Carbon Isotope Event Research Articles

Oceanic organic carbon as a possible first-order control on the carbon cycle during the Bathonian–Callovian

Abstract Oceans are the largest, readily exchangeable, superficial carbon reservoir; a current challenge in investigating past and present environments and predict future evolution relates to the role of oceanic carbon in regulating Earths' carbon cycle and climate. At least one paired δ13Ccarb-TOC decoupling event is noted in the Late Bathonian–Early Callovian. Provokingly, we suggest that this decoupling event and other carbon isotopic events in the Bathonian–Callovian resulted from the addition and removal of carbon from the oceanic organic carbon (OOC) reservoir, likely dominated by dissolved and fine particulate oceanic organic carbon. The decoupling event is characterised by a mainly invariant δ13CTOC record and increasingly more positive δ13Ccarb values. The δ13Ccarb-TOC decoupling is tentatively explained by the expansion of the OOC reservoir, which increased the residence time of carbon in the oceans and buffered (slow equilibrium) δ13COOC (approximated by δ13CTOC) to changes in δ13C of oceanic inorganic carbon, comprised mainly of dissolved inorganic carbon (approximated by δ13Ccarb). Reconversion of OOC to CO2 may have resulted in negative δ13C excursions and increased atmospheric pCO2, whereas the change from accumulation of OOC to export of organic carbon to sediments may have resulted in positive δ13C excursions and widespread accumulation of organic matter. It is speculated that other small-scale (~ 1‰) δ13C excursions in the Mesozoic record may have resulted from similar episodes of OOC accumulation and oxidation. Our study calls attention to the potential of the OOC reservoir to act as a critical driver for planetary-scale changes over short geological time intervals.

Carbon-isotope events during the Pliensbachian (Lower Jurassic) on the African and European margins of the NW Tethyan Realm

Early Jurassic palaeoenvironments and palaeoclimates, based on chemostratigraphy, have been extensively studied for the northern Tethyan margin. For the first time, high-resolution chemostratigraphy for the entire Pliensbachian is proposed for the African Tethyan margin (Morocco), and compared with new sections from the European Tethyan margin (France). Precise ammonite determinations, completed by calcareous nannofossil distribution, provide an accurate biostratigraphic framework from the Upper Sinemurian to the Upper Pliensbachian. Bulk inorganic carbon (δ13Ccarb) and organic carbon (δ13Corg) isotope signals are used to characterise and compare carbon-cycle trends in the Central High Atlas Basin (Amellago-Ikis section, Morocco), the Paris Basin (Montcornet borehole, France), and the Subalpine Basin (Serre-Poncon section, France). Comparison of this new dataset with previously published geochemical data from European basins confirms the existence of five distinct carbon-isotope events, synchronous at the scale of the NW Tethyan Realm: (1) a clear –2‰ negative excursion of δ13Ccarb and δ13Corg, corresponding to the Sinemurian–Pliensbachian Boundary Event (SPBE), probably associated with a massive release of light carbon by volcanism and hydrothermalism during the breakup of Pangea; (2) a positive excursion (+1 to +1.5‰) in the Valdani and Luridum subzones (Ibex Zone), reflecting increased organic matter storage under warm climate conditions; (3) a broadly negative event from the Davoei Zone to the lower part of the Margaritatus Zone, associated with major oceanographic reorganisation in a transgressive context, and possible enhanced hydrothermalism related to the opening of the Hispanic corridor; (4) a positive carbon excursion (+2‰) during the Subnodosus and Gibbosus subzones (Margaritatus Zone), corresponding to the Late Pliensbachian Event (LPE), associated with organic matter storage; (5) an end-Margaritatus–Spinatum negative excursion, associated with sea-level fall, probably driven by glacio-eustasy. This new high-resolution carbon-isotope dataset highlights the synchroneity of carbon-cycle trends throughout the NW Tethyan Realm. Several major isotopic events, prior to those of the Toarcian, must therefore have occurred at a supra-regional to global scale during the Pliensbachian, involving significant internal and external geodynamic mechanisms.

Mercury chemostratigraphy across the Cambrian Series 2 – Series 3 boundary: evidence for increased volcanic activity coincident with extinction?

Flood basalt volcanism represented by the Kalkarindji Province (Australia) is temporally associated with a trilobite mass extinction at the Cambrian Series 2 – Series 3 boundary, providing one of the oldest potential links between volcanism and biotic crisis in the Phanerozoic. However, the relative timing of flood basalt volcanism (Kalkarindji Province, Australia) and the trilobite extinctions, first recorded in North America, is not known. Mercury (Hg) enrichment in the sedimentary record provides a potential proxy for volcanism which may facilitate improved chronologies of eruption and extinction. Here we report mercury records for three sections from mid-shelf strata of the Great Basin (western USA) that straddle the Series 2 – Series 3 boundary. One section (Oak Springs Summit, NV) features a Hg enrichment at the start of the extinction interval, but mercury anomalies are also present at lower levels. These older anomalies may record either earlier phases of Kalkarindji volcanism, eruptions in other locations, or may be the result of sedimentary and/or diagenetic processes affecting the Hg record. In the Carrara Formation at Emigrant Pass, CA, the precise extinction horizon is not well defined, but a carbon isotope anomaly (the Redlichiid-Olenellid Extinction Carbon isotope Event; ROECE) provides a stratigraphic tie point to the Oak Springs Summit section. At Emigrant Pass, Hg enrichments precede the ROECE interval and are absent in the inferred extinction zone. The Pioche Formation at Ruin Wash, NV, lacks Hg enrichment at the extinction horizon but contains older enrichments. The inconsistent Hg records between the three sections demonstrate that factors controlling Hg accumulation and preservation in marine sedimentary environments are not yet fully understood. The effects of redox fluctuations may complicate one-to-one association of sedimentary Hg enrichments and massive volcanism at the Cambrian Series 2 – Series 3 boundary and elsewhere in the geologic record.

The Santonian – Campanian boundary and the end of the Long Cretaceous Normal Polarity-Chron: Isotope and plankton stratigraphy of a pelagic reference section in the NW Tethys (Austria)

The base of the Campanian still lacks a designated primary marker and a defined GSSP (Global Boundary Stratotype Section and Point). We present a Santonian–Campanian boundary section from the Postalm in the Northern Calcareous Alps of Austria as a possible reference section for the northwestern Tethys. Including nearby complementary Gosau Group sections, the stratigraphy for this time interval is based on palaeomagnetic and stable isotope data, planktonic foraminifera and calcareous nannoplankton bio-stratigraphy, and strontium isotope stratigraphy, together with published ammonite, crinoid and inoceramid data. The Postalm section shows a deepening trend from upper Santonian conglomerates and grey shelf marls to pelagic bathyal red marly limestones of mainly Campanian age. Palaeomagnetic data allow identifying the top of the Long Cretaceous Normal Polarity-Chron C34n and the following reversal in the lower part of the red marly limestones. A 1 m-thick interval of high magnetic susceptibility is present at the end of C34n. Two of the main suggested biomarkers to pinpoint the Santonian–Campanian boundary, i. e. the last occurrence of the planktonic foraminifer Dicarinella asymetrica and the first occurrence of the nannofossil Broinsonia parca parca, occur in close proximity above the reversal, which is suggested herein as the main marker event for the base of the Campanian. Strontium isotope stratigraphy indicates a value of 0.707534 (mean of four measurements at the boundary interval) for the base of the Campanian in the Postalm section. Both carbon and oxygen isotope values show a negative excursion just below the boundary. The positive Santonian–Campanian carbon isotope event starts probably just below the reversal but seems to be diagenetically distorted. This interval is considered to correspond to a short sea-level high in the late Santonian followed by a distinct lowstand at the Santonian–Campanian boundary.

Environmental change during the Triassic–Jurassic boundary interval of an equatorial carbonate platform: Sedimentology and chemostratigraphy of the Ghalilah Formation, United Arab Emirates

The sedimentology and chemostratigraphy (δ13Ccarb, δ13Corg, Sr concentrations) of the Triassic-Jurassic (Tr-J) boundary interval has been investigated in detail in sections of the Ghalilah Formation exposed in Wadi Ghalilah, Wadi Milaha and Wadi Naqab, northeastern United Arab Emirates. The sequence of events recorded across the Tr-J boundary interval in Ras Al Khaimah reflects significant environmental change that can ultimately be related to CAMP volcanism. Uppermost Triassic limestones of the Sumra Member rich in coral, calcareous sponges and large-size bivalves are interbedded with siliciclastic mudstones and deposited in an open lagoonal environment. These are abruptly followed by oolites with intercalated calcareous mudstones of the Sakhra Member that are devoid of macrofossil. Thrombolitic microbialites that occur in the lowermost Sakhra Member are interpreted to reflect the demise of hypercalcifying marine biota during the Tr-J boundary interval. The oolites of the Sakhra Member are capped by a subaerial exposure surface, followed by peritidal deposits of the Shuba Member. The available, sparse biostratigraphic data of the Ghalilah Formation are critically discussed and support a position of the Tr-J boundary at the base of the Sakhra Member. A negative excursion in δ13Corg occurs in the upper Sumra Member and possibly correlates with the Late Triassic Spelae carbon-isotope event. The δ13Ccarb and δ13Corg values increase across the boundary interval, and an extended positive excursion in δ13Ccarb occurs in the oolites of the Sakhra Member. Sr concentrations increase in the bioclastic limestones of the uppermost Sumra Member and peak in the oolites of the upper Sakhra Member. High Sr concentrations also occur at correlative stratigraphical levels in the Lombardy Basin (Italy), and are interpreted as an Early Hettangian seawater signal, reflecting the global-scale reduction of biological aragonite precipitation and an increased continental weathering flux.

The Lomagundi-Jatuli carbon isotopic event recorded in the marble of the Tandilia System basement, Río de la Plata Craton, Argentina

The “Lomagundi-Jatuli event” corresponds to the most important δ13C positive anomaly (≥5‰) globally reported in Palaeoproterozoic marine carbonates (between ∼2.30 and 2.06 Ga). In the Tandilia System (Argentina), Río de la Plata Craton, this event was recorded in the basement marble of the San Miguel area. The calcite-diopside marble, hosted by biotite gneiss and intruded by 2.12 Ga garnet-leucogranite, was metamorphosed in amphibolite facies during the Transamazonian Cycle.PAAS-normalised rare-earth elements (REE) and Y for the carbonate rocks are HREE-enriched and display positive Eu and Y anomalies, typical of primary precipitates from a mixed hydrothermal-marine environment carbonate. Additionally, a truly negative Ce anomaly for all the samples indicates that the depositional environment was oxidising.Positive δ13C values ranging from +5.90 to +4.30‰ (V-PDB), and δ18O from +17.45 to +13.84‰ (V-SMOW) were determined in this marble, both gradually decreasing towards the contact with the leucogranites. These values indicate that devolatilization reactions took place during the crystallisation of a wollastonite-vesuvianite-grossular-diopside skarn generated by the leucogranite intrusions into the marble. δ18O values obtained from diopside and calcite crystals, in the marble sectors furthest from the contacts with leucogranite, allowed a 663–623 °C formation temperature to be calculated, considering oxygen in a calcite-diopside geothermometric pair. These temperatures are consistent with the metamorphic degree (amphibolite facies) reached in this portion of the basement.Although the San Miguel marble shows petrographic and mineralogical evidence of regional and contact metamorphism, important geochemical and isotopic characteristics, together with its estimated Palaeoproterozoic age, indicate that the marble protolith was a marine carbonate deposited during the “Lomagundi-Jatuli event”.

Reply to the discussion on ‘Orbital calibration of the late Campanian carbon isotope event in the North Sea’, Journal of the Geological Society, London , 173, 504–517

Smith & Bailey (2017 a ) have criticized the methods applied for time series analysis in our study of a late Campanian chalk core in the North Sea (Perdiou et al. 2016). These critics rely essentially on two points: (1) the resolution spacing that can be applied to our gamma-ray data; (2) the use of the autoregressive order 1 (‘AR1’) noise model, which allows calculation of significance thresholds.

Vase-shaped microfossil biostratigraphy with new data from Tasmania, Svalbard, Greenland, Sweden and the Yukon

The recent revision of the Cryogenian lower boundary from 850 Ma to 720 Ma has nearly doubled the duration of the Tonian Period to 280 Myrs, an interval longer than the Mesozoic and Cenozoic eras combined. Although subdivision of the Tonian will likely emphasize chemostratigraphy, the relatively rich fossil record of this time period may also be useful. In particular, vase-shaped microfossils (VSMs) occur globally and often abundantly in a variety of lithofacies, exhibit a variety of preservational modes, and are stratigraphically constrained by the two major carbon isotopic events of the Tonian Period, the Bitter Springs and Islay anomalies. VSMs have been used as informal, grade-level indicators of late Tonian age (e.g. ca. 800–700 Ma) for several decades but here, based on new data from an assemblage in northwestern Tasmania and restudy of samples from Svalbard, Greenland, Sweden and the Yukon, we report a species-level faunal assemblage indicative of the interval ca. 789 to 729 Ma. Species-level VSM biostratigraphy presents an opportunity for potential biostratigraphic subdivision of the lengthy Tonian Period and is particularly useful in successions where chemostratigraphy and radiometric age constraints are absent.Eight taxa are described from shales and early diagenetic cherts of the Black River Dolomite, Togari Group, Tasmania, including seven previously named species (Bombycion micron, Bonniea dacruchares, Bonniea pytinaia, Cycliocyrillium simplex, Cycliocyrillium torquata, Melanocyrillium hexodiadema and Palaeoarcella athanata), and one newly described genus and species Pakupaku kabin n. gen et n. sp. Study of additional units resulted in new recognition of B. pytinaia, C. simplex and C. torquata in the Draken Formation, Spitsbergen, Svalbard, B. dacruchares and P. athanata in the Ryssö Formation, Nordaustlandet, Svalbard, B. dacruchares, B. pytinaia, C. torquata and P. athanata in Bed 18 of the Eleonore Bay Group, Greenland, and B. dacruchares, B. pytinaia and Bombycion micron in the Visingsö Group, Sweden.

Sequence stratigraphy, chemostratigraphy and facies analysis of Cambrian Series 2 – Series 3 boundary strata in northwestern Scotland

AbstractGlobally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary andOlenellusbiostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to record regressive–transgressive events that produced amalgamated sequence boundaries and ravinement/flooding surfaces overlain by conglomerates of reworked intraclasts. The ROECE has been linked with redlichiid and olenellid trilobite extinctions, but in NW Scotland,Olenellusis found after the negative peak of the carbon isotope excursion but before sequence boundary formation.

Stratigraphic and geochemical expression of Barremian–Aptian global climate change in Arctic Svalbard

Significant changes in global climate and carbon cycling occurred during the Early Cretaceous. This study examines the expression of such climatic events in high-latitude Svalbard together with the stratigraphic utility of carbon-isotope stratigraphies. Isotopic analysis of fossil wood fragments (from the Rurikfjellet, Helvetiafjellet, and Carolinefjellet formations, Festningen, Spitsbergen) record a distinctive pattern including a negative isotope excursion preceding a positive event, correlatable with the global early Aptian isotope event. Our carbon-isotope profile improves the stratigraphic correlation and relative dating of the succession. We show that the upper part of the Helvetiafjellet Formation was deposited during the early Aptian, and not the late Barremian, as previously thought. Furthermore, we estimate an age for the abrupt contact of the Rurikfjellet Formation with the overlying Helvetiafjellet Formation (associated with a pulse of igneous activity) to be ca. 129 Ma or ca. 124 Ma, depending on which age model for the Early Cretaceous is used. The well-known dinosaur footprints of the Helvetiafjellet Formation at Festningen are constrained to the middle Barremian and, coupled with floral data, support a warm late Barremian prior to the Aptian carbon-isotope event. The appearance of glendonites at 655 m in the Carolinefjellet Formation is consistent with global cooling in the late Aptian–early Albian.

Light carbon isotope events of foraminifera attributed to methane release from gas hydrates on the continental slope, northeastern South China Sea

In 2013, the China Geological Survey and Guangzhou Marine Geological Survey conducted the second Chinese gas hydrate expedition in the northern South China Sea (SCS) and successfully obtained visible gas hydrate samples. Five of the thirteen drilling sites were cored for further research. In this work, Site GMGS2-08 is selected for the stable isotopic analysis of foraminifera present in the boreholes in order to reveal the carbon isotopic characteristics of the foraminifera and their response to methane release in the gas hydrate geological system. Our results show that the methane content at Site GMGS2-08 is extremely high, with headspace methane concentrations up to 39300 μmol L−1. The hydrocarbon δ13C values, ranging from −69.4‰ to −72.3‰ PDB, distinctly indicate biogenic generation. Based on the δD analytical results (−183‰ to −185‰ SMOW), headspace methane is further discriminated to be microbial gas, derived from CO2 reduction. By isotopic measurement, five light δ13C events are found in the boreholes from Site GMGS2-08, with foraminiferal δ13C values being apparently lower than the normal variation range found in the glacial-interglacial cycles of the SCS. The δ13C values of benthic Uvigerina peregrina are extremely depleted (as low as −15.85‰ PDB), while those of planktonic Globigerinoides ruber reach −5.68‰ PDB. Scanning electron micrograph (SEM) studies show that foraminiferal tests have experienced post-depositional alteration, infilled with authigenic carbonate, and the diagenetic mineralization is unlikely to be related to the burial depths. The correlation calculation suggests that the anaerobic oxidation of organic matter has only weak influences on the δ13C composition of benthic foraminifera. This means that the anomalous δ13C depletions are predominantly attributed to the overprinting of secondary carbonates derived from the anaerobic oxidation of methane (AOM). Furthermore, the negative δ13C anomalies, coupled with the positive δ18O anomalies observed at Site GMGS2-08, are most likely the critical pieces of evidence for gas hydrate dissociation in the geological history of the study area.

Orbital calibration of the late Campanian carbon isotope event in the North Sea

A new record of carbon isotopes, nannofossil biostratigraphy, gamma-ray and Fe content variations is presented for the upper Campanian of the Adda-3 core, Danish Central Graben, North Sea. The studied interval provides a revision of previously assigned late Coniacian to early Santonian ages. New biostratigraphic data indicate a late Campanian age for the 60 m thick studied interval. The Late Campanian Event (LCE) is well recorded by a 1.5‰ negative excursion in the bulk δ 13 C, along with two stepwise pre-excursion negative shifts (defining the pre-LCE). The amplitude of the LCE appears higher in the North Sea than in other areas as seen from the correlation to Germany, the UK and France. This correlation allows identification of a new 0.4‰ negative excursion (defined as the conica event). Fe and gamma-ray variations are used to calibrate the record with cyclostratigraphy. Fourteen 405 kyr cycles identified in the upper Campanian of Adda-3 can be correlated to North Germany. The compilation of previous results from North Germany and correlation to Adda-3 shows that the Boreal upper Campanian spans a total of 17 cycles each of 405 kyr; that is, 6.885 myr. The duration of the LCE is estimated to be c . 1 myr at Adda-3 and in North Germany. Supplementary materials: Calibration of the HH-XRF data is available at https://doi.org/10.6084/m9.figshare.c.2134362 .

Astronomically tuned age model for the early Eocene carbon isotope events: A new high-resolution δ13 Cbenthic record of ODP Site 1263 between ~ 49 and ~ 54 Ma

The early Eocene represents a time of major changes in the global carbon cycle and fluctuations in global temperatures on both short-and long-time scales. These perturbations of the ocean-atmosphere system have been linked to orbital forcing and changes in net organic carbon burial, but accurate age models are required to disentangle the various forcing mechanisms and assess causal relationships. Discrepancies between the employed astrochronological and radioisotopic dating techniques prevent the construction of a robust time frame between ~ 49 and ~ 54 Ma. Here we present an astronomically tuned age model for this critical time period based on a new high-resolution benthic δ13C record of ODP Site 1263, SE Atlantic. First, we assess three possible tuning options to the stable long-eccentricity cycle (405-kyr), starting from Eocene Thermal Maximum 2 (ETM2, ~ 54 Ma). Next we compare our record to the existing bulk carbonate δ13C record from the equatorial Atlantic (Demerara Rise, ODP Site 1258) to evaluate our three initial age models and compare them with alternative age models previously established for this site. Finally, we refine our preferred age model by expanding our tuning to the 100-kyr eccentricity cycle of the La2010d solution. This solution appears to accurately reflect the long-and short-term eccentricity-related patterns in our benthic δ13C record of ODP Site 1263 back to at least 52 Ma and possibly to 54 Ma. Our time scale not only aims to provide a new detailed age model for this period, but it may also serve to enhance our understanding of the response of the climate system to orbital forcing during this super greenhouse period as well as trends in its background state.

Intercontinental correlation of organic carbon and carbonate stable isotope records: evidence of climate and sea‐level change during the Turonian (Cretaceous)

AbstractCarbon (δ13Corg, δ13Ccarb) and oxygen (δ18Ocarb) isotope records are presented for an expanded Upper Cretaceous (Turonian–Coniacian) hemipelagic succession cored in the central Bohemian Cretaceous Basin, Czech Republic. Geophysical logs, biostratigraphy and stable carbon isotope chemostratigraphy provide a high‐resolution stratigraphic framework. The δ13Ccarb and δ13Corg profiles are compared, and the time series correlated with published coeval marine and non‐marine isotope records from Europe, North America and Japan. All previously named Turonian carbon isotope events are identified and correlated at high‐resolution between multiple sections, in different facies, basins and continents. The viability of using both carbonate and organic matter carbon isotope chemostratigraphy for improved stratigraphic resolution, for placing stage boundaries, and for intercontinental correlation is demonstrated, but anchoring the time series using biostratigraphic data is essential. An Early to Middle Turonian thermal maximum followed by a synchronous episode of stepped cooling throughout Europe during the Middle to Late Turonian is evidenced by bulk carbonate and brachiopod shell δ18Ocarb data, and regional changes in the distribution and composition of macrofaunal assemblages. The Late Turonian Cool Phase in Europe was coincident with a period of long‐term sea‐level fall, with significant water‐mass reorganization occurring during the mid‐Late Turonian maximum lowstand. Falling Δ13C (δ13Ccarb – δ13Corg) trends coincident with two major cooling pulses, point to pCO2 drawdown accompanying cooling, but the use of paired carbon isotopes as a high‐resolution pCO2 proxy is compromised in the low‐carbonate sediments of the Bohemian Basin study section by diagenetic overprinting of the δ13Ccarb record. Carbon isotope chemostratigraphy is confirmed as a powerful tool for testing and refining intercontinental and marine to terrestrial correlations.

New conodont δ18O records of Silurian climate change: Implications for environmental and biological events

A near-continuous, highly dynamic record of Silurian climate has been determined from conodont δ18O compositions (δ18Ophos), representing stratigraphic sections from four palaeocontinents. Following the late Ordovician–early Silurian glaciation, numerous small-scale climate cycles show an overall warming trend until the mid Llandovery (early-mid Telychian), then gradual cooling through the late Llandovery. Two major, multi-step cooling transitions of similar magnitude and duration (+2‰ within~1.5Myrs from onset to peak) occurred during the late Llandovery–early Wenlock and late Wenlock, the former culminating in a prolonged cool interval (~1Myr). These Wenlock δ18Ophos excursions coincided closely with the Ireviken and Mulde biotic and carbon isotope (δ13C) events. Rapid, large, but short-lived shifts reflect climate instability within the mid Ludlow, prior to and during the Lau bio-event. The prime δ18Ophos records are from Laurentia and Baltica, which show mostly consistent and synchronous cycles, albeit slightly offset for much of the Llandovery and warmer intervals of the Wenlock. These offsets most likely reflect differences in the relative palaeogeographic positions of these continents, and changes in ocean dynamics driven by major shifts in glacial–interglacial climate modes. Many of the positive δ18Ophos maxima correlate with sea level lowstands, as well as graptolite faunal turnover throughout the Silurian. Strong correlations between the large, first-order, positive δ18Ophos shifts, increases in global δ13Ccarb, and the major Silurian bio-events (Ireviken, Mulde, Lau) imply that global climate change played an important role in producing these phenomena.

Correlating carbon and oxygen isotope events in early to middle Miocene shallow marine carbonates in the Mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy.

During the Miocene prominent oxygen isotope events (Mi‐events) reflect major changes in glaciation, while carbonate isotope maxima (CM‐events) reflect changes in organic carbon burial, particularly during the Monterey carbon isotope excursion. However, despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions. The Decontra section on the Maiella Platform (central Apennines, Italy), however, allows to resolve them for the first time in such a setting during the early to middle Miocene. The present study improves the stratigraphic resolution of parts of the Decontra section via orbital tuning of high‐resolution gamma ray (GR) and magnetic susceptibility data to the 405 kyr eccentricity metronome. The tuning allows, within the established biostratigraphic, sequence stratigraphic, and isotope stratigraphic frameworks, a precise correlation of the Decontra section with pelagic records of the Mediterranean region, as well as the global paleoclimatic record and the global sea level curve. Spectral series analyses of GR data further indicate that the 405 kyr orbital cycle is particularly well preserved during the Monterey Event. Since GR is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the Decontra section, it follows the same long‐term orbital pacing as observed in the carbon isotope records. The 405 kyr GR beat is thus correlated with the carbon isotope maxima observed during the Monterey Event. Finally, the Mi‐events can now be recognized in the δ18O record and coincide with plankton‐rich, siliceous, or phosphatic horizons in the lithology of the section.

Carbon isotope chemostratigraphy and conodonts of the Middle–Upper Ordovician succession in the Tungus Basin, Siberian Craton

Stable carbon isotope chemostratigraphy has been applied for correlation of Ordovician marine sedimentary successions of many continents, but not yet for those located on the Siberian Craton. In this study we present the first δ13C data from the Middle and Upper Ordovician successions of the Tungus Basin, the extensive Palaeozoic intracratonic basin on the Palaeocontinent Siberia. Carbon isotope curves from two separate areas of the craton, from the Kulyumbe River and Podkamennaya Tunguska River regions, demonstrate a great similarity. Three global carbon isotope events can be recognized in the Tungus Basin: the Mid-Darriwilian Excursion (MDICE), the Upper Kukruse Low, and the lower rising interval of the Guttenberg Excursion (GICE). These data partly support the previous inter-continental stratigraphic correlations but also suggest that the base of the Upper Ordovician in the Siberian succession lies at a lower level than previously thought. Although the conodont fauna in Siberia differs almost completely from that in Baltoscandia, the distribution of selected Upper Ordovician conodont taxa do not contradict the isotope chemostratographic conclusions.

Geochemistry of C, O, and Sr isotopes in the Neoproterozoic carbonates from the southwestern Patom paleobasin, southern Middle Siberia

Scatter of δ13C (from −11.6 to 8.4‰) and sequence of carbon isotope events in the Vendian carbonates from the southwestern Patom paleobasin (Vitim, Bol’shaya Chuya, and Chaya rivers) are similar to those previously established in the reference northeastern sections. It was found that cap dolomites crowning the glaciogenic diamictites of the Dzhemkukan Formation are characterized by moderately low δ13C (from −7.4 to −5.1‰), while the limestones, marls, and calcareous aleurolites of the Zhuya Group (Nikol’skoe and Chencha formations) correlable with the Shuram-Wonoka event (580–650 Ma) have extremely low δ13C values (up to −11.9‰). Intervals with negative δ13C are separated by positive excursion of δ13C (most part of the Barakun, Valyukhta, and Uluntui formations) with extreme up to 8.4‰. One more positive excursion (δ13C up to 6.1‰) was identified in the dolomitic unit sandwiched between the limestones of the Chencha Formation and the sandstones of the Zherba Formation on the Vitim and Bol’shaya Chuya rivers; in the northeastern sections of the Patom Complex, the positive excursion corresponds to the hiatus, but occurs at similar level (∼550 Ma) in many sections of Oman, China, Namibia, Australia, and other regions. Ultrahigh δ13C (from 11.7 to 15.2‰) values were found in ∼150-m-thick succession of “coaly” carbonates in the Lokatyk Block (Bol’shaya Chuya River), which were presumably erroneously ascribed to the Barakun Formation. These carbonates likely marking the Neoproterozoic anoxic peak are not known among the Vendian (Ediakaran) successions, but have previously been described in the sediments with an inferred age of 720–650 Ma in the Bambui Group (eastern Brazil) and Keele Formation of the Neoproterozoic Windermere Group (northwestern Canada). Scatter of δ18O in the studied carbonates (from 6.3 to 28.5‰) was mainly caused by postsedimentary transformations. General correlation between δ18O and δ13C is absent. Both positive and negative correlations can be observed within limited intervals, indicating that the behavior of O and C isotope systems was not controlled by a common mechanism. The lowest 87Sr/86Sr = 0.7084 in the main chemostratigraphic marker (Chencha Formation) in the extreme west (Chaya River) does not differ much from the 87Sr/86Sr value in the Chencha Formation in the northeastern sections, which confirms the hydrological homogeneity of the Patom paleobasin. The lowest 87Sr/86Sr (0.70815) in the carbonates of the Uluntui Formation of the Chaya section, however, is much lower than in the carbonates from the stratotype area (0.70842) of the Uluntui Formation (Kuznetsov et al., 2013). This casts some doubts on the correlation of these stratigraphic units.

A revised northern European Turonian (Upper Cretaceous) dinoflagellate cyst biostratigraphy: Integrating palynology and carbon isotope events

Organic walled dinoflagellate cyst (dinocyst) assemblage data are presented for a new Turonian regional reference core (Bch-1) drilled at Běchary in the Bohemian Cretaceous Basin, east-central Czech Republic. The detailed stratigraphic framework for the section is summarised based on calcareous nannofossil and macrofossil biostratigraphy, regional e-log correlation, sequence stratigraphy and carbon isotope chemostratigraphy. Dinocyst results obtained for 196 samples from the 405m long core offer the highest resolution (~22kyr) stratigraphically well-constrained data set available to date for the Turonian Stage, 93.9–89.8Ma. A dinocyst biostratigraphic framework is presented based on the evolutionary first and last occurrence, first common occurrence, and acmes of key species. Published dinocyst data from English Turonian Chalk successions in East Sussex, Berkshire, Kent and Norfolk are reviewed within a stratigraphic framework provided by macrofossil records and carbon isotope event (CIE) chemostratigraphy. Critical analysis of existing published Turonian dinocyst zonation schemes shows them to be untenable. Correlation of the English Chalk data to Bch-1 provides a basis for defining a regional dinocyst event stratigraphy with 22 datum levels, and a revised dinocyst zonation scheme constrained within a chemostratigraphic framework of 10 major CIEs. The new zones consist of a Cenomanian Litosphaeridium siphoniphorum Zone, followed by the Cauveridinium membraniphorum Zone spanning the uppermost Cenomanian to Lower Coniacian. This is subdivided into: Senoniasphaera turonica (Lower–mid-Middle Turonian); and Raetiaedinium truncigerum (mid-Middle Turonian–mid-Lower Coniacian) subzones. The Oligosphaeridium pulcherrimum Zone (Senonisphaera rotundata Subzone) characterises the Lower Coniacian. The new stratigraphy offers a basis for improved correlation and dating of Upper Cretaceous successions.

The North China Steptoean Positive Carbon Isotope Event: New insights towards understanding a global phenomenon

Precise biostratigraphic correlation of the base of the Paibian Stage, Cambrian, within and beyond the North China craton has been difficult, mostly because of the strong endemism of the trilobite fauna on the shallow platform facies. The use of the Steptoean Positive Carbon Isotope Excursion (SPICE) in defining the Guzhangian-Paibian stage boundary has become a standard practice. Thus, a chemostratigraphic study of the Huangyangshan section from North China has been carried out. This section in Shandong Province clearly records the SPICE, with the most detailed fossil and carbonate carbon isotope data to date. Compared to other sections in the world, all the published SPICE in North China display both reduced peak and reduced difference (Δ13C) values. These may imply unique conditions on the North China craton during the upper Guzhangian to Paibian stages. This study shows that the SPICE is recorded in relatively condensed sections in North China; thus, ≤ 0.5 m sampling density is suggested here in order to evaluate the presence of the SPICE in North China and condensed sections.