Strontium Isotopic Composition Research Articles

‘Do dead men tell no tales?’ The geographic origin of a colonial period Anglican cemetery population in Adelaide, South Australia, determined by isotope analyses

Tooth enamel and dentine samples from 13 individuals buried in the unmarked ‘free ground’ colonial section of St Mary’s Anglican Cemetery in Adelaide were analysed for oxygen and strontium isotopic composition to assist with the determination of their geographic origin. As the life history of these individuals is not well-documented in the historical record, isotopic data provide important information about migration and mobility in a colonial South Australian population. This was supplemented with further analysis of diet from previously published stable isotope data. While the results are somewhat ambiguous, they suggest that of the 13 individuals in this study, one was probably born in Adelaide, eight in Britain/Ireland, three could have been born in either location; one was born elsewhere. This interpretation supplements and supports the results from the analysis of skeletal morphology, microbiomes, and historical records.

Tectonic controls on the isotopic juvenility of mid-Cretaceous continental arcs: Global compilations and implications for chemical weathering

Continental arcs influence the global carbon cycle via degassing and chemical weathering. Several studies also suggested that the isotopic composition of continental arcs plays an important role in controlling the strontium (Sr) isotopic composition of seawater through chemical weathering. Yet, geological or tectonic drivers of isotopic variations of continental arcs on a global scale are missing in previous studies. Here, we compiled two independent global databases for mid-Cretaceous (125-85 Ma) continental arcs. The first database maps the location, geometry, and tectonic nature of the basements upon which the arcs were built. The second compiles Sr-Nd-Hf isotopes data for these continental arcs. We find that isotopically-juvenile arcs form when their basements are generated by tectonic processes such as oceanic terrane accretion, upper plate extension, slab breakoff, and ridge subduction. During the mid-Cretaceous, most continental arcs were fully or partially built on juvenile basements and yielded juvenile isotopes on a global scale. Our compilation reinforces the importance of isotopically-juvenile continental arcs observed in the global Hf isotopes in detrital zircon for the mid-Cretaceous, but also provides the geological context for these trends. Since many of these isotopically-juvenile arcs were located in tropical or warm-temperate regions during the mid-Cretaceous, these uplifted rocks were preferentially eroded and weathered providing juvenile Sr isotopes to the oceans. This study highlights the importance of tectonic processes in controlling isotopic compositions of continental arc, which has implications for ocean chemistry, global chemical weathering feedback, and the long-term carbon cycle.

An apatite trace element and Sr-Nd isotope geochemical study of syenites and carbonatite, exemplified by the Epembe alkaline‑carbonatite complex, Namibia

The Epembe Alkaline Carbonatite Complex (EACC) in northwestern Namibia was emplaced along a fault zone into medium- to high-grade Palaeoproterozoic basement rocks of the Epupa Metamorphic Complex (EMC), and extends over a distance of 9 km in a south-easterly direction with a width of 1 km. Nepheline syenite with minor syenite constitute the main lithologies, cross-cut by a calcite‑carbonatite dyke. Apatite grains from one syenite, six nepheline syenite and five carbonatite samples were studied using cathodoluminescence (CL) imaging, trace element and Sr-Nd isotope compositions as well as U-Pb geochronology. Syenite-hosted apatite is homogenous in CL and contains the highest concentration of REE (9189–44,100 ppm) with light rare-earth element (LREE) enrichment (LaN/YbN = 4–91) relative to heavy (H) REE consistent with a magmatic origin. Negative Eu anomalies (Eu/Eu* = 0.4–0.9) in syenite apatite are attributed to the formation of apatite in an evolved mantle-derived melt associated with plagioclase fractionation. Nepheline syenite and carbonatite-hosted apatite is also commonly homogeneous in CL, while core-rim zoning and patchy textures are observed occasionally. Both texturally homogeneous and core-rim zoned apatite are enriched in LREE (LaN/YbN = 24–9) relative to HREE, consistent with a magmatic origin. Core-rim zoned apatite is characterized by rim-ward increase in REE concentrations, which can be attributed to mineral fractionation. Patchy apatite is depleted in Na, Y and REE, particularly the LREE (LaN/YbN = 4–19) relative to other nepheline syenite apatite, reflecting interaction with fluids (metasomatism). The strontium isotope composition of metasomatic apatite and magmatic apatite is indistinct suggesting a magmatic origin of the alteration fluids. No Eu anomalies (Eu/Eu* = 1) in chondrite-normalized REE patterns are observed in any apatite hosted by nepheline syenite and carbonatite. An LA-ICPMS U-Pb age of 1216 ± 11 Ma (MSWD = 4.3, 2 SE) for apatite constrains emplacement of the syenite, while magmatic nepheline syenite apatite ages are 1193 ± 14 Ma, 1197 ± 17 Ma and 1194 ± 16 Ma (MSWDs <4.0, 2 SE). The Sr and Nd isotopic composition of apatite in syenite (87Sr/86Sr(i) = 0.7035–0.7048; ƐNd(t) = +2.5 to +3.2), nepheline syenites (87Sr/86Sr(i) = 0.7031–0.7037; ƐNd(t) = +1.5 to +4.4) and carbonatite (87Sr/86Sr(i) = 0.7031–0.7033; ƐNd(t) = 0 to +3.3) overlap, pointing to a common but heterogeneous source, located in the sub-lithospheric mantle.

Evaluation of coral skeletal δ88Sr as a paleoclimate proxy in the northern South China Sea

The climate and environmental significance of the stable strontium isotope composition (δ88Sr) in coral skeletons deserves further investigation. To improve our understanding of stable strontium isotope fractionation during the biomineralization process, correlations between monthly coral skeletal δ88Sr values and climatic and environmental variables (along with their corresponding geochemical proxies) between 2008 and 2009 were studied using a massive zooxanthellae Porites coral head from Sanya Bay on the south coast of Hainan Island in the northern South China Sea. Sea surface temperature and its corresponding geochemical proxies (Sr/Ca and δ18O), pH and its proxy δ11B, and precipitation (representing river runoff) show clear annual cycles, but their correlations with coral δ88Sr were not significant during 2008 and 2009. However, both total solar irradiance (TSI) and coral δ88Sr values followed a gradually increasing trend over the study period and showed a statistically significant correlation. These results indicate that the fractionation associated with coral skeleton δ88Sr is not temperature-dependent, but TSI may play a major role in controlling coral δ88Sr values at our study site. The underlying mechanism of TSI-induced 88Sr/86Sr fractionation in coral skeletons may be similar to that associated with coral δ13C. That is, symbiotic zooxanthellae preferentially uptakes 86Sr during photosynthesis leaving the internal strontium reservoirs enriched in 88Sr; consequently, increased uptake of 88Sr by the coral skeleton occurs when photosynthetic rates increase. However, the correlation between coral δ88Sr and δ13C values may be masked by the carbon input from terrestrial river runoff and the kinetic isotope fractionation effect during the calcification process.

Assessing the preservation of biogenic strontium isotope ratios (87 Sr/86 Sr) in the pars petrosa ossis temporalis of unburnt human skeletal remains: A case study from Saba.

RationaleStrontium isotope (87Sr/86Sr) analysis of skeletal remains has become a powerful tool in archaeological studies of human migration and mobility. Owing to its resistance to post‐mortem alteration, dental enamel is the preferred sampling material used for 87Sr/86Sr analysis in bioarchaeological provenance research, although recent studies have demonstrated that cremated bone is also generally resistant to diagenesis. This paper presents the results of a pilot study exploring the potential of unburnt petrous bone (pars petrosa) as a reservoir of biogenic (diagenetically unaltered) strontium, as the otic capsule or bony labyrinth within the petrous bone is extremely dense and is thought to be unable to remodel after early childhood, potentially providing an alternative for dental enamel.MethodsFrom an individual from a colonial‐era (18th century) site on the island of Saba in the Caribbean for whom previous enamel 87Sr/86Sr results had indicated non‐local origins, multiple locations (n = 4) on the petrous were sampled and measured for strontium isotope composition. Saba (13 km2) has been extensively mapped for baseline strontium isotopes (n = 50) with 87Sr/86Sr varying from ca 0.7065 to 0.7090, whereas enamel 87Sr/86Sr (n = 3) ranged from 0.7104 to 0.7112.ResultsAll four petrous 87Sr/86Sr ratios (0.7111–0.7122) are consistently and considerably higher than the local bioavailable range, and very similar to the enamel 87Sr/86Sr. These results provide initial evidence that unburnt petrous bones may preserve biogenic strontium, at least in this specific burial context.ConclusionsWhile more research in diverse burial conditions is needed to validate this observation, if confirmed, it would have broader implications for sample selection strategies in bioarchaeological studies using the strontium isotope method.

Detection of diagenetic alteration in bones and teeth for migration and dietary studies \u2014 a combined FTIR and C-N\u2013O-Sr isotope study on tenth century CE cemeteries in northern and northeastern Hungary

Stable isotope-based dietary information on the tenth century CE Hungarian population serves as a valuable comparative tool to other dietary stable isotope studies in the region. This study presents a multiproxy approach involving skeletal samples with the least diagenetic alteration and the best-preserved primary signals. Dental and bone samples collected from three cemeteries in northeastern Hungary were investigated using a combination of Fourier-transform infrared spectroscopy (FTIR), stable isotope geochemistry, and strontium isotope analysis. FTIR measurements were used to detect the addition of secondary carbonate to the skeletal apatite carbonate component and to differentiate diagenetically altered samples. Our results suggest that all but the bone apatite carbonate stable isotope values and 87Sr/86Sr ratios are trustworthy and may be used to interpret the diet and migration of the researched individuals. We also determined that the inhabitants of the three tenth century CE Hungarian settlements relied primarily on C3 plants, but that C4 plants, most likely broomcorn millet (P. miliaceum), comprised a moderate portion of their plant-based diet and that animal products were generally consumed in moderate-high amounts. Coupled analyses of carbonate oxygen and strontium isotope compositions revealed that most of the bone apatite carbonate was heavily altered, whereas enamel apatite carbonate samples largely preserved their primary compositions. The bones showing the least amount of diagenetic alteration may partially preserve their primary apatite carbonate compositions, as well as show a combination of primary and secondary signals, which should be taken into consideration when bone apatite carbonate data are interpreted.

Moho carbonation at an ocean-continent transition

Abstract Carbonation of mantle rocks during mantle exhumation is reported in present-day oceanic settings, both at mid-ocean ridges and ocean-continent transitions (OCTs). However, the hydrothermal conditions of carbonation (i.e., fluid sources, thermal regimes) during mantle exhumation remain poorly constrained. We focus on an exceptionally well-preserved fossil OCT where mantle rocks have been exhumed and carbonated along a detachment fault from underneath the continent to the seafloor along a tectonic Moho. Stable isotope (oxygen and carbon) analyses on calcite indicate that carbonation resulted from the mixing between serpentinization-derived fluids at ~175°C and seawater. Strontium isotope compositions suggest interactions between seawater and the continental crust prior to carbonation. This shows that carbonation along the tectonic Moho occurs below the continental crust and prior to mantle exhumation at the seafloor during continental breakup.

Tracking the Origin and Evolution of Diagenetic Fluids of Upper Jurassic Carbonate Rocks in the Zagros Thrust Fold Belt, NE-Iraq

Utilizing sophisticated tools in carbonate rocks is crucial to interpretating the origin and evolution of diagenetic fluids from the Upper Jurassic carbonate rocks along the Zagros thrust-fold Belt. The origin and evolution of the paleofluids utilizing in-situ strontium isotope ratios by high resolution laser ablation ICP-MS, integrated with stable isotopes, petrography and fieldwork are constrained. Due to the lack of information on the origin of the chemistry of the fluids, the cements that filled the Jurassic carbonate rocks were analysed from the fractures and pores. This allowed us to trace the origin of fluids along a diagenetic sequence, which is defined at the beginning from the sediment deposition (pristine facies). Based on petrography and geochemistry (oxygen-, carbon- and strontium-isotope compositions) two major diagenetic stages involving the fluids were identified. The initial stage, characterized by negative δ13CVPDB values (reaching −10.67‰), involved evaporated seawater deposited with the sediments, mixed with the input of freshwater. The second stage involved a mixture of meteoric water and hot fluids that precipitated as late diagenetic cements. The late diagenetic cements have higher depleted O–C isotope compositions compared to seawater. The diagenetic cements display a positive covariance and were associated with extra- δ13CVPDB and δ18OVPDB values (−12.87‰ to −0.82‰ for δ18OVPDB and −11.66‰ to −1.40‰ for δ13CVPDB respectively). The distinction between seawater and the secondary fluids is also evident in the 87Sr/86Sr of the host limestone versus cements. The limestones have 87Sr/86Sr up to 0.72859, indicative of riverine input, while the cements have 87Sr/86Sr of (0.70772), indicative of hot fluid circulation interacting with meteoric water during late diagenesis.

Multi-isotopic (O, H, C, S, Sr, B, Li) characterization of waters in a low-enthalpy geothermal system in Havza (Samsun), Turkey

In this study, multi-isotopic (O, H, C, S, Sr, B, Li) compositions were used to perform geochemical characterization, determine the source and reservoir rocks, and explain the water-rock interaction mechanisms for geothermal fluids in the low-enthalpy Havza (Samsun) geothermal field (HGF) in Turkey. The geothermal water of Na-HCO3 water type has a wellhead temperature of 53°C, pH of nearly 7.7 and an EC value of 1140 µS/cm. The geothermal springs of Ca-HCO3 water type have an EC value of nearly 667 µS/cm and a temperature of nearly 26°C. The reservoir temperatures of the HGF geothermal system were calculated as 60–90°C and 108–160°C by silica and SO4-H2O oxygen isotope geothermometers, respectively. Stable isotope compositions (δ2H and δ18O) show that the geothermal well water is mixed with deeply circulated waters fed from higher elevations (∼ 830–1260 m), while the geothermal spring water is mixed with shallow cold water. The positive δ13C value (+3.01‰) indicates that the dissolved inorganic carbon (DIC) in the geothermal well water has no contribution from the atmospheric CO2 but originates in the metamorphic CO2 and marine limestones. However, the DIC in the geothermal springs is derived from C3 plants and silicate weathering. The values of 34SCDT show that the sulfate in the geothermal waters is due to the dissolution of sulfate minerals. The values of δ11B (-1.12 to +9.37 ‰) in the geothermal well and spring waters reflect both leaching of surrounding rocks and mantle-derived B. The reservoir rock may be Late Cretaceous-Permian limestones and Jurassic sandstones considering 87Sr/86Sr ratios (0.707108–0.707688) and δ7Li values (-7.44 to +6.18 ‰), whereas it might be Jurassic sandstones based on δ11B values. The strontium isotope composition of the geothermal spring water indicates the mixing of deep geothermal waters and cold groundwaters.

Lithium and Sr isotopic composition of salar deposits in the Central Andes across space and time: the Salar de Pozuelos, Argentina

The Central Andes of South America host the largest known lithium resources in a confined area, but the primary lithium sources of the salar deposits and the mobilisation process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate near-surface chemical weathering in a cold and dry climate as the dominant mobilisation process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favoured source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by chemical weathering with only minor hydrothermal mobilisation of Li.

Violence among the first horticulturists in the atacama desert (1000 BCE – 600 CE)

The Neolithic or Formative Period in the New World drastically transformed the mode of production in human societies with the domestication of plants and animals. It impacted the way of life and social relations among individuals in permanent farming villages. Moreover, the emergence of elites and social inequality fostered interpersonal and inter- and intra-group violence associated with the defense of resources, socio-economic investments, and other cultural concerns. This study evaluated violence among the first horticulturalists in the Atacama Desert in northern Chile during the Neolithic transition between 1000 BCE – 600 CE. Furthermore, it analyzed trauma caused by interpersonal violence using a sample of 194 individuals. Strontium isotopic composition was examined to determine whether violence was local or among foreign parties. Settlement patterns, weapons, and rock art also were evaluated to assess expressions of violence. Skeletal and soft tissues presented the most direct evidence for violence. About 21% (n = 40) of adult individuals, particularly men, showed trauma compatible with interpersonal violence, with 50% (n = 20) of trauma appearing fatal. The findings suggested that violence was between local groups and that social and ecological constraints likely triggered violence within local communities.

Multi isotope systematics of precipitation to trace the sources of air pollutants in Seoul, Korea

Multiple sulfur (δ34Ssulfate, Δ33Ssulfate, & Δ36Ssulfate), nitrogen and oxygen (δ15Nnitrate & δ18Onitrate) and strontium (87Sr/86Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia. The δ34Ssulfate values (from 1.9 to 14.6‰ with a median of 4.7‰) and the δ15Nnitrate values (from −2.0 to 13.3‰ with a median of 1.0‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is a predominant source for sulfur and nitrogen, but other natural sources including biogenic contributions of DMS also add to their total budget. The seasonal variations are observed in δ34Ssulfate and δ15Nnitrate values (both higher in winter season), which is likely to result from the increase of coal use for domestic heating in China. The δ18Onitrate values also varied seasonally depending on the NOx oxidation pathway, being about 20‰ higher in winter than in summer season. The Δ33Ssulfate and Δ36Ssulfate values are not anomalous, showing the absence of MIF signals in precipitation of Seoul. The 87Sr/86Sr ratio of the precipitation samples range from 0.70988 to 0.71487 with a median of 0.71073, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K++NH4+)/(Ca2++Mg2+) and Cl−/Na+ suggest the overwhelming effect of anthropogenic input rather than carbonate dust on the end-member with lower 87Sr/86Sr ratios.

Filling Provenance in Fracture Cavity Formation within Aksu Area, Tarim Basin, NW China: Indicators from Major and Trace Element, Carbon-Oxygen, and Strontium Isotope Compositions

Abstract With an aim to increase the understanding about sedimentary environment and isotopic and chemical characteristics of fillings in fracture cavities with multiple compositions, we conducted scanning electron microscope (SEM), fluid inclusion testing (FIT), common and trace element chemistry, full analysis testing, isotopic compositions (δ13C, δ18O, 87Sr/86Sr), and apatite fission track testing to study the formation environment of Aksu area, Tarim Basin. According to outfield and microscope observations, combined with SEM results, three textural and compositional type fractures and cavities were distinguished. Through fine analysis of geochemistry characteristics on fractures, cavities, multiple filling periods, and environments were interpreted. Constrained by rare earth element (REE) pattern diagram, relationships between carbon and oxygen isotopes, strontium isotope, the compositional patterns, and generation environment of the fracture and cavities were determined. The results show that (1) cavity, fracture filling, and wall rock primarily consist of calcite, with a proportion of 56.85%, 80.48%, and 81.00%, respectively. (2) Four fracture sets have been distinguished in the Ordovician limestone of the karst cave, Middle-Late Caledonian (Set 1), Early Hercynian (Set 2), Indo-Yanshanian (Set 3), and Himalayan orogeny (Set 4). Two stages of cave filling deposition are distinguished. Stage I was coeval with the Middle-Late Caledonian Set 1 fractures and is attributable to the circulation of freshwater fluid. Stage II was coeval with the Early Hercynian Set 2 fractures and is attributable to deep hydrothermal fluid circulation. (3) Cavity, fracture filling, and wall rock in Ordovician strata are slightly influenced by diagenesis alteration and territorial supply. Three significant filling stages were distinguished, freshwater fluid with strong oxidizing environment (Middle-Late Caledonian), hydrothermal fluid with authigenic abnormal enrichment (indicating obvious hypoxic sedimentary water, Early Hercynian), and high-temperature hydrothermal fluid from deep earth (primarily influenced by magmatism, Indo-Yanshanian, and Himalayan).

The marine terraces of Santa Cruz Island, California: Implications for glacial isostatic adjustment models of last-interglacial sea-level history

Glacial isostatic adjustment (GIA) models hypothesize that along coastal California, last interglacial (LIG, broadly from ~130 to ~115 ka) sea level could have been as high as +11 m to +13 m, relative to present, substantially higher than the commonly estimated elevation of +6 m. Areas with low uplift rates can test whether such models are valid. Marine terraces on Santa Cruz Island have previously been reported to occur at low (<10 m) elevations, but ages of many such localities are not known. Using lidar imagery as a base, marine terraces on Santa Cruz Island were newly mapped, elevations were measured, fossils were collected for U-series dating (corals), strontium isotope compositions and amino acid geochronology (mollusks), and paleozoogeography (all taxa). Sr isotope compositions of mollusks from the highest of three marine terraces give ages of ~2.5 Ma to 1.9 Ma, along with Pliocene ages, from shells interpreted to be reworked. U-series ages of corals from the western part of the island indicate that low-elevation terraces north of the Santa Cruz Island fault correlate to the LIG. Where corals are lacking, amino acid ratios and faunal aspects support terrace correlation to the LIG high stand of sea. Elevations of most terrace localities north of the east-west trending Santa Cruz Island fault, in both the western and eastern parts of the island, range from 5.75 m to 8 m above sea level, well below the modeled paleo-sea-level range. Subsidence is ruled out as a mechanism for explaining the lower-than-modeled elevations, because higher-elevation terraces are present along much of the Santa Cruz Island coast north of the fault, indicating long-term tectonic uplift. The low elevations of the LIG terrace fragments are, however, consistent with a low rate of uplift derived from the higher, ~2.5–1.9 Ma terrace. A number of other localities on the Pacific Coast, also dated to the LIG, have marine terrace elevations below the modeled level. GIA models may have overestimated last interglacial sea level by a substantial amount and need to be revised if used for forecasts for future sea-level rise.

Towards disentangling climatic and tectonic changes of southernmost Africa using strontium isotope stratigraphy and clumped isotope thermometry

Abstract Upper Cretaceous-Cenozoic marine sequences preserved between 30 and 350 masl across southern South Africa record a complex history of climatic and tectonic changes. In this study, we measure the strontium (Sr) isotope composition of fossil shark teeth, echinoderms, corals and oyster shells to chronostratigraphically constrain the ages of these sequences. The method requires careful petrographic screening and micro-drilling of the samples to avoid possible alteration by diagenesis. To assess palaeoenvironmental effects in the shells we measured the Mg/Ca elemental ratios and O isotope values using electron microprobe analysis (EMPA) and secondary ion mass spectrometry (SIMS). In addition, we employed carbonate clumped isotope thermometry to test palaeotemperatures reconstruction. The analysis of recent to modern stromatolites by clumped isotopes yields an average temperature of 20.2°C, in agreement with present day observations. The fossil oyster shells suggest a warmer (23.0°C) seawater palaeotemperature, possibly due to major deglaciation and sea-level rise during the Neogene. We also find that transgressions occurred above 200 to 350 m elevation during: 1) the Campanian-Maastrichian (~75 Ma); 2) the mid-Oligocene (32 to 26 Ma); and 3) the Messinian-Zanclean (6 to 5 Ma). These three episodes are linked to well-known variations in global sea level and regional tectonic processes that could have affected the continental margin differently. The most recent transgression coincides with a maximum global sea-level rise of ~50 m at ca. 5.3 Ma, and a worldwide plate kinematic change around 6 Ma, which in Eurasia led to the closure of the Mediterranean Sea. In the Eastern Cape of South Africa, the new dates of analyzed oyster shells constrain a minimum uplift rate of ca. 150 m/Myr during this tectonic activity. The results have important implications for robust calibration of relative sea level in southern Africa.

Reconstructing paleohydrology in the northwest Great Basin since the last deglaciation using Paisley Caves fish remains (Oregon, U.S.A.)

The arid northwest Great Basin underwent substantial hydroclimate changes in the past 15,000 years, greatly affecting its desert ecosystems and prehistoric people. There are conflicting interpretations of the timing of hydrologic changes in this region, requiring more records to resolve the dominant climatic drivers. The Paisley Caves archaeological site, located near former pluvial Lake Chewaucan, contains well-dated, stratified sediments best known for evidence of early human occupation in North America. We present a novel paleohydrologic record for the Chewaucan basin based on the frequency of fish remains (Salmonidae and Cypriniformes, likely tui chub) and their carbon, oxygen, and strontium isotope compositions, from the Paisley Caves. Cypriniformes abundance peaks first at the start of the Bølling/Allerød warm interval (∼14.7 ka) and again during the early Younger Dryas (∼12.8 ka). Isotope compositions indicate tui chub were derived from an expansive Lake Chewaucan throughout the Bølling/Allerød, but mainly from spring- or stream-influenced sources by the late Younger Dryas to the present. Fish abundance dropped sharply through the Younger Dryas and early Holocene, when isotope compositions indicate a mix of habitats. Isotope compositions indicate the driest conditions during the middle Holocene, followed by slightly wetter conditions up to the present. This record agrees with recent pluvial lake reconstructions, supporting the hypothesis that a northward shift in the winter storm track supported deep lakes throughout the Bølling/Allerød in the northwest Great Basin. Lake level decline during the Younger Dryas suggests drying climate, differing from more southerly records. During the Holocene, however, shifts in Chewaucan basin hydrology are consistent with the rest of the western U.S. This highlights the need for region-specific records to inform predictions of the hydrologic impact of climate change on arid regions.

Silicon isotopic constraints on the genesis of cherts in the Ordovician sedimentary succession in Tarim Basin, Western China

• Hydrothermal fluids play an important role in the formation of cherts . • Si-O-Sr isotopes of the cherts to constrain the source and migration of the fluids. • Fault activity links the channels of hydrothermal migration during the late Hercynian. The Tarim Craton is the largest petroliferous basin in China, and thick chert have been found in the Ordovician carbonate reservoir during drilling. Owing to the tight chert, the storage performance may decrease and lead to drilling failure. In this study, silicon, oxygen, and strontium isotope compositions of chert were tested to constrain the source and migration of Si-rich fluids, which is helpful for understanding the reservoir and avoiding drilling failure. The Ordovician silicon dioxide in cherts have δ 30 Si values from +1.29‰ to +3.50‰, δ 18 O values from 20.21‰ to 27.50‰, and 87 Sr/ 86 Sr values from 0.709 to 0.714. The correlation between δ 30 Si- and δ 18 O reveals that the formation of cherts is related to the activity of low-temperature hydrothermal fluids, and the value of 87 Sr/ 86 Sr indicates the contribution of the deep crust source to the silicon-rich fluid. Comprehensive analyses showed that the deep thermal fluid was active during the formation of cherts. The late Hercynian tectonic movement led to the development and activity of deep and large faults, and the deep-source silica hydrothermal fluid entered the Ordovician reservoir along the fault from bottom to top, filling the pores, densifying the rocks, and causing deterioration of the storage performance. Therefore, through multi-geochemistry (Si-O-Sr isotopes), the spatial distribution characteristics of silica can be determined to avoid the distribution interval and member of silica during drilling. Moreover, the identification and distribution prediction of the genesis of cherts is of great significance for oil and gas exploration.

Diagenetic conditions and geodynamic setting of the middle Permian hydrothermal dolomites from southwest Sichuan Basin, SW China: Insights from in situ U–Pb carbonate geochronology and isotope geochemistry

The presence of hydrothermal dolomites in the middle Permian carbonates from the southwest Sichuan Basin has been suggested by petrographic features including zebra structure and extensive saddle dolomite cementation. Two major tectono-thermal events, i.e., the intensive volcanism related to the Emeishan large igneous province (ELIP) during the latest middle Permian and the tectonic evolution of the Longmenshan Orogenic Belt since the Late Triassic, might have contributed to the regional fluid flow for hydrothermal dolomitization. Here, we apply LA-ICP-MS U–Pb geochronology, petrography and isotopic geochemistry to constrain the diagenetic and geodynamic conditions of these hydrothermal dolomites. These dolomites resulted from injection of hot fluids up to 95 °C higher than the ambient temperatures. U–Pb ages (from 216.4 ± 7.7 Ma to 206 ± 15 Ma), combined with the highly radiogenic 87Sr/86Sr compositions (up to 0.712151), suggest that the previously proposed ELIP-related dolomitization model may not apply to this site. Instead, our new geochronological data suggest a syn-orogenic flow of basinal brines probably driven by thrust-related compression and/or tectonic valving. Moreover, the indistinguishable U–Pb ages and carbon, oxygen and strontium isotopic compositions among the replacement and cement carbonate phases in these hydrothermal dolomites further suggest that the paragenetic sequence of “replacement dolomite→saddle dolomite→blocky calcite” was originated from a common fluid in evolution. This study emphasizes the merits of LA-ICP-MS U–Pb dating in addressing the discrimination of, as well as diagenetic and geodynamic conditions for, hydrothermal dolomites.

Investigation of meteoric water and parent fluid mixing in a two-phase geothermal reservoir system using strontium isotope analysis: A case study from Southern Bandung, West Java, Indonesia

Determinations of the recharge area and recharge mechanism in geothermal systems are essential for reservoir management and a sustainable resource use. To address this problem, studies aplenty have aimed to identify the recharge elevation using stable water isotopes, δ2H and δ18O. Nevertheless, the physical and chemical processes involved in the generation of a reservoir fluid from a deeply infiltrated recharge flow remain poorly understood. This study aims to clarify this process using strontium (Sr) concentrations and isotope composition from water and well rock samples by selecting a geothermal field with a two-phase reservoir system in Southern Bandung, West Java, Indonesia. The water samples are characterized by variable Sr isotopic compositions (87Sr/86Sr) (0.70450–0.70725) and low Sr concentrations (0.01–0.72 ppm). The 87Sr/86Sr of the well rocks is also variable (0.70400–0.70827) with particularly high Sr concentrations (9.1–53 ppm). Three types of domain that are the combinations of the reservoir fluid mixing with groundwater are identified. The first two types are shallow and deep groundwater composed of 90 % meteoric water and 10 % upflow fluids with Sr concentration 0.01 to 0.11 ppm and the 87Sr/86Sr from 0.7055 to 0.70725. The shallow groundwater may possibly carry a 87Sr/86Sr anomaly (higher than 87Sr/86Sr of plagioclase: 0.7065) from the anthropogenic activities through the pathways created by the intersection of the NW-SE and NE-SW inferred regional faults in the west part of the field, hosted by the Wayang Windu Formation. The deep groundwater type is also a mixture of 10 % parent fluid hosted by the deeper aquifer rocks Malabar Formation, with lower strontium isotopes ratio than the first aquifer (87Sr/86Sr 0.7045–0.7055). The third groundwater refers to the perched aquifer with mixture of 30 %–70 % parent fluid that has undergone condensation and mixing processes in Pangalengan Formation (87Sr/86Sr 0.70452–0.7052). This groundwater is thought to be the source of mostly hot springs in the study area.

Geochemical evidence for fugitive gas contamination and associated water quality changes in drinking-water wells from Parker County, Texas.

Extensive development of horizontal drilling and hydraulic fracturing enhanced energy production but raised concerns about drinking-water quality in areas of shale-gas development. One particularly controversial case that has received significant public and scientific attention involves possible contamination of groundwater in the Trinity Aquifer in Parker County, Texas. Despite extensive work, the origin of natural gas in the Trinity Aquifer within this study area is an ongoing debate. Here, we present a comprehensive geochemical dataset collected across three sampling campaigns along with integration of previously published data. Data include major and trace ions, molecular gas compositions, compound-specific stable isotopes of hydrocarbons (δ13C-CH4, δ13C-C2H6, δ2H-CH4), dissolved inorganic carbon (δ13C-DIC), nitrogen (δ15N-N2), water (δ18O, δ2H, 3H), and noble gases (He, Ne, Ar), boron (δ11B) and strontium (87Sr/86Sr) isotopic compositions of water samples from 20 drinking-water wells from the Trinity Aquifer. The compendium of data confirms mixing between a deep, naturally occurring salt- (Cl >250mg/L) and hydrocarbon-rich groundwater with a low-salinity, shallower, and younger groundwater. Hydrocarbon gases display strong evidence for sulfate reduction-paired oxidation, in some cases followed by secondary methanogenesis. A subset of drinking-water wells contains elevated levels of hydrocarbons and depleted atmospherically-derived gas tracers, which is consistent with the introduction of fugitive thermogenic gas. We suggest that gas originating from the intermediate-depth Strawn Group ("Strawn") is flowing along the annulus of a Barnett Shale gas well, and is subsequently entering the shallow aquifer system. This interpretation is supported by the expansion in the number of affected drinking-water wells during our study period and the persistence of hydrocarbon levels over time. Our data suggest post-genetic secondary water quality changes occur following fugitive gas contamination, including sulfate reduction paired with hydrocarbon oxidation and secondary methanogenesis. Importantly, no evidence for upward migration of brine or natural gas associated with the Barnett Shale was identified.