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Fossil charcoal, its recognition and palaeoatmospheric significance
- Source :
- Palaeogeography, Palaeoclimatology, Palaeoecology. 97:39-50
- Publication Year :
- 1991
- Publisher :
- Elsevier BV, 1991.
-
Abstract
- Charcoal is produced by pyrolysis of plant material and its occurrence in the fossil record can be broadly equated with the incidence of palaeowildfire. The past record of such naturally occurring fire, and tha availability of the biomass which represents its fuel, put two constraints on oxygen levels. For combustion of plant material to occur at all requires that the atmospheric oxygen did not drop below a threshold of 13%. Increasing inflammability of plant material at higher oxygen levels suggests that 35% would be a ceiling above which plant biomass would ignite and burn so readily as to be incompatible with sustained forest growth. As we have more or less continuous fossil evidence of forest trees from the Late Devonian onwards, and a similarly sustained record of fossil charcoal from that time to the present (Cope, 1984), this constraints oxygen levels between 13% and 35% over that period (Rabash and Langford, 1968; Watson et al., 1978). However, further experimental work is required to establish the validity of these oxygen values under appropriate conditions and also to sharpen the certainty by which we can discriminate between fusain produced by pyrolysis, and inert wood degradation products produced by other (? biogenic) means. We discuss experiments directed at attempting to establish the validity of physical parameters by which pyrolytically produced fusain can be characterized. The most convincing evidence of pyrolysis hitherto recognised is the apparent homogenization of xylem cell walls, as seen under SEM. Work on charcoal from both wildfires and laboratory wood charring under controlled conditions confirms the homogenization as seen under both SEM and TEM. Controlled temperature experiments show that a further rise in temperature causes the cell walls, initially homogenized, to crack and separate along the site of the middle lamella, giving the charcoal a characteristic fibrous texture. Both of these distinctive phases of response to pyrolysis can be observed in fossil charcoals.
- Subjects :
- Global and Planetary Change
business.industry
Paleontology
chemistry.chemical_element
Mineralogy
Oceanography
Combustion
Pulp and paper industry
Oxygen
Paleoatmosphere
chemistry
visual_art
visual_art.visual_art_medium
Coal
Charring
Charcoal
business
Middle lamella
Pyrolysis
Ecology, Evolution, Behavior and Systematics
Geology
Earth-Surface Processes
Subjects
Details
- ISSN :
- 00310182
- Volume :
- 97
- Database :
- OpenAIRE
- Journal :
- Palaeogeography, Palaeoclimatology, Palaeoecology
- Accession number :
- edsair.doi.dedup.....034fbeff9fe090b90048ef7d4a925be8