Asphalt (geology)

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Sample with natural asphalt. Side rock unknown (possibly limestone). Origin Slovakia.
Slab of an asphalt-impregnated limestone of the Lower Cretaceous from the French part of the Upper Rhone Valley .

Asphalt referred to in the Geosciences a dark brown to black, viscous or solid mixture without significant proportions of mineral substance, by geological either directly or via intermediate processes oil from dehydrated organic matter ( kerogen ) has formed. This mixture is to distinguish between technical asphalt and natural asphalt , bitumen , § bitumen or Bergteer called. In English literature, a distinction is sometimes made between viscous tar ("tar") and solid natural asphalt or rock asphalt . In German, “ tar ” refers to a substance similar in appearance and consistency to natural asphalt, but always artificially produced through pyrolysis and not from petroleum.

Emergence

Natural asphalt or natural bitumen can be produced in two different ways. The first possibility is the degradation (impoverishment) of "mature", light petroleum . If such crude oil rises to just below or directly to the surface of the earth, it is, not infrequently with the participation of microorganisms ( biodegradation ), converted into asphalt by losing the light and thus enriching the heavy crude oil fraction . This process includes a. the shift in the ratio of n-alkanes to cycloalkanes in favor of the cycloalkanes, up to the complete loss of the n-alkanes, as well as the enrichment of heteroatomic compounds, which in addition to carbon and hydrogen also contain nitrogen , sulfur , oxygen and various metals (so-called NSO Compounds or asphaltenes ). Oil, which has passed through the process of degradation only partially and, therefore, even a relatively low viscosity (less than 10,000 mPa · s) and density (more than 10  ° API ) which is also called natural heavy oil (engl. Heavy crude oil ) designated.

The second possibility is the direct escape of bituminous, viscous material from an organic-rich, only weakly thermally influenced, potential petroleum mother rock (" oil shale ") into a host rock. This material, which is considered to be a precursor to petroleum, is known as immature asphalt . Chemically, it is largely similar to the asphalt resulting from petroleum degradation, but is characterized by a broad spectrum of n-alkanes. However, the n-alkane profile alone cannot be used as a differentiating criterion, since secondary n-alkanes can also arise in asphalt from petroleum degradation through subsequent thermal effects. Immature asphalt usually tends to remain close to the bedrock horizon due to its initially relatively high viscosity. It can only rise to the surface of the earth from a greater depth under certain geological conditions. Such special conditions are assumed for the Jordan Rift (Dead Sea Rift) , for example .

Others

If larger amounts of asphalt leak out onto the surface of the earth, real asphalt lakes can form in terrain depressions .

In contrast to the technical production of bitumen, the natural formation takes many times longer. Sand impregnated with natural asphalt or natural bitumen is called oil sand . Natural solid bitumens without any significant mineral content are summarized under the collective term Asphaltite and Ipsonite .

Remarks

§The term bitumen has several meanings in the geosciences, but has a meaning that is roughly equivalent to that of asphalt (in a geoscientific sense).
In contrast, the heavy oil produced in refineries is referred to in English as heavy fuel oil .

Individual evidence

  1. ^ Walter L. Pohl: Economic Geology: Principles and Practice. Wiley-Blackwell, 2011, ISBN 978-1-4443-3662-7 , pp. 530 f.
  2. ↑ heavy fuel oil. Spectrum online encyclopedia of geosciences
  3. ↑ Christopher J. Schenk, Richard M. Pollastro, Ronald J. Hill: National Assessment of Oil and Gas - Natural Bitumen Resources of the United States. USGS Fact Sheet 2006–3133. United States Geological Survey, US Department of the Interior, Washington, DC, 2006 ( PDF 220 kB)
  4. ↑ E. Tannenbaum, Z. Aizenshtat: Formation of immature asphalt from organic-rich carbonate rocks - correlation I. Geochemical. Organic Geochemistry. Vol. 8, No. 2, 1985, pp. 181-192, doi : 10.1016 / 0146-6380 (85) 90037-3 .
  5. ↑ A. Bein, O. Amit: The Evolution of the Dead Sea Floating Asphalt Blocks: Simulations by Pyrolysis. Journal of Petroleum Geology. Vol. 2, No. 4, 1980, pp. 439-447, doi : 10.1111 / j.1747-5457.1980.tb00971.x .
  6. ↑ H. Gvirtzman, E. Stanislavsky: Palaeohydrology of hydrocarbon maturation, migration and accumulation in the Dead Sea Rift. Basin Research. Vol. 12, No. 1, 2000, pp. 79-93, doi : 10.1046 / j.1365-2117.2000.00111.x .

literature

  • Christiane Martin, Manfred Eiblmaier (Ed.): Lexicon of Geosciences. 6 volumes. Spektrum Akademischer Verlag, Heidelberg et al. 2000–2002, ISBN 3-8274-1655-8 .
  • Hans Murawski, Wilhelm Meyer: Geological dictionary. 12th edition. Spektrum Verlag, Heidelberg 2010, ISBN 978-3-8274-1810-4 .

Web links

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