A Aunique feature of the Re-Os isotope system is its ability to provide precise and accurate depositional ages from organic-rich sedimentary rocks. Applications include geologic timescale calibration, stratigraphic correlation, and dating key events such as biological innovations, mass extinctions, carbon cycle perturbations, Snowball Earth glaciations, and atmospheric oxygenation. Multiple sediment types reveal temporal variations in the osmium isotope composition of seawater, driven by changes in osmium inputs from continental weathering, seafloor hydrothermal systems, and extraterrestrial material. These variations provide valuable information on climate-tectonic interactions, glacial-interglacial cycles, large igneous province magmatism, bolide impacts, and crustal evolution. Continental processes can be inferred from lake sediment records. These diverse applications highlight the central role of the Re-Os isotope pair in understanding Earth's evolution.

From the Middle Jurassic to Early Cretaceous, the mudstone-dominated Agardhfjellet Formation was deposited during the prolonged shelf dysoxic-anoxic event (SDAE) recorded predominantly in the circum-arctic polar regions. Commonly, oceanic anoxic events (OAEs) throughout Earth's history are linked to the emplacement of large igneous provinces (LIPs). OAEs and LIPs, alone or jointly, are inferred to be triggers for severe biotic crises in Earth's history. However, the causes for SDAEs remain uncertain. To elucidate these causes, we document the geochemical features of the Agardhfjellet Formation using trace element concentrations and stable isotope ratios. The Agardhfjellet Formation, which consists of the Oppdalen, Lardyfjellet, Oppdalss & aring;ta, and Slottsm & oslash;ya members in ascending order, formed during -13 Myr of prolonged dysoxic, anoxic, and euxinic conditions. The onset of shelf anoxia took place between deposition of the Oppdalen and Lardyfjellet Members. The extent of sea floor anoxia in the basin varied within the Lardyfjellet Member but likely persisted throughout most of the Slottsm & oslash;ya Member. Mo/TOC and Mo EF /U EF ratios in the sedimentary rocks are consistent with the anoxic events. Enhanced continental runoff marked the Oppdalen, Oppdalss & aring;ta, and Slottsm & oslash;ya members, contrasting with most of the Lardyfjellet Member, in which authigenic phases were widespread under anoxic conditions. Our results show that, compared to other OAEs, such as the Toarcian OAE (-183 Ma) or the OAE2 (-94 Ma), the Late Jurassic - Early Cretaceous SDAE recorded in the Agardhfjellet Formation is characterized by prolonged suboxic-anoxic condition, substantial water -mass stratification, and increased continental runoff.

The limited number of accurate and precise radiometric ages through the similar to 100 Myr span of the Cambrian and Ordovician impedes reliable age determinations for stage boundaries in these periods. Here, we fill significant gaps in the early Paleozoic chronostratigraphy by providing precise Re-Os time-pins. Sample selection is linked to a firm biostratigraphic framework built on the appearance and distribution of trilobites, graptolites, and conodonts. A Furongian (upper Cambrian) Alum Shale section (Andrarum-3 drill core, Scania, Sweden) at the onset of the Steptoean Positive Carbon Isotopic Excursion (SPICE) yields highly non-isochronous Re-Os isotopic data from a section with wildly fluctuating delta C-13(org); however, selected data from a narrow sediment band with steady carbon isotope stratigraphy provides an imprecise Re-Os age of 497 +/- 28 Ma (2 sigma; Model 3; n = 3), with an initial Os-187/Os-188 ratio (Os-i) of 0.74 +/- 0.05. Organic-rich Alum Shale (Tomten-1 drill core, V & auml;sterg & ouml;tland, Sweden) from similar to 120 cm below the Cambrian-Ordovician boundary yields a Model 1 age of 488.6 +/- 5.1 Ma (2 sigma; MSWD = 1.5; n = 25) and an Os-i of 0.82 +/- 0.04 for Stage 10, uppermost Cambrian. Biostratigraphic data indicate the dated Alum Shale is from an interval slightly below the Top Of Cambrian Excursion (TOCE) and slightly above the First Appearance Datum (FAD) of the agnostoid Lotagnostus americanus. Organic-rich T & oslash;yen Shale (Lerhamn drill core, Scania, Sweden) yields a precise Model 1 Re-Os age of 469.7 +/- 1.4 Ma (2 sigma; MSWD = 1.0; n = 10) and Os-i of 0.802 +/- 0.002 for the maximum age of the Floian-Dapingian stage boundary (Lower-Middle Ordovician boundary). The Os isotopic composition of seawater from the latest Ediacaran through the Cambrian to Early-Middle Ordovician hovers around 0.8 but falls to 0.54 by early Silurian. This significant decrease in seawater Os-187/Os-188 is consistent with reduced chemical weathering and cooler seawater temperatures through the Middle-Late Ordovician. Overall, Redox Sensitive Element (RSE; Re, Os, Mo, U) abundances correlate positively with Total Organic Carbon (TOC), suggesting efficient removal of these elements from an anoxic water column by organic matter. However, these relationships break down for high TOC (>10%) shales depositing under euxinic conditions. The RSE-TOC relationship breakdown supports enhanced metal drawdown from the water column with local pyrite accumulation. Geochemical data suggest the deposition of Alum and T & oslash;yen shales under hydrographically restricted settings with increased primary productivity along the Baltica's margin during the latest Cambrian to Early-Middle Ordovician.

Ammonite provincialism makes it difficult to link the Boreal and Tethyan realms during the Late Jurassic to Early Cretaceous time. Absolute ages through radiometric dating offer new age information that is independent and complementary to relative ages based on biostratigraphy. In this study, we report seven new Re-Os ages for black shales from the Agardhfjellet Formation, Svalbard. We also report pyrolysis results, carbon and sulfur stable isotopic data, and initial 187Os/188Os ratios to evaluate the paleoenvironment during organic-rich shale deposition. Re-Os ages are derived from three Boreal ammonite zones: (1) 159.2 and 160.1 Ma from the shale intervals containing Cadoceras sp.; (2) 149.6, 149.9, 150.8, and 151.9 Ma from the Rasenia cymodoce Zone in the Early Kimmeridgian, which is the equivalent of the Sutneria platynota and Ataxioceras hypselocyclum zones in the Tethyan realm; (3) 146.8 Ma from an upper Volgian interval above the occurrence of Laugeites sp.. Within this 14.5 Myr interval, the initial Os profile shows a gradually increasing trend from 0.335 (one of the lowest shale values throughout the Phanerozoic) to 0.529, consistent with previous initial Os studies and Sr isotopic ratio chemostratigraphic studies. The trend of increasing initial Os ratios indicates an increase in continental runoff relative to unradiogenic Os input from mantle sources, such as seafloor hydrothermal activity or ultramafic source rocks. We provide new Re-Os geochronological anchors in the Late Jurassic with new Re-Os ages and propose correlations of specific Late Jurassic ammonite zones between the Tethyan and Boreal realms. In turn, the gradual increase in seawater Os isotopic ratios may signal climate change in the Late Jurassic, indicating the increase of radiogenic Os or decrease of unradiogenic Os, induced by high continental runoff or less hydrothermal/volcanic activity.

Two recent advances in instrumentation convey rhenium and osmium elemental and isotopic distribution in molybdenite at the micro-scale: (1) NanoSIMS imaging which reveals heterogeneities that could preclude micro-scale geochronology (spot dating), and (2) reaction-cell LA-ICP-MS/MS which partially resolves overlapping masses of isobaric Re-187 and Os-187 which otherwise confound micro-scale analyses. The results from each of these measurement principles led respective researchers to conclude that no apparent parent-daughter decoupling occurs, at least in their chosen samples. This contradicts 20 years of prior macro- to micro-scale Re-Os molybdenite data. Given these contradictions, we compare their results to our macro-scale isotope dilution (ID) N-TIMS measurement results of NIST Reference Material 8599, Henderson molybdenite. We document the homogeneity of the NIST molybdenite, including model age variability, precision of ID N-TIMS measurement results and statistical treatment. We demonstrate that parent-daughter decoupling cannot be precluded by visual inspection of NanoSIMS isotopic maps. In addition, we prove mathematically that quantifying reaction-cell reacted Os-187 by LA-ICP-MS/MS is far too imprecise to preclude parent-daughter decoupling at an extent that hinders high-precision geochronology, although full 2-D ablation of a molybdenite crystal surface may yield an accurate Re-Os age. Nevertheless, LA-ICP-MS/MS is useful for documenting the spatial extent of heterogeneous parent-daughter distribution within individual crystals and supports whole crystal ID N-TIMS.

Mercury (Hg) enrichment and elevated ratios of Hg to total organic carbon (Hg/TOC) in sedimentary rocks have often been linked to volcanism from large igneous provinces (LIPs). Primary Hg and TOC contents of sediments can be altered by secondary processes like extreme weathering. These effects must be evaluated before tying Hg anomalies in weathered rocks directly to LIP events. However, the effects of incipient weathering on Hg contents and Hg/TOC ratios are not known. In this study, we elucidate the behavior of Hg during incipient weathering by investigating visually pristine black shales from outcrops of the Ravnefjeld Formation in East Greenland (GRL) and comparing them to drill core equivalent intervals acquired from the same outcrop area and correlative shales from the mid-Norwegian shelf (MNS). By using geochemical investigations and principal component analysis, we characterize the main host phases of Hg and relate the different Hg contents of pristine samples from GRL and MNS to different Hg inputs during shale deposition. Compared with pristine drill core samples, incipiently weathered outcrop shales have up to 77% lower Hg contents and up to 64% lower Hg/TOC ratios. Incipient weathering causes the early degradation of Hg signals, which masks the primary Hg and Hg/TOC signals in sedimentary rocks. Therefore, we suggest that the presence and effects of weathering in sedimentary rock should be evaluated before discussing Hg signals.

A range of geochemical data has been used to navigate the complexity of systems that build critical energy resources. Society’s need for hydrocarbons and metals are among these resources. However, petroleum and ore deposits are traditionally studied as two completely different disciplines in geoscience. We argue that they share a common heritage, or at a minimum an intersection in that the source rocks for oil also present source rocks for metals in sedimentary basins. In this presentation, we demonstrate the value of merging the study and teaching of these two disciplines: petroleum geology and ore deposit geology associated with sedimentary basins. We present several possibilities, for example, (1) the hydrothermal fluid may be the hydrocarbon-carrying fluid, and (2) mixing of a hydrocarbon-bearing fluid with a metalliferous brine may precipitate sulfide intermingled with oil. The end locations for the two resulting resources, however, may be spatially displaced from one another. Using a petroleum discovery from the Barents Sea as an example, we will illustrate the intimacy between metal and hydrocarbon deposition, and we will show petrographically the episodic, locally catastrophic events that formed the two resources in the same space. We will show critical relationships between replacement textures and explosive overpressure textures, the latter leading to capture of chalcedony-oil and barite-oil emulsions. We will show sulfide veins with visible oil inclusions. Sphalerite-galena-fluorite are all critical players. Our results highlight poorly understood infusions of sphalerite, co-mingled with oil, residing in biogenic carbonate rocks. Further, from the perspective of ore geology, our interpretations challenge classic replacement textures in some ore-forming environments. Seemingly abrupt changes in sulfide mineralogy, or the switch to oxide minerals, may be violent rupture of earlier sulfides by catastrophic fluid ingress and infilling with a new mineralogy – rather than passive replacement as is the common interpretation. Designing strategic sampling in these complex environments often requires many analyses to build a forest of persuasive evidence to inform exploration models. Reliance on small or isolated data sets may lead to highly erroneous interpretations. Application of Re-Os geochronology and trace element geochemistry places fluid compositions in a time context, useful in both petroleum and sulfide settings. At the same time, this information distinguishes slow continuous deposition from small catastrophic events during construction of petroleum and ore systems. Long-term investment of industry in resource-related research rewards all parties, with the common goal of meeting the needs of society and expanding the technologies that will give humanity a more sustainable future. Cross-disciplinary approaches, marrying metals and hydrocarbons, will be essential for efficient exploration and advancement of resource knowledge. Funding – Partial funding for this project was provided by Lundin Energy Norway. Colorado State University-Geosciences provides no funding for the personnel and operation of the AIRIE Program and its Re-Os laboratories.

Recent Re-Os studies of sulfide concentrations in anorthosite-dominated plutonic suites consistently yield high initial 187Os/188Os ratios in sulfide minerals, indicating a major component of crustal Os. These studies have led to three distinct hypotheses for the origin of the sulfide mineralization, with implications for the genesis of the hosting plutonic rocks: (1) the source of the parental magmas is mafic continental crust; (2) mantle-derived melts achieve sulfide saturation and acquire crustal Os through bulk assimilation of silicate crust; or (3) mantle-derived melts achieve sulfide saturation and acquire crustal Os through selective assimilation of crustal sulfur and metals by volatilization and/or melting of crustal sulfides. We favor the third hypothesis on the basis of modeling of Re-Os data together with other geologic and geochemical constraints. Nevertheless, the available data sets are limited, and we cannot yet preclude the possibility that real differences exist among the complexes examined to date.

As the application of the rhenium–osmium (Re‐Os) chronometer in low‐level (low Re mass fraction) sulfides becomes more popular, there is increasingly a need for a corresponding reference material for analytical quality control. This study presents a new low‐level, highly radiogenic chalcopyrite reference material for Re‐Os geochronology. Chalcopyrite was acquired from the Xiaotongchang (XTC) copper deposit in Yun’nan Province, China. Homogeneity tests were used by performing Re‐Os analyses on eleven randomly selected aliquots of powdered chalcopyrite using ICP‐MS. We also performed stability tests on four bottles of powdered chalcopyrite samples over a period of 36 months. The results from analysis of variance and Student’s t‐test indicated that the XTC sample was homogeneous with respect to Re, 187Os mass fractions and model age. Three laboratories participated in an inter‐laboratory comparison scheme for certification, performed using N‐TIMS and MC‐ICP‐MS, and employing two different spiking techniques. The reported values for model ages obtained for the XTC chalcopyrite in this study resulted in an age RM value of 229.3 ± 3.7 Ma at the 95% confidence level (95% conf.). Additionally, Re and 187Os mass fractions of 26.5 ± 1.9 ng g−1 and 63.7 ± 4.7 pg g−1 (95% conf.), respectively, are also reported, providing further information values.

The Re-Os (rhenium-osmium) chronometer applied to molybdenite (MoS2) is now demonstrated to be remarkably robust, surviving intense deformation and high-grade thermal metamorphism. Successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite such that recognized decoupling of 187Re parent and 187Os daughter within molybdenite is overcome. The use of a reference or control sample is necessary to establish laboratory credibility and for inter-laboratory comparisons. High precision, accurate, and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry (ID-NTIMS). The laser ICP-MS technique should not be used for Re-Os dating of molybdenite. Successful dating of molybdenite by Re-Os is recognized when Re-Os age results are in agreement with the generally robust U-Pb dating method and with observed geologic relationships. The Rb-Sr, K-Ar, and 40Ar/39Ar chronometers are susceptible to chemical and thermal disturbance, particularly in terranes that have experienced subsequent episodes of hydrothermal/magmatic activity, and therefore should not be used as a basis for establishing accuracy of the Re-Os dating, as has been done in the past.

Perceived mercury (Hg) enrichments and elevated ratios of Hg to total organic carbon (Hg/TOC) in sedimentary rocks have often been linked to volcanism from large igneous provinces (LIPs) and mass extinctions, prompting the hypothesis that elevated Hg concentrations are a proxy for intense volcanism from LIPs. However, primary Hg and TOC contents of sedimentary rocks can be altered by secondary processes, for example, intense weathering [1]. Before endorsing cause-and-effect between volcanic Hg emissions and biotic crises or mass extinctions, the magnitude of measured Hg and Hg/TOC anomalies in weathered outcrop samples must be compared to equivalent units in core samples, where the outcrop sample provides, in effect, a minimum concentration value. Here, we investigate the effects of incipient weathering on Hg contents and Hg/TOC ratios. We quantify the behavior of Hg during incipient weathering by determining Hg concentrations in visually pristine black shales from outcrops of the Upper Permian Ravnefjeld Formation in East Greenland, comparing these data to equivalent intervals acquired from drill core taken from a plateau 7 km from the outcrop. Directly correlative Upper Permian shales (drill core) from the mid-Norwegian shelf further enhance our comparison. Using detailed geochemistry and principal component analysis (PCA), we characterize the main host phases of Hg and relate different Hg contents from pristine samples from East Greenland and the mid-Norwegian shelf to different Hg inputs during shale deposition. Importantly, we show the vulnerability of Hg contents and Hg/TOC ratios to incipient weathering of fresh-appearing outcrops of organic-rich shale. Working with drill core rather than outcrop samples is essential to circumvent the problem, and to provide accurate Hg concentration data for primary events in the paleo-record. [1] Charbonnier, G., Adatte, T., Föllmi, K.B., and Suan, G. (2020) Effect of intense weathering and postdepositional degradation of organic matter on Hg/TOC proxy in organic-rich sediments and its implications for deep-time investigations. Geochemistry, Geophysics, Geosystems, 21(2). Funding – HS acknowledges the support of ACS-PRF award #59965-ND2 supporting AIRIE PhD student JP. Drill cores were acquired from GEUS under Petromaks grant (NFR 180015/S30). Colorado State University-Geosciences provides no funding for the personnel and operation of the AIRIE Program and its Re-Os laboratories.

The Re-Os geochronometer constrains the timing of petroleum formation and provides an oil-source isotopic correlation tool for improved geologic knowledge and exploration success. However, the effects of secondary processes that may sometimes complicate interpretations are not well understood. This paper discusses Re-Os systematics in a petroleum system that experienced extensive asphaltene precipitation upon mixing of different oil phases. The Solveig oil field (formerly Luno II), Utsira high, Norwegian North Sea, comprises three structural compartments that capture different stages of the mixing process. In the central compartment, an Re-Os age of circa 40 Ma for whole-rock extracts sampling the residual (asphaltene-rich and biodegraded) oil below the oil–water contact is consistent with burial models for Paleocene–Miocene generation. A 10-m-thick, asphaltene-rich (65 wt. %) tar mat zone precipitated upon mixing of at least two components does not yield meaningful ages. The Re-Os isochrons for the free-flowing crude oil and whole-rock extracts from the oil leg above the tar mat zone indicate circa 10 to 0 Ma ages for the younger oil phase, supporting independent estimates for recent oil influx. Decreasing 187Os/188Os from maltenes to asphaltenes in oil from the southeastern compartment are highly unusual and provide geochemical evidence for recent mixing, consistent with the strong asphaltene-in-oil gradient. Very low and remarkably uniform Re/Os ratios for all petroleum phases, combined with relatively low and uniform 187Os/188Os ratios, strongly support isotopic overprint of the Re-Os system, likely during water–oil interaction. Despite this overprint, Re-Os ages retain information on primary events, whereas initial 187Os/188Os ratios are strongly affected.

Every so often, an analytical advancement or challenging geological occurrence necessitates re-evaluation of well-established geochronological methods. Rhenium-osmium (Re-Os) dating of sulfide minerals, especially molybdenite, by isotope dilution-negative thermal ionization mass spectrometry (ID-NTIMS) yields demonstrably accurate, robust ages. Difficulty in determining an age is caused by either 1) geological complexity including intra-crystalline heterogeneity or 2) inadequate analytical capabilities. Established, systematic methods overcome most of these difficulties, with exceptions. With respect to molybdenite, geological complexity is encountered as macro-scale polyphase overgrowths. Micro-scale complexity is observed as primary Re oscillatory zoning and secondary intra-granular 187 Re parent- 187 Os daughter decoupling. Macro- and micro-scale geologic heterogeneities are overcome by systematic, targeted sampling protocols built upon careful hand sample and microscopic observations linking molybdenite crystallization to the host rock's geologic history.Advances in instrumentation permit more accurate and precise determination of elemental and isotopic compositions at the micro-scale, which ultimately reveals geological complexity and heterogeneity. Yet, newly produced high-resolution data must be carefully scrutinized and interpreted correctly. Two new micro-scale analytical techniques have been proposed: (1) to use NanoSIMS imaging to reveal heterogeneities that could preclude micro-scale geochronology (spot dating) methods, and (2) enable micro-scale geochronology using LA-ICP-MS/MS to distinguish the interfering masses of parent Re and daughter Os isotopes. We turn first to NIST Reference Material 8599, Henderson molybdenite, to compare its Re-Os characteristics and ID-NTIMS results with the newly published Re-Os molybdenite data. We identify the "best possible results" by quantifying the homogeneity of the NIST molybdenite, including model age variability, precision of ID-NTIMS analyses, and statistical treatment. Subsequently, we examine the limitations of the two newly proposed methods. We demonstrate that parent-daughter decoupling cannot be precluded by visual inspection of NanoSIMS isotopic maps. In addition, we prove mathematically that the quantifying the contribution of 187 Os to the total measured mass 187 by LA-ICP-MS/MS is far too imprecise to achieve high-precision geochronology. Statistical data treatment and reporting can also result in misguided conclusions and applications.

Rhenium–osmium geochronometry for samples with low Re and complex matrices requires improved Re extraction methods. Here, we investigate plausible controls on efficiency and efficacy of Re extraction during our anion resin bead purification. Four different protocols are compared, each isolating a single variable to test. Rhenium concentrations for solutions at each step of each protocol document differences in chemical recovery/yield. The negative‐thermal ionisation mass spectrometry (N‐TIMS) signal intensity serves as a proxy for Re yield and purity. These data document correlations between the N‐TIMS signal intensity and (a) the duration of anion resin bead conditioning prior to loading with Re‐bearing solution, and (b) both duration and strength of nitric acid used during rinsing of the Re‐loaded anion resin bead. The optimal protocol improved Re signal intensity around fourteen times compared with our current Re extraction protocol, an aggregate of 2.4 times improvement in chemical recovery (yield) and 5.8 times improvement in emission efficiency (purity). Repeated N‐TIMS isotopic measurements on our in‐house Re standard solution (1407) verify that our optimal protocol‐3 does not fractionate Re isotopes. The improved anion resin bead method considerably lowers the Re detection limit and allows Re‐Os isotopic analysis of picogram‐level Re hosted in geological samples with complex matrices.

The temporal coincidence between the Late Permian mass extinction (LPME) and the emplacement of Siberian Trap basalts suggests a causal link between the two events. Here, we discuss stratigraphic changes of organic and inorganic (including isotopic) geochemical properties of marine sediments across the Permian-Triassic boundary (PTB) in the Hovea-3 core, Western Australia, a key PTB section in the southern Neo-Tethys ocean. These data are compared with published data from the Meishan section, southern China, and from the Opal Creek section in western Canada, providing a view of Tethys and Panthalassa changes at the PTB. Trace metal and N-isotopic data, together with organic matter properties suggest that anoxic conditions were established prior to the LPME, intensified close to the LPME, and continued with photic-zone euxinia into the Early Triassic. For the Hovea-3 section, Re-Os ages confirm Changhsingian (253.5 +/- 1.4 Ma) deposition of the dated interval sampled immediately below the stratigraphic level characterized by major lithological and isotopic changes. Evaluation of Re-Os, N, and Hg elemental and isotopic data for Hovea-3 suggests that anoxic conditions in the latest Permian were generally unrelated to direct magmatic contributions. Amajor increase in the initial Os isotopic ratio of Lower Triassic shales suggest an similar to 8x increase in the Early Triassic continental runoff, based on moderately conservative assumptions for end-members contributing Os to the Permian-Triassic ocean. Comparison to other PTB sections confirms a global signal of increasing Re/Os ratios in the Late Permian, and major and long-lived changes in the isotopic composition of the post-extinction ocean. A distinct peak in Hg concentrations carrying a volcanic isotopic signature, also identified in other PTB sections, likely represents a major pulse of Siberian Trap volcanism. This Hg peak in the Hovea-3 section, however, is detected above the stratigraphic level containing multiple other widely recognized and more permanent geochemical changes. Therefore, direct volcanic inputs to the Permian-Triassic Ocean likely post-date the LPME in this Western Australian section. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved .