Energy & Fuels 1994,8, 1489-1493
1489
Nature and Composition of the Devonian Coals of Russia Idea B. Volkova Laboratory of Coal Petrology, All-Russian Geological Institute NSEGEI), 199026, St. Petersburg, Russia Received May 3, 1994. Revised Manuscript Received September 7, 1994@
The first economic coal accumulation in the territory of Russia is associated with the Devonian deposits of Siberia. In the Barzas area of the Kuznetsk basin a 0.8-3.6 m thick coal seam occurs in Jivetian. The Middle Devonian coals are also recorded in the Urals and in Kazakhstan. They have a peculiar microstructure and contain a great amount of thick psilophytic culticle (to 60%). The Barzas coals are subbituminous and contain a lot of volatile matter and resins. The Upper Devonian coals differ in their composition and original matter from the Middle Devonian ones and are similar to the Lower Carboniferous coals in the European part of Russia. The occurrence areas of the Upper Devonian coals have a submeridional orientation (from the Russian Platform through Timan toward islands in the Arctic Ocean).
Introduction Devonian coals are of great interest in many respects, particularly as these coals are the first economic coals in the geological history of Russia. They result from a mass emergence of plants on land, conquering of new niches by them, and the appearance of the first bog ecosystems. The Devonian coal accumulation marks one of the turning points in the evolution of the plant kingdom. Along with the generally primitive appearance of the Devonian plants, their advanced evolutionary state is evident. The tracheophyte “green revolution” progressed through the Middle and Late Devonian with the development of rooted plants and the appearance of shrubs and trees of terrestrial habitats and with the further enrichment of freshwater ec0systems.l Published papers and the results of the author’s petrological investigations in different regions (Barzas, Timan, Kazakhstan, Arctic islands) are the sources for the characteristics of Devonian coals.
Results The changing character of coal-formingvegetation is reflected in the petrographic features and composition of the Middle and Upper Devonian coals. The Middle Devonian was characterized by one of the largest marine trangressions in the Earth’s history and was also noted for the absence of mountain building or folding movements. The climate was hot and humid in areas of coal accumulation.2 The oldest coal measures are associated with coastal marine sediments. Three provinces of Middle Devonian coal are distinguished in the territory of the former USSR: Siberian, Kazakhstan, and Timan (Figure 1). Coals of the Siberian province are represented by peculiar types, which were initially named sapromixites @Abstractpublished in Advance ACS Abstracts, October 1, 1994. (1)Beerbower, R. In Geological Factors and the Evolution of Plants; Tiffney, B. H., Ed.; Yale University Press: Ithaca, W ,1985;p 47. (2) Nalivkin, D. V.; Slatvinskaya, E. A.; Volkova, I. B. In Atlas of Coal Accumulation on the USSR Territory (Explanatory Notes); Gorsky, I. I., Ed.; Academy of Sciences of the USSR Press: Moscow, 1962;p 44.
Figure 1. Map showing regions of Devonian coal accumulation within USSR territory: (1)Middle Devonian; (2) Upper Devonian. Provinces of Middle Devonian coal accumulation: (I) Siberian, (11)Kazakhstan, (111)Timan. Provinces of Late Devonian coal accumulation: (IV)Central Russia, (V) TimanUrals, (VI) Arctic.
(sapropelites), since they were considered to have formed from brown algae.3 Later, it was demonstrated that the plant remains, of which they are composed, belong to the group psylophytales with genera such as Orestovia and B a r s a ~ s i a . ~ , ~ These coals are confined to the Devonian deposits of Kuznetzk Basin in the South Siberia (Figure 1,part I). As a result of prospecting, several coals and areas with (3) Zalessky, M. D. Natural History of One Coal; ONTI: Petrograd, 1915;p 24. (4) Ergolskaya, Z. V. Petrographic Study of Barzas Coals; ONTI: Moscow, 1936;p 64. ( 5 ) Snigirevskaya, N. S.; Bogdanova, L. A. Botanical J. 1992,77(l), 58.
0 1994 American Chemical Society
1490 Energy & Fuels, Vol. 8, No. 6, 1994
economic coal presence were discovered. The coalbearing Barzas Formation is 300 m thick and is composed of mudstone and sandstone with conglomerate and limestone interbeds. The main coal bed, 0.8-4.8 m thick, occurs in the lower part of the formation and can be traced for 8 km along the strike and for 1.5-2 km across the strike. The mean ash content of beds is 45%. Actual reserves are 31 million tonnes. The overlying redbed sequence also contans a discontinuous thin layer composed of allochthonous breccia-like, strongly mineralized coal, composed of fragments of coals of the Barzas formation. In 1936 there was a pit where the Barzas coal was produced. Experimental semicoking of run of mine product gave from 14 to 21% of pitch.6 The main Barzas seam is made up of several coals units of different types and rock stringers. Three main types are distinguished on the basis of features of the microstr~cture.~ Type I: Slabby Coal. Slabby coal is characterized by distinct sheetlike partings and splits easily into leaflike laminae. The latter are composed of tightly compressed ribbonlike bodies, which are segregated during weathering and form the so-called “paper coal”. Under the microscope, sections perpendicular to bedding display an alternation of light yellow or orange laminae with narrower dark red laminae. Between these laminae are clayey partings. Each set of alternating laminae comprising two light and one dark laminae represent the section through a ribbonlike psylophyte body. The central part, in certain cases, contains structure corresponding to the anatomical structure of the initial plant (Figure 2). Mostly the cuticle of stems was preserved and accounts for 70-80% of the coaly matter. The Barzas coals should be assigned to the cuticular liptobioliths group. In the slabby coal type, depending on coloring and degree of swelling of the cuticle, several microscopic variaties are distinguished. One of these, represented by foliated plicated coal, is known as “plicated coal”. Type 11: Compact Coal. Compact coal is noted for its monolithic structure, density, and hardness. Thin sections display a “confluent” character composed of a light-colored homogeneous groundmass, enclosing fragments similar to some elements of ribbonlike bodies in type I coal. These indicate the common precursor of coals of types I and 11. Type 111: Lustrous Coal. Lustrous coal is a homogeneous pitchlike, lustrous coal with a conchoidal fracture. Type I11 coal is generally similar to type I1 but is distinguished by a brighter color for the groundmass in thin sections and a higher degree of decomposition of dark plant remains. The structure of certain inclusions, recorded here, also indicates the common initial matter, which was, however, subject to different transformation processes. Type I, or slabby paper coal, is the most widespread. It constitutes almost the entire seams in the following deposits: Dmitrovka, Dedushkino, Osinovskoe. Type I1 coal is predominant in the Ustyuzhna deposits, where (6) Tyzhnov, A. V. In Geology of Coal and Oil Shale Deposits of the USSR; Yavorsky, V. I., Ed.; Nedra Press: Moscow, 1969;Vol. 7, p 778 (7) Atlas of the Microstructes of the USSR Coal (Explanatory Text); Jemchujnikov, Yu.A. (Zhemchuzhnikov), Ergolskaya, Z. V., Eds.; Chief Editorial Office of the Mining Fuel and Geological-Prospecting Literature: Leningrad, 1937; p 186.
Volkova
slabby coal is of minor significance. Type I11 coal occurs in the Kamzhal deposit after which it is named. A peculiar petrographic composition of the Middle Devonian coals reflects their chemical characteristics. Coals of the Barzas type, similar to real liptobioliths, are noted for a high yield of volatiles (Vdaf60% or more), a high hydrogen content (7-9%), and a high yield of pitch. In this connection, they represent a valuable raw material for semicoking processes (Tables 1 and 2). Along with cuticular liptobioliths, clarain-like coals, containing megaspores and microspores, also occur at the Barzas deposit. They have a lower hydrogen content and their composition is more similar to the younger Upper Devonian coals. The Middle Devonian coals are also recorded in other regions of Siberia. Thin foliated coal, similar to the Barzas slabby coal, is described from the Middle Devonian deposits in the vicinity of Krasnoyarsk. Petrographically, it is composed of 75-80% of plant cuticle, similar to Orestovia Devonica Erg. The enclosing coal measures contain abundant psilophyte f l ~ r a In . ~the ~~ Irbei region, large blocks and fragments of coal occur, similar to the plicated variety of slabby coal.1° Presumably, these coal fragments are associated with the Middle Devonian deposits, recently eroded by the Irbei River. In Kazakhstan, the indigenous Devonian coals are in the Aidarly deposit, where they are represented by anthracites, and in Ermentau. These coals are similar t o coals of the Barzas deposit, especially microstructure and chemical composition. In Kazakhstan, there are also numerous occurrences of coal Barzas type pebbles in different regions, such as near Lake Alakol, at the Ekibastuz hard coal deposit and in the Kenderlyk Trough.11-13 In southeastern Kazakhstan, In Kenderlyk, pebbles of Barzas type coal were found by the author in the Permian and Upper Triassic conglomerates. The size of pebbles is 8-15 cm x 2-3 cm. The coals split into slabs 0.5-1 cm thick. These slabs are, in turn, composed of foliated partings up to 1 mm, which are difficult to split away from coal. Thin slabs catch fire from a match and give a long smoking flame. Elongated smooth bodies are visible on the bedding surface. Under the binocular microscope, rare annular craterlike bulges are discernible on their surface. They are similar to formations described on the surface of Orestovia petzii cuticles in coals from the Barzas deposit. Sections perpendicular to bedding display the alternation of a yellow-orange thick cuticle with narrower bands of dark red vitrinized matter. The thickness of the cuticles is 0.08-0.24 mm and that of vitrinite is 0.12-0.25 mm. Sometimes, sections of the inner parts of stems display good preservation of the anatomical structure. In the first variety found in Kenderlyk, the content of cutinite is 67-7376, that of vitrinite 13-30%, (8)Larishchev, A. A. J. Chem. Solid Fuel 1937,8 (91, 753. (9) Atlas of Maps of Coal Accumulation on the USSR Territory (Erplanotory Note);Gorsky, I. I. Ed.; Academy of Sciences of the USSR
Press: Moscow, 1962; p 528. (10)Larishchev, A. A. Scientific Lett. Tomsk State Uniu. 1948, No. 11, 79. (11)Lyuber, A. A. J. Chem. Solid Fuel 1935, 6 (l), 14. (12)Volkova. I. B.Dokl. Akad. Nauk SSSR 1961. 141 (3). 715. (13)Lapo, A.’V.; Kuznetsova, A. A.; Slatvinskaya, E. A. Izu. Akad. Nauk SSSR, 1984,4, 133.
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Devonian Coals of Russia
-----
-L
."*
1
A
0
C
D
E
F
Figure 2. Microstructure of Devonian psilophytic coals (transmitted light). (A, B)General view of cuticulous liptobiolith, x50 (A), x 110 (B).(C, D)Sections of the central part of psilophyte stems (in the form of telinite),surrounded by a thick cuticle, x 110. (E)A fragment of a cuticle in maceration, x 110. (F)Structure of Orestovia stoma, x 110.
sporinite 2-3%, and mineral matter 2%. In the second variety of coal the amount of cutinite decreases to 44% due to the presence of wider vitrinite lenses. A specific feature is a darker coloring of cuticle in thin sections
as compared to vitrinite. In the luminescent microscope the cuticle is greenish-yellow and multilayred. In thin sections, in crossed nicols all the constituents reveal a distinct anisotropy. The optical properties and composi-
1492 Energy &Fuels, Vol. 8, No. 6, 1994
Volkova
Table 1. Characteristics of Banas Coalsa moisture, coal type
%W
slabby coal compact “confluent”coal
3.0 2.0 1.1 4.2
pitch-like coal Clarain-like coal a
ash volatile sulfur, % A matter,%Vdaf %S: 21.6 32.1 21.7 13.7 18.5
0.04 87.7 0.13 0.10 0.03
w t % daf
%C
%H
%N
75.98 7.52 0.44 82.02 10.10 0.44 80.89 9.06 0.42 80.69 9.59 0.33 76.67 5.28 0.71
%(O+S)
notes
16.06 7.44 9.63 9.38 17.34
the most widespread coal characteristic of deposit, No. 2 observed in deposit No. 1 widespread
Data from Ergolskaya, 1936 (ref 4) and Atlas, 1937 (ref 3).
Table 2. Characteristics of Barzas Type Coals from Different Regions region
moisture
ash,
% Wa
% Ad
volatile matter, % Vdd
carbon, % Cdaf
hydrogen, % Hdaf
Kazakhstan Kenderlyk
1.4
6.6
71.7
80.97
8.05
Kenderlyk
0.8
4.3
59.6
83.16
7.84
Lake Alakol Ermentan Ekibastuz
4.2-4.6 1.2
81.5 67.2-70.0 81.6
81.0 74.4-78.2 83.9
8.5 7.5-7.7 9.7
89.2
80.65
9.55
Franz Josef Land 1.2
12.9 14.6-17.5 3O.lx) 2.2
tion of the coal correspond t o bituminous coals of the middle stages of coalification. In the Timan region (Northern Urals) coal occurrences are recorded in the Middle and Upper Devonian. According to Pervukhina, in the Middle Devonian deposits of the Kumushka-Belaya River coals occur, described by Zalessky as sapromixites.14 These are correlated with slabby coal of Barzas. Blocks of similar coal have also been found along the Svetlaya Bolshaya River. Vanderflit pointed to occurrence of the Barzas papertype coals in the Upper Devonian outcrops on the Czech Bay coast.15 On the eastern slope of the Northern Urals, along the Kama River, Larishchev described a thin seam of cuticular liptobiolith and noted its similarity with the types known from the Devonian of Siberia.16 The affinity of their nature and facies conditions of emplacement were revealed. Pebbles of cuticular liptobiolith occur in the Rhaetian-Liassic conglomerates of Graham Bell Island (Franz Josef Land.). Based on the peculiar appearance and microstructure, Korzhenevskaya correlated this coal with compact pitchlike, lustruous coal from the Middle Devonian of Siberia.17 The Late Devonian coals differ from the Middle Devonian coals in maceral composition and chemical properties. The coals occur in the Central Russian, Timan-Urals, and Arctic regions. In the Late Devonian era, the number of constant, isolated water bodies, lakes, swamps, and lagoons on the surface of coastal plains increased markedly. Locally, fine-grained thinbedded rocks were enriched in coalified plant remains and contain coal lenses and interbeds. On the northeastern Russian Platform, along the coast, composed of ancient sequences of the Timan Caledonides, during certain intervals of Frasnian and Famenian time, coal seams formed in coastal swamps, sometimes reaching (14)Pervukhina, A. E. J. Sou. Geol. 1940, 8 , 73. (15) Slatvinskaya, E. A.; In Atlas of Maps of Coal Accumulation on the USSR Territory (Explanotory Note); Gorsky, I. I., Ed.; Academy of Sciences of the USSR Press: Moscow, 1962; p 40. (16)Larishchev,A. A.; Scientific Letters of Tomsk State University, 1947, N 7, 126. (17)Korzhenevskaya, E. S. Inform. Bull. NIIGA (Sei. Inst. Arctic Geol.); 1967, I , 29.
characteristic of specimen coal pebbles from T3 conglomerate coal pebbles from PZ conglomerates coal pebbles bedrock occurence coal pebble from Carboniferous rocks coal pebbles from RhaetianLiassic conglomerate
source Volkova (1961)12 Volkowa (1961)12 Ljuber (1935)11 Lap0 et al. (1984)13 Lap0 et al. (1984)13 Korzhenevskaya (1957)17
economical thickness. Their structure is not uniform and ash content is high. In Northern Timan up to nine coal seams 0.3-0.85 m thick occur on the Volonga River. Weathered coal is characterized by the following features: ash content (dry, %) 10.2; total sulfur content (dry, %) 4.1; carbon (dry, ash free, %) 68.9; hydrogen (dry ash free %) 4.17. Semilustrous banded clarain rich coals with microspores, semidull and dull homogeneous argillaceous and striated banded clarain coals with spores, cuticle, ‘and fusain fragments are found. Also distinguished here are dull argillaceous clarain-durain coals which contain large numbers of microspores, fragments of macrospores, vitrain, and fusain fragments. Semidull finely striated coal is composed of alternating vitrinite bands with layers enriched in microspores and fusinite. Most widespread among these types are clarain coals which, according Naumova,15 are similar to coals of Bjorne Island. From coals of the Volonga River A. A. Lyuber mainly defined spores of pteridospermaphytes.l5 The author has studied the Upper Devonian coals of Timan in collections received from geologists over different years. They contain dull and semidull coals, as well as striated and banded coals. Vitrinite reflectance is 0.60-0.62%. Coals commonly display sulfide mineralization. F’yrite forms pseudomorphs after stem fragments and fills inner parts of small stems. F’yritized remains and some vitrinite lenses retain traces of anatomical structures of tissues. According to definitions of paleobotanist Petrosyan, these are remains of higher plants assigned to the Upper Devonian Archeopteris flora (personal communication). Thin lenses of hard coals occur in the Frasnian deposits of Southern Urals. They occur among bauxites in a limestone sequence with marine fauna. Coals are lustrous with a conchoidal fracture. Under the microscope thin bedding is recorded, as well as small ovoids and bauxite stringers. Hard coals, recorded in Frasnian deposits if the southeastern Russian Platform, are also similar to the described humic Late Devonian types. According to Bluforov, thin-banded clarain coals occur here. The Middle Devonian deposits of this area contain
Energy & Fuels, Vol. 8, No. 6, 1994 1493
Devonian Coals of Russia fragments of vitrainized wood and ribbonlike bodies, similar to Orestovia from the Kuznetsk Basin.18 In the Arctic region, the Devonian coals, carbonaceous rocks, and coal pebbles are recorded in conglomerate from Spitsbergen, Novaya Zemlya, and, as noted above, Franz Josef Land. In Bjarne Island, the Tunheim sandy shale sequence contains two coal seams; the Misery Series has abundant thin seams. Sedimentation was in a continental environment. According to Evdokimiva, coals from the Upper Devonian-Lower Carboniferous deposits in Spitsbergen are semilustrous clarain coals of coking coal ranks. Vitrinite reflectance, R,,, is 1.40-1.65%; volatiles content Vdd is 19-25%. These coals are noted for the mediun ash content and are slightly s u l f u r ~ u s . ~ ~ The author has studied samples of highly carbonaceous rocks t o 10 cm thick (collection from the Sevmorgeo Institute) from the Upper Devonian deposits of Severny Island (Novaya Zemlya). These rocks are represented by accumulations of vitrinite lenses. Abundant megaspore remains are seen in the mineral mass. Vitrinite reflectance is 4.9%; the high metamorphic grade results from the contact thermal metamorphism by intrusions. The underlying Middle Devonian deposits are represented by marine sediments-dolomites. The Devonian deposits of the Canadian Arctic Islands, where, according to Goodbody, coals of cannel type mainly occur.20
Discussion From the above facts, it follows that the composition of coals changed from the Middle to the Upper Devonian as a result of the evolution of vegetation. However, the debate concerning the nature of Barzas coals still continues. Recently, Fomin, using data on isotope composition of the coals, concluded that barzassites
should be assigned to sapropelites.21 Carbon from the latter is characterized by a 613C value of -21.38%0;this is similar to the value for the Olenekian sapropelite, -21.07%0). Resinite liptobiolith (80% of resinite) from the Il’ichero deposit has a 613Cvalue of -23.9%0, which is closer to the value for clarain humic coals. However, in the same paper, typical sapropelites, for example the Irkutsk saprocollite and the Estonian kuckersite, had 613C values of -31.97%0 and -32.05%0, respectively. In addition to the favorable tectonoclimatic factors, mass accumulations of plant remains are associated with appearance of the dendritic groups of plants in the Devonian. The stems of these plants in the Middle Devonian of Kazakhstan were up to 10 cm diameter. In the Late Devonian large forms of terrestrial vascular plants existed. The arborescent life form in the history of the plant kingdom was first recorded among Archeopteris, which formed the first forest landscapes. Archeopteris forests were widespread on the Euramerian, Kazakhstan, Siberian, China, and Gondwana continentx22 The Upper Devonian coal formed immediately before the Carboniferous stage, which was one of the periods of the most intense accumulation of plant remains in the form of coals. Elements of a historical connection between the intense Early Carboniferous and quantitatively modest Late Devonian coals show up in a relatively significant extent of the Upper Devonian coaly facies, in similar petrographic compositions of coals, and in a principally monotypical character of coal-forming vegetation. The Middle Devonian coals were as yet segregated, which resulted in a different nature of the initial organic matter and petrographic features.
USSR,Ser. Geol. Sci.
Acknowledgment. I am indebted to Dr. Thomas Robl, President American Society for Organic Petrology (TSOP),to the International Science Foundation (Grant No. 1157), to the reviewers, and to John W. Larsen, Editor, who helped me greatly.
(19) Evdokimova, N. K. Types of coal and the coal measures in Spitsbergen. Abstract of Thesis; VSEGEI: Leningrad, 1982; p 25. (20) Goodarzi, F.;Goodbody, Q.Int. J.Coal. Geol. 1990,14, (31,175.
(21) Fomin, A. N.J. Oil Shale, Tallinn 1990, 7/1, 36. (22) Snigirevskaya, N. S. Formation and Ebolution of Continental Biotas; Nauka Press: Leningrad, 1988; p 115.
(18)Bludorov, A. P. Izu.Kazan Branch Acad. 1954,2, 37.
