Thermal decomposition of the hydrated basic carbonates of lanthanides and yttrium

Thermogravimetry, differential thermal analysis, differential scanning calorimetry, IR absorption spectroscopy, X-ray diffraction, and other methods of analysis have been used in the characterization and study of the thermal decomposition of the basic carbonate hydrates of lanthanides and yttrium. These compounds were obtained by precipitation from homogeneous solutions via the hydrolysis of urea, without the addition of an auxiliary anion. The results show that the TG and DTA curves are characteristic for each compound. The results also permit suggestions concerning the compositions and mechanisms of thermal decomposition of these compounds. © 1989.

Thermal behaviour of the basic carbonates of lanthanum-europium

The basic carbonates of lanthanum with 10%, 20%, 50% and 80% of europium were prepared by precipitation from homogeneous solutions via the hydrolysis of urea, without the addition of an auxiliary anion, at two different temperatures. Elemental analysis, complexometric methods, X-ray diffraction patterns, solid state IR absorption, thermogravimetry/derivative thermogravimetry (TG/DTG) and differential thermal analysis (DTA) were used to characterise the compounds and study their thermal behaviour.

Possible early foraminiferans in post-Sturtian (716-635 Ma) cap carbonates

Foraminifera are an ecologically important group of modern heterotrophic amoeboid eukaryotes whose naked and testate ancestors are thought to have evolved similar to 1 Ga ago. However, the single-chambered agglutinated tests of these protists appear in the fossil record only after ca. 580 Ma, coinciding with the appearance of macroscopic and mineralized animals. Here we report the discovery of small, slender tubular microfossils in the Sturtian (ca. 716-635 Ma) cap carbonate of the Rasthof Formation in Namibia. The tubes are 200-1300 mu m long and 20-70 mu m wide, and preserve apertures and variably wide lumens, folds, constrictions, and ridges. Their sometimes flexible walls are composed of carbonaceous material and detrital minerals. This combination of morphological and compositional characters is also present in some species of modern single-chambered agglutinated tubular foraminiferans, and is not found in other agglutinated eukaryotes. The preservation of possible early Foraminifera in the carbonate rocks deposited in the immediate aftermath of Sturtian low-latitude glaciation indicates that various morphologically modern protists thrived in microbially dominated ecosystems, and contributed to the cycling of carbon in Neoproterozoic oceans much before the rise of complex animals.

Monoalkyl carbonates in carbonated alcoholic beverages

The presence of monoethyl carbonate (MEC) in beer and sparkling wine is demonstrated for the first time, as well as the formation of this species in drinks prepared with a distilled beverage and a carbonated soft drink. A capillary electrophoresis (CE) equipment with two capacitively coupled contactless conductivity detector ((CD)-D-4) was used to identify and quantify this species. The concentrations of MEC in samples of lager beer and rum and cola drink were, respectively, 1.2 and 4.1 mmol/l, which agree with the levels of ethanol and CO2 available in these products. Previous results about the kinetics of the reaction suggest that only a small amount of MEC should be formed after the ingredients of a drink are mixed. However, in all three cases (whisky and club soda: rum with cola; gin and tonic water), MEC was quickly formed, which was attributed to the low pH of the drinks. (C) 2012 Elsevier Ltd. All rights reserved.

Nonclassical crystallization of bivalent metal carbonates

Nichtklassische Kristallisationen tragen heutzutage einen entscheidenden Anteil zum Verständnis von Biomineralisationsprozessen und anspruchsvoller Morphogenese in vitro bei. Die vorliegende Dissertation stellt drei neue Vertreter nichtklassischer Kristallisationen vor, die während der Fällung von Calciumcarbonat und verwandten zweiwertigen Carbonaten auftreten.rn(a) Zum ersten Male wird eine Symmetrie-brechende Phasenselektion von Calciumcarbonat beschrieben, die auf einem subtilen Wechselspiel von verketteten Gleichgewichten basiert und deren Ursache letztendlich der paritätsverletzenden Energiedifferenz (PVED) zugeschrieben wird. rn(b) Die interkristalline Minoritätskomponente eines Mesokristalles, seien es z.B. eingeschlossenes Proteine oder polymere Additive, erfahren eine Morphogenese im Sinne einer Formpressung. Dieser bislang wenig beachtete Effekt in Mesokristallen wurde zur Herstellung von Nanoröhren eingesetzt, die aus verschiedensten Materialien bestehen können (z.B. Calciumcarbonat oder Cadmiumsulfid).rn(c) Das Hauptaugenmerk dieser Dissertation liegt auf dem Auftreten eines flüssig-amorphen Intermediates während der Metallcarbonat-Präzipitation. Durch diffusionskontrollierte und kontaktfreie Versuchsführung konnte die Existenz eines solchen nichtklassischen, flüssigen Intermediates, welches der kristallinen Phase bei neutralen pH vorangeht, sicher nachgewiesen werden. rn

Sonic log prediction in carbonates

This work is conducted to study the complications associated with the sonic log prediction in carbonate logs and to investigate the possible solutions to accurately predict the sonic logs in Traverse Limestone. Well logs from fifty different wells were analyzed to define the mineralogy of the Traverse Limestone by using conventional 4-mineral and 3-mineral identification approaches. We modified the conventional 3-mineral identification approach (that completely neglects the gamma ray response) to correct the shale effects on the basis of gamma ray log before employing the 3-mineral identification. This modification helped to get the meaningful insight of the data when a plot was made between DGA (dry grain density) and UMA (Photoelectric Volumetric Cross-section) with the characteristic ternary diagram of the quartz, calcite and dolomite. The results were then compared with the 4-mineral identification approach. Contour maps of the average mineral fractions present in the Traverse Limestone were prepared to see the basin wide mineralogy of Traverse Limestone. In the second part, sonic response of Traverse Limestone was predicted in fifty randomly distributed wells. We used the modified time average equation that accounts for the shale effects on the basis of gamma ray log, and used it to predict the sonic behavior from density porosity and average porosity. To account for the secondary porosity of dolomite, we subtracted the dolomitic fraction of clean porosity from the total porosity. The pseudo-sonic logs were then compared with the measured sonic logs on the root mean square (RMS) basis. Addition of dolomite correction in modified time average equation improved the results of sonic prediction from neutron porosity and average porosity. The results demonstrated that sonic logs could be predicted in carbonate rocks with a root mean square error of about 4μsec/ft. We also attempted the use of individual mineral components for sonic log prediction but the ambiguities in mineral fractions and in the sonic properties of the minerals limited the accuracy of the results.

Modeling episodic fluid-release events in the ductile carbonates of the Glarus thrust

The exposed Glarus thrust displays midcrustal deformation with tens of kilometers of displacement on an ultrathin layer, the principal slip zone (PSZ). Geological observations indicate that this structure resulted from repeated stick-slip events in the presence of highly overpressured fluids. Here we show that the major characteristics of the Glarus thrust movement (localization, periodicity, and evidence of pressurized fluids) can be reconciled by the coupling of two processes, namely, shear heating and fluid release by carbonate decomposition. During this coupling, slow ductile creep deformation raises the temperature through shear heating and ultimately activates the chemical decomposition of carbonates. The subsequent release of highly overpressurized fluids forms and lubricates the PSZ, allowing a ductile fault to move tens of kilometers on millimeter-thick bands in episodic stick-slip events. This model identifies carbonate decomposition as a key process for motion on the Glarus thrust and explains the source of overpressured fluids accessing the PSZ.

Isotope signature of the Younger Dryas and two minor oscillations at Gerzensee (Switzerland): palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates

Oxygen- and carbon-isotope ratios in the carbonate of benthic ostracodes (Pseudocandona marchica) and molluscs (Pisidium ssp.) were measured across the transitions bordering the Younger Dryas chronozone in littoral lacustrine cores from Gerzensee (Switzerland). The specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk-carbonate oxygen-isotope record (δ18OCc). If corrected for their vital offsets, oxygen-isotope ratios of Pisidium and juvenile P. marchica, both formed in summer, are almost identical to δ18OCc. This bulk carbonate is mainly composed of encrustations of benthic macrophythes (Chara ssp.), also mainly produced during summer. Adult P. marchica, which calcify in winter, show consistently higher δ18O, larger shifts across both transitions, and short positive excursions compared with the summer forms, especially during early Preboreal. Despite such complexity, the δ18O of adult P. marchica probably reflects more accurately the variations of the δ18O of former lake water because, during winter, calcification temperatures are less variable and the water column isotopically uniform. The difference between normalised δ18O of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures. In general, the results indicate warmer summers during the late Allerød and early Preboreal compared with the Younger Dryas. Altogether, the isotopic composition of lake water (δ18OL) and of the dissolved inorganic carbonate (δ13CDIC) reconstructed from adult Pseudocandona marchica, as well as the seasonal water temperature contrasts, indicate that the major shifts in the δ18O of local precipitation at Gerzensee were augmented by changes of the lake's water balance, with relatively higher evaporative loss occurring during the Allerød compared with the Younger Dryas. It is possible that during the early Preboreal the lake might even have been hydrologically closed for a short period. We speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts.

Physical properties and neutron texture measuerments of deep-sea carbonates of DSDP Holes 62-463 and 62-465A

In weakly indurated, nannofossil-rich, deep-sea carbonates compressional wave velocity is up to twice as fast parallel to bedding than normal to it. It has been suggested that this anisotropy is due to alignment of calcite c-axes perpendicular to the shields of coccoliths and shield deposition parallel to bedding. This hypothesis was tested by measuring the preferred orientation (fabric) of calcite c-axes in acoustic anisotropic, calcareous DSDP sediment samples by X-ray goniometry, and it was found that the maximum c-axis concentrations are by far too low to explain the anisotropies. The X-ray method is subject to a number of uncertainties due to preparatory and technical shortcomings in weakly indurated rocks. The most serious weaknesses are: sample preparation, volume of measured sample (fraction of a mm3), beam defocusing and background intensity corrections, combination of incomplete pole figures, and necessity of recalculation of the c-axis orientations from other crystallographic directions. Goniometry using thermal neutrons overcomes most of these difficulties, but it is time consuming. We test the interferences made about velocity anisotropy by X-ray studies about the concentration of c-axes in deep-sea carbonates by employing neutron texture goniometry to eight DSDP samples comprising mostly nannofossil material. Fabric and sonic velocity were determined directly on the core specimens, thus from the same rock volume and requiring no preparation. The c-axis orientation is obtained directly from the [0006] calcite diffraction peak without corrections. The fabrics are clearly defined, but weak (1.1 to 1.86 times uniform) with the maximum about normal to bedding. They have crudely orthorhombic symmetry, but are not axisymmetric around the bedding normal. The observed c-axis intensities, although higher than determined by the X-ray method on other samples, are by far too low to explain the observed acoustic anisotropies.

Chemical and isotopic compositions of ocean authigenic carbonates

Oceanic authigenic carbonates are classified according to origin of the carbonate carbon source using a complex methodology that includes methods of sedimentary petrography, mineralogy, isotope geochemistry, and microbiology. Mg-calcite (protodolomite) and aragonite predominate among the authigenic carbonates. All authigenic carbonates are depleted in 13C and enriched in 18O (in PDB system) that indicates biological fractionation of isotopes during carbonate formation. Obtained results show that authigenic carbonate formation is a biogeochemical (microbial) process, which involves carbon from ancient sedimentary rocks, abiogenic methane, and bicarbonate-ion of hydrothermal fluids into the modern carbon cycle.