainfall, causing non-uniform sediment accretion and sediment reworking. In one trench, however, 210Pb dating, corroborated by 137Cs dating, indicates that a proposed post-1861 surface colluvial unit has been deposited over the period 1950 AD–present (at a rate of ca. 9 mm/year), and overlies a significantly older unit (>120 years old). The dating control provided here by 210Pb and 137Cs dating corroborates the published interpretation of the trench stratigraphy, and refines the 14C-based estimated dates for the upper unit. At two other trenches 210Pb and 137Cs dating only provided minimum ages (based on the presence or absence of 210Pbexcess and 137Cs). Such approximate ages, however, may still useful in corroborating interpretations made using the trench stratigraphy, or, at sites which have long earthquake recurrence intervals, determining which earthquake event was responsible for a particular bed offset.  相似文献   

5.
《Geodinamica Acta》2013,26(3-4):107-122
Abstract

The results of geomorphic analysis of the Concud fault-generated mountain front (central Iberian Chain, Spain) are introduced into classifications of fault activity proposed by previous authors, and compared with slip rates calculated from geologic markers. The Concud fault is an extensional structure active since the mid Pliocene times. It gives rise to a 60 to 120 m high mountain front, where footwall rocks belonging to the Triassic and Jurassic (north-western sector) and Miocene (south-eastern sector) crop out. Conspicuous triangular facets are preserved on Jurassic rocks of the central sector, while short, generally non-incised alluvial fans make the piedmont. The value of the Mountain-front sinuosity index is Smf = 1.24 for the whole mountain front (1.17 and 1.32, respectively, for both segments showing distinct footwall lithology), as obtained by the most conservative procedure. Average valley floor width/height ratios calculated for seventeen gullies crossing the fault are Vf = 0.30 (250 m upstream from the fault trace) and Vf = 0.22 (500 m upstream). These geomorphic indices, together with qualitative features of the escarpment and piedmont landscape, indicate ‘moderate’ to ‘rapid’ fault activity. The range of slip rates estimated from such morphotectonic classification (0.03 to 0.5 mm/y) encloses the range calculated from offset Late Pliocene and Pleistocene stratigraphic markers (0.07 to 0.33 mm/y). Nevertheless, the highest potential slip rate (0.5 mm/y) clearly represents an overestimate: the mountain front could give the impression of an anomalously high level of activity owing to episodic rejuvenation caused by base level drop.  相似文献   

6.
Foreland contraction and hinterland extension in the Southern Apennines orogen of Italy produced a complex spatial and temporal pattern of vertical and horizontal displacement. Remarkably, Late Miocene to mid-Pleistocene foreland migration of the contractional front at ∼16 mm yr−1 was not accompanied by uplift and the frontal thrust belt remained at or below sea level. Only following a mid-Pleistocene reduction in horizontal displacement did the frontal thrust belt and foreland begin uplift at ∼0.5 mm yr−1, a rate that increased to ∼1 mm yr−1 after 125 ka. Although the extensional hinterland experienced net subsidence during formation of the Tyrrhenian basin, an extensional transition zone adjacent to the frontal thrust belt records sustained uplift at ∼0.3 mm yr−1. The interaction of preexisting crustal structure and deep tectonic processes resulted in time-integrated displacement rates suggesting steady-state deformation for periods of 106 years. Displacement rate changes were abrupt and occurred over intervals of 105 years or less.  相似文献   

7.
This reply tackles the three main points of discussion of the comment, carefully distinguishing those constructive contributions from the potentially confusing ones. (1) We accept that we should have utilised previously published datings of the middle terrace, even if we consider them to be less reliable than the used ones, so broadening the slip-rate range from 0.23–0.33 mm/y to 0.16–0.33 mm/y. Nevertheless, their revision of the post-middle terrace slip rate charges us two contradictory imputations: that we underestimate the throw in a 25% (36 m vs. 47 m) and that this results in ‘anomalously high slip rates’. We analyse the adduced error, and we confirm our initial estimate based on our more reliable stratigraphic marker, so rejecting both criticisms. (2) About the paleoseismological interpretation at Los Baños trench, we appreciate the hint about displacement partitioning on the master fault and in our hypothetical blind normal fault during the last three events; however, such partitioning was already considered in our retrodeformation analysis. We believe that there is enough evidence for the two events questioned by the commenters, as well as for the interpretation of the colluvial wedge that evidences one of them. (3) With respect to the fault affecting the youngest terrace: (a) both traces exposed on orthogonal road-cut slopes belong to the same normal fault, and we prove it by means of basic structural constructions, and (b) it does not exhibit any feature suggesting a non-tectonic origin, as the commenters state.  相似文献   

8.
A stratigraphic succession of alternating peat and minerogenic sediments at the foot of a steep mountain slope provides the basis for the reconstruction of a preliminary colluvial history from the alpine zone of Jotunheimen, southern Norway. Layers of silty sand and sandy silt, typically 5–10 cm thick and interpreted as distal debris-flow facies, are separated by layers of peat that have been radiocarbon dated. Deposition from at least 7500 to about 3800 14C yr BP of predominantly minerogenic material suggests relatively infrequent but large-magnitude debris-flow events in an environment warmer and/or drier than today. Particularly low colluvial activity between about 6500 and 3900 14C yr BP was terminated by a succession of major debris-flow events between about 3800 and 3400 14C yr BP. Unhumified peats indicative of higher water tables, separate six debris-flows that occurred between about 3300 and 2300 14C yr BP and signify a continuing high frequency of colluvial activity. Uninterrupted peat accumulation between about 2400 and 1600 14C yr BP indicates reduced debris-flow activity; subsequent renewed activity appears to have culuminated in the ‘Little Ice Age’ after about 600 14C yr BP. This pattern of colluvial deposition demonstrates a long history of natural Holocene low-alpine landscape instability, suggests an increase first in the magnitude and then in the frequency of debris-flow activity coincident with late Holocene climatic deterioration, and points to the potential of debris-flow records as a unique source of palaeoclimatic information related to extreme rainfall events. © 1997 John Wiley & Sons, Ltd.  相似文献   

9.
The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10−20 m2. Water permeability as low as 10−20 m2 is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.  相似文献   

10.
A fault scaling law suggests that, over eight orders of magnitude, fault length L is linearly related to maximum displacement D. Individual faults may therefore retain a constant ratio of D/L as they grow. If erosion is minor compared with tectonic uplift, the length and along‐strike relief of young mountain ranges should thus reflect fault growth. Topographic profiles along the crests of mountain ranges in the actively deforming foreland of north‐east Tibet exhibit a characteristic shape with maximum height near their centre and decreasing elevation toward the tips. We interpret the along‐strike relief of these ranges to reflect the slip distribution on high‐angle reverse faults. A geometric model illustrates that the lateral propagation rate of such mountain ranges may be deciphered if their length‐to‐height ratio has remained constant. As an application of the model, we reconstruct the growth of the Heli Shan using a long‐term uplift rate of ～1.3 mm yr?1 derived from 21Ne and 10Be exposure dating.  相似文献   

11.
The Lower Devonian (Lochkovian‐Emsian) Cosheston Group of south Pembrokeshire is one of the most enigmatic units of the Old Red Sandstone of Wales. It consists of a predominantly green, exceptionally thick succession (up to 1.8 km) within the red c. 3 km‐thick fill of the Anglo‐Welsh Basin, but occupies a very small area (27 km2). Four formations—Llanstadwell (LLF), Mill Bay (MBF), Lawrenny Cliff (LCF) and New Shipping (NSF)—group into lower (LLF + MBF) and upper (LCF + NSF) units on stratigraphical and sedimentological criteria. Two palynostratigraphic associations (Hobbs Point and Burton Cliff) are recognised in the LLF. Overall, the Cosheston succession comprises a fluvial, coarsening‐upward megasequence, mostly arranged in fining‐upward rhythms. It is interpreted as the fill of an east‐west graben bounded by faults to the north and south of the Benton and Ritec faults, respectively. Both ‘lower Cosheston’ formations were deposited by east‐flowing, axial river systems draining a southern Irish Sea landmass. Drainage reversal, early in the deposition of the LCF, resulted in ‘upper Cosheston’ lateral, SW‐flowing rivers which carried predominantly second‐ and multi‐cycle detritus. The ‘lower Cosheston’ is characterized by an abundance of soft‐sediment deformation structures, probably seismically triggered by movements along the graben's northern bounding fault. A minimum average (≥ mesoseismic) earthquake recurrence interval of c. 4000 yr is estimated for the MBF. This and the correlative Senni Formation of south‐central Wales form a regionally extensive green‐bed development that represents a pluvial climatic interval. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
The chronology of near-surface sediments in Lake Illawarra has been investigated using radiocarbon dating and anthropogenically derived substances including trace metals, ash, and137Cs. Sediments at depths about 1 m below the water-sediment interface ranged in age from Modern to 786 calendar years bp on the basis of radiocarbon dating ofNotospisula trigonella valves. Multiple marker (for example ash-trace metals) depth-concentration sediment profiles yielded estimates of sedimentation rate ranging from 3 to 5 mm yr–1 at Griffins Bay to more than 16 mm yr–1 at Macquarie Rivulet. Sedimentation rates of approximately 10 mm yr–1 appeared to be typical of the western and southwestern portions of the lagoon. Rates of sediment accretion, prior to catchment clearing, urbanization, and industrialization have been estimated at less than 1 mm yr–1, thus indicating a general tenfold increase in sediment accumulation adjacent to the western foreshore caused by catchment development. Accelerated sedimentation in shallow coastal lagoons constitutes significant environmental impacts including shoaling, degradation of seagrass beds, and increased turbidity with consequent loss of aesthetic appeal. Management policy should be directed at attempts to reduce the amount of sediment input by the construction of strategically placed sediment retention ponds. Siltation within the shallow embayments of Lake Illawarra could be ameliorated by a carefully planned program of dredging.  相似文献   

13.
The Miocene-Pliocene Siwalik Group records changing fluvial environments in the Himalayan foreland basin. The Nagri and Dhok Pathan Formations of this Group in the eastern Potwar Plateau, northern Pakistan, comprise relatively thick (tens of metres) sandstone bodies and mudstones that contain thinner sandstone bodies (metres thick) and palaeosols. Thick sandstone bodies extend for kilometres normal to palaeoflow, and are composed of large-scale stratasets (storeys) stacked laterally and vertically adjacent to each other. Sandstone bodies represent single or superimposed braided-channel belts, and large-scale stratasets represent channel bars and fills. Channel belts had widths of km, bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3. Individual channel segments had bankfull widths, maximum depths, and slopes on the order of 102 m, 101 m and 10?4 respectively, and sinuosities around 1-1. These rivers are comparable to many of those flowing over the megafans of the modern Indo-Gangetic basin, and a similar depositional setting is likely. Thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe, wedge, sheet and channel-form geometries: they represent crevasse splays, levees and floodplain channels. Mudstones are relatively bioturbated/disrupted and represent mainly floodbasin and lacustrine deposition. Mudstones and sandstones are extremely disrupted in places, showing evidence of prolonged pedogenesis. These ‘mature’ palaeosols are m thick and extend laterally for km. Lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate. The 500 m-thick Nagri Formation has a greater proportion and thicker sandstone bodies than the overlying 700 m-thick Dhok Pathan Formation. The thick sandstone bodies and their large-scale stratasets thicken and coarsen through the Nagri Formation, then thin and fine at the base of the Dhok Pathan Formation. Compacted deposition rates increase with sandstone proportion (0-53 mm/year for Nagri, 0-24 mm/year for Dhok Pathan), and palaeosols are not as well developed where deposition rates are high. Within both formations there are 100 m-scale variations (representing on the order of 105 years) in the proportion and thickness of thick sandstone bodies, and tens-of-m-scale alternations of thick sandstone bodies and mudstone-sandstone strata that represent on the order of 104 years. Formation-scale stratal variations extend across the Potwar Plateau for at least 100 km, although they may be diachronous: however, 100-m and smaller scale variations can only be traced laterally for up to tens of km. Alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel-belt sizes (mainly), average deposition rate and avulsion frequency on a megafan comparable in size to modern examples. 100-m-scale variations in thick sandstone-body proportion and thickness could result from ‘regional’ shifts in the position of major channels, possibly associated with ‘fan lobes’on a single megafan or with separate megafans. However, such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system. Formation-scale and 100-m-scale stratal variations are probably associated with interelated changes in tectonic uplift, sediment supply and basin subsidence. Increased rates of hinterland uplift, sediment supply and basin subsidence, recorded by the Nagri Formation, may have resulted in diversion of a relatively large river to the area. Alternatively, changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland (possibly linked to tectonic uplift). Climate during deposition of the Siwalik Group was monsoonal. Although the deposits contain no direct evidence for climate change, independent evidence indicates global cooling throughout the Miocene, and the possibility of glacial periods (e.g. around 10-8 Ma, corresponding to base of Nagri Formation). If the higher Himalayas were periodically glaciated, a mechanism would exist for varying sediment supply to megafans on time scales of 104-105 years. Although eustatic sea-level changes are related to global climatic change, they are not directly related to Siwalik stratigraphic changes, because the shoreline was many 100 km away during the Miocene.  相似文献   

14.
We derive a slip rate for a frontal thrust in the western Hexi Corridor along the northern Qilian Shan by combining topographic profiling and 10Be exposure dating. The active Yumen‐Beidahe thrust fault offsets late Pleistocene alluvial‐fan deposits, and a prominent north‐facing scarp is well preserved. To quantify the slip rate, we surveyed the uplifted terraces and sampled quartz‐rich pebbles on terrace surfaces and river channels to determine surface exposure ages and pre‐depositional inheritance. The minimum vertical slip rate of the fault is 0.73 ± 0.09 mm a?1. This represents a horizontal shortening rate of 1.26 ± 0.31 mm a?1 for a fault dip of 30 ± 5°. This estimated slip rate supports the inference made from previous geological and GPS constraints that NNE‐directed shortening across the western Qilian Shan and the Hexi Corridor is distributed on several active faults with a total shortening rate of 4–10 mm a?1.  相似文献   

15.
Palaeoseismological and morphotectonic analyses enable us to define a 400-m-wide actively deformed zone associated with the active Eliki normal fault, central Greece, bounded on the south by a second-order fault and on the north by a composite and prominent fault scarp. This scarp is further analysed by trenching. Based on colluvium stratigraphy, displacement of distinct horizons and deposition of sedimentary layers, three faulting events have been identified along four fault strands affecting unconsolidated sediments in the trench. The two younger events, with throws of 0.93 and 1.37 m, respectively, the third event, with a throw of 0.44 m, and the penultimate 373 BC event suggest a variable seismic history.The entire alluvial plain of the Kerynitis and Vouraikos rivers, which cross the Eliki fault, has subsided at a rate of 1.4 mm/year, resulting in the burial of the Late Hellenistic–Roman occupation horizons under 3 m of fluvial and colluvial sediments in places.Extension in the broader area is accommodated by the seismically active Eliki and Egion faults. Structural and palaeoseismological analysis of those two faults indicates that they accommodate 1.5 mm/year, or about 10% of the geodetically estimated extension of up to 13 mm/year.  相似文献   

16.
Holocene stratigraphy from Skelwith Pool, on the northern side of Morecambe Bay, is described. Diatom and pollen analyses and radiocarbon dating have been undertaken for three sampling sites, from which eight sea-level index points have been obtained. These index points come from a small homogeneous area and similar palaeoenvironments. Some published sea-level index points from Morecambe Bay have been re-evaluated and validated by means of diatom analysis. An enhanced sea-level database with 28 index points has been used for the reconstruction of Holocene sea-level history. Relative sea-level rose rapidly around 6870–6510 BC at a maximum rate of +36.7 mm yr−1. Subsequently, the rate of sea-level change has varied between −8 mm yr−1 and +12 mm yr−1. The rate of relative sea-level changes for the last 3500 years is not clear. Uplift driven by deglaciation is believed to have been interrupted in the early Holocene by a rapid rise in relative sea-level. Uplift restarted at 6510 BC but soon declined as glacio-isostatic recovery ended around 3800 BC in the Morecambe Bay area. Since then, crustal movements in the Morecambe Bay area have been minimal. Factors affecting the attitudes of the index points such as sediment compaction of the basal peat and variations in palaeotidal range during the Holocene have been considered. © 1996 John Wiley & Sons, Ltd.  相似文献   

17.
《Geodinamica Acta》2013,26(3-4):333-342
Travertine deposits reflect some aspects of the regional tectonics because of the close association between travertine deposits and active fractures, that later of which provide conduits along which travertine-depositing waters may rise. Fissure-ridge travertines form above extensional fissures which are located in the hanging walls of normal faults, in step-over zones between fault segments, or in active or recently active) volcanic provinces. Numerous active and inactive fissure-ridge travertines are located in the hanging walls of normal faults in the Denizli Basin. A typical fissure-ridge comprises a central fissure along its long axis and flanking bedded travertines dipping away from the fissure. Central fissures of travertine ridges have been dilating since the initiation of the fissures. Samples from both the margins and centres of banded travertine deposits were dated by Th/U methods in order to determine dilation rates. Individual fissures have been dilating at average rates of between 0.008 and 0.1 mm yr–1 during travertine deposition, and ~ 0.001 and 0.007 mm yr–1 after cessation of travertine deposition. There is a noticable decrease in dilation rate from west to east in the Denizli Basin, and this decrease in dilation rate may be related to decrease in overall extension in southwest Turkey, which decreases eastward.  相似文献   

18.
Is compression across the northern Apennine fold‐and‐thrust system (Italy) still active? To address this question, we quantified the long‐term rates of migration and shortening of the system along with the measurement errors. Our approach integrates structural geology, seismicity patterns, and statistical treatment of tectonic activity. On the basis of recently published surface and subsurface data, we found a migration rate of 8.85 ± 0.61 mm yr−1. The inception age of individual fold structures follow closely this average rate, indicating that the system has been migrating at a constant rate for the past 17 Myr. Cumulative shortening of the system also increases linearly through time at 2.93 ± 0.31 mm yr−1. The location of the youngest structures in the easternmost portion of the system coincides with a significant peak of seismic moment released by historical earthquakes. We conclude that not only these easternmost thrusts are still active, but also that they generate earthquakes.  相似文献   

19.
Bedrock fission‐track analysis, high‐resolution petrography and heavy mineral analyses of sediments are used to investigate the relationships between erosion and tectonics in the Western Alps. Along the Aosta Valley cross‐section, exhumation rates based on fission‐track data are higher in the fault‐bounded western block than in the eastern block (0.4–1.5 vs. 0.1–0.3 mm yr−1). Erosion rates based on the analysis of bed‐load in the Dora Baltea drainage display the same pattern and have similar magnitudes in the relative sub‐basins (0.4–0.7 vs. 0.04–0.08 mm yr−1). Results highlight that climate, relief and lithology are not the controlling factors of erosion in the Western Alps. The main driving force behind erosion is instead tectonics that causes the differential upward motion of crustal blocks.  相似文献   

20.
The contact between wave‐influenced foreshore and aeolian‐influenced backshore sediments (BA boundary) in raised spit deposits (Skagen Odde) is here used as a proxy for palaeo‐sea level over the past 7600 years. The elevation of the BA boundary was measured at 57 sample sites along the northwestern coast of the spit, and the age of these sites determined by optically stimulated luminescence (OSL) dating of quartz grains. The elevation of the BA boundary with age gives past variation in relative sea level; relative sea level rose between c. 7600 and c. 6250 years ago, when it reached a peak value around 12.5 m above present mean sea level (apmsl), followed by a slow sea‐level fall until c. 4600 years ago before it dropped rapidly to reach 2 m apmsl c. 2000 years ago. From the new data it is tentatively deduced that the land uplift rate declined from about 3 mm a−1 6000 years ago to about 1.5 mm a−1 2000 years ago (low estimate), or alternatively from 5 mm a−1 5000 years ago to 1.5 mm a−1 2000 years ago (extreme estimate). These data indicate that the long‐term average rate of vertical land movement during the past 5000 years was around 1.8 mm a−1 (low estimate) or around 2.5 mm a−1 (extreme estimate). These values seem reasonable compared with a modern value of about 1.6 to 1.7 mm a−1. The lack of an independent data set illustrating the isostatic uplift history with time, however, precludes the construction of a well‐constrained eustatic sea‐level curve.  相似文献   

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