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What about all that buriedorganic matter?

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Presentation on theme: "What about all that buriedorganic matter?"— Presentation transcript:

1 What about all that buriedorganic matter?
‧Methods for characterization of fossil carbon ‧ Petroleum Generation Migration, leakage and remineralization ‧ Conversion to Deep Gas Leakage to surface; hydrate formation ‧ Uplift and Weathering Processes Microbial utilization ‧ Alternative Hypotheses ‘Myth of Fossil Fuels’

2 Thomas Gold ‧Hydrocarbons are primordial
‧As they upwell into the crust, microbial life invades for a free meal ‧Hydrocarbons are not biology ‘reworked’ but , rather, geology reworked by biology thus explaining the presence of all those biological signatures in oils

3 KEROGEN Kerogen is the component of organic matter that is insoluble in inorganic and organic solvents (Durand, 1980). Bitumen is the soluble component. Both widely distributed in sediments; sometimes massive accumulations as in coal and oil deposits Microscopic examination cansometimes give information on geological age, paleoenvironment, thermal history (colour)- palynology, petrography But most organic matter is amorphous and unicentifiable – need chemical means to quantify and evaluate origins………. Bulk Properties, carbon isotopes, biomarkers

4 Bulk Properties Total organic carbon %TOC % Total C, H, N, O, S
13C (now easily  18O, D,  15N,  34S) elemental H/C ratio (originally 1.3 → 0 for C) solid phase nmr → environment of C ie aromatic C,H vs saturate C…………….. The above give limited information on provenance Further characterisation by pyrolysis (Rock-Eval), pyrolysis-GC, pyrolysis GC-MS and laser ablation-MS Solvent extraction and GC, GC-MS give information on bitumen composition

5 Oris Bulk Properties ‘An organic facies is a mappable subdivision of a stratigraphic unit, distinguished from the adjacent subdivisions on the character of its organic constituents, without regard to the inorganic aspects of the sediment’ R.W. Jones ‘Advances in Petroleum Geochemistry’ (ed. J. Brooks & D. Welte) 1987

6 Source Controls on Organic Carbon
Sapropelic Humic Kerogen Algal + Amorphous Herbaceous Woody Coaly Liptinite Exinite Vitrinite Inertinite Macermal Alginite Sporinite Telinite Fusinite Amorphous Cutinite Collinite Micrinite Resinite Kerogen H/C O/C ORGANIC SOURCE FOSSIL FUELS

7 Oris Bulk Properties ‧API gravity. USA measure related to
specific gravity ‧API = [(141.5 / – 131.5]. Water has gravity 10°API. Heavy oils <25°. Medium 25°to 35°. Light 35°to 45°. Condensates > 45

8 Sulfur, Nickel andVanadium
‧Sulfur: High in marine and some saline lacustrine oils; generally decreases as a function of maturity ‧Can be a useful correlation tool where there are S- rich petroleum systems but Australian oils generally low in sulfur. ‧Nickel and Vanadium contents; largely exist in porphyrin content. Generally decrease with maturation.


10 HYDROCARBONS Regular Pristane C19 Regular Phytane C20 Irregular
ACYCLIC ISOPRENOID ALKANES Regular Pristane C19 Regular Phytane C20 Irregular Botryococcane

11 HYDROCARBONS Irregular C20 branched Irregular C25 branched
ACYCLIC ISOPRENOID ALKANES Irregular C20 branched Irregular C25 branched Derived from diatoms

Toluene Tri-substituted alkyl benzene





GYMNOSPERM RESIN labdatriene polymer “leaf resins” e.g. phyllocladenes, pimaradienes “resin acids”, e.g. abietic acid

18 Anderson’s Resin Classification Scheme
polymeric labdanoid diterpenes; + occluded sesgui-, di and triterpenoids Agathis/Araucaria – Baltic amber Hymenaea – Dominican, Mexican amber polymeric sesquiterpenes;polycadinene + occluded sesqui- and triterpenoids Dammar/Dipterocarpaceae – SE Asia polystyrene non-polymeric cedrane sesquiterpenoids non-polymeric abietane/pimarane diterps

19 Australian Coastal Resinites
Resin Pedigree Bales bay,kangarool Is No Two Rocks SA Three Mile rocks SA Lake Bonney SA Brunei resinite Gippsland resinite Kauri resin Recent dammar

20 Bulk Carbon Isotope Composition of
Modern & Fossil Resins

21 Plants optimise stomatal conductance to maximise access to CO2 & minimise loss of water \ water conservative plants have isotopically ‘heavier’ carbon Needle leaf morphology Water conservative Restricted access to CO2 Discriminates less against 13C Broad leaf morphology Less water conservative Less restricated access to CO2 Discriminates more against 13C values for wood typically: values for wood typically: *Data from Stuiver and Braziunas, 1987 for 40 latitude modem plants

22 Oils with conifer vs Angiosperm OM Carbon Isotopes vs Oleanane/Hopane
Gippsland Basin, Oz Affected by migration contamination Taranaki Basin, NZ Data from AGSO/Geomark Biodegraded oils excluded Oleanane/hopane


24 ‧14C-Dead Living Biomass: Evidence for Microbial Assimilation of
Ancient Organic Carbon During Shale Weathering ‧ S. T. Petsch,* T. I. Eglinton, K. J. Edwards ‧ Prokaryotes have been cultured from a modern weathering profile developed on a ~365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural-abundance carbon-14 analysis of membrane lipids, we show that 74 to 94% of lipid carbon in these cultures derives from assimilation of carbon-14-free organic carbon from the shale. These results reveal that microorganisms enriched from shale weathering profiles are able to use a macromolecular and putatively refractory pool of ancient organic matter. This activity may facilitate the oxidation of sedimentary organic matter to inorganic carbon when sedimentary rocks are exposed by erosion. Thus, microorganisms may play a more active role in the geochemical carbon cycle than previously recognized, with profound implications for controls on the abundance of oxygen and carbon dioxide in Earth's atmosphere over geologic time Science, Vol. 292, Issue 5519, , May 11, 2001

25 Table 2. 14C and 13C analysis of PLFA compound classes isolated from enrichment culture grown on New Albany Shale, and calculated fraction of PLFA carbon derived from ancient kerogen. Total mass PLFA Kerogen in shale substrate Modern atmospheric CO2

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