The Origin of Coal
by Stuart E. Nevins, M.S.
Accumulated, compacted and altered plants form a sedimentary rock called coal. It is not only a resource of great economic importance, but a rock of intense fascination to the student of earth history. Although coal forms less than one percent of the sedimentary rock record, it is of foremost importance to the Bible-believing geologist. Here is where he finds one of his strongest geological arguments for the reality of the great Noachian Flood.
Two theories have been proposed to explain the formation of coal. The popular theory held by many uninformitarian geologists is that the plants which compose the coal were accumulated in large freshwater swamps or peat bogs during many thousands of years. This first theory which supposes growth-in-place of vegetable material is called the autochthonous theory.
The second theory suggests that coal strata accumulated from plants which had been rapidly transported and deposited under flood conditions. This second theory which claims transportation of vegetable debris is called the allochthonous theory.
Fossils In Coal
The types of fossil plants found in coal do not clearly support the autochthonous theory. The fossil lycopod trees (e.g., Lepidodendron and Sigillaria) and giant ferns (especially Psaronius) common in Pennsylvanian coals may have had some ecological tolerance to swampy conditions, yet other Pennsylvanian coal plants (e.g., the conifer Cordaites, the giant scouring rush Calamites, the various extinct seed ferns) by their basic construction must have preferred well-drained soils, not swamps. The anatomy of coal plants is considered by most investigators to indicate tropical or subtropical climate, a conclusion which can be used to argue against autochthonous theory, for modern swamps are most extensive and have the deepest accumulation of peat in the higher-latitude cooler climates. Because of the increased evaporative power of the sun, modern tropical and subtropical regions have the most meager peats.
It is not uncommon to find marine fossils such as fish, moluscs, and brachiopods in coal. Coal balls, which are rounded masses of matted and exceptionally well preserved plant and animal fossils (including marine creatures)1 are found within coal strata and associated with coal strata. The small marine tubeworm Spirorbis is commonly attached to plants in Carboniferous coals of Europe and North America.2 Since there is little anatomical evidence suggesting that coal plants were adapted to marine swamps, the occurrence of marine animals with nonmarine plants suggests mixing during transport, thus favoring the allochthonous model.
Among the most fascinating types of fossils associated with coal seams are upright tree trunks which often penetrate tens of feet perpendicular to stratification. These upright trees are frequently encountered in strata associated with coal, and on rare occasions are found in the coal. In each case the sediments must have amassed in a short time to cover the tree before it could rot and fall down.
One's first impression may be that these upright trees are in their original growth position, but several lines of evidence indicate otherwise. Some of the trees penetrate the strata diagonally, while others are found upside down. Sometimes an upright tree appears to be rooted in growth position in a stratum which is entirely penetrated by a second upright tree. The hollow trunks are commonly filled with sediment unlike the immediately surrounding rocks. Logic applied to the previous examples demonstrates transportation of the trunks.
The most important fossil relating to the controversy over the formation of coal is Stigmaria, a fossil root or rhizome. Stigmaria is frequently found in strata below coal seams and is commonly associated with upright trees. Stigmaria studied nearly 140 years ago by Charles Lyell and J.W. Dawson in the Carboniferous coal sequence of Nova Scotia was considered to provide unambiguous proof of growth-in-place. Many modern geologists still insist that Stigmaria represents an in situ root in the soil below the coal swamp. The Nova Scotia coal sequence was recently restudied by N.A. Rupke3, who found four types of sedimentary evidence for the allochthonous origin of Stigmaria. The fossil is usually fragmental and is rarely attached to a trunk, it shows a preferred orientation of its long axis due to current action, it is filled with sediment unlike the immediately surrounding rock, and it is often found on multiple horizons in beds which are entirely penetrated by upright trees. Rupke's research brings serious doubt upon the popular autochthonous interpretation of other Stigmaria-bearing strata.
Coal commonly occurs in a sequence of sedimentary strata called a cyclothem. An idealized Pennsylvanian cyclothem may have strata deposited in the following ascending order: sandstone, shale, limestone, underclay, coal, shale, limestone, shale. A typical cyclothem will normally be missing one or more of the component strata. In any one locality cyclothems commonly repeat tens of times with each cycle of deposition accumulated on a previous one. There are fifty successive cycles in Illinois and over a hundred in West Virginia.
Although the coal bed forming a portion of the typical cyclothem is usually quite thin (commonly an inch to a few tens of feet thick), the lateral extent of coal is often incredible. Modern stratigraphic research4 has correlated the Broken Arrow coal (Oklahoma), Croweburg coal (Missouri), Whitebrest coal (Iowa), Colchester No. 2 coal (Illinois), Coal IIIa (Indiana), Schultztown coal (W. Kentucky), Princess No. 6 coal (E. Kentucky), and Lower Kittanning coal (Ohio and Pennsylvania). These form a single, vast seam of coal exceeding one hundred thousand square miles in area in the central and eastern United States. No modern swamp has an area remotely approaching the great Pennsylvanian coals.
If the autochthonous model for coal formation is correct, a very unusual set of circumstances must have prevailed. An entire region, often encompassing many tens of thousands of square miles, would have to be raised simultaneously relative to sea level to permit swamp accumulation, and then lowered to permit the ocean to flood the area. If the coal forest was raised too far above sea level, the swamp and its antiseptic water necessary for the accumulation of peat would have been drained. If during the peat accumulation time the sea invaded the swamp, the marine conditions would have killed the plants, and other sediment instead of peat would have been deposited. According to the popular model, the formation of a thick bed of coal, then, would indicate the maintenance of an incredible balance over many thousands of years between the rate of peat accumulation and the rise of sea level. Such a situation seems most improbable, especially when the cyclothem is known to recur a hundred times or more in a vertical section. Could such cycles be better explained by accumulation during successive advances and retreats of flood waters?
One of the most talked about portions of the cyclothem is the underclay. The nonbedded, plastic layer of clay often underlies the coal stratum and is considered by many geologists to be a fossil soil on which the swamp existed. The presence of underclay, especially when it possesses Stigmaria, is often claimed to be prima facie evidence for the autochthonous origin of coal-forming plants.
Modern research, however, has cast some doubt on the fossil soil interpretation of underclays. No soil profile similar to modern soils is evident in underclays. Some of the minerals found in the underclay are not the type which would be expected in a soil. Instead underclays commonly show graded bedding (coarser grained material at the base) and evidence of clay flocculation. These are simple sedimentary features which would form in any water accumulated layer.
Many coal seams do not rest on underclays and little evidence of soil exists. In some cases coal strata rest on granite, schist, limestone, conglomerate or other rock unsuitable for soil. Underclay without a coal bed above is common as well as underclay resting on top of coal. The absence of recognizable soils below beds of coal shows the improbability of any type of luxuriant vegetation growing in place and argues for transportation of the coal-forming plants.
Texture of Coal
Investigation of the microscopic texture and structure of peat and coal contributes to the understanding of the origin of coal. A. D. Cohen5 initiated a comparative structural study between modern autochthonous mangrove peats and a rare modern allochthonous beach peat from southern Florida. Most autochthonous peats had plant fragments showing random orientation with a dominant matrix of finer material, while the allochthonous peat showed current orientation of elongated axes of plant fragments generally parallel to the beach surface with a characteristic lack of the finer matrix. The poorly sorted plant debris in the autochthonous peats had a massive structure due to the intertwining mass of roots, while the allochthonous peat had characteristic microlamination due to the absence of intergrown roots.
Following this study Cohen remarked: "A peculiar enigma which developed from study of the allochthonous peat was that vertical microtome sections of this material looked more like thin sections of Carboniferous coal than any of the autochthonous samples studied."6 Cohen noted that the characteristics of his allochthonous peat (orientation of elongated fragments, sorted granular texture with general lack of finer matrix, microlamination with lack of matted root structure) are also general characteristics of Carboniferous coals!
Boulders in Coal
One of the most striking inorganic features of coal is the presence of boulders. These have been noted in coal beds all over the world for more than one hundred years. P.H. Price7 conducted a study of boulders in the Sewell Coal of West Virginia. The average weight of 40 boulders collected was 12 pounds with the largest weighing 161 pounds. Many of the boulders were igneous and metamorphic rocks unlike any rock outcrops in West Virginia. Price suggested that the boulders may have been entwined in the roots of trees and transported from a distant area. Thus, the occurrence of boulders in coal favors the allochthonous model.
The nature of the process of metamorphosis of peat to form coal has been disputed for many years. One theory suggests that time is the major factor in coalification. The theory, however, has become unpopular because it has been recognized that there is no systematic increase in the metamorphic rank of coal with increasing age. There are some blatant contradictions: lignites representing low metamorphic rank occur in some of the oldest coal-bearing strata while anthracites representing the highest metamorphic rank occur in some of the youngest strata.
A second theory supposes pressure to be the major factor in coal metamorphosis. The theory is refuted by numerous geological examples where metamorphic rank does not increase in highly deformed and folded strata. Furthermore, laboratory experiments demonstrate that increase of pressure can actually retard the chemical alteration of peat to coal.
A third theory (by far the most popular) suggests the temperature is the important factor in coal metamorphosis. Geological examples (igneous intrusions into coal seams and underground mine fires) demonstrate that elevated temperature can cause coalification. Laboratory experiments have also been quite successful. One experiment8 produced a substance like anthracite in a few minutes by using a rapid heating process with much of the heat being generated by the cellulosic material being altered. Thus, the metamorphosis of coal does not require millions of years of applied pressure and heat, but can be produced by quick heating.
We see that many positive evidences have appeared which strongly support the allochthonous theory and the accumulation of many of the coal layers during the Noachian Flood. Upright fossil trees within coal seams suggest rapid accumulation of the vegetable debris. Marine animals and terrestrial (not swamp-dwelling) plants in coal imply transportation. The microstructure of many coal strata shows particle orientation, sorted texture, and microlamination indicating transportation (not growth-in-place) of plant material. Boulders present in coal demonstrate transportation processes. The absence of a soil below many coal strata argues for the drifting of coal-forming plants. Coal appears to form a regular and typical portion of the cyclothem being as clearly water-laid as the other rocks. Experiments in the alteration of vegetable material show that coal resembling anthracite does not require millions of years to form, but can be produced rapidly by a short heating process.
1 S.H. Mamay and E.L. Yochelson, "Occurrence and Significance of Marine Animal Remains in American Coal Balls," U.S. Geological Survey Professional Paper 354-1, 1962, pp. 193- 224.
2 H.G. Coffin, "A Paleoecological Misinterpretation," Creation Research Society Quarterly, 1968, vol. 5, pp. 85-87.
3 N.A. Rupke, "Sedimentary Evidence for the Allochthonous Origin of Stigmaria, Carboniferous, Nova Scotia," Geological Society of America Bulletin, 1969, vol. 80, pp. 2109-2114.
4 C.R. Wright, "Environmental Mapping of the Beds of the Liverpool Cyclothem in the Illinois Basin and Equivalent Strata in the Northern MidContinent Region," unpublished Ph.D. thesis, 1965, Univ. of Illinois; R.M. Kosanke, "Palynological Studies of the Coals of the Princess Reserve District in Northeastern Kentucky," U.S. Geol. Survey Prof. Paper 839, 1973, 20 p.
5 A.D. Cohen, "An Allochthonous Peat Deposit from Southern Florida," Geological Society of America Bulletin, 1970, vol. 81, pp. 2477-2482.
6 Ibid., p. 2480.
7 P.H. Price, "Erratic Boulders in Sewell Coal of West Virginia," Journal of Geology, 1932, vol. 40, pp. 62-73.
8 G.R. Hill, Chemical Technology, May 1972, p. 296.
* At time of publication, the author was Professor of Geology and Archaeology at Christian Heritage College in El Cajon, California.
Cite this article: Nevins, S. E. 1976. The Origin of Coal. Acts & Facts. 5 (11).