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Geowissenschaften

Die Erforschung der Erdgeschichte erfüllt den grundlegenden menschlichen Drang zu wissen, wie die Welt entstanden ist. Im Laufe ihrer 4,6 Milliarden Jahre langen Geschichte hat die Erde eine enorme Transformation durchlaufen, und die Stabilisotopenanalyse steht bei der Erforschung dieser Veränderungsprozesse an vorderster Front. Durch das Verständnis der makro- und mikrozyklischen Mechanismen, welchen die leichten stabilen Isotope in der Lithosphäre durch natürliche Prozesse unterliegen, wächst auch unser Wissen über die Erdgeschichte kontinuierlich.

Paläoklima

Eine der ersten Anwendungen der Stabilisotopenmassenspektrometrie leichter Elemente war die Rekonstruktion des Paläoklimas auf Grundlage der Sauerstoff-Isotopenzusammensetzung (δ18O) von sehr alten, konservierten marinen Carbonaten. Auch heute noch ist dies eine der weitverbreitesten Methoden zur Erforschung der Klimageschichte der Erde. Dieses Paläothermometer basiert auf dem Grundprinzip, dass die Fraktionierung von Sauerstoffisotopen in Calcit temperaturabhängig ist. Das isoprime precisION mit Dual Inlet und MultiCarb ermöglicht eine sehr präzise und zuverlässige, automatisierte Messung von Carbonaten, ideal zur Erzeugung hochauflösender Paläotemperaturaufzeichnungen.

Kosmologie

Die Schwefelisotopenanalyse von extraterrestrischen Sulfidmineralien, z.B. von Meteoriten, hat eine Vielzahl von Erkenntnissen über den Ursprung der Erde und des Sonnensystems ermöglicht. Die Isotopenzusammensetzung von meteoritischem Schwefel (Canyon Diabolo Triolite) wurde auch als der ursprüngliche Bezugspunkt für Erdkruste und -mantel verwendet, von der ausgehend die globalen Fraktionen im Schwefelkreislauf evaluiert werden. Schwefelhaltige Mineralien lassen sich leicht mit unserem vielseitigen Spektrum von EA-IRMS-Systemen analysieren, welche die Advanced Purge and Trap Technologie (APT) für eine unschlagbare Trennung und Peakfokussierung von SO2 nutzen, um eine perfekte Auflösung und eine unvergleichliche Empfindlichkeit für die Mineralschwefelanalyse zu gewährleisten.

Stratigraphie

δ13C-Fluktuationen im Laufe geologischer Zeitalter werden durch Änderungen des Gleichgewichts im Kohlenstoffkreislauf bewirkt. Da die Verweilzeit im Kohlenstoffkreislauf kurz ist (10 ka), werden Änderungen im Kohlenstofffluss im Sediment sehr genau global aufgezeichnet. Als solche sind gelegentliche Spikes im globalen δ13C als stratigraphische Marker für die Chemostratigraphie nützlich, besonders während des Paläozoikums. Der iso FLOW nutzt unsere neuartige UltiTrap-Technologie und ermöglicht so eine präzise, durchgängige Continuous Flow Analyse von Massencarbonaten, um solche Isotopenabweichungen zu identifizieren.

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248 Ergebnisse:

Early Holocene palaeoseasonality inferred from the stable isotope composition of Unio shells from Çatalhöyük, Turkey
Environmental Archaeology (2016)
Jonathan P. Lewis, Melanie J. Leng, Jonathan R. Dean, Arkadiusz Marciniak, Daniella E. Bar-Yosef Mayer, Xiaohong Wu

Seasonal δ13C and δ18O data are presented from 14 Unio sub-fossil shells unearthed at the archaeological site of Çatalhöyük in central Turkey, spanning the occupation period ca. 9150–8000 cal years BP. The shells likely lived in the small lakes/wetlands around the site before being gathered and taken to Çatalhöyük. Wet-dry seasonal cycles are clearly apparent in the δ18Oshell profiles with low winter values reflecting winter precipitation and high δ18O in the summer resulting from evaporation. The most striking trend in the δ18O data is the drop in maximum summer δ18O ca. 8300 years BP, which we infer as indicating lower summer evaporation and hence a reduction in seasonality. Previous palaeoclimate records from the area have suggested cooler and more arid conditions, with reduced precipitation, around this time. While the drop in summer δ18O values could be due to reduced summer temperatures reducing summer evaporation, but there was little change in winter δ18O, perhaps suggesting winter growth cessatio...
Schlagworte: carbon , oxygen , geol , clim , mulitcarb

Water cycle and salinity dynamics in the mangrove forests of Europa and Juan de Nova Islands, southwest Indian Ocean
Rapid Communications in Mass Spectrometry (2016)
Luc Lambs, Perrine Mangion, Eric Mougin, François Fromard

Rationale: The functioning of mangrove forests found on small coralline islands is characterized by limited freshwater inputs. Here, we present data on the water cycling of such systems located on Europa and Juan de Nova Islands, Mozambique Channel. Methods: In order to better understand the water cycle and mangrove growth conditions, we have analysed the hydrological and salinity dynamics of the systems by gauge pressure and isotopic tracing (δ18O and δ2H values). Results: Both islands have important seawater intrusion as measured by the water level change and the high salinities in the karstic ponds. Europa Island displays higher salinity stress, with its inner lagoon, but presents a pluri-specific mangrove species formation ranging from shrub to forest stands. No freshwater signal could be detected around the mangrove trees. On Juan de Nova Island, the presence of sand and detrital sediment allows the storage of some amount of rainfall to form a brackish groundwater. The mangrove surface area is very limited with only small mono-specific stands being present in karstic depression. Conclusions: On the drier Europa Island, the salinity of all the water points is equal to or higher than that of the seawater, and on Juan de Nova the groundwater salinity is lower (5 to 20 PSU). This preliminary study shows that the karstic pothole mangroves exist due to the sea connection through the fractured coral and the high tidal dynamics.
Schlagworte: hydrogen , oxygen , geol , ocea , gashead

A microbial carbonate response in synchrony with the end-Triassic mass extinction across the SW UK.
Scientific reports (2016)
Yadira Ibarra, Frank A Corsetti, Sarah E Greene, David J Bottjer

The eruption of the Central Atlantic Magmatic Province (CAMP)-the largest igneous province known-has been linked to the end-Triassic mass extinction event, however reconciling the response of the biosphere (at local and nonlocal scales) to potential CAMP-induced geochemical excursions has remained challenging. Here we present a combined sedimentary and biological response to an ecosystem collapse in Triassic-Jurassic strata of the southwest United Kingdom (SW UK) expressed as widely distributed carbonate microbialites and associated biogeochemical facies. The microbialites (1) occur at the same stratigraphic level as the mass extinction extinction, (2) host a negative isotope excursion in δ(13)Corg found in other successions around the world, and (3) co-occur with an acme of prasinophyte algae 'disaster taxa' also dominant in Triassic-Jurassic boundary strata of other European sections. Although the duration of microbialite deposition is uncertain, it is likely that they formed rapidly (perhaps fewer than ten thousand years), thus providing a high-resolution glimpse into the initial carbon isotopic perturbation coincident with the end-Triassic mass extinction. These findings indicate microbialites from the SW UK capture a nonlocal biosedimentary response to the cascading effects of massive volcanism and add to the current understanding of paleoecology in the aftermath of the end-Triassic extinction.
Schlagworte: carbon , oxygen , geol , mulitcarb

The carbon isotope and sequence stratigraphic record of the Sheinwoodian and lower Homerian stages (Silurian) of the Midland Platform, UK
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Helen E. Hughes, David C. Ray

New high resolution δ13Ccarb isotope data are presented through the Sheinwoodian and lower Homerian stages of the Wenlock Series (Silurian) from sections in Shropshire, Herefordshire and the West Midlands (UK). This data identifies the well-known Early Sheinwoodian positive Carbon Isotope Excursion (ESCIE), the minor mid-ESCIE negative shift, and an Early Homerian positive Carbon Isotope Excursion (EHCIE) in the region of 1.4‰, as developed upon the Midland Platform and in close proximity to the Sheinwoodian and Homerian GSSPs. These carbon isotope excursions have been correlated against graptolite, conodont and chitinozoan frameworks from across the Midland Platform, and alongside details of sedimentology and faunas, have allowed for the establishment of a sequence stratigraphic framework. These integrated data sets reveal that the shallow-water Barr–Buildwas–Woolhope limestones reflect approximately synchronous deposition across the Midland Platform; in that they all contain the ESCIE and five widely traceable depositional cycles. Moreover, biostratigraphic and sequence stratigraphic frameworks from across the Midland Platform (Avalonia) confirm that both the ESCIE and the five cycles are synchronous with records from other palaeocontinents (Baltica and Laurentia) and indicate that the early Sheinwoodian graptolite zones as established in the type area are in need of review.
Schlagworte: carbon , geol , clim , mulitcarb

Hydrological and Land Use Control of Watershed Exports of DOM in a Large Arid River Basin in Northwestern China
Journal of Geophysical Research: Biogeosciences (2016)
Yue Hu, YueHan Lu, Jennifer W Edmonds, Chuankun Liu, Sai Wang, Oindrila Das, Jie Liu, Chunmiao Zheng

We evaluated variation in dissolved organic matter (DOM) export as a function of hydrology and land use from a large arid river basin in northwestern China. Two soil-derived, humic-like (C1 and C2) and three protein-like fluorescence components (C3, C4, and C5) were identified. During high discharges, river water DOM had higher values of DOC concentration, percent humic fluorescence, and humification index, but lower values of fluorescence index and percent protein fluorescence than found at base flow, suggesting that flow paths shifted to shallower depths flushing out topsoil organic matter. Loading of DOC and soil-derived humic fluorescence were driven largely by discharge, with values over 10 times higher during high discharges than at base flow. Furthermore, both δ13C-DOC and C1 at high flows positively correlated with %agricultural lands within 1 km river buffers, demonstrating that near-river agricultural activities enhanced storm export of soil DOM. At base flow, C4 positively correlated with %agricultural lands, showing stimulation of aquatic bacterial carbon production as a result of elevated nutrient inputs from agricultural lands. Percent contributions of humic fluorescence in groundwater varied with well depths in shallow wells, but this pattern was not observed for deeper groundwater, suggesting that humic DOM could serve as a water source tracer indicating deeper aquifers were isolated from river water and shallow groundwater. Together, our data demonstrate that hydrology and land use controlled the sources and amount of riverine DOM in this large agricultural basin and that regulating storm runoff and near-river agricultural activities should be incorporated in ecosystem-based management of water resources.
Schlagworte: carbon , oxygen , geol , gashead

PRELIMINARY INVESTIGATION OF SEASONAL PATTERNS RECORDED IN THE OXYGEN ISOTOPE COMPOSITIONS OF THEROPOD DINOSAUR TOOTH ENAMEL
PALAIOS (2016)
JEAN GOEDERT, ROMAIN AMIOT, LARBI BOUDAD, ERIC BUFFETAUT, FRANÇOIS FOUREL, PASCAL GODEFROIT, NAO KUSUHASHI, VARAVUDH SUTEETHORN, HAIYAN TONG, MAHITO WATABE, CHRISTOPHE LÉCUYER

Oxygen isotope compositions of tooth enamel increments in theropod dinosaurs are investigated as potential proxies of climate seasonality. Six teeth of large carnivorous theropods collected from four Cretaceous formations deposited under contrasted climates have been sampled. These teeth have been analyzed for the oxygen isotope compositions of their apatite phosphate ({delta}18Op) through incremental sampling performed along the major growth axis. Significant fluctuations in oxygen isotope compositions along the growth axis of each tooth are observed and interpreted as reflecting seasonality in ingested local surface water {delta}18Ow values. Fluctuations in {delta}18Op values of theropod teeth from the Aptian of Thailand and Cenomanian of Morocco vary similarly to meteoric water {delta}18Omw values occurring today in sub-tropical regions subjected to large seasonal amounts of precipitations. A dinosaur tooth recovered from the more inland and mid-latitude Nemegt Formation of Mongolia shows a seasonal pattern similar to present-day cold temperate and continental climate. Finally, the high latitude and coastal Kakanaut Formation (Russia) experienced strongly dampened seasonal variations, most likely due to the influence of warm Pacific oceanic currents. Such conditions occur today in high latitude regions submitted to marine influence. These results further highlight the potential of using the oxygen isotope compositions of large theropod teeth to reconstruct past seasonal variations of terrestrial climates. Increased knowledge of past seasonality may help to better understand the complex interactions between climate and the dynamics of land biodiversity in terms of ecological adaptations, biogeography and the evolutionary history of organisms.
Schlagworte: oxygen , geol , ecol , clim , elem

Isotope-based partitioning of streamflow in the oil sands region, northern Alberta: Towards a monitoring strategy for assessing flow sources and water quality controls
Journal of Hydrology: Regional Studies (2016)
J.J. Gibson, Y. Yi, S.J. Birks

STUDY REGION This study is based on the rapidly developing Athabasca Oil Sands region, northeastern Alberta. STUDY FOCUS Hydrograph separation using stable isotopes of water is applied to partition streamflow sources in the Athabasca River and its tributaries. Distinct isotopic labelling of snow, rain, groundwater and surface water are applied to estimate the contribution of these sources to streamflow from analysis of multi-year records of isotopes in streamflow. NEW HYDROLOGICAL INSIGHTS FOR THE REGION The results provide new insight into runoff generation mechanisms operating in six tributaries and at four stations along the Athabasca River. Groundwater, found to be an important flow source at all stations, is the dominant component of the hydrograph in three tributaries (Steepbank R., Muskeg R., Firebag R.), accounting for 39–50% of annual streamflow. Surface water, mainly drainage from peatlands, is also found to be widely important, and dominant in three tributaries (Clearwater R., Mackay R., Ells R.), accounting for 45–81% of annual streamflow. Fairly limited contributions from direct precipitation illustrate that most snow and rain events result in indirect displacement of pre-event water by fill and spill mechanisms. Systematic shifts in regional groundwater to surface-water ratios are expected to be an important control on spatial and temporal distribution of water quality parameters and useful for evaluating the susceptibility of rivers to climate and development impacts.
Schlagworte: hydrogen , oxygen , geol , poll , aquap

Bitumen in potsherds from two Apulian Bronze Age settlements, Monopoli and Torre Santa Sabina: Composition and origin
Organic Geochemistry (2016)
Marianna Faraco, Antonio Pennetta, Daniela Fico, Giacomo Eramo, Enkeleida Beqiraj, Italo Maria Muntoni, Giuseppe Egidio De Benedetto

Bitumen was found to occur on archaeological potsherds collected from two Apulia Middle Bronze Age sites, Monopoli and Torre Santa Sabina (Italy). Bitumen from two different areas, Majella (Italy) and Selenicë (Albania), were analyzed as potential reference samples to assess the geographic origin of the archaeological bitumen using geochemical analytical techniques. Analysis of the archaeological samples from different layers at both sites showed that the bitumen possesses the same gross composition and biomarker distribution patterns. Sterane and terpane profiles from the archaeological samples were very similar to some of the geological samples collected from Selenicë. In both archeological and selected Selenicë samples, sterane distributions were dominated by the C29 homologues (46–54%), followed by the C27 (26–33%) and C28 homologues (ca. 21%). Other biomarkers, such as gammacerane and oleanane, as well as the stable carbon isotopic composition of the asphaltene fraction, also suggest that the bitumen from the two archaeological sites was imported from Albania during Middle Bronze Age.
Schlagworte: carbon , geol , arch , gaschrom

GEOCHEMICAL CHARACTERIZATION OF THE PERMIAN-TRIASSIC TRANSITION AT OUTCROP, CENTRAL SAUDI ARABIA
Journal of Petroleum Geology (2016)
H. A. Eltom, O. M. Abdullatif, L. O. Babalola, M. A. Bashari, M. Yassin, M. S. Osman, A. M. Abdulraziq

This study presents the results of chemostratigraphic analyses and spectral gamma-ray logging integrated with sedimentological data across the Permian-Triassic boundary at a measured outcrop section in central Saudi Arabia. The studied section encompasses the uppermost part of the Midhnab Member and the Lower and Upper Khartam Members of the Khuff Formation. Lithofacies were interpreted to have been deposited in subtidal, tidal to supratidal, lacustrine and meandering fluvial / flood plain, marginal marine and lagoonal depositional environments. Integration of bulk geochemical and carbon isotope (δ13C) data allowed the identification of a stratigraphic interval with a negative shift in δ13C ratio values, which was interpreted to correspond to the end-Permian mass extinction event. The end of this “first negative shift in δ13C values” is taken to mark the Permian-Triassic boundary. Above this boundary and just below an interval containing scattered thrombolites, a second negative shift in δ13C ratios was observed, and corresponds to an interval with long-term uranium depletion as indicated by the bulk sediment geochemical and spectral gamma-ray uranium data. The Permian-Triassic boundary (PTrB) was placed at the transition between marginal-marine and subtidal deposits. This stratigraphic position corresponds to the end of the “first negative δ13C shift” and the point of greatest uranium depletion. Although previous studies on outcrops of the Khuff Formation in Saudi Arabia identified a major sequence boundary between the Lower and Upper Khartam Members and interpreted it as the P TrB, no evidence is presented in this study for exposure and dissolution at this surface. Accordingly, the Permian-Triassic transition is placed in the transgressive portion of the Upper Khartam Member, while the sequence boundary below is interpreted to correspond to the end-Permian extinction. Correlation of Khuff time-equivalent units in the Arabian Plate is challenging, and this study will contribute to an improved understanding of this important stratigraphic unit, which contains prolific non-associated gas reservoirs. The identification of the Permian-Triassic boundary in central Saudi Arabia will help in the construction of a sequence-stratigraphic scheme for the Khuff, and with the correlation of lithofacies within this heterogeneous reservoir unit.
Schlagworte: carbon , geol , oilg , mulitcarb

Origin and availability of organic matter leading to arsenic mobilisation in aquifers of the Red River Delta, Vietnam
Applied Geochemistry (2016)
Elisabeth Eiche, Michael Berg, Sarah-Madeleine Hönig, Thomas Neumann, Vi Mai Lan, Thi Kim Trang Pham, Hung Viet Pham

Groundwater arsenic (As) concentrations in the Red River Delta (Vietnam) are often patchy and related to the microbially induced reduction of Fe oxy-hydroxides. In this study, we explored the influence of the origin, composition and availability of natural organic matter on the hydrochemical variability in the aquifers of Van Phuc. Carbon isotope signatures (δ13Corg) and C/N ratios were assessed in combination with lithology, geochemistry, hydrochemistry, hydrology and the distribution of specific biomarkers. The elationship of C/N ratios and δ13Corg distinguished four groups of sediment types that differ in their organic carbon sources. This includes organic carbon originating predominantly from vascular C3 plants (C/N: 15.4–21.0, δ13Corg: −28.6 to −26.7‰), C4 plants (C/N: 10.6; δ13Corg: −14.8‰), freshwater derived particulate organic carbon (C/N: ≤8; δ13Corg:≤−24‰) as well as mixtures incorporating both sources. At the high As sites, we found particulate organic carbon (POC) being 1–2‰ less depleted in δ13Corg than at low As sites. More importantly, however, our assessment shows that, the availability of organic matter has to be considered decisive with regard to groundwater As contamination. Fine-grained clayey sediments overlaying sands generally protect organic matter from substantial degradation and its leaching into an adjacent aquifer. However, at the sites that are high in dissolved As in Van Phuc, sediment layers rich in organic matter are hydraulically connected to the underlying aquifer. Here, soluble organic matter seeping into the aquifer can induce and/or enhance reducing conditions, thereby mobilising As from Fe oxy-hydroxides. Our study shows that both the clay content as well as the origin of organic matter are largely controlled by the depositional environment of the sediments.
Schlagworte: carbon , soil , geol , poll , elem