Nitrogen cycling in western India as revealed by nitrogen isotopes,and the historic production of saltpetre

Saltpetre (KNO₃) manufacture was a principal monopoly industry in early Modern India when the United Kingdom governed the social and economic systems. The process represented microbial transformation of excrementitious livestock and human wastes deposited around habitats, resulting in formation of salt efflorescence at an economic scale. Low caste people collected these wastes for extraction and production of rough saltpetre under the administrative control of British India. Stable isotope composition (δ¹⁵N and δ¹⁸O) was used to trace details of the microbial transformation processes, often involving the isotopic fractionation of nitrogen and oxygen. Marked elevation in δ¹⁵N and δ¹⁸O values for nitrates in soils and deposits, relative to those of primary organic nitrogen in diets and water sources, characterizes the unique processes of historic saltpetre manufacture in British India.     

The Provenance of Historical Gunpowder from South‐Western Japan: A Stable Isotopic Approach

Stable isotopic analysis was undertaken for the gunpowder ingredients from crude saltpetre and propellants from several types of gun that prevailed during the late 19th century in south‐western Japan. Stable isotopic signatures for δ¹⁵N_{saltpetre nitrogen}, δ³⁴S_{native sulphur} and δ¹³C_{charcoal carbon} in crude saltpetre, gunpowder magazines bearing the trademark of mills from southern Scotland and cartridges for an improved Sharps rifle (with a US trademark) all imply common assemblages from the same source (saltpetre and native sulphur from British India and Sicily, respectively) in the United Kingdom (UK). One Pritchett patron is common for muzzle‐loading Enfield rifles, while the other suggests a four‐allied lead bullet for an unidentified hand gun. Propellants in the Pritchett patron from the same institution also suggest a common source of these rifles. On the contrary, the ingredients for an unidentified rifle and time fuse for a Paixhans gun with unique stylistic devices showed distinctive isotopic signatures, indicating a local Japanese origin. The Pritchett patron from the Kumamoto Museum involved a mixed provenance from the UK and Japan. The stable isotopic analysis provides direct evidence for the ultimate origin of the propellant.     

The stable isotopic composition of historical black powder applicable to a Japanese Tanegashima matchlock

The objective of the present study is to employ stable isotope ratio measurements (δ¹⁵N, δ³⁴S and δ¹³C) of the nitrogen, sulphur and carbon in black powder (a mixture of saltpetre, native sulphur and charcoal) as a means of source identification. A sum total of 20 samples of historical black powder applicable to matchlocks were collected from six locations throughout Japan. This classic type of hand gun prevailed up to the introduction of the modern rifles, with quicker loading and higher efficiency, in the mid‐to‐late 19th century. δ¹³C_{charcoal carbon} values showed the predominant use of C₃ plants as a source material. Except for a few unusual samples with a probable exotic origin, δ¹⁵N_{saltpetre nitrogen} values were largely consistent with those of domestic products using classical biotechnology. The isotopic analysis for native sulphur (δ³⁴S_{native sulphur}) indicates a complicated marketing route.     

Ancient hydrocarbon seeps from the Mesozoic convergent margin of California: carbonate geochemistry, fluids and palaeoenvironments

More than a dozen hydrocarbon seep‐carbonate occurrences in late Jurassic to late Cretaceous forearc and accretionary prism strata, western California, accumulated in turbidite/fault‐hosted or serpentine diapir‐related settings. Three sites, Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs, were analyzed for their petrographic, geochemical and palaeoecological attributes, and each showed a three‐stage development that recorded the evolution of fluids through reducing–oxidizing–reducing conditions. The first stage constituted diffusive, reduced fluid seepage (CH₄, H₂S) through seafloor sediments, as indicated by Fe‐rich detrital micrite, corroded surfaces encrusted with framboidal pyrite, anhedral yellow calcite and negative cement stable isotopic signatures (δ¹³C as low as ?35.5‰ PDB; δ¹⁸O as low as ?10.8‰ PDB). Mega‐invertebrates, adapted to reduced conditions and/or bacterial chemosymbiosis, colonized the sites during this earliest period of fluid seepage. A second, early stage of centralized venting at the seafloor followed, which was coincident with hydrocarbon migration, as evidenced by nonluminescent fibrous cements with δ¹³C values as low as ?43.7‰ PDB, elevated δ¹⁸O (up to +2.3‰ PDB), petroleum inclusions, marine borings and lack of pyrite. Throughout these early phases of hydrocarbon seepage, microbial sediments were preserved as layered and clotted, nondetrital micrites. A final late‐stage of development marked a return to reducing conditions during burial diagenesis, as implied by pore‐associated Mn‐rich cement phases with bright cathodoluminescent patterns, and negative δ¹⁸O signatures (as low as ?14‰ PDB). These recurring patterns among sites highlight similarities in the hydrogeological evolution of the Mesozoic convergent margin of California, which influenced local geochemical conditions and organism responses. A comparison of stable carbon and oxygen isotopic data for 33 globally distributed seep‐carbonates, ranging in age from Devonian to Recent, delineated three groupings that reflect variable fluid input, different tectono‐sedimentary regimes and time–temperature‐dependent burial diagenesis.     

Exploring Geographic Origins at Cahuachi using Stable Isotopic Analysis of Archaeological Human Tissues and Modern Environmental Waters

In this study, we used oxygen‐ and hydrogen‐isotope data from human bone (δ¹⁸O) and modern environmental water samples (δ¹⁸O and δD) to investigate geographic origins of individuals buried at Cahuachi, a ceremonial centre in the Nasca region of Peru (c.AD1‐1000). Our objective was to characterise the natural variation in water stable isotopic composition in the Rio Grande de Nasca drainage, and then to use these data to better infer place of origin for 30 adults interred at Cahuachi. Using the δ¹⁸O and δD values of 63 modern environmental water samples, it was possible to differentiate among the northern and southern river middle valleys, and to infer the isotopic composition of drinking water at higher elevations. Over half of the individuals included in this study had drinking water oxygen‐isotope compositions consistent with places of origin away from Cahuachi during the last 10 to 25 years of life, perhaps in the northern river middle valleys or in the upper valleys/sierra. The environmental water stable isotopic baseline developed in this study enabled a better understanding of the natural variation of waters in the Rio Grande de Nasca drainage. As a result, it was possible to assess the geographic range of place of origin for these individuals with greater certainty. Taken together, these data support the idea of Cahuachi as a place of both local and regional significance, with individuals from distant parts of the Rio Grande de Nasca drainage travelling to and/or transporting the dead to the site for death or burial. Copyright © 2011 John Wiley & Sons, Ltd.     

Age‐related variation in isotopic indicators of diet at medieval Kulubnarti,Sudanese Nubia

This study compares trends in dietary composition in two large cemetery populations from the site of Kulubnarti (AD 550–800) in Sudanese Nubia. Bone collagen and bone apatite carbonate were analysed to characterise stable carbon, nitrogen and oxygen isotopes. Previous research on these cemeteries has suggested marked differences in nutritional status and health between the populations. Contrary to expectations, there were no significant relationships between any isotopic indicators related to sex or cemetery of burial, suggesting no isotopically‐measurable differences in diet. However, collagen δ¹³C and δ¹⁵N were significantly related to age, suggesting age‐related differences in protein intake or other factors. Weaning trends are gradual and variable, with the range in δ¹⁵N values exceeding 4‰ among infants/young children (0–3 yrs) and standard deviations exceeding 1‰ in collagen δ¹³C and δ¹⁵N for both infants/young children and subadults (4–17 yrs). This suggests varied weaning strategies among both populations and variable diets prior to adulthood. Also observed was a distinct range of isotopic carbon and nitrogen values among individuals classified as subadults (4–17 yrs), who are depleted in collagen δ¹³C and δ¹⁵N relative to adults. However, both infants/young children and subadults are slightly enriched in δ¹⁸O relative to adults, which suggests the presence of non‐local individuals or age‐related variation in water sources. While most isotopic studies of age‐related dietary trends have focused on reconstructing the weaning process, this study presents findings that indicate tripartite isotopic trends distinguishing infancy, subadulthood and adulthood as separate dietary categories. Broad similarities are evident between the results presented here and those from several earlier studies of smaller populations and to nutritional studies of modern communities. These findings suggest that further research into health disparities at Kulubnarti should focus on non‐dietary causal factors, and more generally, that greater attention should be paid to subadulthood in palaeodiet studies. Copyright © 2006 John Wiley & Sons, Ltd.     

REFINING ESTIMATES FOR THE SEASON OF SHELLFISH COLLECTION ON THE PACIFIC NORTHWEST COAST: APPLYING HIGH‐RESOLUTION STABLE OXYGEN ISOTOPE ANALYSIS AND SCLEROCHRONOLOGY

Stable oxygen isotopes from estuarine bivalve carbonate from Saxidomus gigantea were analysed combined with high‐resolution sclerochronology from modern and archaeological shells from British Columbia, Canada, to determine the seasonality of shellfish collection from the archaeological site of Namu. The combination of high‐resolution sclerochronology and a micro‐milled sampling strategy for δ¹⁸O analysis permits a precise estimate of archaeological seasonality, because seasonal freshwater influxes and changes in temperature have dual effects on the δ¹⁸O value of the shell. Sclerochronological analysis identifies the timing and duration of growth that is temporally aligned to stable oxygen isotope results, since δ¹⁸O_shell appears to be strongly influenced by seasonal inputs of very low δ¹⁸O snowmelt‐water from adjacent coastal mountain ranges. The results show that shellfish were collected year‐round at this site over a 4000‐year period, and these data combined with other zooarchaeological lines of evidence support the interpretation of year‐round occupation.     

The effects of PVAc treatment and organic solvent removal on δ13C, δ15N,and δ18O values of collagen and hydroxyapatite in a modern bone

The stable isotopic analysis of archaeological and paleontological bones has become a common method to examine questions of ecology, climate, and physiology. As researchers addressing such questions incorporate museum collections in their studies, it is necessary to understand the isotopic effects of common preservation techniques utilized in such collections to ensure the preservation of original isotopic values. This study examines the effects of PVAc glue (polyvinyl acetate) applied in acetone solution and the subsequent removal of PVAc using various organic solvents on the δ¹³C and δ¹⁵N values of extracted bone collagen, the δ¹³C and δ¹⁸O values of carbonate in bone hydroxyapatite, and the δ¹⁸O values of phosphate in hydroxyapatite. The data demonstrate that isotopic values in the collagen and phosphate are unaffected by any combination of PVAc treatment and solvent application. The carbonates show little variation in δ¹³C values, but exhibit variable δ¹⁸O values upon exposure to the PVAc solution. It is here suggested that δ¹⁸O values from carbonates in PVAc-treated bones do not retain an original isotopic value and should not be included in future studies.     

δ18O measurements of archaeological glass (Roman to Modern age) and raw materials: possible interpretation

The present paper reports results from a systematic study of oxygen isotopic compositions for glass samples from various archaeological sites (i.e., Iulia Felix, Grado, Vicenza, Pozzuoli and Modena in Italy, and Derrière Sairoche in Switzerland) and dated from the Roman period to the 18th century AD, as well as of some raw materials that may have been used for their production. The analysed samples differ essentially in the type of flux, using Roman and high Medieval glass natron and late Medieval and modern glass plant ash, soda and potash, respectively. The aim of this study was to amplify the database of oxygen isotope data for various archaeological glasses and to identify isotopic trends indicating different raw materials, production technology, and/or provenance. Results indicate that natron glass samples of various provenance and age have consistently higher δ¹⁸O values than plant ash ones (about 15.5‰ vs 13.0‰), probably due to the different flux, highly ¹⁸O-enriched in the case of natron. Isotopic data on Belus and Campanian sands, the types mentioned by Pliny for glass production, show that they have similar isotopic composition. Taking into account the oxygen isotopic composition of Roman glass, the “positive natron effect”, and the negligible influence of small amounts of manganese and antimony containing decolourisers, the suitability of both sources for glass production is verified, supporting the hypothesis of multiple sand sources. Notwithstanding this, the isotopic similarity between Belus and Campanian sands prevents us from identifying the starting material from the δ¹⁸O of the final product. In the case of plant ash used as flux, it is not possible to distinguish between soda and potash plant ash, because the addition of ash did not contribute isotopically heavy oxygen and the silica source is presumed to be comparable in the analysed samples. The isotopic data of the present study are also compared with those already published in the literature, and possible interpretations on their analogies and differences are discussed.     

Significance and Limitations of Stable Oxygen Isotope Ratios in the Apatite Phosphate of Archaeological Vertebrate Finds for Provenance Analysis in an Alpine Reference Region

A multi‐isotope fingerprint consisting of δ¹⁸O_phosphate, ⁸⁷Sr/⁸⁶Sr, ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁷Pb was established in the bioapatite of 219 individual archaeofaunal remains (cattle, pig, red deer) excavated from sites located along a specific transect of the European Alps, namely the Inn–Eisack–Adige–Brenner Passage, that has been of eminent importance since European prehistory. This reference area is vertically stratified, and since δ¹⁸O in the skeleton is influenced by climate, water source, physiology and even culture, we tested the relative contribution and importance of δ¹⁸O as a component of the multi‐isotope fingerprint for provenance analysis in this alpine region by a novel mathematical approach. In particular, we adapted a supervised learning approach through expectation–maximization (EM) clustering for fingerprint extraction and evaluated the contribution of each isotopic ratio to the data structure. While an altitude effect was evident in δ¹⁸O, its overall structural importance in the complete isotopic fingerprint was rather low. Therefore, provenance analysis of bioarchaeological finds in this region is possible by measuring stable Sr and Pb ratios alone, which is of considerable importance when δ¹⁸O values are not available, e.g., in cremated finds, although some information is lost. Whether this is tolerable depends on the scientific question to be solved.     

In situ oxygen isotope micro-analysis of faunal material and human teeth using a SHRIMP II: a new tool for palaeo-ecology and archaeology

A Sensitive High Resolution Ion MicroProbe (SHRIMP II) has been used to make high spatial resolution in situ micro-analyses of oxygen isotopes in fish otoliths, and teeth from fossil herbivores and a Neanderthal. Large intra-tooth variations in the oxygen isotopic composition (up to 9‰) were observed in the enamel of herbivores from the Neanderthal fossil site of Payre, consistent with preservation of seasonal cyclicity. The range of isotopic compositions observed in Neanderthal tooth enamel was much smaller (∼3‰), possibly the result of a longer enamel maturation time averaging out variability. An archaeological otolith from a Preceramic site in Northern Peru exhibited marked changes in δ¹⁸O over life, due either to the fish occasionally migrating from the sea to a lower salinity habitat, or to short-lived rises in sea water temperature. A fish otolith from Australia's Willandra Lakes World Heritage Area showed clear seasonal variations, but also a general trend towards isotopically heavier and more saline water, as indicated by higher δ¹⁸O and Sr/Ca values resulting from increased evaporation. The results of these case studies are compared to results of oxygen isotope analysis using more conventional methods and demonstrate the ability of the SHRIMP II to provide precise high spatial resolution in-situ oxygen isotope analyses of a variety of biogenic materials. This approach has major advantages over conventional methods. It can provide rapid, micro-scale isotopic analyses of sub-permil precision without the need for chemical preparation of the sample.     

Fracture-fill calcite as a record of microbial methanogenesis and fluid migration: a case study from the Devonian Antrim Shale, Michigan Basin

The Devonian Antrim Shale is an organic‐rich, naturally fractured black shale in the Michigan Basin that serves as both a source and reservoir for natural gas. A well‐developed network of major, through‐going vertical fractures controls reservoir‐scale permeability in the Antrim Shale. Many fractures are open, but some are partially sealed by calcite cements that retain isotopic evidence of widespread microbial methanogenesis. Fracture filling calcite displays an unusually broad spectrum of δ¹³C values (+34 to ?41‰ PDB), suggesting that both aerobic and anaerobic bacterial processes were active in the reservoir. Calcites with high δ¹³C values (>+15‰) record cementation of fractures from dissolved inorganic carbon (DIC) generated during bacterial methanogenesis. Calcites with low δ¹³C values (13C values between ?10 and ?30‰ can be attributed to variable organic matter oxidation pathways, methane oxidation, and carbonate rock buffering. Identification of ¹³C‐rich calcite provides unambiguous evidence of biogenic methane generation and may be used to identify gas deposits in other sedimentary basins. It is likely that repeated glacial advances and retreats exposed the Antrim Shale at the basin margin, enhanced meteoric recharge into the shallow part of the fractured reservoir, and initiated multiple episodes of bacterial methanogenesis and methanotrophic activity that were recorded in fracture‐fill cements. The δ¹⁸O values in both formation waters and calcite cements increase with depth in the basin (?12 to ?4‰ SMOW, and +21 to +27‰ PDB, respectively). Most fracture‐fill cements from outcrop samples have δ¹³C values between ?41 and ?15‰ PDB. In contrast, most cement in cores have δ¹³C values between +15 and +34‰ PDB. Radiocarbon and ²³⁰Th dating of fracture‐fill calcite indicates that the calcite formed between 33 and 390 ka, well within the Pleistocene Epoch.     

Horticulturists and oxygen ecozones in the tropical and subtropical forests of Southeast South America

We analyse the isotopic values (δ¹³C, δ¹⁵N) of the diet of pre-Columbian horticulturalist populations from tropical and subtropical areas of southeastern South America, belonging to the Guarani and Taquara archaeological units. The data indicate different trends in each one (T?=?4.21; P?=?0.0004), showing a mixed diet with maize consumption in the Guarani samples (δ¹³C_co?=??15.5?±?1.8‰; δ¹³C_ap ?10.4?±?0.8‰) and a depleted one in the Taquara ones (δ¹³C_co ?18.2?±?1.7‰; δ¹³C_ap ?11.9?±?0.9‰), with a significant internal dispersion in both populations. The first population has higher nitrogen values (δ¹⁵N 11.1?±?0.6‰) compared to the Taquara samples (δ¹⁵N 9.3?±?1‰), suggesting a more carnivorous diet. The recognition of these pre-Columbian mixed diets involves the identification of maize cultivation on the Atlantic side of the southernmost area of South America (Parana Delta, 34° SL). Through the analysis of δ¹⁸O we have identified two isotopic ecozones, the first along the Paraná River Valley, with an average value of δ¹⁸O ?3.7?±?0.5‰ (CV?=?13.5%; CI?=??3.83 / ?3.16), and the second one, located in the Planalto of southern Brazil (Araucaria Forest), with a mean value of δ¹⁸O ?1.5?±?0.3‰ (CV?=?16.5%; CI?=??1.69 / ?1.29). The isotopic data (δ¹³C, δ¹⁵N and δ¹⁸O) suggest human movements between these two ecozones.     

THE PROVENANCE AND TECHNOLOGY OF NEAR EASTERN GLASS: OXYGEN ISOTOPES BY LASER FLUORINATION AS A COMPLEMENT TO STRONTIUM*

The ability to make rapid measurements on small samples using laser fluorination enhances the potential of oxygen isotopes in the investigation of early inorganic materials and technologies. δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values are presented for glass from two primary production sites, four secondary production sites and a consumer site in the Near East, dating from Late Antiquity to the medieval period. δ¹⁸O is in general slightly less effective than ⁸⁷Sr/⁸⁶Sr in discriminating between sources, as the spread of measured values from a single source is somewhat broader relative to the available range. However, while ⁸⁷Sr/⁸⁶Sr is derived predominantly from either the lime‐bearing fraction of the glass‐making sand or the plant ash used as a source of alkali, δ¹⁸O derives mainly from the silica. Thus the two measurements can provide complementary information. A comparison of δ¹⁸O for late Roman – Islamic glasses made on the coast of Syria–Palestine with those of previously analysed glasses from Roman Europe suggests that the European glasses are relatively enriched in ¹⁸O. This appears to contradict the view that most Roman glass was made using Levantine sand and possible interpretations are discussed.     

Method-dependent variations in stable isotope results for structural carbonate in bone bioapatite

Stable carbon and oxygen isotope values (δ¹³C, δ¹⁸O) were obtained for structural carbonate in the bioapatite of archaeological bones from Guatemala and Sudan using several common analytical methods. For the Sudan samples, the different methods produced δ¹³C values within ±0.1‰ and δ¹⁸O values within ±0.7‰, on average. The isotopic results for the Guatemala samples were similar in reproducibility to the Sudan samples when obtained using methods that employed lower reaction temperatures and reactions in sealed vessels. However, many Guatemala samples had highly variable and extremely low δ¹⁸O values when reacted at higher temperatures in vessels that remained open to cryogenic traps. The latter arrangement caused reaction products to be removed immediately upon their production. The anomalously low δ¹⁸O values are related to the production of a contaminant gas that causes the m/z 46/44 ratio to be lowered, either by adding to the m/z 44 peak or subtracting from the m/z 46 peak. That said, potential contaminant materials were not detectable in “anomalous” bones using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, or inductively-coupled plasma atomic emission spectroscopy. However, subtle structural and chemical differences between “normal” and “anomalous” samples were observed, most notably in the FTIR ν₂ CO₃ domain. We suggest that these changes promote volatilization of an oxyphosphorus compound and oxygen isotope fractionation between PO⁻ derived from this compound and CO₂ derived from bone carbonate. Production of the contaminant gas and the related “anomalous” δ¹⁸O values is reversible if the reaction occurs within a sealed vessel for a sufficient period of time, which allows a “back-reaction” to occur.     

Can argillaceous formations isolate nuclear waste? Insights from isotopic,noble gas,and geochemical profiles

There is considerable interest in the use of thick argillaceous geologic formations to contain nuclear waste. Here, we show that diffusion can be the controlling transport process in these formations and diffusional time scales for δ¹⁸O and δ²H in water, dissolved He, and Cl transport in shale‐dominated aquitards are typically over 10⁶ years, well exceeding the regulatory requirements for isolation in most countries. Our scientific understanding of diffusive solute transport processes through argillaceous formations would benefit from the application of additional isotopic tracers (e.g., using new ⁴He sampling technology), multidimensional diffusive‐dispersive modeling of groundwater flow and diffusive‐dispersive solute transport over long geologic time scales, and an improved understanding of spatial heterogeneity as well as time‐dependent changes in the subsurface conditions and properties of argillaceous formations in response to events such as glaciation. Based on our current isotopic and geochemical understanding of transport, we argue that argillaceous formations can provide favorable long‐term conditions for isolating nuclear wastes.     

On the homogeneity of fluids forming bedding‐parallel veins

A group of 400–500 m long, bedding‐parallel calcite veins are exposed in the central La Popa Basin of northeastern Mexico. These veins provide a unique opportunity to determine the kilometer‐scale fluid–rock system associated with bedding‐parallel vein formation, and to test for sampling bias in studies that often use one or two samples to constrain the characteristics of regional‐scale paleohydrogeological systems. We use fluid inclusion microthermometry in conjunction with measurements of δ¹³C, δ¹⁸O, and ⁸⁷Sr/⁸⁶Sr ratios to constrain the vein‐forming fluid temperatures, compositions and sources, and compare these values along and between the veins to establish the homogeneity of the vein‐forming fluids and fluid–rock system. The δ¹³C values of the veins are close to those of the host rock, and average – 3.96‰ (PDB). The δ¹⁸O values of the veins are typically 1‰ lower than those of the host rocks, and average – 9.54‰ (PDB). Fluid inclusion homogenization temperatures average 137°C and inclusion salinities are all <6 wt% NaCl equivalent. The ⁸⁷Sr/⁸⁶Sr ratios of the veins average 0.70731 and are substantially lower than the values expected for the host rock. Calculated fluid δ¹⁸O values range from 4 to 10‰ (SMOW). The isotopic and microthermometric data indicate the veins most likely formed at depths of 3–4 km when meteoric water mixed with upward migrating, warm basinal brines. Vein microstructures and field characteristics indicate they formed from multiple slip events that most likely were associated with transport of individual fluid pulses that migrated along bedding planes. The large‐scale homogeneity of vein geochemistry is remarkable and demonstrates that only one or two samples would be sufficient to accurately characterize the kilometer‐scale paleohydrogeological system for these veins.     

Changes in fluid pathways in a calcite vein mesh (Natih Formation,Oman Mountains): insights from stable isotopes

We present a structural, microstructural, and stable isotope study of a calcite vein mesh within the Cretaceous Natih Formation in the Oman Mountains to explore changes in fluid pathways during vein formation. Stage 1 veins form a mesh of steeply dipping crack‐seal extension veins confined to a 3.5‐m‐thick stratigraphic interval. Different strike orientations of Stage 1 veins show mutually crosscutting relationships. Stage 2 veins occur in the dilatant parts of a younger normal fault interpreted to penetrate the stratigraphy below. The δ¹⁸O composition of the host rock ranges from 21.8‰ to 23.7‰. The δ¹³C composition ranges from 1.5‰ to 2.3‰. This range is consistent with regionally developed diagenetic alteration at top of the Natih Formation. The δ¹⁸O composition of vein calcite varies from 22.5‰ to 26.2‰, whereas δ¹³C composition ranges from ?0.8‰ to 2.1‰. A first trend observed in Stage 1 veins involves a decrease of δ¹³C to compositions nearly 1.3‰ lower than the host rock, whereas δ¹⁸O remains constant. A second trend observed in Stage 2 calcite has δ¹⁸O values up to 3.3‰ higher than the host rock, whereas the δ¹³C composition is similar. Stable isotope data and microstructures indicate an episodic flow regime for both stages. During Stage 1, formation of a stratabound vein mesh involved bedding‐parallel flow, under near‐lithostatic fluid pressures. The ¹⁸O fluid composition was host rock‐buffered, whereas ¹³C composition was relatively depleted. This may reflect reaction of low ¹³C CO₂ derived by fluid interaction with organic matter in the limestones. Stage 2 vein formation is associated with fault‐controlled fluid flow accessing fluids in equilibrium with limestones about 50 m beneath. We highlight how evolution of effective stress states and the growth of faults influence the hydraulic connectivity in fracture networks and we demonstrate the value of stable isotopes in tracking changes in fluid pathways.     

The sources and formation processes of brines from the Lunnan Ordovician paleokarst reservoir,Tarim Basin,northwest China

The most important petroleum exploration target in the Tarim Basin, northwest China, is the paleokarst reservoir. To understand the source and evolution of brine in this type of reservoir, a total of 37 formation‐water samples were collected from the Middle‐Lower Ordovician paleokarst reservoir in the Lunnan oilfield. The δD‐δ¹⁸O correlation and Cl/Br ratios reflect the mixture of two fluids: meteoric water and evaporated seawater. The different degree of mixture divided samples into two groups. Group 1 samples, from deep strata (5150–6667 m.b.s.l.) in the east of the field, with elevated δD (?53.5 to ?38.0‰), δ¹⁸O values (0.66–5.99‰), and lower Cl/Br ratios (336–478 for Cl/Br, except LN634‐1 and LN631‐1) were formed by evaporation of seawater plus a small contribution from meteoric water. Group 2 samples, from shallow strata (5038–6067 m.b.s.l.), in the west of the field, have contrasting features (?59.6 to ?48.5‰ for δD, ?0.47 to 2.17‰ for δ¹⁸O, and 501 to 871 for Cl/Br), which reflect a mixture of evaporated seawater with a high proportion of meteoric water. Both of the fluid types exchanged oxygen isotope with minerals. The investigation into cation composition reveals that, before entering into the current reservoir, waters suffered albitization of plagioclase; moreover, meteoric water dissolved evaporites and seawater experienced dolomitization. A mixing trend showed by strontium isotopes (0.709801–0.711628) gave further evidence for the mixture of two fluid types. Based on the correlation of geological history with our data, two infiltration models of meteoric waters can be constructed. According to the chemical and isotopic compositions of the waters, an east fluid regime (Group 1) and a west fluid regime (Group 2) have thus been defined. Better understanding of the subsurface fluid movement patterns may be helpful for the local exploration.     

Oxygen isotopes in cellulose identify source water for archaeological maize in the American Southwest

Maize (Zea mays) was a primary food crop for aboriginal societies of the arid American Southwest. Water used for maize production in these arid zones could have come from precipitation and runoff during the summer monsoon, from perennial streams and springs, or from stored soil water fed by snowmelt. The oxygen stable isotope ratio (δ¹⁸O) of summer and winter precipitation on the Colorado Plateau naturally differ by more than 10‰ providing a powerful tool for distinguishing winter- from summer-derived water sources used in cultivation of maize. We investigated whether variation in δ¹⁸O of potential source waters is preserved in the δ¹⁸O of cellulose (δ¹⁸O_cellulose) of maize cobs by growing four aboriginal and one modern maize variety in pots irrigated with water of known δ¹⁸O composition. The δ¹⁸O_cellulose values of cobs ranged from 26.8 to 36.4‰ (averaged within varieties) and were highly correlated with δ¹⁸O values of the source irrigation water (−15.8 to −8.2‰). Cob δ¹⁸O_cellulose from five archaeological sites on the Colorado Plateau in southeastern Utah ranged from 27.3 to 34.6‰, closely matching the range of values observed in experimental plants. A δ¹⁸O_cellulose model developed originally for tree rings was parameterized and applied to the archaeological maize cobs. The model indicated that monsoonal precipitation accounted for 0–20% of the moisture for archaeological cob samples from a site adjacent to a perennial stream and 43–98% for samples from an upland site, more distant from a perennial water source. These results reveal the potential for using δ¹⁸O_cellulose to investigate prehistoric irrigation practices and source water used for maize production in the American Southwest.