The late Cenomanian event in eastern England

The Cenomanian/Turonian boundary event has been fully documented from a series of localities between Flamborough Head in Humberside and Marham in Norfolk. The carbon isotope excursion can be identified and extrapolated to all the studied sections using bed‐by‐bed correlation. Evidence from studies of the isotope data, trace element geochemistry, and the micropalaeontology are presented. The famous “Black Band” is seen to change laterally into a “red” horizon and then a “green” horizon when traced southwards. This appears to represent the “feather‐edge” of the anoxic event when traced towards a palaeo‐high which is located in the region of the Wash. All the events, so‐identified, can be correlated with the A. plenus Marl succession in southern England.     

The demise of the rudist-bearing carbonate platforms at the Cenomanian/Turonian boundary: a global control

The demise of the rudist-bearing carbonate blatforms at the Cenomanian/Turonian boundary is tudied in different ways through examples from the Vestern Mediterranean Province. During the Late Cenonanian, North and South Tethyan carbonate platforms xtened widely and were subjected to different climatic and oceanographic conditions. The onset of the demise of the carbonate platforms occurred during Upper Arphaeocretacea and Helvetica biozone times and was boeval with the Global Oceanic Anoxic Event (OAE₂). A major biologic turnover affected the benthic organisms i.e. rudists and large foraminifera. The rudists underwent a severe extinction event, leading to the disappearance of the dominantly aragonite secreting rudists, while the dominantly calcitic forms were less affected. The major development of the carbonate platforms occurred during the Latest Cenomanian — Earliest Turonian, involving a transgressive highstand system tract and a keep-up carbonate organization. During the Early Turonian the carbonate sedimentation was disturbed; hard-grounds, condensed beds, terrigenous inputs developed and a gap in the carbonate platform deposition occurred. A combination of several sequentially linked factors, could explain the demise of the carbonate platform and the major change on the benthic ecosystem at the Cenomanian-Turonian boundary.     

Sediment dynamics during the Cenomanian-Turonian (cretaceous) oceanic anoxic event in Northwestern Germany

Summary The epicontinental pelagic to hemipelagic Upper Cenomanian and Lower Turonian successons of the Lower Saxony Basin (northwestern Germany) are represented by the Rotpl?ner facies on swells (multicolored marls and marly limestones) and the basinal Black Shales facies (marly limestones (Turbidites), black shales) in the local basins. Facies units are described with their lateral and vertical variation from both depositional environments and their correlation is discussed. The distinct Cenomanian-Turonian boundary facies is due to dilution of pelagic carbonate by siliciclastic material, volcanic ashfall, and substantial changes in carbonate, sedimentation rates by about an order of magnitude. The observed sediment geometries origin from preservation of sediments in areas where normal faults occur and erosion of the formerly deposited units in unfaulted areas (preservation of relicts). Erosion and redeposition on swells occurs in thin (<50 cm thick) debris flow and mud flow channels (1–100 m wide), sheet flows, and by turbidity currents. During the Upper Cenomanian the sediment transport is governed by gravity flow which is increasingly superimposed by storm deposition during the Lower Turonian. Lense-shaped tempestites (probably below average storm wave base) occur at the base of the Turonian (entry ofMytiloides hattini) in morphologically highest swell positions and migrate across the entire basin until the late Lower Turonian. The basinal facies is characterised by laminated and biotrubated black shales and mud turbidites that vary over short distances. Laminae show graded bedding and erosive contacts and were deposited by turbidity currents. Intercalated marly limestones are mud turbidities (some mudflows) that are coarsening upwards until the early Lower Turonian. Larger slides occurred predominantly in the late Upper Cenomanian. The sediment distribution is closely related to sea level changes and reflects short- and long-term fluctuations generating comparable stratigraphic trend in the sections, although basin and swell facies are always clearly distinguished. Lokal basin margins (e.g. primary fordeeps of sal domes) were probably limited by larger normal faults that prevented facies gradation between both depositional environments.     

Disentangling the long‐term effects of disturbance on soil biogeochemistry in a wet tropical forest ecosystem

Climate change is increasing the intensity of severe tropical storms and cyclones (also referred to as hurricanes or typhoons), with major implications for tropical forest structure and function. These changes in disturbance regime are likely to play an important role in regulating ecosystem carbon (C) and nutrient dynamics in tropical and subtropical forests. Canopy opening and debris deposition resulting from severe storms have complex and interacting effects on ecosystem biogeochemistry. Disentangling these complex effects will be critical to better understand the long‐term implications of climate change on ecosystem C and nutrient dynamics. In this study, we used a well‐replicated, long‐term (10 years) canopy and debris manipulation experiment in a wet tropical forest to determine the separate and combined effects of canopy opening and debris deposition on soil C and nutrients throughout the soil profile (1 m). Debris deposition alone resulted in higher soil C and N concentrations, both at the surface (0–10 cm) and at depth (50–80 cm). Concentrations of NaOH‐organic P also increased significantly in the debris deposition only treatment (20–90 cm depth), as did NaOH‐total P (20–50 cm depth). Canopy opening, both with and without debris deposition, significantly increased NaOH‐inorganic P concentrations from 70 to 90 cm depth. Soil iron concentrations were a strong predictor of both C and P patterns throughout the soil profile. Our results demonstrate that both surface‐ and subsoils have the potential to significantly increase C and nutrient storage a decade after the sudden deposition of disturbance‐related organic debris. Our results also show that these effects may be partially offset by rapid decomposition and decreases in litterfall associated with canopy opening. The significant effects of debris deposition on soil C and nutrient concentrations at depth (>50 cm), suggest that deep soils are more dynamic than previously believed, and can serve as sinks of C and nutrients derived from disturbance‐induced pulses of organic matter inputs.     

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate–carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and an absence of organic biomarker fingerprints for those organisms, suggesting low diversity and relatively small populations compared to the Neoproterozoic era. Nevertheless, the search for diagnostic biomarkers has not been performed with guidance from paleoenvironmental redox constrains from inorganic geochemistry that should reveal the facies that were most likely hospitable to these organisms. Siltstones and shales obtained from drill core of the ca. 1.3–1.4 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid‐Proterozoic redox landscape. The group is well dated and minimally metamorphosed (of oil window maturity), and previous geochemical data suggest a relatively strong connection to the open ocean compared to other mid‐Proterozoic records. Here, we present one of the first integrated investigations of Mesoproterozoic biomarker records performed in parallel with established inorganic redox proxy indicators. Results reveal a temporally variable paleoredox structure through the Velkerri Formation as gauged from iron mineral speciation and trace‐metal geochemistry, vacillating between oxic and anoxic. Our combined lipid biomarker and inorganic geochemical records indicate at least episodic euxinic conditions sustained predominantly below the photic zone during the deposition of organic‐rich shales found in the middle Velkerri Formation. The most striking result is an absence of eukaryotic steranes (4‐desmethylsteranes) and only traces of gammacerane in some samples—despite our search across oxic, as well as anoxic, facies that should favor eukaryotic habitability and in low maturity rocks that allow the preservation of biomarker alkanes. The dearth of Mesoproterozoic eukaryotic sterane biomarkers, even within the more oxic facies, is somewhat surprising but suggests that controls such as the long‐term nutrient balance and other environmental factors may have throttled the abundances and diversity of early eukaryotic life relative to bacteria within marine microbial communities. Given that molecular clocks predict that sterol synthesis evolved early in eukaryotic history, and (bacterial) fossil steroids have been found previously in 1.64 Ga rocks, then a very low environmental abundance of eukaryotes relative to bacteria is our preferred explanation for the lack of regular steranes and only traces of gammacerane in a few samples. It is also possible that early eukaryotes adapted to Mesoproterozoic marine environments did not make abundant steroid lipids or tetrahymanol in their cell membranes.     

More rapid shift to a benthic niche in larger Gadus morhua juveniles

Trophic use by Atlantic cod Gadus morhua juveniles was examined early and late in the shift from pelagic to benthic habitats. Changes in the proportion of pelagic copepods, estimates of benthic prey indicated by isotope mixing models and stable‐isotope values between sample periods suggested a gradual shift towards a benthic niche. Values of the trophic proxies, however, changed most markedly in the largest juvenile group, suggesting a more rapid trophic niche shift, and in turn competitive advantage, of larger juveniles.     

Light and nutrients regulate energy transfer through benthic and pelagic food chains

The amount of energy flowing to top trophic levels depends on primary production and the efficiency at which it is converted to production at each trophic level. In aquatic systems, algal production is often limited by light and nutrients, and the nutritional quality of algae depends on the relative balance of these two resources. In this study, we used a mesocosm experiment to examine how light and nutrient variation affected food chain efficiency (FCE, defined as the proportion of primary production converted to top trophic level production), using a food web with benthic and pelagic food chains. We also related variation in benthic and pelagic efficiencies to the nutritional quality of primary producers, i.e. carbon:nitrogen:phosphorus stoichiometry. As predicted, pelagic and benthic FCEs were highest under low light/high nutrient conditions, the treatment with the best algal food quality, i.e. the lowest C:nutrient ratios. Pelagic FCE and pelagic herbivore efficiency (HE_P) were more responsive than benthic FCE to variation in light and nutrients. Furthermore, pelagic FCE and HE_P were highly correlated with algal C:P, suggesting ‘carryover effects’ of algal food quality on carnivores (larval fish) via effects on herbivore (zooplankton) quality. Benthic (tadpole) production was primarily explained by primary production rate, suggesting food quantity rather than quality drives their production. However, benthic FCE was also highest at low light/high nutrients and was significantly correlated with food quality. The stronger effect of food quality in mediating pelagic compared to benthic efficiencies, is consistent with differences in the stoichiometric mismatches between algae and consumers. Pelagic FCE and HE_P were more likely to be P‐limited, whereas benthic FCE was more likely N‐limited. This study is the first to examine both pelagic and benthic FCE within the same system, and highlights the importance of differential consumer needs in determining how food quality affects energy transfer efficiency.     

Pelagic phytoplankton community change‐points across nutrient gradients and in response to invasive mussels

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Calcareous nannofossils of the Cenomanian/Turonian boundary interval from the Boreal Realm (Wunstorf,northwest Germany)

The Cenomanian/Turonian boundary interval (CTBI) is marked by an intense climatic warming presumably caused by large magmatic eruptions. This warming was characterised by one of the most prominent Mesozoic perturbations of the carbon cycle, the Oceanic Anoxic Event 2 (OAE2), which is marked by a well pronounced positive carbon isotope excursion (CIE). Sediments of the OAE2-interval often consist of organic rich black shales suggesting widespread bottom water anoxia during the CTBI. This study focuses on calcareous nannofossils from the CTBI of a European section (Wunstorf Core; northwest Germany). A total of 105 samples were examined for calcareous nannofossils using the settling technique. Eight bioevents (last occurrences: Corollithion kennedyi, Lithraphidites acutus; first occurrences: Rotelapillus biarcus, Corollithion exiguum, Eprolithus octopetalus, Eprolithus eptapetalus, Quadrum gartneri, Eiffellithus eximius) have been recognised throughout the middle Cenomanian to middle Turonian interval. With the exception of eleven samples preservation is moderate to good. Calcareous nannofossils are abundant (mean 2.0 billion specimens/g sediment) and highly diverse (mean 58 species/sample). Assemblages are dominated by Watznaueria spp. (32.3%), Prediscosphaera spp. (13.4%), Zeugrhabdotus spp. (11.2%) and Biscutum spp. (10.5%). Pre-OAE2 and also post-OAE2 nannofossil assemblages show high abundances of Biscutum spp. (～ 20%) indicative for stable mesotrophic conditions. The assemblages of the OAE2 itself are marked by high values for Watznaueria spp. and low frequencies of Biscutum spp. making oligotrophic conditions during the OAE2 likely. High absolute abundances of organic walled dinoflagellates and the occurrence of frequent stress tolerant nannofossil genera like Retecapsa spp. in the organic rich intervals suggest, however, a deposition of black shales enhanced by high primary productivity. Thus dinoflagellates and calcareous nannofossils are interpreted to reflect different seasonal signals during the time of black shale deposition. Short-term high fertile seasons allowed the blooming of the organic walled dinoflagellates whereas calcareous nannofossils dominated the longer oligotrophic seasons. The black shale deposition was supported by the formation of large amounts of organic matter during fertile seasons as well as by surface water stagnation during oligotrophic seasons.     

How light and nutrients affect the relationship between autotrophic and heterotrophic biomass in a tropical black water periphyton community

This study examines how nutrients and light affect the relationship between autotrophic biomass and non-autotrophic periphyton organic matter in a tropical black water lake biofilm community. We hypothesized that there is no positive correlation between autotrophic and non-autotrophic organic matter in the periphytic community of a black water humic lake, where non-algal components of periphyton can rely on carbon sources external to the periphyton matrix and where nutrient availability is low. Second, we sought to test our hypothesis that non-autotrophic periphyton organic matter will benefit from nutrient enhancement in a lake where the availability of DOC is high. We performed a field experiment using in situ lake mesocosms to manipulate nutrient concentrations and light availability in a 2 × 2 factorial design. Control treatments (no nutrient added) and nutrient treatments (N + P) were compared in different light conditions: high light (near surface water) and low light (near bottom). No positive correlation was found between autotrophic biomass and non-autotrophic periphyton organic matter, but a negative correlation was observed in high nutrient and light conditions. The low C:P and N:P ratios revealed that the non-autotrophic organic matter mostly comprised a heterotrophic microbial biofilm. High levels of light and nutrients together caused significant changes in periphyton community properties. The non-autotrophic periphyton organic matter was negatively affected by nutrient addition, whereas autotrophic biomass was positively affected, especially in high light conditions. Our results strongly suggest that non-autotrophic periphyton organic matter in a humic lake is primarily comprised of a bacterial biofilm that directly competes for nutrients with autotrophs in the periphytic community. We also observed no effect of nutrient addition on periphyton growing in light-limited conditions. These results suggest that heterotrophic periphytic organisms might experience carbon limitation despite the high availability, but usually low quality, of dissolved carbon in the water column of humic lakes.     

The role of platelet ice microalgae in seeding phytoplankton blooms in Terra Nova Bay (Ross Sea,Antarctica): a mesocosm experiment

The aim of this study was to assess the role of platelet ice microalgal communities in seeding pelagic blooms. Nutrient dynamics, microalgal biomass, photosynthetic parameters, cell densities and species succession were studied in two mesocosm experiments, designed to simulate the transition of microalgal communities from platelet ice habitat to pelagic conditions. The microalgal assemblages were dominated by diatoms, 70% of which were benthic species such as Amphiprora kufferathii, Nitzschia stellata, and Berkeleya adeliensis. Photoacclimation of benthic species was inadequate also at relatively low irradiances. Exceptional growth capacity at different light levels was observed for pelagic species such as Fragilariopsis cylindrus and Chaetoceros spp. which may be important in seeding blooms at ice breakup. Fragilariopsis cylindrus showed high growth rates both at 65 and 10% of incident light and in nutrient replete as well as in nutrient depleted conditions. Five days after inoculation, phytoplankton biomass increased and nutrient concentrations decreased in both light conditions. Nutrient uptake rates were up to 9.10 μmol L⁻¹ d⁻¹ of TIN in the high light tank and 6.18 μmol L⁻¹ d⁻¹ in the low light tank and nutrient depletion in the high light tank occurred 3 days prior to depletion in the low light tank. At nutrient depletion, biomass concentrations were similar in both tanks, 30 and 34 μg Chla L⁻¹. This article belongs to a special topic: Five articles on Sea-ice communities in Terra Nova Bay (Ross Sea), coordinated by L. Guglielmo and V. Saggiomo, appear in this issue of Polar Biology. The studies were conducted in the frame of the National Program of Research in Antarctica (PNRA) of Italy.     

Is inorganic nutrient enrichment a driving force for the formation of red tides?: A case study of the dinoflagellate Scrippsiella trochoidea in an embayment

Red tides (high biomass phytoplankton blooms) have frequently occurred in Hong Kong waters, but most red tides occurred in waters which are not very eutrophic. For example, Port Shelter, a semi-enclosed bay in the northeast of Hong Kong, is one of hot spots for red tides. Concentrations of ambient inorganic nutrients (e.g. N, P), are not high enough to form the high biomass of chlorophyll a (chl a) in a red tide when chl a is converted to its particulate organic nutrient (N) (which should equal the inorganic nutrient, N). When a red tide of the dinoflagellate Scrippsiella trochoidea occurred in the bay, we found that the red tide patch along the shore had a high cell density of 15,000 cells ml⁻¹, and high chl a (56 μg l⁻¹), and pH reached 8.6 at the surface (8.2 at the bottom), indicating active photosynthesis in situ. Ambient inorganic nutrients (NO₃, PO₄, SiO₄, and NH₄) were all low in the waters and deep waters surrounding the red tide patch, suggesting that the nutrients were not high enough to support the high chl a >50 μg l⁻¹ in the red tide. Nutrient addition experiments showed that the addition of all of the inorganic nutrients to a non-red-tide water sample containing low concentrations of Scrippsiella trochoidea did not produce cell density of Scrippsiella trochoidea as high as in the red tide patch, suggesting that nutrients were not an initializing factor for this red tide. During the incubation of the red tide water sample without any nutrient addition, the phytoplankton biomass decreased gradually over 9 days. However, with a N addition, the phytoplankton biomass increased steadily until day 7, which suggested that nitrogen addition was able to sustain the high biomass of the red tide for a week with and without nutrients. In contrast, the red tide in the bay disappeared on the sampling day when the wind direction changed. These results indicated that initiation, maintenance and disappearance of the dinoflagellate Scrippsiella trochoidea red tide in the bay were not directly driven by changes in nutrients. Therefore, how nutrients are linked to the formation of red tides in coastal waters need to be further examined, particularly in relation to dissolved organic nutrients.     

Changes in sedimentary patterns of coastal and deep-sea successions from the North Atlantic (Portugal) linked to Early Cretaceous environmental change

Coastal mixed carbonate-siliciclastic and carbonate deposits of Late Barremian to Early Aptian age from the Lusitanian Basin (Portugal) are compared with a deep-sea succession (ODP 641) off the coast of Portugal. The coastal deposits show an abrupt cessation of rudist-dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid-rich marls during the Early Aptian. The subsequent development of the carbonate platform during the Late Aptian is masked by a hiatus. For this time interval shallow-water debris deposits of the deep-sea succession ODP 641 indicate that carbonate production in shallow-water areas resume in the early Late Aptian. Carbon-isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the Portuguese with shallow-water successions from Switzerland, France, Oman and the Pacific. The correlation reveals that during the Early Aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon-isotope values associated with the global deposition of organic rich black shales in the deep sea (OAE 1a). In all compared sections rudist-dominated carbonate deposition is stopped and followed either by orbitolinid-rich deposits, the deposition of microbial carbonates or by the drowning of the carbonate platform. The comparison shows that the deterioration for carbonate platform growth conditions during the Early Aptian occurred essentially simultaneously at the various localities. During this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms. Sea level change combined with local effects like elevated nutrient levels and higher temperatures, were probably determining the nature of sedimentary change in shallow-water environments during the carbonate crisis. In the sections studied in Portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late Early Aptian.     

The Cenomanian–Turonian boundary in the northwestern part of the Adriatic Carbonate Platform (Ćićarija Mtn., Istria,Croatia): characteristics and implications

The Cenomanian–Turonian boundary (CTB) in the ?i?arija Mountain region (northern Istria, Croatia) is characterized by calcisphere limestone successions with a firmground and glauconite horizon, bioturbated intervals, tempestites, and slumped structures as well as microbially laminated and organic-rich interbeds deposited in the northwestern part of the intra-Tethyan Adriatic Carbonate Platform (AdCP). Compilation of the results from three studied sections (Vodice–Jelovica, Martinjak and Planik) of litho-, bio-, and microfacies analyses, X-ray diffraction, SEM, EDS, and stable isotope analyses allowed reconstruction of marine paleoenvironmental conditions during this time period. Shallow-marine carbonate deposits of the Milna Formation underlie a drowned-platform succession of the Sveti (Sv.) Duh Formation. The contact between these two formations is sharp and commonly marked by slumped deposits. The Sv. Duh Formation consists of about 100 m of calcisphere wackestone enriched in organic matter. The results of preliminary δ¹³C and δ¹⁸O stable isotope analyses indicate the influence of the global Oceanic Anoxic Event (OAE2) on the deposition of this carbonate succession. Anoxic and hypoxic conditions in the water column lead to major changes in the shallow-marine carbonate system of the AdCP. Numerous benthic foraminifera declined during that time, but planktonic foraminifera and calcareous dinoflagellates diversified and expanded greatly. The results of this research provide new insights into the character of the CTB interval in this part of the Tethyan realm. Local and regional synsedimentary tectonics combined with global upper Cretaceous sea-level dynamics allows the correlation of the investigated deeper-marine lithostratigraphic units with OAE2.     

Seasonal patterns of nutrient deposition in a Quercus douglasii woodland in central California

The monthly deposition of total nitrogen, phosphorus, potassium, calcium and magnesium via canopy throughfall, and various components of the litterfall was measured for 31 months under mature Quercus douglasii and in the bulk precipitation in the surrounding open grassland. Seasonal patterns of nutrient concentration in leaf litter, throughfall, and precipitation were also measured. Total annual subcanopy deposition exceeded open precipitation deposition by approximately 45–60x for nitrogen, 5–15x for phosphorus, 30–35x for potassium, 25–35x for calcium, and 5–10x for magnesium. Total annual subcanopy deposition was low in comparison to other oak woodland sites reported in the literature. Throughfall and leaf litter were the primary sources of nutrients and thus determined the seasonal peaks of nutrient deposition. The first autumn rains and leaf fall were associated with one peak in nutrient deposition, and throughfall during early spring leaf emergence was associated with a second peak in potassium, magnesium and phosphorus. Non-leaf plant litter (excluding acorns) provided approximately 15–35% of most nutrients, with twigs and bark depositing over 12% of the annual calcium flux in 1987–1988, and flower litter depositing over 8% of the annual nitrogen flux in 1986–1987. Acorns had high concentrations of phosphorus and nitrogen and during the mast season of 1987–1988 they contained a large proportion of the total subcanopy annual flux of these elements. With acorns excluded, total annual nutrient deposition was similar between years, but timing of nutrient deposition differed. Late summer leaf fall associated with drought, variation in precipitation, and variation in deposition of non-leaf parts were associated with seasonal differences in nutrient deposition between years.     

Nutrient resorption from senescing leaves in two Stipa species native to central Argentina

Abstract Nutrient resorption from senescing leaves enables plants to conserve and reuse nutrients. As such, it could be expected that plant species adapted to infertile soils have a higher nutrient resorption efficiency (percentage reduction of nutrients between green and senesced leaves) and/or higher nutrient resorption proficiency (absolute reduction of nutrients in senesced leaves) than those adapted to fertile soils. Our objective was to compare nitrogen (N) and phosphorous (P) resorption of two congener grasses that successfully occupy uplands of relatively low fertility (Stipa gynerioides) or lowlands of relatively high fertility (Stipa brachychaeta) in natural grasslands of central Argentina. The two Stipa species did not differ in N and P resorption efficiency, but S. gynerioides had a higher N and P resorption proficiency than S. brachychaeta. As a consequence, leaf‐level N and P use efficiency were higher in the species adapted to low fertility conditions than in the species adapted to high fertility conditions. The higher nutrient resorption proficiency of S. gynerioides was also associated with relatively low leaf‐litter decomposition and nutrient release rates found in a previous study.     

Trace-element budgets in the Ohio/Sunbury shales of Kentucky: Constraints on ocean circulation and primary productivity in the Devonian–Mississippian Appalachian Basin

The hydrography of the Appalachian Basin in late Devonian–early Mississippian time is modeled based on the geochemistry of black shales and constrained by others' paleogeographic reconstructions. The model supports a robust exchange of basin bottom water with the open ocean, with residence times of less than forty years during deposition of the Cleveland Shale Member of the Ohio Shale. This is counter to previous interpretations of these carbon-rich units having accumulated under a stratified and stagnant water column, i.e., with a strongly restricted bottom bottom-water circulation. A robust circulation of bottom waters is further consistent with the palaeoclimatology, whereby eastern trade-winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment, fresh waters, and riverine nutrients. The model suggests that primary productivity was high (~ 2 g C m^− 2 d^− 1), although no higher than in select locations in the ocean today. The flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments. Calculations based on the average accumulation rate of the marine fraction of Ni suggest the flux of organic carbon settling out of the water column was approximately 9% of primary productivity, versus an accumulation rate (burial) of organic carbon of 0.5% of primary productivity. Trace-element ratios of V:Mo and Cr:Mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic (sulfate reducing) during deposition of the Huron Shale Member of the Ohio Shale to predominantly suboxic (nitrate reducing) during deposition of the Cleveland Shale Member and the Sunbury Shale, but with anoxic conditions occurring intermittently throughout this period.     

Integrating palynological and geochemical data in a new approach to palaeoecological studies: Upper Cretaceous of the Banterwick Barn Chalk borehole, Berkshire, UK

The dinoflagellate cyst record from an Upper Cretaceous (uppermost Cenomanian–upper Coniacian) Chalk core, drilled at Banterwick Barn, Berkshire, is described and statistically correlated with elemental and stable isotope bulk sediment geochemical data from the same core. Seventy-two dinocyst species and subspecies are recorded, and stable carbon and oxygen isotopic (δ¹³C, δ¹⁸O) trends are documented. Lithostratigraphy and chemostratigraphic correlation of the δ¹³C curve with an expanded section at Dover, Kent, are used to identify stratigraphically significant marls, and determine the positions of macrofossil zones and stage boundaries in the Banterwick Barn core. These data indicate that >30 m of chalk at Dover are represented by <2 m of Chalk Rock at Banterwick Barn, with much of the succession being absent due to erosion and non-deposition. First and last appearance datums (FAD, LAD), first and last common occurrences, and acmes of key Turonian–Coniacian dinocyst species are documented and compared with other records from the Anglo–Paris Basin. A new subspecies, Senoniasphaera rotundata alveolata is proposed, which has a FAD in the lower Turonian and last appears (LAD) in the lower Coniacian. Senoniasphaera rotundata rotundata [autonym, herein] has its FAD in the middle Turonian, first common occurrence in the uppermost Turonian, and LAD in the upper Coniacian. An extremely impoverished assemblage of dinocysts in the highest Cenomanian to lowest Turonian is considered to be largely a preservational artefact of intraclastic nodular and calcarenitic chalks, and is not related directly to the well-documented global oceanic anoxic event (OAE2) occurring at that time (93.5 Ma). A sharp increase in dinocyst abundance in the lower Turonian corresponds with a change in lithology to more marly chalks. A gradual decrease in the number of species is observed through the middle Turonian to upper Coniacian; δ¹⁸O records show that this was associated with global climatic cooling. Cluster analysis of the dinocyst abundance record with geochemical data indicates four distinct species groups with characteristic geochemical associations, i.e. Groups 1–4. Groups 1 and 2 are associated with phases of increased siliciclastic supply; a positive correlation with higher δ¹³C values differentiates the latter. Group 3 is independent of carbonate and detrital input, and Group 4 is associated with high carbonate flux and low detrital supply. These groupings suggest that cyst-forming dinoflagellates exhibited a range of ecological niches in the Late Cretaceous. Although the relationship between the encystment process and the geochemical associations is unclear, key environmental factors are likely to be sea-level and climate related, including water depth, turbidity, nutrient supply, sea-surface temperature, and environmental stability/predictability. Integrated geochemical and palynological studies have great potential for inter-regional correlation and palaeoenvironmental interpretation.     

Cenomanian-Turonian carbon isotope events recorded in terrestrial organic matter from northern Japan

Carbon isotopic fluctuations recorded in terrestrial organic matter from the Upper Cretaceous Cenomanian-Turonian succession of Hokkaido, Japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern England and the Italian Apennines. Chronological correlation for the Cenomanian-Turonian section of Japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils, allowing a detailed comparison of isotope stratigraphies for Japan and Europe. Three distinct features of the isotope profile, namely a positive spike near the Cenomanian/Turonian boundary, a shoulder in the lower-middle Turonian and a level segment in the middle-upper Turonian are observed in Japan. These features are biostratigraphically comparable and correlative with isotope profiles reported from Europe. The single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global CO₂ reservoir of the ocean-atmosphere system. If these three carbon isotope features are synchronous, they may be inferred as having been caused by global phenomena and as providing global high-resolution chemo-stratigraphic markers. Carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences.     

高营养级捕食者在浅水湖泊沿岸带与敞水区能量耦合的维持作用

研究利用保安湖沿岸带与敞水区两种生境中高营养级捕食者(达氏鲌与红鳍原鲌)的碳(δ13C)、氮(δ15N)稳定同位素数据,通过稳定同位素质量平衡混合模型、非度量多维尺度分析(NMDS)等方法,分析了两种生境中鲌类食物来源的差异.结果表明,两种生境中鲌类食物来源基本一致,且食物来源较为广泛,包括沿岸带饵料鱼类、敞水区饵料鱼...