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Oceanic Anoxic Event 2 (OAE2) at the Cenomanian/Turonian Boundary (CTB: 93.9Ma) involved the global deposition of organic carbon-rich sediments, a distinctive positive shift in carbon isotope values, and significant species turnover, including changes in calcareous nannofossil assemblages. While it is thought that volcanismtriggered organic C-rich sediment deposition during OAE2, it is unclear whether enhanced productivity, increased stratification, of some combination of the two increased organicmatter preservation. Calcareous nannofossil assemblages have the potential to qualitatively assess changes in ocean nutrient and temperature conditions to disentangle such ecological dynamics during OAE2. Here we study an expanded section of the Tropic Shale in a drill core in southern Utah near thewestern margin of theWestern Interior Seaway (WIS) to understand how circulation changed during the event and how this may have influenced primary productivity and organic carbon burial. Relative abundance data of well-preserved nannoplankton are complemented with measurements of trace metal, and organic carbon and carbonate concentrations to determine changes in temperature and water column structure, as well as controls on surface water productivity. Detailed statistical analysis helps refine species paleoecologies combined with information from planktic and benthic foraminiferal assemblages and organic biomarkers. Changes in calcareous nannofossil assemblages indicate that near the start of OAE2 the westernWIS surface ocean actually cooled for a short time. Following this, surface waters became warmer and more stratified as a Tethyan water mass invaded the seaway. Assemblages suggest that warmth persisted for much of the OAE2 interval, while stratification waxed and waned. The local seaway cooled near the end of OAE2 as Boreal water masses streamed along the western margin. Variations, including the decrease in the abundance of Biscutum constans and short-lived peaks in the abundance of Eprolithus spp. are super regional or possibly global in extent. There is no correlation between calcareous nannofossil assemblages and trace metal concentrations, suggesting they were unaffected by volcanism-related nutrient inputs. Assemblages support other data that suggest increased stratification influenced organic carbon burial in theWestern Interior Seaway, and possibly elsewhere, during OAE2. [ABSTRACT FROM AUTHOR] more...

This study aims to investigate a marlstone and claystone succession located at the southern end of the Eastern Carpathians, a region where oceanic anoxic event 2 (OAE2) has not been pointed out so far. Toward the upper half of this succession, a 17-cm-thick black shale was identified. The investigated depositional interval lies within the late Cenomanian–early Turonian, encompassing the UC3d up to UC7 nannofossil zones. The δ13C values fluctuated between 2.06‰ and 3.89‰, showing a positive isotope excursion that was assigned to OAE2. The δ13C isotope curve displays the following intervals: pre-excursion, first build-up, trough, second build-up, plateau, and post-excursion. Within the second build-up interval of OAE2, a substantial shift in CaCO3 values, accompanied by high concentrations of total organic carbon and a significant decline in the abundance and diversity of calcareous nannofossil assemblages, was observed. The nannofossil turnover related to OAE2 climax revealed predominance of Watznaueria barnesiae and temporary disappearance from the record of surface-water higher fertility taxa, such as Biscutum constans, Zeugrhabdotus erectus, and Discorhabdus ignotus. Above OAE2, peaks of Eprolithus floralis, followed by increased abundance of Eiffellithus turriseiffelii and Nannoconus spp., were identified. In the lower part of the studied succession (i.e., the upper Cenomanian UC3d nannofossil subzone), during the pre-excursion characterized by low δ13C values and less negative δ18O values, a small group of nannofossils more related to mid- and high-paleolatitudes, such as Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum, is present, always showing a low abundance. more...

Cenomanian/Turonian boundary (upper Sarvak Formation) benthic foraminiferal assemblages were analyzed to reconstruct oxygen level, primary productivity, and water turbulence in the Izeh Zone, Zagros Basin. The interplay between environmental perturbations during the Oceanic Anoxic Event 2 (OAE2) and regional tectonic activities in the Zagros Basin resulted in formation of various benthic foraminiferal assemblages in the study section. The OAE2 interval at the region of study starts with extinction of rotaliporids at the onset of δ13C positive excursion (peak "a"), which is associated with population of infaunal benthic foraminifera (especially Bolivina alata). The following interval at the onset of Whiteinella archaeocretacea Biozone is characterized by the total absence of benthic taxa and dominance of planoheterohelicids (" Heterohelix shift") in the black shale strata, indicating expansion of oxygen minimum zone and unhospitable conditions for both benthic and planktic foraminifera. The upper part of OAE2 interval (including δ13C peaks "b" and "c") coincides with harbinger of Neo-Tethys closure in the Arabian Plate, causing a compressional tectonic regime, and creation of uplifted terrains in the basin. The relative sea level started to locally fall in this succession, which was accompanied by a better ventilation of seafloor, lower TOC contents, and reappearance of benthic foraminifera. Unlabelled Image • The study interval was deposited during OAE2 across the C/T boundary. • OAE2 starts with rotaliporid extinction and population of infaunal benthic foraminifera. • Benthic foraminifera became absent in the black shale strata of W. arch. Zone. • From the middle of OAE2 upward local tectonic inversion controls benthic assemblage. [ABSTRACT FROM AUTHOR] more...

Abstract Mercury (Hg) enrichments in sediments are increasingly used as tracer for distal volcanism in deep‐time investigations. The impact of changes in organic‐matter deposition and preservation on sedimentary Hg sequestration is, however, poorly understood. In this study, we evaluate the potential role of intense weathering and postdepositional organic‐matter degradation on the Hg/TOC proxy in sediments. For this, we investigate weathering profiles in organic‐rich sediments from lowermost Toarcian sediments (T‐OAE; Lafarge cement quarry, France) and organic‐rich deposits from the uppermost Cenomanian‐lowermost Turonian Bonarelli level (OAE2; Furlo and Monte Velo, Italy; Manilva and El Chorro, Spain). The comparison of Hg data along weathering profiles in lowermost Toarcian sediments indicates that recent intense oxidation of the originally organic‐rich deposits has removed up to 89% of the Hg signal. The organic‐rich sediments of the Furlo and Manilva sections are characterized by lower Hg/total organic carbon (TOC) ratios, which suggest important Hg scavenging by organic matter (OM) deposition. At the opposite, in equivalent successions, three significant positive Hg/TOC excursions persist at El Chorro and Monte Velo. These samples exhibit low Hydrogen Index (HI) values, which plot in the field of type‐III OM. This resulted from postdepositional degradation of marine OM type II to type III, which largely modified the amount and the quality of OM. Consequently, the recorded Hg/TOC ratios do not reflect original Hg drawdown but postdepositional oxidation, suggesting that extreme care is needed in the evaluation of the history of OM preservation when using Hg as a proxy for volcanic activity. more...

Mercury (Hg) enrichments in sediments are increasingly used as tracer for distal volcanism in deep‐time investigations. The impact of changes in organic‐matter deposition and preservation on sedimentary Hg sequestration is, however, poorly understood. In this study, we evaluate the potential role of intense weathering and postdepositional organic‐matter degradation on the Hg/TOC proxy in sediments. For this, we investigate weathering profiles in organic‐rich sediments from lowermost Toarcian sediments (T‐OAE; Lafarge cement quarry, France) and organic‐rich deposits from the uppermost Cenomanian‐lowermost Turonian Bonarelli level (OAE2; Furlo and Monte Velo, Italy; Manilva and El Chorro, Spain). The comparison of Hg data along weathering profiles in lowermost Toarcian sediments indicates that recent intense oxidation of the originally organic‐rich deposits has removed up to 89% of the Hg signal. The organic‐rich sediments of the Furlo and Manilva sections are characterized by lower Hg/total organic carbon (TOC) ratios, which suggest important Hg scavenging by organic matter (OM) deposition. At the opposite, in equivalent successions, three significant positive Hg/TOC excursions persist at El Chorro and Monte Velo. These samples exhibit low Hydrogen Index (HI) values, which plot in the field of type‐III OM. This resulted from postdepositional degradation of marine OM type II to type III, which largely modified the amount and the quality of OM. Consequently, the recorded Hg/TOC ratios do not reflect original Hg drawdown but postdepositional oxidation, suggesting that extreme care is needed in the evaluation of the history of OM preservation when using Hg as a proxy for volcanic activity. Key Points: Oxidation of the T‐OAE organic‐rich deposits has removed a large part of Hg signalDegradation of OAE2 organic‐matter has largely affected the Rock Eval parametersThe recorded Hg/TOC ratios do not reflect original Hg signature [ABSTRACT FROM AUTHOR] more...

The paper presents a detailed review of chemostratigraphic data on the Bonarelli oceanic anoxic event (OAE2) at the Cenomanian-Turonian boundary from different regions worldwide, with a focus on the respective redox conditions in the basins, metal anomalies, and δ13C excursions. Marine sediments with OAE2 signatures in Eastern Kamchatka are compared with their counterparts from submarine volcanic rises in the northwestern Pacific. The available isotope ages of lavas from some large igneous provinces are correlated with the age of OAE2. The Bonarelli event was triggered and governed by several interrelated factors: volcanism, climate, and ocean circulation. The supply of nutrients into oceans as a result of enhanced magmatism, hydrothermal activity, and weathering on continents played an important role in maintaining anoxia. The spatial patterns of black-shale deposition were controlled by ocean circulation. Geochemical and biochemical processes associated with high productivity ultimately led to its reduction and to the recovery of oxic conditions in oceans. [ABSTRACT FROM AUTHOR] more...

Cenomanian–Turonian organic-rich clays deposited under periodic anoxic conditions in the basins of that time are recorded in carbonate sections. Cenomanian–Turonian boundary deposits were studied in the Biyuk-Karasu River section (Central Crimea). Dark organic-rich clays were found to intercalate with carbonate-poor clays in the formation during oceanic anoxic events. Mixed type II–III kerogens are abundant in these black beds which constitute oil source strata that are similar in their mineral assemblages but different in their organic matter contents. [ABSTRACT FROM AUTHOR] more...

Abstract In northern Tunisia, the Cenomanian-Turonian sediments are characterized by organic-rich material. These deposits are commonly attributed to the Bahloul Formation and record the worldwide OAE2 event. In general, the Bahloul Formation is related to paleogeographic and tectonic events, these results suggest that multiple causes, including primary productivity, sea level changes, climatically driven organic carbon burial and structural framework. This formation is composed of three differentiated units, the first unit (U1) is composed of laminated limestones with small intercalations of marls (%CaCO 3 varies between 48 and 83), the second unit (U2) is characterized by very thin beds of marls, argillaceous and laminated limestones (%CaCO 3 ranging from 57 to 85). Lastly, the third unit (U3) is represented by a set of thick-black shales (with some levels of marls). Isotopic δ13C carb study shows a large positive excursion in the Bahloul Formation. It is characterized by three peaks that exceed 3‰. First and the second peaks are identified at the lower unit U1 with isotopic values recording 3.2 and 3.3‰ respectively. Third peak is recorded in the middle of the unit U2 and it attains 3.2‰. This section records important TOC values reaching up to 3.84% in unit U1, with average values exceeding 3%. The Rock-Eval data shows a marine organic matter with kerogen Type II (429 < HI < 615 mg HC/g TOC), (T max > 435 °C), which can generate oils. A significant enrichment of major and trace elements are also recorded which took place during the deposition of the Bahloul Formation. In general, high levels of P, Cu and Ni indicate a high surface primary productivity, which led to the accumulation of large quantities of organic matter on the sea floor. Highlights • Tectonic controls and structural disposition in Paleoproductivity and redox condition. • Cenomanian-Turonian boundary referring to δ13C_carb. • Petroleum implications (Organic richness, maturity and Kerogen type). • Detrital inputs and Paleoproductivity. • Factors controlling deposits of OM-rich sediments throughout C/T Boudary. [ABSTRACT FROM AUTHOR] more...

Abstract A biostratigraphic study based on the planktonic foraminifera and isotope stratigraphy of the Cenomanian-Turonian interval has been undertaken in the western part of the Kopet-Dagh Basin (NE Iran). In this research, two stratigraphic sections including: Maraveh Tappeh and Qareh Galdy have been sampled and studied. Based on planktonic foraminifera, three biozones were assigned to this interval. These are the Rotalipora cushmani Zone, Whiteinella archaeocretacea Zone and Helvetoglobotruncana helvetica Zone, These biostratigraphic data confirm a gradual faunal turnover of planktonic foraminifera, at the Cenomanian-Turonian boundary in Whiteinella archaeocretacea Zone characterized by: absences, low abundance and disappearances of complex morphotypes. After this event, in Helvetoglobotruncana helvetica Zone, along with simple globular chamber morphotypes, single keeled and double-keeled morphotypes appeared and flourished. The carbon-isotope curves in both sections, record a negative shift values below the Aitamir-Abderaz formations boundary in Whiteinella archaeocretacea Zone, and then, a positive excursion of about 5.50‰, along with several fluctuations are well evident in both sections. The δ18O values show, from the bottom to the top, a gradual increase of averagely 2‰. Based on these results, the Cenomanian-Turonian succession in this part of the Kopet-Dagh Basin is continuous and corresponds to the siltstone and chalky limestone layers of the upper part of the Aitamir Formation and the lower part of the Abderaz Formation. Highlights • The Cenomanian-Turonian boundary is defined based on planktonic foraminifera. • 29 species belonging to 9 genera and three biozones of Cretaceous of planktonic foraminifera were recognized. • New middle Cretaceous (Cenomanian-Turonian boundary) paleoenvironmental conditions were reconstructed in this part of Tethys ocean based on the O, C stable isotopes. • A positive excursion of about 5.50‰, along with several fluctuations, are well evident in both sections. [ABSTRACT FROM AUTHOR] more...

Abstract Early Turonian fishes are known from only a few localities in the Northern Hemisphere, including three in the present-day European/Mediterranean region and three in northern Canada. One of the latter localities, Lac des Bois (66°52.087ʹ N), preserves a diverse marine fauna composed of trace fossils, foraminifera, molluscs and actinopterygian fishes including early acanthomorphs. The molluscan fauna, as well as a radiometric date from bentonites recovered from the site, support an age of latest Cenomanian/early Turonian for the locality. This interval spans the global Oceanic Anoxic Event 2, a time characterized globally by high temperatures and high carbon burial. Although the Cenomanian/Turonian boundary interval has been documented in North America in the Arctic Sverdrup Basin and the southern Interior Seaway, the present study provides the first account of a faunal assemblage that inhabited the northern Western Interior Seaway during this interval. Organic-rich shales and sandstones indicate limited organic decomposition and low oxygen conditions, although the presence of trace fossils (Skolithos, Planolites , Taenidium and Alcyonidopsis , as well as fugichnia) indicates that the sea floor was not completely anoxic. The presence of coiled planktic foraminifera indicates warmer water and extends the known migration limit of these Tethyan-derived forms some 6° further north. Surprisingly, the fish fauna of localities in the Bohemian Cretaceous Basin (Czech Republic) bears a close resemblance to that of Lac des Bois, although acanthomorph fish have not been recorded from the former. This suggests faunal connections between the two regions, either through the northern Polar Sea, or through the postulated Hudson Strait. [ABSTRACT FROM AUTHOR] more...

The Cenomanian-Turonian transition marks one of the most important extinction episodes of the Mesozoic era. This extinction event was associated with the development of widespread oceanic anoxia and pronounced stable carbon isotopic excursion. Despite its importance, the effects of the perturbation on higher latitude biotas, and from the Baltic region in particular, are currently underexplored. Therefore, in this contribution we present the fossil record of a foraminifera succession integrated with δ13C trends from two deep cores: Bliūdsukiai-19 from western Lithuania and Baltašiškė-267 from southern Lithuania. Two foraminiferal zones were distinguished: Rotalipora cushmani from the upper Cenomanian and Whiteinella archaeocretacea from the boundary strata between the Cenomanian and Turonian in the Baltašiškė-267 core section, and a W. archaeocretacea Zone in the Bliūdsukiai-19 core section. A chemostratigraphical analysis of the stable carbon isotopes revealed a positive Cenomanian-Turonian δ13C anomaly, with maximum values reaching 3.57‰ in the upper part of the Bliūdsukiai-19 core section. A non-metric multidimensional scaling analysis of the foraminifera communities revealed that the major changes in their assemblages were strongly temporally organized and associated with the changes in the stable carbon isotopic ratios. This fact points to the significant effects of the C-T extinction event on the northern Neotethys paleocommunities. [ABSTRACT FROM AUTHOR] more...

Résumé La coupe de Douar Menkouchi est un affleurement cénomano-turonien dans le massif de l’Ouarsenis oriental (domaine tellien) du Nord-Ouest algérien, constituant la partie orientale de la paléomarge de la Téthys Maghrébide. Elle est représentée par des alternances de marnes et calcaires en plaquettes riches en matière organique ( black shales ) devenant massifs avec l’intercalation d’une barre siliceuse (phtanites) vers le sommet. L’étude micropaléontologique a révélé une microfaune diversifiée et bien préservée, assez riche en foraminifères et radiolaires. L’étude biostratigraphique des radiolaires a permis, pour la première fois en Algérie, d’identifier des assemblages diagnostiques du passage Cénomanien-Turonien (C/T). Les niveaux riches en matière organique ( black shales ) d’âge Cénomanien, situés au-dessous d’une barre siliceuse ont livré une association de radiolaires dominée par des espèces appartenant à la famille des Pseudodictyomitrae telles que P . pseudomacrocephala et P . tiara , cantonnées à la Zone à Silvae. Vers le sommet, la faune devient plus riche et diversifiée, elle montre une association d’espèces appartenant aux Hagiastridae, dont Crucella cachensis , Alievium cf. superbum , Dictyomitra cf. napaensis et D . undata indiquant un âge Turonien inférieur. Cela suggère que les alternances marno-calcaires situées au-dessus de la barre à phtanites sont attribuées à la Zone à Alievium superbum . Tenant compte des processus taphonomiques et diagénétiques affectant les assemblages, nous déduisons que les niveaux riches en matière organique et biosiliceux soulignent le sommet du Cénomanien. Le contenu des assemblages étudiés montre des similitudes taxinomiques avec ceux de l’intervalle Bonarelli en Italie centrale. Des similitudes morphologiques sont également observables sur des morphotypes de Pseudodictyomitrae tiara (synonyme de P . nakasekoi ) qui ressemblent à ceux identifiés dans les séries ophiolitiques à Chypre et en Oman. The Ouarsenis Massif belongs to the Algerian Tell domain which is considered as the eastern part of the Maghrebian Tethys former margin. The Cenomanian-Turonian Douar Menkouchi section outcropping in the eastern side of the Ouarsenis massif is composed of marls and laminated limestone alternations, including massive limestone and a biosiliceous bed toward the upper part of the succession. It reveals the presence of well-preserved and diversified radiolarians. In this study, we have identified for the first time in the Algerian domain, age-diagnostic radiolarian assemblages characterizing the Cenomanian-Turonian transition (C/T). The organic-rich laminated beds (black shales) confined to Silvae Zone, Cenomanian in age and underlying a biosiliceous interval, have provided radiolarian assemblages dominated by Pseudodictyomitrae. The successions overlying the biosiliceous interval have provided diversified radiolarian assemblages including Hagiastridae (i,e. Crucella cachensis , Alievium cf. superbum ) and abundant Dictymitrae taxa (i,e. Dictyomitra cf. napaensis and Dictyomitra undata ) indicating early Turonian age. These marl-limestone alternations are assigned to the Alievium superbum Zone. Considering taphonomic and diagenetic implications on assemblages content, we conclude that organic-rich beds and biosiliceous interval outline the latest Cenomanian. The radiolarian assemblage composition exhibits similarities to microfauna recovered from Bonarelli Horizon in Central Italy. Morphological similarities are also deduced from assemblages containing Pseudodictyomitrae tiara morphotypes (synonym of P . nakasekoi ) which resemble those recovered from ophiolitic intervals in Cyprus and Oman areas. [ABSTRACT FROM AUTHOR] more...

Four indeterminate pliosaurid remains from the Cenomanian and Turonian of the Yezo Group in Hokkaido, northern Japan, are described/re-described. Although their fragmentary nature does not allow identification to lower taxonomic levels, two specimens represent large individuals whose skull size approaches that of Megacephalosaurus from North America. The late Turonian age of the youngest specimen indicates that the Pliosauridae survived in the northwestern Pacific to least the time when the entire clade was nearing extinction. Along with the known stratigraphic distributions of the Elasmosauridae and Polycotylidae in the Japanese Cretaceous, the described pliosaurid specimens demonstrate that all three major plesiosaurian clades of the Late Cretaceous crossed the Cenomanian–Turonian boundary at least in this region. • Four pliosaurid fossils from Japanese Upper Cretaceous are described/redescribed. • Two specimens represent large individuals whose skull size approaches that of Megacephalosaurus from North America. • Described materials demonstrate that the Pliosauridae survived the Cenomanian–Turonian boundary in northwestern Pacific. [ABSTRACT FROM AUTHOR] more...

In order to evaluate Oceanic Anoxic Event 2 (OAE2) at the Cenomanian-Turonian boundary and its effects on benthic foraminifera, the Taherabad stratigraphic section in the east of Kopet-Dagh basin was studied for pattern of changes in benthic foraminiferal communities. Total Organic Carbon (TOC) concentration at the Taherabad section shows that black shale was not deposited in this succession but TOC increases up to 0.68 wt% in the three intervals of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. Also, Total Nitrogen (TN) values were measured in our study succession. High TOC/TN ratios (up to 18) occur in the intervals of TOC enrichment. Foraminiferal assemblages, TOC, TOC/TN and Detrital Index (DI, an index for detrital input) changes in the study section allowed us to divided study section into 4 intervals. Interval A and C are associated with low abundance and diversity of benthic assemblages coeval with lack of planktic foraminifera. Benthic assemblages are strongly dominated by shallow and deep infaunal agglutinated foraminifera including Lagenammina , Saccammina , Reophax and Tritaxia . The foraminiferal composition associated with higher TOC, TOC/TN and DI suggest an influx of fresh water to the basin in the warm-wet periods, which diminished hospitable conditions for planktic foraminifera and probably enhanced land-derived organic matter and/or primary productivity. The hyposaline cap led to development of salinity-stratified water and induce bottom water oxygen depletion. By contrast, the assemblages found in the interval B and D are more diverse and contain high abundance of planktic and calcareous benthic foraminifera. Common benthic taxa in these parts are praebuliminids, lenticulinids, gavelinellids and Valvulineria . These assemblages associated with lower TOC, TOC/TN and DI indicate decreased detrital input and more normal marine condition resulted in improved ventilation of sea-floor, which is favorable for planktic and benthic taxa. [ABSTRACT FROM AUTHOR] more...

The Cretaceous Oceanic Anoxic Event 2 (OAE2) is a greenhouse episode of severe marine anoxia at the Cenomanian-Turonian boundary. This time interval is characterized by rising sea surface temperature, enhanced marine biological productivity, and widespread occurrence of organic-rich black shales. With an export of biological production to the deep ocean, organisms consume vast amounts of oxygen and subsequently utilize nitrate and sulfate as electron acceptors in organic matter degradation, thereby affecting biogeochemical cycles of nitrogen and sulfur. However, due to a lack of comprehensive compilation of global records, the temporal and spatial distribution of oceanic oxygen loss is yet to elucidate. To bridge this gap, this review summarizes the published marine nitrogen and sulfur isotope data sets from worldwide locations across the Cenomanian-Turonian boundary. The compiled records suggest that anoxic and euxinic waters have initially developed on the southern edge of the proto-North Atlantic before the OAE2 and spread to open oceans of the proto-North Atlantic, epicontinental seas of the Western Tethys and Western Interior Seaway at the onset of the OAE2. Meanwhile, sites above the storm base and in deep seas of the Tethys remain relatively oxic throughout the time. We suggest that distinct nutrient levels and circulation structures primarily control the regional difference in marine redox states. Our findings depict the evolutionary history of ocean deoxygenation and biogeochemical cycles during the past hyperthermal event, with implications for how future global warming may impact seawater chemistry and marine ecosystems. • First compilation of global-scale N and S isotope records across the OAE2. • Changes in N and S cycles suggest three types of marine redox evolution. • Nutrient level and circulation structure control temporal-spatial heterogeneities. • Potential application to other ocean deoxygenation events under climatic warmth. [ABSTRACT FROM AUTHOR] more...

Biomarker analyses for evaluating maturity of organic matter and depositional environments such as redox conditions, were performed in sediments across the Cenomanian-Turonian boundary (CTB) in the Saku Formation of the Yezo Group distributed along the Shumarinai-gawa River and the Omagari-zawa River, both in the Tomamae area, Hokkaido, Japan. Maturity indicators using steranes and hopanes, show that organic matter in sediments from the Shumarinai-gawa and Omagari-zawa sections are of lower maturity than those from the Hakkin-gawa section (Oyubari area). Moreover, the ββ hopane ratios clearly show that the maturity of the Shumarinai-gawa samples is lower than that of the Omagari-zawa samples. These variations in the maturity of organic matter presumably reflect the difference in their burial histories. The results for the pristane/phytane (Pr/Ph) ratios suggest that the Shumarinai-gawa samples were deposited under dysoxic to anoxic environments across the CTB, while the depositional environments of the Omagari-zawa samples were relatively oxic. By another paleoredox indicator using C35 homohopanoids including a homohopene index (HHenI), higher values are observed in the Shumarinai-gawa section, particularly in the horizons of the preceding period and an early stage of the first negative shift phase and the latest oceanic anoxic event 2 (OAE2) interval. These results suggest that the Shumarinai-gawa samples record dysoxic to anoxic environments across the CTB. In contrast, the signals for the C35 homohopanoid index values show a relatively oxic condition in the Omagari-zawa section. The trends of stratigraphic variations in redox conditions are different from those in the OAE2 interval in the proto-Atlantic and Tethys regions as reported previously. Hence, the redox variations in the Tomamae area were basically related to a local environmental setting rather than global anoxia. However, the prominent anoxic emphasis observed in the HHenI profile of the Shumarinai-gawa section can be a distinctive, and possibly global, event in the North-West Pacific just before the OAE2. [ABSTRACT FROM AUTHOR] more...

Walaszczyk, I., Plint, A.G. and Kennedy, W.J. 2016. Biostratigraphy and Inoceramus survival across the Cenomanian- Turonian (Cretaceous) boundary in the Ram River section, Alberta, Canada. Acta Geologica Polonica, 66 (4), 715-728. Warszawa. The biostratigraphy of the uppermost Cenomanian - Lower Turonian succession in the lower part of the Blackstone Formation exposed in the Ram River (Alberta, Canada), is interpreted in terms of the standard inoceramid/ammonite zonation of the interval. Four successive inoceramid zones are recognized, those of Inoceramus pictus, Mytiloides puebloensis, M. kossmati, and M. mytiloides, as established in the stratotype section at Pueblo, Colorado. Their correlation to Pueblo is confirmed by ammonite data. The mid-Early Turonian zone of M. kossmati yielded an assemblage of Inoceramus, with species showing close affinity to the latest Cenomanian lineages. This multi-species sample proves the survival of Inoceramus lineages into the otherwise Mytiloides-dominated Early Turonian, and indicates that their disappearance from the record of the North American Western Interior was not because of their extinction. It is suggested that the apparent lack of Inoceramus in Lower Turonian strata is due to an extremely low population abundance in the Early Turonian sea. [ABSTRACT FROM AUTHOR] more...

Through the correlation of a ten of sections from platform to basin we suggest that the Cenomanian-Turonian Boundary Event and the deposition of black shales are at least in part linked to morphologic changes due to shallow-water carbonate production during a rise in relative sea-level, at first slow, faster later. more...

A set of 11 abstracts and short papers (extended abstracts) of presentations given at a meeting organized by the "Groupe Français du Crétacé (GFC)", held on November 27-28, 2007 at the "École des Mines" in Paris, France. These contributions are available only in English or in French. 1- Les bioévénements de la limite Albien (Vraconnien) - Cénomanien aux marges nord et sud de la Téthys (S.E. de la France et Tunisie centrale) - Bioevents at the Albian (Vraconnian) - Cenomanian boundary at the North and South margins of the Tethyan Ocean (SE France and Central Tunisia) 2- Échanges et colonisations fauniques (Ammonitina) entre Téthys et Atlantique sud au Crétacé supérieur : voies atlantiques ou sahariennes ? - Late Cretaceous faunal exchange and colonization (Ammonitina) between the Tethys and the South Atlantic: Atlantic or Saharan routes? 3- Phosphorus and trace-metal records during Cretaceous oceanic anoxic events: Example of the Early Aptian OAE in the western Tethys - Évolution de la concentration du phosphore et des métaux-traces durant les événements anoxiques du Crétacé inférieur : exemple de l'événement de l'Aptien inférieur (OAE 1a) dans la Téthys occidentale 4- L'évolution tectono-sédimentaire du système "Golfe de Gascogne-Pyrénées Occidentales" au Crétacé inférieur : un nouveau regard - The tectonic and sedimentary evolution of the Bay of Biscay-Western Pyrenees during the Early Cretaceous : a new point of view 5- The marine squamates (reptiles) from the Cenomanian-Turonian of the Tethys: a noteworthy radiation - Les squamates (reptiles) marins du Cénomanien-Turonien de la Téthys : une radiation remarquable 6- Influences boréales dans le bassin de Mons (Belgique) à l'Albien - Boreal influences in the Mons basin (Belgium) during the Albian 7- On the track of a major trans-Tethyan discontinuity - Sur la piste d'une discontinuité majeure trans-Téthys 8- The Cretaceous of Lebanon in the Middle East (Levant) context - Le Crétacé du Liban dans le cadre du Moyen-Orient (Levant) 9- Le Cénomanien-Turonien de l'Atlas saharien (Algérie) 10- Endémisme et cosmopolitisme des faunes d'ammonites de la plaque arabique au Cr&#233 ;tacé moyen (Aptien - Turonien) - Endemism vs. cosmopolitanism of the ammonite faunas from the Arabian plate during mid-Cretaceous times (Aptian – Turonian 11- La discontinuité albienne à l'échelle globale et ses implications paléobiogéographiques et biostratigraphiques - The Albian unconformity at a global scale and its palaeobiogeographic and biostratigraphic implications more...

The late Cenomanian-early Turonian deposits in Tunisia recording the OAE2 event are commonly attributed to the Bahloul Formation. These deposits are composed of dark clayey limestone and organic-rich black shales with abundant planktic foraminifera. At the Bargou area, Oued Kharroub section, these organic-rich deposits include siliceous beds with abundant radiolarians recalling the 'Livello Bonarelli'. A total of 25 radiolarian species are identified with a maximum of 18 species per sample. Moreover, the species skeleton preservation is usually poor to moderate in the most studied samples [estimated preservation index (PI) values ranging between 4 and 6]. Two successive assemblages are distinguished. The oldest one (R) is dominated by nassellarians, which includes mainly Stichomitra, Pseudodictyomitra and Rhopalosyringium genera. It is included within the upper part of foraminiferal Rotalipora cushmani Zone and lower part of Whiteinella archaeocretacea zone. In contrast, the youngest assemblage (R), which belongs to the upper part of the W. archaeocretacea zone and the earliest Turonian Watinoceras ammonite assemblage, is dominated by spumellarians and includes mainly Archaeocenosphaera, Cavaspongia, Pseudoeucyrtis and Pyramispongia genera. In addition, major and trace elements are analysed to test whether the geochemical record was synchronous to the biotic event or not. Thus, selected crossplots, AlO vs. SiO and AlO vs. TiO, are used to evaluate the detrital input, and V/Cr vs. V/(V + Ni) and U/Th vs. V/(V + Ni) are used to evaluate the bottom redox conditions and the primary productivity within the Bahloul Formation. A strong Si/Al increase is marked in the lower part of the siliceous and organic-rich Bahloul Formation that could be explained by a local increase in upwelling-related biogenic SiO (silica-secreting organisms). Relative low abundance of terrigenous-related Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba (organic matter related trace elements) suggests that the Bahloul was of relatively elevated primary productivity and minimal detrital input. Enrichments in redox-sensitive trace metals U and V in the Bahloul Formation deposits and redox indices, such as V/(V + Ni), U/Th and V/Cr, indicate that oxygen-restricted conditions prevailed during the late Cenomanian-earliest Turonian times and correlate well with relative abundances of some radiolarian and foraminiferal paleo-environmental indicators. In addition, indicators of detrital flux variations are used. AlO shows a slight positive correlation with TiO and a less distinct correlation with SiO. [ABSTRACT FROM AUTHOR] more...

Abstract: High-resolution foraminiferal biostratigraphic analysis has been undertaken on the Bahloul Formation, in Bargou, Jerisa, Guern Halfaya (Central Tunisia), Kherij (North-eastern Tunisia) and Gafsa (southern Tunisia) sections, which prove the preservation of the worldwide expression of the Cenomanian–Turonian transition (C–T) Oceanic Anoxic Event (OAE2). This study confirms that the OAE2 was rather a long-term global event. The high resolution biostratigraphical analysis has allowed subdividing the Whiteinella archaeocretacea zone of the standard biostratigraphic scheme. The ability to apply same subzones in both Tethyan and transitional/Boreal provinces during the C/T boundary has important palaeobiogeographical and palaeoecological implications. The palaeoecological framework shows that the OAE2 development is composed of several successive phases. In addition, a faunal turnover during the W. archaeocretacea zone interval is recorded. However, we confirm that the faunal turnover in the W. archeocretacea zone did not result in a loss of biodiversity, but rather in replacement through originations. [Copyright &y& Elsevier] more...

Abstract: The Ultrahelvetic Rehkogelgraben section of the Eastern Alps of Austria comprises a c. 5 m thick sequence of upper Cenomanian to lower Turonian pelagic sediments including black shales in a northwestern Tethyan paleogeographic setting. The following calcareous nannofossil events were recognized in stratigraphic order: The first occurrence (FO) of Quadrum intermedium, the LOs of Lithraphidites acutus and Corollithion kennedyi, the FO of Eprolithus octopetalus, and the FO of Quadrum gartneri. Thus, nannofossil zones UC 4, UC 5c, UC 6 and UC 7 could be recognized. Palynological investigations and palynofacies analysis give additional information especially from the black shale layers and the carbonate-free interval in the section. Five out of seven samples from this interval have yielded some low diversity but distinctive palynological associations. Sporomorphs dominate in the associations, being represented mainly by age diagnostic Normapolles species as Atlantopollis microreticulatus, Atlantopollis reticulatus together with Complexiopollis praeatumescens, Complexiopollis christae and Complexiopollis funiculus. The concurrent presence of these pollen species is regarded as characteristic for latest Cenomanian and early Turonian assemblages. A low diversity dinocyst association is identified, dominated by the Cyclonephelium compactum –Cyclonephelium membraniphorum complex, together with Isabelidinium and Circulodinium species. The dinocyst association is encountered in palynofacies rich in marine organic matter of granular amorphous composition. The palynofacies points to deposition in a distal, low-energy, stressed anoxic environment with high continental input. The palaeoenvironmental significance of the low diversity Cyclonephelium/Eurydinium association is typical for Cenomanian-Turonian black shale sequences. Nannofossil indices and dinoflagellate associations indicate rather low-productivity, low-nutrient settings during at least the later part of OAE 2, and thus confirm interpretations based on foraminiferal assemblages. [Copyright &y& Elsevier] more...

Abstract: Upper Cenomanian pelagic sediments from the northern Alpine Helvetic fold-and-thrust belt (northern Tethyan margin) coeval with Oceanic Anoxic Event (OAE) 2 are characterized by the temporal persistence of micrite sedimentation and lack of organic carbon-rich layers. We studied an expanded section in the Chrummflueschlucht (east of Euthal, Switzerland), which encompasses the OAE 2 time interval. In order to identify the paleoceanographic and paleoenvironmental conditions during OAE 2 in this part of the northern Tethyan margin, and more specifically to trace eventual changes in nutrient levels and oxic conditions, we investigated the biostratigraphy (planktonic foraminifera), the bulk-rock mineralogy, and measured stable carbon- and oxygen-isotopes, total phosphorus (P) and redox-sensitive trace-element (RSTE) contents. We were able to determine – with some remaining uncertainties – the different planktonic foraminiferal biozones characteristic of the Cenomanian–Turonian boundary interval (Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones). In the lower part of the section (R. cushmani total range zone), the bulk-rock δ 13C record shows a long-term increase. Within sediments attributed to the W. archaeocretacea partial range zone, δ 13C values reach a maximum of 3.3‰ (peak “a”). In the following the values decrease and increase again to arrive at a plateau with high δ 13C values of around 3.1‰, which ends with a peak of 3.3‰ (peak “c”). At the top of the section, in sediments belonging to the H. helvetica total range zone, δ 13C values decrease to post-OAE values of around 2.2‰. The last occurrence of R. cushmani is observed just above the positive δ 13C shift characterizing OAE 2. P contents display small variations along the section with a long-term decreasing trend towards the top. Before the OAE 2 interval, P values show higher values and relatively good covariation with detrital input, indicating higher nutrient input before OAE 2. In sediments corresponding to the onset of the δ 13C positive excursion, P content is marked by a sharp peak probably linked to a slowdown in sedimentation rates and/or the presence of a small hiatus, as is shown by the presence of glauconite and phosphatic grains. In the interval corresponding to OAE 2, P values remain low and increase slightly at the end of the positive shift in the δ 13C record (in the H. helvetica total range zone). The average contents of RSTE (U, V, As, Co, Mo and Mn) remain low throughout the section and appreciable RSTE enrichments have not been observed for the sedimentary interval corresponding to OAE 2. No correlation is observed with stratigraphic trends in RSTE contents in organic-rich deeper-water sections. The presence of double-keeled planktonic foraminifera species during most of the Cenomanian/Turonian boundary event is another evidence of relatively well-oxygenated conditions in this part of the northern Tethyan outer shelf. Our results show that the Chrummflueschlucht section corresponds to one of the most complete section for the Cenomanian–Turonian boundary interval known from the Helvetic realm even if a small hiatus may be present at the onset of the δ 13C record (peak “a”). The evolution of P contents suggests an increase in input of this nutritive element at the onset of OAE2. However, the trends in RSTE contents and the planktonic foraminifera assemblages show that the Helvetic realm has not been affected by strongly depleted oxygen conditions during OAE 2. [Copyright &y& Elsevier] more...

The ridge of Jbel Tselfat is located at about 30 km north of Meknes (Morocco). It is composed of a Jurassic core surrounded by Miocene levels. Some fossiliferous outcrops of black shales, dated from Late Cretaceous, are present in a thrust sheet in the north and east. Jbel Tselfat was carefully explored by the French paleontologist Arambourg, between 1934 and 1954, and a large amount of actinopterygian fishes has been collected from two localities, Ain el Kerma and Sigda. In the framework of the ongoing collaborative Franco-Moroccan research project, a fieldwork has been carried out in autumn 2008 in three sites near Ain el Kerma and in Sigda. An abundant material has been collected. This new fish assemblage is dominated by dercetids, but yielded also pycnodonts, clupavids, protostomiids and acanthopterygians. Other taxa never observed until now in this locality have been found associated with fishes, such as one ammonite and several plant remains. Ongoing geological studies and thin sections analysis allow a better understanding of geological and paleoenvironmental contexts of these vertebrate bearing strata of Jbel Tselfat. They show a deep and quiet marine paleoenvironment, probably close to the coast, in good agreement with Arambourg's ideas. Comparison with other 'mid-Cretaceous' fossil fish localities permits to review the dating of Jbel Tselfat and considers it close to the Cenomanian-Turonian boundary. The deposition of black shales is possibly associated to the Oceanic Anoxic Event 2. [ABSTRACT FROM AUTHOR] more...

Abstract: In central Tunisia, the thickness of the Bahloul Formation varies generally between 20 to 40m such as for example, respectively, at wadi Smara near Kalaat Senan and at wadi Bahloul near Maktar. The thickness is also of several tens metres at Koudiat el Azreg near Jerissa and at Tajerouine. In these sites where the thickness of the Bahloul Formation is dilated, in addition to five geochemical events (δ13C), nine bio-events were defined near the Cenomanian-Turonian transition, successively in ascending order: 1. LO Rotalipora cushmani, 2. Heterohelix bio-event, 3. FO Pseudaspidoceras pseudonodosoides, 4. LO P. pseudonodosoides, 5. LO Thalmanninella multiloculata, 6. “filaments” bio-event, Cenomanian-Turonian transition, 7. FO Watinoceras sp., 8. FO Pseudaspidoceras flexuosum, 9. FO Helvetoglobotruncana helvetica. Even though the Bahloul Formation in the Bou Ghanem site is only 7.7m thick (from which only 2.4m of laminated black limestones), all nine marker bio-events were recorded, almost in the same order except some small differences. A good number of these bio-events are global as they are also present at Pueblo (Colorado, USA), the stratotype for the base of the Turonian stage. Consequently, at a global scale, it is possible to place the Cenomanian-Turonian boundary with one or several of these bio-events, with a good level of confidence. [Copyright &y& Elsevier] more...

Abstract: The Thomel Level of the Lambruisse section in the Vocontian Basin (southeast France), which is marked by intercalations of black shales and organic-rich marls, accumulated during the oceanic anoxic event 2 (OAE2) occurring in the Cenomanian-Turonian (C-T) boundary interval. Calcareous nannofossil biostratigraphic investigation of this interval revealed a total of five nannofossil zones, corresponding to the UC3-UC8 zones (Middle Cenomanian-Middle Turonian) as defined by Burnett. Biostratigraphically important taxa observed in the section include Cretarhabdus striatus, Axopodorhabdus albianus, Lithraphidites acutus, Corollithion kennedyi, Helenea chiastia, Quadrum gartneri, Q. intermedium, Eiffellithus eximius, Eprolithus octopetalus and E. eptapetalus. The two nannofossil events commonly used in the delineation of the C-T boundary, namely the LO of H. chiastia and the FO of Q. gartneri, occur less than 2 m apart in the studied section. These two bioevents define the limits of the UC6 nannofossil Zone and occur within the Whiteinella archaeocretacea foraminifer Zone. Previous litho- and chemostratigraphic analyses indicate that the δ13C profile of the section corresponds well with changes in lithofacies and fluctuations in the total organic carbon (TOC) and calcium carbonate content of the section. Initial increase in the δ13C values occurs within the UC3-UC4a undifferentiated zone, coinciding with the onset of the deposition of the organic-rich sediments of the Thomel Level and a drastic decline in the CaCO3 values. The plateau of high δ13C values, on the other hand, occurs within the UC5 zone, between the LO of C. kennedyi and the LO of H. chiastia (and FO of Q. gartneri). This interval of high δ13C values also corresponds to the interval of high TOC and low CaCO3 values. The integrated nannofossil, planktonic foraminifer and δ13C data provide a precise biostratigraphic and chemostratigraphic framework of the C-T boundary in the Lambruisse section that can be used in future studies in the Vocontian Basin and allow correlations with other well-studied C-T boundary sections. [Copyright &y& Elsevier] more...

Deciding which of two bioevents is the less diachronous is a common problem in biostratigraphy. The most accurate correlation uses the finest timescale available. Chemostratigraphy or cyclostratigraphy offer a potential precision of about 10 ka. Graphic correlation can then be used to test the precision of bioevents and to quantify any mismatch. It can also be used to determine in which section any event occurs earlier. Application of these ideas to correlation of the Cenomanian-Turonian and Coniacian-Santonian boundaries demonstrates that some bioevents are as precise as chemo- and cyclostratigraphy, but that most are not. Two problems occur with bioevents. First they may not be recognizable in all sections. Second, where they are recognizable, they may be diachronous. In the former case, calculating confidence intervals on known ranges in sections where the relevant fossil has been recorded is an alternative test. Large confidence intervals suggest that both first and last occurrences of a fossil may be diachronous bioevents. At the Cenomanian-Turonian boundary the following bioevents (in stratigraphic order) appear to be reliable time planes for international correlation. The last occurrences of (1) Corolithion kennedyi, (2) Rotalipora greenhornensis, (3) Axopodorhabdus albianus, (4) Rotalipora cushmani, (5) Lithraphidites acutus, (6) Microstaurus chiastius and (7) the first occurrence of Quadrum gartneri. At the Coniacian-Santonian boundary only the first and last occurrences of Platyceramus undulatoplicatus, and the first occurrences of Platyceramus cycloides and Lucianorhabdus cayeuxii have been identified as potentially reliable bioevents. [ABSTRACT FROM AUTHOR] more...

Abstract: Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter Tmax (<424°C) indicate low maturity. HI values range from 261 to 362mg HC/g TOC. δ13C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5mm/ka) are significantly lower than those at Pueblo and Eastbourne. [Copyright &y& Elsevier] more...

Abstract: Thin-bedded and millimetrically laminated platy marly limestone quarried near Vallecillo, north-eastern Mexico, contains abundant excellently preserved marine fossils. Planktic foraminifers, inoceramids, and ammonites occur throughout the 7.7-m-thick section of this plattenkalk and provide a precise and detailed biostratigraphic zonation from the uppermost Cenomanian to early Turonian, with a mixed assemblage of Tethyan and Western Interior Seaway faunal elements. Five species of inoceramids are present and described herein: Inoceramus pictus pictus, Mytiloides hattini, M. puebloensis, M. goppelnensis, and M. kossmati. The faunal characteristics of the Vallecillo fossil assemblage combined with the monotonous lithology are favourable attributes for correlation with the GSSP at Pueblo, Colorado, and the Eastbourne section in southern England. The first appearances (FAs) of Watinoceras and Mammites nodosoides are considered approximately isochronous and thus suited for long-distance correlation. In contrast, the FAs of Pseudaspidoceras flexuosum, Fagesia catinus, and Helvetoglobotruncana helvetica are clearly diachronous. The range of M. kossmati needs further evaluation. [Copyright &y& Elsevier] more...

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Abstract: Carbon isotope measurements have been made on bulk carbonate and organic matter in three sections across the Cenomanian–Turonian boundary. The stratigraphy records the positive carbon isotopic excursion that is associated with the major oceanic anoxic event (OAE2). Comparison of TOC and isotopic data in sections from a range of different environments suggests that the positive excursion is a response to increased burial of organic matter in the deep ocean. The lack of coupled negative shifts in δ13Corg and δ13Ccarb records at the onset of OAE2 does not support a causal role for volcanism or methane hydrate dissociation. [Copyright &y& Elsevier] more...

Abstract: On the northern side of the Central High Atlas, new lithological and biostratigraphical data, especially realized in the Naour syncline, allow us to precise the Cenomanian-Turonian boundary. We recognized in that syncline an apparently complete series, the Ben Cherrou series, that represent the Upper Cenomanian-Turonian interval. We recommend it as the referring section of the Ben Cherrou Formation, that takes the place of the incomplete and not representative Aït Attab Formation. More, the sedimentological and paleontological analysis, suggest a Tethyan origin for the Cenomanian-Turonian transgressions in the studied area. [Copyright &y& Elsevier] more...

Stable isotopes of bulk sediment and well preserved tests of planktonic and benthic foraminifera from mid-latitude NE Atlantic DSDP Site 551 (Goban Spur) provide the first estimates of carbon isotope gradients within the water column at a lower bathyal site during the Cenomanian/Turonian boundary interval (CTBI). The CTBI carbon isotope excursion is prominent (up to 2‰ shift in δ13C) in the bulk (coccolith) signal, but less pronounced (approximately 0.5‰ shift in δ13C) in planktonic and benthic foraminifera. This difference indicates a very steep 13C gradient in the upper water column and a very efficient biological pump during the CTBI carbon isotope excursion. We suggest significantly increased seasonal primary production in the uppermost water column with an enhanced shallow water chlorophyll maximum as a cause for this steep carbon isotope gradient. Deep-water and surface-water temperature changes during the CTBI are estimated using benthic and planktonic foraminiferal oxygen isotopes. Warm deep-water masses (13–16°C) and a low temperature gradient within the water column prevailed in the late Cenomanian. Additional warming (approximately 2°C for both surface and deep water) occurred in the latest Cenomanian prior to CTBI black shale deposition. This pattern of CTBI black shale deposition during a temperature maximum is also evident at two low latitude locations (ODP Site 1050, Blake Nose and Tarfaya, southern Morocco). [Copyright &y& Elsevier] more...

• We report the first high-resolution Os isotope record of the OAE2 interval in Southern Hemisphere. • The Os data indicate episodes of successively intensifying volcanism proximal to the onset of OAE2. • An interval of cooling equivalent to the Plenus Cold Event of Northern Hemisphere is recognized. • The CIEs of OAE2 intervals of the Iona-1 core (WIS, North America) and Yezo Group (Japan) are refined. • Enhanced ocean connectivity was essential for the global onset of OAE2 at ∼94.5 Ma. Oceanic Anoxic Event 2 (OAE2) exemplifies an episode of global oceanographic and climatic changes in the mid-Cretaceous greenhouse. However, the timing and mechanism of its global initiation remain elusive. Here we report a high-resolution initial osmium isotope (187Os/188Os i , Os i) and δ 13 C org record from an expanded OAE2 interval in southern Tibet, China that was deposited in the Southern Hemisphere. The Os i record documents episodic, intensifying volcanism with the highest intensity episode marked by a large Os i excursion at ∼94.5 Ma and a subsequent ∼200 kyr Os i minimum concomitant with a cooling interval, which is broadly synchronous with the Plenus Cold Event (PCE) recorded in the Northern Hemisphere. Also, the large Os i excursion lags the onset of OAE2 by ∼50 kyr and occurred during a near synchronous global transgression based on high-resolution correlation with other major OAE2 records. These results are interpreted as indicating that enhanced ocean connectivity played a critical role in helping trigger the global onset of OAE2 at ∼94.5 Ma. [ABSTRACT FROM AUTHOR] more...

The pelagic sediments from Integrated Ocean Drilling Program (IODP) Site U1407 in the western North Atlantic are characterized by a sequence of organic-lean and organic-rich sediments representing a major global episode of organic matter (OM) burial during Oceanic Anoxic Event 2 (OAE2). The OM-rich deposits (up to 16% total organic carbon) consist primarily of radiolarians which are rare/absent in the organic-lean sediments. New nannofossil biostratigraphy and the correlation with the global ẟ13C curve were used to constrain the timing of paleoceanographic changes below, within, and above OAE2 sediments. Data were combined from elemental concentrations, biomarkers, and abundances of benthic foraminifera, biserial (heterohelicids) planktic foraminifera, and radiolarians to reconstruct the evolution of these changes. The ẟ13C curve records a global negative excursion within organic-lean sediments not typically recorded in other sections preceding the initial rise in isotopic values that signals OM burial worldwide. Maximum OM accumulation occurred during the second positive isotopic excursion, which is associated with higher terrigenous input (indicated by long-chain n -alkanes and terrestrially derived elements) and water column stratification (suggested by the paleoindicator gammacerane). In addition, sesquiterpene biomarkers derived from cypress and other conifers suggest flooding of gymnosperm forests from increased rainfall coupled with rising sea levels and resulting higher water tables. Within mid-OAE2 sediments, a sharp increase in radiolarians and fish teeth/debris and a decrease in benthic foraminifera implies deposition of OM from increased productivity/upwelling under low oxygen in the lower part of the water column. Upwelling and water column stratification occurring asynchronously at the surface resulted from changes in precipitation, with stratification developing during more humid/wet conditions. Greenhouse warming during OAE2 likely increased precipitation, weathering and nutrient inputs. However, prolonged anoxia caused buried phosphorus to be recycled as indicated by higher redox-sensitive trace element and biolimiting element concentrations, sustaining primary production and further enriching the sediments in OM. We suggest that increased marine paleoproductivity was the primary control on the OM-rich sediment accumulation during OAE2, while low-oxygen conditions resulting from stratification of surface waters were essential to its preservation. • Negative carbon isotope excursion precedes characteristic OAE2 global ẟ13C increase. • Thermally immature OAE2 sediments that are dominantly marine contain up to 16% TOC. • Asynchronous upwelling and water column stratification caused OM accumulation. • Paleoproductivity was main control, but improved preservation was key for higher OM. [ABSTRACT FROM AUTHOR] more...

The Cenomanian-Turonian boundary represents a time of biotic changes affecting the diversity of larger foraminifera in shallow-water carbonate platform facies. Apart of the several taxa that suffered extinction, there is an additional cluster showing some stratigraphic occurrences before and after the CTB. Here we report a further example from the Cenomanian of the Mount Pastrik (Albanian-Kosovan boundary) that is represented by a new species within the Peneroplidae, Vandenbroeckia causae sp. nov. So far, representatives of this genus were only reported from the Campanian and Maastrichtian. The retrieval of Vandenbroeckia before CTB suggests that the genus escaped the extinction, re-appearing in the uppermost Cretaceous under a renewed specific status. [ABSTRACT FROM AUTHOR] more...

Organic-rich black shales intercalated with green radiolarian shales and bentonites, 2.2 m thick, represent an equivalent of the Bonarelli Level in the Outer Carpathian deep-water succession. Carbon stable isotope data from four sections in the Outer Carpathians show that termination of organic-rich accumulation, related to the oceanic anoxic event 2 (OAE2), occurred at the same time in this part of the Western Tethys. The excellent marker of this event is a first horizon of Fe–Mn layer (nodules), a few centimeters thick, directly covering the youngest black shale layer of the Bonarelli-equivalent Level, which is regarded as the regional chronohorizon. The youngest succession of the organic-rich shales, ca. 30 cm thick, corresponds to the latest Cenomanian interval of δ13Corg values displaying a negative trend, which represents a terminal part within the OAE2 carbon isotope excursion. A deep negative shift which ends this falling trend, close to the Cenomanian–Turonian boundary in δ13C curves from many sections around the world, is not visible in the Outer Carpathian successions. The reason for this was the long period of stratigraphic condensation, which is reflected in the ferromanganese sediments of this area. [ABSTRACT FROM AUTHOR] more...

Speculation that elliptical to circular segments of surface exposed lithospheric mantle belts might mark rims of large terrestrial impact basins suggests that the ophiolite rimmed Sulu Sea, Loyalty and Yucatan basins may have resulted from middle Miocene, late Eocene and K‐Pg boundary mantle excavating hypervelocity impacts on Earth (Olds, 2019). The Semail ophiolite suggests such a circular rim segment with a ∼250 km radius of curvature implying an originally ∼500 km diameter impact basin before subsequent deformation/destruction at plate boundaries. Presently the Arabian plate is being actively consumed at the Makran subduction zone (Penney et al., 2017) which evidently will result in subduction of the Gulf of Oman and suturing of the adjacent Semail ophiolite in the near geological future. For large impact basins on the rocky planets, O'Keefe and Ahrens (1993) estimate maximum excavation depth to be roughly 5% of final crater diameter. In this case maximum ejecta source depths of ∼25 km are implied, a number roughly comparable with observed thicknesses of crust plus mantle sections for the Semail ophiolite (Aldega et al., 2017) and depths of burial due to over‐thrusting (obduction) implied by the exhumed metamorphic sole (Cowan et al., 2014). Hacker et al. (1996) and Roberts et al. (2016) place peak metamorphism timing of the Semail metamorphic sole within uncertainty of the C‐T Boundary at 94 Ma. Study of possible correlation of peak obduction timing with end‐Cenomanian global extinction plus anoxic events (Wan et al., 2003) and C‐T boundary impact ejecta plus tsunami deposits (Monteiro et al., 2001) may be warranted. [ABSTRACT FROM AUTHOR] more...