Black Layer (black + layer)

Distribution by Scientific Domains
Earth and Environmental Science60%

Selected Abstracts

Biogeochemistry of a gypsum-encrusted microbial ecosystem

GEOBIOLOGY, Issue 3 2004
D. E. CANFIELD
ABSTRACT Gypsum crusts containing multicolored stratified microbial populations grow in the evaporation ponds of a commercial saltern in Eilat, Israel. These crusts contain two prominent cyanobacterial layers, a bright purple layer of anoxygenic phototrophs, and a lower black layer with active sulphate reduction. We explored the diel dynamics of oxygen and sulphide within the crust using specially constructed microelectrodes, and further explored the crust biogeochemistry by measuring rates of sulphate reduction, stable sulphur isotope composition, and oxygen exchange rates across the crust,brine interface. We explored crusts from ponds with two different salinities, and found that the crust in the highest salinity was the less active. Overall, these crusts exhibited much lower rates of oxygen production than typical organic-rich microbial mats. However, this was mainly due to much lower cell densities within the crusts. Surprisingly, on a per cell-volume basis, rates of photosynthesis were similar to organic-rich microbial mats. Due to relatively low rates of oxygen production and deep photic zones extending from 1.5 to 3 cm depth, a large percentage of the oxygen produced during the day accumulated into the crusts. Indeed, only between 16% to 34% of the O2 produced in the crust escaped, and the remainder was internally recycled, used mainly in O2 respiration. We view these crusts as potential homologs to ancient salt-encrusted microbial ecosystems, and we compared them to the 3.45 billion-year-old quartz barite deposits from North Pole, Australia, which originally precipitated gypsum. [source]

The black layer in cephalopods from the German Muschelkalk (Triassic)

PALAEONTOLOGY, Issue 6 2004
Christian Klug
Thin, dark, probably phosphatic coatings were found on the dorsum in front of and sometimes behind the aperture of 50 specimens of Paraceratites and Ceratites (Ammonoidea) belonging to 14 species and subspecies and in three specimens of Germanonautilus, all from the Middle Triassic of Germany. The proportions, occurrences, position, outline, and preservation in fossil Nautiloidea and Ammonoidea (originally organic matter) of this structure support the hypothesis that it is homologous with the black layer in Recent Nautilus and Allonautilus. It is not yet possible to test whether these cephalopods show homologous styles of the development of these structures or whether the black layer can be identified in a common ancestor. In contrast to many ammonoids, Ceratites and Paraceratites, most Palaeozoic ammonoids, and some Mesozoic ammonoids probably did not have lower mandibles that were suitable for the closure of the aperture. They probably possessed a dorsally extending mantle (supracephalic mantle fold) and a hood, as in Recent Nautilus and Allonautilus, that was attached to the black layer. This interpretation is corroborated by a similar morphology of the black layer in an adult specimen of the nautilid Cenoceras from the South German Middle Jurassic and three specimens of Germanonautilus from the South German Middle Triassic (both Nautiloidea). [source]

THE STUDY OF NABATAEAN ORGANIC RESIDUES FROM MADĀ'IN SĀLIH, ANCIENT HEGRA, BY GAS CHROMATOGRAPHY , MASS SPECTROMETRY,

ARCHAEOMETRY, Issue 4 2009
C. MATHE
Four Nabataean samples collected in some of the monumental tombs of Madā'in Sālih, ancient Hegra, in Saudi Arabia, have been studied by gas chromatography coupled with mass spectrometry. These samples are textile fragments that are either covered with a black layer or bound together with some black amorphous substance. Fatty acids and triterpenoic compounds were detected. Eight triterpenic compounds were identified: ursa-9(11),12-dien-3-ol, ursa-9(11),12-dien-3-one, olean-9(11),12-dien-3,-ol, ,-amyrone, ,-amyrin, ,-amyrone, ,-amyrin and lupeol. The resinous chemical composition and these pentacyclic alcohols, in considerable proportion, indicate a resin of the Burseraceae family, possibly of the genus Canarium. [source]

Hardened foliated fault gouge from the Nojima Fault zone at Hirabayashi: Evidence for earthquake lightning accompanying the 1995 Kobe earthquake?

ISLAND ARC, Issue 3-4 2001
Yuji Enomoto
Abstract Two anomalous features were found in the Nojima Fault zone at Hirabayashi in Awaji Island, south-west Japan: (i) hard foliated gouge between weathered granitic fault breccia and weakly consolidated mudstone of the Osaka Group; and (ii) mudstone near the gouge showing anomalous magnetization behavior. Roots of herbaceous vegetation near the foliated gouge were extraordinarily charred. In order to understand the nature of the gouge, shallow drillings were made to a depth of 3,14 m across the fault zone. Various physicochemical measurements of the gouge at depths and charred roots of herbaceous vegetation were conducted. The main results were: (i) Using electron spin resonance (ESR) analysis, the carbon radical peak (g = 2.006) of the charred roots was found to be 25 times larger than that of the non-charred roots of the same vegetation taken near the fault, indicating that the charred roots were subjected to baking; (ii) the hard foliated gouge clearly showed a lamellar structure consisting alternately of gray and black layers; (iii) the black layers in most of the foliated gouge showed flow structures almost parallel to the fault, but the gray layers rarely showed flow patterns; (iv) natural remanent magnetization (NRM) of the foliated gouge was 430 times greater than that of the granitic fault breccia and approximately 70 times greater than that of the mudstone; (v) the NRM intensity of the mudstone near the fault was highest near the ground level and decreased as the depth increased, although the magnetic susceptibility of the mudstone was almost constant and independent of depth; (vi) the high-coe civity magnetization component vectors of both the mudstone and the foliated gouge in a Schmidt equal-area projection was quite different from that of the present direction of the Earth's field; and (vii) using a magnetic force microscope, intense magnetic force lines were found in the black parts of the foliated gouge. It is suggested that these anomalies were possibly caused by earthquake lightning that accompanied the 1995 Kobe earthquake. In a spark plasma sintering test, which was conducted to simulate the possibility of earthquake lightning-induced sintering of the gouge, weakly altered gouge was successfully sintered within 10 s. The hardness of sintered sample was comparable to that of the hard foliated gouge. [source]

Effect of laser cleaning on granite color

COLOR RESEARCH & APPLICATION, Issue 2 2007
Carlota M. Grossi
Abstract This article presents the effect of laser radiation on the color of ornamental granites used for external cladding. The laboratory experimentation was undertaken on a widely used coarse-grain granite commercially known as Rosa Porrińo. The irradiation was carried out with a Q-switched Nd:YAG laser at 1064 nm and several energy densities (fluences) on polished surfaces, dry and wet, uncoated, and artificially coated-simulating a black crust. Laser effects on the granite surface were determined by color measurements with a colorimeter. These measurements made possible to determine probable damage due to laser radiation and the diverse response of different minerals. The analysis of the data also suggests potential causes for the color change and applicability limits of the technique. The a*-parameter, or red,green component, is the most affected, leading to a change in hab (hue) and was interpreted as a result in variations in the Fe compounds, which strongly condition stone color. No significant changes in L* (luminosity or lightness) or Cab* (chroma) may indicate no relevant alterations in the surface polish. When using laser irradiation to remove black layers on granite surfaces, variations of L* can be indicative of the cleaning effectiveness. This research results may be useful to select laser parameters when managing ornamental granite cleaning operations. However, they also suggest the need of further experimentation in specific techniques of analysis as well as different laser wavelengths. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 152 , 159, 2007 [source]