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1.
The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

2.
The small recently infilled lake basin of Marcacocha (13°13′S, 72°12′W, 3355 m) in the Cuzco region of Peru has a morphology and location that renders it extremely sensitive to environmental change. A record of vegetation, human impact and climatic change during the past 4200 yr has been obtained from a highly organic core taken from the centre of the basin. Sustained arid episodes that affected the Peruvian Andes may be detectable using the proxy indicator of sedge (Cyperaceae) pollen abundances. As the lake‐level was lowered during sustained drier conditions, the local catchment was colonised by Cyperaceae, whereas during lake floods, they retreated or were submerged and pollen production was correspondingly reduced. Drier episodes during prehistoric times occurred around 900 bc , 500 bc , ad 100 and ad 550, with a longer dry episode occurring from ad 900 to 1800. Evidence from the independently derived Quelccaya ice‐core record and the archaeological chronology for the Cuzco region appears to support the climatic inferences derived from the sedge data. Many of these aridity episodes appear to correspond with important cultural changes in the Cuzco region and elsewhere in the Central Andes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

3.
The complex lithological, geochemical, geochronological, and micropaleontological (diatoms, spores, pollen) investigations of stratified bottom sediments that constitute facies-variable sedimentary sequences in a small isolated lake located near the upper limit of the sea on the White Sea coast made it possible to define lithostratigraphic units (LSU) forming the complete sedimentary succession in deep parts of isolated basins. It is shown that stratigraphy of heterogeneous sequences is determined by two regional transgressive–regressive cycles in relative sea level fluctuations: alternating late Glacial and Holocene transgressions and regressions. The lower part of a clastogenic clayey–sandy–silty sequence successively composed of freshwater (LSU 1) and brackish-water (LSU 2) sediments of the ice-marginal basins and marine postglacial facies (LSU 3) was formed during the late Glacial glacioeustatic marine transgression. Its upper part formed in different isolated basins at different stages of the Holocene is represented depending on its altimetric position on the coastal slope by costal marine sediments (LSU 4) and facies of the partly isolated inlet (LSU 5). The organogenic sapropelic sequence, which overlies sediments of the marine basin and partly isolated bay, corresponds to lithostratigraphic units represented by Holocene sediments accumulated in the meromictic lake (LSU 6), onshore freshwater basin (LSU 7), and freshwater basin with elevated water mineralization (LSU 8) deposited during maximum development of Holocene transgression and lacustrine sediments (LSU 9) formed in coastal environments during terminal phases of the Holocene. The defined lithostratigraphic units differ from each other in lithological, micropaleontological, and geochemical features reflected in structural and textural properties of their sediments, their composition, inclusions, and composition of paleophytocoenoses and diatom assemblages.  相似文献   

4.
Knudsen, K. L., Jiang, H., Kristensen, P., Gibbard, P. L. & Haila, H. 2011: Early Last Interglacial palaeoenvironments in the western Baltic Sea: benthic foraminiferal stable isotopes and diatom‐based sea‐surface salinity. Boreas, 10.1111/j.1502‐3885.2011.00206.x. ISSN 0300‐9483. Stable isotopes from benthic foraminifera, combined with diatom assemblage analysis and diatom‐based sea‐surface salinity reconstructions, are used for the interpretation of changes in bottom‐ and surface‐water conditions through the early Eemian at Ristinge Klint in the western Baltic Sea. Correlation of the sediments with the Eemian Stage is based on a previously published pollen analysis that indicates that they represent pollen zones E2–E5 and span ～3400 years. An initial brackish‐water phase, initiated c. 300 years after the beginning of the interglacial, is characterized by a rapid increase in sea‐surface and sea‐bottom salinity, followed by a major increase at c. 650 years, which is related to the opening of the Danish Straits to the western Baltic. The diatoms allow estimation of the maximum sea‐surface salinity in the time interval of c. 650–1250 years. After that, slightly reduced salinity is estimated for the interval of c. 1250–2600 years (with minimum values at c. 1600–2200 years). This may be related to a period of high precipitation/humidity and thus increased freshwater run‐off from land. Together with a continuous increase in the water depth, this may have contributed to the gradual development of a stratified water column after c. 1600 years. The stratification was, however, particularly pronounced between c. 2600 and 3400 years, a period with particularly high sea‐surface temperature, as well as bottom‐water salinity, and thus a maximum influence of Atlantic water masses. The freshwater run‐off from land may have been reduced as a result of particularly high summer temperatures during the climatic optimum.  相似文献   

5.
Hewn blocks from submerged ruins associated with the name Thronion are exposed during low, low tide along the northeastern shoreline of the fan delta which separates the Gulf of Euboea from the Maliakos Gulf, central Greece. Although the date of these ruins is not known, their submergence indicates that they predate the most recent marine transgression. Late Holocene sediments of the coastal plain adjacent to the ruins were studied using 34 auger cores drilled along two 1.3 and 1.1 km shore-normal sections. Cores were described in the field and sampled for sedimentologic and microfossil analyses. These analyses show that late Holocene transgressive marine and strandline units interfinger inland with deposits of a brackish water embayment. Subsequent progradation of the shoreline is marked by overlying slightly brackish to freshwater marsh sediments. A soil horizon developed on these marsh sediments defines a period of aerial exposure and land stability. Late Roman to Byzantine sherds (ca. 4th-13th Century A.D.) within the buried soil and a high phosphate content suggest that this soil developed in association with human habitation. the buried soil may be the surface on which the now-submerged ruins were built. the deposits below the buried soil indicate that prior to the period of soil formation, most of this area was under water and the paleoshoreline was landward of its present position. the ruins were later covered by lake or marsh deposits radiocarbon dated as 1400 A.D. the depth of the dated wood samples, 2.5–3.0 meters below the surface, indicates rapid sediment accumulation (ca. 40–55 cm/100 yrs) over the past 550 years. A small exposure of the ca. 1400 A.D. marsh silt and overlying post-1950 land fill near the ruins is the result of post-1400 A.D. erosion and recession of the shoreline. the lower pre-occupational and post-1400 A.D. transgressions were caused by a combination of eustatic sea level rise, tectonic subsidence, and fluctuations of sediment supply to this portion of the Kenourion fan delta.  相似文献   

6.
The glaciomarine model for deglaciation of the Irish Sea basin suggests that the weight of ice at the last glacial maximum was sufficient to raise relative sea‐levels far above their present height, destabilising the ice margin and causing rapid deglaciation. Glacigenic deposits throughout the basin have been interpreted as glaciomarine. The six main lines of evidence on which the hypothesis rests (sedimentology, deformation structures, delta deposits, marine fauna, amino‐acid ratios and radiocarbon dates) are reviewed critically. The sedimentological interpretation of many sections has been challenged and it is argued that subglacial sediments are common rather than rare and that there is widespread evidence of glaciotectonism. Density‐driven deformation associated with waterlain sediments is rare and occurs where water was ponded locally. Sand and gravel deposits interpreted as Gilbert‐type deltas are similarly the result of local ponding or occur where glaciers from different source areas uncoupled. They do not record past sea‐levels and the ad hoc theory of ‘piano‐key tectonics’ is not required to explain the irregular pattern of altitudes. The cold‐water foraminifers interpreted as in situ are regarded as reworked from Irish Sea sediments that accumulated during much of the late Quaternary, when the basin was cold and shallow with reduced salinities. Amino‐acid age estimates used in support of the glaciomarine model are regarded as unreliable. Radiocarbon dates from distinctive foraminiferal assemblages in northeast Ireland show that glaciomarine sediments do occur above present sea‐level, but they are restricted to low altitudes in the north of the basin and record a rise rather than a fall in sea‐level. It is suggested here that the oldest dates, around 17 000 yr BP, record the first Late Devensian (Weichselian) marine inundation above present sea‐level. This accords with the pattern but not the detail of recent models of sea‐level change. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

7.
The macrofossils, lithology and chronology of two lake basins on Disko in central West Greenland have been investigated. Both lakes were isolated from the sea in the mid-Holocene as a result of relative land uplift. A marine-brackish-limnic sequence was recovered from the Qivittut Lake. The marine fauna is unusually diverse, whereas the brackish water fauna consists only of few species. Immediately after isolation the lake passed through a short-lived eutrophic phase, after which stable, mesotrophic conditions were established. From the second lake basin, the Fortunebay Lake, only limnic sediments were recovered. This lake record demonstrates that rather stable conditions have persisted since mid-Holocene times. Both lakes show anomalously high accumulation rates.  相似文献   

8.
华北晚古生代内陆表海大型聚煤盆地的极平坦的地势是煤聚积的良好场所，而事件性海侵为泥岩沼泽发育及泥炭迅速得以保存最终形成煤层提供了条件。研究表明，石炭二叠纪煤系中可识别出若干个重要的事件性海侵层，研究这些海侵层的形成，对探明富煤单元的分布具有重要的实际意义。本文讨论了事件性海侵与富煤单元形成及分布的成因联系，应用层序地层学理论和方法，分析了鲁西煤田煤聚积规律。  相似文献   

9.
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   

10.
The marine benthic fauna and the δ18Oc of foraminifers and ostracods from six sites situated on a west–east transect through central Sweden have been analysed in order to estimate the palaeosalinity and palaeocirculation in this shallow‐marine environment. The measurements have been undertaken on material from the early Preboreal, when the Baltic Basin was in contact with the North Sea through straits in central Sweden. The δ18Oc values have a more negative value towards the east, indicating decreasing salinity. This was the result of limited possibilities for marine water to penetrate into the Baltic Basin and the mixing with freshwater from the melting Fennoscandian ice‐sheet. Four water masses existed in the area: a surface layer of freshwater, marine water from the North Sea, brackish–marine intermediate water on the Swedish west coast and brackish Yoldia Sea water in the Baltic Basin. The chronology is based on radiocarbon dates of marine fossils and, at one site, on the occurrence of the Vedde Ash (10 400–10 300 14C yr BP). This is the first record from marine settings in Sweden. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

11.
Assemblages of foraminifers, ostracods and molluscs from temperate Ipswichian Stage (last temperate stage) sediments and overlying cold Devensian Stage (last cold stage) sediments at Somersham in the southern Fenland of Cambridgeshire have been analysed. The Ipswichian sediments contain faunas consistent with temperate brackish water conditions under tidal influence. The Devensian assemblages were recovered from a series of sands and gravels laterally accreting in a channel cutting into Ipswichian sediments. In contrast to the Ipswichian faunas, the faunas of particular Devensian samples show a complex mixture of temperate freshwater, brackish and marine taxa. The molluscs are mainly freshwater, with few land snails; they occur together with foraminifers and ostracods. Freshwater, brackish water and marine ostracods are present with foraminifers. A sample of Devensian fine laminated sediment in the channel was analysed for pollen; only abundant pre-Quaternary spores were present, with abundant foraminifers in the same sample. The taphonomy of the assemblages and the difficulties of their interpretation in environmental terms are discussed. The importance of taphonomy in assessing environments, climate, range of taxa and dating is stressed.  相似文献   

12.
Shallow estuarine lagoons characterize >70 % of the eastern Alaskan Beaufort Sea coastline and, like temperate and tropical lagoons, support diverse and productive biological communities. These lagoons experience large variations in temperature (?2 to 14 °C) and salinity (0 to >45) throughout the year. Unlike lower latitude coastal systems, transitions between seasons are physically extreme and event-driven. On Arctic coastlines, a brief summer open-water period is followed by a 9-month ice-covered period that concludes with a late-spring sea ice breakup and intense freshwater run-off. From 2011 to 2014, we examined interannual variations in water column physical structure (temperature, salinity, and δ18O) in five lagoons that differ with respect to their degree of exchange with adjacent marine waters and magnitude of freshwater inputs. Temperature, salinity, and source water composition (calculated using a salinity and δ18O mixing model) were variable in space and time. During sea ice breakup in June, water column δ18O and salinity measurements showed that low salinity waters originated from meteoric inputs (50–80 %; which include river inputs and direct precipitation) and sea ice melt (18–51 %). Following breakup, polar marine waters became prevalent within a mixed water column over the summer open-water period within all five lagoons (26–63 %). At the peak of ice-cover extent and thickness in April, marine water sources dominated (75–87 %) and hypersaline conditions developed in some lagoons. Seasonal runoff dynamics and differences in lagoon geomorphology (i.e., connectivity to the Beaufort Sea) are considered key potential drivers of observed salinity and source water variations.  相似文献   

13.
《Chemical Geology》2007,236(3-4):281-290
Ostracods preserved in late Quaternary sediments of Wallywash Great Pond, a fresh coastal lake in SW Jamaica, record temporal variations in the strontium-isotope composition of lake water. Oxygen-isotope and Sr/Ca ratios in ostracods reveal temporal variations in the lake's hydrology, related to effective precipitation, and in its salinity related to varying marine-saline groundwater input from changes in relative sea level. Evaluation of isotopic and trace-element data indicates that the stratigraphic variations in 87Sr/86Sr ratios during the late Quaternary are best explained by climatically-controlled hydrological changes. During wetter periods, the lake's Sr budget was dominated by springwater input with relatively low 87Sr/86Sr ratio, whereas during drier times reduced springflow, possibly coupled with input of more-radiogenic Sr from other sources, such as sea-spray aerosols and perhaps Saharan dust, led to an increase in the Sr-isotope ratio of the lake water. Despite proximity of the lake to the sea and evidence for slight intrusion of marine saline groundwater in the past, however, the extent of marine input appears to have had limited influence on the lake's Sr-isotope ratios. Whereas the 87Sr/86Sr ratios cannot be used as a palaeosalinity proxy in this particular lake, they do provide valuable information about the mechanisms underlying hydrological change.  相似文献   

14.
The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.  相似文献   

15.
The geology of the central portion of Kos island (Greece) is described. A geological map shows the distribution of the Neogene Konstantinos, Gurniati, Stefanena und Tafi formations and of the Pleistocene Plateau-tuff in the vicinity of the Dikeos mountain chain. The Neogene and Pleistocene sedimentary formations of Kos are reviewed, and a detailed sketch of the history of the island from the Miocene till now is given. The deposition of marine sediments of lower to middle Miocene age was followed by tectonic movements and accumulation of lacustrine sedimentary rocks in the upper Miocene. During that time, Kos was part of a land mass including Anatolia, the Aegean Sea and the Greek mainland. Sediments, which can be assigned to the lower Pliocene with certainty, are not known from Kos until now. From the middle Pliocene to lower Pleistocene a continuous sequence of sediments was deposited. In the lowermost lithologic units (Gurniati and Stefanena formations in central Kos, Phoka and Sefto formations in east Kos) continental sediments predominate. In central Kos, about eight marine intercalations can be traced, but the sea did not reach the eastern area. The Tafi formation (central Kos, uppermost Pliocene to lower Pleistocene) was mainly accumulated in marine environments. During the same time, in east Kos in a lake of varying size the Kos up to the Elia formations were deposited. Its endemic gastropods include some of the best examples of evolutionary lineages. When by the beginning of the Pleistocene the sea invaded this basin, the endemic fauna was destroyed. After tectonic displacement of the Plio-Pleistocene sediments, what began during accumulation of the lower Tafi formation, and after their elevation above sea-level, the area of Kos and surrounding islands was covered by the Pleistocene Plateau tuff. At about the same time, Kos became separated from the Anatolian Datça peninsula and was transformed into an island. During periods of glacial sea-level fall, however, it was more than once united with the Anatolian mainland via a northern connection. The gradual phyletic change of the freshwater snail,Melanopsis sporadum into M.gorceixi is described. The evolutionary rate was influenced by marine transgressions causing a reduction of the population size.  相似文献   

16.
Late- and postglacial history of the Great Belt, Denmark   总被引：3，自引：0，他引：3  
On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200–300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP.  相似文献   

17.
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP25, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
Seventeen vibrocores from the inner part of Joseph Bonaparte Gulf off northwestern Australia penetrate a range of marine and marginal‐marine sediments deposited in the post‐glacial transgression and highstand. Ranging from gravelly sand to fine silt, these sediments contain a diverse fossil biota dominated by molluscs and bryozoans, but also including ostracods and foraminifers. Minor components include solitary corals, echinoids, soft coral and sponge spicules, wood debris and bone fragments. The biota can be divided into five major marine or marginal‐marine environments (intertidal, lagoonal, estuarine, strandline and shelf) and one terrestrial (riverine) environment. The intertidal environment contains four sub‐assemblages (mangroves, salt marsh, mud flat and sand flat) and the shelf environment six sub‐assemblages (hard substrate inner shelf, sandy substrate inner shelf, muddy substrate inner shelf, epiphytic, inshore and oceanic). The most useful organisms for palaeoenvironmental reconstruction are bryozoans for differentiating various shallow‐marine substrates, and foraminifers and ostracods for defining water depths, euryhaline, freshwater and oceanic influences. Palynomorphs were the only microfossils capable of providing control on terrestrial environments. The scarcity of marine plankton and the dominance of terrestrial palynomorphs in these marine sediments provides a salutary warning of the dangers of relying on plant microfossils alone when no independent environmental data are available to test the interpretation. The mollusc and bryozoan biota in the inner part of Joseph Bonaparte Gulf superficially resembles the bryomol assemblage of cool‐water shelves. This biotic assemblage is the result of turbidity rather than water temperature. The turbidity suppresses the photosynthetic, zooxanthellate and hermatypic organisms allowing molluscs, bryozoans and other apparently cool‐water biotic elements to dominate.  相似文献   

19.
This study takes a comprehensive approach to characterizing the isolation sequence of Heimerdalsvatnet, a coastal lake in the Lofoten Islands, northern Norway. We use established methods and explore new techniques to assess changes in marine influence. Bathymetric and sub-bottom profiles were acquired to examine basin-wide sedimentation and a 5.8 m sediment core spanning the last 7800 cal yr BP was analyzed. We measured magnetic susceptibility, bulk organic matter properties, molecular biomarkers, diatom assemblages, and elemental profiles acquired by scanning X-ray fluorescence. These characteristics of the sediment reflect detailed changes in salinity and water column conditions as the lake was progressively isolated. Three distinct litho/chemo-stratigraphic units represent a restricted marine phase (7800-6500 cal yr BP), a transitional phase characterized by intermittent marine influence (6500-4900 cal yr BP), and complete isolation and freshwater sedimentation (4900 cal yr BP to present). Although there are uncertainties in the estimate of the threshold elevation of the lake, the timing of these phases generally corresponds with previous interpretations of the local relative sea-level history. This record captures sea-level regression following the Tapes transgression and supports the interpretation of a subsequent sea-level stillstand, dated in Heimerdalsvatnet from 6500 to 4900 cal yr BP.  相似文献   

20.
Microfossils in isolation basin sediments are frequently used to reconstruct sea‐level change, but preservation problems and non‐analogue situations can limit their usefulness. Here we investigate the potential of stable carbon isotopes (δ13C) and C/N ratios from bulk organic matter, as an alternative proxy of salinity within isolation basin sediments from a basin in northwest Scotland. Within the Holocene sediment δ13C and C/N are determined largely by the mean weighted values of the predominant source of the organic material. Analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high δ13C and variable C/N. In the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low δ13C and high C/N. The application of δ13C and C/N ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

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