Peat dolomite

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Peat dolomite, mass approx. 19 kg

Peat dolomites are concretions of permineralized peat found in coal seams . They appear as roughly spherical tubers or as irregular flat plates. Peat dolomites were formed by the permineralization of peat by calcite in marshes of the Carboniferous before it was converted into coal . As a result, they contain detailed information about the tissue structure of the carbonaceous plants that would have been lost if they were charred.

Peat dolomites were first described in England in 1855 by scientists Joseph Dalton Hooker and Edward William Binney . They occur in North America and Eurasia. In North America they were first described by Adolf Carl Noé in 1922 ; there they are more widespread both geographically and stratigraphically . The oldest known peat dolomites come from the Namurian and were found in Germany and the former Czechoslovakia. The study of peat dolomites has led to the discovery of hundreds of species and genera .

Early Scientific Theories

Peat dolomites were first scientifically described by Joseph Dalton Hooker and Edward William Binney. They reported specimens from the coal seams of Lancashire and Yorkshire . Much of the early work on peat dolomites is from European scientists.

In North America, peat dolomites were first found in the coal seams of Iowa in 1894 , although it was not until 1922 that Adolf Carl Noé brought them to the European peat dolomites. Noë's publication sparked a renewed interest in peat dolomites, and in the 1930s European paleobotanists traveled to the Illinois Basin in search of peat dolomites .

There are two theories - the autochthonous in-situ theory and the allochthonous drift theory - which attempt to explain the formation of the peat dolomites, although this topic is often speculative.

Proponents of the in situ theory believe that organic matter near where it was found collected in a peat bog and, shortly after it was buried, was permineralized - minerals penetrated the organic matter and formed an internal cast. Water with a high content of dissolved minerals was buried in the bog along with the plant material. When the dissolved ions crystallized, concretions containing plant material formed , which were retained as rounded stone lumps. This prevented coalification and the peat was preserved and eventually formed a peat dolomite. Most peat dolomites are found in coal seams , in places where the peat has not been compressed enough to turn into coal.

Marie Stopes and David Watson analyzed peat dolomite samples and determined that peat dolomites form in situ . They emphasized the importance of the interaction with seawater, which they saw as a necessary prerequisite for the formation of peat dolomites. Some supporters of the in situ theory see in Stopes and Watson's discovery of a plant stem that protrudes through several peat dolomites as proof of the in situ theory, since the drift theory could not explain this observation. They also point to fragile pieces of organic material that protrude from some peat dolomites and that, had the drift theory been correct, should have been destroyed. After all, some peat dolomites are so big that they cannot be transported at all.

According to the drift theory, the organic material did not form near the site, but was transported there by a flood or a storm. Proponents of drift theory such as Sergius Mamay and Ellis Yochelson believed that the presence of marine animals in peat dolomites proves that material has been transported from the sea to a non-marine environment. According to Edward C. Jeffrey, the in situ theory "did not have good evidence"; he believed that formation from transported material was likely, as peat dolomites often contain materials that result from transport and sedimentation in open water.

composition

Flat structures surrounded by smaller bubbles;
Calcites and microdolomites are often part of peat dolomites

Peat dolomites are not made of coal. They are not flammable. They are calcium-rich, permineralized life forms that contain mainly calcium and magnesium carbonates as well as pyrite and quartz . Gypsum , illite , kaolinite and lepidocrocite also occur in smaller quantities . The size of peat dolomites varies from the size of a walnut to a diameter of 90 cm; they are usually the size of a fist. Peat dolomites smaller than a thimble were also found.

Peat dolomites contain dolomites , aragonites and amounts of organic material that has decomposed to varying degrees . Hooker and Binney analyzed a peat dolomite and noted "a lack of coniferous wood ... and fronds of fern"; the discovered plant material appeared to be arranged "exactly as it fell from the plants that produced it". Usually peat dolomites do not contain leaves .

In 1962, Sergius Mamay and Ellis Yochelson studied North American peat dolomites. After discovering marine organisms, peat dolomites were divided into three types: normal (including floral), which contain only plant material; faunals, which contain only animal fossils , and mixed ones, which contain both plant and animal material. The mixed ones were in turn subdivided into heterogeneous, in which plant and animal material were present separately, and homogeneous, which showed no such separation.

Degree of conservation

The degree of conservation of organic material in peat dolomites varies from no conservation to so good that the cell structures could be examined. Some peat dolomites received root hairs , pollen and spores and are described as "more or less perfectly preserved"; they do not contain “what the plant once was” but the plant itself. Others are “botanically worthless”; the organic matter had decomposed before turning into peat dolomite. Well-preserved peat dolomites are useful to paleobotanists. They were used to study the geographical distribution of vegetation and provided evidence that the same plants grew in the tropical belts of Ukraine and Oklahoma during the Cretaceous Period. Peat dolomite research also resulted in the discovery of more than 130 genera and 350 species.

Three main factors determine the quality of the material obtained in a peat dolomite: the mineral composition, how quickly the material was buried, and how much it was compressed before permineralization. In general, peat dolomites are best preserved from poorly decomposed material that has been quickly buried under low pressure; however, plant material in peat dolomites almost always shows some signs of decomposition. Peat dolomites that contain iron sulfide are considerably poorer than peat dolomites that have been permineralized by magnesium or calcium carbonates; therefore iron sulfide was also called the "main curse of the peat dolomite hunters".

distribution

A peat dolomite from southern Illinois

Peat dolomites were first discovered in England, then in other areas including Australia, Belgium, the Netherlands, former Czechoslovakia, Germany, Ukraine, China and Spain. They are also found in North America; there they are more geographically distributed than in Europe. In the United States, they were found from Kansas to the Illinois Basin and the Appalachians .

The oldest peat dolomites come from the early final phase of the Namurian (326 to 313 million years ago); they were found in Germany and the former Czechoslovakia. The common ages range from the Permian (299 to 251 million years ago) and the Pennsylvania . Some American peat dolomites come from layers between the late Westfalian (about 313 to 304 million years ago) and the late Stefanian (about 304 to 299 million years ago). European peat dolomites usually come from the early Westphalian.

In coal seams, peat dolomites are completely surrounded by coal. They are often found in isolated groups randomly spread across the seam, usually in the upper half of the seam. Their occurrence can be extremely rare or frequent; many coal seams do not contain peat dolomites at all, while some contain so much that miners avoid the areas.

Investigation methods

A number of thin, net-like disks that overlap each other more, sometimes less. The peat dolomite cut is reminiscent of a cracked pane of glass. There is a thick, dark line at the bottom.
A thin section of a peat dolomite

Thin section was an early method of studying fossil materials in peat dolomites. For this purpose, a peat dolomite was cut with a diamond saw and the thin disc was smoothed and polished with an abrasive. Then it was observed under a polarizing microscope. Although this process could be mechanized, it was replaced by a more convenient method because of the time required and the poor quality of the thin section specimens.

In 1928 the liquid peel technique, which is still in use today, replaced thin sections. Samples are cut with a diamond saw, polished with silicon carbide on a glass plate and etched with hydrochloric acid. The acid dissolves the minerals from the peat dolomite, leaving a protruding layer of plant material. After using acetone , a piece of cellulose acetate is placed on top of the peat dolomite. As a result, the cells contained in the peat dolomite are embedded in the cellulose acetate. After drying, the acetate can be removed from the peat dolomite with a razor blade and the resulting splinters can be colored with a weakly acidic dye and observed under the microscope. In this way, up to 50 samples can be obtained from a 2 mm thick piece of peat dolomite.

However, the samples disintegrate over time if they contain iron sulfide ( pyrite or marcasite ). Shya Chitaley remedied this problem by improving the separation of the preserved organic material from the inorganic minerals, including iron sulfide. This means that the sample retains its quality longer. In Chitaley's method, after polishing, the sample is heated and repeatedly treated with solutions of paraffin in xylene , the paraffin concentration increasing with each treatment so that the wax can completely penetrate the peat dolomite. The sample is then treated with nitric acid and acetone. After that, Chitaley's technique resembles the usual liquid splinter technique.

Also, X-ray diffraction in powder diffraction was used to investigate Torfdolomiten. X-rays of a given wavelength are passed through a sample to study its structure, particularly its crystallographic structure, chemical composition, and physical properties. The intensity of the diffracted X-ray radiation is observed and analyzed, with the measured variables consisting of the angle of incidence and diffraction, polarization and wavelength (energy).

See also

swell

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  5. ↑ a b c Tom L. Phillips, Herman L. Pfefferkorn, Russel A. Peppers: Development of Paleobotany in the Illinois Basin (PDF) Illinois State Geological Survey. 1973. Archived from the original on February 11, 2012. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved September 15, 2011. @1@ 2Template: Webachiv / IABot / library.isgs.uiuc.edu
  6. ↑ a b c d e f g h i Tom Phillips, Matthew J. Avcin, Dwain Berggren: Fossil Peats from the Illinois Basin: A guide to the study of coal balls of Pennsylvanian age . In: University of Illinois . 1976. Archived from the original on October 9, 2011. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved July 16, 2011. @1@ 2Template: Webachiv / IABot / library.isgs.uiuc.edu
  7. ↑ a b c Joseph Dalton Hooker, Edward William Binney: On the structure of certain limestone nodules enclosed in seams of bituminous coal, with a description of some trigonocarpons contained in them . In: Royal Society (Ed.): Philosophical Transactions of the Royal Society . 145, Britain, 1855, pp. 149-156. JSTOR 108514 . doi : 10.1098 / rstl.1855.0006 .
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  15. ^ Edward C. Jeffrey: Petrified Coals and Their Bearing on the Problem of the Origin of Coals . In: Proceedings of the National Academy of Sciences of the United States of America . 3, No. 3, 1917, pp. 206-211. bibcode : 1917PNAS .... 3..206J . doi : 10.1073 / pnas.3.3.206 . PMID 16576220 . PMC 1091213 (free full text).
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  21. ↑ a b c Sergius H. Mamay, Ellis L. Yochelson: Occurrence and significance of marine animal remains in American coal balls . In: United States Geological Survey (Ed.): Shorter Contributions to General Geology . 354, 1962, pp. 193-224.
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  25. ↑ a b W. John Nelson: Geologic disturbances in Illinois coal seams Archived from the original on April 17, 2012. Information: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) In: Illinois State Geological Survey . 530, 1983. Retrieved January 19, 2012. @1@ 2Template: Webachiv / IABot / library.isgs.uiuc.edu
  26. ↑ Tom L. Phillips, Russel A. Peppers: Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence . In: International Journal of Coal Geology . 3, No. 3, February 1984, pp. 205-255. doi : 10.1016 / 0166-5162 (84) 90019-3 .
  27. ^ Adolf C. Noé: A Paleozoic Angiosperm . In: The Journal of Geology . 31, No. 4, June 1923, pp. 344-347. JSTOR 30078443 30078443 . bibcode : 1923JG ..... 31..344N . doi : 10.1086 / 623025 .
  28. ^ A b Jean Galtier: Coal-ball floras of the Namurian-Westphalian of Europe . In: Elsevier Science BV (Ed.): Review of Palaeobotany and Palynology . 95, 1997, pp. 51-72. doi : 10.1016 / S0034-6667 (96) 00027-9 .
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  32. ↑ Shya Chitaley: A New Technique for Thin Sections of Pyritized Permineralizations . In: Review of Paleobotany and Palyntology . No. 45, 1985, pp. 301-306.
  33. ^ Materials Research Lab - Introduction to X-ray Diffraction . In: Materials Research Lab . University of Santa Barbara, California . 2011. Archived from the original on August 26, 2011. Retrieved on August 25, 2011.