NERC Isotope Geosciences Laboratory

Publications

A full list of publications can be found in the NIGL Annual Reports. This section highlights some of our high-impact papers as they go to press. A full list of NERC staff publications and outputs can be found in the NERC Open Research Archive (NORA)

Quaternary Science Reviews - May 2012

Mackay, A.W., Bezrukova, E.V., Leng, M.J., Meaney, M., Nunes, A., Piotrowska, N., Self, A., Shchetnikov, A., Shilland, E., Tarasov, P., Wang, L., White, D. 2012. Aquatic ecosystem responses to Holocene climate change and biome development in boreal, central Asia. Quaternary Science Reviews, 41, 119-131.

More information

Science — ²³⁸U/²³⁵U Systematics in Terrestrial Uranium Bearing Minerals — 30th March 2012

The new ²³⁸U/²³⁵U ratio will allow geologists to place more accurate limits on the exact timing of a broad range of geological processes, from the initial formation of our planet, continents and economic mineral deposits, to past evolutionary events and climate changes. In addition to the implications for U-Pb zircon geochronology, this study provides insight into uranium isotopic fractionation processes at magmatic temperatures, the possible role of weathering to driving changes of ²³⁸U/²³⁵U in seawater, and comparison of the terrestrial ²³⁸U/²³⁵U database to extra-terrestrial meteorite samples.

Hiess, J., Condon, D.J., McLean, N., and Noble, S.R. 2012. 238U/235U Systematics in Terrestrial Uranium Bearing Minerals. Science, 335, 1610-1613

Also see Science Perspective article by Claudine Stirling - Keeping Time with Earth's Heaviest Element. Science, 335, 1585-1586

Gondwana Research - May 2012

The volume of Earth's continental crust depends on the rate of addition of continental crust from the mantle compared to the rate of continental loss back to the mantle, which at present is roughly balanced. Models for the growth rate of continental crust vary, with isotope data suggesting various episodes of increased growth rate throughout Earth's history; these episodes have been correlated with the supercontinent cycle, but may be a consequence of preferential preservation of continental crust during these cycles. The global balance between addition and loss of continental crust is controlled by: 1) the extent of internal orogens versus exterior orogens, with the latter favouring continental addition, and 2) the balance between exterior orogens in retreating mode versus those in advancing mode, with the latter favouring continental loss. A greater balance of continental addition versus loss should exist during supercontinent break-up, due to a high magmatic flux in retreating accretionary orogens, whereas the amalgamation of supercontinents should involve increased continental loss due to increased sediment subduction and tectonic erosion. Zircon U-Pb and Hf isotopes provide insight to models of crustal growth rate since they sample the continental crust at their time of formation. Using the distribution of data within εHf(t)-time space of a global zircon database, it is demonstrated that the data are in accord with the concept of increased continental loss during supercontinent amalgamation.

Periods featuring increased continental addition relative to continental loss, and hence increased continental crust growth rate, occur at ~ 1.7–1.2 Ga, ~ 0.85–0.75 Ga, and ~ 0.45–0.35 Ga, and follow the formation of the Columbia (Nuna), Rodinia and Gondwana supercontinents respectively. Distinct increases in continental loss compared to continental addition, i.e. decreased continental growth rate, occur at c. 1.0–0.9 Ga, and ~ 0.6–0.55 Ga, correlating with the periods of Rodinia and Gondwana amalgamation respectively. Formation of Pangea by introversion rather than extroversion, means that continental addition in exterior orogens was concurrent with continental loss in interior orogens; a similar process may have been responsible for formation of the Columbia supercontinent. Peaks in the compilation of U-Pb zircon ages correlate with the timing of supercontinent amalgamation, and are likely to be a consequence of preferential preservation of continental crust during this part of the supercontinent cycle.

Roberts, N. M. W., 2012. Increased loss of continental crust during supercontinent amalgamation. Gondwana Research 21, 994-1000.

• More information

Palaeogeography, Palaeoclimatology, Palaeoecology - February 2012

We aim to reconstruct the climatic and environmental conditions in the Valsequillo Basin during the deposition of the Valsequillo gravels between c. 40 000 and 8000 years ago, when large mega-fauna and potentially humans occupied the basin. Fossil freshwater (Fossaria sp. and Sphaeriidae (Family)) and terrestrial (Polygyra couloni, Holospira sp. and Cerionidae (Family)) snail shells from sections within the Barranca Caulapan were collected for oxygen and carbon stable isotope analysis. Oxygen and carbon isotopes in terrestrial and freshwater snail shells relate to local climatic parameters and environmental conditions prevailing during the lifetime of the snail. Whole shell isotope analysis showed that c. 35 000 years ago climate in the Valsequillo Basin was similar to the present day. Between c. 35 000 and 20 000 BP conditions became increasingly dry, after which conditions became wetter again, although this record is truncated. Intra-shell isotopic analyses show that the amount of precipitation varied seasonally during the late Pleistocene. If people did reach this part of the Americas in the late Pleistocene they would have experienced changing long-term and seasonal climatic conditions and would have had to adapt their life strategies accordingly.

Stevens, R.E., Metcalfe, S.E., Leng, M.J., Lamb, A.L., Sloane, H.J., Naranjo, E., Gonzalez, S. 2012. Reconstruction of late Pleistocene climate in the Valsequillo Basin (Central Mexico) through isotopic analysis of terrestrial and freshwater snails. Palaeogeography, Palaeoclimatology, Palaeoecology, 319-320, 16-27.

• More information

Rapid Communications in Mass Spectrometry - February 2012

Stable isotope analysis of cellulose is an increasingly important aspect of ecological and palaeoenvironmental research. Since these techniques are very costly, any methodological development which can provide simultaneous measurement of stable carbon and oxygen isotope ratios in cellulose deserves further exploration. A large number (3074) of tree-ring a-cellulose samples were used to compare the stable carbon isotope ratios (δ¹³C) produced by high-temperature (1400 °C) pyrolysis/gas chromatography (GC)/isotope ratio mass spectrometry (IRMS) with those produced by combustion GC/IRMS. Although the two data sets are very strongly correlated, the pyrolysis results display reduced variance and are strongly biased towards the mean. The low carbon isotope ratios of tree-ring cellulose during the last century, reflecting anthropogenic disturbance of atmospheric carbon dioxide, are thus overestimated. The likely explanation is that a proportion of the oxygen atoms are bonding with residual carbon in the reaction chamber to form carbon monoxide. The 'pyrolysis adjustment', proposed here, is based on combusting a stratified sub-sample of the pyrolysis results, across the full range of carbon isotope ratios, and using the paired results to define a regression equation that can be used to adjust all the pyrolysis measurements. In this study, subsamples of 30 combustion measurements produced adjusted chronologies statistically indistinguishable from those produced by combusting every sample.

This methodology allows simultaneous measurement of the stable isotopes of carbon and oxygen using high-temperature pyrolysis, reducing the amount of sample required and the analytical costs of measuring them separately.

Woodley, E.J., Loader, N.J., McCarroll, D., Young, G.H.F, Robertson, I, Heaton, T.H.E., Gagen, M.H. and Warham, J.O. 2012. High-temperature pyrolysis/gas chromatography/isotope ratio mass spectrometry: simultaneous measurement of the stable isotopes of oxygen and carbon in cellulose. Rapid Communications in Mass Spectrometry, 26, 109-114.

• More information

Terra Nova - February 2012

A shell of Gigantoproductus okensis shows twenty growth lines with marked changes of fabric, indicating periodical reduction of growth rates caused by environmental perturbations. The number of growth lines suggests a lifespan of 20 years in agreement with the survival rates of extant brachiopods, and with spiral deviation analysis. Geochemical analyses across the growth profile show a heterogeneous distribution of stable isotopes and trace elements. It is possible to distinguish primary from altered carbonate, and to interpret the isotopic data. The oxygen isotope signal in the unaltered parts is periodical and annual, with oscillation of 1.1 per mille. The higher values are at the growth lines (winter), and therefore most likely related to monsoon circulation during the Visean. The annual periodicity seems also present in the altered part of the shell, suggesting that diagenesis could have reset the primary values, but preserved their cyclicity.

Angiolini, L., Stephenson, M., Leng, M.J., Jadoul, F., Millward, D., Aldridge, A., Andrews, J., Chenery, S., Williams, G. 2012. Heterogeneity, cyclicity and diagenesis in a Mississippian brachiopod shell of palaeoequatorial Britain. Terra Nova, 24, 16-26.

• More information

Geochimica et Cosmochimica Acta - February 2012

This paper presents a significantly simplified method for in-situ U-Th-He dating removing the need to know any absolute concentrations. This is done by calculating the normalised U, Th, and He concentrations of a conventionally dated calibration standard from its measured Th/U ratio and known U-Th-He age, and scaling these concentrations to the raw U, Th, and He signals of the sample. The Th/U ratio of the standard can be determined from its measured 208Pb/206Pb ratio, removing the need to use NIST glass as a reference material. We introduce an LA-ICP-MS-based method to correct for variable ablation depths between the standard and the unknown, using the strength of the ablated 29Si signal. Finally, we propose a pseudo-depth profile method to assess the effects of compositional zoning on the accuracy of in-situ U-Th-He data.

The effectiveness of the proposed method has been demonstrated on three samples of gem-quality Sri Lanka zircon, which yield ages that are in agreement with previously published conventional U-Th-He measurements.

Vermeesch, P., Sherlock, S. C., Roberts, N. M. W., Carter, A., 2012. A simple method for in-situ U-Th-He dating. Geochimica et Cosmochimica Acta 79, 140-147.

• More information

Chemical Geology - February 2012

Stable carbon isotope time-series (δ13C) from tree-rings are capable of providing valuable palaeoclimatic information, but analysis of individual tree-rings is time consuming and expensive. Pooling material from several tree-rings prior to isotopic analysis reduces costs, but does not allow the magnitude of uncertainty in the mean δ13C chronology to be calculated unless the pool is broken and each tree-ring measured individually at regular intervals. Here we use a comparison of pooled and mean individual (the arithmetic mean of isotopic data from tree series measured individually) δ13C records between AD 1650 and 2007, comprising cores from 21 Scots pine (Pinus sylvestris L.) trees growing in the western Highlands of Scotland. The aim is to determine whether the true error structure of the time series is better captured by using the overall mean error estimate for the entire time series or by linear interpolation between the equally spaced measurements.

We conclude that where autocorrelation exists within the error structure of a chronology, annual estimates of 95% confidence intervals, developed through linear interpolation at 5-year or 10-year intervals, are preferable to using the overall mean uncertainty. The method outlined increases the viability of pooled δ13C records for palaeoclimatic research by retaining error structure whilst reducing analytical time and costs. The method is applied here using tree-ring data, but could theoretically be applied to any well-replicated time-series.

Woodley, E. J., Loader, N. J., McCarroll, D., Young, G. H. F., Robertson, I., Heaton, T. H. E., Gagen, M. J., 2012. Estimating uncertainty in pooled stable isotope time-series from tree-rings. Chemical Geology 294-295, 243-248.

• More information

Journal of Hydrology - January 2012

Levels of nitrate in Malta's groundwater are amongst the highest in Europe (median concentrations of 14 mg NO₃-N L^-1 in the main sea-level aquifer, and 37 mg NO₃-N L^-1 in the younger groundwaters of the perched aquifers). As part of a Rural Development Programme for Malta, the British Geological Survey was contracted to investigate the source/s of this nitrate, with specific emphasis on a combined ¹⁵N/¹⁴N and ¹⁸O/¹⁶O study. In addition to analysing a wide variety of groundwater samples, a special feature of the study was a determined effort to measure, rather than assume (as is common in many studies) the ¹⁵N/¹⁴N and ¹⁸O/¹⁶O compositions of the major potential sources of nitrate: fertilizers, septic and sewage wastes, animal manures, and soils. The data allowed the former two sources to be ruled out and, whilst some direct leaching of manure-derived nitrate could not be discounted, the data suggested that soil nitrification is the major source of nitrate in the groundwaters. Malta has a very long history of cultivation, during which time the soils may have developed high ¹⁵N/¹⁴N values reflecting greater mobility of nitrogen in soils with low C/N ratios.

The ¹⁵N/¹⁴N and ¹⁸O/¹⁶O values of nitrate in the groundwaters suggest that it is derived by microbial nitrification of organic N in these soils, with virtually no reduction in nitrate levels by denitrification.

Heaton, T.H.E., Stuart, M.E., Sapiano, M. and Micallef Sultana, M. 2012. An isotope study of the sources of nitrate in Malta's groundwater. Jounal of Hydrology, 414-415, 244-254.

• More information

Geology - November 2011

Multiproxy analysis of a well-dated 25 ka lake sediment sequence from Lake Challa, on the eastern flank of Mount Kilimanjaro (East Africa), reveals the climatic controls that govern both the lake's paleohydrology and the climate-proxy record contained in the mountain's receding ice cap. The oxygen isotope record extracted from diatom silica (δ¹⁸O_diatom) in Lake Challa sediments captured dry conditions during the last glacial period and a wet late-glacial transition to the Holocene interrupted by Younger Dryas drought. Further, it faithfully traced gradual weakening of the southeastern monsoon during the Holocene. Overall, δ¹⁸O_diatom matches the branched isoprenoid tetraether (BIT) index of rainfall-induced soil runoff, except during 25–22 ka and the past 5 k.y. when insolation forcing due to orbital precession enhanced the northeastern monsoon.

This pattern arises because during these two periods, a weakened southeastern monsoon reduced the amount of rainfall during the long rainy season and enhanced the opposing effect of evaporation intensity and/or length of the austral winter dry season. Importantly, our lake-based reconstruction of moisture-balance seasonality in equatorial East Africa also helps us understand the oxygen isotope record contained in Mount Kilimanjaro ice. Negative correlation between ice core δ¹⁸O and Lake Challa δ¹⁸O_diatom implies that moisture balance is not the primary climate control on the long-term trend in ice core δ¹⁸O

Barker, P.A., Hurrell, E.R., Leng, M.J., Wolff, C., Cocqyut, C., Sloane, H.J., Verschuren, D. 2011. Seasonality in equatorial climate over the last 25 k.y. revealed by oxygen isotope records from Mount Kilimanjaro. Geology, 39, 1111-1114.

• More information

Quaternary Science Reviews - November 2011

Glacioeustatic- and temperature-corrected planktonic foraminiferal oxygen isotope records from the Amazon Fan provide a means of monitoring past changes in the outflow of the Amazon River. This study focuses on the last deglaciation and reveals that during this period there were significant variations in the outflow, which implies large changes in moisture availability in the Amazon Basin. Aridity in the Amazon Basin seems to occur between 20.5 ka (calendar) to 17.0 ka and 13.6 ka to 11 ka. The second arid period correlates with the start of the Antarctic Cold Reversal and aridity continues throughout the Younger Dryas period. We find that the large-scale trends in Amazon River outflow are dissimilar to high-latitude variability in either hemisphere. Instead high-resolution variations correlate with the δ¹⁸O difference between Greenland and Antarctica ice core temperature records. This suggests a link between Hemispheric temperature gradients and moisture availability over the Amazon.

Based on our results and previously published work we present a new testable 'dynamic boundary-monsoon intensity hypothesis', which suggests that tropical moisture is not a simple belt that moves north or south. Rather, the northern and southern boundaries of the South American Summer Monsoon (SASM) are independently dynamic and driven by temperature gradients within their individual hemispheres. The intensity of rainfall within the SASM, however, is driven by precessionally modulated insolation and the resultant convection strength. Combining these two influences produces the dynamic heterogenic changes in the moisture availability observed over tropical South America since the Last Glacial Maximum.

Maslin, M.A., Ettwein, V.J., Wilson, K.E., Guilderson, T.P, Burns, S.J., Leng, M.J. 2011. Dynamic boundary-monsoon intensity hypothesis: evidence from the deglacial Amazon River discharge record. Quaternary Science Reviews, 30, 3823-3833.

• More information

PLoS one - November 2011

The Intergovernmental Panel on Climate Change (IPCC) provides a conservative estimate on rates of sea-level rise of 3.8 mm/yr at the end of the 21st century, which may have a detrimental effect on ecologically important mangrove ecosystems. Understanding factors influencing the long-term resilience of these communities is critical but poorly understood. We investigate ecological resilience in a coastal mangrove community from the Galapagos Islands over the last 2700 years. Palaeoecological methods (AMS radiocarbon dating, stable carbon isotopes) were used to reconstruct sedimentation rates and ecological change at Diablas lagoon. Bulk geochemical analysis was also used to determine local environmental changes, and salinity was reconstructed using a diatom transfer function. Changes in relative sea level (RSL) were estimated using a glacio-isostatic adjustment model.

Non-linear behaviour was observed in the Diablas mangrove ecosystem as it responded to increased salinities following exposure to tidal inundations. A negative feedback was observed which enabled the mangrove canopy to accrete vertically, but disturbances may have opened up the canopy and contributed to an erosion of resilience over time. A combination of drier climatic conditions and a slight fall in RSL then resulted in a threshold response, from a mangrove community to a microbial mat.

Seddon, A.W.R., Froyd, C.A., Leng, M.J., Milne, G.A., Willis, K.J. 2011. Ecosystem Resilience and Threshold Response in the Galápagos Coastal Zone. PLOS ONE, 6 (7), DOI: 10.1371/journal.pone.0022376.

• More information

Journal of Archaeological Science - November 2011

Carbon and oxygen isotope ratios in the shells of the freshwater Unio mollusc yield information on the isotopic composition of the water in which the shell was formed, which in turn relates to climatic conditions prevailing during the bivalves' life span. Here we analysed shells from one modern Unio, from a modern lake shore in Anatolia, and 4 subfossil Unio shells from Çatalhöyük (dated between 7200 BC and 5000 BC, Neolithic and Chalcolithic periods). Sequential carbon and oxygen isotope analysis along the surface of the shells provides information on seasonal or shorter-term variability of lake waters during the lifetime of the organisms. Stable isotope analysis along the growth of freshwater bivalves is one of the few methods for investigating seasonal water fluctuations in the past.

Bar-Yosef, D., Leng, M.J., Aldridge, D.C., Arrowsmith, C., Gümüs, B.A., Sloane, H.J. 2011. Modern and early-middle Holocene shells of the freshwater mollusc Unio, from Çatalhöyük in the Konya basin, Turkey: Preliminary palaeoclimatic implications from molluscan isotope data. Journal of Archaeological Science, 39, 76-83.

• More information

Geochimica et Cosmochimica Acta - November 2011

This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the oxygen isotope analysis of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of oxygen isotope values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by SEM were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a SD for oxygen isotope analysis values between 0.3 and and 0.9‰.

Based on the results, we propose four additional biogenic silica working standards for oxygen isotope analysis, available on request through the relevant laboratories.

Chapligin, B., Leng, M.J., Webb, E., Alexandre, A., Dodd, J.P., Ijiri, A., Lucke, A., Shemesh, A., Abelmann, A., Herzschuh, U., Longstaffe, F.J., Meyer, H., Moschen, R., Okazaki, Y., Rees, N.H., Sharp, Z.D., Sloane, H.J., Sonzogni, C., Swann, G.E.A., Sylvestre, F., Tyler, J.J., Yam, R. 2011. Inter-laboratory comparison of oxygen isotope compositions from biogenic silica. Geochimica et Cosmochimica Acta, 75, 7242-7256.

• More information

Journal of Archaeological Sciences - October 2011

This paper explores the impact of animal manure application on the δ¹⁵N values of a broad range of crops (cereals and pulses): under a range of manuring levels/regimes, and at a series of locations extending from northwest Europe to the eastern Mediterranean. We included both agricultural field experiments and areas where 'traditional' farming is practised. Our aim is to ground-truth interpretation of δ¹⁵N values in archaeobotanical crop remains as evidence of past growing conditions and husbandry practices. The results confirm the potentially radical impact of manuring on δ¹⁵N values in cereals, depending on manuring level, but indicate only a slight effect on pulses, which can fix atmospheric nitrogen. The expected geographical trend towards greater δ¹⁵N with increasing climatic aridity is not apparent, probably because the growing conditions for crops are 'buffered' through crop management. Each of these observations has fundamental implications for archaeobotanical interpretation of δ¹⁵N values as evidence of land use practices and (together with analysis of bone collagen/tooth enamel in potential consumers) palaeodiet.

Fraser, R., Bogaard, A., Heaton, T., Charles, M., Jones, G., Christensen, B.T., Halstead, P., Merbach, I., Poulton, P.R., Sparkes, D. and Styring A., 2011. Manuring and stable nitrogen isotope ratios in cereals and pulses: towards a new archaeobotanical approach to the inference of land use and dietary practices. Journal of Archaeological Sciences, 38, 2790-2804.

• More information

Ecosystems - September 2011

Various studies over the last 15 years have attempted to describe the processes of N retention, saturation and NO3-leaching in semi-natural ecosystems based on stable isotope studies. Forest ecologists and terrestrial biogeochemists have used 15N labelled NO3 and NH4 tracers to determine the fate of atmospheric deposition inputs of N to terrestrial ecosystems, with NO3 leaching to surface waters being a key output flux. Separate studies by aquatic ecologists have used similar isotope tracer methods to determine the fate and impacts of inorganic N species, leached from terrestrial ecosystems, on aquatic ecosystems; usually without reference to comparable terrestrial studies. A third group of isotopic studies has employed natural abundances of 15N and 18O in precipitation and surfacewater NO3 to determine the relative contributions of atmospheric and microbial sources. These three sets of results often appear to conflict with one another. Here we attempt to synthesize and reconcile the results of these differing approaches to identifying both the source and the fate of inorganic N in natural or semi-natural ecosystems, and identify future research priorities. We conclude that the results of different studies conform to a consistent conceptual model comprising:

(1) rapid microbial turnover of atmospherically deposited NO3 at multiple biologically active locations within both terrestrial and aquatic ecosystems; (2) maximum retention and accumulation of N in carbon-rich ecosystems; and (3) maximum leaching of NO3 ,most of which has been microbially cycled, from carbon-poor ecosystems exposed to elevated atmospheric N inputs.

Curtis, C.J., Evans, C., Goodale, C.L. and Heaton, T.H.E., 2011. What have stable isotope studies revealed about the nature and mechanisms of N saturation and nitrate leaching from semi-natural catchments? Ecosystems, 14, 1021-1037.

• More information

Quaternary Science Reviews - September 2011

Precise relative sea level (RSL) data is important for inferring regional ice sheet histories, as well as helping to validate numerical models of ice sheet evolution and glacial-isostatic adjustment. Here we develop a new RSL curve for the Fildes Peninsula, South Shetland Islands (SSIs), a sub-Antarctic archipelago peripheral to the northern Antarctic Peninsula ice sheet, by integrating sedimentary evidence from isolation basins with geomorphological evidence from raised beaches. This combined approach yields not only a Holocene RSL curve, but also the spatial pattern of how RSL change varied across the archipelago.

Watcham, E.P., Bentley, M.J., Hodgson, D.A., Roberts, S.J., Fretwell, P.T., Lloyd, J.M., Larter, R.D., Whitehouse, P.L., Leng, M.J., Monien, P. and Moreton, S.G. 2011. A new Holocene relative sea level curve for the South Shetland Islands, Antarctica. Quaternary Science Reviews, 30, 3152-3170.

• More information

Quaternary Science Reviews - September 2011

There is a known bias in C/N, δ¹³C and δ¹⁵N values of organic matter (OM) due to pre-analysis acid treatment methods. We report here, for the first time, the results of a pre-analysis acid treatment method comparison of measured C/N, δ¹³C and δ¹⁵N values in bulk OM from a sedimentary sequence of samples to illustrate this bias. Here we show that acid treatment significantly reduces the accuracy (between method biases) and precision (within method bias) of δ¹³C and δ¹⁵N values of OM, suggesting a differential response of sample OM between methods and sample horizons, and in some cases inefficient removal of inorganic carbon. We show that different methods can significantly influence environmental interpretation in some of our sample horizons (i.e. interpretation of aquatic vs. terrestrial OM source; C₃ vs. C₄ vegetation).

Brodie, C.R., Casford, J.S.L., Lloyd, J.M., Leng, M.J., Heaton, T.H.E., Kendrick, C.P., Zong, Y.Q. (2011) Evidence For Bias In C/N, δ¹³C and δ¹⁵N Values Of Bulk Organic Matter, And On Environmental Interpretation, From A Lake Sedimentary Sequence By Pre-Analysis Acid Treatment Methods. Quaternary Science Reviews. 30, 3076 - 3087. doi: 10.1016/j.quascirev.2011.07.003

• More information

Application note - September 2011

At NIGL we are closely collaborating with Nu Instruments to develop the Nu Attom HR ICP-MS as a functional, reliable and efficient tool for isotope ratio analysis. Laser ablation sampling coupled to measurement via ICP-MS is an increasingly used tool within Earth and environmental science, and can be used for determining quantitative trace element concentrations of materials, as well as for isotopic dating of minerals in particular within U-Pb geochronology. Within this application note, we report the use of the Nu Attom for determining U-Th-Pb isotopes in zircon and monazite crystals, and demonstrate the ability to combine these isotope ratio measurements with other trace element concentrations using the wide mass range available in rapid peak scanning mode.

Nick M W Roberts, Sabine Pawlig, Matthew Horstwood. 2011. Nu Attom HR ICP-MS: Laser Ablation U-Pb Geochronology, Nu Instruments Application Note AN11.

• More information

Global and Planetary Change - September 2011

Magnetic and geochemical core data spanning the last 17,000 years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence. The lake deepened at 15.3 cal kyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5 cal kyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5 cal kyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2 cal kyr BP.

Precipitation declined after 6.8 cal kyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~ 4.2 cal kyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.

Marshall, M.H., Lamb, H.F., Huws, D., Davies, S.J., Bates, R., Bloemendal, J., Boyle, J., Leng, M.J., Umer, M., Bryant, C. 2011. Late Pleistocene and Holocene drought events at Lake Tana, the source of the Blue Nile. Global and Planetary Change, 78, 147-161.

• More information

Lethaia - July 2011

The Paleocene-Early Eocene carbonate successions of the Indus Basin in Pakistan formed on the north-western continental shelf margin of the Indian Plate in the eastern Tethys Ocean. Based on Larger Benthic Foraminifera eight Tethyan foraminiferal biozones spanning the Paleocene-Eocene boundary interval are identified. Stable isotope analysis through the P-E boundary interval identifies more positive δ¹³C values for the Late Paleocene and less positive values for the earliest Eocene. However, there is insufficient sampling resolution to identify the PETM δ¹³C maximum negative excursion itself. During Late Paleocene times LBF assemblages in the Indus Basin were taxonomically close to those of west Tethys, facilitating biostratigraphic correlation. However, this faunal continuity is lost at the P-E boundary and the earliest Eocene succession lacks typical west Tethys Nummulites, whilst Alveolina are rare: LBFs such as Miscellanea and Ranikothalia continue to dominate.

The apparent absence of Nummulites from the earliest Eocene of Pakistan and rarity of Alveolina -elsewhere used as the prime marker for the base of the Eocene, may imply a geographical barrier between East and West Tethys faunas, perhaps caused by India-Asia collision. Later, faunal links were re-established and many foraminifera with west Tethys affinities appeared in east Tethys.

Afzal, J., Williams, M., Leng, M.J., Aldridge, R.J., Stephenson, M.H. 2011. Evolution of Paleocene to Early Eocene larger benthic foraminifera assemblages of the Indus Basin, Pakistan. Lethaia, 44, 299-320.

• More information

Journal of the Geological Society - July 2011

The Tyrone Igneous Complex is one of the largest areas of ophiolitic and arc-related rocks exposed along the northern margin of Iapetus within the British and Irish Caledonides. New U-Pb zircon data and regional geochemistry suggest that the Tyrone Plutonic Group represents the uppermost portions of a c. 480 Ma suprasubduction-zone ophiolite accreted onto an outboard segment of Laurentia prior to 470.3 ± 1.9 Ma. The overlying Tyrone Volcanic Group formed as an island arc that collided with the Laurentian margin during the Grampian phase of the Caledonidan orogeny. Early magmatism is characterized by transitional to calc-alkaline, light REE (LREE)-enriched island-arc signatures, with an increasing component of continentally derived material up sequence. Tholeiitic rhyolites with flat to U-shaped REE profiles and LREE-depleted basalts, located stratigraphically below a c. 473 Ma rhyolite of the upper Tyrone Volcanic Group, suggest initiation of intra-arc rifting at c. 475 Ma.

Metamorphic cooling ages from the Tyrone Central Inlier imply arc-continent collision before 468 ± 1.4 Ma, with the emplacement of the Tyrone Volcanic Group onto the margin. A suite of 470.3 ± 1.9 Ma to 464.3 ± 1.5 Ma calc-alkaline intrusions are associated with the continued closure of Iapetus.

Cooper, M.R., Crowley, Q.G., Hollis, S.P., Noble, S.R., Roberts, S., Chew, D., Earls, G., Herrington, R. and R.J. Merriman. 2011. Age constraints and geochemistry of the Ordovician Tyrone Igneous Complex, Northern Ireland: implications for the Grampian orogeny. Journal of the Geological Society,168, 837-850.

• More information

Journal of the Geological Society - July 2011

An isotope dilution thermal ionization mass spectrometry U-Pb zircon age of 411.5 ± 1.3 Ma obtained from an andesitic lava occurring within the Lower Devonian Rhynie Outlier (Aberdeenshire, NE Scotland) effectively dates the Rhynie Chert Konservat-Lagerstätte. Biostratigraphical constraints on the Rhynie Chert-bearing succession indicate that this age lies within the interval early (but not earliest) Pragian-(?)earliest Emsian. Accordingly, the Pragian-Emsian boundary must post-date or closely approximate to 411.5 ± 1.3 Ma, while the Lochkovian-Pragian boundary must predate 411.5 ± 1.3 Ma. Integration of this new high-precision age with an improved temporal framework for late Caledonian intrusive activity in NE Scotland suggests that the Rhynie hot-spring system (the 'parental' hydrothermal system to the Rhynie cherts) was unrelated to any 'Newer Granite' intrusion.

Rhynie was instead powered by a basaltic andesite magma whose generation and ascent were directly linked to the transcurrent fault movements responsible for the formation of the Rhynie basin.

Parry, S.F., Noble, S.R., Crowley, Q.G. and Wellman, C.H., 2011. A high-precision U-Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications. Journal of the Geological Society, 168, 863-872.

• More information

Geochemistry. Geophysics, Geosystems. - June 2011

Here we present combined radioisotopic dating (U-Pb zircon) and cyclostratigraphic analysis of the carbon isotope excursion at the Paleocene-Eocene (P-E) boundary in Spitsbergen to determine the numerical age of the boundary. Incorporating the total uncertainty from both radioisotopic and cyclostratigraphic data sets gives an age ranging from 55.728 to 55.964 Ma, within error of a recently proposed astronomical age of ∼55.93 Ma. Combined with the assumption that the Paleocene Epoch spans twenty-five 405 kyr cycles, our new age for the boundary suggests an age of ∼66 Ma for the Cretaceous-Paleogene boundary. Furthermore, our P-E boundary age is consistent with the hypothesis that the onset of the Paleocene-Eocene thermal maximum at the boundary occurred on the falling limb of a 405 kyr cycle, suggesting the event was initiated by a different mechanism to that which triggered the other early Eocene hyperthermals.

Charles, A. J., D. J. Condon, I. C. Harding, H. Pälike, J. E. A. Marshall, Y. Cui, L. Kump, and I. W. Croudace. 2011. Constraints on the numerical age of the Paleocene-Eocene boundary. Geochemistry. Geophysics, Geosystems., 12, Q0AA17, doi:10.1029/2010GC003426.

• More information

Earth and Planetary Science Letters - June 2011

We present LA-MC-ICPMS and ID-TIMS U-Pb ages of metamorphic allanite from the Eclogite Zone, Tauern Window, which when coupled with rare earth element analysis and thermobarometric modelling, demonstrate that the European continental margin was subducted to between 8 and 13 kbar (30-45 km) by 34.2 ± 3.6 Ma. These data define: (i.) an upper limit on the timing of eclogite facies metamorphism at 26.2 ± 1.8 kbar (70-80 km) and 553 ± 12 °C, (ii.) plate velocity (1-6 cm·a-1) exhumation of the Eclogite Zone from mantle to mid-crustal depths, and (iii.) a maximum duration of 10 Ma (28-38 Ma) for juxtaposition of Alpine upper-plate and European basement units and subsequent conductive heating thought to have driven regional Barrovian (re)crystallisation at ca. 30 Ma.

Given that the Tauern Window is a classic locality for understanding rates of conductive thermal relaxation in tectonically thickened crust, this work raises questions of fundamental importance concerning the length scales of the mechanisms responsible for heat transfer within orogenic crust.

Andrew J. Smye, Mike J. Bickle, Tim J.B. Holland, Randall R. Parrish and Daniel J. Condon. 2011. Rapid formation and exhumation of the youngest Alpine eclogites: A thermal conundrum to Barrovian metamorphism. Earth and Planetary Science Letters, Volume 306, Issues 3-4, Pages 193-204, doi:10.1016/j.epsl.2011.03.037.

• More information

Earth and Planetary Science Letters - June 2011

In this study, we have used in-situ U-Pb, Hf and O isotopic analyses of zircon grains to gain insights into both magmatic processes and duration of magmatism in igneous rocks from the Tuscan Magmatic Province (0.1-9 Ma), Italy. From zircon isotopic data we show that construction of the Monte Capanne pluton (Elba) may have occurred over a period of c. 0.5 Ma. A significant range of both 176Hf/177Hf (determined by LA-MC-ICPMS) and δ¹⁸O (determined by ion microprobe) in zircon (∼ 7 epsilon Hf units and ∼ 5‰, respectively) is present, which, together with zircon morphology and trace element data, emphasises the importance of mixing and replenishment involving magma batches with both metaluminous and peraluminous affinities. While mixing undoubtedly occurred between mafic (metaluminous) and felsic (peraluminous) magmas, the range of Hf and O isotopic data suggests a diversity within the peraluminous component.

The unradiogenic Hf composition (εHf(t) <- 4) and relatively heavy δ¹⁸O signature (> 6‰) of the inferred mantle-derived component strongly supports the idea that the mantle source involved in Tuscan magmatism was severely modified by subduction-related, crustal-derived metasomatic fluids.

D. Gagnevin, J.S. Daly, M.S.A. Horstwood and M.J. Whitehouse. 2011. In-situ zircon U-Pb, oxygen and hafnium isotopic evidence for magma mixing and mantle metasomatism in the Tuscan Magmatic Province, Italy. Earth and Planetary Science Letters, Volume 305, Issues 1-2, Pages 45-56, doi:10.1016/j.epsl.2011.02.039.

• More information

Journal of the Geological Society - May 2011

Three dated (U-Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire and Pembrokeshire delimit the traditional “Lower”/”Middle” Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.50 ± 0.25 million years (Ma) from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, while a date of 509.02 ± 0.20 Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates directly constrain the age of the intervening Comley Limestones, which contain diverse small shelly fossils, and a key early occurrence of exceptional, three-dimensionally preserved arthropods.

In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.38 ± 0.28 Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level where trilobites make their first local appearance.

Harvey, T.H.P., Williams, M., Condon, D.J., Wilby, P.R., Siveter, D.J., Rushton, A.W.A., Leng, M.J., Gabbott, S.E. 2011. A refined chronology for the Cambrian succession of southern Britain. Journal of the Geological Society, London, 168, 705-716.

• More information

Rapid Communications in Mass Spectrometry - April 2011

This systematic study compares the effects of pre-analysis acid treatment methods on the measured δ¹⁵N values of terrestrial and aquatic, modern and ancient, environmental materials. We investigate the effect of acid treatment on the measured δ¹⁵N of sample organic matter in light of the increasing application of "dual-mode" isotope analysis, where δ¹³C and δ¹⁵N are measured simultaneously from the same pre-treated sample aliquot. We investigate 3 common methods;

1. untreated samples
2. acidification followed by sequential water rinse (rinse method)
3. acidification in silver capsules (capsule method)

We also investigate the influence of capsule type (silver and tin) on δ¹⁵N.

Brodie, C.R., Heaton, T.H.E., Leng, M.J., Kendrick, C.P., Casford, J.S.L., Lloyd, J.M. 2011. Evidence for bias in measured d15N values of terrestrial and aquatic organic materials due to pre-analysis acid treatment methods. Rapid Communications in Mass Spectrometry, 25, 1089-1099.

• More information

Chemical Geology - March 2011

This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ¹³C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods:

1. acidification followed by sequential deionised water rinses ("rinse method")
2. acidification in silver capsules ("capsule method")
3. acidification by exposure to an acid vapour ("fumigation method")

Brodie, C.R., Leng, M.J., Casford, J. S. L., Kendrick, C.P., Lloyd, J.M., Yongqiang, Z., and Bird, M.I. 2011. Evidence for bias in C and N concentrations and δ¹³C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation methods. Chemical Geology, 282, 67-83.

• More information

Quaternary Science Reviews - March 2011

The last millennium is a key period for understanding environmental change in East Africa, as there is clear evidence of marked fluctuations in climate (effective moisture) that place modern concern with future climate change in a proper context, both in terms of environmental and societal impacts and responses. Here, we compare sediment records from two small, nearby, closed crater lakes in western Uganda (Lake Kasenda and Lake Wandakara), spanning the last 700 (Wandakara) and 1200 years (Kasenda) respectively.

Ryves, D.B., Mills, K., Bennike, O., Brodersen, K.P., Lamb, A.L., Leng, M.J., Russell, J.M. and Ssemmanda. I. 2011. Environmental change over the last millennium recorded in two contrasting crater lakes in western Uganda, eastern Africa (Lakes Kasenda and Wandakara). Quaternary Science Reviews, 30, 555-569.

• More information

Journal of Paleolimnology - February 2011

This paper covers the sedimentology, benthic foraminifera, molluscs, and δ¹⁸O and δ¹³C of Ammonia tepida tests in two late Holocene sediment cores from Lake Qarun (Egypt). The cores, QARU2 (upper section, 8.2 m) and QARU4 (1.4 m), span approximately the past 500 years of sedimentation.

Abu-Zied, R., Flower, R., Keatings, K., Leng, M.J. 2011. Benthic foraminifera and their stable isotope composition in sediment cores from Lake Qarun, Egypt: changes in water salinity during the past ∼500 years. Journal of Paleolimnology, 45, 167-182.

• More information

Palaeogeography, Palaeoclimatology, Palaeoecology - January 2011

Biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes. Changes in the isotopic composition of the diatom frustules (δ¹⁸O_diatom and δ¹³C_diatom) in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes. The Lago Chungará diatomaceous laminated record is made up of white and green multiannual rhythmites related to mixing events and deposition over several years. Analyses of both δ¹⁸O_diatom and δ¹³C_diatom in these rhythmites are interpreted in terms of shifts in the precipitation/evaporation ratio and changes in the lake water dissolved carbon concentration, respectively.

ENSO and solar activity are the most likely main climate forcing mechanisms.

Hernández, A., Bao, R., Giralt, S., Barker, P.A., Leng, M.J., Sloane, H.J., Sáez, A. 2011. Biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in Late Glacial to Holocene lacustrine ryythmites. Palaeogeography, Palaeoclimatology, Palaeoecology, 299, 413-425.

• More information

Journal of the Geological Society, London - January 2011

The Moine Thrust Zone in the Scottish Highlands developed during the Scandian Event of the Caledonian Orogeny, and now forms the boundary between the Caledonian orogenic belt and the undeformed foreland. The Scandian Event, and the formation of the Moine Thrust Zone, have previously been dated by a range of isotopic methods, and relatively imprecise ages on a suite of alkaline intrusions localized along the thrust zone have provided the best age constraints for deformation. Recent British Geological Survey mapping has improved our understanding of the structural relationships of some of these intrusions, and this work is combined with new U-Pb dates in this paper to provide significantly improved ages for the Moine Thrust Zone. Our work shows that a single early intrusion (the Glen Dessarry Pluton) was emplaced within the orogenic belt to the east of the Moine Thrust Zone at 447.9 ± 2.9 Ma.

A more significant pulse of magmatism centred in the Assynt area, which temporally overlapped movement in the thrust zone, occurred at 430.7 ±; 0.5 Ma. Movement in the thrust zone had largely ceased by the time of emplacement of the youngest intrusions, the late suite of the Loch Borralan Pluton, at 429.2 ± 0.5 Ma, and the Loch Loyal Syenite Complex.

Goodenough, K.M., Millar, I.L., Strachan, R.A., Krabbendam, M. & Evans, J.A. Timing of regional deformation and development of the Moine Thrust Zone in the Scottish Caledonides: constraints from the U-Pb geochronology of alkaline intrusionsJournal of the Geological Society, London, Vol. 168, 2011, pp. 99-114. doi: 10.1144/0016-76492010-020.

• More information

Proceedings of the Geologists Association - January 2011

Using material from the Aeronian (Silurian) interval from Wales and Scotland as examples, we show that the carbon isotope composition of graptolite periderm (δ¹³C_grap.) provides a signal that is locally different but not consistently so from surrounding whole-rock samples (δ¹³C_whole-rock). Graptolite periderm δ¹³C seems not influenced by astogenetic stage of development or gross rhabdosome type and differences between δ¹³C_grap. from different metamorphic grades are minimal. Taken as a whole, the Aeronian interval examined shows little overall change, but large variations are seen on the small scale, possibly reflecting very local carbon cycling.

For carbon isotope stratigraphy in such rocks, therefore, large-scale bulk sampling will likely reduce inhomogeneities and give more reproducible results. Furthermore, in situations where terrestrial organic matter has been incorporated into the sediment, then graptolite carbon may more faithfully reflect bulk marine organic matter.

Andrea M. Snelling, Melanie J. Leng, Jan A. Zalasiewicz, Christopher C. Kendrick and Alex A. Page. 2011. Carbon isotope composition of graptolite periderm and whole-rock from the Aeronian (Silurian, Llandovery) in Wales and Scotland and its use in chemostratigraphy. Proceedings of the Geologists Association 122 (1) 82-91

• More information