12 research outputs found
Geothermometry by Raman spectroscopy of dispersed organic matter
Raman-Spektroskopie an kohligem Material (RSCM) ist eine hÀufig verwendete
Methode, um die maximale Temperatur der Metamorphose oder die thermische Reife
von Kohlen und organikreichen Sedimenten zu bestimmen. FĂŒr die TemperaturabschĂ€tzung
wurden bereits mehrere Kalibrationskurven ermittelt, jedoch wird die Ăbertragbarkeit dieser
Kalibrationen auf andere Labore durch methodische Aspekte eingeschrÀnkt und die Vergleichbarkeit
zwischen den Laboren dadurch reduziert. Die subjektive Auswertung von Spektren, das
verwendete Messsystem und die ProbenheterogenitĂ€t bedingen die gröĂte Streuung der Ergebnisswerte
und ein Ansatz, mit dem Ziel die Vergleichbarkeit zu erhöhen, wurde formuliert. Um die
SubjektivitĂ€t der spektralen Auswertung zu veringern, wurde das âIFORSâ (Iterative Fitting Of
Raman Spectra) Programm geschrieben, das die automatische, Benutzer-unabhÀngige Auswertung
von Raman-Spektren ermöglicht. Um die Streuung aufgrund des verwendeten Messsystems
zu reduzieren, wurde ein Referenzprobensatz zusammengestellt, der einen Temperaturbereich
von 160 °C bis 600 °C abdeckt. WÀhrend der Probenaufbereitung wurde Resonanz-Raman-
Spektroskopie mit mehreren AnregungswellenlĂ€ngen an dispersen Vitriniten durchgefĂŒhrt, die
diagenetische bis epizonale Druck- und Temperaturbedingungen erfahren hatten, um die Gleichwertigkeit
der RSCM-Methode und Vitrinitreflexion zu ermitteln.
Mit Hilfe des IFORS Programms wurde der âscaled total areaâ (STA) Raman Parameter
ermittelt, der das Raman Spektrum von kohligem Material prÀzise beschreibt. Auf Grundlage
der Resonanz-Raman Daten konnte gezeigt werden, dass die Methodiken der STA-Raman Spektroskopie
und Vitrinitreflexion analog zueinander sind, dass die STA-RSCM Methode gegenĂŒber
der Probenaufbereitung, insbesondere dem Polieren, robust ist, und dass die Resonanz-Raman
Spektren der Vitrinite eine zweistufige molekulare Entwicklung wÀhrend der Inkohlung und
Graphitisierung aufzeichnen. WĂ€hrend der ersten Stufe, die kurz nach dem Durchschreiten
des Gas-Fensters endet, wachsen vor allem lineare, polyzyklische, aromatische Kohlenwasserstoffe,
wĂ€hrend in der anschlieĂenden zweiten Stufe kondensierte Formen von polyzyklischen,
aromatischen Kohlenwasserstoffen wachsen.
Um die Raman Spektren von metamorphem, kohligem Material zu beschreiben, wurde die
STA-RSCM Methodik erweitert und erfolgreich gegen die Temperaturinformation des Referenzprobensatzes
kalibriert, so dass ein neues, ĂŒberarbeitetes RSCM-Geothermometer vorgestellt
werden konnte, das ĂŒber einen Temperaturbereich von 160°C bis 600°C zulĂ€ssig ist. Der Referenzprobensatz
steht öffentlich zur VerfĂŒgung und es wird erwartet, dass der Probensatz verbessert
werden kann, wenn er um Proben aus der wissenschaftilchen Gemeinschaft erweitert wird. Wenn
beide AnsÀtze, die STA-RSCM Methodik und der Referenzprobensatz, miteinander kombiniert
werden, erhöht sich die Vergleichbarkeit zwischen den Laboren und gleichzeitig steht diese
geothermometrische Methode allen Laboren zur VerfĂŒgung.Raman spectroscopy of carbonaceous material (RSCM) is frequently used to determine
peak metamorphic temperature or to infer the coal rank as well as the degree of organic
maturation. Several temperature calibrations exist, but methodical aspects limit the portability
of these calibrations among laboratories and reduce overall comparability of the method. By
identifying the subjectivity of spectral evaluation, experimental setup and sample heterogeneity
as major sources of bias in the method, an outline to increase comparability could be established.
To reduce the subjectivity during spectral evaluation the automated, user-input independent
curve-fitting software âIFORSâ (Iterative Fitting Of Raman Spectra) has been written. To reduce
the bias due to the experimental setup, a reference sample series has been collected that
covers a temperature range of 160 °C to 600 °C. Multi-wavelength resonance Raman spectroscopy
was performed during sample preparation on dispersed vitrinites that experienced diagenetic to
epizonal pressure and temperature conditions to infer the analogy between the RSCM-method
and reflectance of dispersed organic matter.
The IFORS software allowed to derive the scaled total area (STA) Raman parameter which
accurately characterizes Raman spectra of carbonaceous matter. Based on the resonance Raman
data it could be shown that STA-RSCM method can be used in analogue to vitrinite reflectance,
that this method is robust to sample preparation, especially polishing, and that the resonance
Raman spectra of vitrinite reflect a two-stage molecular evolution during coalification and graphitization.
During the first stage, which ends approximately after the CM passed through the
gas-window, linear polycyclic aromatic structure grow, while the second stage indicates growth
of condensed polycyclic aromatic structures.
The STA-RSCM method has been extended to describe the Raman spectra of metamorphic
CM and was successfully calibrated to the reference sample series. Thus, a revised RSCMgeothermometer
valid from 160 °C to 600 °C is proposed. The sample series is available to the
public and is supposed to be extended by the scientific community to further increase the quality
of the reference series. When used in combination, the STA-RSCM method and the reference
sample series will improve the overall comparability among laboratories and will advance the
general applicability of this geothermometric method.2018-04-3
Inherited GrainâSize Distributions: Effect on HeavyâMineral Assemblages in Modern and Ancient Sediments
AbstractHeavyâmineral suites are used widely in sandstone provenance and are key when connecting source and sink. When characterizing provenance related signatures, it is essential to understand the different factors that may influence a particular heavyâmineral assemblage for example, chemical weathering or diagenetic processes. Hydrodynamics, causing sizeâdensity sorting, exert major control on the distribution of heavy minerals. Here, we highlight the effect of grainâsize inheritance, essentially the absence of certain grain sizes within a specific heavyâmineral species, on two distinct types of sediments. Modern deposits from a highâenergy beach in NW Denmark give an analog for heavily reworked sediment, primarily controlled by hydrodynamic processes. In contrast, three Palaeogene turbidite successions in the Eastern Alps were sampled, presenting a more complex history that includes diagenesis. All samples were processed for their heavyâmineral compositions using Raman spectroscopy, and several techniques applied to determine the effect of grainâsize inheritance. Results show that (a) even within the hydrodynamically wellâsorted beach and placer deposits, evidence of grainâsize inheritance is apparent, and (b) turbidites of variable heavyâmineral composition show strong effects of grainâsize inheritance for several mineral species. Moreover, considerable intersample contrasts within single turbidite beds are observed. We enforce the importance of understanding grainâsize inheritance, as well as other processes effecting sizeâdensity relations in clastic sediment that go well beyond purely hydrodynamic control of intrasample heavyâmineral variability.Plain Language Summary: Heavy minerals are commonly found within sediments and sedimentary rocks and can tell us from which source regions the sediment may have originated. However, it is important to understand that the type, size, and abundance of particular heavy minerals can change depending on factors such as environmental conditions. The size, shape, and density of the heavy minerals also limits when and where they will settle and/or stay. A lack of big or small grains of a particular heavy mineral in the source rocks dictates the size of the minerals deposited; this is known as grainâsize inheritance. Using both ancient and modern sediment, we are looking for traces of grainâsize inheritance. Surprisingly, in all samples investigated we noted effects of grainâsize inheritance, for different heavyâmineral types. The modern beach sediments, as expected, show more impact of hydraulic processes, but inherited grain sizes are still apparent. Within the ancient examples, grainâsize inheritance is more obvious, with further variations even observed between samples collected from the same area. Having identified this control on grain size, we can highlight the importance of understanding this effect when analyzing clastic sediments.Key Points:
Understanding factors that can modify a heavyâmineral assemblage is fundamental in provenance analysis
Heavy minerals of two distinct sedimentary environments were analyzed and compared to their âidealâ hydrodynamically sorted compositions
Several heavyâmineral species of modern and ancient settings were identified to be influenced by grainâsize inheritance from the source
https://doi.org/10.25625/MVUIJ
Semi-Automated Heavy-Mineral Analysis by Raman Spectroscopy
A significant amount of information on sedimentary provenance is encoded in the heavy minerals of a sediment or sedimentary rock. This information is commonly assessed by optically determining the heavy-mineral assemblage, potentially followed by geochemical and/or geochronological analysis of specific heavy minerals. The proposed method of semi-automated heavy-mineral analysis by Raman spectroscopy (Raman-HMA) aims to combine the objective mineral identification capabilities of Raman spectroscopy with high-resolution geochemical techniques applied to single grains. The Raman-HMA method is an efficient and precise tool that significantly improves the comparability of heavy-mineral data with respect to both overall assemblages and individual compositions within solid solution series. Furthermore, the efficiency of subsequent analysis is increased due to identification and spatial referencing of the heavy minerals in the sample slide. The method is tested on modern sediments of the Fulda river (central Germany) draining two Miocene volcanic sources (Vogelsberg, Rhön) resting on top of Lower Triassic siliciclastic sediments. The downstream evolution of the volcanic detritus is documented and the capability to analyze silt-sized grains has revealed an additional eolian source. This capability also poses the possibility of systematically assessing the heavy-mineral assemblages of shales, which are often disregarded in sedimentary provenance studies
Analytical data of rutile and garnet chemistry of sandstone samples from the Enticho Sandstone and the Edaga Arbi Glacials (Palaeozoic, Ethiopia)
We use heavy minerals and rutile and garnet chemical compositions to constrain the provenance of two glaciogenic sandstone formations that build up the Palaeozoic succession in Ethiopia. The heavy mineral assemblage of the Upper OrdovicianâLower Silurian Enticho Sandstone is dominated by ultra-stable minerals, implying high maturity of the sediment. Variable amounts of garnet are present as well. The CarboniferousâPermian Edaga Arbi Glacials contain mainly less stable heavy minerals, such as garnet and apatite, suggesting little chemical alteration. A combination of magmatic and metamorphic source rocks is likely for both formations. Rutile and garnet chemistry point to mainly amphibolite-facies and to a lesser extent granulite-facies metamorphic source rocks with generally slightly higher metamorphic temperatures for detrital heavy minerals in the Enticho Sandstone. We conclude that the Enticho Sandstone is mainly the product of reworked mature CambrianâOrdovician sediment, which may have been supplied via the Gondwana super-fan system. Locally, glaciers of the Late Ordovician glaciation eroded fresh basement material, delivering the garnet. For the Edaga Arbi Glacials, a rather proximal provenance is likely. The potential source area is the southern hinterland, where Precambrian low-to higher grade metamorphic rocks of the ArabianâNubian Shield occur at the transition to the Mozambique Belt.Final thirt published dataset from the dissertatio
Estimation of radiation damage in titanites using Raman spectroscopy
International audienceRecent studies have shown that a-damage in titanite influences He diffusivity and thus the closure temperature of the (U-Th)/He system in titanite. We compare different methods for measuring the alpha-dose in titanite by Raman spectroscopy. Raman spectra of randomly oriented titanite fragments from the Archean Karelian domain in eastern Finland along with some well-studied young titanites and U-Pb standard reference materials were analyzed and related to the concentration of alpha-emitting elements (U and Th) that generated damage in the respective grains. Automated curve-fitting was performed by the IFORS software and different curve-fitting protocols were tested and compared.The Raman bands at 424 and 465 cm(-1) show a good correlation of full-width at half maximum (FWHM) and position with the alpha-dose. However, these bands are not always present because titanite is highly anisotropic implying that Raman spectra are sensitive to orientation. The intensity-weighted mean FWHM (iw-FWHM) of all Raman bands of a spectrum proves to be the most robust measure of the alpha-dose. A simplified fitting approach considering 15 peaks is sufficient to describe the accumulated alpha-dose. For alpha-doses below 5 x 10(16)alpha/g the iw-FWHM is independent of alpha-dose and ranges from 25 to 50 cm-1. Above this value the iw-FWHM increases linearly with increasing alpha-dose up to 3 x 10(18)alpha/g. The linear correlation can be described as iw-FWHM[cm(-1)] approximate to 39(+/- 1.2)[cm(-1)] + 3.84(+0.61,-0.26) x 10(-17)[cm(-1)/(alpha/g)] x alpha-dose[alpha/g]. The approach provides a pre-selection method to optimize the range of alpha-doses of titanite crystals to be dated by (U-Th)/He thermochronology
Post-Caledonian brittle deformation in the Bergen area,West Norway: results from KâAr illite fault gouge dating
Post-Caledonian extension during orogenic collapse and Mesozoic rifting in the West Norwayânorthern North Sea region was accommodated by
the formation and repeated reactivation of ductile shear zones and brittle faults. Offshore, the Late PalaeozoicâMesozoic rift history is relatively well
known; extension occurred mainly during two rift phases in the PermoâTriassic (Phase 1) and MidâLate Jurassic (Phase 2). Normal faults in the
northern North Sea, e.g., on the Horda Platform, in the East Shetland Basin and in the Viking Graben, were initiated or reactivated during both rift
phases. Onshore, on the other hand, information on periods of tectonic activity is sparse as faults in crystalline basement rocks are difficult to date. Kâ
Ar dating of illite that grows synkinematically in fine-grained fault rocks (gouge) can greatly help to determine the time of fault activity, and we apply
the method to nine faults from the Bergen area. The KâAr ages are complemented with X-ray diffraction analyses to determine the mineralogy, illite
crystallinity and polytype composition of the samples. Based on these new data, four periods of onshore fault activity could be defined: (1) the earliest
growth of fault-related illite in the Late DevonianâEarly Carboniferous (>340 Ma) marks the waning stages of orogenic collapse; (2) widespread latest
CarboniferousâMid Permian (305â270 Ma) fault activity is interpreted as the onset of Phase 1 rifting, contemporaneous with rift-related volcanism
in the central North Sea and Oslo Rift; (3) a Late TriassicâEarly Jurassic (215â180 Ma) period of onshore fault activity postdates Phase 1 rifting and
predates Phase 2 rifting and is currently poorly documented in offshore areas; and (4) Early Cretaceous (120â110 Ma) fault reactivation can be linked
either to late Phase 2 North Sea rifting or to North Atlantic rifting
The onshore West Baram Delta deposits: Provenance and drainage in the Middle Miocene to Pliocene in NW Borneo and comparison to the Champion Delta
The Baram Delta province in NW Borneo forms a major hydrocarbon reservoir offshore northern Sarawak and Brunei. The delta sequence is thereby subdivided into the West Baram delta to the south and the Champion delta to the north. Onshore are the remains of the Neogene delta deposits exposed and provide the possibility to study the equivalent offshore successions in outcrop. This study focuses on the Neogene West Baram delta successions which were studied for sedimentological facies and provenance characteristics. The successions consist of the Lambir, Miri, Tukau, and the enigmatic southern Lambir/Belait-Sarawak formations. Deposition took place in various mixed-energy delta environments between the Langhian and early Pliocene. The sediments are all quartz-rich and heavy minerals are dominated by ultra-stable zircon, rutile and tourmaline. Dominant detrital zircon age clusters are in the Early Cretaceous and Permian-Triassic. Based on light mineral petrography, heavy mineral assemblages, and detrital zircon UâPb geochronology, all formations are interpreted as derived from multi-recycled sources, likely the underlying Paleogene Rajang Group turbidites and the Oligocene to Lower Miocene Nyalau-Tatau delta deposits. Additionally, literature data of the Champion Delta and one sample from Labuan analysed for provenance in this study are used to demonstrate that the Champion Delta can be distinguished from the West Baram Delta by having higher chrome spinel and garnet contents and slightly different detrital zircon age populations. The Champion Delta deposits are interpreted as sourced by recycling of the Crocker Formation and older turbidites (e.g., Sapulut Formation) with potentially input from ultra-mafic basement rocks of Sabah