Oceanic Anoxic Events

The Ekenkpon bivalves were used to deduce the environment of deposition in the Calabar Flank. During the Cenomanian-Turonian times, regionally based marine transgression and regression occurred along the Calabar Flank Epicontinental Sea in Nigeria, leading to the extinction of plants and animals. Notably, the shells of bivalves served as a better indicator of the depositional environment of marine system.
Furthermore, biostratigraphic zones, characterized by various species of Bivalves, Ammonites, Foraminiferas, and Palynomorphs form the basis of the chronology established for these rocks. This phenomenon explains the Global Oceanic Anoxic Events of the Cretaceous times, marked by the deposition of finely laminated organic carbon-rich sediments deposited under oxygen depleted conditions popularly known as the Ekenkpon Shale.
Based on the results obtained, the recovered shells of bivalves’ points to deposition within a shallow marine environment while the dark-grey colour of shales indicate an anoxic reducing environment, together forming a low-energy marine environment.

The El Djehaf section (DLF) in Northern Tunisia offers a detailed record of palaeoenvironmental and geochemical changes associated with the Oceanic Anoxic Event (OAE)1d during the late Albian. The upper part of this section, including the F3-DLF unit, is characterized by an increase in total organic carbon (TOC) content that is accompanied by an overall positive δ¹³Corg excursion. Geochemical data reveal prevailing anoxic redox conditions during deposition, which, along with evidence of abundant calcispheres and opportunistic r-strategist forms of planktic foraminifera including hedbergellids, suggest high surface productivity driven by enhanced nutrient input. These conditions likely resulted in the formation and the preservation of organic matter in sediments, emphasizing the critical role of nutrient flux and redox dynamics in organic matter sequestration. The δ¹³C org excursion observed in the El Djehaf section is coeval with the Breistroffer black shale level and is correlated with global records from Europe and Mexico, providing a robust framework for the occurrence of OAE1d-related black shale deposits. Moreover, the geochemical patterns observed in the El Djehaf section highlight the interplay between local and global factors during OAE1d. Enhanced nutrient input played a crucial role in sustaining elevated productivity, while bottom-water anoxia allowed organic matter to be efficiently preserved. The data emphasise the importance of regional studies in refining our understanding of global oceanic anoxic events, particularly in reconstructing the mechanisms driving carbon cycle perturbations and their impacts on marine ecosystems.

Although ocean circulation plays an essential role in the climate system, its response to major carbon-cycle perturbations during the mid-Cretaceous, including the Mid-Cenomanian Event I (MCE I) and Cenomanian-Turonian ocean ic anoxic event (OAE 2), is poorly constrained. Here we present Nd -isotope evidence for episodic increases in the influence of boreal seawater in the European epicontinental Chalk Sea during MCE I. The start of this reorganization of circulation lagged the onset of the o 13 C positive excursion defining MCE I. This sequence of change is similar to that observed during OAE 2 in the same area, showing a consistent response of circulation to changes in the global carbon cycle. Brief intervals of southerly spread of boreal fauna into mid-latitudinal seas, two during MCE I and one during OAE 2 (Plenus Cold Event), always started after the influence of boreal seawater was enhanced, implying a slower biological response to climatic cooling, rather than passive transport of fauna by boreal waters. The lack of an Nd-isotope positive excursion in our record across MCE I supports a volcanic origin for prominent increases in seawater Nd-isotope values found in the European epicontinental Chalk Sea and tropical Atlantic sequences during OAE 2. The observed tight circulation-carbon cycle coupling potentially serves as an impo1tant route for replenishing upper-ocean nutrients from deep waters and/or volcanic sources, providing a critical feedback allowing continuation of MCE I and OAE 2 over considerable time periods.

Benthonic marine species show a wide range of biological reactions to seawater chemical changes through time, from subtle adjustments to extinction. The Early Toarcian Oceanic Anoxic Event (T-OAE) was recently recognized in the Neuquén Basin, Argentina, confirming its global scope. The event was identified

The Aptian was characterized by dramatic tectonic, oceanographic, climatic and biotic changes and its record is punctuated by Oceanic Anoxic Events (OAEs). The timing and duration of these events are still contentious, particularly the age of the Barremian-Aptian boundary. This study presents a cyclostratigraphic evaluation of a high-resolution multiproxy dataset (δ13C, δ18O, MS and ARM) from the Poggio le Guaine core. The identification of Milankovitch-band imprints allowed us to construct a 405-kyr astronomically-tuned age model that provides new constraints for the Aptian climato-chronostratigraphic framework. Based on the astronomical tuning, we propose: (i) a timespan of ~7.2 Myr for the Aptian; (ii) a timespan of ~420 kyr for the magnetic polarity Chron M0r and an age of ~120.2 Ma for the Barremian−Aptian boundary; and (iii) new age constraints on the onset and duration of Aptian OAEs and the ‘cold snap’. The new framework significantly impacts the Early Cretaceous geological ...

Instittute for People, Innovation & Change in Organizations (PICOTeam) International Water Management Institute 3 Institute for Land, Water and Society Charles Sturt University, Australia. University of Zimbabwe Environmental Management Agency, Zimbabwe 6 University of Eduardo Mondlane Sustainable wetlands management Agreed-upon and functional institutional arrangements which facilitate and regulate sustainable wetland utilization and conservation

We used the nitrogen isotope ratio of algae, suspended particles and nitrate in the water column to track spatial variations in the marine nitrogen cycle in the Mediterranean Sea. Surface PON (5-74 m) was more depleted in 15 N in the eastern basin (À0.370.5%) than in the western basin (+2.471.4%), suggesting that nitrogen supplied by biological N 2 fixation may be an important source of new nitrogen in the eastern basin, where preformed nitrate from the Atlantic Ocean could have been depleted during its transit eastward. The d 15 N of nitrate in the deep Mediterranean (B3% in the western-most Mediterranean and decreasing toward the east) is significantly lower than nitrate at similar depths from the North Atlantic (4.8-5%), also suggesting an important role for N 2 fixation. The eastward decrease in the d 15 N of surface PON is greater than the eastward decrease in the d 15 N of the subsurface nitrate, implying that the amount of N 2 fixation in the eastern Mediterranean is great enough to cause a major divergence in the d 15 N of phytoplankton biomass from the d 15 N of the nitrate upwelled from below. Variations in productivity associated with frontal processes, including shoaling of the nitracline, did not lead to detectable variations in the d 15 N of PON. This indicates that no differential fertilization or productivity gradient occurred in the Almerian/Oran area. Our results are consistent with a lack of gradient in chlorophyll-a (chl-a) and nitrate concentration in the Alboran Sea. 15 N enrichment in particles below 500 m depth was detected in the Alboran Sea with respect to surface PON, reaching an average value of +7.470.7%. The d 15 N in sinking particles caught at 100 m depth (4.9-5.6%) was intermediate between suspended surface and suspended deep particles. We found a consistent difference in the isotopic composition of nitrogen in PON compared with that of chlorophyll (Dd 15 N[PON-chlorin]=+6.471.4%) in the surface, similar to the offset reported earlier in cultures for cellular N and chl-a. This indicates that d 15 N of phytoplankton biomass was retained in surface PON, and that alteration of the isotopic signal of PON at depth was due to heterotrophic activity.

Recent evidence from the sulfur isotopic record indicates a transition Â/2.5 billion years ago from an ocean chemistry first dominated by iron and then by sulfide. It has been hypothesized that the selection of metal centers in metalloenzymes has been influenced by the availability of metals through geological time, in particular as a result of large differences in the solubility of metals-sulfides. In this study, we examine the trace metal requirements and sensitivities of marine cyanobacteria and use recent stability constants to model the abundance and chemical speciation of metals across this chemical transition Â/2.5 billion years ago. Two major results are reported here: (1) the marine cyanobacterial species studied thus far show trace metal preferences and sensitivities that are consistent with their evolution in a sulfidic marine environment, and (2) in an ancient ocean dominated by high fluxes and concentrations of iron, the relative availability of trace metals would have been similar to that of a sulfidic system */Fe!/ Mn, Ni, Co '/Cd, Zn, Cu */as a result of the formation of dissolved sulfide complexes. Thus, the formation of strong aqueous metal-sulfide complexes was likely as important as the precipitation of minerals in influencing the selection of metals in biology. These results suggest that marine biogeochemical cycles and marine bioinorganic chemistry have co-evolved, and that the evidence for this co-evolution has been preserved in the physiology and genomes of modern descendants of the early cyanobacteria.

The oceanic anoxic event in the Early Toarcian, often referred to as the ‘Torcian Oceanic Anoxic Event’, led to widespread deposition of organic‐rich black shales and geochemical anomalies in elemental distribution and multiple isotope systems in the Early Jurassic ocean. Best characterized by its hallmark carbon isotope anomaly, the event is widely regarded as a prime example of rapid greenhouse warming‐related changes in the Mesozoic Earth system. However, despite numerous studies, details of its forcing mechanisms, exact duration and the role of regional effects remain debated. This article presents new data (high‐resolution organic carbon isotope, calcareous nannofossil and elemental geochemical analyses) from the black shale‐bearing Lower Toarcian section in the Réka Valley, Hungary, with the aim of assessing any regional differences in the sedimentary and geochemical record and their bearing on the underlying oceanographic and climatic processes. Following a short segment with...

The Degree of Pyritization (DOP) and the Indicator of Anoxicity (IA) were used as tools to assess the degree of redox conditions in Lower and Middle Jurassic strata from Bulgaria. Normally-oxygenated (with DOP values < 0.45 and IA values < 0.4), oxygen-restricted (0.45 < DOP < 0.7; 0.4 < IA < 0.5), and oxygen-depleted (DOP > 0.7 and IA > 0.5) bottom-water conditions were recognized on a selection of samples, mainly from the Ozirovo Formation (upper Pliensbachian-Toarcian), but also from the Etropole Formation (lower Bajocian). DOP and IA yielded the highest values (> 0.9 for DOP and > 0.5 for IA) from samples of the lower Toarcian Tenuicostatum and Falciferum ammonite zones, and thus, denoted declined oxygen levels and enrichment of reactive Fe at the sea floor. Beyond this stratigraphic level, both parameters indicated for prevailing normally-oxygenated to oxygen-restricted setting, with limitedly imposed environments beneath stratified water-column.

The Jurassic sequences in Bulgaria include widespread shelf sediments that often contain organicrich strata. The bulk of these rocks comprise dispersed organic components covering a wide range of amount and composition. However, a defined number of stratigraphic intervals correspond to sedimentary rocks with elevated organic carbon contents and denote sedimentary accumulations under oxygen-deficient conditions. The organic-rich shelf deposits of the Lower Jurassic in Bulgaria mainly correspond to the transgressive mudrock lithologies of the Ozirovo Formation. It is known that in these strata the fade of the oxygen bottom deficiency accumulation settings concurs around with the Pliensbachian/Toarcian boundary. It is also known that most of them do not correspond to typical black shale facies, as being relatively coarse-grained and often with scarce organic carbon contents. Both their lithologies and fossil biofacies indicate frequent intervals of seafloor oxygenation (e.g., Sapunov e...

The Degree of Pyritization (DOP) and the Indicator of Anoxicity (IA) were used as tools to assess the degree of redox conditions in Lower and Middle Jurassic strata from Bulgaria. Normally-oxygenated (with DOP values &lt; 0.45 and IA values &lt; 0.4), oxygen-restricted (0.45 &lt; DOP &lt; 0.7; 0.4 &lt; IA &lt; 0.5), and oxygen-depleted (DOP &gt; 0.7 and IA &gt; 0.5) bottom-water conditions were recognized on a selection of samples, mainly from the Ozirovo Formation (upper Pliensbachian–Toarcian), but also from the Etropole Formation (lower Bajocian). DOP and IA yielded the highest values (&gt; 0.9 for DOP and &gt; 0.5 for IA) from samples of the lower Toarcian Tenuicostatum and Falciferum ammonite zones, and thus, denoted declined oxygen levels and enrichment of reactive Fe at the sea floor. Beyond this stratigraphic level, both parameters indicated for prevailing normally-oxygenated to oxygen-restricted setting, with limitedly imposed environments beneath stratified water-column.

Lehmann, Jens / Küchelmann, Hans Christian / Juhl, Frederick / Mutterlose, Jörg (2025): Fossil brachiopods from the Roman site on Mogador Island (Essaouira, Morocco): Implications for past exchange of products. – Journal of Island and Coastal Archaeology
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Abstract:
Archaeological excavations on Mogador Island (Essaouira, Morocco) in 2009 yielded two fossil marine brachiopods found in a refuse layer with Roman finds dated from the first to third century AD (pottery, glass, metal). These fossils originated from marine sediments of the Early Cretaceous age (a geological epoch, about 145–100 million years ago). Four more brachiopods of the same species had previously been found in the 1960s within a Roman building. As the island of Mogador consists entirely of geologically young (about 2 million-year-old) Pleistocene dunes, the provenance of the rachiopods is not of local origin. Geological strata of Cretaceous age are unknown from Mogador. In order to record the source area of the well-preserved brachiopods, the material has been studied in detail. Based on their external morphology and internal structures revealed by serial sectioning, the brachiopods under discussion were identified as Lamellaerhynchia rostriformis. Marine Early Cretaceous sediments containing abundant specimens of this species crop out in the area between Agadir and Essaouira and further to the east. The two fossil brachiopods discussed here most likely came from this area ca. 50 km east-southeast of Mogador. The source rocks for the specimens under discussion can be assigned to the Hauterivian geological period (132–129 million years ago) of the Early Cretaceous, according to the local mass occurrence of L. rostriformis on mainland Morocco. Based on the archaeological evidence associated with the brachiopod fossils we discuss possible modes and reasons for their translocation. We see clear evidence for a purposeful collection and storage of these fossils.

We investigated the paleo-redox change across the Triassic-Jurassic (T-J) boundary (∼200 Ma) and the Early Toarcian oceanic anoxic event (T-OAE; ∼183 Ma) recorded in the Upper Triassic to Lower Jurassic pelagic deep-sea cherts in the Inuyama area, Central Japan. The present 57 Fe Mössbauer spectroscopic analysis for these cherts identified five iron species, i.e., hematite (α-Fe 2 O 3 ), pyrite (FeS 2 ), paramagnetic Fe 3+ , and two paramagnetic Fe 2+ with different quadrupole splittings. The occurrence of hematite and pyrite in deep-sea cherts essentially indicates primary oxidizing and reducing depositional conditions, respectively. The results confirmed that oxidizing conditions persisted in deep-sea across the T-J boundary. In contrast, across the T-OAE, deep-sea environment shifted to reducing conditions. The first appearance of the gray pyrite-bearing chert marked the onset of the deep-sea oxygen-depletion in the middle Pliensbachian, i.e., clearly before the shallow-sea T-OAE.

This report serves as a comprehensive review of relevant legislation, formal regulations, and policies concerning water resources use, water rights, and water ownership in Thailand. Its primary aim is to establish a fundamental understanding of legal and formal water rights systems as an initial step. It is also intended to serve as a supporting document to guide subsequent fieldwork and analysis of water tenure, facilitating a better understanding of the array of relationships, whether legally or customarily defined, between individuals or groups (including Gender Equality and Social Inclusion (GEDSI) analysis) in relation to water resources. The report was conducted through desktop reviews of pertinent land and water laws, policies, and research, along with discussions with water experts. This activity is part of the Asia Pacific Water Scarcity Programme (WSP), initiated by the Food and Agriculture Organization (FAO). The Programme aims to address the impacts of climate change on water resources and strives to bring water usage within sustainable limits, preparing the region for a productive future with reduced water availability. Within this framework, FAO has collaborated with the Australian Water Partnership (AWP) to leverage Australian expertise in supporting national governments to develop policies and processes for inclusive water accounting and allocation in Cambodia, Indonesia, Thailand, and Vietnam.

A climatic, geological and biological global event resulted in sedimentation of black shales at the Cenomanian/Turonian (C/T) boundary, coinciding with the Oceanic Anoxic Event 2 (OAE2) or Bonarelli Event. We present an interdisciplinary analysis of the C/T transition at the Spanish El Chorro section (Betic Cordillera), and show the results of studies on planktic and benthic foraminifera, calcareous nannoplankton, radiolaria and environmental magnetic properties. The planktic foraminiferal biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica and the calcareous nannoplankton biozones NC11, NC12 and NC13 have been recognized. Diversity of the radiolarian assemblages gradually decreases from the upper Cenomanian towards the middle part of the OAE2 interval, where it reaches the lowest values, recovering above the OAE2. Oxygenation of the sea-bottom waters decreased towards the late Cenomanian, as inferred from a decrease in species size of benthic foraminifera 40 cm below the OAE2. Assemblages from the upper part of the section contain abundant and tiny epifaunal, trochospiral species and representatives of Tappanina, Pleurostomella and small buliminids. These data indicate that low oxygen conditions persisted towards the top of the section, 370 cm above the top of the OAE2 black shales.

The version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication 1 State of the Science: Mesozoic climates and oceans -a tribute to Hugh

Operations at Site U1515 consisted of coring a single hole (U1515A) with the rotary core barrel (RCB) system to 517.1 m drilling depth below seafloor (DSF) (Table ). The original plan for this site included coring in three holes and a full suite of wireline logging runs. However, hole conditions were generally poor, precluding logging, and core recovery was low, thus shortening the time spent at this site. Overall, 55 RCB cores were recovered, with 93.62 m recovered of the 517.1 m cored (18.1%). The total time at Site U1515 was

The eastern South Pacific (ESP) oxygen minimum zone (OMZ) is a permanent hydrographic feature located directly off the coasts of northern Chile and Peru. The ESP OMZ reaches from coastal waters out to thousands of kilometers offshore, and can extend from the near surface to depths greater than 700 m. Oxygen minimum zones support unique microbial assemblages and play an important role in marine elemental cycles. We present results from two autonomous profiling floats that provide nine months of time-series data on temperature, salinity, dissolved oxygen, chlorophyll a, and particulate backscattering in the ESP OMZ. We observed consistently elevated backscattering signals within low-oxygen waters, which appear to be the result of enhanced microbial biomass in the OMZ intermediate waters. We also observed secondary chlorophyll a fluorescence maxima within low-oxygen waters when the upper limit of the OMZ penetrated the base of the photic zone. We suggest that autonomous profiling floats are useful tools for monitoring physical dynamics of OMZs and the microbial response to perturbations in these areas.

During the Pliensbachian-Toarcian of Early Jurassic, there is a well-known second order marine extinction that is observable at the species and genus levels. Ammonite diversity data from successions throughout Europe and parts of the Arctic suggest that this extinction may have been multi-phased with diversity declining over six separate intervals. The main-phase of decline begins at the Pliensbachian-Toarcian boundary and extends into the Lower Toarcian, to a level that is correlative with the Tenuicostatum / Serpentinum Zone boundary. To date, only the main-phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups. This multi-phased extinction has been attributed to regional and global controlling mechanisms that are associated with the Volcanic Greenhouse Scenario which links the eruption of the Karoo-Ferrar large igneous province (LIP) to global warming and mass extinction. We compare stratigraphic ranges of ammonite and foraminiferal species in Pliensbachian-Toarcian successions of western North America to the record in Europe and parts of the Arctic in order to test the geographic extent of the multiple phases of extinction. Our results show six intervals of species level decline that correlate with those recognized in Europe: 1) middle of the Lower Pliensbachian (middle Whiteavesi-middle Freboldi Zones), 2) middle of the Upper Pliensbachian (upper Kunae-lower Carlottense Zone), 3) Pliensbachian / Toarcian boundary into the Lower Toarcian (upper Carlottensemiddle Kanense Zones), 4) Middle Toarcian (upper Planulata-lower Crassicosta Zones), 5) upper Middle-lower Upper Toarcian (middle Crassicosta-Hillebrandti Zones) and 6) Upper Toarcian (lower Yakounensis Zone). Recognition of this multi-phased event in three separate ocean basins (paleo Pacific, paleo Arctic, and Tethys Oceans), in at least two taxonomic groups, greatly expands the known geographic extent of this multi-phased event and argues for a controlling mechanism that is global in its reach. In relation to the Volcanic Greenhouse Scenario, our study shows that four of the six pulses of extinction occur within the mainphase of Karoo magmatism. The decline in the Early Pliensbachian, previously thought to be separate from this event, occurs within error range of the onset of Karoo magmatism and the decline in the Late Toarcian coincides with the later stages of magmatism. These observations extend the known duration of this multi-phased extinction event to the Early Pliensbachian and support the Volcanic Greenhouse Scenario, specifically the eruption of the Karoo-Ferrar LIP, as a preeminent factor driving the multi-phased extinction of the Pliensbachian-Toarcian.

We used petrofacies analysis and stable isotope data to interpret the isotopic variations in the marine carbonate succession of the Early Cretaceous Mural Formation of northeastern Sonora (Pitaycachi section), Mexico. The petrographic study reveals a range of lithofacies from bioclastic mudstones to boundstones. Allochems consist of corals, algae, rudists, echinoids, sponge spicules, radiolarians, foraminifera and calpionellids. Samples analyzed for stable isotope are significantly depleted with δ 18 O values of -15.19‰ to -6.32‰ and exhibit positive δ 13 C values ranging from 2.91‰ to 4.39‰. The lack of correlation between δ 13 C and δ 18 O values also supports a primary marine origin for the δ 13 C values of limestones from the Pitaycachi section. In the δ 13 C profile, the Cánova Member shows an upward increasing trend from 3.09‰ to 4.36‰ interpreted to indicate an increase in the rate of marine organic production and/or organic burial in the basin during early Albian time. The abrupt increase in carbon isotope values in the lower part of the section correlates with OAE1b. The shape of the C-isotope curve of the present study is similar to other C-isotope curves from Mexico and other continents (e.g., Vacontian basin, France) indicating that OAE1b may have been global in extent.

Our contribution presents an integrated litho-, bio-and chemostratigraphic study of the bestpreserved outcrops of the post-Urgonian marly cover (A 1 unit) of the North Provence carbonate platform. The study of the rich ammonite fauna from the Apt-Gargas area (SE Vaucluse) confirms that the A 1 unit is older than previously assumed and dated to the upper (but non-uppermost) part of the lower Aptian Deshayesites forbesi Zone of the Mediterranean standard zonation. This interval is assigned to the lower part of the Roloboceras hambrovi Subzone as defined in the present contribution which is time equivalent to the spreading of the OAE 1a. Microfossil occurrences previously documented in the A 1 unit are consistent with our ammonite-age calibration. Unfortunately, the curves of the carbon and oxygen stable isotopes exhibit a correlative signal probably caused by an early diagenetic overprint which questions the previous use of the C-isotope signal for precise chronostratigraphic correlation with respect to the OAE 1a excursion. The top of the A 1 unit is marked by a burrowed firmground locally infilled and capped by glauconite-rich sandy marls which grade into the blue-grey muddy marls of the overlying A 2 unit. The hiatus associated to this discontinuity is equivalent to the culmination of the OAE 1a, including the uppermost D. forbesi Zone (= upper R. hambrovi Subzone as herein defined) and the lower D. deshayesi Zone. The revised calibration of the post-Urgonian marl imply that the ammonite-age calibration of the North Provence carbonate platform should be revised and questions the timing and driving mechanisms of its stepwise demise.

Crude Petroleum" as it occurs in nature, is mainly a mixture of hydrocarbons belonging to the paraffin, benzene and naphthene series. Some varieties are viscous solids, some are liquid and . others are gaseous. The great oil-fields of the world occur commonly in shallow water marine sediments. The exact nature of the original material which by slow distillation has given rise to the oil is a matter of dispute: land-plant residues, marine algae, phyto-plankton and remains of marine animals have been suggested. For the preservation of these, deficiency of oxygen at the site of deposition may be important. That which distinguishes petroleum from other sedimentary rocks is its powers of migration from the rocks in which it was formed to "reservoir rocks". these, by reason of their open texture afford storage room. Such rocks are sandstones and cellular limestones. Where these rocks are covered and sealed by relatively impervious beds such as shales, the petroleum may accumulate under great pressure due to the buoyant effect of ground water. When the covering rocks are pierced by the drill, the petroleum may rise to the surface. Channels of escape such as joints, faults, or the oil-bearing stratum itself at its outcrop, may be impregnated with solid bitumen representing the residue of the petroleum from which the lighter fractions have evaporated.

Environmental analysis of offshore shale members of Upper Pennsylvanian Midcontinent cyclothems was undertaken using a combination of high-resolution X-radiography, petrography, and geochemical analyses. A hierarchical sampling strategy permitted investigation of (1) broad stratigraphic and geographic patterns of compositional variation through analysis of three shale members (Hushpuckney, Stark, and Muncie Creek) in five cores along a proximality gradient, and (2) fine stratigraphic variation within each study unit through continuous cm-scale sampling of dmthick compositional cycles. Offshore shales consist of (1) three major non-clastic components, i.e., organic carbon, Fe-sulfide, and phosphate, which can be effectively proxied by TC, TS, and P 2 O 5 , respectively, and (2) a clay-mineral matrix composed predominantly of illite and smectite (or mixedlayer I/S), the relative proportions of which can be proxied by Al 2 O 3 /SiO 2 ratios. Spatio-temporal variation in sediment fluxes permitted identification of two clastic components: (1) a southernderived smectite-rich component associated with high concentrations of inertinite, and (2) a northern-derived illite-rich component associated with high concentrations of vitrinite. Strong covariation between the flux of the illitic component and TOC concentrations implies control of sediment composition by an organic dilution process associated with variable influx of low-salinity surfacewaters from continental areas to the north or northeast. Cm-scale correlation within each offshore shale member across the 150-200-km-long study area based on (1) alternating dm-thick high-TOC and low-TOC layers and (2) systematic upsection changes in phosphate layer character (from thin laminae to large nodules to diaclasts and wispy laminae) demonstrated an absence of intraformational erosion and winnowing, suggesting widely uniform sub-pycnocline conditions and a lack of strong bottom currents. Authigenic phosphate ( ) is concentrated at a fine scale along the upper and lower contacts of high-TOC layers, and (2) mirrors broad spatio-temporal patterns of variation in bottomwater anoxia; these observations suggest control of phosphate formation by a combination of slow sedimentation rates, permitting downward diffusion of seawater PO 4 3-and slow nodule growth, and low but fluctuating bottomwater oxygen levels (e.g., ca. 0.1-0.2 ml O 2 l -1 H 2 O), permitting retention of PO 4 3-through redox cycling of iron oxyhydroxides. These observations favor a model for the Late Pennsylvanian Midcontinent Seaway of starved sedimentation under a strong proximal halocline that was subject to fluctuations at timescales associated with the deposition of dm-thick compositional cycles; upwelling intensity was weak and evidence for upwelling-enhanced primary productivity is lacking.

Profiles of Mo/total organic carbon (TOC) through the Lower Toarcian black shales of the Cleveland Basin, Yorkshire, United Kingdom, and the Posidonia shale of Germany and Switzerland reveal water mass restriction during the interval from late tenuicostatum Zone times to early bifrons Zone times, times which include that of the putative Early Toarcian oceanic anoxic event. The degree of restriction is revealed by crossplots of Mo and TOC concentrations for the Cleveland Basin, which define two linear arrays with regression slopes (ppm/%) of 0.5 and 17. The slope of 0.5 applies to sediment from the upper semicelatum and exaratum Subzones. This value, which is one tenth of that for modern sediments from the Black Sea (Mo/TOC regression slope 4.5), reveals that water mass restriction during this interval was around 10 times more severe than in the modern Black Sea; the renewal frequency of the water mass was between 4 and 40 ka. The Mo/TOC regression slope of 17 applies to the overlying falciferum and commune subzones: the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years. The more restricted of the two intervals has been termed the Early Toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to NW Europe. Crossplots of Re, Os, and Mo against TOC show similar trends of increasing element concentration with increase in TOC but with differing slopes. Together with modeling of 187 Os/ 188 Os and d 98 Mo, the element/TOC trends show that drawdown of Re, Os, and Mo was essentially complete during upper semicelatum and exaratum Subzone times (Mo/TOC regression slope of 0.5). Drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of Re, Os, and Mo, via a low-salinity surface layer, created isotopic excursions of up to 1.3% in d 98 Mo and up to 0.6% for 187 Os/ 188 Os. Restriction thereby compromises attempts to date Toarcian black shales, and possibly all black shales, using Re-Os chronology and introduces a confounding influence in the attempts to use d 98 Mo and initial 187 Os/ 188 Os for palaeo-oceanographic interpretation.

ABSTRACT: Microfossils from Cretaceous coal-bearing strata can be used to establish key stratigraphic surfaces that mark marine flooding events with intermediate-frequency (fourth-order) and high-frequency (fifth-order) periodicities. We document several examples of this cyclicity from the transgressive and regressive facies at the land–sea transition of the Greenhorn Marine Cycle on the Colorado Plateau. Estuarine strata from the upper Cenomanian Dakota and middle Turonian Straight Cliffs Formations yield four primary fossil assemblages: Assemblage A, the lagoonal assemblage, comprising a rich agglutinated foraminiferal population of Trochammina and Verneuilinoides and brackish ostracodes and molluscs in a skeletal shell accumulation; Assemblage B, the proximal estuarine assemblage, comprising the brackish ostracode Fossocytheridea, charophytes, and smooth admetopsid gastropods within bituminous coal zones giving rise to distal estuary with the addition of brackish gastropods and s...

The Cenomanian/Turonian boundary interval (CTBI) at Site 1050 (30؇6N, 76؇14W) was investigated to characterize climatic and oceanographic changes during the Oceanic Anoxic Event that was associated with it (OAE 2). Because of unusually good foraminiferal preservation for sediments of this age, we have obtained an unaltered oxygen and carbon isotope profile and an accompanying record of planktic and benthic foraminifer abundance changes across the OAE 2 interval. Biostratigraphic, sedimentologic, and chemostratigraphic analyses indicate that more than 0.5 m.y. between the onset and tail end of OAE 2 are missing. This explains why organicrich sediments are absent from the Site 1050 sequence and why the planktic and benthic carbon isotope shifts are minor (ϳ0.8‰) compared with the most complete OAE 2 sections. While planktic species diversity shows relatively minor change across the OAE 2 interval, extinction of the rotaliporids and Globigerinelloides bentonensis, a shift to Heterohelix-dominated assemblages, and increased abundance of helvetoglobotruncanids at the onset of OAE 2 cause a dramatic change in the planktic foraminifer assemblage composition. The rotaliporid extinction occurs at the level where middle bathyal temperatures are estimated to have increased from 15 to 19؇C, which is warmer than any other time during the Cretaceous and Cenozoic. This deep water warming may have caused a breakdown in the vertical structure of the water column, and could explain the extinction of deeper dwelling planktic species, including Rotalipora and G. bentonensis. On the other hand, sea surface temperature estimates based on planktic foraminiferal ␦ 18 O values (corrected for salinity) remain steady throughout the CTBI, varying between 23 to 26؇C. The presence of volcaniclastic sediments within the OAE 2 interval at Site 1050 is consistent with previous suggestions that the CTBI was a time of anonymously high rates of CO 2 flux into the atmosphere and oceans during a major phase of explosive volcanic activity and large igneous province emplacement in the Caribbean and other regions worldwide. Further investigation of the CTBI is needed to establish whether increased pCO 2 can be accepted as the primary forcing mechanism for the middle Cretaceous ''supergreenhouse''.

Organic biomarkers were used to investigate the infl uence of seasonal changes in oxygenation and water chemistry on the distribution of archaea and bacteria in the water column and surface sediments of the continental shelf off central Chile (ca. 36°S), an area infl uenced by seasonal upwelling and the development of an oxygen minimum zone. We were interested in establishing if occurrence of archaea and bacteria responds to oxygenation and water chemistry for which we analyzed archaeal isoprenoid (i) and bacterial branched (br) glycerol dialkyl glycerol tetraethers (GDGTs). Our results combined with molecular data from a year round observational program at the same sampling site and depths indicatives the occurrence and dominance of the marine pelagic group Thaumarchaeota. Changes in the distribution of iGDGTs might be explained by (i) the presence of archaeal populations in sub-oxic waters, phylogenetically different from those in surface water, (ii) changes in the relative contribution of Euryarchaeota with depth, and (iii) a relationship between Thaumarchaeota and environmental factors other than temperature. Branched GDGTs were more abundant in the upper, oxic layer during the non-upwelling season, may be a result of higher river runoff, whereas their diversity was higher within sub-oxic waters. Our results indicate a vertical segregation of iGDGTs and brGDGTs, with predominance of archaeal biomarkers during the low productivity season.

The Corg:P ratios of organic-rich facies (TOCN1%) exhibit considerable variation through the Phanerozoic, from b10:1 in the Permian Phosphoria Formation to N1000:1 in some Devonian black shales. Relative to the composition of phytoplankton (C:P ∼106:1), which provide the bulk of organic C and P to organic-rich marine sediments, the range of Phanerozoic sedimentary Corg:P ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of C and P remobilization. Enhanced preservation of organic C at lower redox potentials combined with enhanced sedimentary retention of remineralized organic P at higher redox potentials results in a strong relationship between benthic redox conditions and sedimentary Corg:P ratios. The strong secular coherence of the Phanerozoic Corg:P record (i.e., limited variation within narrow time slices) suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale, such as atmospher...

Ancient black shales have considerable potential for generation of long, high-resolution paleoclimate proxy records, given the availability of a geochemical proxy that can be easily measured. Owing to substantial differences in density between the siliciclastic matrix of black shales (2.6-2.7 g cm-) and the major non-clastic components, i.e., organic carbon, Fe-sulfide, and phosphate (ca. 1.0-1.2, 5.1-5.2, and 3.1-3.2 g cm-, respectively), rock density may represent a suitable proxy. This paper presents a new procedure for rapid analysis of fine-scale compositional variation in black shales, using X-radiography as a primary tool for measurement of rock density. The procedure entails (1) generation of X-radiographs over the complete stratigraphic interval of interest in laminated black shale cores, (2) geochemical and petrographic analysis of limited intervals within the cores to quantify variance in major rock components, and (3) statistical analysis of compositional controls on var...

Sedimentary molybdenum, [Mo]s, has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic‐rich marine facies deposited under oxygen‐depleted conditions. A detailed analysis of [Mo]s–total organic carbon (TOC) covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that (1) [Mo]s, while useful in distinguishing oxic from anoxic facies, is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and (2) patterns of [Mo]s‐TOC covariation can provide information about paleohydrographic conditions, especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal. These inferences are based on data from four anoxic silled basins (the Black Sea, Framvaren Fjord, Cariaco Basin, and Saanich Inlet) and one upwelling zone (the Namibian Shelf), representing a spectrum of aqueous chemical condit...

The~90% biodiversity loss among marine invertebrate species during the end-Permian mass extinction, the most severe Phanerozoic biocrisis, has been attributed to widespread oceanic anoxia ("superanoxia"). Recent studies of the lithofacies, inorganic geochemistry, and biomarkers of Permian-Triassic boundary (PTB) sections have yielded an inferred pattern of oceanic redox changes that is complex and sometimes inconsistent. In this contribution, we review the ecology of radiolarians, an important microzooplankton group during the Permo-Triassic transition, and consider its implications for contemporaneous changes in paleoceanographic conditions. Our analysis shows that (1) Late Permian radiolarian faunas were cosmopolitan with different orders having specific depth preferences, i.e., albaillellarians favoring deeper waters and spherical forms (entactinarians and spumellarians) shallower waters; (2) deep-water taxa declined earlier than shallow-water taxa; (3) many Paleozoic-type taxa survived into the Early Triassic but went extinct during a second crisis in the Dienerian ("dead clade walking"), followed by the appearance or expansion of Mesozoic-type taxa during the Olenekian; and (4) the survival of Paleozoic-type taxa during the Early Triassic was greater at higher paleolatitudes than in the tropics. These observations are consistent with a first-order redox control on radiolarian faunal distributions, specifically a shallowing and poleward expansion of the oceanic oxygen-minimum zone during the PTB crisis. The consequent adaptation of some deepwater taxa to shallower environments resulted in Early Triassic radiolarian faunas in continental basins becoming more similar to those in pelagic settings. Enhanced survival of Paleozoic-type taxa in high-latitude regions indicates that the main stressor on Permo-Triassic radiolarian communities was reduced oceanic oxygen levels (stronger in the tropics) rather than climatic warming (stronger at the poles).

The boundary conditions and environmental characteristics conducive to widespread benthic anoxia in ancient epeiric seas are not well understood, in part due to a paucity of modern analogues. Three modern epicontinental seas (Hudson Bay, Baltic Sea and Gulf of Carpentaria) are examined with the goal of identifying key factors that contribute to the development of water-column stratification and deep-water oxygen depletion in such systems. The insights gained are applied to an analysis of the North American Late Pennsylvanian Mid-continent Sea (LPMS), an ancient epicontinental sea that developed sulfidic bottomwaters over a large area (~10 6 km 2) during a series of glacioeustatic highstands. None of the modern epicontinental seas is a good analogue for the LPMS. The Gulf of Carpentaria, located at low latitudes in proximity to an active orogen subject to monsoonal precipitation, is closest to the LPMS in terms of geographic, tectonic and climatic boundary conditions, but its bottom-waters are well oxygenated owing to strong tidal mixing and anti-estuarine circulation. Hudson Bay is closest to the LPMS in terms of size, but diminished primary productivity at higher latitudes and lateral advection of oxygenated deep-waters inhibit development of benthic anoxia. The Baltic Sea is closest to the LPMS in terms of benthic redox conditions, with sulfidic bottom-waters over ~15% of its area, but its redox status is dependent on shallow marginal sills (<30 m) limiting deep-water renewal and on rates of primary productivity (120-240 g C m-2 y-1) sufficient to deplete bottom-water of dissolved oxygen. By contrast, the LPMS seafloor was widely anoxic despite marginal sill(s) too deep (>100 m) to restrict renewal of the subpycnoclinal watermass and levels of primary productivity (<21 g C m-2 y-1) insufficient to impose a high respiratory oxygen demand. Although the LPMS shares certain important boundary conditions with the modern Baltic Sea (e.g., a humid climate and largely landlocked setting), while necessary were insufficient factors for the development of widespread

The Hushpuckney Shale Member of the Swope Formation (Missourian Stage, eastern Kansas) is the core shale of a Kansastype cyclothem, formed during the late transgressive to early regressive phases of a Late Pennsylvanian glacio-eustatic cycle. Coeval high-frequency climato-environmental dynamics of the Midcontinent Seaway are preserved in the KGS Orville Edmonds No. 1A study core as centimeter-scale variation in major components (organic carbon, authigenic sulfides and phosphate, detrital siliciclastics), organic macerals, trace-element redox proxies (Mo, U, V, Zn), and ichnofabric features. Benthic O 2 levels declined sharply from the base of the black shale (0 cm), went sulfidic at f4 cm, and reached a redox minimum at f21 cm; above this level, redox potential gradually rose, fluctuating between sulfidic and nonsulfidic conditions from f35 cm to the black shale/gray shale contact at 52 cm. Onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft-bodied organisms comprised of deep-tiered tracemakers tolerant of low-O 2 conditions (Trichichnus), and shallow-tiered tracemakers favoring ''soupground'' (Helminthopsis) or ''firmground'' substrates (the Zoophycos-Phycosiphon-Schaubcylindrichnus-Planolites association). Most geochemical records exhibit a ''low-order'' cycle spanning the full 52 cm thickness of the black shale submember, reflecting a dominant glacio-eustatic control. The base and top of the black shale submember record lateral migration of the pycnocline across the Midcontinent Shelf during the transgressive and regressive phases, respectively. The maximum flooding surface (MFS) is at f17-23 cm, an interval containing the euxinic peak and characterized by high concentrations of illite (representing a cratonic siliciclastic flux) and terrestrial organic macerals, the product of transient increases in humidity, weathering rates, and the export of coal-swamp vegetation associated with the interglacial highstand of the Swope cyclothem. Although a transgressive ''surface of maximum starvation'' (SMS) cannot be confidently identified, a phosphate-rich ''regressive condensation surface'' at f28-34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth; a correlative shift in dominance from terrestrial-to marine-derived organic macerals reflects increased upwelling of nutrient-rich deepwaters and enhanced primary productivity. Penecontemporaneous paleogeographic and-climatic factors (e.g., semirestricted circulation, monsoonal precipitation) predisposed the Midcontinent Seaway toward sensitivity to high-frequency climato

This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Contents 1 Background and objectives 2 Operations 5 Lithostratigraphy 10 Biostratigraphy and micropaleontology 17 Paleomagnetism 24 Petrophysics 29 Geochemistry 33 Stratigraphic correlation 35 References

Cenomanian through Campanian strata of the Kaiparowits Basin in south-central Utah record the eastward migration of the Western Interior foredeep axis as the Sevier Thrust Belt approached from the west. Four, mostly conformable, depositional sequences were produced. With the exception of the lowest sequence, each is divided into four parts distinguishable on the basis of alluvial architecture. Together, the upper three sequences make up a nearly 2 km-thick succession comprised almost exclusively of fluvial deposits. At the base of each of these sequences are relatively thin, restricted sandstone sheets that grade both laterally and vertically into fine-grained deposits. Next are thick intervals of predominantly fine-grained material containing scattered lenses and thin sheets of sandstone. These intervals grade upward into extensive multistoried sandstone sheets that contain very little fine-grained material. Sequences are capped by laterally extensive multistory sheets of gravely s...

The analysed 70 m of the uppermost Albian-Cenomanian sediments at El Djehaf outcrop, northern Tunisia, shows the occurrence of an oscillation between black to grey organic-rich pelagic limestones-black laminated limestones and organic-poor light grey limestones. The CaCO 3 contents range between 77 and 97% (X-ray analysis). A punctual biostratigraphic investigation based on the first occurrence (FO) of the Rotalipora Globotruncanoides and its associated species defines the beginning of the Cenomanian. Geochemically, the black laminated limestones (U 1 and U 3 of Mouelha Member) mark the highest TOC content reaching 9.07%. These levels are inferred as very good oil-prone (type II/III) mature source rock which was deposited in an anoxic environment. The mineralogical (XRD) and geochemical characteristics suggest a good play for conventional and unconventional resources. Furthermore, based on TOC data, facies characteristics constrained by biozonation, the section can be correlated to that of "Monte Petrano" in Italy. This study underlined the OAE1d event in the El Djehaf section and reconfirms its occurrence as a global anoxic event. Albian-Cenomanian boundary El Djehaf section OAE1d event • Sedimentology • TOC • Correlation

Cedar and Parowan Canyons are incised into the western margin of the Markagunt Plateau (figure 1) at the transition between the Basin and Range and the Colorado Plateau. This area was also transitional in the Cretaceous when sediments were being shed from the Sevier orogenic belt a short distance to the west and epicontinental seaways were flooding in from the east. The region underwent high rates of subsidence during much of the Late Cretaceous (Cenomanian-Campanian?) with renewed subsidence in the Paleocene and ...

The Aptian was characterized by dramatic tectonic, oceanographic, climatic and biotic changes and its record is punctuated by Oceanic Anoxic Events (OAEs). The timing and duration of these events are still contentious, particularly the age of the Barremian-Aptian boundary. This study presents a cyclostratigraphic evaluation of a high-resolution multiproxy dataset (δ13C, δ18O, MS and ARM) from the Poggio le Guaine core. The identification of Milankovitch-band imprints allowed us to construct a 405-kyr astronomically-tuned age model that provides new constraints for the Aptian climato-chronostratigraphic framework. Based on the astronomical tuning, we propose: (i) a timespan of ~7.2 Myr for the Aptian; (ii) a timespan of ~420 kyr for the magnetic polarity Chron M0r and an age of ~120.2 Ma for the Barremian−Aptian boundary; and (iii) new age constraints on the onset and duration of Aptian OAEs and the ‘cold snap’. The new framework significantly impacts the Early Cretaceous geological ...

Reçu le 2 octobre 2002 ; accepté le 18 mars 2003 Résumé Les auteurs décrivent plusieurs coupes de Calcaires urgoniens représentatives du Jura plissé et des Chaînes subalpines septentrionales (Bornes, Aravis). Les nouvelles données acquises sur une transversale d'une centaine de km, orientée NW-SE et passant par Genève, sont essentiellement basées sur l'étude des orbitolinidés, et dans une moindre mesure sur les échinides et sur les ammonites, ainsi que sur la stratigraphie séquentielle. Elles permettent d'illustrer la progradation de la plate-forme urgonienne, qui débute à l'Hauterivien inférieur terminal dans le Jura plissé et n'atteint la chaîne des Aravis qu'au Barrémien inférieur, et ainsi de proposer un modèle dynamique d'installation et d'évolution d'une plate-forme carbonatée dans l'espace et dans le temps.

Iron-rich rocks of Orosirian Period in the Chilpi Group on the northern margin of the Bastar Craton, Central India, contain an association of hematite-magnetite-greenalite-chamosite-quartz in oxide-silicate facies. Additionally chert (quartz) and siderite occur in chert and carbonate facies. Presence of these mineral assemblages was investigated to infer the redox state of the depositional basin. The results have indicated formation temperature variation of 116-255 °C (average 198 °C) and log P (O2) between-37 and-60 (average-44). A ferruginous state of the shallow water depositional environment, having oxygen content of 10-2 to 10-5 times the present atmospheric level, is inferred. The variations in composition of greenalite-chamosite association indicate development of the mineral phases from the reaction involving kaolinite-illite and magnetite-siderite as end-members. Thermodynamic requirements for the formation of the rare association of magnetite-greenalite-cronstedtite indicate the precipitation of the mineral phases from seawater with enhanced activities of Fe 2+ , Al, Si, Mg and C compared to the level in the present day seawater. The results indicate a steep fall in the atmospheric oxygen content immediately after the Great Oxidation Event of 2400-2000 Ma.

Cesium-137 and cobalt-60 are major radionuclides detected in various categories of radioactive waste streams generated due to the peaceful applications of nuclear technology in our life. Both are γ emitters. Cs-137(γ= 0.662 MEV) is extremely soluble alkaline, highly radiotoxic and long lived element with half-life of 30.5 years. Co-60(T 1/2 = 5.25 years) has two gamma energy peaks at 1.17 and 1.33 MEV. The two radioisotopes reported to have immense applications in medicine, industry, agriculture, research and others. Hence, the generated liquid waste streams spiked with 137 Cs and /or 60 Co need adequate treatment before their release to the environment. During recent years biosorption has gained imperative credibility because of its good performance and low cost. The present work puts forward an effective green chemistry approach to radioactive liquid waste treatment. Spent Black Tea leaves (the dregs), (SBT), have been used as biosorbent for removal of these two radionuclides from...

The use of molybdenum isotope data (δ 98 Mo) from organic-rich shales to draw inferences concerning marine paleoredox conditions at a global scale is predicated upon the assumptions of (1) a residence time of Mo in seawater much greater than the ocean mixing time, and (2) quantitative removal of Mo from a strongly euxinic ([H 2 S] aq > 11 μM) water column to the sediment, thus preserving the seawater δ 98 Mo signature. In this study we analyze Mo isotopic variation in the Hushpuckney Shale, a 73-cm-thick unit representing the late transgressive to early regressive stages of a glacio-eustatic cyclothem (Swope Formation) deposited in the Late Pennsylvanian Midcontinent Sea (LPMS) of North America. The Hushpuckney can be subdivided into four stratigraphic zones of distinctive geochemical character. Zones I and III, which accumulated under weakly euxinic conditions, acquired relatively high δ 98 Mo values (+0.9 to +1.1‰), whereas Zone II, which accumulated under intensely euxinic conditions, acquired lower δ 98 Mo values (~+0.6‰). Zone IV, which accumulated under suboxic conditions in the water column, acquired the heaviest δ 98 Mo values (+1.1 to + 1.8‰). These results contrast with the pattern of redox-δ 98 Mo covariation in modern marine environments, in which the heaviest δ 98 Mo values are found in the most intensely euxinic facies. We evaluate three different hypotheses to account for the Mo isotopic patterns of the Hushpuckney Shale. One hypothesis, seawater-freshwater mixing, is rejected owing to isotopic mass balance considerations. A second hypothesis is a local control on δ 98 Mo by water-column redox cycling of Mn, with particulate Mnoxyhydroxides adsorbing isotopically light Mo and transferring it to the sediment, a process that was most active during deposition of Zone II. The significance of this scenario is that euxinic black shales may not reliably record global seawater δ 98 Mo in areas where a Mn-particulate shuttle is operative. A third hypothesis is based on rapid secular variation of the Mo isotope composition of Late Pennsylvanian global seawater. In order to account for δ 98 Mo trends within the Hushpuckney Shale, seawater δ 98 Mo must have varied by~1.2‰ at a~100-kyr timescale, which would have been possible only if the residence time of Mo in Late Pennsylvanian seawater was b 100 kyr. Although both the second and third hypotheses are viable based on the present limited δ 98 Mo dataset, we discuss how each model might be tested through additional Mo isotope data.

Delta-13-carbon and delta-I8,-oxygen values are recorded in brachiopod shell material covering the almost complete succession of the epicontinental Oxfordian in Central Poland. A positive intercorrelation of the carbon and oxygen isotope curves is recognized. The high carbon isotopic ratio suggests the Oxfordian was a time of overfed ocean conditions in the study area, when put in terms of the overfed-to-hungry ocean fluctuation model. In the Upper Oxfotdian,precisely in the Bimammatum and the lower Planula Zones, a distinct discrepancy in the magnitude of the carbon and oxygen isotopic shifts is correlated with two invasions of the Boreal fauna, ailcl hence possible inflows of less saline waters from the hydrochemicalIy distinctive Boteal Realm.