Range Of Radiocarbon Research Articles

Performance and automation of ancient DNA capture with RNA hyRAD probes

DNA hybridization‐capture techniques allow researchers to focus their sequencing efforts on preselected genomic regions. This feature is especially useful when analysing ancient DNA (aDNA) extracts, which are often dominated by exogenous environmental sources. Here, we assessed, for the first time, the performance of hyRAD as an inexpensive and design‐free alternative to commercial capture protocols to obtain authentic aDNA data from osseous remains. HyRAD relies on double enzymatic restriction of fresh DNA extracts to produce RNA probes that cover only a fraction of the genome and can serve as baits for capturing homologous fragments from aDNA libraries. We found that this approach could retrieve sequence data from horse remains coming from a range of preservation environments, including beyond radiocarbon range, yielding up to 146.5‐fold on‐target enrichment for aDNA extracts showing extremely low endogenous content (<1%). Performance was, however, more limited for those samples already characterized by good DNA preservation (>20%–30%), while the fraction of endogenous reads mapping on‐ and off‐target was relatively insensitive to the original endogenous DNA content. Procedures based on two instead of a single round of capture increased on‐target coverage up to 3.6‐fold. Additionally, we used methylation‐sensitive restriction enzymes to produce probes targeting hypomethylated regions, which improved data quality by reducing post‐mortem DNA damage and mapping within multicopy regions. Finally, we developed a fully automated hyRAD protocol utilizing inexpensive robotic platforms to facilitate capture processing. Overall, our work establishes hyRAD as a cost‐effective strategy to recover a set of shared orthologous variants across multiple ancient samples.

Luminescence dating of Quaternary alluvial successions, Sellicks Creek, South Mount Lofty Ranges, southern Australia

Quaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160 ± 15 ka; MIS 6), an unnamed alluvial succession (42 ± 3.2 ka; MIS 3), a late last glacial colluvial succession within bedrock depressions (ca 15 ka; MIS 2) and a late last glacial alluvium (ca 15 ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5 ± 0.3 ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9 ± 7 ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118 ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments.KEY POINTSLuminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present.Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating.Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.

New electron spin resonance (ESR) ages from Geißenklösterle Cave: A chronological study of the Middle and early Upper Paleolithic layers

Geißenklösterle Cave (Germany) is one of the most important Paleolithic sites in Europe, as it is characterized by human occupation during the Middle and early Upper Paleolithic. Aurignacian layers prior to 37–38 ka cal BP feature both musical and figurative art objects that are linked to the early arrival in Europe of Homo sapiens. Middle Paleolithic layers yielded lithic artifacts attributed to Homo neanderthalensis. Since human occupation at the site is attributed to both Neanderthals and modern humans, chronology is essential to clarify the issues of Neanderthal disappearance, modern human expansion in Europe, and the origin of the Aurignacian in Western Europe. Electron spin resonance (ESR) dating was performed on fossil tooth enamel collected from the Middle Paleolithic layers, which are beyond the radiocarbon dating range, and from the nearly sterile ‘transitional’ geological horizon (GH) 17 and the lower Aurignacian deposits, to cross-check ESR ages with previous radiocarbon, thermoluminescence and ESR age results. The Middle Paleolithic layers were dated between 94 ± 10 ka (GH 21) and 55 ± 6 ka (GH 18) by ESR on tooth enamel. Mean ages for GH 17, at 46 ± 3 ka, and for the lower Aurignacian layers, at 37 ± 3 ka, are in agreement with previous dating results, thus supporting the reliability of ESR chronology for the base of the sequence where dating comparisons are not possible. These results suggest that Neanderthals occupied the site from Marine Isotope Stage (MIS) 5 to the second half of MIS 3 and confirm the antiquity of early Aurignacian deposits. The presence of an almost sterile layer that separates Middle and Upper Paleolithic occupations could be related to the abandonment of the site by Neanderthals, possibly during Heinrich Stadial 5 (ca. 49–47 ka), thus before the arrival of H. sapiens in the area around 42 ka cal BP. These dates for the Middle Paleolithic of the Swabian Jura represent an important contribution to the prehistory of the region, where nearly all of the excavations were conducted decades ago and prior to the development of reliable radiometric dating beyond the range of radiocarbon.

Stratigraphical and palynological appraisal of the Late Quaternary mangrove deposits of the west coast of India

The organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the Late Quaternary sequence of Kerala–Konkan Basin. Three generations of such deposits have been identified. The older one is dated to around 43,000–40,000 14C yr B.P., with a few dates beyond the range of radiocarbon. The younger ones date from the Middle Holocene to latest Pleistocene (10,760–4540 14C yr B.P.) and the Late Holocene (<4000 14C yr B.P.). Pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation. Peat accumulation during the period 40,000–28,000 14C yr B.P. can be correlated with the excess rainfall, 40–100% greater than modern values, of the Asian summer monsoon. The low occurrence of mangrove between 22,000 and 18,000 14C yr B.P. can be attributed to the prevailing aridity and/or reduced precipitation associated worldwide with Last Glacial Maximum, because exposure surfaces and ferruginous layers are commonly found in intervals representing this period. The high rainfall of 11,000–4000 14C yr B.P. is found to be the most significant as the mangrove reached an optimum growth around 11,000 14C yr B.P. but with periods of punctuated weaker monsoons. From the present and previous studies, it has been observed that after about 5000 or 4000 14C yr B.P., the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems. A case study of Hadi profile provided an insight to the relevance of magnetic susceptibility (χ) to record the ecological shift in Late Holocene.

Extending the geochronometry of arctic lake cores beyond the radiocarbon limit by using thermoluminescence

Reconstructing detailed paleoclimatic/paleoenvironmental histories from Pleistocene sediments in the Arctic is an ongoing challenge because of the difficulty of measuring accurate timescales beyond the range of radiocarbon (14C) dating. Important archives of such histories are arctic lakes that exist outside the known extent of the last major glaciations. To develop reliable geochronometry of sediment cores from arctic and other lakes, we applied thermoluminescence (TL) sediment‐dating methods to 24 samples (8 reported earlier but some reanalyzed here) selected from cores from Squirrel and Joe Lakes in northwestern Alaska. A sequence of 2314C ages from the upper parts of these cores permitted tests of the zeroing assumption of TL dating: that all fine‐silt grains were exposed to daylight before final burial. We performed multiple TL tests on most samples to isolate stable TL signals and measured TL emissions spectra to help characterize samples. TL ages generally agree with the ∼30 kyr age‐depth trend derived from14C dating and extend the timescale apparently to ∼180 ka for Squirrel Lake and to at least ∼60 ka for Joe Lake. An anomalously old TL result from Squirrel Lake is attributed to failure of the TL zeroing assumption within that sediment horizon. In the lower Joe Lake core we assign a timing of 45 ka to 50 ka for the beginning of an apparently climatic warming interval. These results identify and quantify the main TL sources of TL age inaccuracy and the preferred TL protocols for accurate TL sediment dating in northern high‐latitude lake deposits. They also provide the first direct chronology beyond the14C dating range for these lakes.

Amino acid geochronology applied to the correlation and dating of central european loess deposits

Numerous localities in the Czech Republic, Slovakia, and Austria have been sampled for fossil gastropod shells for the purpose of an aminostratigraphic evaluation of loess sequences. In all three regions alloisoleucine/isoleucine (aIle/Ile) ratios are observed to be significantly higher in shells from loess deposited during the penultimate glacial period (cycle C) relative to samples from loess of the last glaciation (cycle B). The difference in aIle/Ile ratio reflects both difference in age of the samples plus the impact on the older samples of the relatively high effective temperature of the last interglacial period. Amino acid data support the previous correlation suggested between PK II+III in the Czech Republic and Slovakia and the ‘Stillfried A’ in Austria. Samples have also been recovered from older loess units, and previously published correlations within the Czech and Slovak Republics are tested. AIIe/Ile ratios appear to distinguish between samples from loess of the last four glacial cycles. Beyond cycle E ( 18O Stages 10 and 11), the increase in alle/Ile ratio is relatively small from cycle to cycle. In addition, shells tend to be poorly preserved and are absent at many localities. Nevertheless, amino acid geochronology offers a means of resolving ages of loess units in the critical time period that is beyond the range of radiocarbon and thermoluminescence methods but post-dates the Brunhes-Matuyama paleomagnetic reversal.

Palynostratigraphy and paleoenvironments of Wellington, New Zealand, during the last 80 ka, based on palynology of drillholes

Abstract About 20 pollen profiles from the Wellington area are correlated and zoned according to their pollen characteristics. Sequences from many of the larger sedimentary deposits are shown to contain little or no sediment of late Last Glacial and early Postglacial age, while late Postglacial sedimentation is restricted to a few localities. Sediments of middle and early Last Glacial age are well represented and widespread over the Wellington area. Pollen diagrams from Last Glacial and Postglacial sediments are zoned as follows: Zone A, 80 000–60 000 yr B.P. (lower end of range more likely) and provisionally correlated with oxygen isotope stages 5a and basal 4; Zone B, 70 000–50 000 yr B.P. (lower end of range more likely), provisionally correlated with upper oxygen isotope stages 4 and basal stage 3; Zone C, a short zone just beyond the range of radiocarbon dating at the top of Zone B of 60 000–50 000 yr B.P., correlated with the middle of oxygen isotope stage 3; Zone D, 50 000–10 000 yr B.P., with a ma...

New Zealand thesis in Earth sciences

This study attempts to reconstruct the vegetational and climatic history of the last 300 000 years for the Taranaki-Wanganui district, North Island, New Lignites in the cover beds of a wellpreserved sequence of marine terraces in South Wanganui Basin provide excellent material for pollen analysis from sequences that are chronologically constrained by the ages of the marine terraces and by the loessand tephrostratigraphy of their cover beds. Anthropogenic influences in New Zealand affect only the last c. 1000 years. Modern pollen samples from a variety of vegetation types from central-western North Island, together with previous modern pollen studies, indicate the palynological representation of taxa and allow the characterisation of the major vegetation types, although these data provide only a limited picture of the source vegetation. This information is used for helping to interpret the fossil pollen spectra. Two sites from the Waverley district, near Wanganui, which together cover the mid and late Holocene, provide an analogue of vegetation assemblages and their sequence of development in the area, for use in interpreting the Pleistocene pollen sequences. The vegetation history from these sites conforms to the known Holocene pattern from sites elsewhere. Polynesian deforestation at Lake Waiau Swamp is estimated to have occurred some time between 685 CAL B.P. and 210 years ago. Five sites from the Pleistocene marine terrace cover beds are pollen analysed in detail. The pollen assemblage zones are correlated with the established deep-sea oxygen isotope record. Combined with previous pollen studies from the terrace cover beds, the results provide a relatively continuous, detailed vegetation history dating from c. 400 ka ago to the present, for the fIrst time in New This record is closely linked to the marine terrace, loess-, and tephrostratigraphy of this region. Because the record is mostly from sequential rather than coeval sites, further work is required to corroborate certain details. The vegetation on the lowlands of Taranaki-Wanganui alternated from grass-shrubland communities during glacial periods, to podocarp-hardwood forest, dominated in the pollen assemblages by Dacrydium cupressinum, during the interglacial times. No particular period is uniquely characterised by its pollen assemblages. In interglacial pollen assemblages, generally some of the hardwood forest elements are severely underrepresented (e.g., Beilschmiedia tawa). The warmest, wettest, and mildest (with rare frosts and droughts) climates during interglacials are suggested by pollen assemblages matching those of the early to mid Holocene, with common Ascarina lucida and Dodonaea viscosa pollen in nearcoastal sites. Interstadial and stadial pollen assemblages are more diffIcult to characterise. In general, interstadial assemblages seem to be dominated by Prumnopitys taxifolia pollen, and· stadial assemblages seem to be dominated by Nothofagus fusca type or Libocedrus pollen, together with common shrub and grasS pollen. The vegetation for Some of the climatic stages, such as the Last and Penultimate Interglacials sensu stricto, are clearly demonstrated for the first time in New N. fusca type, N. menziesii, Libocedrus, Halocarpus, Phyllocladus, Empodisma minus, and Gleichenia are some taxa for which geographic range expansion. can be demonstrated when climates were cooler than present However, the vegetation history of the area generally agrees with the hypothesis that the flora of the Taranaki-W~ganui district has remained essentially the same through the Q\1aternary, although a few records of taxa well outside their present ranges require special explanation. Glacial period pollenrecords show that, while forest was probably largely excluded from the lowlands, it remained in the region during the coldest climatic periods and probably occupied sheltered areas. Broadly synchronous records from separate sites suggest that regional vegetational differences existed, probably due to local site and climate differences, analogous to the present pattern. Occasional natural fIres appear to have occurred throughout the periods studied, but there is no evidence that deforestation due to severe fIres occurred during the late Pleistocene. Palynology and radiocarbon dating of the Ohawe Beach Site, near Hawera, demonstrate that the marine terraces in this region have previously been mapped incorrectly, but in general the marine terrace mapping and chronology of B. J. Pillans (1983:. Upper Quaternary marine terrace chronology and deformation, south Taranaki, New Zealand. Geology 11: 292-297;) is upheld. Radiocarbon dating of separate organic fractions from degraded fossil wood samples at Ohawe Beach show that chemical contamination by young radiocarbon had occurred· and that the real age is beyond the radiocarbon range. This serves as· a warning against simple interpretation of radiOCarbon ages on wood from cover beds in the area. Pollen analyses also suggest that the Fordell Ash is younger than the Mt Curl Tephra, as opposed to previous interpretations . The extinct palynomorphs, Acacia· type andPeromonolites problematicus Couper, are identifIed from the cover beQ sediments, and their time ranges in New Zealand extended until c .. 11 0 ka ago and 90 ka ago, respectively. The implications of these fIndings are discussed. .

Amino acids in buried paleosols on Mount Kenya

A sequence of buried paleosols ranging from ∼900 to > 42,000 radiocarbon yr BP, formed in a succession of different parent materials on Mount Kenya, East Africa, was utilized to determine the fate of amino acids over time. Amino acids were studied in whole-soil samples, hydrolyzed for 24 hours following standard laboratory procedures. Aspartic acid proved most useful as a relative age indicator yielding progressively higher D/L ratios with increasing age. The sequential change in composition with time confirms that the amino acids are mostly fossil types. This technique appears useful for determining whether paleosol samples used for radiocarbon dating might be contaminated with younger material. The sequential decline in amino acids in paleosols appears useful also as a relative dating method, and may eventually prove useful in dating paleosols beyond the range of radiocarbon.

Recent Advances in Thermoluminescence Dating

Abstract Initially application was to ancient pottery and other baked clay, detection of forgeries in art ceramics having a particularly powerful impact. In recent years there has been a growing extension of TL into non-pottery materials. Heated flints from paleolithic fire-places is one application. Another is in the dating of igneous rocks from recent volcanic events; formerly this had been impossible on account of the malign phenomenon of non-thermal ('anomalous') fading exhibited by volcanic minerals but this is now being circumvented by utilising TL in the 600 oC region of the glow curve. TL dating has also been extended to unburnt calcite, one application being stalagmitic floors in paleolithic caves. Another recent development is the use of TL for dating aeolian sediment and some types of waterborne sediment. These developments give prospect of establishing a TL-based chronology, both for archaeology and quaternary research, extending back well beyond the range of radiocarbon, perhaps reaching a million years ago.

Late Quaternary Paleoceanography of the Gulf of Aqaba (Elat), Red Sea

The quantitative distribution of planktonic foraminifera, pteropods, and coccolithophorids, as well as oxygen-isotope variations were analyzed in four deep-sea cores from the Gulf of Aqaba (Elat) and the northernmost Red Sea. The core record covers about 150,000 yr. Detailed stratigraphic subdivision is facilitated by combining all calcareous plankton groups. Time-stratigraphic correlation and dating beyond the radiocarbon range are possible by comparison of the oxygen-isotope curves. During the glacial maximum salinity rose to more than 50‰, while winter temperature of the upper waters fell by at least 4°C compared to the present. The rise in salinity can be accounted for by sea-strait dynamics and lowering of sea level. The Gulf of Aqaba and the Red Sea were continuously connected through the Straits of Tiran, and there is no indication of desiccation during the glacial maximum.

Extending the range of radiocarbon dating

Extending the range of radiocarbon dating