Sea-level Movements Research Articles

Relative Sea Level and Coastal Vertical Movements in Relation to Volcano-Tectonic Processes at Mayotte Island, Indian Ocean

During the last 10 kyr, significant subsidence and uplift occurred on Mayotte Island in the Comoros archipelago (Indian Ocean), but the role of volcanic processes in Holocene vertical movements has been neglected in the research so far. Here, we show that an abrupt subsidence of 6–10 m occurred between 9.4 and 10 kyr ago, followed by an uplift of the same amplitude at a rate of 9 mm/yr from 8.1 to 7 kyr ago. A comparison of the relative sea level of Mayotte and a reference sea level curve for the global ocean has been conducted using a modeling approach. This shows that an increasing and decreasing pressure at depth, equivalent to the process caused by a deep magma reservoir (50–70 km), was responsible for ~6–10 m subsidence and 6–10 m uplift, whereas loading by new volcanic edifices caused subsidence during the last few thousand years. Surface movements and deep pressure variations may be caused by pulses from the deep mantle, related to superplume activity, but uncertainties and unknowns about these phenomena are still present and further studies are needed. A better understanding of the volcano-tectonic cycle may improve assessments of volcanic hazards.

Sedimentary paleoenvironment and organic matter accumulation model of the Lower Silurian Gaojiabian Formation shales in the Lower Yangtze region, South China

A set of organic-rich shales developed in the lower part of the Lower Silurian Gaojiabian Formation in the Lower Yangtze region, South China. The paleoenvironment and the organic matter (OM) accumulation mechanism in the Lower Yangtze region are rarely studied, restricting the in-depth understanding of the shale gas exploration prospects of this region. This study described the petrological, mineralogical characteristics and geochemical properties of the organic-rich shales of the Gaojiabian Formation in the Lower Yangtze region (Well TD2) using multidisciplinary approaches. The purpose is to study the palaeoenvironment evolution of organic rich shales, and reveal the controlling factors and accumulation mechanism of OM. Two shale sections with high TOC content developing in the lower part of the Gaojiabian Formation were identified through petrological observations and geochemical analysis, namely the lower shale section (LSS) and the upper shale section (USS) with TOC content of 0.79–4.62% and 0.65–2.92%, respectively. The two organic-rich shale sections were formed in a suboxic-anoxic environment. The Cd/Mo, Co × Mn, Mo/TOC values show that the USS and the LSS were formed in a strongly restricted water environment and were not affected by upwelling, and the environment of the USS was more restricted than that of the LSS. The paleoproductivity proxies indicate the two sections have a high-productivity background, and that the LSS has a higher paleoproductivity level than the USS. The terrigenous input shows a long-term growth trend. Compared with the LSS, the USS had more terrigenous input and was closer to the source area. The chemical index of alteration (CIA) indicates that the shale was formed in a warm and humid climate. The index of compositional variability (ICV) shows that the USS has a more mature composition than the LSS and was likely dominated by recycling. The relationships between TOC content and several geochemical proxies indicate that the OM accumulation was mainly controlled by redox condition, paleoproductivity and terrigenous input, whereas these three factors are determined by the combined impact of the sea level and regional tectonic movement. On this basis, this study reconstructed the paleoenvironment and the OM accumulation model. The OM accumulation of the LSS was mainly controlled by relatively high regional sea level affected by global transgression, the anoxic-suboxic water environment, the high paleoproductivity, and a small quantity of terrigenous input, while the OM accumulation of the USS was primarily controlled by the suboxic condition affected by decreased relative sea level resulting from the strengthened regional tectonic movement, the relatively weakened paleoproductivity, and the increased recycled terrigenous input. The above understanding provides important enlightenment for deepening the study of OM enrichment and shale gas exploration direction of the Gaojiabian Formation in the Lower Yangtze region.

Sistem Monitoring Pasang Surut Air Laut Berbasis Web Menggunakan Fuzzy Logic Pada Kuala Langsa

Abstract - Tides are a phenomenon of periodic and periodic ups and downs of sea level movements. The tidal period is the time between the crest of a wave to the crest of the next wave, the time of the tidal period varies from 12 hours 25 minutes to 24 hours 50 minutes. Information about tides is very useful for activities related to the marine world. In the area of ​​​​Kuala Langsa, tides often occur, fishermen and anglers in Kuala Langsa only rely on the poles of residents' houses to determine the time of the tide. The system is made useful so that fishermen and anglers can find out the time and state of the tides using smartphones, by creating a “Sea Tidal Monitoring System using Ultrasonic Sensors and nodeMCU which can provide results of monitoring the time and tidal status in Kuala Langsa and will displayed on a Web page”. Ultrasonic sensors can detect well and can provide tidal data to be displayed on a web page and can be accessed using smartphones and other devices during the testing period in Kuala Langsa village, Langsa City with 62.5% success being tested.

Evidence of Former Sea Levels from a Passive Seismic Survey at a Sandy Beach; Perranporth, SW England, UK

Since the end of the last glaciation, the United Kingdom’s land surface has been altered by isostatic rebound, rising in the north and sinking in the south. Numerous studies have been published documenting the impact of isostatic rebound on relative sea levels. However, due to the difficulties in acquiring evidence to prove former sea levels, locally, these data can be sparse or absent. In this work, we explored the suitability of the passive seismic survey (PSS) method to estimate the contemporaneous beach thickness in coastal environments where there is a high impedance contrast between the beach deposits and the underlying wave-cut platform. We conducted a three-day survey at Perran Beach, Cornwall, collected 149 measurements using PSS, and interpreted the observations supported by auxiliary topographical, geological, and independent geophysical observation in the study area. The study site is a contemporaneous beach mostly composed of sand underlain by a wave-cut platform composed of igneous and sedimentary rock, therefore high impedance contrast with the sandy beach is anticipated. The elevation of the bedrock relative to the topographical elevation suggests that the bedrock elevation is −15 m ± 5 m below the present day mean sea level, which is coherent with the observation of relative sea level rise along the region of the south-west. The present study contributes to our current limited understanding of land and sea level movements by providing further subsurface information to the coastal geological archive of south-west England, a region currently in need of more data to reconstruct land- and sea-level movements.

Holocene sea-level change and estuary infill in North West Nelson, central New Zealand

The sedimentary sequences found within estuaries in the north west Nelson region of central New Zealand are investigated in order to quantify the timing of the end of the Post Glacial Marine Transgression. This region has been identified as being relatively stable in terms of vertical tectonic movement during the Holocene, but is yet to yield any reconstructions of eustatic sea level. In this study, we investigate the Holocene infill of a barrier estuary (Parapara Inlet) through sedimentological analysis and radiocarbon dating of 18 vibracores up to 4.2 m in length. It is found that the estuary infilled through a combination of lateral flood tide and fluvial delta progradation as well as vertical central basin infill. The central basin infilled at a consistent rate of 0.4 mm/year in both the mid (7.0–6.0 ka) and late-Holocene (2.5–1.5 ka). By the time of early human (Maori) settlement (c. 1 ka), the estuary surface was at low intertidal elevations with sediment being transported from the fluvial to tidal delta. A discernible change in sedimentation rates could not be associated with Maori settlement; however, infill rates increased to at least 12.5 mm/year in the past 150 years due hydraulic sluicing associated with mining. The sedimentary history of Parapara Inlet is compared to nearby Whanganui Inlet, d’Urville Island and Nelson to establish the character of regional Holocene sea level movement. It is found that relative sea level reached modern elevations between 8 and 7 ka in the region. The similarity between sea level curves for the end of the post glacial marine transgression (PMT) to other tectonically stable sites in northern New Zealand suggests that this curve can now be considered a true eustatic signal for the New Zealand archipelago.

Paleozoic sequence stratigraphy, depositional systems, and hydrocarbon habitats across the Arabian plate

The Paleozoic sedimentary section of the Arabian plate recorded the effects of numerous fluctuations in sea level and gentle epeirogenic movements. Eustatic changes in sea level over the Arabian plate resulted in transgressions and regressions and created many local and regional unconformity surfaces, identified by missing section and nondeposition. The distant deformation of the Caledonian tectonic orogeny and mountain building of the North Atlantic region, and the later Hercynian tectonic event, are partially responsible for eustatic sea-level changes. Additionally, detailed evidence of Paleozoic glacial erosion and glacial eustasy in the regressive sedimentary section over uplifted paleohighs comes from deep wells penetrating local exotic tectonic blocks. The resulting surfaces mark the sea-level falls associated with the glacial events in the Ordovician, Late Devonian, and Carboniferous–early Permian sediments. The depositional settings of the Cambrian–upper Permian rocks include deltaic and glacial settings and are expressed as alluvial–fluvial fans that grade into braided plains and shallow-marine carbonates flanked by distal shales. Late Permian sediment fill accompanied the development of widespread accommodation, resulting from a major sea-level rise, coinciding with a major period of carbonate–evaporite deposition, in which clastic sediments were only a minor factor. The regional sedimentary facies have good reservoir quality and are juxtaposed to regional source rocks and seals associated with both structural and minor stratigraphic traps. Production occurs in Precambrian through Permian strata in which mature clastic and shallow-water carbonate reservoirs occur, commonly sealed by shales, and sourced by Silurian hot shales or older source rocks in the section.

Carbon isotope (δ13Ccarb) stratigraphy of the Early–Middle Ordovician (Tremadocian–Darriwilian) carbonate platform in the Tarim Basin, NW China: implications for global correlations

AbstractGuided by conodont biostratigraphy and unconformities observed in the field, stable carbon isotopic analysis (δ13Ccarb) was performed on 210 samples from Lower–Middle Ordovician (Tremadocian to Darriwilian) sections and wells in the Tarim Basin, NW China. The δ13C trend in the Tarim Basin sections has three distinct characteristics: (1) from the Tremadocian to the Floian, a positive shift from −1.9 ‰ to −0.2 ‰ is observed near the boundary between the Penglaiba Formation and the Yingshan Formation; (2) from the Floian to the Dapingian, a positive shift in δ13C from −3 ‰ to −0.7 ‰ occurred under large-scale sea-level rise and a change in the sedimentary environment from a restricted platform to an open platform. Changes in the conodont type are also observed in the Tabei region; and (3) from the Dapingian to the Darriwilian, δ13C first decreased and then increased, showing a negative shift at the Dapingian–Darriwilian boundary. During the Floian, δ13C decreased in the study area, while it first decreased and then increased in other regions, which may reflect local sea-level movements in response to isostatic crustal movements. Two types of positive shift were identified at the Floian–Dapingian boundary, which likely show the effects of local factors, including a disconformity, dolomitization, and platform restriction, superimposed on the global signal of the carbon isotope. Some conodont zonations and recurrent negative excursions in Tremadocian, Floian and Dapingian stages appear to be truncated by unconformities, which are accompanied by short-term subaerial exposure due to sea-level fall and local tectonic uplift.

Modeling of Coastal Dynamics of the Anapa Bay-Bar

Abstract—The trend of the recent development of the Anapa bay-bar is considered based on modeling of sediment transport and morphodynamic processes. It is shown that longshore sediment transport does not have a crucial influence on the coastal dynamics. Most coastlines undergo degradation despite accumulation due to unloading of the longshore sediment flux. The probable reason is the relative sea level rise due mainly to tectonic processes. The proposed model of the coastal barrier following the sea level movement explains to a certain extent the observed trends.

Specifying the External Impact on Fluvial Lowland Evolution: The Last Glacial Tisza (Tisa) Catchment in Hungary and Serbia

External impact on the development of fluvial systems is generally exerted by changes in sea level, climate and tectonic movements. In this study, it is shown that a regional to local differentiation of fluvial response may be caused by semi-direct effects of climate change and tectonic movement; for example, vegetation cover, frozen soil, snow cover and longitudinal gradient. Such semi-direct effects may be responsible for specific fluvial activity resulting in specific drainage patterns, sedimentation series and erosion–accumulation rates. These conclusions are exemplified by the study of the fluvial archives of the Tis(z)a catchment in the Pannonian Basin in Hungary and Serbia from the middle of the last glacial to the Pleistocene–Holocene transition. Previous investigations in that catchment are supplemented here by new geomorphological–sedimentological data and OSL-dating. Specific characteristics of this catchment in comparison with other regions are the preponderance of meandering systems during the last glacial and the presence of very large meanders in given time intervals.

A Mesoproterozoic palaeokarst on the North China Craton in the Xingcheng area of Liaoning Province, China: characteristics and significance on paleogeography

ABSTRACTPalaeokarsts are rarely preserved and recognized from Precambrian strata. However, a Mesoproterozoic palaeokarst was recently discovered on the top of the Tuanshanzi Formation in Xingcheng, Liaoning Province, China. This palaeokarst recorded karstification fissures, three types of breccias and unique vadose filling. Four factors: no bedding fillings, vadose cements, restricted palaeokarst development, and the overlying beds without involved any karstification, supported this palaeokarst occurred before the deposition of the Dahongyu Formation. Relative sea-level changes and tectonic movement provided the essential external cause for this palaeokarst, which revealed the hiatus between the Dahongyu Formation and the Tuanshanzi Formation in the Yan-Liao Aulacogen of the North China Craton. This finding was significant and valuable for discussing the ‘Xingcheng Movement’ and unconformity contact relationships between the two formations observed around the basin. As the palaeokarst did not extend to the interior of the basin and the unconformity occurred mainly in the margins of basin, the significance of them is always underestimated. Nevertheless, this palaeokarst and other sedimentary features could represent an apparent transition of Yan-Liao Aulacogen basin evolved from rift to depression under the background of Supercontinent Columbia breakup.

Depositional and sea-level history from MIS 6 (Termination II) to MIS 3 on the southern continental shelf of South Africa

Pleistocene shoreline deposits comprised of calcified shallow marine (palaeobeach) and aeolian (palaeodune) facies found along mid-latitude coastlines can be useful indicators of past sea levels. Here, we describe a succession of such deposits that are presently exposed both above (subaerial) and below (submerged) mean sea level along the southern Cape coast of South Africa, 18 km east of the town of Mossel Bay. The submerged units provide a window on Late Pleistocene coastal processes, as palaeoshoreline deposits in this study extend to water depths of up to 55 m on the mid-shelf. Five sedimentary facies were identified in the strata and were compared to modern depositional environments of the local littoral zone, which include aeolian dune, upper shoreface, foreshore, intertidal swash and back-barrier settings. Twenty-two geological units were observed and mapped. Some of these units were directly dated with optically stimulated luminescence (OSL) dating. OSL ages were obtained for ten samples from the subaerial and twelve samples from the submerged deposits. Those geological units not directly dated were interpreted based on sedimentology and field/stratigraphic relationships to dated units. The stratigraphy and chronology of the succession indicates a record of initial deposition during Termination II (T-II) meltwater events, preceding and leading to marine isotope stage (MIS) 5e. Indicators for multiple sea-level fluctuations between MIS 5d and MIS 4, and sediment deposition at the end of MIS 4 and start of MIS 3 are also found. Both regressive and transgressive depositional cycles are well-preserved in the succession. We propose that palaeodune and palaeobeach deposits along the South Coast of South Africa have no clear preference for deposition during sea-level transgressions or regressions. Sediment deposition more closely mirrors the rate of sea level change, with deposition and preservation either during times of rapid sea-level movement, or oscillation around still-stand events. Periods of relatively slow average rise or fall of sea level are represented by erosional planation surfaces in this record.

Dispositional characteristics of Ordovician Wufeng Formation and Silurian Longmaxi Formation in Sichuan Basin and its adjacent areas

According to data of gas wells and typical sections of Wufeng Formation and Longmaxi Formation in Sichuan Basin, shale of various graptolite zones were analyzed to determine depositional environment, lithology and thickness characteristics of the graptolite shale interval of WF2-WF3 in the lower part of Wufeng Formation, the graptolite shale interval of WF4 in Guanyinqiao Member of Wufeng Formation and the graptolite shale interval of LM1-LM4 in the bottom of Longmaxi Formation, and characteristics of shale horizontal distribution were also investigated. During the depositional period of the graptolite shale interval of WF2-WF3, the study area was less affected by the Guangxi movement, the depositional environment was the deep water of open sea, where black shale was mainly deposited; the sedimentation center was developed in northeast Guizhou-northeast Sichuan and south Sichuan, the maximum thickness was from 4 to 6 m in the sedimentation center. During the depositional period of the graptolite shale interval of WF4, the depositional environment in the study area changed greatly due to global sea level fall and enhanced Guangxi movement; the central Sichuan paleouplift, the central Guizhou paleouplift and the Jiangnan-Xuefeng palaeouplift were further expanded, and the area of the sedimentary basin decreased; the depositional environment was mainly carbonate bioclastic shoal of shallow sea, and partially deep sea which only was distributed in the Shizhu-Fuling-Wuxi area in east and northeast Sichuan and the Gongxian-Yongchuan area in south Sichuan; sediments of shallow water were dominated by limestone and argillaceous limestone with abundant Hirnantia, sediments of deep water were dominated by calcareous mudstone and shale with Hirnantia. During the depositional period of the graptolite shale interval of LM1-LM4, due to rise of global sea level and Guangxi movement, the sedimentary area was larger than that in the depositional period of Guanyinqiao Member, and the sedimentary environment mainly was stagnant deepwater; thickness of black shale in the graptolite shale interval of LM1-LM4 was large, and the maximum thickness was over 20 m. Furthermore, control of the central Sichuan paleouplift, the central Guizhou paleouplift and the Jiangnan-Xuefeng paleouplift on black shale was discussed, and control of the Zhiliujing underwater highland/uplift, Huayingshan highland and Dingshan highland as well as western Hubei-Hunan underwater highland/uplift on shale deposition and preservation was also investigated.

Sea-level proxies in Holocene raised beach ridge deposits (Greenland) revealed by ground-penetrating radar

Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic beach ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the beach ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of beachface deposits and upper shoreface deposits; the contact between steeply dipping beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied beach ridge systems represent long time intervals and only relatively small spatial extents.

伊拉克M油田Asmari组碎屑岩与碳酸盐岩混合沉积特征

结合薄片、岩心、测井等及相关生产资料，对伊拉克M油田Asmari组B段储层特征及成因进行了分析。Asmari组B段岩性复杂，碳酸盐岩与陆源碎屑岩呈现互层和成分的混积，储层非均质性强，研究认为沉积相以三角洲、混积台地和局限台地的交替变化为特点。构造运动和海平面频繁震荡共同控制碎屑岩和碳酸盐岩的分布，形成了两种不同岩性储层的混积现象。 Based on thin section, core, well logging and production data, the characteristics and genesis of B reservoir in Asmari formation in Iraq were studied. The lithology of B reservoir is complex: carbonate and terrigenous clastic rock present interbeding and mixed composition; reservoir heterogeneity is strong. The sedimentary facies alternate among delta, mixed platform facies and restricted platform facies. Tectonic movement and frequent change of sea level control the distribution of clastic rock and carbonate rock, which results in two different lithologic reservoir of mixed phenomenon.

Last deglacial relative sea level variations in Antarctica derived from glacial isostatic adjustment modelling

We present relative sea level (RSL) curves in Antarctica derived from glacial isostatic adjustment (GIA) predictions based on the melting scenarios of the Antarctic ice sheet since the Last Glacial Maximum (LGM) given in previous works. Simultaneously, Holocene-age RSL observations obtained at the raised beaches along the coast of Antarctica are shown to be in agreement with the GIA predictions. The differences from previously published ice-loading models regarding the spatial distribution and total mass change of the melted ice are significant. These models were also derived from GIA modelling; the variations can be attributed to the lack of geological and geographical evidence regarding the history of crustal movement due to ice sheet evolution. Next, we summarise the previously published ice load models and demonstrate the RSL curves based on combinations of different ice and earth models. The RSL curves calculated by GIA models indicate that the model dependence of both the ice and earth models is significantly large at several sites where RSL observations were obtained. In particular, GIA predictions based on the thin lithospheric thickness show the spatial distributions that are dependent on the melted ice thickness at each sites. These characteristics result from the short-wavelength deformation of the Earth. However, our predictions strongly suggest that it is possible to find the average ice model despite the use of the different models of lithospheric thickness. By sea level and crustal movement observations, we can deduce the geometry of the post-LGM ice sheets in detail and remove the GIA contribution from the crustal deformation and gravity change observed by space geodetic techniques, such as GPS and GRACE, for the estimation of the Antarctic ice mass change associated with recent global warming.

Organic geochemistry of late Jurassic paleosols (Dirt Beds) of Dorset, UK

Paleosols from the lower part of the Purbeck Limestone Group, which crops out extensively in Dorset, southern England, are shown to contain type IV kerogens. Comparisons with Mesozoic organic materials suggest that some of the paleosol kerogen is composed of fossil charcoal. The charcoal would have been produced by wildfires in the undergrowth of Purbeck gymnosperm forests. Contrasting the paleosol charcoal with laboratory produced counterparts suggest that, originally, significant amounts of functionalised organic matter should have persisted. Secondary oxidation and decay processes, therefore, must have removed all but the most resistant aromatic units in the charcoal. The importance of post-fire processes implies a strong influence on preservation from oxygen supply, water washing and host sediment type. These factors may have been related to pedogenesis, relative sea level and local fault movement in the late Jurassic.

Holocene environmental changes in the Lower Thames Valley, London, UK: Implications for understanding the history of Taxus woodland

A radiocarbon-dated multiproxy palaeoenvironmental record from the Lower Thames Valley at Hornchurch Marshes has provided a reconstruction of the timing and nature of vegetation succession against a background of Holocene climate change, relative sea level movement and human activities. The investigation recorded widespread peat formation between c. 6300 and 3900 cal. yr BP (marine ‘regression’), succeeded by evidence for marine incursion. The multiproxy analyses of these sediments, comprising pollen, Coleoptera, diatoms, and plant and wood macrofossils, have indicated significant changes in both the wetland and dryland environment, including the establishment of Alnus (Alder) carr woodland, and the decline of both Ulmus (Elm; c. 5740 cal. yr BP) and Tilia (Lime; c. 5600 cal. yr BP, and 4160–3710 cal. yr BP). The beetle faunas from the peat also suggest a thermal climate similar to that of the present day. At c. 4900 cal. yr BP, Taxus (L.; Yew) woodland colonised the peatland forming a plant community that has no known modern analogue in the UK. The precise reason, or reasons, for this event remain unclear, although changes in peatland hydrology seem most likely. The growth of Taxus on peatland not only has considerable importance for our knowledge of the vegetation history of southeast England, and NW Europe generally, but also has wider implications for the interpretation of Holocene palaeobotanical records. At c. 3900 cal. yr BP, Taxus declined on the peatland surface during a period of major hydrological change (marine incursion), an event also strongly associated with the decline of dryland woodland taxa, including Tilia and Quercus, and the appearance of anthropogenic indicators.

Holocene environmental change and Neolithic rice agriculture in the lower Yangtze region of China: A review

In this paper, we summarize the Holocene environmental history of the lower Yangtze region, east China, based on the sedimentary records and microfossil diatom, pollen, fungal and charcoal data that were published in the past two decades. We then examine the linkage between changes in the coastal environment and the development of rice agriculture in the region, with reference to the available archaeological evidence and historical archives. Based on the sedimentary and archaeological evidence, we conclude that during the early Holocene sea-level movements and sedimentary processes significantly changed the region’s landscape from an open, brackish water environment to a largely enclosed, wetland system. This newly established freshwater marsh environment provided a habitat favourable to rice agriculture. The early Neolithic farmers took the opportunity presented to them and started rice cultivation in locations where freshwater wetland systems were established. During the middle Holocene, environmental conditions were largely stable, and the coastal wetlands evolved slowly. Environmental change was only a supportive player in the Neolithic cultural processes, because the Neolithic people were able to adapt to these changes and took advantages of the newly emerging marsh land for food collection and production. Around 4200 years ago, the prosperous Liangzhu society fell, but there is no evidence to suggest the fall was related to a significant environmental change. The coastal environment continued to evolve slowly during the late Holocene. But this period saw rapid technological development in irrigation and flood protection, and the environmental factor was reduced to background noise. Throughout the Holocene, the main strategy taken by the Neolithic people to cope with environmental change was migration to find better food sources. Along with this strategy was the development of technology in landscape management to ensure a more reliable food production in addition to food collection through hunting, gathering and fishing.

Reconstructing middle to late Holocene sea-level change: A methodological review with particular reference to ‘A new Holocene sea-level curve for the southern North Sea’ presented by K.-E. Behre

A number of disciplines are involved in the collection and interpretation of Holocene palaeoenvironmental data from coastal lowlands. For stratigraphic frameworks and the assessment of relative sea-level (RSL) change, many non-specialists rely on existing regional models. It is, however, important that they are aware of major developments in our understanding of the factors controlling coastal change and of the potential sources of error in sea-level reconstructions. These issues are explored through a critical evaluation of a new sea-level curve presented by Behre (2003, 2007) for the southern North Sea. In contrast to most sea-level curves published from this region over the last 20 years, the curve shows strong fluctuations that are interpreted as representing vertical movements of sea level. We present a detailed examination of the data used by Behre. From this analysis it is clear that many of the data points used are unsuitable for high-resolution (centimetre or decimetre) sea-level reconstruction. This paper also gives an overview of possible sources of error with respect to the age and altitude of sea-level index points and of changes in our understanding of the processes that underpin the interpretation of the organic and occupation levels used as index points. The constraints on the spatial scale over which sea-level reconstructions can be applied (changes in palaeotidal range and crustal movements) are also considered. Finally, we discuss whether the large-amplitude centennial-scale sea-level fluctuations proposed by Behre can be reconciled with the known mechanisms of sea-level change and other recent high-resolution studies from this region. We conclude that such fluctuations are highly unlikely to be real features of the sea-level history of the southern North Sea. © 2011 The Authors. Boreas © 2011 The Boreas Collegium.

The observed postglacial recovery of Québec and Nouveau-Québec Since 12,000 BP

Radiocarbon dated relative sea levels, the tilts of proglacial lake shorelines and raised marine shorelines, the directions of the tilt of these features, and postglacial delevelling are used to construct six isobase maps showing relative sea level movements over the last 12,000, 10,000, 8000, 4000, and 2000 years, No map has more than 30 control points and usually there are only 12 "good" points controlling the isobase patterns. Each map shows the relationship of the isobases to the current ice sheet extent. Along the southern margin of the Laurentide Ice Sheet, the maximum postglacial emergence has been quite uniform with the 240 to 200 m isobase always close to the ice margin. Along the northeastern margin of the ice sheet, the postglacial emergence at the retreating ice edge was closer to 100 m. Equidistant diagrams are drawn along planes southeast from southern Hudson Bay and eastward from Southampton Island. If these diagrams are compared on a Shoreline Relation Diagram, the two profiles appear similar and compare moderately well with a theoretical SR Diagram published in 1969. The isobases show a major uplift center located around the area of James Bay and southern Hudson Bay where a maximum emergence of nearly 300 m occured in the last 7500 years. High marine limits southwest of Ungava Bay need to be dated because if they date close to 8000 BP as we suggest, then more emergence is suggested for the region southwest of Ungava Bay than we currently allow for.