Conventional Radiocarbon Ages Research Articles

SOIL DEVELOPMENT ON LATE PLEISTOCENE MORAINES AT PINE CREEK, EAST-CENTRAL SIERRA NEVADA, CALIFORNIA

Late Pleistocene moraines at Pine Creek in the east-central Sierra Nevada Range are differentiated into three separate relative-age groups using soil morphological properties, with increasing soil development on progressively older deposits. Tiogaage soils (oxygen-isotope stage-2 equivalent) are weakly developed with A/AB/Bw/Cox profiles. Organic material extracted from Tioga-age till matrix has a conventional radiocarbon age of 19,570 ± 420 years B.P. Soils formed on Tahoe-age moraines (stage 4) show A/2BA/2Bw1/2Bwq2/2BC/2Cox horizonation with rubification to about 50 cm depth and slight clay enrichment. Organic matter from the Tahoe-age till matrix yields an infinite radiocarbon age (>38,000 years B.P.). Rovana moraines (stage 6) have moderate soil development, with A1/A2/2Bt1/2Bw2/2BC/2Cox profiles, conspicuous rubification down to about 103 cm, and significant clay accumulation in the Bt horizon. A soil-profile development index reflects the chronologic trend; however, lithologic and climatic variabil...

A macrofossil flora from sediments in a lagoon marginal to Lake Coleridge, Canterbury, New Zealand

Abstract Macrofossils from woody plants and a radiocarbon date (conventional radiocarbon age 7273 ± 104 yr B.P.) from the bottom sediments in a lagoon marginal to Lake Coleridge indicate that mixed podocarp-angiosperm forest was present in the middle Rakaia River basin during most of the Aranuian (post-glacial) period. Among the forest species at Lake Coleridge were some (Prumnopitys taxifolia, Elaeocarpus hookerianus, and Melicope simplex) not present there now and only sparsely represented now anywhere in the middle Rakaia basin. Other aspects of forest history in the region are considered, including changes during the Aranuian and widespread destruction by fire within the last few centuries.

A comparison of sediment accumulation chronologies by the radiocarbon and 230Th excess methods

Four Northeast Atlantic cores which exhibited well-correlated linear progressions of conventional radiocarbon age with depth were analysed to provide 230Th excess profiling data. The current evaluation of marine radiocarbon data suggests that conventional radiocarbon ages consistently underestimate true time. This deficit progressively increases from 4 to 22 ky BP. As a result, steady-state sediment accumulation rate models based on conventional radiocarbon ages are expected to be in error by up to 17%, dependent on the period over which the estimates are made. When proxy timescales from the radiocarbon and 230Th excess data for the four cores are compared over periods between 0–11.5 and 0–18.2 ky BP, the trend of cumulative time derived from the 230Th excess profiling data is shown to be consistent with the expected trend of conventional radiocarbon age vs the best current estimate of true time. This agreement supports the use of 230Th excess as a tracer for detailed estimates of changing deep-sea sediment accumulation fluxes.

Problems encountered with the 14C dating of peat

Pairs of neighbouring short columns of peat from two sites in Northern England were divided into contiguous 1 cm thick slices that were sub-sampled for pollen and plant macro fossil analysis. For each slice the remaining peat was then split into humic acid, humin and fulvic acid fractions and radiocarbon dated. This research demonstrates that significant variations can occur in the radiocarbon content of discrete chemically defined fractions of peat. A total of 127 radiocarbon dates was obtained. The results from the four columns of peat are highly variable and mutually inconsistent. The fulvic acid fraction, although normally younger than the corresponding humic acid and humin fractions, has very little effect on a combined date in these samples. However, it is removed from all samples prior to dating in order to remove any carbonates which could contaminate samples. The variations in the ages obtained for the humic acid and corresponding humin fractions range from the humin fraction being 630 years older than the humic acid (SRR-4029) to the humic acid being 1210 years older than the humin fraction (SRR-4007), even when a two sigma confidence is allowed. No correlation was apparent between pollen concentration, 13C enrichment, degree of humification and the conventional radiocarbon ages.

An Assessment of the Radiocarbon Dating of the Dead Sea Scrolls

I suggest, on the basis of a statistical analysis, that recently determined “conventional radiocarbon ages” of Dead Sea Scroll documents are offset systematically by about +40 yr, leading to a similar overestimate of the ages of these documents. Much closer agreement with paleographic and specific dates is obtained when a correction of this magnitude is made to the “conventional 14C” values. This indicates that 14C dates may convey more precise information about the ages of these documents than initially recognized.

The role of scale in the biostratigraphy and chronostratigraphy of the Holocene Series in The Netherlands

In this paper the diachronous nature of some chronostratigraphic boundaries which are derived from the standard biostratigraphic subdivision of the Holocene Series in The Netherlands is discussed. Diachroneity is illustrated with an example from the fluvial area in The Netherlands and with relevant results of recent palynological research in other parts of the country. In explaining the time-transgressive nature of pollen zones it is argued that scale should be taken into account. It is proposed to subdivide The Netherlands into landscape regions for which future palynological research may indicate that they are characterized by common pollen trends, useful for correlation in time. Biostratigraphic correlation, when applied within landscape regions, may then remain an important tool for the establishment of relative chronologies. The designation of landscape regions in the Holocene calls for a large palynological programme that will take much time to accomplish. In the meantime, the Holocene Series can be either subdivided into chronozones defined by conventional radiocarbon ages, or by the direct application of radiocarbon ages without any subdivision.

Climatic and geomagnetic influences on the Lac du Bouchet palaeomagnetic SV record through the last 110 000 years

Abstract Palaeomagnetic secular variation records stacked from five cores ∼ 20 m long extend back through the last glacial cycle to ∼ 100 000 years ago. The time-scale has been constructed from conventional and accelerator radiocarbon ages back to ∼ 45 Ka BP and beyond this by comprehensive pollen studies which identify forest and steppe cycles that have been related to marine oxygen isotopic stages 4 and 5. Spectral analyses of the intensity and directional records using both Fourier and maximum entropy methods reveal strong low-frequency components which fall in the range of the Milankovitch obliquity and precession periodicities (40-20 Ka). It is concluded that although part of this signal may have fed indirectly into the natural remanence via the influence of climatic change on sediment facies, part has been impressed directly by perturbation of the geomagnetic dynamo process at the core-boundary by variations in the Earth's obliquity and precession. These long periods envelop a well-defined pattern, registered also by the independent ‘Mackereth’ core stack back to 50 Ka BP, of irregular secular oscillations of the geodynamo with periods of a few thousands of years.

Calibration of radiocarbon dates: tables based on the consensus data of the Workshop on Calibrating the Radiocarbon Time Scale

A calibration is presented for conventional radiocarbon ages ranging from 10 to 7240 years BP and thus covering a calendric range of 8000 years from 6050 BC to AD 1950. Distinctive features of this calibration include 1) an improved data set consisting of 1154 radiocarbon measurements on samples of known age, 2) an extended range over which radiocarbon ages may be calibrated (an additional 530 years), 3) separate 95% confidence intervals (in tabular from) for six different radiocarbon uncertainties (20, 50, 100, 150, 200, 300 years), and 4) an estimate of the non-Poisson errors related to radiocarbon determinations, including an estimate of the systematic errors between laboratories.

Tree Ring, Varve and Carbon-14 Chronologies

CARBON-14 dating has become of great importance and it is therefore necessary to determine the possible deviations between radiocarbon and actual ages. A radiocarbon age, given in radiocarbon years elapsed since the origin of the sample, is based on 14C decay and is calculated from the ratio of the present 14C activity of the sample to the 14C activity of the standard (95 per cent of the 14C activity of NBS oxalic acid). The standard 14C activity is assumed to be identical to the atmospheric 14C activity over the whole time interval over which 14C dating is used. Thus the conventional radiocarbon age does not allow for deviations in atmospheric 14C content during the past. As a result, radiocarbon years need not always be equal to solar years.

Errors in Radiocarbon Age Determination and Correction of Radiocarbon Dates

The errors in radiocarbon age determination on the wood samples are estimated from the possible variations in the concentration of radiocarbon in the atmosphere. Recent results of measurements on the secular variation of the atmospheric 14C are presented and compared in order to find a general variation. Based on this general variation a correction curve for conventional radiocarbon ages to calender years is computed.