Geology topics

Lauren T Reid

Publications and source records attributed to Lauren T Reid.

5 recordsLinked to original sources

USGS2026

Reaffirming the consistency of the original stock of NBS 19 limestone and its byproduct with finer grain size for δ13C and δ18O calibrations—Both distributed internationally

Rationale Approximately 3–4 kg of NBS 19 limestone, prepared in 1982 by the U.S. Geological Survey (USGS), serves as a primary reference for the carbon isotope scales VPDB and VPDB-LSVEC and the oxygen isotope scale VPDB. Its consensus values are +1.95‰ for δ 13 C and −2.2‰ for δ 18 O measurements. After more than three decades of distribution, the number of units labeled “NBS 19” shrunk substantially, and the remaining material was quarantined, with a small fraction retained at the USGS and a larger fraction entrusted to the International Atomic Energy Agency (IAEA) for secure storage. Given the critical role of NBS 19, verifying the integrity of its δ 13 C and δ 18 O values across these storage locations is essential. Method Samples from IAEA and USGS stock materials were selected to ensure traceability of carbon and oxygen isotopes to NBS 19 distribution units from various storage locations. To achieve this, distribution units labeled as NBS 19 from both the IAEA and the National Institute of Standards and Technology (NIST) were included. During evaluation, two distinct grain sizes were identified within these units. Grain size was assessed using sieves on five selected samples. The δ 13 C and δ 18 O values of finer and coarser fractions (both labeled NBS 19) were measured at USGS using continuous-flow isotope-ratio mass spectrometry on 100- and 200-μg samples. Results Expanded 95% measurement uncertainties ( k = 2) for δ 13 C and δ 18 O determinations are 0.027‰ and 0.038‰ or better, respectively, for quarantined NBS 19 stocks and finer byproduct calcite, which we term “NBS-19 byproduct,” regardless of storage location. Between the 1990s and circa 2011, NBS-19 byproduct labeled “NBS 19,” distributed by NIST and the IAEA, shows these findings. Conclusions NBS 19 primary isotopic reference material should be used for calibration of new isotopic reference materials rather than NBS-19 byproduct secondary isotopic reference material.

Rapid Communications in Mass Spectrometry↗

USGS2026

Three new calcium formate reference materials for δ13C measurements and a redetermination of the R(13C/12C) ratio for VPDB based on proton nuclear magnetic resonance measurements

Rationale Isotope ratio mass spectrometry (IRMS) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy are independent techniques for determining the isotope ratio R ( 13 C/ 12 C) in organic compounds. However, the lack of suitable reference materials has limited intercalibration of results from these methods. Methods Three high-purity calcium formate isotopic reference materials were developed, each ideal for accurate isotope ratio measurements by both 1 H NMR and isotope-ratio mass spectrometry (IRMS). For each material, R ( 13 C/ 12 C) was determined by 1 H NMR, and the relative isotope abundance ( δ 13 C VPDB-LSVEC ) by IRMS. The combined IRMS and NMR results were used to determine the R ( 13 C/ 12 C) value of Vienna Peedee belemnite (VPDB). Results The combined datasets yield a value for R ( 13 C/ 12 C) of 0.0111050 ± 0.0000047 ( k = 2) for VPDB, which is 6.7‰ lower than the commonly cited value of 0.011180, but similar to other recent determinations. These three calcium formate reference materials exhibit high accuracy across both analytical methods and provide robust tools for instrument calibration, method validation, and inter-laboratory comparison in carbon stable isotope ratio analysis. Conclusions An accurate R ( 13 C/ 12 C) value for VPDB strengthens the link between relative ( δ 13 C VPDB-LSVEC ) values from IRMS and R ( 13 C/ 12 C) isotope ratios from NMR and other techniques. These three calcium formate isotopic reference materials (USGS106, USGS107, and USGS108) are available from the US Geological Survey and provide reference materials for calibration, method validation, and inter-laboratory comparison in carbon isotope ratio analysis.

Rapid Communications in Mass Spectrometry↗

USGS2024

Using stable oxygen isotope dual-inlet isotope-ratio mass spectrometry to elucidate uranium transport and mixed 230Th/U calcite formation ages at the seminal Devils Hole, Nevada, natural laboratory

Rationale Vein calcite in Devils Hole has been precipitating continuously in oxygen-isotope equilibrium at a constant temperature for over 500 000 years, providing an unmatched δ 18 O paleoclimate time series. A substantial issue is that coeval calcite (based on matching δ 18 O values) has uranium-series ages differing by 12 000 years. Methods An unparalleled high-accuracy δ 18 O chronology series from continuously submerged calcite was used to correct the published uranium-series ages of non-continuously formed calcite in two cores, cyclically exposed by water-table decline during glacial–interglacial transitions. This method relies on the premise that the δ 18 O values of coevally precipitated calcite are identical, allowing matching calcite δ 18 O values to establish formation ages. Results Exposed calcite can have apparent ages that are 12 000 years too young due to unrecognized uranium mobility and resulting mixed ages identified in over 50 mixed uranium-series ages from previous studies. Secondary uranium in fluids, sourced from the formation or dissolution of porous carbonate deposits (folia) with high uranium-238 ( 238 U) concentrations, has migrated up to 10 mm into vein calcite. Conclusions The continuously submerged Devils Hole δ 18 O chronology is not explained by orbital forcing. Rather, this chronology represents a regional climate record in the southern Great Basin of sea-surface-temperature (SST) variations off California, variations that preceded the last and penultimate deglaciations by 5000 to approximately 10 000 years. Temporal discrepancies between the continuously submerged Devils Hole chronology and other regional δ 18 O records (e.g., the Leviathan chronology) can be explained by unrecognized cryptic, pernicious uranium mobility, leading to model estimations that may be thousands of years younger than actual ages. Consequently, paleo-moisture availability, water-table, and groundwater recharge models based on these mixed uranium-series ages are too young by as much as 12 000 years. The potential for post-formation uranium addition in subaerial cores and speleothems underscores the need for caution in uranium-series dating, highlighting δ 18 O time-series comparisons as a method for identifying mixed ages.

Nevada↗

USGS2021

USGS44, a new high-purity calcium carbonate reference material for δ13C measurements

Rationale The stable carbon isotopic ( δ 13 C) reference material (RM) LSVEC Li 2 CO 3 has been found to be unsuitable for δ 13 C standardization work because its δ 13 C value increases with exposure to atmospheric CO 2 . A new CaCO 3 RM, USGS44, has been prepared to alleviate this situation. Methods USGS44 was prepared from 8 kg of Merck high-purity CaCO 3 . Two sets of δ 13 C values of USGS44 were determined. The first set of values was determined by online combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO 3 ( δ 13 C VPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1‰), and LSVEC Li 2 CO 3 ( δ 13 C VPDB = −46.6 mUr exactly), and normalized to the two-anchor δ 13 C VPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI)-IRMS of CO 2 evolved by reaction of H 3 PO 4 with carbonates, corrected for cross contamination, and normalized to the single-anchor δ 13 C VPDB scale. Results USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr. Single-anchor δ 13 C VPDB values of −42.08 ± 0.01 and −41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination. Conclusions The new high-purity, well-homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr for both EA/IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13 C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope delta measurements to the δ 13 C VPDB-LSVEC scale. It is useful in quantifying drift with time, determining mass-dependent isotopic fractionation (linearity correction), and adjusting isotope-ratio-scale contraction. Due to its fine grain size (smaller than 63 μm), it is not suitable as a δ 18 O reference material. A δ 13 C VPDB-LSVEC value of −29.99 ± 0.05 mUr was determined for NBS 22 oil.

Rapid Communications in Mass Spectrometry↗

USGS2020

Food matrix reference materials for hydrogen, carbon, nitrogen, oxygen, and sulfur stable isotope-ratio measurements: Collagens, flours, honeys, and vegetable oils

An international project developed, quality-tested, and measured isotope–delta values of 10 new food matrix reference materials (RMs) for hydrogen, carbon, nitrogen, oxygen, and sulfur stable isotope-ratio measurements to support food authenticity testing and food provenance verification. These new RMs, USGS82 to USGS91, will enable users to normalize measurements of samples to isotope–delta scales. The RMs include (i) two honeys from Canada and tropical Vietnam, (ii) two flours from C3 (rice) and C4 (millet) plants, (iii) four vegetable oils from C3 (olive, peanut) and C4 (corn) plants, and (iv) two collagen powders from marine fish and terrestrial mammal origins. An errors-in-variables regression model included the uncertainty associated with the measured and assigned values of the RMs, and it was applied centrally to normalize results and obtain consensus values and measurement uncertainties. Utilization of these new RMs should facilitate mutual compatibility of stable isotope data if accepted normalization procedures are applied and documented.

Journal of Agricultural and Food Chemistry↗