Organic Geochemistry of Paleodepositional Environments with a Predominance of Terrigenous Higher-Plant Organic Matter

1995 ◽  
Author(s):  
Gary H. Isaksen
Keyword(s):  
Organic Matter ◽  
Organic Geochemistry ◽  
Higher Plant

scholarly journals Petrography and Organic Geochemistry Characterizations of Lower Paleozoic Organic-Rich Shale in the Northwestern Upper Yangtze Plate: Niutitang Formation and Longmaxi Formation, Dabashan Foreland Belt

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 439 ◽  
Author(s):  
Delu Li ◽  
Rongxi Li ◽  
Di Zhao ◽  
Feng Xu
Keyword(s):  
Gas Chromatography ◽  
Organic Matter ◽  
Organic Geochemistry ◽  
Source Rocks ◽  
Gas Chromatography Mass Spectrometry ◽  
Mature Stage ◽  
Type I ◽  
Lower Paleozoic ◽  
Longmaxi Formation ◽  
Niutitang Formation

Measurements of total organic carbon, Rock-Eval pyrolysis, X-ray diffraction, scanning electron microscope, maceral examination, gas chromatography, and gas chromatography-mass spectrometry were conducted on the organic-rich shale of Lower Paleozoic Niutitang Formation and Longmaxi Formation in Dabashan foreland belt to discuss the organic matter characteristic, organic matter origin, redox condition, and salinity. The results indicate that the Niutiang Formation and Longmaxi Formation organic-rich shale are good and very good source rocks with Type I kerogen. Both of the shales have reached mature stage for generating gas. Biomarker analyses indicate that the organic matter origin of Niutitang Formation and Longmaxi Formation organic-rich shale are all derived from the lower bacteria and algae, and the organic matter are all suffered different biodegradation degrees. During Niutitang Formation and Longmaxi Formation period, the redox conditions are both anoxic with no stratification and the sedimentary water is normal marine water.

The formation of ferromanganese nodules in the southwest Indian Ocean; an abiotic process

2014 ◽  
Vol 78 (4) ◽  
pp. 941-955
Author(s):  
B. E. Van Dongen ◽  
N. J. Ashton ◽  
R. A. D. Pattrick
Keyword(s):  
Organic Matter ◽  
Indian Ocean ◽  
Depositional Environments ◽  
Higher Plant ◽  
Southwest Indian Ocean ◽  
Ferromanganese Nodules ◽  
Naturally Occurring ◽  
Minor Contribution ◽  
Geochemical Analyses ◽  
A Minor

AbstractFerromanganese nodules have been recognized widely as potentially important resources for strategic metals. However it remains unclear if the formation of these nodules is purely an abiotic process or if microorganisms are involved in their formation. To determine the microbial contributions, detailed organic geochemical analyses were performed on ferromanganese nodules collected from across the southwest Indian Ocean. These analyses reveal the presence of specific terrestrial, marine and petroleum derived biomarkers, consistent with formation in a marine setting with a substantial influx of terrestrially derived (higher plant detritus) and naturally occurring petroleum-related organic matter. In contrast, only trace amounts of general bacterial biomarkers, commonly present in these types of depositional environments, were present. This indicates that the formation of these ferromanganese nodules is predominantly an abiotic process although a minor contribution from microbial mediated processes to the growth of these nodules cannot be completely ruled out.

Precession-paced climate oscillations in Messinian sulphate evaporites recorded by carbon stable isotopes of leaf wax derived n-alkanes

2020 ◽  
Author(s):  
Dave Stolwijk ◽  
Marcello Natalicchio ◽  
Francesco Dela Pierre ◽  
Daniel Birgel ◽  
Jörn Peckmann
Keyword(s):  
Organic Matter ◽  
Terrestrial Organic Matter ◽  
Higher Plant ◽  
Humid Climate ◽  
Climate Oscillations ◽  
Proxy Records ◽  
The Mediterranean ◽  
Nw Italy ◽  
Paleoclimatic Proxy ◽  
Long Chain

<p>During the Messinian salinity crisis (MSC), the Mediterranean Sea was gradually isolated from the Atlantic Ocean due to tectonics, ultimately resulting in the deposition of enormous volumes of evaporites on the Mediterranean seafloor. In marginal Mediterranean sub-basins, the first phase of the MSC is represented by a cyclic succession of gypsum and shales (Primary Lower Gypsum unit; PLG), changing laterally into an alternation of shales, marls and carbonates towards the deeper parts of the basins. The current consensus is that the lithological cyclicity is the expression of precession-paced climate oscillations, with shales deposited during insolation maxima (precession minima) and gypsum deposited during insolation minima (precession maxima). However, this hypothesis has yet to be validated, because this assumption is primarily based on the continuation of sedimentary cyclicity from the open marine pre-MSC sediments into the Primary Lower Gypsum unit. To assess the possible role of orbitally-driven paleoclimate change on the deposition of the PLG unit, we have analysed molecular fossils (lipid biomarkers) preserved in shales and gypsum of the Pollenzo section (Piedmont basin, NW Italy).</p><p>Long-chain n-alkanes are reliable biomarkers that are used to track the input of terrestrial organic matter and allow to reconstruct paleovegetation. By using the distribution of higher plant-derived long chain n-alkanes and their compound specific carbon isotope signature (δ<sup>13</sup>C), we show that the sedimentary cyclicity in the PLG unit is indeed controlled by precession. Our high-resolution paleoclimatic proxy records cover approximately 300 Ka (6.003 Ma – 5.721 Ma) and comprise the onset of the MSC (5.971 Ma) and the first 12 cycles of the PLG unit. Cyclic fluctuation of δ<sup>13</sup>C values is observed, with higher δ<sup>13</sup>C values typifying long-chain n-alkanes extracted for gypsum, while lower values correspond to shales.</p><p>Our results, which represent the first paleoclimatic proxy data derived from Messinian gypsum, show that riverine flux of organic matter to the basin varied significantly during the first phase of the MSC. In agreement with a precessional control on paleoclimate, lower n-alkane abundance in gypsum reflects drier conditions, while higher n-alkane abundance in shales indicates more humid climate and increased input of terrestrial organic matter to the basin.</p>

scholarly journals Organic-matter quality of deep permafrost carbon – a study from Arctic Siberia

2015 ◽  
Vol 12 (7) ◽  
pp. 2227-2245 ◽  
Author(s):  
J. Strauss ◽  
L. Schirrmeister ◽  
K. Mangelsdorf ◽  
L. Eichhorn ◽  
S. Wetterich ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Stable Carbon Isotopes ◽  
Average Chain Length ◽  
Frozen Ground ◽  
Higher Plant ◽  
Organic Matter Quality ◽  
Microbial Decomposition ◽  
Geochemical Parameters

Abstract. The organic-carbon (OC) pool accumulated in Arctic permafrost (perennially frozen ground) equals the carbon stored in the modern atmosphere. To give an idea of how Yedoma region permafrost could respond under future climatic warming, we conducted a study to quantify the organic-matter quality (here defined as the intrinsic potential to be further transformed, decomposed, and mineralized) of late Pleistocene (Yedoma) and Holocene (thermokarst) deposits on the Buor-Khaya Peninsula, northeast Siberia. The objective of this study was to develop a stratigraphic classified organic-matter quality characterization. For this purpose the degree of organic-matter decomposition was estimated by using a multiproxy approach. We applied sedimentological (grain-size analyses, bulk density, ice content) and geochemical parameters (total OC, stable carbon isotopes (δ13C), total organic carbon : nitrogen (C / N) ratios) as well as lipid biomarkers (n-alkanes, n-fatty acids, hopanes, triterpenoids, and biomarker indices, i.e., average chain length, carbon preference index (CPI), and higher-plant fatty-acid index (HPFA)). Our results show that the Yedoma and thermokarst organic-matter qualities for further decomposition exhibit no obvious degradation–depth trend. Relatively, the C / N and δ13C values and the HPFA index show a significantly better preservation of the organic matter stored in thermokarst deposits compared to Yedoma deposits. The CPI data suggest less degradation of the organic matter from both deposits, with a higher value for Yedoma organic matter. As the interquartile ranges of the proxies mostly overlap, we interpret this as indicating comparable quality for further decomposition for both kinds of deposits with likely better thermokarst organic-matter quality. Supported by principal component analyses, the sediment parameters and quality proxies of Yedoma and thermokarst deposits could not be unambiguously separated from each other. This revealed that the organic-matter vulnerability is heterogeneous and depends on different decomposition trajectories and the previous decomposition and preservation history. Elucidating this was one of the major new contributions of our multiproxy study. With the addition of biomarker data, it was possible to show that permafrost organic-matter degradation likely occurs via a combination of (uncompleted) degradation cycles or a cascade of degradation steps rather than as a linear function of age or sediment facies. We conclude that the amount of organic matter in the studied sediments is high for mineral soils and of good quality and therefore susceptible to future decomposition. The lack of depth trends shows that permafrost acts like a giant freezer, preserving the constant quality of ancient organic matter. When undecomposed Yedoma organic matter is mobilized via thermokarst processes, the fate of this carbon depends largely on the environmental conditions; the carbon could be preserved in an undecomposed state till refreezing occurs. If modern input has occurred, thermokarst organic matter could be of a better quality for future microbial decomposition than that found in Yedoma deposits.

Molecular organic geochemistry of a proposed stratotype for the Oxfordian/Kimmeridgian boundary (Isle of Skye, Scotland)

2012 ◽  
Vol 149 (5) ◽  
pp. 857-874 ◽  
Author(s):  
APOLLINE LEFORT ◽  
YANN HAUTEVELLE ◽  
BERNARD LATHUILIÈRE ◽  
VINCENT HUAULT
Keyword(s):  
Organic Matter ◽  
Depositional Environment ◽  
Organic Geochemistry ◽  
Soluble Organic Matter ◽  
Precise Location ◽  
Exceptional Preservation ◽  
The North ◽  
Nodular Limestone ◽  
First Time ◽  
Isle Of Skye

AbstractThe composition of the soluble organic matter of the Oxfordian–Kimmeridgian Flodigarry Shale Member (Isle of Skye, Scotland) is presented for the first time. A continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of Staffin Bay. This succession is proposed as a potential stratotype of the boundary between the Oxfordian and Kimmeridgian stages. This paper points out the exceptional preservation and very low thermal degradation of the organic matter. Indeed, the molecular composition is characterized by the abundance of unsaturated biomarkers (hopenes and diasterenes) as well as undamaged bioterpenoids (ferruginol and sugiol). The abundance of long-chainn-alkanes characterized by an odd-over-even predominance reveals a dominant continental contribution. This is also attested to by the relatively high amounts of plant biomarkers (e.g. ferruginol, sugiol, cadalene and retene), which suggest a palaeovegetation largely composed of pinophytes, especially Cupressaceae, Taxodiaceae and Cheirolepidiaceae, on the nearest emerged lands. The water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part. The composition of the organic matter does not significantly change along the Flodigarry Shale Member. In other words, no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks, and it does not allow us to support a precise location for the Oxfordian/Kimmeridgian boundary in the succession.

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