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At least 145 records · Page 8Linked to original sources
PubMed1989

Paleoenvironmental distribution of microfossils and stromatolites in the Upper Proterozoic Backlundtoppen Formation, Spitsbergen.

The Upper Proterozoic (ca. 700-800 Ma old) Backlundtoppen Formation, northeastern Spitsbergen, preserves an abundant and varied record of ancient microbial life. Five distinctive microfossil assemblages occur in five equally distinct sedimentary settings; differences among the assemblages appear to reflect original ecological heterogeneity, although taphonomic circumstance may contribute to some distinctions. Microfossil assemblages occur in: oncolites, oolites, and pisolites; stratiform stromatolites and associated intraclastic rudites; partially silicified micrites; and siltites interbedded with quartz arenites. Individual assemblages contain one to eight differentiable taxa; a minimum of 17 distinct populations is present in the formation as a whole. Additional microbial community diversity an be inferred from the presence of domal, columnar, pseudocolumnar, and coniform stromatolites, none of which contains microfossils. On the basis of macrostructure, four stromatolite types appear to be present, but only three distinct mat-building communities can be inferred from microstructural features. Eohyella elongata n. sp., a euendolithic cyanobacterium found in silicified pisolites, is described as new.

Animals↗
PubMed1988

Microfossils in metasediments from Prins Karls Forland, western Svalbard.

The stratigraphic importance of fossils is never more apparent than in attempts to unravel the complexities of metamorphic terrains. The age and stratigraphic relationships of the thick metasedimentary and metavolcanic succession of Prins Karls Forland, western Svalbard, have been the subject of investigation and debate since the early part of this century (Hoel 1914; Craig 1916; Tyrrel 1924), and sharply different interpretations have been proposed (e.g. Harland et al. 1979; Hjelle et al. 1979). Until now, such interpretations have been unconstrained by palaeontological data, an understandable consequence of the metamorphic alteration undergone by these rocks. In this paper, we report the discovery of stratigraphically useful microfossils preserved in chert nodules from carbonaceous, dolomitic shales on northern Prins Karls Forland. These fossils have significant implications for the stratigraphic and structural interpretation of Forland metasediments, as well as for the more general problem of palaeontological prospecting in severely deformed and metamorphosed terrains, including those characteristic of the Archean Eon.

Fossils↗
PubMed1994

Microfossils in cherts from the Mesoproterozoic (Middle Riphean) Debengda Formation, the Olenek Uplift, northeastern Siberia.

Silicified shallow-water marine carbonate deposits of the Proterozoic Debengda Formation (the Olenek Uplift, northeastern Siberia) contain well preserved microfossils. One or two distinct assemblages consists only of filamentous Siphonophycus microfossils, which are presumably the extracellular sheaths of hormogonium cyanobacteria. The other is dominated by coccoidal microfossils, first by the entophysalidacean cyanobacterium Eoentophysalis. The coccoidal assemblage was recognized in the layered carbonate precipitate structures of a superficially stromatolite appearance. Despite its simple composition, the microfossil assemblage supports the generally accepted Mesoproterozoic (middle Riphean) age of the Debengda Formation. This conclusion corresponds to the available data on isotopic geochronology, and to the composition of columnar stromatolites from the Dehengda Formation. Both the structural features and carbon isotopic composition of its rocks are comparable to those of rocks of known Mesoproterozoic age, but differ from the characteristics of definitely Neoproterozoic deposits.

Cyanobacteria↗
PubMed1997

Microbes all around.

Explore the source record for details and available documents.

Environmental Microbiology↗
PubMed1996

Impact process: an important geological phenomenon.

The impact process was for a long period of time, even after a wider acceptance among the geological community, considered to be a marginal phenomenon in the Earth sciences. The first decade or two have showed an importance of the process itself and consequent events only too clearly. The present paper is a review describing the history and development of the impact hypothesis, structure and origin of impact craters, influence of huge impacts on the living environment and other aspects of the impact process from the point of view of geology s.l.

Animals↗
PubMed1996

Lithofacies and biofacies of mid-Paleozoic thermal spring deposits in the Drummond Basin, Queensland, Australia.

The Devonian to Carboniferous sinters of the Drummond Basin, Australia, are among the oldest well established examples of fossil subaerial hot springs. Numerous subaerial and subaqueous spring deposits are known from the geological record as a result of the occurrence of economic mineral deposits in many of them. Some are reported to contain fossils, but very few have been studied by paleobiologists; they represent an untapped source of paleobiological information on the history of hydrothermal ecosystems. Such systems are of special interest, given the molecular biological evidence that thermophilic bacteria lie near the root of the tree of extant life. The Drummond Basin sinters are very closely comparable with modern examples in Yellowstone National Park and elsewhere. Thirteen microfacies are recognisable in the field, ranging from high temperature apparently abiotic geyserite through various forms of stromatolitic sinter probably of cyanobacterial origin to ambient temperature marsh deposits. Microfossils in the stromatolites are interpreted as cyanobacterial sheaths. Herbaceous lycopsids occur in the lower temperature deposits.

Australia↗
PubMed1998

The quantum event of oceanic crustal accretion: impacts of diking at mid-ocean ridges.

Seafloor diking-eruptive events represent the irreducible, quantum events of upper oceanic crustal accretion. They record events by which a large portion of the oceanic crust has formed through geological history. Since 1993, the U.S. Navy's real-time Sound Surveillance System has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast Pacific. These diking-eruptive events trigger a sequence of related, rapidly evolving physical, chemical, and biological processes. Magmatic volatiles released during these events may provide nutrients for communities of subsea-floor microorganisms, some of which thrive in high-temperature anaerobic environments. Many of the organisms identified from these systems are Archaea. If microorganisms can thrive in the water-saturated pores and cracks within deep, volcanically active portions of our planet, other hydrothermally active planets may harbor similar life forms.

Archaea↗
PubMed2001

Cadmium status in Egypt.

It is inferred from these studies that releases of Cd are still increasing and it is recommended that measures must be taken to reduce emissions of cadmium. Any cadmium discharged into the Egyptian environment may move from one compartment to another at varying rates, resulting in an accumulation in compartments such as soils and biota. Such accumulation can be expected to increase with continued emissions, and attention should be given to all sources of cadmium, natural as well as anthropogenic especially in the industrial cities in Egypt. Cadmium present in sewage, as well as industrial effluent (also, other liquid and solid wastes) and sewage sludge will increase levels in soils and is expected to contribute to dietary levels and body burdens. The current information indicates that such effects may have to be evaluated over long periods of time, possibly as long as 50-100 years.

Cadmium↗
PubMed1998

Selenium content in sulfide ores from the Chalkidiki peninsula, Greece.

Selenium (Se) was assessed in galena, sphalerite, and pyrite samples. These are components of mixed sulfide ores from the Olympias and Madem Lakkos-Mavres Petres deposits and the Skouries porphyry-copper deposit. We used atomic absorption spectroscopy (AAS) with a hydride generator system. The highest concentration of Se (516 ppm) was found in the fine-grained galena at the -135 level of the Olympias deposits. In the Madem Lakkos-Mavres Petres deposit, the highest concentration of Se (33 ppm) was found in the pyrites of the level 30. The concentration of Se in the arsenopyrites and chalcopyrites is lower than the detection limit of the analytical method (< 100 ppb). The concentrated chalcopyrite from the porphyry copper deposit at Skouries exhibits a significant Se content (average 200 ppm) in contrast to the chalcopyrite from the Olympias and the Madem Lakkos-Mavres Petres. Variations in the Se content of the sulfide minerals studied could be caused by redox-pH and/or temperature conditions, as well as by the difference in crystal structure. The Se found in the areas studied may positively affect the environment. Sulfide minerals are oxidized by microorganisms, infiltrate in the soil-water in the form of selenate or selenite ion, and directly or indirectly influence the human organism.

Arsenicals↗
PubMedDate not supplied

The riddle of hepatic neoplasia in brown bullheads from relatively unpolluted waters in New York State.

Since 1985, pathologists at Cornell University have investigated the causes of lesions in freshwater fish throughout New York waters in order to clarify possible impairment of fish health by environmental contaminants. Fishermen and biologists alerted us to several relatively protected reservoirs and ponds in which we have found no evidence of elevated levels of anthropogenic environmental contaminants but in which up to 100% of brown bullheads exhibited skin neoplasia. Complete necropsies and histologic study revealed that over 30% of mature brown bullheads from some of these sites had benign or malignant hepatocellular or biliary liver neoplasia. Up to 50% of brown bullheads had benign or malignant liver neoplasia in other relatively unpolluted waters with no evidence of skin neoplasia in bullheads. Multiple samplings of brown bullheads from several of these sites have revealed puzzling variability in the prevalence of skin, liver, and other neoplasia in these fish populations. The cause of these striking epizootics of neoplasia in brown bullheads in unpolluted waters in New York State remains unclear. We hypothesize that natural carcinogens such as N-nitroso compounds formed in aquatic sediments or radon from geologic formations may contribute to epizootic fish neoplasia in New York waters.

Animals↗
PubMed2003

Sediment and porewater geochemistry in a metal contaminated estuary, Dulas Bay, Anglesey.

Remobilisation of contaminant metals from sediments can occur by chemical, biological or physical changes. This in turn can lead to contaminant fluxes to the porewaters and ultimately the water column. The aim of the research presented here is to document post-depositional controls on metal mobility and fluxes in a heavily metal-contaminated estuary. This will allow for an improved understanding of the impact of contaminated sediments on water quality from both a short-term and long-term perspective. Dulas Bay is situated on the east coast of Anglesey, North Wales, and receives polluted waters from Parys Mountain. Metals within Dulas Bay sediments show surface enrichment and variations in mineralogical form. Diagenesis clearly plays a role in post-depositional behaviour of the metals, forming sulphides and potentially carbonates. The presence of a dominant exchangeable/carbonate fraction, and elevated porewater metals, in this sulphidic system is significant and could indicate the presence of freshwater diagenesis, or, reflect the high levels of metals in the sediment.

Carbonates↗
PubMed2004

Geochemical controls on the production and distribution of methylmercury in near-shore marine sediments.

We examined temporal differences in sedimentary production of monomethylmercury (MMHg) at three sites in Long Island Sound (LIS). Sediment-phase concentrations of Hg species decreased from west to east in LIS surface sediments, following the trend of organic matter. However, Hg methylation potentials, measured by incubation with an isotopic tracer (200Hg), increased from west to east. 200Hg methylation potentials were enhanced in August relative to March and June, attributable to differences in activity of sulfate-reducing bacteria. Organic matter and acid-volatile sulfide influenced the distribution coefficient (KD) of inorganic Hg (Hg(II) = total Hg - MMHg) and inhibited 200Hg methylation in surface sediments. 200Hg methylation varied inversely with the KD of Hg(II) and positively with the concentration of Hg(II), mostly as HgS0, in LIS pore waters. Accordingly, we posit that a principal control on MMHg production in low-sulfide, coastal marine sediments is partitioning of Hg(II) between particle and dissolved phases, which regulates availability of Hg substrate to methylating bacteria. Most of the partitioning in LIS sediments is due to Hg-organic associations. This suggests that reductions in the organic content of coastal sediment, a potential result of nutrient abatement programs intended to inhibit eutrophication of near-shore waters, could enhance MMHg production by increasing the bioavailability of the large reservoir of "legacy Hg" buried within the sediment.

Biological Availability↗
PubMed2003

Use of O2 consumption and CO2 production in kinetic cells to delineate pyrite oxidation-carbonate buffering and microbial respiration in unsaturated media.

Identifying zones of sulphide oxidation and carbonate buffering is important in the development of a management plan for mine waste-rock piles. In this study, we used a kinetic cell technique to measure rates of O2 consumption and CO2 production in low sulphide (<0.12 wt.% S), low inorganic carbon (<0.20 wt.% C(inorganic)), gneissic waste rock and associated organic-rich lake sediment (0.7 wt.% C(organic)), and forest soil (1.4 wt.% C(organic)) collected from the Key Lake uranium mine in Saskatchewan, Canada. Solid chemistry, stable carbon isotope, pore water sulphate concentration data, and stoichiometric considerations indicated that O2 consumption and CO2 production were constrained by microbial respiration in the lake sediment and forest soil and by pyrite oxidation-carbonate buffering in the gneissic waste rock. Mean ratios of molar CO2 production to O2 consumption rates were 0.5 for lake sediment, 0.7 for forest soil, and 0.2 for gneissic waste rock. The different O2/CO2 ratios suggested that O2-CO2 monitoring may provide a practical tool for identifying the zones of microbial respiration and pyrite oxidation-carbonate buffering in mine waste-rock piles. Rates of O2 consumption and CO2 production were about one order of magnitude greater in lake sediment than in gneissic waste rock, indicating that microbial respiration would exert a control on the distribution of O2 and CO2 gas in waste-rock piles constructed upon the dewatered lake sediments.

Carbon Dioxide↗
PubMed1991

Sulfate reduction in deep-sea sediments.

Sulfate reduction rates calculated from about 200 DSDP pore water sulfate profiles have been contoured and plotted on a map covering most areas of the world ocean. Rates show a remarkable spatial consistency, with high rates observed near the continental margins, becoming progressively lower toward the central ocean basins. Relatively elevated rates are also found in the eastern equatorial Pacific, a site of upwelling and correspondingly high rates of primary organic production. Overall, the distribution of sulfate reduction in pelagic sediments looks very similar to the distribution of primary organic carbon production. When rates are directly compared, however, the correlation between sulfate reduction and primary production is only moderately strong. Perhaps the most important influence on sulfate reduction is sediment deposition rate and the control this has over the fraction of the sedimentary organic carbon flux that becomes available for sulfate reduction. The slower the rate of sediment deposition the more time for oxic respiration and the less organic carbon that escapes to the zone of sulfate reduction. To predict most accurately sulfate reduction rates, however, the variables of primary production, water depth, and sediment deposition rate must all be integrated.

Algorithms↗