scholarly journals The carbon and oxygen isotopic records of fossils from the Lower Oxford Clay

1992 ◽  
Vol 6 ◽  
pp. 7-7 ◽  
Author(s):  
T. F. Anderson ◽  
B. N. Popp ◽  
L. Z. HO ◽  
A. C. Williams
Keyword(s):  
Isotopic Composition ◽  
Surface Waters ◽  
Isotope Effects ◽  
Carbon Isotopic Composition ◽  
Good Opportunity ◽  
High Productivity ◽  
Carbon Isotopic ◽  
Isotopic Analyses ◽  
Oxygen Isotopic ◽  
Isotopic Records

The excellent preservation of calcareous invertebrates and phosphatic vertebrates in the Lower Oxford Clay provides a good opportunity for paleooceanographic reconstruction based on stable isotopic abundances. We present here our initial results and interpretations on carbon and oxygen isotopic analyses on fossils of different depth habitats. Benthic fossils include epifaunal oysters and infaunal nuculacean bivalves. We also analyzed “pendant” bivalves whose depth habitat is uncertain. Fossil nekton are represented by ammonites and belemnites. Organisms that inhabited the uppermost part of the water column are represented by marine reptiles, such as icthyosaurs and plesiosaurs, and probable pelagic fish.The oxygen isotopic compositions of calcareous benthos and nekton overlap substantially (δ180 = −2 to +1 permil vs. PDB). The wide scatter in δ180 values probably reflects physiological (non-equilibrium) effects in calcification rather than paleoenvironmental variations. Mean δ180 values for oysters, pendant bivalves, and belemnites (all calcitic) and nuculacean bivalves (aragonitic) correspond to precipitation at isotopic equilibrium with non-glacial seawater at temperatures of 15°-18°. The mean isotopic paleotemperature for ammonites (aragonitic) is slightly higher (20°) but is probably not significantly different from those for other calcareous macro-invertebrates. Preliminary oxygen isotopic results on phosphate extracted from bones, teeth, and gill rays correspond to paleotemperatures of 20°–25°.Carbon isotopic results are limited to data from calcareous benthos and nekton. δ 13C values for individual taxa are quite variable (+2 to +5 permil for aragonitic fossils, 0 to +3 permil for calcitic fossils), suggesting physiological isotope effects. Nonetheless, mean δ 13C values are consistent with calcification in seawater having a carbon isotopic composition similar to that of modern average seawater. The presumably high flux of 13C-depleted CO2 into bottom waters from the diagenesis of sedimentary organic matter is not recorded in the carbon isotopic composition of benthic fossils.Thermal stratification implied by the oxygen isotopic record suggests the penetration of cool, nutrient-rich waters into the Lower Oxford Clay sea. Upward advection of deep waters together with runoff from adjacent landmasses must have provided sufficient nutrients to maintain the inferred high productivity of surface waters. The influence of productivity on the carbon isotopic composition of surface waters will be tested by the analysis of calcareous phytoplankton.

scholarly journals Chemical and isotopic composition of secondary organic aerosol generated by <i>α</i>-pinene ozonolysis

2016 ◽  
Author(s):  
Carl Meusinger ◽  
Ulrike Dusek ◽  
Stephanie M. King ◽  
Rupert Holzinger ◽  
Thomas Rosenørn ◽  
...  
Keyword(s):  
Chemical Analysis ◽  
Isotopic Composition ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Isotope Effects ◽  
Isotope Analysis ◽  
Carbon Isotopic Composition ◽  
Organic Aerosol ◽  
Total Carbon ◽  
Carbon Isotopic

Abstract. Secondary organic aerosol (SOA) plays a central role in air pollution and climate. However, an exact description of the sources and mechanisms leading to SOA is elusive despite decades of research. Stable isotope analysis may help to constrain atmospheric SOA budgets but the isotope effects associated with the underlying processes have to be determined in order to do so. In this paper, SOA formation from ozonolysis of α-pinene – an important precursor and perhaps the best-known model system used in laboratory studies – was investigated using stable carbon isotope analysis, position-specific isotope analysis (PSIA), and high-resolution chemical analysis based on a thermal-desorption proton-transfer-reaction mass-spectrometer (PTR-MS). SOA was formed in a constant-flow chamber under dark, dry and low-NOx conditions, with OH scavengers in the absence of seed particles. Product SOA was collected on doubly-stacked quartz filters (front and back filters). During analysis, the filters were heated stepwise over the range of 100–400 °C to desorb organic compounds that were (i) detected using PTR-MS for chemical analysis and to determine the O:C ratio, and (ii) converted to CO2 for 13C analysis. In addition, the total carbon isotopic composition of selected samples was measured. For the first time PSIA has been performed for α-pinene. More than 400 ions in the mass range from 39–800 Da were detected and quantified using the PTR-MS. The largest mass fraction desorbed from the filters at 150 °C. The measured O:C ratio of front filter material increased from 0.18 to 0.25 as the desorption temperature was raised from 100 to 250 °C. The rising trend is consistent with the fact that functionalization decreases the volatility of chemical species. At temperatures above 250 °C the O:C ratio of thermally desorbed material, presumably from oligomeric precursors, was constant. The observation of a number of components across the full range of desorption temperatures suggests that they are generated by thermal decomposition of oligomers. SOA on front filters was enriched in 13C by 0.2–2.9 ‰ relative to the initial α-pinene, at all desorption temperatures. The total carbon isotopic composition was similar to the enrichment of the major fraction desorbing at 150 °C. Gas-phase compounds desorbing from the back filters showed much lower concentrations but were depleted in 13C by 0.7 ‰ compared to the initial α-pinene and by 1.9 ‰ compared to the corresponding front filter. PSIA showed that the isotope enrichment at individual carbon positions in α-pinene ranged from −6.9 to +10.5 ‰ relative to the bulk composition. However, there was not a clear mechanistic connection between those values and the observed isotopic enrichment of bulk SOA. Instead, fragmentation reactions favouring the loss of small, isotopically light products to the gas phase are consistent with the observations. In monoterpene ozonolysis, functionalization is known to follow fragmentation, however it is the fragmentation step that seems to govern the isotope budget. The isotope effect associated with oligomerization is small. The suggested isotope effects are important for the interpretation of isotopic compositions of ambient aerosol.

Source identification of n-alkanes and isoprenoids using diagnostic ratios and carbon isotopic composition on crude oils and surface waters from the Gulf of Mexico

2021 ◽  
Vol 193 (10) ◽  
Author(s):  
Félix Augusto Hernández-Guzmán ◽  
José Vinicio Macías-Zamora ◽  
Nancy Ramírez-Álvarez ◽  
Cristina Quezada-Hernández ◽  
Roxana Ortiz-López
Keyword(s):  
Gulf Of Mexico ◽  
Isotopic Composition ◽  
Surface Waters ◽  
Source Identification ◽  
Carbon Isotopic Composition ◽  
Crude Oils ◽  
Diagnostic Ratios ◽  
Carbon Isotopic

U/Th age constraints on the absence of ice in the central Inn Valley (eastern Alps, Austria) during Marine Isotope Stages 5c to 5a

2006 ◽  
Vol 66 (1) ◽  
pp. 167-175 ◽  
Author(s):  
Christoph Spötl ◽  
Augusto Mangini
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotopic Composition ◽  
Ice Cores ◽  
Eastern Alps ◽  
Oxygen Isotopic Composition ◽  
Low Carbon ◽  
Carbon Isotopic ◽  
Oxygen Isotopic ◽  
Temperature Records ◽  
Marine Isotope Stage 5

AbstractCalcitic flowstones are present in fractures of a Pleistocene breccia near Innsbruck, Austria, and record periods of carbonate precipitation in the unsaturated zone between 101,500 ± 1500 and 70,300 ± 1800 yr, constrained by U-series disequilibrium dates. The occurrence of these speleothems, their low carbon isotopic composition, and the lack of infiltrated siliciclastic material demonstrate that the central Inn valley – which harbored one of the most extensive valley glaciers during the last glacial maximum – was ice-free during Marine Isotope Stages 5c to 5a. Climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite, attributed to strong and possibly seasonally biased atmospheric cooling. During these intervening stadials, which mirror those identified in the Greenland ice cores and marine sea-surface temperature records, calcite deposition apparently came to a halt, but the Inn Valley remained ice-free. The youngest calcite layer formed between ∼74,000 and ∼70,000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the Marine Isotope Stage 5/4 transition, consistent with other speleothem records.

scholarly journals Isotope-geochemical characteristics of Wenlock carbonate and terrigenous-carbonate deposits of the Subpolar Urals and the southern part of the Chernyshev ridge

LITOSFERA ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 829-848
Author(s):  
D. N. Shebolkin
Keyword(s):  
Isotopic Composition ◽  
Isotope Analysis ◽  
Carbon Isotopic Composition ◽  
Time Intervals ◽  
Subpolar Urals ◽  
Carbon Isotopic ◽  
Carbonate Carbon ◽  
Wide Range ◽  
Chernyshev Ridge ◽  
Oxygen Isotopic

Research subject. Wenlock deposits in the Subpolar Urals and southern part of the Chernyshev Ridge. Materials and methods. Carbonate and terrigenous-carbonate rock samples from sections of the Subpolar Urals (outcrops 212, 217) and the southern part of the Chernyshev Ridge (outcrop 479) were studied by isotope analysis of carbonate carbon and oxygen.Results. The isotopic composition of the studied sections varies across a wide range of δ13С (–6.4…–0.05‰) and δ18O (20.0–26.9‰). Therefore, three time intervals characterized by distinctive isotopic characteristics can be distinguished, roughly corresponding to early Sheinwoodian (I), late Sheinwoodian (II) and Homerian (III). Interval I is characterized exclusively by the rocks of outcrop 479 with δ13С (–3.6…–3.0‰) and δ18O (22.4–23.6‰). In Interval II, the average values of isotopic characteristics of outcrop 479 indicate a tendency to weighting carbon (–5.5…–3.5‰) and somewhat heavier oxygen (23.2–25.2‰) isotopes. In outcrop 212, the average isotopic values for carbon and oxygen vary from –2.9 to –1.3‰ and from 21.9 to 24.3‰, respectively. In outcrop 217, the average values are δ13C (–1.8…–0.8‰) and δ18O (22.4–25.4‰). In Interval III, the average values of carbon isotopic composition in outcrop 479 are becoming heavier from –2.5 to –0.7‰. In outcrop 212, the isotopic values of oxygen (21.9–23.1‰) and carbon (–4.9…–2.5‰) tend to become weighting; however, in outcrop 217, the average isotopic values of δ13C (–1.9…–0.5‰) and δ18O (22.3–24.5‰) remain constant. The conducted litho-facial studies showed that the weighting carbon isotopic composition ranging from –6.4…to –3.0‰ is associated with an increase in microbial activity in sediments, the manifestation of vadose-phreatic conditions, and the intake of light carbon dioxide with a flow of terrigenous material from the earth. In the latter case, oxygen isotopic values are also the most lightweight (20.0–23.0‰).Conclusions. The obtained isotopic characteristics of the Wenlock rocks under study indicate the expedience of identifying three time intervals and their correlation with paleogeographic reconstructions of Wenlockian sedimentation in the Timan-northern Ural region.

scholarly journals Oxygen and Carbon Isotopic Composition of Carbonate Rocks of the Permian Qixia Formation, Sichuan Basin: Thermal Effects of Emeishan Basalt

2016 ◽  
Vol 20 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Keke Huang ◽  
Xiaoning Li ◽  
Zuowei Hu ◽  
Yijiang Zhong
Keyword(s):  
Isotopic Composition ◽  
Thermal Effects ◽  
Sichuan Basin ◽  
Early Stage ◽  
Carbon Isotopic Composition ◽  
Oxygen Isotopic Composition ◽  
Rock Properties ◽  
Carbon Isotopic ◽  
Emeishan Basalt ◽  
Oxygen Isotopic

<p>The late Permian thermal events related to Emeishan Basalt has made a great impact on the underlying carbonate rock properties in the western margin of the Yangtze Platform. In this paper, we investigate the carbon and oxygen isotopic composition of the Qixia Formation carbonates from two sections: the Qiaoting Section in the northeastern part of the Sichuan Basin and the Changjianggou Section at the northwestern edge of the Basin. The data reveal that: (i) Samples from Qiaoting section show a relatively narrow range of δ<sup>13</sup>C and δ<sup>18</sup>O, varying from 2.7‰ to 5.2‰ with an average of 4.2‰, and -3.8‰ to -7.8‰ with an average of -5.4‰, respectively. In contrast, Samples from Changjianggou section exhibit larger magnitude of variation in δ<sup>13</sup>C and δ<sup>18</sup>O, ranging from -1‰ to 3.8‰ with an average of 1.5‰, and -2.1 to -9.2‰, with an average of -6.0‰ respectively; (ii) δ<sup>13</sup>C and δ<sup>18</sup>O records in carbonates from Qiaoting section are similar to those of Middle Permian seawater whereas carbonates from the Changjianggou section are depleted in <sup>13</sup>C and <sup>18</sup>O compared to contemporary seawater; (iii) On the basis of combined petrographic and paleo-heat flow evidence, the lower carbon and oxygen isotopic composition of the carbonates from the Changjianggou section are interpreted to be the results of thermal effects of Emeishan Basalt because of its proximity to the eruption center of the basalt. The high temperature reduced the δ<sup>18</sup>O values of the carbonates and forced the organic matter to mature at an early stage, thus producing <sup>13</sup>C-enriched carbon dioxide to participate in the formation of carbonates.  </p><p> </p><p><strong>Composición Isotópica de Oxígeno y Carbón en Rocas de Carbonato de la Formación de Edad Pérmica Qixia, en la Cuenca de Sichuan: Efectos Térmicos del Basalto Emeishan  </strong></p><p><strong><br /></strong></p><p><strong>Resumen</strong></p><p>Los eventos térmicos del Pérmico tardío relacionados con el Basalto Emeishan han tenido un gran impacto en las propiedades de las rocas de carbonato subyacentes en el margen occidental de la plataforma Yangtze. En este artículo se investiga la composición isotópica de carbonatos de la formación Qixia en dos secciones: la sección de Qiaoting en la parte nororiental de la cuenca Sichuan y la sección Changjianggou, en el noroccidente de la cuenca. La información evidencia que, (i) las muestras de la sección Qiaoting tienen un espectro más angosto que va de δ<sup>13</sup>C a δ<sup>18</sup>O, con variación de 2.7 ‰ a 5,2 ‰, con un promedio de 4.2 ‰, y -3.8 ‰ a -7.8 ‰, con una media de -5.4 ‰, respectivamente. En contraste, las muestras de la sección Changjianggou tienen una variación de mayor magnitud en δ<sup>13</sup>C a δ<sup>18</sup>O que va desde -1 ‰ hasta 3.8 ‰, con un promedio de 1.5 ‰, y de -2.1 a -9.2 ‰, con una media de -6.0 ‰, respectivamente; (ii) los registros de δ<sup>13</sup>C y δ<sup>18</sup>O en carbonatos son similares a los de agua marina del pérmico medio, mientras que los carbonatos de la sección Changjianggou se ven empobrecidos en 13C y 18O comparados al agua marina de esta edad; con base en la petrografía combinada y la evidencia del flujo paleotérmico, la baja composición isotópica de oxígeno y carbón de los carbonatos en la sección de Changjianggou se interpretó como resultado de los efectos térmicos del Basalto Emeishan debido a la proximidad con el centro de erupción. La alta temperatura redujo los valores de δ<sup>18</sup>O de los carbonatos y llevó a la maduración temprana de la materia orgánica, lo que produjo dióxido de carbono enriquecido en <sup>13</sup>C durante la formación de los carbonatos.</p>

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