GEOCHEMICAL CHARACTERIZATION (geochemical + characterization)

Distribution by Scientific Domains


Selected Abstracts


GEOCHEMICAL CHARACTERIZATION OF A BIODEGRADED CRUDE OIL, ASSRAN FIELD, CENTRAL GULF OF SUEZ

JOURNAL OF PETROLEUM GEOLOGY, Issue 4 2009
A. H. Hegazi
A crude oil sample from the Assran field in the Central Gulf of Suez (Egypt) was analysed geochemically and characterized in terms of a variety of source and maturity dependent biomarkers. Biodegradation was indicated by increasing concentration ratios of Pr/n-C17 and Ph/n-C18. However, biodegradation was only slight as GC-MS analyses of the saturate and aromatic fractions showed that hopanes, steranes, aromatic steroids and polycyclic aromatic compounds including sulphur heterocycles remained intact. The sterane and hopane distributions showed a predominance of C27 steranes, a low diasterane index, an abundance of gammacerane, a high homohopane index and an oleanane index < 0.2. The results indicate that the Assran-10 crude oil was derived from a marine carbonate source deposited in a highly reducing saline environment with a high bacterial contribution, consistent with the Upper Cretaceous Brown Limestone or Lower Eocene Thebes Formation containing Type IIS kerogen. Maturity parameters based on changes in the stereochemistry at chirality centres in hopane and sterane nuclei, such as C30,,/(,,+,,) and C31 22S/(22S+22R) hopanes and C29,,/(,,+,,) and C29 20S/(20S+20R) steranes, together with triaromatic sterane cracking ratios, indicate that the oil sample was marginally mature. The results also suggest that biodegradation is probably due to sulphate-reducing anaerobic bacteria. [source]


PROVENANCE OF MARBLES FROM NAXOS BASED ON MICROSTRUCTURAL AND GEOCHEMICAL CHARACTERIZATION

ARCHAEOMETRY, Issue 2 2010
A. EBERT
A detailed quantitative microstructural study coupled with cathodoluminescence and geochemical analyses on marbles from Naxos demonstrates that the analysis of microstructures is the most sensitive method to define the origin of marbles within, and between, different regions. Microstructure examination can only be used as an accurate provenance tool if a correction for the second-phase content is considered. If second phases are not considered, a large spread of different microstructures occurs within sample sites, making a separation between neighbouring outcrops difficult or impossible. Moreover, this study shows that the origin of a marble is defined more precisely if the microstructural observations are coupled with cathodoluminescence data. [source]


MINERO-PETROGRAPHIC AND GEOCHEMICAL CHARACTERIZATION OF ,GRECO SCRITTO' MARBLE FROM CAP DE GARDE, NEAR HIPPO REGIUS (ANNABA, ALGERIA)*

ARCHAEOMETRY, Issue 3 2009
F. ANTONELLI
This work presents the results of the first mineralogical, petrographical and geochemical characterization of the marble quarried from the Cap de Garde headland, not far from Annaba (Algeria). This site is traditionally held by archaeologists to be the main source of supply of the so-called ,greco scritto' marble, which was much used by the Romans for architectural and decorative,ornamental purposes, locally from the first century bc, and in Rome and central and southern Italy from the late Flavian period until the fourth century ad. The databank relating to the quarried material, created here for the first time, is used to establish the origin of ,greco scritto' found in six important Roman cities of North Africa: Hippo Regius and Cuicul (Djemila), in Algeria; Volubilis, in Morocco; Cyrene, in Libya; and Carthage and Utica in Tunisia. The results of this archaeometric study support the hypothesis (already put forward by authors) that the ,greco scritto'used in the Roman Mediterranean originated from different sites, and suggest the existence of a number of North African quarries, also in the vicinity of Annaba. [source]


THE ORIGIN AND GEOCHEMICAL CHARACTERIZATION OF RED OCHRES FROM THE TITO BUSTILLO AND MONTE CASTILLO CAVES (NORTHERN SPAIN)*

ARCHAEOMETRY, Issue 2 2009
E. IRIARTE
Ochres were the most common source materials for pigments used in Palaeolithic rock art paintings. This work analyses the petrographic and geochemical signatures of different ochre samples from outcrops inside Tito Bustillo Cave and the Monte Castillo Caves using the most common techniques (petrography, XRD, SEM,EDS and ICP,MS) in archaeological pigment characterization studies. The results obtained permit the identification and characterization of the different source ochre types and, furthermore, allow the establishment of mineralogical and geochemical proxies for the study of questions related to ochre characterization, formation processes and provenance. [source]


Mineralogical and Geochemical Characterization of Beryl-Bearing Granitoids, Eastern Desert, Egypt: Metallogenic and Exploration Constraints

RESOURCE GEOLOGY, Issue 2 2009
Hamdy M. Abdalla
Abstract Mineral chemistry and geochemical characteristics of beryl-bearing granitoids in Eastern Desert of Egypt, were examined in order to identify the metallogenetic processes of the host granitoids. The investigated Be-bearing granitoids and type occurrences are classified into two groups: (i) peraluminous, Ta , Nb + Sn + Be W-enriched, Li-albite granite (e.g. Nuweibi and Abu Dabbab); and (ii) metasomatized, Nb >> Ta + Sn + Be W Mo-enriched alkali feldspar granite (i.e. apogranite; e.g. Homr Akarem, Homr Mikpid and Qash Amir). In these two groups, beryl occurs as stockwork greisen veins, greisen bodies, beryl-bearing cassiterite wolframite quartz veins, dissemination, and miarolitic pegmatites. Beryl of the Be-granitoids, particularly those of miarolitic pegmatites, contains appreciable contents of Fe, Na, and H2O. An important feature of the Be-apogranites is the occurrence of white mica as the sole mafic mineral in the unaltered alkali feldspar granite in lower zones. Presence of white mica as volatile-rich pockets suggests that the melt underwent disequilibrium crystallization, rapid nucleation rates, and exsolving and expulsion of volatiles. [source]


Geochemical characterization of moldavites from a new locality, the Cheb Basin, Czech Republic

METEORITICS & PLANETARY SCIENCE, Issue 3 2008
anda
Detailed comparison of the Cheb Basin moldavites with moldavites from other substrewn fields in both major and trace element composition shows that the Cheb Basin is a separate substrewn field. The geochemical data obtained are discussed with respect to the source materials and processes leading to formation of moldavites. The data show that three groups of Cheb Basin moldavites exist. Ten samples of group 1 are characterized by the lowest content of Al, Fe, Na, and other elements representing phyllosilicate minerals, and by high Ca + Mg contents related probably to carbonates. They resemble the "poisonous green" moldavites, a subgroup of the Southern Bohemian moldavites. Seven samples of group 2 and 6 samples of group 3 are similar to typical moldavites of the Southern Bohemian substrewn field. These two groups differ from each other mainly in Al contents; with higher contents of Al and the elements associated with phyllosilicate minerals (namely Ba and Sr), group 3 also resembles the Moravian moldavites. Significant positive correlations between K, Ca, Mg, and Mn found in group 2 of the Cheb Basin moldavites and the enrichment in these elements observed generally in all moldavites, as well as other facts, e.g., high K/Na and K/Rb ratios and the reduced conditions during formation of moldavites, have been attributed to possible contribution to the moldavite source materials of the ash produced by burning of vegetation and soil organic matter present at the pre-impact area. [source]


Geochemistry, Petrography and Spectroscopy of Organic Matter of Clay-Associated Kerogen of Ypresian Series: Gafsa-Metlaoui Phosphatic Basin, Tunisia

RESOURCE GEOLOGY, Issue 4 2008
Mongi Felhi
Abstract This work presents geochemical characterization of isolated kerogen out of clay fraction using petrography studies, infrared absorption and solid state 13C nuclear magnetic resonance (NMR) spectroscopy, with N -alkane distributions of saturated hydrocarbon. Mineralogical study of clay mineral associations was carried out using X-ray diffraction (XRD), on Ypresian phosphatic series from Gafsa-Metlaoui basin, Tunisia. The XRD data indicate that smectite, palygorskite and sepiolite are the prevalent clay minerals in the selected samples. In this clay mineral association, the N -alkane (m/z = 57) distribution indicates that the marine organic matter is plankton and bacterial in origin. The kerogens observed on transmitted light microscopy, however, appear to be totally amorphous organic matter, without any appearance of biological form. The orange gel-like amorphous organic matter with distinct edges and homogenous texture is consistent with a high degree of aliphaticity. This material has relatively intense CH2 and CH3 infrared bands in 13C NMR peaks. This aliphatic character is related to bacterial origin. Brown amorphous organic matter with diffuse edges has a lower aliphatic character than the previous kerogen, deduced from relatively low CH2 and CH3 infrared and 13C NMR band intensities. [source]


MINERO-PETROGRAPHIC AND GEOCHEMICAL CHARACTERIZATION OF ,GRECO SCRITTO' MARBLE FROM CAP DE GARDE, NEAR HIPPO REGIUS (ANNABA, ALGERIA)*

ARCHAEOMETRY, Issue 3 2009
F. ANTONELLI
This work presents the results of the first mineralogical, petrographical and geochemical characterization of the marble quarried from the Cap de Garde headland, not far from Annaba (Algeria). This site is traditionally held by archaeologists to be the main source of supply of the so-called ,greco scritto' marble, which was much used by the Romans for architectural and decorative,ornamental purposes, locally from the first century bc, and in Rome and central and southern Italy from the late Flavian period until the fourth century ad. The databank relating to the quarried material, created here for the first time, is used to establish the origin of ,greco scritto' found in six important Roman cities of North Africa: Hippo Regius and Cuicul (Djemila), in Algeria; Volubilis, in Morocco; Cyrene, in Libya; and Carthage and Utica in Tunisia. The results of this archaeometric study support the hypothesis (already put forward by authors) that the ,greco scritto'used in the Roman Mediterranean originated from different sites, and suggest the existence of a number of North African quarries, also in the vicinity of Annaba. [source]