scholarly journals Stratigraphy around the Cretaceous-Paleogene boundary in sediment cores from the Lord Howe Rise, Southwest Pacific

2021 ◽  
Author(s):  
Junichiro Kuroda ◽  
Kyoko Hagino ◽  
Yoichi Usui ◽  
Paul R. Bown ◽  
Kan-Hsi Hsiung ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Sediment Cores ◽  
Carbon Isotopic Composition ◽  
Time Interval ◽  
Calcareous Nannofossils ◽  
Impact Event ◽  
Southwest Pacific ◽  
Carbon Isotopic ◽  
Carbonate Carbon ◽  
Chicxulub Impact

During Deep Sea Drilling Project (DSDP) Leg 21, Cenozoic and latest Cretaceous sediments were recovered at Site 208 on the Lord Howe Rise, Southwest Pacific. We provide new biostratigraphic, magnetostratigraphic and chemostratigraphic data from Site 208 to constrain the stratigraphy around the Cretaceous-Paleogene (K-Pg) boundary and to determine the depth of the K-Pg boundary more precisely. Biostratigraphic data from calcareous nannofossils indicate a near-continuous succession of sediments from the mid-Maastrichtian (Late Cretaceous) to lowermost Thanetian (Paleocene) at depths of 540−590 m below seafloor (mbsf). The biostratigraphic data suggest that the K-Pg boundary corresponds to a siliceous claystone at the base of an interval of silicified sediments (576.0−576.8 mbsf). Carbonate carbon isotopic composition (δ13Ccarb) reveals a negative shift across this interval, which is consistent with global patterns of δ13C across the K-Pg boundary. Osmium concentration and Os isotopic composition (187Os/188Os) can also be used to identify the K-Pg boundary interval, as it is marked by a peak in Os concentration and a drop in 187Os/188Os values to 0.12−0.15, both of which are the result of the Chicxulub impact event. Our 187Os/188Os data show trends similar to those of coeval global seawater with the lowest value of 0.12−0.16 in the siliceous claystone (576.8 mbsf). However, the concentration of Os is low (<80 pg g−1) in this sample, which suggests that this siliceous claystone was deposited around the K-Pg boundary but may not include the boundary itself. Although the sedimentary record across the K-Pg interval at Site 208 may not be completely continuous, it nevertheless captures a time interval that is close to the Chicxulub impact event.

Carbon and oxygen isotopic composition of Lower to Middle Cambrian sediments at Taijiang, Guizhou Province, China

2005 ◽  
Vol 142 (6) ◽  
pp. 723-733 ◽  
Author(s):  
QING-JUN GUO ◽  
HARALD STRAUSS ◽  
CONG-QIANG LIU ◽  
YUAN-LONG ZHAO ◽  
DAO-HUI PI ◽  
...  
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Southern China ◽  
Carbon Isotopic Composition ◽  
Bacterial Biomass ◽  
Oxygen Isotopic Composition ◽  
Guizhou Province ◽  
Middle Cambrian ◽  
Carbon Isotopic ◽  
Carbonate Carbon

Secular variations in the carbon isotopic composition of organic and carbonate carbon characterize the Lower to Middle Cambrian transition that is exposed on the Yangtze Platform at Taijiang, Guizhou Province, southern China. δ13C values for organic matter range between −33.4 and −26.5‰. The carbon isotopic composition for carbonate carbon fluctuates between −2.7 and +3.1‰. A progressive decrease in the isotopic difference (Δδ) between these two isotope records reflects a decrease in the proportional contribution of bacterial biomass to the total sedimentary organic matter. In general, the observed changes are interpreted to reflect primary depositional values, notably variations in the burial rates of organic matter. These, in turn, are linked to biological changes across the Lower to Middle Cambrian transition. No distinct shift in the carbon isotopic composition marks the proposed Lower–Middle Cambrian boundary.

scholarly journals Source, composition, and environmental implication of neutral carbohydrates in sediment cores of subtropical reservoirs, South China

2016 ◽  
Author(s):  
Dandan Duan ◽  
Dainan Zhang ◽  
Yu Yang ◽  
Jingfu Wang ◽  
Jian'an Chen ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
South China ◽  
High Performance ◽  
Sediment Cores ◽  
Carbon Isotopic Composition ◽  
Anion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Carbon Isotopic ◽  
Key Factor ◽  
Algal Productivity

Abstract. Neutral carbohydrates along with algal organic matter (AOM) content, carbon isotopic composition, and elemental C/N ratios were investigated in three sediment cores of various trophic reservoirs in South China. Neutral monosaccharides, AOM, and carbon stable isotope ratios were determined by high-performance anion-exchange chromatography, Rock-Eval pyrolysis, and Finnigan Delta Plus XL mass spectrometry, respectively.The carbon isotopic compositions were corrected via the Suess effect. The concentrations of total neutral carbohydrates (TCHO) range from 0.51 to 6.4 mg/g at mesotrophic reservoirs, and from 0.83 to 2.56 mg/g at an oligotrophic reservoir. Monosaccharide compositions and diagnostic parameters indicate a predominant contribution of phytoplankton in each of the three cores, which is consistent with the results inferred by the corrected carbon isotopic composition and C/N ratios. The sedimentary neutral carbohydrates are largely structural polysaccharides and, thus, are resistant to degradation in the sediments. Moreover, the single neutral carbohydrate content is highly related with the carbon isotopic composition, algal productivity (hydrogen index), and increasing mean air temperature during the past 60 years. The nutrient input, however, is not a key factor affecting the primary productivity in the three reservoirs. The above evidence shows that neutral carbohydrates have been significantly elevated by climate change even at low latitude regions.

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.

New equation to decipher the relationship between carbon isotopic composition of methane and maturity of gas source rocks

2021 ◽  
Vol 64 (3) ◽  
pp. 470-493 ◽  
Author(s):  
Jianping Chen ◽  
Xulong Wang ◽  
Jianfa Chen ◽  
Yunyan Ni ◽  
Baoli Xiang ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotopic Composition ◽  
Source Rocks ◽  
Carbon Isotopic ◽  
Gas Source ◽  
New Equation ◽  
The Relationship

The carbon isotopic composition of individual petroleum lipids

1984 ◽  
Vol 6 ◽  
pp. 665-670 ◽  
Author(s):  
I. Gilmour ◽  
P.K. Swart ◽  
C.T. Pillinger
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotopic Composition ◽  
Carbon Isotopic
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