StalAge – An algorithm designed for construction of speleothem age models

Here we present a new algorithm (StalAge), which is designed to construct speleothem age models. The algorithm uses U-series ages and their corresponding age uncertainty for modelling and also includes stratigraphic information in order to further constrain and improve the age model. StalAge is applicable to problematic datasets that include outliers, age inversions, hiatuses and large changes in growth rate. Manual selection of potentially inaccurate ages prior to application is not required. StalAge can be applied by the general, non-expert user and has no adjustable free parameters. This offers the highest degree of reproducibility and comparability of speleothem records from different studies. StalAge consists of three major steps. Firstly, major outliers are identified. Secondly, age data are screened for minor outliers and age inversions, and the uncertainty of potential outliers is increased using an iterative procedure. Finally, the age model and corresponding 95%-confidence limits are calculated by a Monte-Carlo simulation fitting ensembles of straight lines to sub-sets of the age data.We apply StalAge to a synthetic stalagmite ’sample’ including several problematic features in order to test its performance and robustness. The true age is mostly within the 95%-confidence age limits of StalAge showing that the calculated age models are accurate even for very difficult samples. We also apply StalAge to three published speleothem datasets. One of those is annually laminated, and the lamina counting chronology agrees with the age model calculated by StalAge. For the other two speleothems the resulting age models are similar to the published age models, which are both based on smoothing splines. Calculated uncertainties are in the range of those calculated by combined application of Bayesian chronological ordering and a spline, showing that StalAge is efficient in using stratigraphic information in order to reduce age model uncertainty.The algorithm is written in the open source statistical software R and available from the authors or as an electronic supplement of this paper.     

Methods and codes for reservoir–atmosphere 14C age offset calculations

Reservoir ¹⁴C age offsets are invaluable tracers for past changes in carbon cycle and oceanic circulation. Reconstruction of reservoir age offsets with time is also required for calibration purposes (reconstruction of atmospheric calibration curve, calibration of non-atmospheric radiocarbon ages). Thus, properly propagating the various uncertainties linked to reservoir age offset is important for proper interpretation. However, approaches for reservoir age offset calculation – especially when considering pairs of reservoir-derived ¹⁴C and calendar ages – are usually not detailed and inadequate for proper propagation of uncertainties. Here, the various ways to properly calculate reservoir age offsets are described with a focus on a new approach when considering pairs of ¹⁴C and calendar ages. This approach maps the calendar age distribution onto the ¹⁴C time scale prior to reservoir age offset calculation – the “uncalibration-convolution process”. R codes computing reservoir age offsets based on available data are presented. Finally, a case study focusing on the reconstruction of the speleothem-atmosphere ¹⁴C age offsets of speleothem ¹⁴C data used in the latest release of the atmospheric calibration curve is discussed.     

Paleomagnetic age and palaeobiological significance of hominoid fossil strata of Yuanmou Basin in Yunnan

The Yuanmou area in Yunnan Province is a fa-mous place for origin of mankind. Qian Fang et al. found tooth fossils of Yuanmou man in Shangnabang Village of Yuanmou in 1965. Jiang Nengren et al. identified the hominoid teeth from animal fossils un-earthed near Zhupeng Village in the Xiaohe Basin which were delivered by the local peasants. Hominoid fossils were also found in Leilao Village of Yuanmou afterward. These great discoveries have aroused ex-tensive concern in academic circle[1,2…     

Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition

~~Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition@E. Deloule$CRPG-CNRS Nancy,54501,France1. Vavra, G, Gebauer. D., Schmid. R. et al., Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Tri-assic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study, Contrib. Mineral Petrol., 1996, 122:337-358 2. Vavra, G, Schmid, R., Gebauer, D., Internal morphology, ha…     

Evaluation of the 87Rb decay constant by age comparison against the U–Pb system

The Rb–Sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic, metamorphic, and hydrothermal events. It has also been extensively applied to date extraterrestrial, early solar system events. The accuracy of Rb–Sr ages, however, strongly depends on the accuracy of the ⁸⁷Rb decay constant (λ⁸⁷Rb). We determined λ⁸⁷Rb relative to the decay constants of ²³⁵U and ²³⁸U by comparing Rb–Sr ages of minerals with U–Pb ages obtained from the same intrusion. Comparison of U–Pb emplacement ages with high-precision Rb–Sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca. 2.5 Ga yields an unweighted mean λ⁸⁷Rb of 1.393 ± 0.004 × 10^?11 yr^?1 (i.e., ± 0.3%), corresponding to a half-life of 49.76 × 10⁹ years. Because this decay constant is 2% lower than the presently recommended one, many previously published ages are 2% too young and the resulting geologic interpretations may need revision.     

SHRIMP zircon U-Pb age and Nd isotopic study on the Nyainqêntanglha Group in Tibet

The Nyainqêntanglha Group, called Nyainqêntan- glha orthogneisses and schist sequence by Li et al.[1], is traditionally viewed as the oldest metamorphic basement in the Lhasa block[1―4]. The uplifted blocks of basement have exposed in two regions, middle segment of Nyainqêntanglha Mountain Range and west of Nam Co. The Nyainqêntanglha Group is sparsely dated, for its protolith age, the previous ideas were very different, such as Proterozoic, Pre-Sinian, Precambrian, or early Paleozo…     

Assessing the use of U–Th methods to determine the age of cold-water calcareous algae

Calcitic crusts of calcareous red algae could be suitable material for age determination of raised marine deposits and palaeothermometry at annual to sub-annual resolution. We examined the potential of U–Th dating of cold-water calcareous algae by analysing fossil specimens (n=10) from Kapp Ekholm (Svalbard) and recent specimens from Norway (n=3) and Scotland (n=1). After initial measurements using α-spectrometry, thermal ionisation mass spectrometry (TIMS) was used to study the material in more detail. Recent specimens contain 0.19–1.55 μg g⁻¹ U, and the measured (²³⁴U/²³⁸U) activity ratios vary between 1.12 and 1.30. Fossil specimens contain 1–168 μg g⁻¹ U, and display variable and highly elevated initial (²³⁴U/²³⁸U) activity ratios. In general, the TIMS results show increasing (²³⁴U/²³⁸U) activity ratios and concentrations of U and Th with increasing stratigraphic age. From this it is evident that marine calcareous red algae contain U in-vivo and they experience substantial post-mortem uptake of U. We conclude that direct U–Th dating of fossil calcareous algae from raised marine deposits is not viable without further geochemical understanding of the in-vivo uptake and post-depositional pathways of U and Th in such deposits. Despite the convincing open-system behaviour of the material, comparison with previously published chronostratigraphy from the site shows that the calcareous algae generally yield ages that are too old. This is in contrast to the expected result based on simple continuous post-mortem U accumulation and calls for a complex model comprising migration of U and multi-component addition of Th (detrital/colloidal) to explain the observed trends.     

Re-establishment of zooplankton communities in temporary ponds after autumn flooding: Does restoration age matter?

In temporary ponds, reestablishment of zooplankton communities depends on recruitment from the egg bank, the arrival of dispersers from within the region, and on successful establishment of newly arrived species following interaction with local abiotic and biotic factors. When the ponds dry up, zooplankton species may survive as dormant eggs, and since not all eggs hatch in the next season, eggs will accumulate in the sediment over time, representing an archive of the pond's historical biodiversity.To study the effect of “restoration age” (the time since a water body was restored), we studied groups of ponds that were restored in different years (1998, 2003 and 2007). The restoration process involved extensive dredging of sediments which were used to bury the ponds in the 1960s. Our expectation was that the oldest ponds would have the richest zooplankton community, as they have been accumulating biodiversity over a longer time period. We took weekly quantitative samples of zooplankton during four consecutive weeks after flooding to compare taxon richness and zooplankton community composition between ponds of different restoration age during an early stage of zooplankton community re-establishment.Taxon richness was high and similar to regional levels in all the ponds under investigation, suggesting restoration success and unlimited dispersal. Although cumulative richness at the end of the period was not significantly different between ponds, we observed temporal changes within the study period and certain age-related trends in relation to differences in zooplankton composition. These results suggest a difference in the succession of zooplankton communities depending on restoration age (which could be due to historical or local factors) and that this effect becomes evident from the beginning of the pond hydroperiod.     

SHRIMP zircon U-Pb age and Nd isotopic study on the Nyainqêntanglha Group in Tibet

The Nyainqêntanglha Group is traditionally viewed as the oldest metamorphic basement in the Lhasa block, but its formation age and tectonic setting remain debate. Zircons extracted from the metamorphic sequence of volcanics and intrusions of the Nyainqêntanglha Group, 10 km west of Nam Co in northern Lhasa block, have been investigated by cathodoluminescence (CL), backscattered (BSE) and dated by ion microprobe (SHRIMP). We conclude that the U-Pb age of 787 ê9 Ma of zircons from the trondhjemite imposes a constraint on maxi-mum protolith age, and minimum formation age of the Nyainqêntanglha Group is constrained by U-Pb age of 748 ê8 Ma of zircons from the granite. The formation age of the Nyainqêntanglha Group is consistent with sedimentary age of Greater Himalayan rocks, showing that they devel-oped coevally in an arc-basin tectonic setting of Neoproterozoic active continental margin along the northern margin of the India shield. The inherited zircons from the tholetiite and granite give older 207 Pb/206 Pb ages from 947 to 1766 Ma. The positive å Nd(t) value indicates that the mafic rocks were derived from the depleted mantle, but contaminated by the older continental crustal material. Integrated Nd model age and U-Pb age data provide excellent evidence for the existence of Mesoproterozoic basement in the Lhasa block during Neoproterozoic time.     

Geochemistry and Zircon U–Pb age of the Yao'an pseudoleucite porphyry,Yunnan Province,China

The Yao'an Pb–Ag deposit, located in the Chuxiong Basin, western Yangtze Block, is an important component of the Jinshajiang–Ailaoshan alkaline porphyry–related polymetallic intrusive belt. This complex suite of rock bodies includes a vein of pseudoleucite porphyry within deposits of syenite porphyry and trachyte.The pseudoleucite is characterized by a variable greyish,greyish-white, and greyish-green porphyritic texture. Phenocrysts are mainly pseudoleucite with small amounts of alkali feldspar and biotite. In an intense event, leucite phenocrysts altered to orthoclase, kaolinite, and quartz.Both the pseudoleucite porphyry and the syenite porphyry samples were typical alkali-rich, K-rich, al-rich rocks with high LaN/YbNratios; enriched in light rare earth elements and large-ion lithophile elements, and depleted in high field strength elements; and with strongly negative Ta, Nb, and Ti(TNT) anomalies and slightly negative Eu anomalies—all characteristics of subduction-zone mantle-derived rock.We obtained a LA-ICP-MS zircon U–Pb age of 34.1 ± 0.3 Ma(MSWD = 2.4), which is younger than the established age of the Indian and Eurasian Plate collision.The magma derived from a Type-II enriched mantle formed in a post-collisional plate tectonic setting. The geochemical characteristics of the Yao'an pseudoleucite porphyry are powerful evidence that the porphyry'sdevelopment was closely linked to the Jinshajiang–Ailaoshan fault and to the Indian-Eurasian collision.     

Could surface roughness be a poor proxy for landslide age? Results from the Swabian Alb,Germany

The potential of surface roughness to quantify geomorphological landforms and processes has been enhanced with the availability of high‐resolution digital terrain models (DTM). Recent studies that attempt to identify landslide features with surface roughness have suggested that this measure of topographic heterogeneity may also be applied to estimate the relative age of landslides. This is a provisional study that explores the potential of this relationship by assessing the ability of surface roughness to act as a proxy for relative landslide age. The surface roughness for a set of 12 dated landslides in the Swabian Alb that occurred between 1789 and 1985 was calculated from a 1 m² spatial resolution LiDAR DTM with three algorithms: root‐mean‐square‐height (RMSH), standard deviation of slope (SDS), and direction cosine eigenvalue ratios (DCE). Scale‐dependence was analysed by calculating surface roughness for a range of moving window sizes (3 × 3, 5 × 5, 9 × 9 and 15 × 15), and surface roughness for each landslide was summarized by the median and upper quartile. Only weak correlations (best Spearman's rho 0.58) were present between landslide age and surface roughness. This correlation becomes weaker with increasing moving window size. Given weak observed associations and discussed challenges pertaining to the complexities of landslide morphology change over time, we currently find that surface roughness alone may not be justifiable to act as a proxy for landslide age for our study region. Furthermore, we recommend future studies should focus on addressing possible natural and anthropogenic factors such as land use change that may alter surface roughness. These studies may focus on one of the three roughness measures used here as they are strongly correlated. Copyright © 2014 John Wiley & Sons, Ltd.     

KV01 zircon—A potential New Archean reference material for microbeam U-Pb age and Hf-O isotope determinations

Science China Earth Sciences - To meet the rapid development of zircon U-Pb geochronology and Hf-O isotope geochemistry, it is imperative to develop well-characterized zircon reference materials...     

High-precision 40Ar/39Ar age of the Jänisjärvi impact structure (Russia)

The ～ 14 km diameter Jänisjärvi impact structure is located in Svecofennian Proterozoic terrain in the southeastern part of the Baltic shield, Karelia, Russia. Previous radioisotopic dating attempts gave K/Ar and ⁴⁰Ar/³⁹Ar ages of 700 ± 5 Ma and 698 ± 22 Ma, respectively, with both results being difficult to interpret. Recent paleomagnetic results have challenged these ages and proposed instead ages of either 500 Ma or 850–900 Ma. In order to better constrain the age of the Jänisjärvi impact structure, we present new ⁴⁰Ar/³⁹Ar data for the Jänisjärvi impact melt rock. We obtained five concordant isochron ages that yield a combined isochron age of 682 ± 4 Ma (2σ) with a MSWD of 1.2, P = 0.14, and ⁴⁰Ar/³⁶Ar intercept of 475 ± 3. We suggest that this date indicates the age of the impact and therefore can be used in conjunction with existing paleomagnetic results to define the position of the Baltica paleocontinent at that time. Argon isotopic results imply that melt homogenization was achieved at the hundred-micrometer scale certainly, because of the low-silica content of the molten target rock that allows fast ⁴⁰Ar^? diffusion in the melt. However, the large range of F(⁴⁰Ar^?_inherited) (4.1% to 11.0%) observed for seven grains shows that complete isotopic homogenization was not reached at the centimeter and perhaps the millimeter scale. The F(⁴⁰Ar^?_inherited) results are also in good agreement with previous Rb and Sr isotopic data.     

Improving age estimates for late Holocene glacial landforms using dendrochronology – Some examples from Garibaldi Provincial Park,British Columbia

Dating of late Holocene landforms below treeline in high mountains is commonly done using dendrochronology. Four factors can reduce the accuracy of ages obtained by dendrochronology: (1) locating the oldest living tree on a surface; (2) the method of counting the rings; (3) the age-height correction factor; and (4) ecesis, which is the time it takes trees to successfully germinate on a bare surface. A review of published studies from the western Cordillera of the Americas shows that some of these issues have not been fully addressed. Research in Garibaldi Provincial Park in the southern Coast Mountains of British Columbia shows that the accuracy of tree-ring ages can be improved if (1) crossdating and chronology construction, rather than simple ring counts, are done; (2) individual age-height correction factors are applied; and (3) site-specific ecesis estimates are made. While these suggestions are not always necessary to their fullest extent, researchers should at least report their methods in more detail and provide uncertainties in their age estimates that take into account age-height and ecesis corrections.     

Monazite age spectra in the Late Cenozoic strata of the Changjiang delta and its implication on the Changjiang run-through time

Uplift of the Tibetan Plateau, inversion of eastern and western geomorphology, eastward flowing of large rivers, and run-through of the Changjiang River exert great influence on sedimentation and environ-mental variations in the East China Sea. Provenance discrimination of Tibetan-Plateau-originated sediments in the river-mouth areas and marginal seas is key to figure out these issues.In the past, most studies of the run-through time of the Changjiang and the Yellow rivers focused on geomo…     

SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

A great deal of practical data in recent years have proved that the East Kunlun orogenic belt and even the China central orogenic belt are complex orogenic belts that underwent polycycle orogenic evolvement[1―7]. Each orogenic cycle has left a compositional print, the multi-period ophiolites[4―6] and various types of tec-tono-magmatic production in the same orogenic belt. There is a suite of shallow metamorphic volcanic rocks in the Nuomuhong area in the east part of the East Kunlun orogen…     

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Introduction Artificial seismic sounding is a geophysical exploration technique developed in prospectingfor oil and gas and other mineral resources and consists of reflection wave and refraction waveexploration methods. With rapid development of computer techniques and sounding instruments,the reflection wave method became a high-resolution imagery technique for underground struc-tures and is widespreadly used in detection of underground caves and in engineering exploration.In previous se…     

Homo erectus pekinensis''''s age and environment——with discussion on the relationship among Homo erectus from Beijing,Nanjing and Chenjiawo

This paper inspects the relationship between Homo erectus from Beijing, Nanjing and Chenjiawo on the viewpoint of environmental variations. Pieces of evidence show that Nanjing and Chenjiawo Homo erectus lived in glacial age at the Marine Oxygen Isotope Stage (MIS) 16, while Homo erectus pekinensis in major interglacial age at MISs 15-13. It is also recovered that the cave deposits in Tangshan, Nanjing, and Zhoukoudian, Beijing, as well as the deposits at the Homo erectus site in Chenjiawo, have undergone some similar development process. All of them originated from early-middle Middle Pleistocene, and have gone through the test of the major glacial age at MIS 16 and the major interglacial period at the paleosol stage S5. At the same time, they were also closely connected with some environment events, such as the uplift of the Qinghai-Xizang Plateau, the formation of glaciations and the loess accumulations.     

SHRIMP U-Pb zircon age,geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan:Petrogenesis and tectonic significance

Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super- continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780―760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplace- ment, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.