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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

The Magnetic Properties Of Aggregate Polycrystalline Diamond: Implications For Carbonado Petrogenesis

Carbonados are a type of diamond, which are made up of many aggregrates of small crystalline diamonds or microdiamonds. The term "carbonado" comes from the Portuguese word carbonated. They are only found in sedimentary deposits in the Central African Republic (CAR) and the Bahia Province of Brazil. They were once the source of the world's supply of industrial diamonds. Their origin is uncertain but several mutually exclusive hypotheses have been proposed. This theories are: (1) extraterrestrial, that is they formed from the dust cloud of original solar nebulae; (2) produced by the high temperatures and pressures of the Earth's mantle; (3) or as the result of an extra-terrestrial impact into a carbon rich layer of sediment. Our study was done to further the understanding of their origin. We measured the magnetic properties on some twenty samples from the CAR. An earlier study was done on whole samples of carbonados and the "common" or kimberlitic diamond. Our work differed in that we started at the surface and subsequently removed the surface layers (by days of acid immersion) into the interior; measuring the magnetic properties at each interval. This procedure permits us to monitor the distribution of magnetic substances within the samples. Our results showed that the magnetic carriers are distributed on the surface including the open pores and that the carbonado interior is essentially non-magnetic. This result suggests that the initial formation environment was deficient in magnetic particles. Such a situation could indicate that their formation was the result of an extra-terrestrial body impacting carbon-rich sediment. Obviously, more work will be required on isotopic and chemical analyses before a more detailed ori-in can be determined.

Kleteschka, Gunther↗
NASA NTRS1986

Archean sedimentary styles and early crustal evolution

The distinctions between and implications of early and late Archean sedimentary styles are presented. Early Archean greenstone belts, such as the Barberton of South Africa and those in the eastern Pilbar Block of Australia are characterized by fresh or slightly reworked pyroclastic debris, orthochemical sediments such as carbonates, evaporites, and silica, and biogenic deposits including cherts and stromatolitic units. Terrigenous deposits are rare, and it is suggested that early Archean sediments were deposited on shallow simatic platforms, with little or no components derived from sialic sources. In contrast, late Archean greenstone belts in the Canadian Shield and the Yilgarn Block of Australia contain coarse terrigenous clastic rocks including conglomerate, sandstone, and shale derived largely from sialic basement. Deposition appears to have taken place in deepwater, tectonically unstable environments. These observations are interpreted to indicate that the early Archean greenstone belts formed as anorogenic, shallow water, simatic platforms, with little or no underlying or adjacent continental crust, an environment similar to modern oceanic islands formed over hot spots.

Lowe, D. R.↗
NASA NTRS1993

New constraints on Precambrian ocean composition

The Precambrian record of carbonate and evaporite sedimentation is equivocal. In contrast to most previous interpretations, it is possible that Archean, Paleoproterozoic, and to a lesser extent, Meso to Neoproterozoic seawater favored surplus abiotic carbonate precipitation, as aragonite and (hi-Mg?) calcite, in comparison to younger times. Furthermore, gypsum/anhydrite may have been only rarely precipitated prior to halite precipitation during evaporation prior to about 1.8 Ga. Two effects may have contributed to these relationships. First, sulfate concentration of seawater may have been critically low prior to about 1.9 Ga so the product mCa++ x mSO4-- would not have produced gypsum before halite, as in the Mesoproterozoic to modern ocean. Second, the bicarbonate to calcium ratio was sufficiently high so that during progressive evaporation of seawater, calcium would have been exhausted before the gypsum field was reached. The pH of the Archean and Paleoproterozoic ocean need not have been significantly different from the modern value of 8.1, even at CO2 partial pressures of a tenth of an atmosphere. Higher CO2 partial pressures require somewhat lower pH values.

NASA Discipline Exobiology↗
NASA NTRS1993

Carbon Isotope Biogeochemistry of Methane from Anoxic Sediments

The isotopic composition of naturally occurring methane was used to constrain the tropospheric budget of that radiatively active gas. Numerous studies have shown that the isotopic composition is not constant, even for a specific source, and may vary temporally and spatially. The objective was to develop a process-level model that reproduced the seasonal variations in the C-13/C-12 composition of methane observed at the coastal site, Cape Lookout Bight, NC. Details of the mass balance are provided. Experiments and models designed to determine what factors incluence C-13/C-12 ratio of dissolved CO2 are reported. All the factors described were combined in a model that faithfully reproduces the seasonal C-13/C-12 variations observed at Cape Lookout. The model is described.

Blair, Neal E.↗
NASA NTRS2020

230Th Normalization: New Insights on an Essential Tool for Quantifying Sedimentary Fluxes in the Modern and Quaternary Ocean

230Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever more diverse marine environments, the nuances of 230Th systematics, with regard to particle type, particle size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000 sedimentary records of 230Th from across the global ocean at two time slices, the late Holocene (0–5,000 years ago, or 0–5 ka) and the Last Glacial Maximum (18.5–23.5 ka), and investigated the spatial structure of 230Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during the Last Glacial Maximum (1.79–2.17 g/sq.cmkyr, 95% confidence) relative to the Holocene (1.48–1.68 g/sq.cmkyr, 95% confidence). We then examined the potential confounding influences of boundary scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and carbonate dissolution on the efficacy of 230Th as a constant flux proxy. Anomalous 230Th behavior is sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that 230Th normalization is a robust tool for determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m water depth).

Costa, Kassandra M.↗
NASA NTRS2014

The Signs of Life Detector (SOLID): An Instrument to Detect Molecular Biosignatures on Mars

The case for life on Mars grows stronger. Investigations at Gale Crater by Curiosity have revealed fine-grained sedimentary rocks inferred to represent an ancient lake environment suited to support life. In addition, Curiosity tentatively found a heterogeneous distribution of organic carbon within these sediments, consistent with the detection of native organic C in Mars meteorites. Furthermore, modern potentially habitable environments have been recognized on Mars including the N. Polar region visited by Phoenix, gully features suggesting modern water flows, and RSLs that occur seasonally suggest liquid processes. The time is ripe for missions to Mars incorporating a search for biochemical evidence of life.

The SOLID Instrument↗
NASA NTRS1987

Phosphorus in foraminiferal sediments from North Atlantic Ridge cores and in pure limestones

Samples of foraminiferal ooze from two North Atlantic cores were cleaned and progressively dissolved. Most of the P, Fe, and Mn was released during the first of two reductive cleaning steps. Most of the remainder of these elements and most of the Ca were released during the final acid dissolution step. The P in these samples is present largely in Fe- and Mn-rich coatings, not as a constituent of the foraminiferal shells themselves. Our results are consistent with those of earlier studies. The concentration of P in carbonate oozes in which it is clearly associated with coatings is similar to that of modern calcareous sediments in general, and with that of reasonably pure limestones of all ages. Phosphorus is apparently associated with (Fe, Mn)-oxide coatings in many carbonate sediments. The rate of removal of P from the oceans as a constituent of such sediments depends on the rate of formation of (Fe, Mn) coatings, not on the rate of incorporation of P into calcium carbonate.

NASA Discipline Exobiology↗
NASA NTRS1992

The carbon isotope biogeochemistry of acetate from a methanogenic marine sediment

The delta C-13 value of porewater acetate isolated from the anoxic sediments of Cape Lookout Bight (North Carolina) ranged from -17.6 percent in the sulfate reduction zone to -2.8 percent in the underlying methanogenic zone. The large C-13 enrichment in the sulfate-depleted sediments appears to be associated with the dissimilation of acetate to CH4 and CO2. Fractionation factors for that process were estimated to be 1.032 +/- 0.014 and 1.036 +/- 0.019 for the methyl and carboxyl groups. A subsurface maximum in delta C-13 of the total acetate molecule, as well as the methyl and carboxyl carbons at 10-15 cm depth within the sediment column, indicate that changes in the relative rates of acetate cycling pathways occur in the methanogenic zone. The methyl group of the acetate was depleted in C-13 by 7-14 percent relative to the carboxyl moiety. The intramolecular heterogeneity may be the result of both synthetic and catabolic isotope effects.

Blair, N. E.↗
NASA NTRS1988

Rate of production, dissolution and accumulation of biogenic solids in the ocean

The equatorial current system, by its response to global circulation changes, provides a unique recording mechanism for long range climatic oscillations. A permanent record of the changes in rate of upwelling and organic production is generated in the equatorial deep sea sediments, particularly by such biogenic components which are unaffected by secondary dissolution. In order to determine the rates of accumulation of various sedimentary components, a reliable differential measurement of age of the strata must be obtained. Various approaches to this problem are reviewed, and sources of error discussed. Secondary dissolution of calcium carbonate introduces a substantial and variable difference between the dissolution-modified, and hence a priori unknown, rate of deposition on one hand and the rate of accumulation, derivable from the observed concentration, on the other. The cause and magnitude of these variations are of importance, particularly since some current dating schemes are based on assumed constancy in the rate of accumulation of this and, in some cases, also all other sedimentary components. The concepts used in rate evaluation are discussed with emphasis on the difference between the state of dissolution, an observable property of the sediment, and the rate of dissolution, a parameter that requires deduction of the carbonate fraction dissolved, and of the time differential. As a most likely cause of the enhanced state of dissolution of the interglacial carbonate sediments is proposed the lowered rates of biogenic production and deposition, which cause longer exposure of the carbonate microfossils to corrosion in the bioturbated surface layer of the sediment. Historical perspective is included in the discussion in view of the dedication of the Symposium to Hans Pettersson, the leader of the Swedish Deep Sea Expedition 1947-1948, an undertaking that opened a new era in deep sea research and planetary dynamics.

NASA Discipline Exobiology↗
NASA NTRS2014

Carbon and Sulfur Isotopic Composition of Yellowknife Bay Sediments: Measurements by the Sample Analysis at Mars (SAM) Quadrupole Mass Spectrometer

Since landing at Gale Crater in Au-gust 2012, the Sample Analysis at Mars (SAM) instru-ment suite on the Mars Science Laboratory (MSL) “Curiosity” rover has analyzed solid samples from the martian regolith in three locations, beginning with a scoop of aeolian deposits from the Rocknest (RN) sand shadow. Curiosity subsequently traveled to Yellowknife Bay, where SAM analyzed samples from two separate holes drilled into the Sheepbed Mudstone, designated John Klein (JK) and Cumberland (CB). Evolved gas analysis (EGA) of all samples revealed the presence of H2O as well as O-, C- and S-bearing phas-es, in most cases at abundances below the detection limit of the CheMin instrument. In the absence of definitive mineralogical identification by CheMin, SAM EGA data can help provide clues to the mineralogy of volatile-bearing phases through examination of tem-peratures at which gases are evolved from solid sam-ples. In addition, the isotopic composition of these gas-es may be used to identify possible formation scenarios and relationships between phases. Here we report C and S isotope ratios for CO2 and SO2 evolved from the JK and CB mudstone samples as measured with SAM’s quadrupole mass spectrometer (QMS) and draw com-parisons to RN.

Franz, H. B.↗
NASA NTRS1985

A review of tectonic aspects of the Limpopo belt and other Archean high-grade gneissic terranes

Published information on the Archean high grade terrains varies a great deal in the detail available. Such information as exists indicates marked differences in the lithic types and proportions present in the central Limpopo belt compared with the better studies of the other Archean high grade terrains. These differences may be important because they are expressed by the presence in the Limpopo belt of subordinate, but significant quantities (about 5% each) of two rock suites likely to have formed on a shallow marine platform of significant size (Eriksson and Kidd, in prep.). These suites consist of thick sections dominantly consisting of either carbonate and calc-silicate, or of pure metaquartzites, often fuchsite bearing, whose lithic characters are unlike those expected for metacherts but are very like those expected for platform arenites. Isotopic ages suggest these sediments are probably older than 3.3 Ga and younger than 3.5 Ga. Studies lead to the conclusions that (1) continental fragments large enough to provide a substrate for significant platform arenite and carbonate sedimentation existed by 3.3 to 3.5 Ga ago; (2) Wilson cycle tectonics seems to adequately explain most major features of the Archean gneissic terranes; and (3) Tibetan-Himalayan style collisional tectonics 2.6 Ga and older accounts for the large scale relationships between the Limpopo belt and the adjacent Archean greenstone granitoid terrane cratons. By inference, other more fragmentary Archean gneissic terranes may have once been part of such collisional zones.

Kidd, W. S. F.↗
NASA NTRSDate not supplied

To Cage or Not to Cage Seagrass; Is There Even a Question?

To Cage or Not to Cage Seagrass; Is There Even a Question? Loraé T. Simpson1, Morgan K. Gilligan1, Douglas M. Scheidt2 1Florida Oceanographic Society, Stuart, FL; 2Herndon Solutions Group/NEMCON, Kennedy Space Center, FL Contact email: lsimpson@floridaocean.org Diminished water quality has led to the decline of seagrasses and their associated ecosystem services in the Banana River Lagoon (BRL), resulting in increased restoration initiatives. Restoration success may be hindered by herbivory and the addition of herbivore exclusion devices may limit grazing stress on newly established seagrasses. These structures may alter sediment dynamics, influencing seagrass productivity. To test whether herbivore exclusion devices impact restoration success and sediment dynamics, we caged half of our seagrass restoration plots in the BRL. Treatments were monitored monthly for seagrass growth, and at three months for porewater nutrients, sediment bulk density, and carbon to nitrogen ratio. On average, caged plots had 87% more seagrass cover and 81% taller blades than control plots, highlighting the importance of caging newly transplanted seagrasses. There was no significant difference in porewater or sediment characteristics between treatments, suggesting that pedogensis and nutrient cycling need extended monitoring to capture changes in temporal scales.

Indian River Lagoon↗
NASA NTRSDate not supplied

To Cage or Not to Cage Seagrass; Is There Even a Question?

Diminished water quality has led to the decline of seagrasses and their associated ecosystem services in the Banana River Lagoon (BRL), resulting in increased restoration initiatives. Restoration success may be hindered by herbivory and the addition of herbivore exclusion devices may limit grazing stress on newly established seagrasses. These structures may alter sediment dynamics, influencing seagrass productivity. To test whether herbivore exclusion devices impact restoration success and sediment dynamics, we caged half of our seagrass restoration plots in the BRL. Treatments were monitored monthly for seagrass growth, and at three months for porewater nutrients, sediment bulk density, and carbon to nitrogen ratio. On average, caged plots had 87% more seagrass cover and 81% taller blades than control plots, highlighting the importance of caging newly transplanted seagrasses. There was no significant difference in porewater or sediment characteristics between treatments, suggesting that pedogensis and nutrient cycling need extended monitoring to capture changes in temporal scales.

Indian River Lagoon↗
NASA NTRS1993

The anaerobic degradation of organic matter in Danish coastal sediments - Iron reduction, manganese reduction, and sulfate reduction

A combination of porewater and solid phase analysis as well as a series of sediment incubations are used to quantify organic carbon oxidation by dissimilatory Fe reduction, Mn reduction, and sulfate reduction, in sediments from the Skagerrak (located off the northeast coast of Jutland, Denmark). Solid phase data are integrated with incubation results to define the zones of the various oxidation processes. At S(9), surface Mn enrichments of up to 3.5 wt pct were found, and with such a ready source of Mn, dissimilatory Mn reduction was the only significant anaerobic process of carbon oxidation in the surface 10 cm of the sediment. At S(4) and S(6), active Mn reduction occurred; however, most of the Mn reduction may have resulted from the oxidation of acid volatile sulfides and Fe(2+) rather than by a dissimilatory sulfate. Dissolved Mn(2+) was found to completely adsorb onto sediment containing fully oxidized Mn oxides.

Canfield, Donald E.↗
NASA NTRS1997

Isotopic Signature of the Ancient Biosphere

The age distribution of 261 field localities, sampled for their well-preserved Archean and Proterozoic sedimentary rocks, revealed a 500-700 Ma episodicity. Assuming that the numbers of sites are a proxy for mass of sediments, the record of well-preserved sediments is more abundant in the intervals 3.5-3.3, 2.8-2.5, 2.1-1.8, 1.5-1.3, and 1.0-0.54 Ga than in the intervening intervals. It is proposed that the crustal inventory of photosynthetic organic carbon was modulated by the volume of sedimentation in sites favorable for the burial and long-term preservation of organic carbon. Tectonic processes controlled this sediment volume. Episodic increases in the organic inventory led to stepwise increases in oxidized reservoirs (e.g., O2, SO4(2-), Fe(3+). The interval 2.9-2.5 Ga recorded a large rise in seawater Sr-87/Sr-86, the oldest-known extensive banded iron formations, and the first evidence (C-13-depleted kerogens) of O2 use by methylotrophic bacteria. The interval 2.2-1.8 Ga has both carbon isotopic evidence for a stepwise increase in the organic reservoir and also paleosol evidence for an O2 increase. The interval 1.1-0.6 Ga shows isotopic evidence for another organic carbon increase. The interval 1.5-1.3 Ga revealed no such increases as yet, perhaps because incomplete rifting of the mid-Proterozoic supercontinent was associated with extensive sedimentation in oxidized continental basins, producing redbeds, coarse clastics, etc. Such sedimentation did not promote the burial of reduced carbon.

DesMarais, D. J.↗
NASA NTRS1976

Melanoidin and aldocyanoin microspheres - Implications for chemical evolution and early Precambrian micropaleontology

Two new classes of organic microspheres are described. One of them (melanoidin) is synthesized from amino acids and sugars in heated aqueous solutions. The other (aldocyanoin) is formed in aqueous solutions of ammonium cyanide and formaldehyde at room temperature. The general properties of these microspheres, including conditions of synthesis, size and shape, mechanical and pH stability, and solubility, are compared with corresponding properties of other protocell model systems. It is concluded that melanoidin and aldocyanoin microspheres are plausible candidates for precellular units in the primitive hydrosphere. Since the bulk of the organic carbon in early Precambrian sediments is insoluble kerogen-melanoidin, it is suggested that some Precambrian microfossils may be abiotic melanoidin microspheres.

Kenyon, D. H.↗