Anomalously high metal concentrations including iron enrichments are recorded in marine carbonates deposited during Ocean Anoxic Event 2 (OAE 2). These metal enrichments have been attributed to massive submarine eruptions during the formation of one or more large igneous provinces, the proposed trigger for OAE 2 (hydrothermal hypothesis), or to the release of metals from the reoxidation of formerly anoxic marine sediment during a period of temporary cooling during OAE 2 (sediment release hypothesis). Here we use iron stable isotopes to help distinguish between the two hypotheses for a trace metal enriched interval during OAE 2 in the Iona-1 core in the Western Interior Seaway, Texas. Our results show a two-step negative excursion during OAE 2 that is coincident with osmium isotope volcanic proxies measured in the same core, with peak negative values centered on a trace metal-enriched interval. After corrections for detrital and locally supplied iron to the study setting, the delta Fe-56 value of the remotely supplied iron is -0.28 +/- 0.05 parts per thousand, falling in the range of iron delta Fe-56 values observed in modern hydrothermal plumes (-0.1 to -0.5 parts per thousand), thus supporting the hydrothermal hypothesis as the source of iron and other associated trace metals enriched in the study core during OAE 2. By contrast, the sediment release hypothesis predicts much lower delta Fe-56 values, between -1.0 parts per thousand to -3.3 parts per thousand predicted for benthic supplies of iron from anoxic marine sediment overlying re-oxygenated bottom waters. This study shows that combining iron with other proxies for environmental change, particularly submarine volcanism, can distinguish hydrothermally supplied iron from dust, rivers, and shelf sediment supplies of iron despite iron's reputation for complicated cycling.

The spatio-temporal analysis of rifts and passive margin evolution is often done based on regional case studies, using non-standardized terminology and classification models to characterize crustal boundaries and basin infill. As example, the use of “continent-ocean boundary” to delineate crustal types or “syn-rift” as basin infill characterization has proven to be no longer adequate, given our evolved understanding of passive margins. In general, such local approaches do not lean themselves to aggregate data for global and large-scale comparative analysis and often struggle to reconcile the spatially varying magmatic/weakly magmatic margin architecture in a rift system context. They also do not allow efficient deployment of spatio-temporal data analytic models due to a lack of standardized data classification. To overcome these limitations, we have designed a novel “data science-ready” data model for crustal architecture that is based on commonly accepted terminologies, can be used independent of input data heterogeneity and can be deployed globally across the whole spectrum of margin types and complex 3D margin geometries/microplate settings. We classify two key crustal boundaries, the oceanward limit of continental crust ("OLCC") and the landward limit of oceanic crust ("LaLOC"), along with several key crustal interfaces, such as the top basement and base crust which are further subdivided into sub-categories. This approach allows us to easily generate standardized data products on rift system scale, which quantitatively describe key parameters relevant to understand lithosphere extension dynamics, such as volumes, ratio, and distribution of continental and magmatic crust, crustal stretching factors, and amount of crustal embrittlement. Coupled with plate kinematic models, these data products allow to build reproducible, extensible, and quantitative models of rift and margin evolution through time and highlight the dynamics of stretching, localization of deformation, the basin infill response, and spatio-temporally varying patterns and types of magmatism. Applying this data model, we have characterized the crustal architecture of the conjugate South Atlantic passive margins, interpreting more than 100k line-kilometers of 2D and 3D seismic reflection data. Our findings highlight substantial shortcomings of current plate models to reconcile the crustal type distributions in the southern South Atlantic with a tight pre-breakup fit, the temporal emplacement dynamics of SDRs and plume-related magmatism along the whole South Atlantic rift, as well as the localization of deformation and dynamics of basin infill.

This contribution summarizes a decade of data acquisition, analysis, and interpretation of the Cretaceous Eagle Ford Group in West Texas by Shell, in collaboration with many academic institutions and independent industry consultants to demonstrate the value of integrated high-resolution studies in mudstone analysis, useful for exploration of geo-resources, as well as refinement of greenhouse climate state earth systems evolution, and carbon cycle analyses.

Over the past 70 years, the potential of organic-walled dinoflagellate cysts (or dinocysts) for the dating and correlation of marine deposits from the Upper Triassic onwards has been increasingly realized, and dinocyst biostratigraphy has developed into a valuable stratigraphic method both in academic and industrial applications. Its utility is traditionally considered to be greatest in shelfal settings, but dinocyst biostratigraphy has also been successfully applied to deep-ocean sedimentary successions. As such, dinocystderived age information is complementary to that of other microfossil groups with typically more offshore distribution centers such as planktonic foraminifera, calcareous nannofossils, diatoms, and radiolaria. Due to the limited preservation potential of calcareous and siliceous microfossils in high-latitude settings, dinocysts are particularly important for age determinations in polar to sub-polar regions. The versatility of dinocyst signals is further enhanced in microscope slide preparations containing these microfossils because they typically also include terrestrial palynomorphs such as pollen and spores, yielding direct land-sea correlations. Regardless of its impressive potential, dinocyst biostratigraphy comes with specific challenges. The present article aims to provide a critical and comprehensive review of dinocyst biostratigraphy. It first discusses the principles of dinocyst morphology and taxonomy, as well as current concepts in dinoflagellate (cyst) paleo-ecology, because accurate identification and an understanding of environmental tolerances are indispensable for successful dinocyst-based biostratigraphic analysis. It then considers the suitability of dinocysts as bi-ostratigraphic markers in terms of morphological distinctiveness and abundances, taxonomic diversity, strati-graphic ranges, and (paleo-) geographic distributions. Finally, it identifies perspectives and potential for fu-ture work.

Carbon isotope excursions (CIEs) serve as key geological markers that coincide with global climate change, extinctions, Oceanic Anoxic Events, and hydrocarbon source rocks. Accurate delineation of CIEs is essential for global-scale correlations, calculation of their duration and generation of Earth System process models. However, defining the initiation and termination boundaries of CIEs remains subjective, resulting in a wide variety of boundaries in published literature. In this study, various statistical approaches for delineating carbon isotope excursions are reviewed and quantitatively assessed. By evaluating these approaches, the aim is to enhance precision in determining the beginning and end of CIEs, thereby enabling accurate calculation of durations and identification of potential lead-lag relationships with causal mechanisms. Additionally, an integrated workflow methodology is proposed that combines the selected statistical techniques to establish a new standard for CIE delineation. The significance of this research extends beyond the field of CIEs. The proposed approaches and workflow methodology have the potential to be applied in other disciplines for correlating trends and detecting shifts in various datasets, such as climatological, petrophysical, geological, and geochemical data, across different scales.

Abstract Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.

Lake hydrological change and its driving mechanisms in the Eocene warmhouse climate are important to evaluating environmental and ecological changes induced by global warming. Our limited understanding of lake hydrological changes during the Eocene is in part due to the scarcity of well-dated and continuous terrestrial records. Here we refine the middle-late Eocene cyclostratigraphy and decipher high-resolution lake hydrology changes using sedimentary noise modeling and proxy data at four terrestrial basins (Dongying Depression, Nanxiang Basin, Jianghan Basin, and Fushun Basin) in mid-latitudes of East Asia. Our new astrochronology provides a robust timescale for the period of 48.5-38.5 Ma, and our tuned magnetostratigraphy is at least comparable with other timescales between Chrons C18n.1r and C20n. The new astrochronology reveals synchronous lake-level changes in the four basins in East Asia following 1.2 Myr obliquity and 2.4 Myr eccentricity cycles, indicating astronomical forcing on lake-level changes. The 2.4 Myr cycles of lake-levels are generally in phase with 2.4 Myr cycles of global sea-level changes, suggesting that East Asian lake hydrology was modulated by global sea-level variations in the Eocene warmhouse. Therefore, global sea-level variations may be an important driver of East Asia hydroclimate and freshwater resources.

Early Cretaceous rift basins of the incipient South Atlantic have been the focus of intense hydrocarbon exploration and production activities and host some large oil accumulations in sections predating an interval of major salt deposition, particularly in the central segment of the South Atlantic. Understanding the timing (and associated uncertainties) of source rock and reservoir deposition and their relationship with rift evolution is critical for successful exploration. However, there are still many unresolved issues and data gaps regarding the precise age and duration of salt deposition. Better chronological constraints are particularly needed to determine the timing of deposition of Pre-Salt reservoirs and the primary evaporites, as well as the secondary phase of halokinensis that resulted in variable reservoir sealing potential. To help address this gap, stable carbon isotope (delta C-13) records from bulk organic matter and insoluble kerogen were generated for the Early Cretaceous salt and Pre-Salt intervals from two exploration wells offshore of Gabon. The bulk organic delta C-13 stratigraphies for the two wells were then integrated with palynological and ostracod biostratigraphy and placed within a sequence stratigraphic and regional tectonic framework, providing new constraints on the timing of rift lake evolution and salt deposition. The good correlation between the offshore Gabon delta C-13 record with other published sections calibrated to the current Geologic Time Scale as well as other regional sections from NE Brazil, supports the reliability of our new Gabon delta C-13 record. Several delta C-13 excursions are identified in the Pre-Salt sequence and are correlated with the Valanginian Weissert event and Early Aptian delta C-13 event(s). Salt deposition on the Gabon margin is interpreted to have occurred during an interval straddling the Early-Late Aptian boundary (similar to 118.4-116.8 Ma). These findings are comparable with other published estimates for salt deposition from northeast Brazil but differ from published estimates from the Campos-Santos basins; the latter are critically discussed. This study provides an important stratigraphic dataset for offshore Gabon and contributes to the ongoing debate regarding the timing of rifting and salt deposition in the Early Cretaceous of the South Atlantic passive margin system.

Chromium is a redox sensitive element that exhibits a large range of isotopic compositions in Earth's surface environments because of Cr(VI)-Cr(III) transformations. This property of Cr has been exploited as a tracer of Earth's oxygenation history using marine sediments. However, paleoredox applications using Cr are difficult to implement due to its complicated cycling, which creates spatial variability in seawater δ53Cr values. Applications are further hindered by the potential for variability in the major inputs of Cr, such as submarine volcanism, to mask redox processes. Two previous reports of negative excursions in sedimentary δ53Cr values during the middle Cretaceous Ocean Anoxic Event 2 (OAE 2) demonstrate these complications. Observed negative shifts in marine sediments conflict with the positive shifts expected in response to the increased drawdown of isotopically light Cr(III) prompted by the expansion of anoxic depositional sinks. In this study, a marine carbonate succession cored from the Eagle Ford Formation in Texas, USA, in the southern part of the Western Interior Seaway, depicts the negative 1.5‰ δ53Cr excursion occurring in two steps, with the second step reaching peak minimum values indistinguishable from isotopically unfractionated igneous sources. In contrast to published δ53Cr records, each step stratigraphically matches proxy evidence for increased eruption frequency and/or intensity of volcanic activity using combined 187Os/188Os, 87Sr/86Sr and Os concentration proxies previously measured from the same core, supporting higher inputs of volcanically sourced Cr to the oceans as the driver for the negative Cr isotope excursion.

Background of the studied interval, time series analysis of the grayscale of the marls, micropaleontology, and supplemental figures and tables.

Data tables and additional text discussion and methodology.

A stable carbon isotope (delta C-13) profile of the Early Cretaceous to Paleogene (Berriasian - Danian) was generated from ditch-cuttings material recovered from well 30/2a-7, Central North Sea. The profile of delta C-13 values was integrated with calcareous nannofossil biostratigraphy and sequence stratigraphy from the Cromer Knoll Group to provide an integrated stratigraphic framework for the Early Cretaceous. Although, nannofossil data was not collected from most of the overlying Chalk Group, the associated delta C-13 profile was sufficiently resolved to correlate with other similar delta C-13 records from both the Boreal and Tethyan Realms. The delta C-13 profiles and nannofossil data from well 30/2a-7 were stacked with the nearby Shearwater A9 well data to create a composite section that provides a long-term near continuous record of the Early Cretaceous to Paleogene from the basinal deposits of the Central North Sea. Sequence stratigraphic analyses was conducted to provide an integrated bio-chemo-sequence stratigraphic framework for regional correlation. Several major globally recognized delta C-13 events that are recognized in the wells are seismically resolvable and can be correlated regionally across the Central North Sea, providing a chronostratigraphic framework for constraining hydrocarbon play elements for both exploration, production and carbon capture and storage projects.

The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2).Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear.In this study, a reconstruction of mid-Cenomanian seawater 187 Os/ 188 Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE.The absence of a prolonged unradiogenic Os isotope excursion (low 187 Os/ 188 Os) at the onset of the MCE interval argues against LIP involvement in the event's initiation.Rather, more radiogenic 187 Os/ 188 Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering.The combination of decreasing 187 Os/ 188 Os from the middle of the MCE onward, coincident with a 40 Ar/ 39 Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE.These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.

This chapter summarizes geochronologic and other data for major Phanerozoic Large Igneous Provinces (LIPs), Oceanic Anoxic Events (OAEs) and organic-rich petroleum source rocks. It also evaluates the models that support or refute genetic links between the three groups. The evidence appears to favor genetic links between the three groups, however, additional high precision age and geochemical data are needed to validate several events. Furthermore, the chapter provides insights into the importance of LIPs in hydrocarbon exploration.

Ocean anoxic events (OAE) are characterized by increased organic content of marine sediment on a global scale with accompanying positive excursions in sedimentary organic and inorganic δ 13C values. To sustain the increased C exports and burial required to explain the C isotope excursion, increased supplies of nutrients to the oceans are often invoked during ocean anoxic events. The potential source of nutrients in these events is investigated in this study for Oceanic Anoxic Event 2, which spans the Cenomanian-Turonian boundary. Massive eruptions of one or more Large Igneous Provinces (LIPs) are the proposed trigger for OAE 2. The global warming associated with volcanogenic loading of carbon dioxide to the atmosphere has been associated with increased continental weathering rates during OAE 2, and by extension, enhanced nutrient supplies to the oceans. Seawater interactions with hot basalts at LIP eruption sites can further deliver ferrous iron and other reduced metals to seawater that can stimulate increased productivity in surface waters and increased oxygen demand in deep waters. The relative importance of continental and submarine weathering drivers of expanding ocean anoxia during OAE 2 are difficult to disentangle. In this paper, a box model of the marine Sr cycle is used to constrain the timing and relative magnitudes of changes in the continental weathering and hydrothermal Sr fluxes to the oceans during OAE 2 using a new high-resolution record of seawater 87Sr/86Sr ratios preserved in a marl-limestone succession from the Iona-1 core collected from the Eagle Ford Formation in Texas. The results show that seawater 87Sr/86Sr ratios change synchronously with Os isotope evidence for the onset of massive LIP volcanism 60 kyr before the positive C isotope excursion that traditionally marks the onset of OAE 2. The higher temporal resolution of the seawater Sr isotope record presented in this study warrants a detailed quantitative analysis of the changes in continental weathering and hydrothermal Sr inputs to the oceans during OAE 2. Using an ocean Sr box model, it is found that increasing the continental weathering Sr flux by ∼1.8-times captures the change in seawater 87Sr/86Sr recorded in the Iona-1 core. The increase in the continental weathering flux is smaller than the threefold increase estimated by studies of seawater Ca isotope changes during OAE 2, suggesting that hydrothermal forcing may have played a larger role in the development of ocean anoxic events than previously considered

A highly resolved record of stable carbon isotope values (δ13C) of the Late Cretaceous to Palaeogene (Cenomanian – Danian) was generated from ditch-cuttings material recovered from the Shearwater A9 hydrocarbon production well, Shearwater Field, Central North Sea. The profile of δ13C values was integrated with calcareous nannofossil and foraminifera biostratigraphy to provide an integrated stratigraphy for the Late Cretaceous Chalk Group. Detailed correlation between Shearwater A9 carbon isotope stratigraphy and associated biostratigraphic events with other similar records from both the Boreal and Tethyan Realms, including several proposed and/or ratified Global Boundary Stratotype Sections and Points had enabled the identification of major Stage and sub-Stage boundaries. This study provides a long-term and near-continuous stratigraphic record of the Late Cretaceous and earliest Palaeogene from more basinal facies of the Central North Sea. The record is punctuated with several short duration hiatal intervals, and a longer hiatus is identified whereby most of the Cenomanian is missing at this location.

Organic palynological content in rocks, which commonly occurs in aquatic and terrestrial sediments, is essential for sediment dating, palaeoenvironmental reconstructions and determination of hydrocarbon potential. Unfortunately, the palynological signal may be blurred or even completely destroyed by intra- and post-depositional diagenetic processes. Fossil shells of foraminifera constitute another tool for dating and/or palaeoenvironmental reconstructions and, unlike palynological matter, they are not affected by post-depositional oxidation or thermal alteration. Herein, we present a preliminary palynological study of Upper Cretaceous formations in northern and central Guatemala and we compare it to foraminiferal data. Rocks that are often full of foraminifera, visible without magnification, yielded monotonous palynofacies dominated by black-opaque equidimensional phytoclasts. The palynological signal may potentially be explained by: (i). unfavourable aquatic conditions and habitat; (ii). a high-sedimentation rate combined with organic matter dilution; (iii). organic matter oxidation related to subaerial exposure; (iv). post-depositional weathering and oxidation; (v). thermal conversion of organic matter during burial and/or interaction with volcanic intrusions. Due to the complicated tectonic history of the Yucatán region, all of these factors need more extensive discussion.

Abstract Intervals of extreme warmth are predicted to drive a decrease in the oxygen content of the oceans. This prediction has been tested for the acme of short (<1 million years) episodes of significant marine anoxia in the Phanerozoic geological record known as Oceanic Anoxic Events (OAEs). However, there is a paucity of data spanning prolonged multimillion‐year intervals of geological time before and after OAEs. We present a Mo‐isotope record from limestones and marlstones of the Eagle Ford Group, South Texas, which was deposited in the southern Cretaceous Western Interior Seaway of North America during a 6‐million‐year period encompassing OAE 2 (Late Cenomanian–early Turonian: ∼94 Ma). Mo‐isotope compositions from deposits that formed in euxinic (sulfidic) conditions before OAE 2 allow the paleo‐seawater composition to be constrained to 1.1%–1.9%. This range of values overlaps previous estimates of up to ∼1.5% for the peak of OAE 2 determined from similarly sulfidic sediments deposited in the restricted proto‐North Atlantic Ocean. Mo‐isotopes thus varied by less than a few tenths of per mil across one of the most extreme intervals of global deoxygenation in the Late Phanerozoic. Rather than a limited change in oceanic deoxygenation, we suggest that the new data reflect changes to global iron cycling linked to basalt‐seawater interaction, terrestrial weathering and expanded partially oxygenated shallow shelf‐seas that played a key role in the burial of isotopically light molybdenum, thus acting as a counterbalance to its removal into sulfidic sediments.

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long‐term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX 86 . Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low‐latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

Sedimentary couplets that are generated by astronomical forcing are common in pelagic and hemipelagic depositional settings. This study disentangles the time scales (sedimentation rates) of the two lithofacies that contribute to such astronomically-forced couplets, by introducing the Alpha method. This new method can be applied to precession or obliquity-forced sedimentary records, and compares the frequency modulation of an astronomical cycle model with the thicknesses of the couplets. The method is demonstrated on a synthetic model of a precession index-forced succession of limestone-marlstone couplets. Finally, the methods is applied to two case studies: for the Middle Cenomanian Eagle Ford Formation (Iona-1 core, Texas), sedimentation rates are estimated as 0.85-1.02 cm/kyr for the marlstone and 4.70-5.65 cm/kyr for the limestone; for the Middle Eocene IODP Expedition 342 Site U1408, sedimentation rates are 1.70-1.84 cm/kyr for the white nannofossil ooze and 2.54-2.75 cm/kyr for the greenish nannofossil-rich clay. More generally, studies of paleoclimate and geochemical evolution at the sub-Milankovitch scale can benefit from this method.