Talk:Oil shale geology

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[edit] Oil shale geologically

I changed the opening sentence of the article from "Oil shale geologically includes a group of fine-grained sedimentary rocks which contain significant amounts of kerogen." to "Oil shale includes a group of fine-grained sedimentary rocks which contain significant amounts of kerogen." because I felt it was an unnecessary qualification. This article is about the geology of oil shale anyway. I think it reads better too. Unlike other (more significant) geological terms including "rock" and "volcano", I doubt oil shale is confused with anything non-geological. GeoWriter 08:15, 19 August 2007 (UTC)

[edit] Macerals in oil shale

Found following information, which is probably worth to add into this article. However, as I'm not the expert on this field, maybe somebody who is more familiar with this topic, could assist.

"Hutton (1987) recognised three major macerals in oil shale: telalginite, lamalginite, and bituminite. Telalginite is defined as structured organic matter composed of large colonial or thick-walled unicellular algae such as Botryococcus and Tasmanites. Lamalginite includes thin-walled colonial or unicellular algae that occur as distinct laminae, but displays little or no recognisable biologic structures. Under the microscope, telalginite and lamalginite are easily recognised by their bright shades of yellow under ultraviolet/blue fluorescent light. The third maceral, bituminite, is another important component in many oil shales. It is largely amorphous, lacks recognisable biologic structures, and displays relatively low fluorescence under the microscope. This material has not been fully characterised with respect to its composition or origin, although it is often a quantitatively important component of the organic matter in many marine oil shales. Other organic constituents include vitrinite and inertinite, which are macerals derived from the humic matter of land plants. These macerals are usually found in relatively small amounts in most oil shales." http://www.worldenergy.org/publications/survey_of_energy_resources_2007/oil_shale/647.asp Beagel 19:53, 24 October 2007 (UTC)

[edit] Formation

There is a problem with following block:

Most oil shale deposits were formed during middle Cambrian, early and middle Ordovician, late Devonian, late Jurassic, and Paleogene times.[1] They are formed by the deposition of organic matter in a variety of depositional environments including freshwater to highly saline lakes, epicontinental marine basins and subtidal shelves and restricted estuarine areas such as oxbow lakes, peat bogs, limnic and coastal swamps, and muskegs.[5] When plants die in such anaerobic aquatic environments, low oxygen levels prevent their complete decay by bacteria. For masses of undecayed organic matter to be preserved and to form oil shale the environment must remain uniform for prolonged periods of time to build up sufficiently thick sequences of algal matter.

Eventually the algal swamp or other restricted environments are disrupted and oil shale accumulation ceases. Burial by sedimentary loading on top of the algal swamp deposits converts the organic matter to kerogen by the following normal diagenetic processes:

  • Compaction due to loading of the sediments on the coal which compresses the organic matter
  • Removal of the water in the peat
  • With ongoing compaction, removal of water from the intracellular structure of fossilized plants
  • With heat and compaction, removal of molecular water
  • Methanogenesis; similar to treating wood in a pressure cooker, methane is produced, removing hydrogen, some carbon, and some further oxygen (as water)
  • Dehydration, which removes hydroxyl groups from the cellulose and other plant molecules, resulting in the production of hydrogen-reduced coals.

The problem is that this information, obtained from http://www.solarnavigator.net/coal.htm and http://www.eng.uwo.ca/people/esavory/ES%20832_Lect%204.ppt , talks about formation of coal. It needs also verification and additional references to prove that same process applies also to oil shale. Beagel 18:00, 8 November 2007 (UTC)

I guess I don't exactly see how this info comes from the links you cite here. Ref 1, the Estonian source, provides the material about geologic times, and although I didn't check thoroughly the Dyni ref (#5) seems to support most of the rest of the info. The section might do with some explicit information about differences between oil shale and coal, such as might be derived from Dyni: In terms of mineral and elemental content, oil shale differs from coal in several distinct ways. Oil shales typically contain much larger amounts of inert mineral matter (60–90 percent) than coals, which have been defined as containing less than 40 percent mineral matter. The organic matter of oil shale, which is the source of liquid and gaseous hydrocarbons, typically has a higher hydrogen and lower oxygen content than that of lignite and bituminous coal.In general, the precursors of the organic matter in oil shale and coal also differ. Much of the organic matter in oil shale is of algal origin, but may also include remains of vascular land plants that more commonly compose much of the organic matter in coal. The origin of some of the organic matter in oil shale is obscure because of the lack of recognizable biologic structures that would help identify the precursor organisms. Such materials may be of bacterial origin or the product of bacterial degradation of algae or other organic matter.
Thanks for all your good work on this article. Cheers Geologyguy 18:18, 8 November 2007 (UTC)
Thanks. I hope this solves the problem.Beagel 19:04, 8 November 2007 (UTC)