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1.
A flight of marine terraces along the Cuban coast records Quaternary sea‐level highstands and a general slowly uplifting trend during the Pleistocene. U/Th dating of these limestone terraces is difficult because fossil reef corals have been affected by open system conditions. Terrace ages are thus often based on geological and geomorphological observations. In contrast, the minimum age of the terraces can be constrained by dating speleothems from coastal mixing (flank margin) caves formed during past sea‐level highstands and carving the marine limestones. Speleothems in Santa Catalina Cave have ages >360 ka and show various cycles of subaerial–subaqueous corrosion and speleothem growth. This suggests that the cave was carved during the MIS 11 sea‐level highstand or earlier. Some stalagmites grew during MIS 11 through MIS 8 and were submerged twice, once at the end of MIS 11 and then during MIS 9. Phreatic overgrowths (POS) covering the speleothems suggest anchialine conditions in the cave during MIS 5e. Their altitude at 16 m above present sea level indicates a late Pleistocene uplift rate of <0.1 mm/ka, but modelling also shows uplift to have been insignificant over a long timespan during the middle Pleistocene since the cave was carved. Our study shows that some flank margin caves in the region of Matanzas are older than commonly believed (i.e. MIS 11 rather than MIS 5). These caves not only can be preserved but are good markers of interglacial sea‐level highstands, more reliable than marine abrasion surfaces. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

2.
Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.  相似文献   

3.
This study focuses on the late Quaternary landscape evolution in the Chifeng region of Inner Mongolia, China, its relations to the history of the Pleistocene‐Holocene loess accumulation, erosion and redeposition, and their impact on human occupation. Based on 57 optically stimulated luminescence (OSL) ages of loess sediments, fluvial sand and floodplain deposits accumulated on the hill slopes and floodplains, we conclude that during most of the Pleistocene period the region was blanketed by a thick layer of aeolian loess, as well as by alluvial and fluvial deposits. The loess section is divided into two main units that are separated by unconformity. The OSL ages at the top of the lower reddish loess unit yielded an approximate age of 193 ka, roughly corresponding to the transition from MIS 7 to 6, though they could be older. The upper gray loess unit accumulated during the upper Pleistocene glacial phase (MIS 4–3) at a mean accumulation rate of 0·22 m/ka. Parallel to the loess accumulation on top of the hilly topography, active fans were operating during MIS 4–2 at the outlet of large gullies surrounding the major valley at a mean accumulation rate of 0·24 m/ka. This co‐accumulation indicates that gullies have been a long‐term geomorphic feature at the margins of the Gobi Desert since at least the middle Pleistocene. During the Holocene, the erosion of the Pleistocene loess on the hills led to the burial of the valley floors by the redeposited sediments at a rate that decreases from 3·2 m/ka near the hills to 1–0·4 m/ka1 in the central part of the Chifeng Valley. This rapid accumulation and the frequent shifts of the courses of the river prevented the construction of permanent settlements in the valley floors, a situation which changed only with improved man‐made control of the local rivers from the tenth century AD. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
In the present study, we applied the IRSL50°C dating method to both K- and Na-feldspar coarse grains from interglacial coastal deposits in north-eastern Tunisia. We used the yellow IRSL50°C signal of Na-feldspars and the blue IRSL50°C signal of K-feldspars. The key-sites for this study are at El Hajeb (Sahel area) and Dar Oufa (Cap Bon Peninsula). These deposits belong to the “Douira Unit” which has previously been assigned to marine isotope stage (MIS) 7 on the basis of amino acid ratios and chronostratigraphic evidence.In order to assess the reliability of the IRSL50°C ages of the “Douira Unit”, we extended the IRSL dating technique to K- and Na-feldspars from two MIS 5 samples, with independent age control, collected within shallow-marine sands in the Sahel area and on the Jerba island (southern Tunisia).Two protocols of age correction for the observed fading in K- and Na-feldspars have been applied: (1) the Huntley and Lamothe (2001) fading correction and (2) the dose rate correction developed by Lamothe et al. (2003). The fading corrected IRSL ages of the “Douira Unit” and both MIS 5 control samples, measured on K- and Na-feldspars, are in good agreement with their expected ages.  相似文献   

5.
Pleistocene uplift of the Chilean coast is recorded by the formation of wave-cut platforms resulting from marine erosion during sea-level highstands. In the Altos de Talinay area (~ 31°S), we have identified a sequence of 5 wave-cut platforms. Using in situ produced 10Be exposure ages we show that these platforms were formed during interglacial periods at 6, 122, 232, 321 and 690 ka. These ages correspond to marine isotopic stages (MIS) or substages (MISS) 1, 5e, 7e, 9c and 17. Shoreline angle elevations used in conjunction with our chronology of wave-cut platform formation, illustrate that surface uplift rates vary from 103 ± 69 mm/ka between 122 and 6 ka, to 1158 ± 416 mm/ka between 321 and 232 ka. The absence of preserved platforms related to the MIS 11, 13 and 15 highstands likely reflects slow uplift rates during these times. We suggest that since 700 ka, the Altos de Talinay area was predominantly uplifted during 2 short periods following MIS 17 and MISS 9c. This episodic uplift of the Chilean coast in the Pleistocene may result from subduction related processes, such as pulses of tectonic accretion at the base of the forearc wedge.  相似文献   

6.
A thick Middle and Late Pleistocene loess-palaeosol sequence is exposed at the Stari Slankamen section in the Vojvodina region situated in the south-eastern part of the Pannonian basin, Serbia. The profile exposes an about 45 m thick series of loess intercalated by at least eight pedocomplexes. Ten samples were dated by luminescence methods using a modified single aliquot regenerative dose (SAR) protocol for polymineral fine grains and for quartz extracts from the upper part of the Stari Slankamen loess sequence. The infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (OSL) signals from all polymineral samples showed anomalous fading, suggesting that the post-IR OSL signal is still dominated by feldspar OSL. The ages ranging from 4.6 to 193 ka were obtained after fading correction. These ages indicate that the loess unit V-L1L1, the weakly developed soil complex V-L1S1 and the loess unit V-L1L2 were deposited during marine isotope stage (MIS) 2, 3, and 4, respectively, and also indicate that the loess unit V-L2 is of the penultimate glacial age.  相似文献   

7.
Relatively little is known about the long-term sediment accumulation dynamics of Naracoorte Cave Complex (NCC) solution pipe cavities, and many of the megafauna-bearing infill deposits at this globally significant Australian Pleistocene fossil locality remain partially dated or lack any numerical age control. In this study, we assess the suitability of three different luminescence dating signals for improving existing chronologies at six Late and Middle Pleistocene NCC sites (n = 22 samples), and we undertake multi-site examinations of NCC sediment infill dynamics spanning the last 550 thousand years (ka). Modern analogue samples collected from above and beneath two active cave entrances confirm that single-grain OSL, single-grain TT-OSL and multi-grain pIR-IRSL signals can be reset down to insignificant residual levels (<10−1–100 Gy) when compared with the natural dose ranges of interest for most NCC palaeontological applications. Replicate luminescence dating comparisons performed at six NCC fossil sites (n = 15 samples) reveal consistent ages for twenty-eight out of thirty-one paired OSL–TT-OSL, OSL–pIR-IRSL and TT-OSL–pIR-IRSL datasets. Nineteen of the twenty Middle to Late Pleistocene samples analysed from the NCC sites produce homogeneous OSL, TT-OSL and pIR-IRSL De datasets suggesting that the NCC solution pipe deposits considered here are generally not affected by syn-depositional mixing complications that can take place within closed karst cavities (i.e., the remobilisation of unbleached grains from pre-existing cave floor sediments, and their subsequent translocation and incorporation into deposits within deeper parts of the cavity along with externally bleached, allochthonous grain populations). Detailed examination of solution pipe dynamics at Smoke Tortoise Cave (SMT) reveals a complex accumulation history focused on the marine isotope stage (MIS) 9 and MIS 7 interglacial complexes, as well as the MIS 8e interstadial. The SMT case study highlights that NCC solution pipes are not simply associated with short-lived opening and sediment accumulation events, but may involve multiple, discontinuous deposition episodes and reactivation events. An initial multi-site examination of all published NCC infill chronologies (n = 70) appears to suggest statistically significant, preferential solution pipe development during the relatively wet parts of interglacial or interstadial cycles. The non-uniform infill age distribution implies that NCC solution pipe dynamics may have exerted taphonomic biases on fossil accumulation, which should be taken into consideration when reconstructing long-term palaeoecological histories from NCC solution pipe cavities.  相似文献   

8.
Loess-palaeosol deposits of the Upper Pleistocene cover an extensive territory in the south of Western Siberia. Previously, most studies of loess-palaeosol sequences were carried out on river bank sections of the Ob river around Novosibirsk and upstream of this location (Ob Loess plateau); more recently, the focus of research has shifted towards the inner part of the Cis-Altai plain. Despite a good knowledge of the structure of regional loess-palaeosol sequences, there is a considerable lack of absolute dating beyond the radiocarbon limit. However, recent high resolution luminescence dating of a key Marine Isotope Stage 5 (MIS 5) stratotype at Lozhok has identified the presence of a long hiatus in the deposit. As a result, the published ages of the main units have been underestimated, because the existing chronology is largely based on palaeosol counting. This new observation argues for an urgent re-evaluation of the accepted chronostratigraphy of Western Siberian Late Quaternary. Here we present the first luminescence data for a loess-palaeosol sequence of the Cis-Altai plain, at the Solonovka key section, using both quartz optically stimulated luminescence and feldspar post-infrared infrared stimulated luminescence from 25 samples. The results show that the deposits were formed during the Late Pleistocene. The ∼1 m thick well-developed upper pedocomplex (PC1) has cryoturbation cracks filled with upper loess; this a characteristic regional benchmark for stratigraphic correlation. Two distinct hiatuses in sedimentation are found in the section: at the boundary of MIS 3/2, and after the formation of the MIS 5 Berdsk pedocomplex (PC3 and 2) until the beginning of the formation of MIS 3 deposits. The age of the thick PC3 palaeosol at the base of the section is determined as MIS 5, confirming evidence for the pronounced Kazantsevo (Eemian) interglacial in the loess-palaeosol record of Western Siberia. The results of our study emphasize the importance of understanding the palaeogeomorphological background to soil development, and the necessity of absolute chronology; we consider that the position of MIS 5 in the regional chronostratigraphic chart of South Western Siberia requires further study.  相似文献   

9.
The south of Western Siberia is an important part of the Eurasian loess belt, containing an extensive record of Quaternary landscape and climate evolution in up to 100 m thick loess deposits with as many as 10 pedocomplexes. However, this important Quaternary archive lacks a reliable absolute chronology, and this has prevented the linking of the widely accepted regional chronostratigraphic correlations with those of other parts of the Eurasian loess belt. Here we present the first results of detailed luminescence dating of the Late Pleistocene loess-palaeosol sequence at the Western Siberian stratotype section of Lozhok. According to the classical regional chronostratigraphic scheme, this sequence records the main stages of the environmental evolution of the region, including three palaeosols correlated with the warming stages of MIS 5e, MIS 5c and MIS 3. Our absolute chronology is based on 38 new luminescence ages (OSL, IR50, pIRIR290). Good agreement between the OSL and pIRIR290 ages suggests sufficient bleaching before deposition. The resulting chronology reveals that, rather than being only Upper Pleistocene in age, the loess-palaeosol sequence at Lozhok actually formed in the Middle and Upper Pleistocene. The ages of individual horizons do not correspond to the previously accepted stratigraphic units and morphological features of pedocomplexes. Our Bayesian chronological model reveals remarkable variation in dust accumulation and preservation at the site. The new results unambiguously identify the presence of an erosional boundary with a hiatus lasting ∼90 ka. The upper pedocomplex, immediately below this discontinuity, formed in sediment deposited between 131 ± 9 ka and 122 ± 11 ka and clearly corresponds to MIS 5. The lower pedocomplex is found in sediment deposited between 240 ± 12 and 199 ± 9 ka, and correlates closely with MIS 7. These new findings demonstrate the urgent need for a wider programme to date the main stratotypes of loess-palaeosol sections in Western Siberia. Only then can the global implications of the regional climate record in this important continental-scale archive be correctly interpreted.  相似文献   

10.
Despite the nearly 600 named species of the land snail Cerion, studies of the geological and paleontological framework of modern species are few. To address this deficiency, the biostratigraphic succession of Cerion was investigated at several areas on Long Island, Bahamas. A chronostratigraphic framework was developed through whole-rock and Cerion land snail aminostratigraphies. About 175 individual Cerion shells from last interglacial and Holocene deposits were age-ranked using stratigraphic position and amino acid racemization (AAR) geochronology. AAR ages were generated using an existing AAR-14C age model for Cerion from the central Bahamas. The age structure of Cerion fossils in sediments was determined with AAR ages, and the magnitude of “dead carbon” anomalies was evaluated using this chronological approach.Temporal changes in gross shell morphology were examined from four study areas. The last interglacial, marine isotope stage/substage (MIS) 5e (Aminozone E) is characterized by generally large shells and in some cases, bimodal sets of very small (α shells) and very large forms (β shells) coexisting in the same stratigraphic levels (primarily soils), which may encompass the transition from between MIS 5e and 5d/c. Similar bimodality of nearly identical α and β shell forms and sizes is observed at other late MIS 5e sites from the furthest reaches of Great Bahama Bank (including Long, Exumas, Eleuthera, and New Providence Islands). The widespread distribution of α and β forms in soils capping MIS 5e marine and eolian deposits implies that there may have been a synchronous, regional morphological convergence on Great Bahama Bank. None of these forms are observed in Holocene deposits of Aminozone A.The earliest MIS 1 Cerion appear in a oolite deposited 6500 a BP, and are of intermediate size compared to the Pleistocene α and β forms. As MIS 1 progressed, the diversity of shell sizes and shapes increased into modern times. The greater variety of shell forms over the past 1000–2000 a suggests that humans may have played a role in the introduction and redistribution of Cerion across the region. The potential for frequent and widespread human introductions, combined with the propensity of Cerion to hybridise freely may explain the farrago of shell sizes and shapes in the recent snail faunas of Long Island and other Bahama islands.  相似文献   

11.
The taxonomy of the land-snail genus Cerion, and the relevance of hundreds of shell forms to phylogenetic and evolutionary processes has been the subject of much discussion over the past few decades. Fundamental to understanding evolutionary trends is the independent confirmation of the age, biostratigraphic, and chronostratigraphic order of a comprehensive set of fossil forms. Amino acid racemization (AAR) is a geochronological tool applicable to dating living and fossil Cerion shells. The extent of racemization of aspartic acid (Asp D/L) and glutamic acid (Glu D/L) were determined for 507 Cerion shells dating between the early last interglaciation (marine isotope stage (MIS) 5e, c. 125 ka) and the present from the Bahamas. The AAR data based on Cerion support the established morphostratigraphic succession of deposits younger than MIS 5e and provide greater resolution, particularly for biostratigraphic successions of Holocene age. Age models were constructed for Asp and Glu using D/L values paired with 14C ages and historical collection dates from 23 Cerion shells. In addition to the relative-age time series, the Holocene age models developed from D/L Glu and Asp apply to the last 7 ka and geographically within the central Bahamas. In two case studies, large numbers of AAR-generated ages provide insights into the age structure of accretionary soils and rates and age constraints on evolutionary processes related to Cerion land snails.  相似文献   

12.
We have established a plausible rate of uplift near Siracusa in southeastern Sicily (Italy) over the last glacial–interglacial cycle using U-series ages of submerged speleothem calcite and 14C ages of calcite serpulid layers that encrust the speleothems during cave submergence. The precisely determined ages of these sea level benchmarks were compared with expected relative sea level position based on glacio-hydro-isostatic modeling to assess the rate of uplift in this region. When combined with the age of various late Holocene archaeological sites that have been recently described and characterized in terms of their functional position relative to sea level these data collectively define a rate of uplift ≤0.4 mm a?1 along this portion of the Sicilian coastline. These results are consistent with an age assignment of marine isotope stage (MIS) 5.3 or 5.5 for the Akradina terrace, which in turn places temporal constraints on paleoshorelines above and below this level.  相似文献   

13.
Reliable chronology is critical for reconstructing estuarine delta process. In this study, detailed chronological framework has been performed on a core HPQK01 (52 m in depth) from the central Pearl River delta (PRD) of China. Both quartz OSL and feldspar post-IR IRSL (pIRIR) methods for late Pleistocene sediments, as well as radiocarbon dating for Holocene sediments, were applied to date the core. Results show that quartz OSL ages range from 125 ± 18 ka to 58 ± 6 ka, and that all of them were minimum ages due to the OSL signal saturation. Feldspar pIR200IR290 protocol shows some overestimation in dose recovery test, with the recovered to the given ratio of 1.2, while a ratio of around 1 was obtained for feldspar pIR50IR250 signals. Robust ages have been obtained from feldspar fading corrected pIR50IR250 dating with ages ranging from 150 ± 17 ka to 98 ± 12 ka. AMS 14C results suggest that subtidal-intertidal zone was deposited during the middle Holocene from 8.21 ± 0.19 cal ka BP to 4.99 ± 0.25 cal ka BP. The sedimentology of core HPQK01 record two marine transgressive-regressive cycles. Based on the dating results, the lower fluvial sediment unit (T2) could be correlated to marine isotope stage (MIS) 6, and the lower marine unit (M2) was deposited during MIS 5. A sedimentary hiatus occurred with age range of from MIS 4 to MIS 2. Since middle Holocene, another marine stratum (M1) has been accumulated. Overall, our findings suggest that feldspar pIRIR dating method has the potential to establish the Quaternary chronostratigraphic framework of the PRD for samples with ages within 150 ka.  相似文献   

14.
The Galería de las Estatuas is a Mousterian site located within the Cueva Mayor-Cueva del Silo karstic system at the Sierra de Atapuerca (Burgos, Spain). This site is characterised by an important Upper Pleistocene stratigraphic sequence in which a large number of lithic artefacts exhibiting clear Mousterian affinities and a rich assemblage of faunal remains have been found.Additionally, this site has yielded a foot phalanx of a clear Neanderthal affinities and its sediment has yielded Neanderthal mitochondrial and nuclear DNA.Two test pits, GE-I and GE-II, have been excavated since 2008 which have been divided in 5 and 2 lithostratigraphical units, respectively. A minimum age of 45 ka cal BP for this site was obtained by radiocarbon dating in GE-II. This chronology was refined using single-grain Optically Stimulated Luminescence (OSL: 80–112 ka in GE-I and 70–79 ka in GE-II) and single-grain thermally transferred OSL (TT-OSL). Although in all case TT-OSL ages were systematically older than their single-grain counterparts. The detrital sequence is sealed by a flowstone whose base is dated to 53.7 ± 3.5 ka cal BP using U-series dating.In order to better constrain the age of this site, nine herbivorous teeth were collected from the whole sedimentary sequence to be dated by the ESR/U-series dating method though only seven provided modelled ages. Six of them were collected from levels 2 to 5 of the GE-I test pit while the last tooth was taken from level 2 of the GE-II test pit. Our results, ranging between 80 and 110 ka, are in agreement with those obtained by single grain TT-OSL and suggest that the sedimentological levels containing Mousterian lithic artefacts and faunal and human remains began to be deposited during the second part of the MIS5. These results fill a temporal gap in the chronology of the Atapuerca sites for which no contemporary MIS5 date was obtained until recently.  相似文献   

15.
The establishment of a chronology for late Middle Palaeolithic sites on the right bank of the Rhône valley in southeastern France is important for the knowledge of Neandertal dynamics and their demise in this area. The suite of dating methods that are directly applicable to fossils is limited for this period, especially around 50 ka where radiocarbon dating is beyond its technical limits. Currently applied to Middle and Lower Pleistocene periods, the use of combined ESR/U-series dating on Upper Pleistocene samples led to new issues, such as the acquisition of an age for samples yielding low equivalent doses and low uranium content in dental tissues. The gamma dose rate measurement thus plays a key role in age calculation. Beyond the discussion on methodological issues, the present study contributes to the establishment of a chronological framework that covers the Neandertal occupations between MIS 5 and MIS 3 for this area.  相似文献   

16.
The major uncertainty in relating cosmogenic-nuclide exposure ages to ages measured by other dating methods comes from extrapolating nuclide production rates measured at globally scattered calibration sites to the sites of unknown age that are to be dated. This uncertainty can be reduced by locating production rate calibration sites that are similar in location and age to the sites to be dated. We use this strategy to reconcile exposure age and radiocarbon deglaciation chronologies for northeastern North America by compiling 10Be production rate calibration measurements from independently dated late-glacial and early Holocene ice-marginal landforms in this region. 10Be production rates measured at these sites are 6–12% lower than predicted by the commonly accepted global 10Be calibration data set used with any published production rate scaling scheme. In addition, the regional calibration data set shows significantly less internal scatter than the global calibration data set. Thus, this calibration data set can be used to improve both the precision and accuracy of exposure dating of regional late-glacial events. For example, if the global calibration data set is used to calculate exposure ages, the exposure-age deglaciation chronology for central New England is inconsistent with the deglaciation chronology inferred from radiocarbon dating and varve stratigraphy. We show that using the regional data set instead makes the exposure age and radiocarbon chronologies consistent. This increases confidence in correlating exposure ages of ice-marginal landforms in northeastern North America with glacial and climate events dated by other means.  相似文献   

17.
Chronologies of glacial advances during the last glacial period in the Nyainqentanglha mountain range may provide constraints on the past climate in a transition zone of the Asian monsoon.We present 15 new10Be exposure ages from two moraines in the Payuwang valley,on the north slope of the range.The inner moraine has exposure ages ranging from 18.0±1.7 to 30.6±2.8 ka(n=10),with a mean age of 23.8±4.0 ka,corresponding to the global Last Glacial Maximum(LGM).The outer moraine yields exposure ages ranging from 18.0±1.6 to 39.9±3.7 ka(n=5).Evidence for weathering leads us to view the oldest age as a minimum age,placing moraine formation during MIS3.Chronologies from the last glacial period from south slope of the Nyainqentanglha support this interpretation.Thus,there appears to have been a local LGM(LLGM)during MIS3 and a more limited glacial advance during the global LGM.Glacial advances during MIS3 in the Nyainqentanglha may correlate with millennial-scale climate change(Heinrich events).  相似文献   

18.
A major reduction in summer temperatures during a Middle Pleistocene glacial cycle caused the most extensive glaciation recorded in the Mediterranean region. Glaciers in the mountains of Greece formed during marine isotope stage (MIS) 12 (474 000–427 000 years BP) under climatic conditions characterised by mean summer temperatures at least 11 °C cooler than today and annual precipitation of ≤ 2300 mm at the equilibrium line altitude (1741 m a.s.l.). This represents the coldest mean summer temperatures recorded in Greece during at least the last 430 000 years. Later Pleistocene glaciations (MIS 6 and 5d-2) were characterised by warmer summer temperatures and higher annual precipitation.  相似文献   

19.
Optically stimulated luminescence (OSL) dating of a series of glaciofluvial/glaciodeltaic sediments in central Buchan and Aberdeen has recently been undertaken. The aims of this project are to test the chronological model proposed by the most recent regional review and the suggestion that parts of Buchan may have remained ice-free during the last glacial maximum (late marine isotope stage (MIS) 3 and MIS 2 29–15 ka). The preliminary results indicate that during the Devensian (ca. 116–12 ka), extensive areas of Buchan may have been glaciated earlier than previously believed (possibly during MIS 4, 72–60 ka), but parts of the region show no depositional evidence of later glaciation. Some waterlain sediments from the Ugie Valley have yielded OSL ages indicating deposition during MIS 5d to MIS 5a (116–72 ka). We discuss whether the absence of overlying glaciogenic sediments at these locations raises questions about the reliability of the OSL ages or about existing models of the Devensian glaciation of Buchan.  相似文献   

20.
Quartz optically stimulated luminescence (OSL) forms the basis for the chronology of Weichselian ice advances in Arctic Eurasia developed over the last few years. There is almost no age control on this chronology before 40 ka, except for some marine sediments correlated with marine isotope stage (MIS) 5e on the basis of their palaeofauna. Results from more southern latitudes have shown that dose estimates based on quartz OSL and the single aliquot regenerative (SAR) dose procedure may underestimate the age of MIS 5e deposits. Here we use the same method to date well-described marine sediments, thought to have been deposited during the very beginning of the Eemian interglacial at 130 ka, and exposed in two sections on the river Sula in northern Russia. Various quality-control checks are used to show that the OSL behaviour is satisfactory; the mean of 16 ages is 112±2 ka (σ=9 ka). This represents an underestimate of 14% compared to the expected age, a discrepancy similar to that reported elsewhere. In contrast to SAR, the single aliquot regeneration and added (SARA) dose procedure corrects for any change in sensitivity during the first OSL measurement. The SARA results are shown to be 10% older than those from SAR, confirming the geological age estimate and suggesting that SAR ages may underestimate older ages (larger doses), despite their good performance in the younger age range.  相似文献   

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