Optimizing sampling strategy for radiocarbon dating of Holocene fluvial systems in a vertically aggrading setting

In this paper we address the question of how to determine the period of activity (sedimentation) of fossil (Holocene) fluvial systems in vertically aggrading environments. Our data base consists of almost 100 ¹⁴C ages (partly AMS) from the Rhine–Meuse delta in the central Netherlands. Radiocarbon samples from the tops of lithostratigraphically correlative organic beds underneath overbank deposits (sample type 1) yield consistent ages, indicating a synchronous onset of overbank deposition over distances of at least up to 20 km along channel belts. Similarly, ¹⁴C ages from the base of organic residual channel fills (sample type 3) generally indicate a clear termination of within-channel sedimentation. In contrast, ¹⁴C ages from the base of organic beds overlying overbank deposits (sample type 2), commonly assumed to represent the end of fluvial sedimentation, show a large scatter reaching up to 1000 ¹⁴C years. This setting usually produces ¹⁴C ages significantly younger than residual channels of the same fluvial system, indicating the presence of non-depositional unconformities. These usually occur on top of slightly elevated sediment bodies (especially natural levee deposits), which often contain palaeosols. Such hiatuses appear to be much more abundant than hitherto supposed. We conclude that a combination of sample types 1 and 3 generally yields a satisfactory delimitation of the period of activity of a fossil fluvial system. The problems associated with ¹⁴C samples of type 2 may also be present in coastal areas with an alternation of tidal deposits and organic beds.     

Cosmogenic 10 Be ages on the Pomeranian Moraine, Poland

Rinterknecht, V. R., Marks, L., Piotrowski, J. A., Raisbeck, G. M., Yiou, F., Brook, E. J. & Clark, P. U. 2005 (May): Cosmogenic ¹⁰Be ages on the Pomeranian Moraine, Poland. Boreas , Vol. 34, pp. 186–191. Oslo. ISSN 0300–9483.
We measured the ¹⁰Be concentrations in boulders collected from the Pomeranian Moraine in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS) in the Polish Lowland. The mean age of 8 ¹⁰Be ages of the Pomeranian Moraine in northwestern Poland is 14.30.8 ¹⁰Be ka, while in northeastern Poland the mean age of 19 ¹⁰Be ages of the moraine is 15.00.5 ¹⁰Be ka. Given the excellent agreement between the two age groups, we calculate a mean age of 14.80.4 ¹⁰Be ka for final deposition of the Pomeranian Moraine of northern Poland. The age of the Pomeranian Moraine suggests that the southern margin of the SIS was near its maximum extent in Poland at a younger time than previously inferred, and that retreat from the moraine at 14.80.4 ¹⁰Be ka probably occurred in response to the onset of the Bølling interstade.     

Chronology and organic chemistry of the Black Creek Swamp Megafauna site (Late Pleistocene), Kangaroo Island, Australia

The timing of the extinction of the Australian Megafauna and whether it was simultaneous and widespread has been a much researched topic in Quaternary geoscience. The Black Creek Swamp Megafauna site on Kangaroo Island was thought to be a refugium for Megafauna; however, recent and multidiscipline age determinations have established that the fossils are considerably older than the well-quoted extinction age of 45 kyr. Further radiocarbon age determinations, δ¹³C isotope analysis and ¹³C-NMR spectroscopy of the fossil containing organic matter demonstrates that it is highly soluble and accumulated as recently as 31–18 cal. kyr BP. These radiocarbon ages are much younger than the 100–50 kyr age bracket ascertained for the fossil material itself, implying separate episodes of death, deposition and burial. The soluble nature of the organic matter and increasing radiocarbon ages with depth suggests lateral accumulation, probably transported by subsurface waters from elevated areas proximal to the low-lying swamp. Such depositional conditions and ¹⁴C age range implies that the site may have experienced an unusually wet Last Glacial Maximum, due maybe to its proximity to the continental shelf and thus to maritime conditions. C3 vegetation dominates the Black Creek Swamp and its organic matter (δ¹³C; −30‰ and −23‰); however, variations in δ¹³C may indicate climatic shifts. ¹³C-enrichment and an abundance of salt-tolerant gastropods within the site's final phase of sediment accumulation (<6 cal. kyr BP) suggest that conditions during this most recent period were not as wet as those of the Last Glacial Maximum.     

Lateglacial older and younger coversand in northwest Europe: chronology and relation to climate and vegetation

Kolstrup, E. 2007 (January): Lateglacial older and younger coversand in northwest Europe: chronology and relation to climate and vegetation. Boreas , Vol. 36, pp. 65–75. Oslo. ISSN 0300–9483.
Dutch, Belgian, German and Danish Lateglacial localities with both coversand and well-dated organic deposits are used to relate older and younger coversand development to changes in climate and vegetation. The number of well-dated coversand sequences in northwest Europe is low, but it appears that the transition from older to younger coversand was asynchronous and spanned Bølling sensu stricto to late Allerød, so there is no clear single cause for the change in grain-size composition of the sediment. Aeolian activity took place during all parts of the Lateglacial and seems to have continued well into the Holocene. The effect of changing temperatures is mainly reflected indirectly as periods with denser vegetation, especially forest, that led to reduced coversand net-accumulation. The outline proposes that the lithostratigraphic position of a peat layer cannot be used as an Allerød marker because even a well-developed peat layer within coversands may differ in age from one area to the next. The combined coversand and vegetation development shows that local conditions were important for the accumulation and preservation of sediments.     

The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia

BOREAS Griffey, N. J. & Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66^oN. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread 'Little Ice Age' event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the 'Little Ice Age' maximal limit appear to date from about 3000-2500 ¹⁴C years B.P. and a younger period tentatively dated as about 1250-1000 ¹⁴C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 ¹⁴C years B. P. and prior to 3000 ¹⁴C years B.P. was forthcoming.     

A chronostratigraphic comparison of Late-Weichselian and Late-Devensian subdivisions, illustrated by two radiocarbon-dated profiles from western Britain

¹⁴C-dated percentage and absolute late-glacial pollen diagrams from (1) Blelham Bog, north-west England and (2) Cam Loch, north-west Scotland arc subdivided into chronozones Bølling, Older Dryas, Allerød, and Younger Dryas as proposed for the Late-Weichselian sequence by Mangerud et al., Boreas 3 (1974), with boundaries defined in conventional ¹⁴C years. It is shown how these chronozone boundaries coincide in the two British pollen diagrams with boundaries between pollen assemblage zones which are interpreted as the results of environmental (climatic) changes. Differences between the pollen zones found in western Britain and those of the classic South Scandinavian profiles, which are interpreted as the consequence of regional differentiation in the vegetation of north-west Europe circa 14,500 to 10,000 years ago, pose serious problems in the correlation of Late-Weichselian and Late-Devensian subdivisions on the basis of pollen assemblage zones, but a chronostratigraphical classification makes it possible to compare the Late-Devensian profiles from western Britain with the Late-Weichselian subdivisions of Mangerud et al., in which 'chronozone boundaries seem to be climatically conditioned within southern Scandinavia'.     

Norwegian corals: radiocarbon and stable isotopes in Lophelia pertusa

The ahermatypic coral Lophelia pertusa which produces aragonitic skeletons is widely distributed along the Norwegian coast. Specimens from a number of localities have been analyzed for oxygen and stable carbon isotope composition and ¹⁴C age. Stable isotope ratios of recent corals provide information on growth rate and seasonality of oceanographic conditions. Lophelia can be useful in paleoenvironmental reconstructions. ¹⁴C dates of fossil Lophelia from Drøak in the Oslofjord, collected from 20 m ahove and 40 m below present day sea-level, indicate regional extinction between 8700 and 7800 years ago. We suggest that the extinction resulted from the cut-off of deep waters by a rising sill in connection with the postglacial shoreline displacement. Radiocarbon dating of coral bushes suggests a fairly rapid growth rate as older and younger parts of recent corals do not reveal any difference in activity despite the short time scale of the history of bomb-produced ¹⁴C in the oceans.     

Late Glacial stable isotope record, radiocarbon stratigraphy, pollen and mollusc analyses from the Geiseltal area, Central Germany

Combined investigations of isotopes, pollen, and molliisc shells were carried out on a Latc Glacial limnic high-resolution sediment sequence from the Geiseltal open-cast mine in Central Gcrmany. The dala confirm thc division of the Late Glacial biozones into two colder (Older and Younger Dryas) and two warmer periods (Bølling, Allcrød), which have already bccn cstablishcd lor the Central and Northern German area. Radiocarbon data, mainly based on wood material, cover a time span between c , 10 800 BP and 12 760 BP, indicating a mean sedimentation rate of c . 2 mm/yr. The stable isotope data (δ¹⁸O, δ¹³C) reflect the transition periods between the climatic phases as changes in relative air humidity (transition from dry, cold to warmer. more humid conditions). The dominance of evaporation effects, however, is superimposed on any ternpcratiirc aignal throughout the profile. Repeated conversions of the hydrologic regime (silting-up phases. lake-level variations) characterize the specific history of the lake development.     

A widespread positive δ13Ccarb anomaly at around 2.33–2.06 Ga on the Fennoscandian Shield: a paradox?

Carbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ¹³C (PDB) spanning - 20.5% to + 11%. A general δ¹³C secular trend shows that prior to 2.33 Ga values are typically 'normal' marine, averaging around - 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ¹³C of around + 6%. Post-Jatulian time is characterized by δ¹³C of sedimentary carbonates fluctuating between - 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ¹³C between - 14 % and - 6% . The c. 6% positive δ¹³C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of 'red beds', but does not coincide with the maximum of buried C_org mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ¹³C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the 'Ronov ratio', and/or 'Broecker ratio' and other possible models are discussed as the target for future investigations.     

Deglaciation and palaeoclimate of the Andfjord-Vågsfjord area, North Norway

This paper reviews the deglaciation history and palaeoclimate from 22 to 9.5 ¹⁴Cka BP in the Andfjord-Vagsfjord area. Eight main glacial events are recorded: The Egga-I (>22 ¹⁴Cka BP), the Bjerka, the Egga-II (>14.6 ¹⁴Cka BP), the Flesen (14.5 ¹⁴Cka BP), the D (13.8–13.2 ¹⁴Cka BP), the Skarpnes (12.2 ¹⁴Cka BP), the Tromsø–Lyngen (10.7–10.3 ¹⁴C ka BP) and the Stordal (10.0–9.5 ¹⁴Cka BP). Onset of the final deglaciation occurred about 14.6 ¹⁴Cka BP. Most of the western part of the Fennoscandian and Barents Sea Ice Sheets receded from the outer continental shelf 15–14 ¹⁴Cka BP. The delivery and melting of icebergs at this time to the Norwegian-Greenland Sea resulted in a low oxygen isotope event recorded in a number of cores in the region. Atlantic water intruded the area 13.2 ¹⁴Cka BP, and an atmospheric warming commenced 12.9/12.8 ¹⁴Cka BP. A marked glacial recession occurred before the Skarpnes event. During Allerød time, the glaciers retreated to the fjord heads or even farther inland. The Fennoscandian outlet glaciers readvanced (locally more than 40 km), reached their Younger Dryas outer limit after 10.7 ¹⁴Cka BP and retreated from this position before about 10.3 ¹⁴Cka BP.     

Late-Glacial radiocarbon- and palynostratigraphy on the Swiss Plateau

A detailed late-glacial radiocarbon stratigraphy for the Swiss Plateau has been established on the basis of over 90 accelerator ¹⁴C dates on terrestrial plant macrofossils. Two plateaux of constant.,¹⁴C age were observed, occurring at 12,700 B.P. and at 10,000 B.P. The consequences of these plateaux for palaeo-ecological investigations are threefold: (1) a more refined ¹⁴C dating within the plateaux is not possible, (2) in teleconnections between different sites (if based on ¹⁴C dating and concerning the periods around 12,700 B.P. and 10,000 B.P.) events are considered synchronous which are only synchronous within a plateau of constant age, and (3) exact time-depth relationship and therefore influx calculations are made impossible during these plateau periods. A comparison of the radiocarbon ages derived from terrestrial, telmatic and limnic material at different sites on the Swiss Plateau yields a proposal for modifying the zonation system of Welten for the Late-Glacial. By retaining the limits of chronozones (at 13, 12, 11 and 10ka B.P.) and by refining the palynostratigraphic criteria for the limits of biozones, a separation between chrono- and biozonation at the beginning of the Belling and at the beginning of the Younger Dryas becomes obvious.     

The Use of Multiple Reference Samples for the Monitoring of Ion Microprobe Performance During Zircon 207Pb/206Pb Age Determinations

Data from a series of extended analytical sessions using a range of different zircon reference samples have been used to investigate the periodic derivation of abnormal ²⁰⁷Pb/²⁰⁶Pb ages during microbeam analysis%For the Canberra SHRIMP II, this phenomenon probably results from the presence of a signal at mass 204 that is alien to the Pb spectrum; isotopic fractionation is unlikely to be a significant contributor. In contrast, abnormal ²⁰⁷Pb/²⁰⁶Pb ages obtained from SHRIMP I at the same research centre require a different, but as yet unknown explanation. Assessment of the reasons for atypical ^207Pb/²⁰⁶Pb measurements and the means of correcting for them should therefore be independently assessed for individual analytical instruments. The use of reference samples with very different ages is an effective way of doing this, because older reference samples are more useful for documenting isotopic fractionation, whereas younger ones are more sensitive indicators of isobaric interference.     

10Be chronology of the last deglaciation of County Donegal, northwestern Ireland

A well-preserved moraine on the northern coast of County Donegal, Ireland, has played a critical role in our understanding of the glacial history of this sector of the Irish Ice Sheet (IIS). Because of a lack of numerical dating of the moraine, however, previous interpretations of its age and significance to the glacial history of this region have varied widely. Here we report eight in situ cosmogenic ¹⁰Be ages on boulders sampled from the moraine. Two of these ages are outliers, with the remaining six ranging from 18.8±1.0 ¹⁰Be kyr to 20.9±1.3 ¹⁰Be kyr, with an uncertainty-weighted mean age of 19.4±0.3 ¹⁰Be kyr (19.4±1.2 kyr accounting for production rate uncertainty). Our results confirm one previous ¹⁰Be age obtained from the moraine, with the combined data ( n =7) constraining the age of initial deglaciation of the IIS from its LGM position on the continental shelf to be 19.3±0.3 ¹⁰Be kyr (19.3±1.2 kyr accounting for production rate uncertainty). These ages are in excellent agreement with calibrated ¹⁴C ages that constrain retreat of the IIS margin from the continental shelf elsewhere in northwestern and western Ireland and the Irish Sea Basin associated with the start of the Cooley Point Interstadial (≥20–≤18.2 cal. kyr BP), suggesting widespread deglaciation of the IIS ∼19.5–20 kyr ago.     

The Fossvogur marine sediments in SW Iceland - confined to the Allerød/Younger Dryas transition by AMS 14 C dating

An exhaustive ¹⁴C dating programme of molluscs from the Fossvogur sediments in Reykjavik. Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm earlier conclusions of a widespread occurrence of marine sediments of Allerød age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow ¹⁴C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional ¹⁴C age is 11,400 BP. Assuming a reservoir effect of 400 years. this corresponds to a reservoir-corrected age of I1,000 BP. i.e. the Allerød- Younger Dryas transition for the sampled units, These new ¹⁴C dates from Fossvogur confirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The dates suggest that the marine units in Fossvogur accumulated within a restricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explain anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. δ¹³C and δ¹⁸O results suggest that temperatures may have ranged up to 60°C.     

Chronology and paleoenvironments during the late Weichselian deglaciation of the southwest Iceland shelf

Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 ¹⁴C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Foraminifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 ₁₄C ka BP with an abrupt increase in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 ¹⁴C ka BP. A slight warming recorded in the uppermost glacial-marine sediments was interrupted by an inferred jökulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 ¹⁴C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 ¹⁴C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 ¹⁴C ka BP. Conditions similar to those today were established by 9.7 ¹⁴C ka BP.     

Pollenanalytische und geochronologische Untersuchungen zur Piottino-Schwankung (Jüngere Dryas)

New pollen-analytical investigations and two ¹⁴C series indicate that, at the Bedrina on Mount Piottino (Tessin, Switzerland), the post-Allerød NAP phase (Piottino oscillation) represents the well-marked Younger Dryas at least for the most part. The late-glacial part of the profile is re-classified, and the term Piottino oscillation is rejected, as it is largely identical with the Younger Dryas. Individual ¹⁴C dates from the transition between the Younger Dryas and the Preboreal should be considered critically. Considerable fluctuations in the ¹⁴C level are supposed for this period.     

Late and Middle Weichselian stratigraphy of Andøya, north Norway

BOREAS Vorren, K.-D. 1978 03 01: Late and Middle Weichselian stratigraphy of Andøya, north Norway, Boreas, Vol. 7, pp. 19–38. Oslo. ISSN 0300–9483.
Bio-stratigraphy and ¹⁴C datings from Lake Endletvatn, 69^o 44'N and 19^o05'E, approx. 35 m above sea level, suggest that the lacustrine sedimentation started about 18,000 B.P. The Middle Weichselian vegetation was probably a dry arctic, partly barren, grassland type with abundant Draba spp. and perhaps also Braya spp. Two climatic ameliorations of this chronal substage, named Endletvatn thermomers 1 and 2 (ET 1 and 2), have been recorded. During ET 2, the beginning of which has been dated at about 15,000 B.P., a humid climate prevailed, with a July temperature probably not deviating much from the present one. The colonization by low alpine and subalpine species probably started in the Bølling Chronozone. During the early Allerød Chronozone, protocratic conditions with grasses RumexlOxyria, Papaver and Sagina of. saginoides prevailed. During the middle of the Allerød, stable soil and continuous vegetation was established at sheltered places. At the transition to the Younger Dryas Chronozone a climate favouring Artemisia changed this vegetational development. The middle of the Younger Dryas was cool and humid, probably with an upper low alpine vegetation. The end of this chronozone was characterized by a vegetation of low alpine heaths with Empetrum and Dryas.
Diatom analysis (Foged 1978) suggests that there has been no direct marine influence in the basin. The marginal moraine stratigraphy, the marine limit and the climatic development are discussed.     

Late Pleistocene glacial history of Jameson Land, central East Greenland, derived from cosmogenic 10Be and 26Al exposure dating

Previous work has presented contrasting views of the last glaciation on Jameson Land, central East Greenland, and still there is debate about whether the area was: (i) ice-free, (ii) covered with a local non-erosive ice cap(s), or (iii) overridden by the Greenland Ice Sheet during the Last Glacial Maximum (LGM). Here, we use cosmogenic exposure ages from erratics to reconcile these contrasting views. A total of 43 erratics resting on weathered sandstone and on sediment-covered surfaces were sampled from four areas on interior Jameson Land; they give ¹⁰Be ages between 10.9 and 269.1 kyr. Eight erratics on weathered sandstone and till-covered surfaces cluster around ∼70 kyr, whereas ¹⁰Be ages from erratics on glaciofluvial landforms are substantially younger and range between 10.9 and 47.2 kyr. Deflation is thought to be an important process on the sediment-covered surfaces and the youngest exposure ages are suggested to result from exhumation. The older (>70 kyr) samples have discordant ²⁶Al and ¹⁰Be data and are interpreted to have been deposited by the Greenland Ice Sheet several glacial cycles ago. The younger exposure ages (≤70 kyr) are interpreted to represent deposition by the ice sheet during the Late Saalian and by an advance from the local Liverpool Land ice cap in the Early Weichselian. The exposure ages younger than Saalian are explained by periods of shielding by non-erosive ice during the Weichselian glaciation. Our work supports previous studies in that the Saalian Ice Sheet advance was the last to deposit thick sediment sequences and western erratics on interior Jameson Land. However, instead of Jameson Land being ice-free throughout the Weichselian, we document that local ice with limited erosion potential covered and shielded large areas for substantial periods of the last glacial cycle.     

Palynological and oxygen isotope investigations on Late-Glacial sediment cores from Swiss lakes

Results from detailed pollen and ¹⁸O/¹⁶O studies on two sediment profiles from small Swiss lakes are reported. ¹⁸O/¹⁶O records in lacustrine carbonate contain paleoclimatic information because they reflect mainly the isotope ratio in rain and snow which is correlated to temperature. Several transitions between different climatic periods determined palyno-logically are also indicated by marked changes in the isotope ratios in both profiles, namely the transitions Oldest Dryas - Bøiling and Allerød - Younger Dryas - Preboreal. ¹⁸o/¹⁶O was 2 to 3 %0 lower during Younger Dryas than during the adjacent periods, corresponding to a temperature drop of a few degrees Centigrade according to a tentative estimate.     

Occurrence of varved lake sediment sequences in Varmland, west central Sweden: lake characteristics, varve chronology and AMS radiocarbon dating

Varved lake sediments can be used to set multiple environmental proxies within a calendar year time scale. We undertook a systematic survey of lakes in the Province of Värmland, west central Sweden, with the aim of finding continuous varved lake sediment sequences covering the majority of the Holocene. In Fennoscandia, such sediments have previously only been recorded in northern Sweden and in southern and central Finland. By following a selective process and fieldwork we discovered three new varved sites (i.e. Furskogstjärnet, Mötterudstjärnet and Kälksjön). We found that lakes with varved sediments have several common lake morphometry properties and lake catchment characteristics such as maximum water depth, maximum water depth/lake surface area ratio, catchment soil types, altitude and number of inflows. Varve chronologies, supported by AMS-¹⁴C dating and tephrochronology were established for two of the sediment profiles. These varve chronologies are the longest geological records with an annual resolution known to exist in Sweden. In Furskogstjärnet, the AMS- ¹⁴C dates based on terrestrial plant macrofossils at several levels deviate significantly from the varve based time-depth curve. In Motterudstjarnet, a fully reasonable time-depth model based on the ¹⁴C dates gives older ages in the lower part of the sequence compared to the varve chronology. These results highlight that seemingly acceptable AMS radiocarbon dates may be erroneous. They also point to the fact that varved lake sediments are reliable geological archives with respect to chronological control and accuracy. Thus, these archives should be of prime interest for studies of climate and environmental change undertaken with the aim of providing sub-decadal resolution proxy data sets.