Anoxic Event Research Articles

EARLY JURASSIC BENTHIC FORAMINIFERAL ECOLOGY FROM THE CENTRAL HIGH ATLAS MOUNTAINS, MOROCCO

Abstract The Central High Atlas Mountains of Morocco have an extensive record of Lower Jurassic deposits from the Tethyan Ocean. In the Amellago region, Ziz Valley, and Dadès Valley several fossilized reef outcrops preserve benthic foraminifera spanning the Pliensbachian and Toarcian stages. This study analyzes benthic foraminiferal assemblage changes across the bi-phased extinctions at the Pliensbachian/Toarcian boundary and the Jenkyns Event (also referred to as the Toarcian Oceanic Anoxic Event). In Pliensbachian samples, assemblages with abundant Glomospira sp., Glomospirella sp., Siphovalvulina sp., Haurania deserta, Placopsilina sp., Mesoendothyra sp., and Everticyclammina praevirguliana are observed. Following both the Pliensbachian/Toarcian boundary event and the Jenkyns Event, benthic foraminiferal density, evenness, and species richness decreased, indicating these communities underwent ecologic stress; however, loss of diversity was most substantial between samples that pre-date and post-date the Jenkyns Event. Whereas the Pliensbachian/Toarcian boundary event coincides with the demise of the large benthic foraminifera Mesoendothyra sp. and Everticyclammina praevirguliana, the Jenkyns Event was detrimental for most clades of benthic foraminifera, including many small, resilient taxa. Based on the evidence provided, we suggest that the Pliensbachian/Toarcian boundary and the Jenkyns Event were distinct events, potentially caused by distinct environmental perturbations.

Elevated sea surface temperature and enhanced primary productivity during Ocean Anoxic Event 1d in the eastern Tethys: Calcareous nannofossil evidence from southern Tibet, China

Mid-Cretaceous oceanic anoxic events (OAEs) are characterized by major disturbances to the global carbon cycle and are considered ancient analogs for anthropogenic global warming. Among these events, OAE 1d, occurring around the Albian-Cenomanian boundary, remains understudied in the eastern Tethys region, leaving a critical palaeogeographic gap that hampers a global understanding of its impacts. In this paper, we present a detailed record of calcareous nannofossil assemblages from the lower to middle part of the Lengqingre Formation in the Chaqiela section of Gamba, southern Tibet, China. The study interval contains abundant, moderately to well preserved calcareous nannofossil assemblages, with Watznaueria barnesiae, Discorhabdus ignotus, Biscutum constans, and Zeugrhabdotus erectus as the dominant species constituting >50% of the assemblages. These nannofossil assemblages allow the study interval to be constrained to Upper Cretaceous (UC) Biozones UC0 through UC2, with the Albian-Cenomanian boundary located in the lower part of the Lengqingre Formation, and the middle part assigned to Cenomanian in the study area. As such, the position of OAE 1d in this section is accurately determined. Calculated nutrient and temperature indices based on nannofossil species with preferred ecologies reveal significant palaeoceanographic changes across the OAE 1d. These changes show increased abundance of warm-water taxa (e.g., Rhagodiscus asper and Zeugrhabdotus diplogrammus) and high-productivity taxa (e.g., D. ignotus, B. constans, and Z. erectus), suggesting increased sea surface temperature and enhanced productivity during OAE 1d in the southwestern shelf sea of the eastern Tethys Ocean.

New insights on Late Pliensbachian-Early Toarcian seawater chemistry based on belemnite rostra element content

Belemnites were a type of cephalopod abundant in the Jurassic and Cretaceous, whose fossils have been extensively used for paleo-oceanographic studies. For this study, we analyzed 69 elements by Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS) in 15 belemnite rostra from the West Rodiles section in the Asturian Basin, Northern Spain. We aim to determine if belemnite rostra carbonate chemistry reflects changes in seawater chemistry during the Late Pliensbachian–Early Toarcian time interval and examine how belemnites can be used to trace known drivers of the Early Toarcian Oceanic Anoxic Event (T-OAE) and associated oceanographic processes.Discarding drastic intra-species effects and assuming a similar influence of growth rates, diet, and other physiological processes for all analyzed belemnite specimens and taking into consideration the sizeable analytical uncertainty, we assess if determined belemnite rostra element chemistry reflects broad and relative changes in paleo-seawater chemistry. Many determined elements are present in only ppb amounts, and their interpretation is uncertain. We found that Mg, Mn, and P increase in the interval chronocorrelative to the T-OAE. This is interpreted to have resulted from an increase in these elements' inventory in seawater due to an increase in continental weathering and fluvial runoff associated with this global event. Iron, K, and Na contents decrease upwards in the section, potentially indicating that these elements became limited and likely hampered oceanic productivity. Our study also found a correspondence between a change in the behaviour of several elements, warming, the T-OAE negative CIE, and a reduction in the diversity and size of both calcareous nannofossils and belemnites in the study area.

High extinction risk in large foraminifera during past and future mass extinctions.

There is a strong relationship between metazoan body size and extinction risk. However, the size selectivity and underlying mechanisms in foraminifera, a common marine protozoa, remain controversial. Here, we found that foraminifera exhibit size-dependent extinction selectivity, favoring larger groups (>7.4 log10 cubic micrometer) over smaller ones. Foraminifera showed significant size selectivity in the Guadalupian-Lopingian, Permian-Triassic, and Cretaceous-Paleogene extinctions where the proportion of large genera exceeded 50%. Conversely, in extinctions where the proportion of large genera was <45%, foraminifera displayed no selectivity. As most of these extinctions coincided with oceanic anoxic events, we conducted simulations to assess the effects of ocean deoxygenation on foraminifera. Our results indicate that under suboxic conditions, oxygen fails to diffuse into the cell center of large foraminifera. Consequently, we propose a hypothesis to explain size distribution-related selectivity and Lilliput effect in animals relying on diffusion for oxygen during past and future ocean deoxygenation, i.e., oxygen diffusion distance in body.

Geochemistry and clay mineralogy of shales in the Sulu Orogenic Belt, East China: suggestion for continental weathering during an Early Cretaceous hyperthermal interval

ABSTRACT Understanding past weathering–climate feedback mechanisms under greenhouse conditions has significance for guiding the development of climate mitigation strategies. The continental paleoweathering state of Early Cretaceous shales in the Sulu Orogenic Belt of East China during a hyperthermal interval related to oceanic anoxic event 1a (OAE1a) was investigated via geochemical and clay mineralogical analyses of shale samples. The resulting diagrams of ternary 15Al2O3–Zr–300TiO2 discrimination, Th/Sc and Zr/Sc show that the geochemical composition was mainly controlled by source composition. This is supported by observations of low Zr contents, high indexes of compositional variability (ICV; &amp;gt; 1), and micropetrological characteristics. All samples showed narrow SiO2/Al2O3 and (Fe2O3 + MgO)/Al2O3 ranges that were within the predicted weathering trends of the ternary A-CN-K diagram, indicating that the shale geochemistry was not influenced by silicification and K-metasomatism. The chondrite-normalized rare-earth-element pattern suggests that all samples had the same felsic igneous parent rock. The geochemistry of whole rocks and their silicate fractions indicates that the shale had low chemical indexes of alteration (CIA) but high ICV values compared to post-Archean Australian Shale, indicating low sediment maturity and extremely weak chemical weathering in the source terrane and/or sedimentary basin under hot-dry conditions. Moreover, the clay minerals in the shale were mainly illite, suggesting low mineral weathering. Thus, during the OAE1a-related hyperthermal interval, chemical weathering was relatively weak in some mid-latitude arid inland areas. This may be mainly due to aridification decreasing water–rock reactions. Chemostratigraphic analysis suggests that the CIA, Ga/Rb, and Rb/Sr values of shales from the upper strata of the Yangjiazhuang and Shuinan formations were greater than those from lower strata. Moreover, the opposite trend in K2O/Al2O3 ratios was found. These indices suggest gradual increases in chemical weathering as the climate changed from hot-dry to warm-humid. In contrast, proxy indices of shale from the Zhifengzhuang Formation showed the opposite trend, suggesting a gradual decrease in chemical weathering as the climate changed from warm-humid to hot-dry. Considering the composition of the clay minerals, it is speculated that continental weathering was dependent on atmospheric humidity rather than temperature under the extreme greenhouse conditions, resulting in ineffective climate regulation by chemical weathering. This comprehensive study advances our understanding of the weathering–climate feedback mechanism under greenhouse regimes.

Ginkgoites manchurica from the Lower Cretaceous Shahezi Formation of Liaoning, China, and its palaeoclimate implications

The extreme greenhouse climate during the period of oceanic anoxic events (OAEs) in the Cretaceous is recognized based on marine stratigraphy, whereas the palaeoclimate remains poorly understood based on the terrestrial record due to the limitations of quantitative methods. The nearest living equivalent method, such as using the stomatal index of Ginkgo as a proxy, provides insight into reconstructing the terrestrial palaeoclimate during OAEs. However, due to the lack of well-preserved fossils with epidermal features and applicable quantitative methods, there are still controversies regarding the classification and nomenclature of species in the genus Ginkgoites, which have been assigned to Baiera, Ginkgo, or Ginkgoites. Here, we report well-preserved Ginkgoites fossil leaves from the Lower Cretaceous Shahezi Formation in Changtu County, Liaoning Province, Northeast China. The fossil dry leaf mass per area (LMA) was estimated as a quantitative morphological and ecological proxy. The LMA results of 192–241 g/m2 for different specimens are very close, suggesting that these homonyms should be assigned to the same species. Therefore, combining the detailed epidermal features and a quantitative morphological proxy (LMA), we summarized and amended the previously described fossils into Ginkgoites manchurica. Moreover, using the stomatal index of G. manchurica, the palaeo-atmospheric CO2 concentration was calculated at 1270 ppmv using the Barclay SI-pCO2 curve during the middle to late Aptian, indicating a typical greenhouse climate, which may be associated with the OAE global temperature increase event.

A mid-Cretaceous carbon isotope reference curve for the SE Neo-Tethys region (Zagros, W Iran)

Stable carbon isotope chemostratigraphy and the associated reference curves have proved to be valuable tools for stratigraphic calibration and long-distance correlations. Nonetheless, the reference curves covering the Cretaceous have mostly been produced from localities located within the W Neo-Tethys. In order to establish a reference curve for the SE Neo-Tethys margin, an Aptian–Albian hemipelagic carbonate-rich succession deposited along the Zagros Basin (SW Iran) was examined for planktic foraminifera biostratigraphy, carbon isotope stratigraphy, and sedimentological characteristics. Eight biozones including Globigerinelloides ferreolensis, Globigerinelloides algerianus, Hedbergella trocoidea, Paraticinella bejaouaensis, Muricohedbergella planispira, Ticinella (T.) primula, Biticinella breggiensis, and Pseudothalmanninella (P.)ticinensis as well as two subzones enclosing T. praeticinensis and P. subticinensis assign the strata to the early late Aptian–late Albian age. A carbon isotope record constrained by the planktic foraminifera zonation scheme shows good concordance with existing composite reference curves from the W Neo-Tethys region. Several carbon isotope excursions (CIEs) characterizing global marine events including Oceanic Anoxic Event (OAE) 1a, OAE1b, OAE1c and associated sub-events can be identified in the studied section. Deoxygenated bottom waters associated with the formation of OAE1a and OAE1b are indicated by distinct lithological signatures including enrichment in pyrite and glauconite, nodular and stratiform chert beds, as well as enhanced organic matter contents. We integrate the here-studied interval with a previously published upper Albian−Turonian succession from the same outcrop section, forming a composite, stratigraphically well-constrained section. This results in a high-resolution carbon isotope record for the SE Neo-Tethys margin, considered to represent an expedient reference Aptian–Turonian curve for this region. Correlation of this new curve with previously published records from the Middle East has helped to address ambiguities regarding the stratigraphic positions of the early/late Aptian and Aptian/Albian boundaries identified by previous studies.

Dolostone-barite-phosphorite sequence in the basal Doushantuo Formation: Origin and implications for post-Marinoan ocean chemistry and phosphogenesis

Barite (BaSO4) represents a major component of many post-Marinoan cap dolostones worldwide, recording important information on climate upheavals during the terminal Neoproterozoic. However, its origins and relations with other lithofacies remain to be explored. Here we report new occurrences of barite in the basal Ediacaran Doushantuo Formation at a major phosphate mine in Weng'an, South China, and present results of detailed petrographic and geochemical investigations on the barites and related phases. At the outcrop scale, barite is mainly present as a 1–2 cm-thick layer at the contact of the cap dolostones and overlying phosphorites. Detailed petrographic observations reveal a lithofacies transition from dolostone through a mixture of barite, dolomite and apatite to barite and finally to granular phosphorite. The barites can be categorized into three generations in stratigraphic order, which are present as loose, randomly-oriented blades (B1), dense aggregates (B2), and radially aligned crystal fans (B3), respectively. B1 is dispersed in a matrix of apatite and dolomite, which has an average δ13Ccarb of −0.61‰. This, along with the common presence of organic matter (OM) in this barite, point to a possible source of Ba from organic degradation. B3 forms a centimeter-scale layer of barite fans that laterally extends over the entire mining pit, whereas B2 is locally distributed between B1 and B3, and occurs as relatively unoriented aggregates. δ34S values of B3 show a narrow range between +25.9‰ and +30.9‰, which is similar to that of contemporaneous seawater and indicate a seawater source of sulfate in barite. Based on the present investigation and a compilation of published data, we propose that B1 is diagenetic barite with a main source of Ba from degradation of organic matter and possibly also from dissolution of previous pelagic barite, whereas B2 and B3 represent seafloor precipitates that resulted from interactions between deep, anoxic Ba-rich waters and oxic, sulfate-rich surface waters during the post-glacial transgression. This episode of barite precipitation was immediately followed by massive accumulations of phosphorites in Weng'an and many areas of South China. The consecutive deposition of cap dolostone, barite and phosphorite signifies the transition from an alkalinity-rich, stagnant anoxic ocean to a dynamic marine regime featuring oxygenated surface waters and upwelling currents. These pH and redox changes likely facilitated the cycling and enrichment of phosphate in the shallow waters that was necessitated by the unprecedented accumulation of Ediacaran phosphorites in South China.

Exploring the phylogeny and depth evolution of cusk eels and their relatives (Ophidiiformes: Ophidioidei)

With 289 known species in 51 genera, the ophidiiform family Ophidiidae together with their relatives from the Carapidae (36 species in eight genera) of the same suborder Ophidioidei dominate the deep sea, but some occur also in shallow water habitats. Despite their high species diversity in the deep sea and wide bathymetric distributions, their phylogenetic relationships and evolution remain unexplored due in part to sampling difficulties. Thanks to the biodiversity exploratory program entitled “Tropical Deep-Sea Benthos” and joint efforts between Taiwan and French teams for sampling from different localities across the Indo-West Pacific over the last two decades, we are able to compile comprehensive datasets for investigations. In this study, 59 samples representing 36 of 59 known ophidioid genera are selected and used to construct a multi-gene dataset to infer the phylogenetic relationships of ophidioid fishes and their relatives. Our results reveal that the Ophidiidae forms a paraphyletic group with respect to the Carapidae. The four main clades of Ophidioidei resolved are the (1) clade comprising species from the subfamily Brotulinae; (2) clade that includes species in the genera Acanthonus and Xyelacyba; (3) clade grouping Hypopleuron caninum with species from the family Carapidae; and (4) clade containing the species in the subfamily Brotulotaenilinae, Neobythitinae (in part), and Ophidiinae. Accordingly, we suggest the following new revisions based on our results and proposed morphological diagnoses. The subfamily Brotulinae should be elevated to the family level. The genera Xyelacyba and probably Tauredophidium (unsampled in this study) should be included in the newly established family Acanthonidae with Acanthonus. The families Carapidae and Ophidiidae are re-defined. Our time-calibrated phylogenetic and ancestral depth reconstructions enable us to clarify the evolutionary history of ophidiiform fishes and infer past patterns of species distributions at different depths. While Ophidiiformes is inferred to have originated in shallow waters around 96.25 million years ago (Mya), the common ancestor to the Ophidioidei is inferred to have invaded the deep sea around 90.22 Mya, the dates coinciding with the global anoxic event of the OAE2. The observed bathymetric distribution patterns in Ophidioidei most likely point to the mesopelagic zone as the center of origin and diversification. This was followed by multiple events of depth transitions or range expansions towards either shallower waters or greater depth zones, which were likely triggered by past climate changes during the Paleogene-Neogene.

Heterogeneous marine response during the Toarcian Oceanic Anoxic Event (TOAE): The potential role of storminess

The Toarcian Oceanic Anoxic Event (TOAE; ∼183 Ma) represents an important hyperthermal and deoxygenation event in the Early Jurassic. However, TOAE marine records are spatially heterogeneous with regard to nutrient levels, primary productivity, redox conditions and organic enrichment. This non-uniform response to global hyperwarming is not readily accounted for by local variations in paleogeography, climate, or water depth. Largely overlooked to date is the intensified storm activity that characterized the TOAE, and the role that this may have played in controlling marine responses to that event. A review of TOAE studies from multiple marine environments suggests that storm intensity covaried with paleoceanographic conditions, such as nutrient availability, primary productivity, redox conditions, and organic-rich sedimentation. At mid-paleolatitude sites, relatively weak storm activity during the TOAE induced short-term watermass oxygenation, and marine settings were mainly characterized by enhanced anoxia (even euxinia), water-column stratification, increased primary productivity (fueled by terrestrial runoff and P regeneration in euxinic settings), and organic-rich sedimentation. At low-paleolatitude sites, TOAE storm activity was relatively strong, and contributed to marine environments characterized by oxic to suboxic conditions, reduced water-column stratification, decreased primary productivity (possibly due to limited P regeneration and upwelling), low sedimentary organic content, and locally high oolite abundance. TOAE marine sites at all paleolatitudes exhibit: i) sea-level rise and enhanced continental weathering fluxes linked to an intensified hydrological cycle; ii) reduced dinoflagellate and increased cyanobacterial activity; and iii) low δ15N values (mainly −1‰ to +3‰) linked to enhanced diazotrophic nitrogen fixation. The spatial heterogeneity of the response of TOAE marine systems is difficult to reconcile with scenarios linking increased terrestrial flux to marine eutrophication, primary productivity increase and organic-rich sedimentation. Consequently, we hypothesize that the intensity of storm activity influenced TOAE marine systems, and that this factor can, at least partially, account for heterogeneous patterns of environmental changes at middle versus low paleolatitudes and open versus restricted marine settings. Importantly, increased storm activity can induce pycnocline deepening via vertical water-column mixing, thereby promoting: i) enhanced aerobic degradation of organic matter (low sediment organic matter content) due to a reduced oxygen-minimum zone; ii) less nutrient upwelling from deep waters into the photic zone (nutrient-depleted upper ocean), and iii) blooms of nitrogen-fixing cyanobacteria (low δ15N) and calcification (ooid formation). Thus, the interaction between storminess and pycnocline depth is a potentially important factor affecting marine environmental changes during TOAE. These findings have implications for modern oceans now experiencing climatic warming and intensified tropical storm activity.

Exploratory case–control study on childhood cancer near the Mar Menor lagoon Region of Murcia (Spain) 2000 to 2018

The Mar Menor, Europe’s largest saltwater lagoon in the Mediterranean basin (Murcia, southeastern Spain), is an ecosystem facing severe pollution, anoxia events, and marine biodiversity loss. This exploratory study examines the association between residential proximity to the Mar Menor and childhood cancer incidence in Murcia from 2000 to 2018. In our case–control study of 594 cancer cases and 3564 controls, matched by birth year and sex, participants were categorized by proximity to the lagoon (G1 ≥ 20 km, G2 = 10–20 km, G3 = 2–10 km, G4 = ≤ 2 km). Odds ratios (ORs) and 95% confidence intervals (95%CI) were adjusted for sociodemographic and environmental covariates. Analysis of distance as a continuous variable indicated a decrease both in all types of cancer and lymphoid acute leukemia risk with greater distance (OR = 0.99; 95% CI 0.98–0.99), while as a categorical variable, it revealed a non-linear pattern. Specifically, the risk did not increase for those living within 2 km of the lagoon (OR = 0.87; 95% CI 0.52–1.37), whereas increased risks were observed in the 2–20 km range within Campo de Cartagena (G2; OR = 1.32; 95% CI 1.01–1.73 and G3; OR = 1.43; 95% CI 1.00–2.02). This suggests modulating factors near the lagoon may counterbalance risks from broader environmental contamination. These findings highlight the complexity of environmental health dynamics and the importance of detailed research to guide public health strategies and urban planning for environmental and child health protection.

Contourite-drift archive links Late Devonian bioevents with periodic anoxic shelf water cascading

Analysis of a Devonian contourite depositional system in the eastern Anti-Atlas of Morocco reveals the formation of widespread erosional hiatuses and organic-rich bioclastic contourites (ORCs) coinciding with the expansion of an anoxic water mass during Frasnian bioevents, ultimately culminating in the Kellwasser crisis (Frasnian-Famennian extinction event). The identified contourite terrace formed on the uppermost slope of the northern passive margin of Gondwana. Its inner part was bounded by an along-slope contourite channel and a small mounded drift at its downslope margin. Facies- and drift-scale contourite features evidence northwest-directed bottom currents driven by repeated overflows of dense, highly saline, anoxic water originating from the northern Gondwana Epicontinental Sea. These periodic overflows were channeled through the Ougarta trough, then deflected westward over the Tafilalt contourite terrace by the Coriolis force and cascaded downslope until reaching a density equilibrium level, probably forming an intermediate water mass. The cascading of dense, anoxic shelf water supports the photic-zone eutrophication (top-down) model proposed for the Kellwasser crisis and related Devonian anoxic events. We propose a direct link between the anoxic overflows and the Devonian evolutionary events.

Oceanic anoxic event 3 in Arctic Canada—Arc volcanism and ocean fertilization drove anoxia

The global extent of the Late Cretaceous oceanic anoxic event 3 (OAE 3) remains uncertain. It is not considered to have extended into the Boreal Realm. To test this, we examined Late Cretaceous organic- and metal-rich black mudstones of the Smoking Hills Formation in Arctic Canada. New high-precision U-Pb zircon ages indicate that deposition of the Smoking Hills Formation (88.535−78.230 Ma) was temporally coincident with OAE 3, indicating a much broader global expression of this event than previously thought. OAE 3 was likely manifest throughout the proto−Arctic Ocean (now Arctic Canada). Abundant bentonite layers and cryptotephra within the Smoking Hills Formation have rare earth element (REE) patterns that are consistent with ashfall derived from Cretaceous arc volcanism. Anomalously high organic matter content in the Smoking Hills Formation, as compared to underlying and overlying units, suggests that ocean fertilization led to enhanced productivity and metal drawdown. A peak in arc volcanism may have been a key driver of the OAE 3 event. We also explored the potential use of cadmium as a geochemical marker of volcanism and show that high volcanogenic metal loading could affect the use of Cd and other proxies for marine productivity (e.g., Zn, Cu).

Discovery of giant and conventional magnetofossils bookending Cretaceous Oceanic Anoxic Event 2

Conventional magnetofossils are the remains of magnetotactic bacteria and giant magnetofossils are the remains of iron biomineralizing organisms that have not yet been identified. We report the oldest robust conventional and giant magnetofossil records, ~97 Ma, from marine sediments drilled in Holland Park, Virginia, USA. The Holland Park core records the Cenomanian-Turonian boundary and Oceanic-Anoxic Event 2 (OAE2). Magnetic datasets indicate single domain magnetite within the clay-rich sediments bookending OAE2. Electron microscopy images from these intervals highlight conventional and giant magnetofossil morphologies, including three potentially new giant magnetofossil morphologies: seeds, squash, and spades. There is an overall high abundance and morphological disparity of magnetofossils at Holland Park. However, we observe abundance, disparity, and preservation changes between the magnetofossil assemblages bookending OAE2. Our observations provide clues toward understanding the ecological thresholds of the enigmatic organisms that produce giant magnetofossils and evidence that magnetofossils may be widely distributed in the geologic record.

Palaeoenvironmental and palaeoclimatic study of the Olazagutia (Spain) and Ten Mile Creek-Arbor Park (USA) sections during the Coniacian–Santonian interval

The mechanisms and palaeoenvironmental conditions leading to and occurring through the Coniacian–Santonian Ocean Anoxic Event 3 (OAE3) are poorly known, particularly with regard to the marine phosphorus cycle and the climatic conditions in general. To explore these issues further, two famous locations have been studied, Olazagutia (Spain) and Ten Mile Creek–Arbor Park (TX, USA), which are located in different palaeogeographical areas and deposited at different palaeodepths. The study of these two locations is based on mineralogy (bulk and clay), geochemistry (stable isotopes, organic matter, phosphorus and major element) and high-resolution biostratigraphy (nannofossils) to infer changes in climate and primary productivity across OAE3. The investigated sections were both previously proposed as candidates for the base Santonian global boundary stratotype section and point (GSSP). The Olazagutia section was ratified in 2013, where the base of the Santonian was defined by the first appearance datum of the inoceramid Platyceramus undulatoplicatus . Both sections, deposited in oxygenated conditions, record the δ 13 C patterns which characterized the Coniacian–Santonian OAE3 interval, in particular the positive carbon-isotope excursions comprising the K2, Michel Dean and Bedwell events. New nannofossil biostratigraphy for both sections is presented including new occurrences. Significant diachronism of marker taxa is observed between the Spanish and Texan sections. Based on a weathering index and mineralogy, similar climate changes are observed in all sections. The climate shifted synchronously from relatively drier to warmer and wetter conditions above the Coniacian–Santonian boundary from the Michel Dean event to above the Bedwell event during the early Santonian. Fluctuations in total phosphorus contents appear mainly to have been driven by changes in detrital input and consequently by climate change in Spain and Texas. Several bentonite layers were observed in Texas close to the Coniacian–Santonian boundary, but only one located 7 m above the Coniacian–Santonian boundary provided sufficient well-preserved zircon minerals, and gives an age of 86.24 ± 0.12 Ma based on U–Pb geochronology, consistent with an early Santonian age.

Acceleration of phosphorus weathering under warm climates.

The release of phosphorous (P) via chemical weathering is a vital process that regulates the global cycling of numerous key elements and shapes the size of the Earth's biosphere. It has long been postulated that global climate should theoretically play a prominent role in governing P weathering rates. Yet, there is currently a lack of direct evidence for this relationship based on empirical data at the global scale. Here, using a compilation of temperature and P content data of global surface soils (0 to 30 cm), we demonstrate that P release does enhance at high mean annual surface temperatures. We propose that this amplification of nutrient supply with warming is a critical component of Earth's natural thermostat, and that this relationship likely caused expanded oceanic anoxia during past climate warming events. The potential acceleration of phosphorus loss from soils due to anthropogenic climate warming may pose threats to agricultural production, terrestrial and marine ecosystems, and alter marine redox landscapes.

Spatial heterogeneity in nutrient utilization during the end-Devonian ocean anoxic event: a case study of the Western Canada sedimentary basin

The Devonian-Carboniferous (D-C; 359 Ma) boundary is marked by widespread deposition of organic-matter-rich black shales associated with the Hangenberg mass extinction event. The Exshaw Formation spans the D-C boundary in the Western Canada Sedimentary Basin (WCSB) and includes the basal Exshaw Shale deposited under broadly anoxic waters. The sediments at the base of the Exshaw Shale were deposited synchronously during a transgressive event across the WCSB, spanning the geographic variability of the basin. The variable Corg content of the shale was affected by local nutrient upwelling and paleotectonic features impacting water depth and circulation. To characterize the link between paleogeography and nutrient cycling, geographic (N = 20 locations) and stratigraphic (N = 6 locations) trends of δ13Corg and δ15Nbulk were examined throughout the WCSB, representing a range of depositional settings. The δ15Nbulk values range between 0.0 and 6.3‰ and δ13Corg from −29.5 to −26.8‰. Phytoplankton production in focused upwelling zones acquired a relatively 15N-depleted signature through isotopic fractionation during nutrient assimilation, and the residual nutrient pool was 15N-enriched. The advection of surface waters away from the location of upwelling supported additional phytoplankton growth and the deposition of sediments with higher δ15N values. The stratigraphic sections include black laminated and burrowed mudrock sequences that record changes in paleoredox conditions, water depth, and tectonism over time. Up-core from the base of the Exshaw, the Corg content decreases and simultaneously δ15Nbulk increases, suggesting a decrease in eutrophic conditions. Variable δ13Corg and δ15Nbulk trends demonstrate that there is no “type” isotopic profile spanning the D-C boundary in the WCSB.

The Cretaceous to Eocene: a biostratigraphical review and a new detailed palynostratigraphy of Greenland and adjacent areas

The present paper compile and correlate for the first time Cretaceous to Eocene palynostratigraphies across the Arctic. It focus on Greenland and adjacent areas, including the Labrador–Baffin Seaway, onshore Nuussuaq Basin in central West Greenland, onshore southern East Greenland, central East Greenland, North-East Greenland, eastern North Greenland and the Danmarkshavn Basin, but also extends to Canadian Arctic Archipelago and the Barents Sea region off Norway. The paper compile data from more than three decades of detailed Arctic palynological analyses, based mainly on dinoflagellate cysts. The paper gives a historical overview of the Cretaceous to Palaeogene paleontological studies of Greenland and presents an overview of 85 palynological intervals and numerous events. The palynological assemblages from the Labrador–Baffin Seaway, Nuussuaq Basin and north-east Baffin Bay reflect the opening of the Labrador–Baffin Seaway from brackish to freshwater environment in a large embayment in the Early Cretaceous to an open marine seaway in the Late Cretaceous. Assemblages reveal in dinoflagellate cyst provincialism between the opening stages of the Labrador–Baffin Seaway and the already opened Greenland–Norwegian–Barents seaway. The Upper Cretaceous global Oceanic Anoxic Event 2 (OAE2) spanning the Cenomanian/Turonian boundary is recognised from Arctic Canada, north-east Baffin Bay, Nuussuaq Basin in central West Greenland, and North-East Greenland, and is mapped and correlated based on dinoflagellate cyst stratigraphy and carbon isotope (δ13Corg) curves. The dinoflagellate cysts assemblages of the Cretaceous/Palaeogene boundary are correlated from the Labrador Sea across to the Nuussuaq Basin in central West Greenland; in both areas the earliest Danian palynological assemblage is represented by incoming warm-water species. The presence of the global Paleocene–Eocene Thermal Maximum (PETM) in the Palaeogene successions in North-East Greenland and in exploration wells in the Labrador–Baffin Seaway is indicated by the incoming of the warm-water dinoflagellate cyst species Axiodinium augustum.

Unveiling a new oceanic anoxic event at the Norian/Rhaetian boundary (Late Triassic)

The latest Triassic was characterised by protracted biotic extinctions concluding in the End-Triassic Extinction (~ 200 Ma) and a global carbon cycle perturbation. The onset of declining diversity is closely related to reducing conditions that spread globally from upper Sevatian (uppermost Norian) to across the Norian-Rhaetian boundary, likely triggered by unusually high volcanic activity. We correlate significant organic carbon cycle perturbations to an increase of CO2 in the ocean–atmosphere system, likely outgassed by the Angayucham igneous province, the onset of which is indicated by the initiation of a rapid decline in 87Sr/86Sr and 188Os/187Os seawater values. A possible causal mechanism involves elevated CO2 levels causing global warming and accelerating chemical weathering, which increased nutrient discharge to the oceans and greatly increased biological productivity. Higher export production and oxidation of organic matter led to a global O2 decrease in marine water across the Norian/Rhaetian boundary (NRB). Biotic consequences of dysoxia/anoxia include worldwide extinctions in some fossil groups, such as bivalves, ammonoids, conodonts, radiolarians.

Carbon isotope chemostratigraphy of the Yucca Formation from the Solitario, Big Bend Ranch State Park, Texas

Introduction: The Yucca Formation is a Lower Cretaceous sedimentary unit present in West Texas. Based on its relative stratigraphic position in the Cretaceous succession of West Texas, it is expected that the Yucca Formation is of Albian and/or Aptian age. It is also expected that the carbon isotope excursions associated with OAE 1a and OAE 1b should be identified in the Yucca Formation. The goals of this project are to 1. construct a carbon isotope chemostratigraphic record of the Yucca Formation, and 2. correlate the Yucca Formation with strata of similar age using chemostratigraphy.Methods: 163 samples were collected from Big Bend Ranch State Park (BBRSP) to determine the δ13C value of bulk sedimentary organic matter.Results: C-isotope values range from −27.02‰ to −18.42‰.Discussion: Carbon isotope excursions (CIEs) that are associated with the Aptian-Albian Boundary are identified as well as CIEs associated with Oceanic Anoxic Events (1a and 1b). This allows us to conclude that the Aptian-Albian boundary is recorded within the Yucca Formation strata at about 71 m above the base of the section exposed in the Lower Shutup of the Solitario in Big Bend Ranch State Park. Regional correlation of the Yucca Formation to other chemostratigraphic records from other Cretaceous strata suggests that the Yucca Formation in BBRSP is time equivalent to the Sligo, Pine Island, James, Bexar, and a portion of the lower Glen Rose Formation on the Comanche Platform and to a portion of the lower Glen Rose Formation in Big Bend National Park.