Calibrated Radiocarbon Ages Research Articles

Lime muds and their genesis off-Northwestern India during the late Quaternary

Two sediment types were found in five gravity cores collected from water depths between 56 m and 121 m along the northwestern continental margin of India: lime muds were abundant in the lower section while siliciclastic sediments dominated the upper section. Lime mud-dominated sediments in shelf cores contained 60%–75% carbonate, 0.3%–0.6% Sr and terrigenous minerals, whereas those at the shelf break were found to have >90% carbonate, 0.6%–0.8% Sr and traces of terrigenous minerals. Aragonite needles showing blunt edges, jointed needles and needles wrapped in smooth aragonite cement were found to be common. Stable (O and C) isotopes of lime mud indicate a potentially freshwater contribution for shelf cores and purely marine contribution for those at the shelf break. Calibrated radiocarbon ages of the lime muds ranged from 17.6–11.9 ka in different cores. The results reported here suggest that the lime muds in the shallow shelf are probably reworked from the Gulf of Kachchh, whereas those at the shelf break were biodetrital, initially formed on the carbonate platform during low stands of sea level and then exported. The change in lime mud-dominated to siliciclastic-dominated sediments in the cores may be due to climate change and rapid rise in sea level during the early Holocene.

Hydrological control of the dead carbon fraction in a Holocene tropical speleothem

Over the past decade, a number of speleothem studies have used radiocarbon (14C) to address a range of palaeoclimate problems. These have included the use of the bomb pulse 14C to anchor chronologies over the last 60 years, the combination of U-Th and 14C measurements to improve the radiocarbon age-calibration curve, and linking atmospheric 14C variations with climate change. An issue with a number of these studies is how to constrain, or interpret, variations in the amount of radioactively dead carbon (i.e. the dead carbon fraction, or DCF) that reduces radiocarbon concentrations in speleothems. In this study, we use 14C, stable-isotopes, and trace-elements in a U-Th dated speleothem from Flores, Indonesia, to examine DCF variations and their relationship with above-cave climate over the late Holocene and modern era. A strong association between the DCF and hydrologically-controlled proxy data suggests that more dead carbon was being delivered to the speleothem during periods of higher cave recharge (i.e. lower δ18O, δ13C and Mg/Ca values), and hence stronger summer monsoon. To explore this relationship, we used a geochemical soil-karst model coupled with 14C measurements through the bomb pulse to disentangle the dominant components governing DCF variability in the speleothem. We find that the DCF is primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than kinetic fractionation and/or variations in the age spectrum of soil organic matter above the cave. Therefore, we infer that periods of higher rainfall resulted in a higher DCF because the system was in a more closed state, which inhibited carbon isotope exchange between the karst water dissolved inorganic carbon and soil-gas CO2, and ultimately led to a greater contribution of dead carbon from the bedrock.

沖縄県宮古島南東部，マイバーバマに打ち上げられた津波石の分布とハマサンゴ化石の較正年代

沖縄県宮古島南東部，マイバーバマに打ち上げられた津波石の分布とハマサンゴ化石の較正年代

口絵3：沖縄県宮古島の南東海岸に打ち上げられた津波石の分布と較正年代

口絵3：沖縄県宮古島の南東海岸に打ち上げられた津波石の分布と較正年代

Holocene lake salinity changes in the Wimmera, southeastern Australia, provide evidence for millennial-scale climate variability

Palaeosalinity records for groundwater-influenced lakes in the southwest Murray Basin were constructed from an ostracod-based, weighted-averaging transfer function, supplemented with evidence from Campylodiscus clypeus (diatom), charophyte oogonia, Coxiella striata (gastropod), Elphidium sp. (foraminifera), Daphniopsis sp. ephippia (Cladocera), and brine shrimp (Parartemia zietziana) faecal pellets, the δ18O of ostracods, and >130μm quartz sand counts. The chronology is based on optically stimulated luminescence and calibrated radiocarbon ages. Relatively wet conditions are marked by lower salinities between 9600yr and 5700yr ago, but mutually exclusive high- and low-salinity ostracod communities suggest substantial variability in effective precipitation in the early Holocene. A drier climate was firmly in place by 4500yr and is marked at the groundwater-dominated NW Jacka Lake by an increase in aeolian quartz and, at Jacka Lake, by a switch from surface-water to groundwater dominance. Short-lived, low-salinity events at 8800, 7200, 5900, 4800, 2400, 1300 and 400yr are similar in timing and number to those recorded on Australia's southern continental shelf, and globally, and provide evidence for the existence of the ~1500-yr cycle in mainland southern Australia. We surmise that these are cool events associated with periodic equatorward shifts in the westerly wind circulation.

Rapid settlement of Majuro Atoll, central Pacific, following its emergence at 2000 years CalBP

[1] Atoll islands are areas of low, flat land, and the sustainability of habitable land in such environments is sensitive to even slight changes in sea level. The projected rise in sea level during this century may lead to the submergence of atoll islands and the widespread loss of habitable land. However, the actual time sequence of past sea level change, island emergence events, and human settlement of newly emerged islands remain poorly constrained. The results of geomorphological and archaeological surveys, combined with calibrated radiocarbon age dates, at Majuro Atoll, Marshall Islands, central Pacific, reveal that the emergence of the island, triggered by a fall in sea level, was quickly followed by human settlement. The elevation of the central body of the island exceeded high water level at 2000 years CalBP, and the complete formation of the island occurred within an interval of 100 years. The island was colonized by people shortly after emergence, at 2000 years CalBP, prior to the establishment of dense vegetation, and has been continuously settled since that time.

Radiocarbon dating of ancient Japanese calligraphy sheets and the discovery of 45 letters of a lost manuscript

Abstract The Miidera-gire is an ancient paper sheet with different, elegant calligraphy on both sides. One side contains a part of a Buddhist scripture from around the ninth to the twelfth century and written in cursive hand, while the other side contains a part of Monzen (an anthology of Chinese literary works). The paleographical style of this Monzen seems to be older than that of the Buddhist scripture and is similar to some Chinese manuscripts written in the Tang Dynasty (AD 618–907). However, amid these elegant calligraphic writings, there exist many copies and counterfeits that were written several centuries later. We, therefore, measured the radiocarbon age of the Miidera-gire by using accelerator mass spectrometry. The calibrated radiocarbon age indicated 666–776 [cal AD] (2σ error), thus leading to the conclusion that the Monzen was first written on the obverse side, and long afterwards, the Buddhist scripture was written on the reverse side. Since only a few incomplete books of Monzen were written before the ninth century, this calligraphy is one of the oldest of the existing Monzen manuscripts.

Sediment facies and Holocene deposition rate of near-coastal fluvial systems: An example from the Nobi Plain, Japan

Floodplains are a major component of present near-coastal fluvial systems that have evolved in response to postglacial changes in climate and sea level. Knowledge of sedimentary facies and deposition rates on a centennial to millennial time scale is required for considering floodplain evolution. Two cores, AP1 and AP2, were acquired from an abandoned channel of the Ibi River and its natural levee on the Nobi Plain, central Japan. Sediment facies analysis, electrical conductivity, and radiocarbon dating of borehole samples showed that in both cores organic-rich dark gray floodbasin mud overlies deltaic deposits dating to after approximately 3200 years calibrated radiocarbon age (cal BP) in relation to delta progradation. The accumulation of floodbasin mud continued at the both sites until about 400 cal BP. Around 400 cal BP, the mud was eroded by the overlying channel sand and gravel at AP1 and was covered by fine-grained natural levee deposits at AP2 with an abrupt contact. This timing is concordant with the historical record of avulsion of the Ibi River during the Keicho Era (AD 1596–1615). Averaged aggradation rates at the AP1 and AP2 sites were approximately 2.2 and 3.2 mm/yr, respectively. Faulting-related subsidence along the western edge of the plain has influenced these rates by creating accommodation. Averaged deposition rates differed greatly between the floodbasin and the levee, suggesting that rapid aggradation of the natural levee also occurred on a centennial to millennial scale. These empirical data may be useful for testing models of the architecture and evolution of near-coastal fluvial systems.

宮古島東平安名岬西方、太陽泉（ティダガー）で確認された石灰華段の形成年代

宮古島東平安名岬西方、太陽泉（ティダガー）で確認された石灰華段の形成年代

The 12.9-ka ET Impact Hypothesis and North American Paleoindians

A hypothesized extraterrestrial impact in North America at ∼12,900 calendar years BP (12.9 ka) has been proposed as the cause of Younger Dryas climate changes, terminal Pleistocene mammalian extinctions, and a supposed “termination” of the Clovis archaeological culture. In regard to the latter, however, an examination of archaeological, geochronological, and stratigraphic evidence fails to provide evidence of a demographic collapse of post-Clovis human populations, especially where the Clovis and post-Clovis site records are reasonably well constrained chronologically. Although few Clovis sites contain evidence of an immediate post-Clovis occupation, interpreting that absence as population collapse is problematic because the great majority of Paleoindian sites also lack immediately succeeding occupations. Where multiple occupations do occur, stratigraphic hiatuses between them are readily explained by geomorphic processes. Furthermore, calibrated radiocarbon ages demonstrate continuous occupation across t...

Optically stimulated luminescence dating of cave deposits at the Xiaogushan prehistoric site, northeastern China

The Xiaogushan cave site is one of the most important prehistoric sites in North China. The stone and bone artifacts found in the cave are similar to European contemporaneous artifacts. Cave deposits consist of five layers that have been dated from 46,353±1179 to 4229±135 cal. yr BP, using radiocarbon dating techniques on charcoal and bone samples collected from Layers 2–5. In this paper, optically stimulated luminescence (OSL) techniques were applied to date six samples taken from Layers 1–3. The luminescence properties of the fine-grained and coarse-grained quartz extracts indicate that the materials are suitable for OSL dating using a single-aliquot regeneration-dose (SAR) protocol. The OSL ages obtained are broadly consistent with the stratigraphy and the associated calibrated radiocarbon ages. The dating results show that the cave was first occupied by humans about 70ka. The human occupation of the cave may be related to climate change. An occupation hiatus is inferred to between ∼17 to ∼10ka. The stone and bone artifacts found in Layers 2 and 3 may indicate the Middle to Upper Paleolithic transitions in the region.

Aspartic acid geochronology of sediments from the ocean margin off of India

Aspartic acid racemization was studied in the clay and coarse fractions of sediments from southwestern Bay of Bengal (Core 1) in order to understand the role of terrestrial organic matter in the amino acid geochronology of Indian marginal sediments. Conventional radiocarbon ages were determined for the coarse carbonate fraction (>25 μm) of sediments, the core covering an age back to ∼40 kyr BP. Aspartic acid racemization rate constants ( k asp) were calculated for clay and coarse fractions of bulk sediments using a first order kinetic model and three horizons with constant k asp values were identified, corresponding to the periods from 0 to 5.5 kyr, 5.5 to 19 kyr and >19 kyr. Best fit models of high significance were derived from the relationship between aspartic acid D/ L ratio and calibrated radiocarbon ages as an alternative to racemization rate constants. To test the applicability of these first order kinetic and logarithmic models derived for Core 1, they were used to calculate ages for another sediment core (Core 2), calculated aspartic acid ages being consistent with radiocarbon ages. However, the logarithmic model gave better results than the first order kinetic model for older samples, suggesting that the logarithmic model is a better choice for the amino acid geochronology of Indian margin sediments. For both sediment fractions, aspartic acid ages based on the logarithmic model gave similar ages, consistent with radiocarbon ages and suggesting that there is no significant difference in aspartic acid racemization between both fractions of bulk sediment. As a result, the clay fraction can also be used for amino acid dating of Indian margin sediments.

An expanded radiocarbon age calibration procedure to correct for the marine reservoir effect in mixed marine and terrestrial samples

Recently, the importance of statistical and probabilistic analysis to derive accurate 14 C data has been recognized. This paper discusses a 14 C calibration procedure to correct marine reservoir effect using the marine source contribution estimated as a probability distribution. In addition, we also developed the marine source estimation with δ 13 C and δ 15 N for the 14 C calibration in order to cover a complex mixture of terrestrial and marine carbon such as a human. In our calibration procedure, the 14 C date is weighted with the probability distribution of marine source contribution and the calibrated date depended on the marine 14 C intake can be evaluated. The age range calibrated by our procedure can be also reduced more than by conventional calibration methods. We illustrated the character of our calibration procedure by the example of human bones found from the archaeological shell mounds in Japan.

Late Pleistocene and Holocene environments in the Nile basin

Owing to the very gently sloping nature of the flood plain in the lower White Nile valley, which is underlain by a former lake-bed, the depositional record in that area is unusually well preserved. In Egypt and along the Blue Nile phases of erosion have destroyed segments of the sedimentary record, but the White Nile sequence is a good proxy for both the main Nile and the Blue Nile. During the last 15 ka, at least, times of high flow in the Blue Nile and main Nile were synchronous with those in the White Nile. Not all the White Nile flood deposits have been preserved but calibrated radiocarbon dates obtained on fossil freshwater and amphibious Pila shells and fish bones indicate that White Nile levels were high around 14.7–13.1 ka, 9.7–9.0 ka, 7.9–7.6 ka, 6.3 ka and 3.2–2.8 ka. The Blue Nile record is more fragmentary and that of the main Nile even more so except for the Holocene Nile delta. Calibrated radiocarbon ages for high Blue Nile flows indicate very high flood levels towards 13.9–13.2 ka, 8.6 ka, 7.7 ka and 6.3 ka. Incision by the Blue Nile and main Nile has caused progressive incision in the White Nile amounting to at least 4 m since the terminal Pleistocene ∼ 15 ka ago and at least 2 m over the past 9 ka. The Blue Nile seems to have cut down at least 10 m since ∼ 15 ka and at least 4 m since 9 ka. The time-transgressive and relatively late inception of plant domestication in the Nile valley may partly reflect this history of incision. Nile incision would propagate upstream into the White Nile valley, draining previously swampy areas along the valley floor, which would then become accessible to cultivation.

Luminescence dating of baked earth and sediments from the Qujialing archaeological site, China

The Qujialing site is a representative Neolithic archaeological site in the middle reaches of the Yangtze River, China. Absence of suitable material for radiocarbon dating in this region makes the timing of the similar sites difficult. Here we applied optically stimulated luminescence (OSL–SAR) and thermoluminescence (TL–SAR) techniques to date the archaeological and natural deposits from the Qujialing site with known age, testing the techniques on samples at archaeological sites in this region. The results showed that the luminescence properties of quartz from sediment and baked earth samples are very similar. The quartz OSL ages obtained for a sediment sample and a baked earth sample from the cultural layer are 5.4 ± 0.3 and 5.1 ± 0.3 ka, respectively. The quartz TL age of the baked earth sample is 5.6 ± 0.5 ka. These dates are consistent with the calibrated radiocarbon ages (4.9 ± 0.1 and 5.1 ± 0.1 ka cal BP (±1σ)) of the two charcoal samples from the cultural layer at a nearby locality, and are also in agreement with the age of Qujialing culture period. The results indicate that the OSL dating techniques can be applied to date similar archaeological sites in the middle reaches of the Yangtze River, China.

Late-Holocene mega-tsunamis in the Tasman Sea: an assessment of the coastal archaeological record of New South Wales

Bryant and others have interpreted geomorphological and archaeological evidence from south-central New South Wales (NSW) to infer repeated inundation of this coast by mega-tsunamis in late Holocene time. However, the stratigraphy of two well-dated archaeological sites (Pambula Lake, Bass Point) shows no evidence that these camps were abandoned, or that the marine component of the diet of local Aboriginal peoples changed at or about 500 or 1500 cal. BP, the time of the two most recent inferred mega-tsunamis. In addition, the mean probability distribution of the youngest calibrated radiocarbon ages from 52 archaeological sites on the south-central NSW coast (grouped in three tsunami-susceptibility classes on the basis of site elevation and distance from the shore) does not differ from random expectations, and shows no evidence that sites were permanently abandoned in the aftermath of these inferred events. The mean probability distributions of calibrated radiocarbon ages from 108 charcoal samples from these sites does not differ from random expectations, and offers little support for the inference that the sites were temporarily abandoned about 500 or 1500 cal. BP. Probability distributions based on 70 marine shell ages show strong century-scale cyclicity, but this is likely too regular to be a product of mega-tsunamis. Moreover, changes in shellfish exploitation patterns and adoption of new fishing technologies by Aboriginal people on this coast do not coincide with the times of inferred tsunamis. The archaeological evidence offers no support for the hypothesis that mega-tsunamis inundated this coastline in the late Holocene.

Calibrated radiocarbon ages of beach rock samples and late Holocene sea-level change of Amami Islands, southwest Japan

A total of 87 beach rock samples were collected from 37 sites of Amami Islands in order to determine formative ages of beach rocks on Amami Islands, and to clarify the sea-level change during the late Holocene period. Beach rocks began to form 5,720 yrs cal BP on Yoron Island at first, and formed continuously between 4,050 yrs cal BP and 380 yrs cal BP on the sandy coasts of Amami Islands. Relative sea-levels during the late Holocene period on Yoron Island and Okinoerabu Island were slightly higher than those of the present sea-level. Geomorphic evidences indicate that the islands have probably uplifted by earthquakes occurred along the subduction zone of Eurasian Plate. However the sea-level has remained similar to the present since at least the past 4,000 years at Amami-Oshima Island.

Coral growth rates from the Holocene Cañada Honda fossil reef, Southwestern Dominican Republic: Comparisons with modern counterparts in high sedimentation settings

The Holocene Cañada Honda fossil reef, located in southwestern Dominican Republic, provides a unique opportunity to examine a well-preserved fossil coral reef that thrived in a high-sedimentation environment between 9,000 to 5,000 years ago. Measurements of coral growth rates from the corals Montastraea faveolata and Siderastrea siderea were conducted and comparisons made with growth rate data of these same species from modern coral reefs throughout the Caribbean. Also, assessments of coral species abundance, morphology, age, and distribution, as well as reef sediment composition, were made to determine the paleoenvironment of reef accretion. This reef is characterized by a high relative abundance of sediment-tolerant coral species that have a tendency to form almost monospecific stands. Individual colonies have a propensity to grow as encrusting, dome-shaped, platy-like forms and specimens of Montastraea faveolata commonly contain bands of sediment incorporated into the skeleton. Calibrated radiocarbon ages of fossil corals range from 9,256±137 to 6,737±94.5 BP. Correlation of radiocarbon ages with well-established Holocene sea-level curves indicates that most corals on this reef developed at depths >15m. Measured growth rates in Siderastrea siderea (0.2–0.4 cm/yr) and Montastraea faveolata (0.09–0.44 cm/yr) are relatively low compared with growth rates from modern reef sites, indicating reduced light intensity caused by coral growth at depths greater than 15 m. Reef sediment is characterized by more than 85% carbonate material. A significant portion of the carbonate is allochtonous and was derived from nearby Neogene limestones. The reef was able to survive under high-sedimentation conditions because the high carbonate content of incoming terrigenous sediment would have allowed better light penetration and probable sporadic storms would provide intervening low-sedimentation periods during which reef corals could respond and grow back, keeping-up with sedimentation.

The Middle to Upper Paleolithic transition: dating, stratigraphy, and isochronous markers

Accurate and precise dating is vital to our understanding of the Middle to Upper Paleolithic transition. There are, however, a number of uncertainties in the chronologies currently available for this period. We attempt to examine these uncertainties by utilizing a number of recent developments in the field. These include: the precise dating of the Campanian Ignimbrite (CI) tephra by 40Ar/ 39Ar; the tracing of this tephra to a number of deposits that are radiocarbon dated; the publication of revised radiocarbon calibration data for the period, showing a much better convergence with other available data than during the recent IntCal comparison; and a layer-counted ice-core chronology extending beyond 40,000 cal BP. Our data comparisons suggest that a reasonable overall convergence between calibrated radiocarbon ages and calendar dates is possible using the new curves. Additionally, we suggest that charcoal-based radiocarbon ages, as well as bone-based radiocarbon determinations, require cautious interpretation in this period. Potentially, these issues extend far beyond the sites in this study and should be of serious concern to archaeologists studying the Middle to Upper Paleolithic. We conclude by outlining a strategy for moving the science forward by a closer integration of archaeology, chronology, and stratigraphy.

Radiocarbon dating and its applications in Quaternary studies

Abstract. This paper gives an overview of the origin of 14C, the global carbon cycle, anthropogenic impacts on the atmospheric 14C content and the background of the radiocarbon dating method. For radiocarbon dating, important aspects are sample preparation and measurement of the 14C content. Recent advances in sample preparation allow better understanding of long-standing problems (e.g., contamination of bones), which helps to improve chronologies. In this review, various preparation techniques applied to typical sample types are described. Calibration of radiocarbon ages is the final step in establishing chronologies. The present tree ring chronology-based calibration curve is being constantly pushed back in time beyond the Holocene and the Late Glacial. A reliable calibration curve covering the last 50,000-55,000 yr is of great importance for both archaeology as well as geosciences. In recent years, numerous studies have focused on the extension of the radiocarbon calibration curve (INTCAL working group) and on the reconstruction of palaeo-reservoir ages for marine records.