Range Of δ13C Values Research Articles

Persistent organic pollutants (POPs) in fish species from different lakes of the lesser Himalayan region (LHR), Pakistan: The influence of proximal sources in distribution of POPs

Fish dwelling in remote mountain water systems are sensitive to long term exposure of POPs and can be used as an important bioindicator of POPs pollution in fragile mountain ecosystems. Current study aimed to investigate the concentrations and patterns of organic pollutants in fish tissues from different lakes of the Lesser Himalayan Region (LHR). OCPs, PCBs, PBDEs were analyzed in four common edible fish species of the LHR: Oncorhynchus mykiss, Labeo rohita, Hypophthalmichthys molitrix and Orechromis aureus. The fish were collected from lakes with different types of catchment areas (glacial, non-glacial mountain region and urban region) and extent of anthropogenic influence. The levels OCPs, PCBs and PBDEs analyzed in the selected fish species were in range of 0.21–587, 6.4–138 and 1.2–14 ng g−1 lw, respectively. The ∑DDTs, higher chlorinated PCBs, tetra- and penta-BDEs were more prevalent in urban and remote lakes whereas pp’-DDE, lower chlorinated PCBs and BDE-47 and -99 were predominant in fish species from glacial lakes. ∑DDTs, ∑PCBs and ∑PBDEs showed statistically significant differences (p < 0.05) among species, trophic guilds (carnivore, herbivore and omnivore) and feeding regimes (surface, bottom and column feeder) and ∑HCH showed a significant difference only among trophic guilds. The stable isotope values of δ 15N and δ13C differed significantly among species for ∑HCH, ∑PCBs, ∑PBDEs (p < 0.05) and ∑DDT (p < 0.01). The range of δ13C values (−34 to −19‰) indicated the importance of littoral and pelagic sources of dietary carbon. Trophic position and dietary proxies were identified as important variables for explaining the variability of the studied compounds. Kohonen self-organizing maps (SOM) showed that in addition to trophic position and other physiological characteristics of fish, that the type of lakes and proximal sources of POPs were the most important predictors for distribution of organic contaminants in fish samples from LHR.

The Formation of Authigenic Carbonates at a Methane Seep Site in the Northern Part of the Laptev Sea

Authigenic carbonates from cold seeps are unique archives for studying environmental conditions, including biogeochemical processes associated with methane-rich fluid migration through the sediment column. The aim of this research was to study major oxide, mineralogical, and stable isotopic compositions of cold-seep authigenic carbonates collected in the northern part of the Laptev Sea. These carbonates are represented by Mg-calcite with an Mg content of 2% to 8%. The δ13C values range from −27.5‰ to −28.2‰ Vienna Peedee belemnite (VPDB) and indicate that carbonates formed due to anaerobic oxidation of methane, most likely thermogenic in origin. The authigenic pyrite in Mg-calcite is evidence of sulfate reduction during carbonate precipitation. The δ18O values of carbonates vary from 3.5‰ to 3.8‰ VPDB. The calculated δ18Ofluid values show that pore water temperature for precipitated Mg-calcite was comparable to bottom seawater temperature. The presence of authigenic carbonate in the upper horizons of sediments suggests that the sulfate–methane transition zone is shallowly below the sediment–water interface.

Does rapid glacial recession affect feeding habits of alpine stream insects?

Abstract Glacial retreat, accompanied by shifts in riparian vegetation and glacier meltwater inputs, alters the energy supply and trophic structure of alpine stream food webs. Our goal in this study was to enhance understanding of dietary niches of macroinvertebrates inhabiting different alpine streams with contrasting glacial and non‐glacial (groundwater, precipitation, snowmelt) water inputs in conjunction with seasonal and habitat‐specific variation in basal resource availability. We measured a range of stream physico‐chemical attributes as well as carbon and nitrogen isotopes (δ13C, δ15N) of macroinvertebrates and primary food sources at seven sites across seasons within a Swiss glaciated catchment (Val Roseg) undergoing rapid glacial retreat (1–2 km between 1997 and 2014). Sampling sites corresponded to streams used in a previous (1997/1998) study within the same alpine catchment. Physico‐chemical attributes showed wide variation in environmental conditions across streams and seasons. Significant correlation among physico‐chemical proxies of glacier meltwater (phosphate‐P, total inorganic carbon, conductivity, turbidity) and macroinvertebrate δ13C, δ15N, and size‐corrected standard ellipse area (a proxy for feeding niche width) values showed that the extent of glacial water input shapes the energy base among alpine streams. Feeding niche differences among common alpine stream insect taxa (Chironomidae, Baetidae, Heptageniidae) were not significant, indicating that these organisms probably are plastic in feeding behaviour, opportunistically relying on food resources available in a particular stream and season. Seasonal trends in macroinvertebrate δ13C largely followed patterns in periphyton δ13C values, indicating that autochthonous resources were the main consumer energy source within the stream network, as shown previously. The overall range in macroinvertebrate δ13C (−33.5 to −18.4‰) and δ15N (−6.9 to 6.7‰) values also corresponded to values measured in the previous study, suggesting that macroinvertebrates altered diets in line with changes in environmental conditions and food resources during a period of rapid glacial retreat. Our results suggest that environmental changes brought on by rapid glacial retreat have not yet caused a profound change in the trophic structure within these fluvial networks.

Extending the record of the Lomagundi–Jatuli carbon isotope excursion in the Labrador Trough, Canada

The Labrador Trough in northern Québec and Labrador is a 900 km long Rhyacian–Orosirian orogenic belt containing mixed sedimentary–volcanic successions. Despite having been studied intensively since the 1940s, relatively few chemostratigraphic studies have been conducted. To improve our understanding of the Labrador Trough in the context of Earth history, and better constrain the local record of the Lomagundi–Jatuli carbon isotope excursion, high-resolution sampling and carbon isotope analyses of the Le Fer and Denault formations were conducted. Carbonate carbon isotopes (δ13C) in the Le Fer Formation record a large range in values from −4.4‰ to +6.9‰. This large range is likely attributable to a combination of post-depositional alteration and variable abundance of authigenic carbonate minerals; elemental ratios suggest that the most 13C-enriched samples reflect the composition of the water column at the time of deposition. Cumulatively, these data suggest that the Lomagundi–Jatuli Excursion was ongoing during deposition of the Le Fer Formation, approximately 2 km higher in the stratigraphy than previously recognised. However, the possibility of a post-Lomagundi–Jatuli Excursion carbon isotope event cannot conclusively be ruled out. The directly overlying Denault Formation records a range in δ13C values, from −0.5‰ to +4.3‰, suggesting that it was deposited after the conclusion of the Lomagundi–Jatuli Excursion and that the contact between the Le Fer and Denault formations occurred sometime during the transition out of the Lomagundi–Jatuli Excursion, ca. 2106 to 2057 Ma.

Bulk and position-specific isotope geochemistry of natural gases from the Late Cretaceous Eagle Ford Shale, south Texas

A dataset of bulk and position-specific isotope compositions of shale gases from the Late Cretaceous Eagle Ford Shale, south Texas is reported. The chemical and bulk isotopic compositions of the seven samples in this study and those available from the literature show that across the play, produced natural gas from the Eagle Ford Shale preserves a wide range of gas compositions (wetness, ~5 to >90%) and δ13C values of C1–C3. The depth profiles of the isotopic compositions suggest that the western region of the Eagle Ford Shale deposit had experienced as much as 700–800 m of uplift-erosion or gas migration. The timing of and lost-gas fractions by gas expulsion events very likely affected their gas compositions and bulk isotope compositions. Some deep (>3000–3500 m), matured (%Ro > 1.5) gases with heavy δ13C(C1–C3) values indicate significant loss (>50%) of the early-stage gases. For the position-specific isotope deviations of propane, the ΔC2-1 values of the five samples show small decrease with well depths, while the ΔH2-1 values have a general increasing trend. Although some samples fall very close to the equilibrium model trajectories with reasonable calculated temperatures (138–148 °C), the position-specific isotope compositions of propane from the Eagle Ford Shale gases are likely results of thermal cracking of various organic molecules within the source rocks, which have different activation energy for cracking and non-statistical distributions of C/H isotope within them.

Oxygen and carbon stable isotope composition of the weathering Mg‐carbonates formed on the surface of the LEW 85320 ordinary chondrite: Revisited

AbstractNew δ13C and δ18O values were measured to constrain the formation mechanisms of two previously identified generations (Antarctica and Houston) of terrestrial weathering carbonates, nesquehonite, which formed on the surface of the Lewis Cliff 85320 ordinary chondrite. These two nesquehonite generations exhibit a characteristic carbon and oxygen isotopic trend which starts with a linear δ13C‐δ18O covariation followed by a continuous increase in δ18O with little to no change in δ13C. Based on the newly developed nesquehonite‐water oxygen isotope thermometry and the measured δ18O value of melted ice from Antarctica, the formation temperature of the Antarctic nesquehonite generation was estimated to be −1.9 ± 3 °C. Houston nesquehonite generation was most likely formed from an evaporative residue of the melted Antarctic ice at 30 ± 4 °C. Modeling the isotopic trend of the two generations suggests that evaporation created large δ18O variations in the nesquehonite while carbon isotopes were stabilized by exchange between the parent liquid and atmospheric CO2. Thus, we suggest that carbonates formed by terrestrial weathering in Antarctica should possess a wide spread in δ18O values and a narrow range in δ13C values under dry and cold conditions. Finally, the observed wide spread of δ18O in Martian carbonates (e.g., Allan Hills 84001 and Nakhla) can be explained by evaporation near 0 °C and may have formed by a similar mechanism to that of the nesquehonite in the LEW 85320. Meanwhile, the wide spread of δ13C suggests that two carbon reservoirs with distinct isotope compositions on Mars (e.g., the atmospheric carbon and magmatic carbon) may be actively participating in the formation process.

MICROBIALITE OCCURRENCE AND PATTERNS IN HOLOCENE REEFS OF BORA BORA, SOCIETY ISLANDS

ABSTRACT The thickness of microbialite crusts in Holocene barrier and fringing reefs of Bora Bora was quantified in drill cores from windward and leeward settings to decipher possible spatial and temporal patterns as well as controlling environmental factors. Based on the analysis of 145 occurrences in nine rotary cores, microbialite thickness ranges from 0.1–11.0 cm with an average value of 1.97 cm (SD = 2.47). Microbialites occur only from 9.5–5.6 ka corresponding to a period of rapid sea-level rise and reef accretion in the early Holocene. However, there is no statistically significant correlation between microbialite thickness and reef accretion rate. Also, there is no correlation between microbialite abundance and age. The upcore increase in microbialite abundance, however, suggests that time available for carbonate accretion in shallow water plays a role in microbialite formation. Crust thickness is greater on windward as compared to leeward fringing reef settings indicating that flushing of pore space is a likely factor controlling microbialite accretion. Other environmental factors potentially being responsible for the Holocene decrease in microbialite abundance include climate, i.e., decreasing temperatures and precipitation (supporting nutrient input by runoff) as well as decreasing seawater alkalinity. At the mesoscale, structureless and laminated microbialites are by far the most common types. Coated debris, boring infill, and digitate types are less common. Textures at the microscale, including laminated, clotted, and peloidal, do not necessarily match mesoscale textures. The Bora Bora microbialites consist in more or less equal parts of high-magnesium calcite and aragonite. The δ13C values range from +3.0 to +4.1‰ and the δ18O from -0.8 to +0.1‰. The contents of easy soluble sulfate (ESS) and carbonate associated sulfate (CAS) are relatively high. The δ18OCAS (+11.0 to +12.7‰) and δ34SCAS values (+21.9 to +23.6‰) exceed the seawater sulfate standard NBS-127 value and are in the same range as observed in other cryptic, Holocene reefal microbialites. The Bora Bora microbialites contain lipid biomarkers derived from sulfate-reducing bacteria (2–8 wt%), marine plankton, land plants, and unspecified bacteria. The former include branched, short-chain fatty acids and terminally branched fatty acids, whereby iso-fatty acids are more abundant than anteiso-fatty acids. Other compounds with terminally branched alkyl chains include iso- and anteiso-C15 and -C17 alcohols, which are interpreted as degradation products of monoalkyl glycerol ethers (MAGE). Collectively, the organic and inorganic geochemical data together with the sedimentological and mineralogical data suggest that sulfate-reducing bacteria were involved in microbialite development. The temporal and spatial distribution patterns suggest that factors such as exposure to waves and currents, time, nutrient availability, alkalinity, and climate play important roles, however, more quantitative data from other occurrences are needed to be able to better discriminate among them.

Anoxic oceanic conditions during the late Permian mass extinction-evidence from the Chutani formation, Bolivia

We analyze diagenesis of carbonate rocks from the Late Permian Chutani Formation of western Bolivia (San Pablo de Tiquina section) in the southern Lake Titicaca zone, which is a sedimentary succession of semiarid tidal flat comprised of mixed carbonate and siliciclastic units. The diagenetic study includes petrographic analysis (conventional petrography and cathodoluminescence) and geochemical analysis (carbon and oxygen isotopes and minor element chemistry). An integrated study of lithofacies and isotope stratigraphy of carbonates shows a succession of five types of depositional environments: tidal barrier, tidal flat, shoal coastal and shoreface. The Chutani Formation was subjected to different diagenetic processes including micritization, cementation, mechanical compaction, dissolution, neomorphism, dolomitization and dedolomitization that occurred during marine to shallow burial stages. Carbon isotope (δ13C) values range between −7 and 2.9‰ (VPDB) with variations linked to stratigraphic changes. The transgressive stage of the basin exhibits an upwards decreasing trend of δ13C values whereas regression is marked by an increase in such values. The oxygen isotope values (δ18O) vary from −16.6 to −1‰ VPDB with lighter values towards the top of the stratigraphy. The transgressive trend may reflect mixing of meteoric water and/or volcanic-hydrothermal fluids with seawater or progressive oxygenation with enhanced circulation conditions. Heavier values during regression may reflect more evaporitic and anoxic conditions towards the Permian-Triassic boundary. Significant variation in isotope values among neighbouring samples is observed, especially during trangression, which may be the result of different diagenetic processes.

Isotopic and Elemental Content of Deep-Sea Sediments from the Black Sea. Preliminary Results

The unraveling of the geological processes, which are recorded in the chemical and isotopic fingerprinting of the deep-sea sediments, demands the introduction of a sensitive parameter over time. The aim of this study is to analyze the deep-sea sediments from the Black Sea, using the stable isotopic and elemental content. For this purpose, 41 sediment samples were taken from five cores, having lengths between 2.66 and 4.24 m using a gravitational core. Additional nine samples were taken from three cores using a multicore equipment. All samples were collected during a two weeks marine expedition, in the beginning of September 2018, in the western part of the Black Sea. The isotopic values (δ13C; δ18O) and elemental concentrations (macro-, micro-elements, and heavy metals) were determined in the sediments samples, along with δ18O and δ2H in extracted water from sediments. Preliminary results obtained from sediments show that δ13C values of the bulk organic component range between -27.9 ‰ and -22.3 ‰ with a mean value of -25.3 ‰, while for inorganic component, the δ13C and δ18O values range between -4.3 ‰ and 1.5 ‰ for δ13C, and from -10.6 ‰ to -0.07 ‰ for δ18O, respectively, with a mean of -0.32 for δ13C and -5.74 ‰ for δ18O, versus Vienna Pee Dee Belemnite (VPDB) international standard. In the extracted water, the δ18O variation range was between -3.5 and 1.6 ‰, with a mean of -1.7 ‰, while the δ2H values range between -32.4 ‰ and -16.5 ‰ with a mean of -23.1 ‰. The results of this research will be the basis of the new paleoclimatic reconstruction using stable isotopes in the deep-sea sediments from the Black Sea.

Sr-Nd-Pb isotopic systematic and geochronology of ultramafic alkaline magmatism of the southwestern margin of the Siberian Craton: Metasomatism of the sub-continental lithospheric mantle related to subduction and plume events

To provide new insights into the origin and evolution of ultramafic lamprophyres (UMLs) and their mantle source, we examined two UML (aillikite and damtjernite) occurrences of different ages in the western portion of the Siberian Craton (Ilbokich and Chadobets). New age, mineral and rock geochemistry, along with Sr–Nd–Pb–C–O isotope data was obtained. Our new 206Pb/238U perovskite age (399 ± 4 Ma) confirms the previously published Early Devonian age of the Ilbokich aillikite. RbSr isochron and 40Ar/39Ar dating yielded a Middle Triassic age (243 ± 3 Ma and 241 ± 1 Ma, respectively) for the Chadobets aillikites, indicating post-Trap emplacement of these rocks.Both UMLs are characterized by incompatible elements, including light rare earth element (LREE) enrichments (La is up to ×200 chondrite concentration), and strong fractionation of REEs ((La/Yb)n: 33–84). Despite the close geochemical affinity of both UMLs, the Nd isotopic compositions of aillikites, as well as the Pb isotopic composition of Chadobets and Ilbokich UMLs, do not overlap and are distinctly different from each other. The initial Sr and Nd isotopic compositions of the Ilbokich UMLs fall in within a narrow 87Sr/86Sr0 range (0.7032–0.7042) and εNd(T) (4.03–3.97). Chadobets UMLs have a similar Sr isotopic signature (87Sr/86Sr0: 0.7031–0.7043) and a more depleted Nd isotopic signature (εNd(T) 4.09–5.08). The initial Pb isotope compositions of the Chadobets UMLs are moderately radiogenic, ranging between 206Pb/204Pb = 18.4–19.0, 208Pb/204Pb = 38.3–38.8, and are characterized by a narrow 207Pb/204Pb ratio between 15.5 and 15.6. The Ilbokich Pb isotope compositions are less variable and range between 206Pb/204Pb = 18.0–18.4, 208Pb/204Pb = 37.8–38.4 and 207Pb/204Pb ratios between 15.5 and 15.6. The oxygen isotopic composition of carbonate from both UMLs is characterized by highly variable δ18O values from +12.1 and up to +20.5‰ (SMOW). The isotopic composition of δ13C values range from −1.3‰ to −7.1.Based on the minor impact of crustal contamination in both aillikites, it is inferred that their radiogenic isotope composition reflects a mantle source signature. The mantle source of the Chadobets aillikites is likely to include carbonatitic magma as a metasomatic agent. In contrast, phlogopite-rich metasomes within the lithospheric mantle could have contributed more significantly to the Ilbokich aillikites. These metasomes could be formed during the Caledonian orogeny, which did not only affect the southwestern boundary of the Siberian Craton, but also expanded to the craton interior. This study provides additional support for the evolution of the south-western portion of the Siberian SCLM, ranging from mantle containing phlogopite enrichment domains during the Early Devonian to hydrous-phase reduced mantle in the Triassic due to the thermal impact of the Siberian Traps.

Corrigendum to “Distribution of Trace Elements, Sr-C Isotopes, and Sedimentary Characteristics as Paleoenvironmental Indicator of the Late Permian Linxi Formation in the Linxi Area, Eastern Inner Mongolia”

The Late Permian on the periphery of the Songliao Basin, eastern Inner Mongolia, is an important hydrocarbon source rock system. Its sedimentary environment plays an important role in the evaluation of hydrocarbon prospects in the area. Unfortunately, until now, the interpretation of the sedimentary environment of this area has been controversial. We investigated the Late Permian sedimentary environment by studying the sedimentary characteristics and geochemistry. Based on these investigations, we conclude that the Linxi Formation is mainly composed of clastic sediments, interbedded with limestone lenses, with bioherm limestone at the top of the formation. Inner-layer marine fossils (calcium algae, bryozoans, and sponges) and freshwater and blackish water microfossils (bivalves) are all present, indicative of a typical shallow water sedimentary environment with an open and concussion background. In terms of geochemistry, the formation is relatively light rare Earth enriched, with significant positive Eu anomaly, slight positive La and Y anomaly, weak positive Gd anomaly, and lack of Ce anomaly. The average B/Ga ratio of the mudstone is greater than 3.3, and the average Sr/Ba ratio of the limestone is greater than 1.0. The range of the 87Sr/86Sr ratio is from 0.707285 to 0.707953. The range of δ13C values is from −4.0‰ to 2.4‰. The sediment assemblages, rare Earth elements, trace elements, and 87Sr/86Sr and C isotopes of the formation indicate that the Linxi Formation formed in a marine sedimentary environment and occasional marine-terrestrial transitional facies. The formation can be further divided into littoral facies, neritic facies, bathyal facies, and delta front.

Distribution of Trace Elements, Sr-C Isotopes, and Sedimentary Characteristics as Paleoenvironmental Indicator of the Late Permian Linxi Formation in the Linxi Area, Eastern Inner Mongolia

The Late Permian on the periphery of the Songliao Basin, eastern Inner Mongolia, is an important hydrocarbon source rock system. Its sedimentary environment plays an important role in the evaluation of hydrocarbon prospects in the area. Unfortunately, until now, the interpretation of the sedimentary environment of this area has been controversial. We investigated the Late Permian sedimentary environment by studying the sedimentary characteristics and geochemistry. Based on these investigations, we conclude that the Linxi Formation is mainly composed of clastic sediments, interbedded with limestone lenses, with bioherm limestone at the top of the formation. Inner-layer marine fossils (calcium algae, bryozoans, and sponges) and freshwater and blackish water microfossils (bivalves) are all present, indicative of a typical shallow water sedimentary environment with an open and concussion background. In terms of geochemistry, the formation is relatively light rare Earth enriched, with significant positive Eu anomaly, slight positive La and Y anomaly, weak positive Gd anomaly, and lack of Ce anomaly. The average B/Ga ratio of the mudstone is greater than 3.3, and the average Sr/Ba ratio of the limestone is greater than 1.0. The range of the 87Sr/86Sr ratio is from 0.707285 to 0.707953. The range of δ13C values is from −4.0‰ to 2.4‰. The sediment assemblages, rare Earth elements, trace elements, and 87Sr/86Sr and C isotopes of the formation indicate that the Linxi Formation formed in a marine sedimentary environment and occasional marine-terrestrial transitional facies. The formation can be further divided into littoral facies, neritic facies, bathyal facies, and delta front.

Can stable isotopes of carbon and oxygen be used to determine the origin of freshwater shells used in Neolithic ornaments from Central Europe?

Neolithic burials rich in grave goods, referred to as “princesses burials”, were excavated in the Kuyavia Lowland, central Poland, Central Europe. The most common elements of grave equipment recorded in these burials were ornaments composed of disc beads made of freshwater bivalve (Unio spp.) shells. Our study was aimed at determining the origin of the shells in question by analysing, for the first time, carbon and oxygen stable isotope compositions (δ13C and δ18O) of the beads and comparing the results with C and O isotope ratios in modern shells sampled in central Poland. In the research, the isotope values of modern shells were grouped into two data sets representing riverine and lacustrine endmembers. Unio spp. shells sampled from rivers were isotopically lighter (i.e. isotope values were more negative) compared with the shells collected from lakes. The range of δ13C and δ18O values in the beads was similar to the one observed in modern Unio spp. shells. However, the isotope values differed within and between the archaeological sites studied. In Krusza Zamkowa and Oslonki, two distinct isotopic groups of beads were recognised—riverine and lacustrine—suggesting changes in the shell source in time. The C and O isotope values of beads sampled from Brześc Kujawski indicated the lacustrine origin of the shells used for their production. Also, it was confirmed that shells used to produce one ornament were derived from a single source, and the choice of sources changed in time. Our research revealed that the selection of specific local sources of shells was important for the prehistoric communities under study, and it may be considered the evidence of the existence of a regional exchange network.

Palaeodiet reconstruction inferred by stable isotopes analysis of faunal and human remains at Bronze Age Punta di Zambrone (Calabria, Italy)

AbstractRecent research has shown that the Bronze Age is a crucial period of dietary changes in Italy. Following this line of enquiry, the paper reports the results of stable isotope analysis (δ13C and δ15N) of faunal bone collagen as well as of collagen extracted from a few human bones dated to the Recent Bronze Age (13th/12th century BCE) and excavated at the coastal settlement of Punta di Zambrone (PdZ) in Calabria, southern Italy. They constitute the first such data on that period from the Italian south and can be used to determine an isotopic baseline of human food sources providing new insights on the diet of humans inhabiting Calabria.Overall, isotopic data of the faunal samples are fairly uniform, and there is no significant discrepancy to be observed between exclusively herbivorous animals (sheep/goats, bovine, and red deer) and those having a mixed diet, such as dogs and pigs. All the animals have similar δ15N values with only slightly higher values for dog (6.5‰ ± 1.1), and the average of δ15N for both domestic and wild animals fits well with published results for herbivorous mammals. Enriched δ13C values (range between −19.3‰ and −14.9‰) in most of the faunal samples suggest a terrestrial diet dominated by a mixing of C3 and C4 plants (e.g.. millet). The human diet also reflects an impact of C4 plants in accordance with the archaeobotanic remains. In an interregional comparison, PdZ stands out in this respect among the sites of the Italian south. Human remains from northern Italian sites suggest a much stronger intake of C4 plants than at PdZ.

δ13C values of wood and Charcoal Reveal Broad Isotopic ranges at the base of the Food Web

ABSTRACTThe aim of this study is to investigate the range, the degree of variability, and a possible time or species dependence of wood and charcoal δ13C values within one small study area. To achieve this, we used δ13C and 14C determinations of more than 400 archaeological samples from a ca. 300 ha area in Denmark, spanning 5000 years and covering several different species. The δ13C values of the wood and charcoal range from −32.8‰ to −21.2‰. We found no time-dependence of wood and charcoal δ13C values, neither in general nor within one species. The mean δ13C of all wood samples is −28.5‰, while the means of individual species range from −30.6‰ to −26.3‰. The mean of all charcoal samples is −25.7‰, with the means of individual species ranging from −28.1‰ to −24.3‰. The wood δ13C values can be used to infer the possible range of plant δ13C values, which otherwise are not available. They imply that a high degree of variability can be expected at the base of the food chain. This is relevant for palaeodietary studies that rely on the measurement of baseline isotope values.

Stable isotopic fingerprint of Sangyod rice

Sangyod rice is the geographical indication product of Phatthalung province in Thailand. In this work, the stable isotopic fingerprint of Sangyod rice samples was investigated using isotope ratio mass spectrometry. A total of fifty rice samples collected from ten districts in Phatthalung were analyzed for stable isotopic composition (δ13C, δ15N and δ18O). The range of δ13C, δ15N and δ18O values in rice samples was − 28.41 to − 26.81, + 3.06 to + 8.31 and + 23.46 to + 29.46‰, respectively. The highest mean δ13C value was observed for rice samples from Tamot whereas the lowest value was found for rice samples from Si Banphot. δ15N was highest in samples from Si Banphot and lowest in samples from Khao Chaison. Kong Ra showed the highest δ18O value. Pak Phayun had the lowest δ18O. Most Sangyod rice samples from Si Banphot can be distinguished from other cultivation areas by a scatter plot of isotopic values.

Precise Measurements of 12CH2D2 by Tunable Infrared Laser Direct Absorption Spectroscopy.

We present precise measurements of doubly deuterated methane (12CH2D2) in natural methane samples using tunable infrared laser direct absorption spectroscopy (TILDAS). Using a 413 m optical path length astigmatic Herriott cell and two quantum cascade lasers (QCLs) scanning the spectral regions of 1090.46 ± 0.1 and 1200.23 ± 0.1 cm-1, the instrument simultaneously measures the five main isotopologues of methane. The ratios 13CH3D/12CH4 and 12CH2D2/12CH4 are measured at 0.01‰ and 0.5‰ (1σ) instrumental precision, respectively. The instrumental accuracy was assessed by measuring a series of methane gases with a range of δ13C and δD values but with the abundances of all isotopologues driven to thermal equilibrium at 250 °C. The estimated accuracy of Δ12CH2D2 is 1‰ (1σ) on the basis of the results of the heated methane samples. This new TILDAS instrument provides a simple and rapid technique to explore the sources of methane in the environment.

Origin of deep oil accumulations in carbonate reservoirs within the north Tarim Basin: Insights from molecular and isotopic compositions

Large amounts of light oil have been produced from carbonate reservoirs at depths below 7 km in the recently discovered Shunbei and Yuecan oil fields within the north Tarim Basin. Eighteen samples were investigated for molecular and isotopic compositions to help understand the origin of these deep oil accumulations. Several ratios based on C6 and C7 hydrocarbons suggest that they were not affected by evaporative fractionation. Linear relationships between the carbon number and log of the mole fraction of n-alkanes support no fractionation alteration. The correlation between concentrations of methyldiamantanes and stigmastane indicates that these oils were not severely cracked and probably at the beginning or an early stage of intense oil cracking. C29 sterane isomerization ratios 20S/(20S + 20R) and ββ/(ββ + αα) have reached their equilibrium points while a good linear relationship between the concentrations of terpanes and steranes suggests variations in maturity. Calculated vitrinite reflectance of source rocks based on phenanthrene and diamondoid hydrocarbons shows different ranges, which may reflect multiple oil charges to these deep oil accumulations. A narrow range of δ13C values of whole oil and oil fractions suggest a genetic correlation of these oils. Triangular plots based on C6 and C7 hydrocarbons and diamantanes also indicate a very similar source. In addition, several ratios based on n-alkanes, isoprenoids, tri-, tetra-, and pentacyclic saturated hydrocarbons support a common source. However, oil SB7 seems to differ from the others in terms of source rock depositional environment, indicated by its much higher pristane/phytane ratio and lower dibenzothiophene/phenanthrene ratio as well as a much lower dibenzothiophenes concentration.

Canopy structure in Late Cretaceous and Paleocene forests as reconstructed from carbon isotope analyses of fossil leaves

Abstract While modern forests have their origin in the diversification and expansion of angiosperms in the Late Cretaceous and early Cenozoic, it is unclear whether the rise of closed-canopy tropical rainforests preceded or followed the end-Cretaceous extinction. The “canopy effect” is a strong vertical gradient in the carbon isotope (δ13C) composition of leaves in modern closed-canopy forests that could serve as a proxy signature for canopy structure in ancient forests. To test this, we report measurements of the carbon isotope composition of nearly 200 fossil angiosperm leaves from two localities in the Paleocene Cerrejón Formation and one locality in the Maastrichtian Guaduas Formation of Colombia. Leaves from one Cerrejón fossil assemblage deposited in a small fluvial channel exhibited a 6.3‰ range in δ13C, consistent with a closed-canopy forest. Carbon isotope values from lacustrine sediments in the Cerrejón Formation had a range of 3.3‰, consistent with vegetation along a lake edge. An even-narrower range of δ13C values (2.7‰) was observed for a leaf assemblage recovered from the Cretaceous Guaduas Formation, and suggests vegetation with an open canopy structure. Carbon isotope fractionation by Late Cretaceous and early Paleogene leaves was in all cases similar to that by modern relatives, consistent with estimates of low atmospheric CO2 during this time period. This study confirms other lines of evidence suggesting that closed-canopy forests in tropical South America existed by the late Paleocene, and fails to find isotopic evidence for a closed-canopy forest in the Cretaceous.

Trace elements and C-O isotopes of calcite from Carlin-type gold deposits in the Youjiang Basin, SW China: Constraints on ore-forming fluid compositions and sources

The Carlin-type gold deposits in the Youjiang Basin, SW China can be further classified into three sub-types; strata-bound, fault-controlled, and diabase-associated. The compositions and sources of the ore-forming fluids for each deposit type are evaluated using the texture of calcite by CL (Cathode luminescence), its chemistry by EMPA (Electron probe microanalysis) and LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry), and its C-O isotopic compositions by SIMS (Secondary ion mass spectroscopy). The studied deposits are the stratabound Zimudang deposit, the fault-controlled Lannigou deposit, and the diabase-associated Badu deposit. Calcite in the Zimudang and Lannigou deposits formed at three different stages: pre-ore stage pore-filling and massive calcite (Cal 1), late-ore stage vein calcite (Cal 2) associated with realgar and pyrite, and post-ore stage vein calcite (Cal 3). Calcite in the Badu deposit formed in two stages: ore stage vein and replacement calcite (Cal 2) associated with pyrite and post-ore stage calcites (Cal 3). Calcite with brighter red CL color has higher Mn and lower Fe content than calcite with darker red CL color. Furthermore, the higher the total REE content, the brighter the CL color. The host rocks are characterized by light REE (Rare earth element) enrichments. In contrast, the ore stage calcite shows middle REE enrichments. The ore stage calcite has higher concentrations of Fe, Mn, Mg, Si and Sr, and lower concentrations of Cu, Sb and Zn than both the pre- and post-ore calcite. The ranges of carbon (PDB) and oxygen (SMOW) isotope compositions of calcite are from −11.29 to 6.89‰ and from 16.49 to 22.60‰ for the Zimudang deposit, from −13.31 to 2.80‰ and from 9.12 to 29.71 for the Lanningou deposit, and from −11.94 to 0.49‰ and from 10.51 to 18.97‰ for the Badu deposit. Generally, the ore stage calcite has a wider range of δ13C and δ18O values than the other stage calcite. The isotope data indicate that a deep crustal fluid was involved in the formation of all of these three deposits. Meteoric water containing abundant organic matter was also involved in the formation of the Badu deposit as well as the Zimudang deposit, whereas a basin brine was also involved in the formation of the Lanningou deposit.