Well-oxygenated Environment Research Articles

Molybdenum evidence for expansive sulfidic water masses in ~ 750 Ma oceans

The Ediacaran appearance of large animals, including motile bilaterians, is commonly hypothesized to reflect a physiologically enabling increase in atmospheric and oceanic oxygen abundances (pO 2). To date, direct evidence for low oxygen in pre-Ediacaran oceans has focused on chemical signatures in the rock record that reflect conditions in local basins, but this approach is both biased to constrain only shallower basins and statistically limited when we seek to follow the evolution of mean ocean chemical state through time. Because the abundance and isotopic composition of molybdenum (Mo) in organic-rich euxinic sediments can vary in response to changes in global redox conditions, Mo geochemistry provides independent constraints on the global evolution of well-oxygenated environments. Here, we establish a theoretical framework to access global marine Mo cycle in the past from the abundance and isotope composition of ancient seawater. Further, we investigate the ~ 750 Ma Walcott Member of the Chuar Group, Grand Canyon, which accumulated in a rift basin with open connection to the ocean. Iron speciation data from upper Walcott shales indicate that local bottom waters were anoxic and sulfidic, consistent with their high organic content (up to 20 wt.%). Similar facies in Phanerozoic successions contain high concentrations of redox-sensitive metals, but in the Walcott Member, abundances of Mo and U, as well as Mo/TOC (~ 0.5 ppm/wt.%) are low. δ 98 Mo values also fall well below modern equivalents (0.99 ± 0.13‰ versus ~ 2.35‰ today). These signatures are consistent with model predictions where sulfidic waters cover ~ 1–4% of the global seafloor, corresponding to a ~ 20–80 fold increase compared to the modern ocean. Therefore, our results suggest globally expansive sulfidic water masses in mid-Neoproterozoic oceans, bridging a nearly 700 million-year gap in previous Mo data. We propose that anoxic and sulfidic (euxinic) conditions governed Mo cycling in the oceans even as ferruginous subsurface waters re-appeared 800–750 Ma, and we interpret this anoxic ocean state to reflect a markedly lower atmospheric and oceanic O 2 level, consistent with the hypothesis that pO 2 acted as an evolutionary barrier to the emergence of large motile bilaterian animals prior to the Ediacaran Period.

Increased expression of HIF-1A and its implication in the hypoxia pathway in primary advanced uterine cervical carcinoma

The development of cervical cancer exhibits some unique differences compared to other solid tumors. Normal cervical stratified epithelia have characteristics of hypoxic tissue. Lack of oxygen (hypoxia) induces the HIF-1 (hypoxia-inducible factor-1) transcription factor, which is a heterodimer composed of a constitutively expressed β subunit and a hypoxia-inducible α-subunit. HIF-1A targets the transcription of over 70 genes involved in many aspects of cancer biology. In well-oxygenated environments, the HIF-1A subunit is hydroxylated, recognized and marked for proteosomal destruction by an E3 ubiquitin ligase, the von Hippel-Lindau protein (pVHL) complex. Under hypoxic stress, proline hydroxylase (PHD) activity is diminished, and stabilized HIF-1A is involved in the activation of the tissue response to hypoxia. Here, we examined the HIF-1A and VHL transcript levels and HIF-1A protein levels in cancerous tissue (n=30) and non-cancerous, normal uterine cervical tissue (n=30). We also compared the methylation status of HIF-1A and of the VHL promoter regions in cancerous and normal tissue samples. Significantly higher levels of HIF-1A and VHL transcripts (p<0.0001 and p=0.0042, respectively) and of HIF-1A protein (p=0.0037) were detected in cancerous tissue compared to normal samples. We did not observe DNA methylation in the HIF-1A and VHL promoter region in either control or cancerous tissue samples. VHL has a functional hypoxia response element (HRE) in the promoter region, and the induction of this HRE acts within a negative feedback loop to limit the hypoxic HIF-1A response. Our findings may suggest that HIF-1A could promote its own degradation by the induction of VHL gene expression (Spearman correlation coefficient, 0.515; p=0.003). Our study shows for the first time that this increase in VHL expression could be HIF-1A-dependent and serves within a negative feedback pathway during hypoxia to regulate the cell-specific oxygen threshold for HIF-1A activation.

The Late Cretaceous–Early Paleocene palaeobathymetric trends in the southwestern Barents Sea — Palaeoenvironmental implications of benthic foraminiferal assemblage analysis

The Late Cretaceous foraminiferal assemblages from five wells drilled in the southwestern Barents Sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area. Morphogroup analysis of assemblages in the Upper Cretaceous Kveite Formation suggests stable, possibly middle to lower bathyal, mesotrophic and relatively well-oxygenated environments in the Tromsø Basin during the Late Cretaceous. The depositional setting of Upper Cretaceous Kviting Formation in the tectonically more stable Hammerfest Basin was probably shallower, but still represents a deep-water environment similar to that of the Kveite Formation. A shallowing regional bathymetry in the southwestern Barents Sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages, which reflects the regional Late Cretaceous–Paleocene uplift prior to the break-up of the Greenland–Norwegian Sea. Changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from Rhizammina to Rhabdammina near the top of Kveite Formation agree with the possible existence of bottom water currents.

Estudo multidisciplinar (geoquímica e associações de foraminíferos) para caracterizar e avaliar intervenções antrópicas na Baía do Araçá, Canal de São Sebastião, SP

The goal of this study was to assess possible human-induced changes in the environment due to the discharge of domestic sewage into the Araca Bay, Sao Sebastiao Channel, Sao Sebastiao, Brazil. In order to achieve this goal, in April 2006, we conducted grain size and geochemical (Toc, N, S, and P) analysis and determined the assemblage composition and distribution of live benthic foraminifera from shallow marine sediments collected around diffusers of the domestic sewage submarine outfall at the Araca Bay. Results showed that the area studied is a lithoclastic shallow environment with predominance of sandy sediments. However, in the northeastern area of the sampling grid, it was observed high concentrations of fine sediments (silt plus clay), with significant Toc (>; 1%), N (>; 0.2%) and S (0.3%) contents. The organic enrichment is inferred based on the phosphorus and sulphur contents, as well as on the oxidation-reduction potential, which was inferred using the Eh values and C/S ratios. In relation to the benthic foraminiferal assemblages, low richness was observed and the association is mainly composed of infaunal and detritivore species. There is a high abundance of Epifaunal species, which are bioindicators of well-oxygenated environments, in stations with no impact of the sewage discharged by submarine outfall. The occurrence of medium and small-sized foraminifera shells is qualitatively associated with low oxygen concentrations at the sediment-water interface. The dominance of a few species, especially Ammonia tepida, may indicate environmental stress.

Controlling factors of recent clastic coastal sediments (Viransehir, Mersin bay, S Turkey)

The Plio-Quaternary conglomeratic sets within the marine environment of the Viransehir coast (W Mersin, S Turkey) are responsible for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity, wave energy, and organic activity. The conglomeratic sets close to the shoreline (50–150 cm) act as wave breakers, creating hard substratum and high energy, well-oxygenated environment for organisms like Patella sp., Phoronida worms and Brachidontes pharaonis (Fischer P. 1870). The boring activities of these organisms have disintegrated the sandy matrix of these sets. Finer-grained matrix sediments have been transported to the interset and open sea, while cobble–pebbles have been carried landwards and have created imbricated gravely beach deposits without matrix. Sandy beach is evolving where the conglomeratic sets away from the shoreline (5.0–10.0 m). In this example, sets form a bar; causing fivefold division as backshore, berm, surf zone, bar and offshore from land to sea. Poorly sorted, cobbles-pebbles cobbles and pebbles are found associated with the high-energy environments of bars, whilst well-sorted sands are observed in low energetic environments on shore. The sets and recent shell fragments are the main sources of coastal sediments in Viransehir. However, the amount of shell fragments decrease towards the active river mouth. This is due to sediment and fresh water influx from the river causing deteriorated temperature, salinity and light penetration of the marine environment resulting in less organic diversity.

Early Maastrichtian benthic foraminiferal assemblages from the western North Atlantic (Blake Nose) and their relation to paleoenvironmental changes

Benthic foraminiferal faunas from the Lower Maastrichtian ( Globotruncana falsostuarti– Gansserina gansseri Planktic Foraminiferal Zone) of DSDP Site 390 (Blake Nose, western North Atlantic) were investigated in order to characterize changes in organic matter flux and bottom-water oxygenation and their relation to paleoceanographic changes. Benthic foraminiferal faunas in the lower part of the studied succession show high abundances of Praebulimina reussi and Nuttallides truempyi and are proposed to reflect fluctuations in organic matter flux to the seafloor (meso- to eutrophic) under oxygenated bottom-water conditions. The middle interval is characterized by very low numbers of benthic foraminiferal specimens but a dominance of thick-walled species (e.g., lenticulinids, laevidentalinids), may reflect carbonate dissolution. In contrast to the lower part, benthic foraminifera from the upper part of the succession show well-oxygenated bottom waters. The most dominant species during this interval are Gavelinella beccariiformis, Reussella szajnochae, and N. truempyi. Parallel to this change in the benthic foraminiferal assemblages the number of inoceramid shells decreases, reflecting a significant increase in bottom-water oxygenation. Based on these data we speculate, that the observed changes in benthic foraminiferal assemblages towards a well-oxygenated environment within the Early Maastrichtian of DSDP Site 390 could reflect the onset of a shift from low-latitude to high-latitude deep-water sources. This speculation will predate the major reorganization of the oceanic circulation resulting in a circulation mode similar to today at the Early/Late Maastrichtian boundary by ∼ 1 Ma.

The distribution of deep-sea benthic foraminifera in core tops from the eastern Indian Ocean

Relative abundances of benthic foraminifera in 57 core tops collected within a depth-range between 700 and 4335 m below sea level [b.s.l.] from the eastern Indian Ocean (mostly between Australia and Indonesia) were investigated quantitatively using Detrended Correspondence Analysis (DCA) to analyse species spatial-distribution. Canonical Correspondence Analysis (CCA) and correlation matrices were used to evaluate the relationships between the species distribution and environmental variables (temperature, salinity, dissolved oxygen, nitrate and phosphate concentrations, carbon-flux rate). Seven key-species proved useful for distinguishing environmental parameters. Two groups of species are identified by means of the first DCA ordination axis. The first group increases in relative abundances with depth and includes three taxa: Oridorsalis tener umbonatus, Epistominella exigua and Pyrgo murrhina. These three taxa prefer a cold (< 3 °C) and well-oxygenated (> 3.5 ml/l) environment, with low carbon flux to the sea floor (< 3 g C m − 2 year − 1). O. tener umbonatus and P. murrhina tend to indicate reduced food availability, whereas E. exigua may indicate periodic delivery (seasonal) of organic matter to the sea floor. The second group includes Nummoloculina irregularis and Cibicidoides pseudoungerianus, typical of upper-bathyal depths. C. pseudoungerianus is correlated with a warm (> 2.5 °C) environment characterised by high carbon-flux rate (> 2.5 g C m − 2 year − 1). N. irregularis is associated with high dissolved-oxygen concentrations (> 3 ml/l) and its distribution is limited to south of 20 °S. In this area, the contemporary presence of the low salinity and well oxygenated Antarctic Intermediate Water and low primary productivity at the sea-surface (which causes low oxygen consumption at the sea floor) create the ideal conditions for this species. The second ordination-axis scores identify another taxon, Uvigerina proboscidea. The distribution of this species is mainly limited to low latitudes (north of 25°S), where carbon flux rate is high (> 3.5 g C m − 2 year − 1), due to higher primary productivity levels at the sea surface, and oxygen levels are low (< 3 ml/l) due to the organic matter oxidation and the presence of oxygen-depleted Indonesian Intermediate Water and North Indian Intermediate Water.

High resolution record of environmental changes constrained by volcanic ashes : Western Interior Basin, Cenomanian-Turonian stage boundary (USA)

Abstract Five altered volcanic-ash beds have been correlated near the Cenomanian-Turonian stage boundary through much of the Western Interior Basin. These instantaneous events constitute independent chronostratigraphic marker-beds enabling the synchroneity of lithological, biological or geochemical records to be tested. In this way, the Greenhorn Sea is a unique place where the potentiality of this high-resolution stratigraphic tool is illustrated. The Cenomanian-Turonian interval is the ideal period for this sort of study because major oceanic changes, including the global expansion of the oxygen minimum zone, are recognised across OAE2 event, involving the disappearance of Rotalipora, complex keeled foraminifera which previously occupied deep oceanic waters. Biostratigraphic data coupled with bentonite correlation, in several sections of Colorado, show the diachronism of the occurrences of R. cushmani and H. helvetica. Consequently, the extension of the W. archaeocretacea partial range zone is extremely variable at the regional scale. Thus, this association has a low temporal value. Planktonic foraminiferal analyses also reveal an A. multiloculata event in the M. mosbyense zone. During tens of thousands of years, this species, plentiful in the Western Interior Basin, multiplies and prevails on Rotalipora before a gradual decline. Rotalipora gave rise to Anaticinella by the atrophy of its keel. Thus, Anaticinella may stay in shallower habitats and avoid the expansion of the oxygen minimum zone. However, even if this adaptation allowed a return to the surface water, this selective advantage would not be enough for Anaticinella to survive the ecologically drastic modifications. Extinction of Anaticinella and its ancestor Rotalipora occurred contemporaneously. Carbon stable isotope analyses show that main paleoceanographic events have occurred at Pueblo during the Cenomanian-Turonian stage boundary. The initial rapid increase and first peak of δ13C indicate the first anoxic event (event 1) before a decrease in values and a main manganese enrichment which are the evidence for a well-oxygenated environment (event 2). This assumption is supported by the occurrence of an abundant and diversified benthic community at the same interval. The second increase in δ13C proxies signs the rise of anoxia (event 3). The temporal distribution of these events with the bentonite marker beds and the ammonite biostratigraphy attest to the synchroneity of events 2 and 3 over 600 km between the Pueblo and Lohali Point sections. The absence of event 1 at Lohali Point in the S. gracile zone implies the existence of a hiatus. Thus, thanks to the five bentonite marker beds, extending from the S. gracile to the M. nodosoides ammonite zone over 2 Ma, we have not only achieved precise regional correlation but, dealing with facies variations, our observations also indicate gaps in the sedimentary record. Thus, in detail, some thin levels expressed in Pueblo (reference section) cannot be correlated in any other eastern sections. Furthermore, supposed continuous sections may contain important hiatuses. An example is given at El Vado (New Mexico) where two bentonite marker beds are missing. In spite of the lack of significant planktonic foraminifera, the indications provided by bentonite geometries and by nannofossils reveal the existence of a hiatus of at least 850 kyr. It could be explained by the location of the area along the trend of a tectonic forebulge linked to the Sevier orogeny. This bathymetric high had great consequences on the currents flows in this large interior sea where tethysian and boreal water masses competed.

Thermodynamic Constraints on Microbially Mediated Processes in Lakes of the McMurdo Dry Valleys, Antarctica

Recent research has shown that the distribution of biogenic nitrogen and sulfur compounds (in particular, N 2 O, DMS and dissolved DMSO) observed in five perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica, appear to lack obvious biogeochemical explanations. This study examined the hypothesis that the distribution of these compounds resulted from thermodynamic constraints on microbially mediated processes. The thermodynamic favorableness of a number of ecologically important redox reactions in these lakes was assessed using a simplified Nernst equation and mathematically modified E h measurements. Our qualitative analysis revealed that the relative dominance of denitrification and nitrification as formation and loss processes for N 2 O was a complex pattern that was related to the redox conditions present. The results indicate that nitrification was initially the sole pathway for the formation of N 2 O with denitrification being thermodynamically unfavorable. As the redox conditions became less oxic, both denitrification and nitrification were possible. Once complete anoxia occurred, the importance of nitrification decreased considerably and the loss of N 2 O via denitrification became increasingly important. With respect to DMSO, the results indicated that DMSO was thermodynamically unfavorable as an electron acceptor for the respiration of organic material by bacteria in well-oxygenated environments, giving a partial explanation for the relatively elevated levels of DMSO found in many aquatic environments. Overall, the results of this study showed that subtle variations in the redox conditions present provided a plausible explanation for the unusual distributions of biogenic sulfur and nitrogen compounds observed in the lakes of the McMurdo Dry Valleys.

Recent developments in chemical oceanography of the East (Japan) Sea with an emphasis on CREAMS findings: A review

The understanding on the chemistry of the East (Japan) Sea, a typical mid-latitude marginal sea, has been dramatically improved through the CREAMS expeditions, an international cooperative study, carried out during 1990s. The CREAMS studies confirmed that the East Sea has undergone dramatic changes during the last 50–60 years. One of the most prominent characteristics of these changes is a rapid decrease of dissolved oxygen in deep waters. There even has been a claim that the East Sea might become an anoxic sea by next 200 years. While the causes for these changes are still under investigation, it has been shown that these changes are mainly due to the modification in the mode of deep water ventilation system in the East Sea: a slow down and complete stop of bottom water formation accompanied by an enhancement of upper water formation instead. A simple moving-boundary box model (MBBM) was developed in order to quantify the processes involved in such changes for the last 50–60 years. The model predicts that the East Sea may remain as a well-oxygenated sea despites recent rapid oxygen decreases in deep waters in association with structural changes such as a shrinking of oxygen-depleted deeper waters and an expansion of oxygen-rich upper in the East Sea in next few decades. The sedimentary record, however, shows that the East Sea has undergone oscillation between well-oxygenated environment and anoxic environment during last glacial period in association with the eustatic sea-level change. Several flooding processes such as intrusion of cold Oyashio Current and less saline, nutrient-rich seawaters from East China Sea and Yellow Sea has been proposed. Being a semi-closed basin, the carbon cycle of the East Sea has been a subject of CREAMS investigation. The East Sea serves as a strong sink of atmospheric CO2; penetration of anthropogenic CO2 all the way to the bottom is clear with its very rapid conveyor-belt system.

Statoil awards sn↓hvit contract to Dragados

The Late Cretaceous foraminiferal assemblages from five wells drilled in the southwestern Barents Sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area. Morphogroup analysis of assemblages in the Upper Cretaceous Kveite Formation suggests stable, possibly middle to lower bathyal, mesotrophic and relatively well-oxygenated environments in the Tromsø Basin during the Late Cretaceous. The depositional setting of Upper Cretaceous Kviting Formation in the tectonically more stable Hammerfest Basin was probably shallower, but still represents a deep-water environment similar to that of the Kveite Formation. A shallowing regional bathymetry in the southwestern Barents Sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages, which reflects the regional Late Cretaceous–Paleocene uplift prior to the break-up of the Greenland–Norwegian Sea. Changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from Rhizammina to Rhabdammina near the top of Kveite Formation agree with the possible existence of bottom water currents.

Eat and run: anoxic feeding and subsequent aerobic recovery by Orchomene obtusus in Saanich Inlet, British Columbia, Canada

The lysianassid amphipod Orchomene obtusus (Sars) is known as an epibenthic scav- enger, but it is abundant in the water column of Saanich Inlet, British Columbia, a temperate fjord with poorly oxygenated deep water. Sampling with vertically-stratified nets and baited traps indi- cates that O. obtusus is abundant within the oxycline at 100 to 140 m, is present in anoxic deep waters at low abundances, and is also abundant in the anoxic benthic environment. Shipboard incubations revealed that O. obtusus can survive between 10 and 33 h of anoxia at in situ conditions. Stable iso- tope and gut fluorescence measurements suggest that these amphipods feed on material produced in surface waters, and not on the isotopically dissimilar suspended detrital material present in the vicin- ity of the oxycline. The amphipods do not enter surface waters, and it appears that O. obtusus has adapted to oxygen gradients in this environment by feeding on surface-water-derived material in the food-rich and predator-poor anoxic benthos and subsequently migrating into the water column to conduct aerobic respiration. These vertical excursions are probably a modification of the swimming behavior exhibited by hyperbenthic amphipods in well-oxygenated environments, and may consti- tute an important mechanism for benthic-pelagic coupling.

OXYGEN LEVEL CONTROL ON FORAMINIFERAL DISTRIBUTION IN EFFINGHAM INLET, VANCOUVER ISLAND, BRITISH COLUMBIA, CANADA

Samples were analyzed from Effingham Inlet, southwestern Vancouver Island, British Columbia, to assess the oceanographic controls on benthic foraminiferal distribution. The resultant proxy data will be used to interpret cores collected throughout the basin, and assess the causes of periodic variation in fish populations over time. Seven foraminiferal assemblages were recognized with the primary controlling factors being oxygen content, and proportion of organic matter in the sediment. The estuarine Buliminella Assemblage characterizes well-oxygenated environments with high levels of terrestrial plant matter. This assemblage disappears when oxygen levels fall beneath suboxic levels of 40 μM/kg. The Buccella Assemblage, dominated in part by attached forms and islandiellids, is typical of well-oxygenated bank environments in the region. The Psammosphaera Assemblage is related to the lower salinity and variable conditions present in the shallow water where it occurs. The Stainforthia-Nonionella Assemblage characterizes one well-oxygenated environment outside the inlet. The Stainforthia-Bolivinellina Assemblage is typical of suboxic/dysoxic conditions (10–40 μM/kg) in the outer basin. The Stainforthia Assemblage is identified from dysoxic environments of deepest parts of the outer basin. A gradation between the Stainforthia-Bolivinellina Assemblage and the Stainforthia Assemblage is significant as a whole range of suboxic/dysoxic/anoxic conditions are detectable, potentially permitting recognition of even subtle variations in paleoceanographic/atmospheric circulation. The Stainforthia-Buccella Assemblage was recovered from the least oxygenated area of Effingham Inlet under fully anoxic (with H2S) conditions, and provides evidence that even the most isolated portions of Effingham Inlet are periodically oxygenated.

Foraminifera in the Arabian Sea oxygen minimum zone and other oxygen-deficient settings: taxonomic composition, diversity, and relation to metazoan faunas

Previous work has shown that some foraminiferal species thrive in organically enriched, oxygen-depleted environments. Here, we compare `live’ (stained) faunas in multicorer samples (0–1 cm layer) obtained at two sites on the Oman margin, one located at 412 m within the oxygen minimum zone (OMZ) (O 2=0.13 ml l −1), the other located at 3350 m, well below the main OMZ (O 2∼3.00 ml l −1). While earlier studies have focused on the hard-shelled (predominantly calcareous) foraminifera, we consider complete stained assemblages, including poorly known, soft-shelled, monothalamous forms. Densities at the 412-m site were much higher (16,107 individuals.10 cm −2 in the >63-μm fraction) than at the 3350-m site (625 indiv.10 cm −2). Species richness (E(S 100)), diversity (H′, Fishers Alpha index) and evenness (J′) were much lower, and dominance (R1D) was higher, at 412 m compared with 3350 m. At 412 m, small calcareous foraminifera predominated and soft-shelled allogromiids and sacamminids were a minor faunal element. At 3350 m, calcareous individuals were much less common and allogromiids and saccamminids formed a substantial component of the fauna. There were also strong contrasts between the foraminiferal macrofauna (>300-μm fraction) at these two sites; relatively small species of Bathysiphon, Globobulimina and Lagenammina dominated at 412 m, very large, tubular, agglutinated species of Bathysiphon, Hyperammina, Rhabdammina and Saccorhiza were important at 3350 m. Our observations suggest that, because they contain fewer soft-shelled and agglutinated foraminifera, a smaller proportion of bathyal, low-oxygen faunas is lost during fossilization compared to faunas from well-oxygenated environments. Trends among foraminifera (>63 μm fraction) in the Santa Barbara Basin (590 and 610 m depth; O 2=0.05 and 0.15 ml l −1 respectively), and macrofaunal foraminifera (>300 μm) on the Peru margin (300–1250 m depth; O 2=0.02–1.60 ml l −1), matched those observed on the Oman margin. In particular, soft-shelled monothalamous taxa were rare and large agglutinated taxa were absent in the most oxygen-depleted (<0.20 ml l −1) stations. Foraminifera often outnumber metazoans (both meiofaunal and macrofaunal) in bathyal oxygen-depleted settings. However, although phylogenetically distant, foraminifera and metazoans exhibit similar population responses to oxygen depletion; species diversity decreases, dominance increases, and the relative abundance of the major taxa changes. The foraminiferal macrofauna (>300 μm) were 5 times more abundant than the metazoan macrofauna at 412 m on the Oman margin but 16 times more abundant at the 3350 m site. Among the meiofauna (63–300 μm), the trend was reversed; foraminifera were 17 times more abundant than metazoan taxa at 412 m but only 1.4 times more abundant at 3350 m. An abundance of food combined with oxygen levels which are not depressed sufficiently to eliminate the more tolerant taxa, probably explains why foraminifera and macrofaunal metazoans flourished at the 412-m site, perhaps to the detriment of the metazoan meiofauna.

Late Cenozoic basin development of the eastern North Sea Basin

The Cenozoic succession in the Danish part of the North Sea Basin includes two significant breaks in sedimentation; 1) at the Eocene-Oligocene boundary and 2) at mid Miocene time. The sediment transport direction was from the west during the Middle-Late Eocene and mainly from northeast and east in post Eocene times, and a change from a concordant seismic reflection pattern to a progradational pattern is seen. A clear change in Iithology occurs at the Eocene-Oligocene boundary, from a finegrained clay-dominated deposit below the boundary to a clay with silt and mica above. Near shore marine and fluvial sediments of Early Oligocene to mid Miocene age are known from the offshore and onshore areas, witnessing that the coastline migrated into the basin for the first time since the earliest Cretaceous. This change in sedimentation pattern was probably caused by the initial uplift of Scandinavia. At mid Miocene time a significant environmental change occurred in the North Sea. A change from dark coloured to light coloured deposits indicates introduction of a well-oxygenated environment. A marked increase in rate of sedimentation (and subsidence) is evidenced by the approx. 1500 m thick sedimentary package in the central part of the basin. Late Middle Miocene starved sedimentation seen in the central North Sea may indicate a significant increase in subsidence rates. The base of the Quaternary is a major erosional unconformity, mainly created by erosion caused by uplift of Scandinavia. 1000-1200 m of uplift is calculated for the eastern part of the North Sea Basin. With a post-Eocene subsidence of 2500 m in the central North Sea, the amplitude of the post-Eocene tectonic movements is approx. 3700 m.

Sedimentary geochemistry of manganese; implications for the environment of formation of manganiferous black shales

The sedimentary geochemistry of manganese is dominated by the redox control of its speciation, higher oxidation states (Mn (super 3+) and (super 4+) ) occurring as insoluble oxyhydroxides in well-oxygenated environments and the lower oxidation state (Mn (super 2+) ) being much more soluble in oxygen-deficient settings. Its geochemical behavior is therefore quite different in oxic and anoxic environments, and where oxic and anoxic conditions are juxtaposed, Mn is recycled between the two environments. In modern marine sediments, Mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating (pelagic) sediments of the deep ocean and in surficial deposits of continental margin environments. Diagenetic recycling of Mn in the latter causes surficial deposits to have larger Mn enrichments than in many pelagic sediments. Bottom sediments of permanently anoxic basins show no enrichments and have Mn concentrations that are controlled solely by the aluminosilicate fraction. Manganese carbonates (kutnohorite and calcic rhodochrosite) are found only in anoxic sediments accumulating beneath surface oxic horizons (and therefore under oxygenated bottom waters) in many nearshore environments. Such enrichments are due to delivery of Mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved. Pore-water Mn levels can reach saturation with respect to a mixed Mn-Ca carbonate phase in such sediments. The diagenetic origin for these phases is shown by their carbon isotope compositions, which typically indicate a carbon source from decomposing organic matter. The presence of Mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters.On the basis of this information it is proposed that, in contrast to several current explanations for the formation of Mn carbonates (kutnohorite and rhodochrosite) in ancient organic-rich shales, limestone, and marl sequences and in many Mn ore deposits, the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters. By analogy with the present, Mn carbonates could not have formed in the bottom waters of anoxic basins. These diagenetic phases, however, did form where Mn was supplied at a high rate, namely, by the burial of oxyhydroxide-enriched surface sediments, to a subsurface anoxic environment. This situation could only have occurred under oxygenated bottom waters. The presence of Mn carbonates in ancient black shales (and in some carbonate-rich rocks) lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters, probably in continental margin settings.

Influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales

Abstract Organic P and organic C concentrations were measured in several well-characterized Phanerozoic marine shale sequences with the primary focus being the Camp Run Member of the Devonian-Mississippian New Albany Shale. Sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters, respectively. Average organic C/P mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the New Albany. Differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment-water interface can account for the C/P ratios of buried organic matter. Low C/P ratios of bioturbated sediments are attributed to 1. (1) the increased ability of bacteria to store P in well-oxygenated environments which leads to the production of low C/P ratio bacterial biomass and 2. (2) the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low C/P ratios. High organic C/P ratios of laminated sediments are explained by a combination of 1. (1) the limited ability of bacteria to store P under anoxic conditions, 2. (2) extensive P regeneration from sedimentary organic matter, 3. (3) enhanced C preservation relative to the bioturbated shales. It is also shown that relative to organic C, laminated shales are not as effective a P sink as are bioturbated shales. This provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the P needed to sustain further productivity.

A redescription of a Maastrichtian lobster Hoploparia antarctica Wilckens, 1907 (Crustacea: Decapoda), from Chubut, Argentina

The discovery of beautifully preserved specimens of a macruran decapod provides the basis for redescription of Hoploparia antarctica Wilckens, a hitherto poorly known species from the Campanian–Maastrichtian of the Austral basin of Southern Patagonia. Analyses of the associated molluscan fauna, trace fossils, and sedimentary structures indicate that the material is mostly preserved in calcareous sandstones and coquinas deposited in shallow, well-oxygenated environments. These new findings of H. antarctica in Maastrichtian deposits of the Lefipán Formation of Chubut expand the geographic distribution of the species and add a new element for the comparison of the Lefipán fauna with that of the austral Wedellian Province.

Les associations de kystes de dinoflagellés du Cénomanien-Turonien de vergons (Bassin Vocontien France)

In black shales of the Thomel horizon which is the result of the Cenomanian-Turonian anoxic event in the Vocontian Basin, the only benthos found is annelids. The plankton records the variations in oxygen content since foraminifera, belonging to the genus Rotalipora, disappear. Dinoflagellates, also, record these variations in the disphotic zone. Four dinoflagellate associations are defined. The lowest and the highest in a stratigraphical sense are named: 1— Palaeohystrichophora infusoriodes and Spiniferites complex association (association A) and 2— Subtilisphaera pontis-mariae and Spiniferites complex association (association D). They are both characteristic of well-oxygenated environments. The great abundance of cavate cysts in the two associations could be taken to indicate cool water a conclusion which is probably true for samples under the Thomel horizon but erroneous for the top of the section. The other two associations which are restricted to the black shales are the Leberidocysta chlamydata and Spiniferites complex association (association B) and Cyclonephelium and Spiniferites complex association (association C); they typify a more highly stressed environment with a low oxygen content. The ratio of cavate cysts/total dinoflagellates is low compared to that at the base of the section, in this case, it could reflect a warmer climate. Such an interpretation is in contradiction with some previous conclusions concerning the Cenomanian-Turonian black shales but it supports the view that Spiniferites forms, common in all four associations, lived through the water column but were better adapted to well-aerated surface waters. By contrast, cavate cysts such as P. infusorioides and S. pontis-mariae, are regarded as being fairly typical of oxygenated deep waters. Dinoflagellates which produced Cyclonephelium, L. chlamydata or Eurydinium cysts, for example, could have been tolerant of the effects of variations in oxygen-depletion within disphotic zone. Hence, Cenomanian-Turonian cavate cysts have no global climatic value as in the case of Jurassic forms.

Benthic foraminiferal evidence for reduced deep-water circulation during sapropel deposition in the eastern Mediterranean

An analysis of deep-sea benthic foraminifera from six eastern Mediterranean piston cores was carried out to determine the faunal response to the deposition of sapropel S5, formed between 125,000 and 116,000 yrs B.P. The pre-S5 population is the most diverse, being composed of miliolids, Articulina tubulosa, Gyroidina spp., and various rotaliids. An assemblage found near the base and top of S5 is dominated by Chilostomella mediterranensis, Globobulimina affinis, and Bolivina spp, and the post-S5 fauna is dominated by A. tubulosa and Gyroidina spp. The faunal data are interpreted in terms of the microhabitat preferences of the fauna, based on living (stained) benthic foraminiferal data and associated morphological characteristics from the North Atlantic. Epifaunal species dominate pre-S5 and post-S5 sediments and are associated with low organic carbon values ranging from 0.1 to 0.4%. Infaunal species, occurring near or within sapropel layers, are found with organic carbon values of >0.7% and live in environments characterized by low dissolved oxygen levels. The dominance of epifaunal species within the pre-S5 and post-S5 sediments is interpreted to reflect low levels of food in a well-oxygenated environment, while the low abundance and dominance of infaunal taxa at the base and top of S5 reflects low food and low oxygen conditions. Although an increase in surface productivity may have occurred immediately preceding and during the deposition of S5, the critical factor in deposition of sapropel S5 is anoxia resulting from reduced ventilation of the deep waters. The similarity of the faunal patterns in the six cores suggests that bathyal environmental conditions were uniform in the eastern Mediterranean at depths ranging from 2042 to 3150 m during deposition of sapropel S5.