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Notes on the origin of inertinite macerals in coals: Observations on the importance of fungi in the origin of macrinite
International Journal of Coal Geology 80 (2009) 135–143
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International Journal of Coal Geology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j c o a l g e o
Notes on the origin of inertinite macerals in coals: Observations on the importance of fungi in the origin of macrinite James C. Hower a,⁎, Jennifer M.K. O'Keefe b, Michael A. Watt c, Timothy J. Pratt d, Cortland F. Eble e, J.D. Stucker f, Allison R. Richardson f, Irena J. Kostova g a
University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, Kentucky 40511, United States Department of Physical Sciences, Morehead State University, Morehead, Kentucky 40351, United States Weatherford Laboratories, Arvada, Colorado 80007, United States d Formerly: Ticora Geosciences, Arvada, Colorado 80007, United States e Kentucky Geological Survey, Lexington, Kentucky 40506, United States f Department of Earth & Environmental Sciences, University of Kentucky, Lexington, KY 40506, United States g Sofia University “St. Kliment Ohridski”, Department of Geology and Paleontology, 15, Tzar Osvoboditel Blvd., 1000 Sofia, Bulgaria b c
a r t i c l e
i n f o
Article history: Received 10 March 2009 Received in revised form 4 August 2009 Accepted 6 August 2009 Available online 20 August 2009 Keywords: Fungus Funginite Macrinite Degradation Rot
a b s t r a c t Macrinite is a, generally, rare inertinite maceral, often incorporating remnants and fragments of other macerals, including vitrinite, liptinite, and other inertinite. The associated inertinites include multiple forms of funginite. Funginite is also commonly found in association with vitrinite of slightly elevated reflectance and with degraded varieties of vitrinite. Together with the highly degraded macrinite, the latter two associations are here inferred to be part of a continuum of fungal and microbial degradation of peat. In any case, the origin of some macrinite is potentially distinct from that of inertinite generated by fire. © 2009 Elsevier B.V. All rights reserved.
1. Introduction A number of taphonomic processes have been proposed to account for the generation of inertinite-group macerals. In recent years, an emphasis has been placed on fire as a mechanism for the generation of most macerals of the inertinite group, macrinite and funginite included (Scott, 1989, 2000, 2002; Winston, 1993; Scott and Jones, 1994; Guo and Bustin 1998; Petersen, 1998; Bustin and Guo, 1999; Scott et al., 2000; Scott and Glasspool, 2005, 2006, 2007; McParland et al., 2007). In general, we do not dispute this mechanism and recognize that macrinite can be charred and originate from the same starting material as fusinite. We emphasize that fire does not fully address the origin of some nonfusinite/non-semifusinite inertinites and we seek to expand the dialogue on the origin of these macerals, in part by revisiting older voices on the subject and also through the introduction of new examples. Most micrinite, not discussed further in this paper, is clearly of a different origin than fusinite and semifusinite, and are generally thought to be the product of cracking of hydrocarbons in the coal, perhaps at the onset of the oil window (Teichmüller, 1974). Very fine
⁎ Corresponding author. E-mail address: [email protected] (J.C. Hower). 0166-5162/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2009.08.006
inertodetrinite might be confused with micrinite, however, leading to a broader definition of the maceral (International Committee for Coal and Organic Petrology, 2001). Secretinite, formally established as a maceral in the 1994 International Committee for Coal and Organic Petrology (ICCP) nomenclature (International Committee for Coal and Organic Petrology, 2001), is considered to be charred resins. Perhaps, in light of its pathway as an inertinite, it can be considered to be part of the fusinite/semifusinite track of inertinite formation. Funginite, long recognized in coal (Jeffrey and Chrysler, 1906; although Jeffrey, 1924, later dismissed the importance of fungi in coal development), and recognized as a discrete maceral since the Third Congress of Carboniferous Stratigraphy and Geology (Heerlen, Limbourg, The Netherlands, 25–30 June1951) (Beneš, 1959), refers to the fossil spores, sclerotia, and hyphae of fungal bodies. Funginite, while it can be charred, is clearly different from other inertinite macerals, first as being the product of a non-plant organism1 and second in not universally attaining high reflectance. Funginite as a maceral was
1 In general discussions of coal, we would argue that it is generally overlooked that coal is a product of all five (or six, depending upon who is counting) kingdoms of life. In terms of shaping the humic coals as we see them, aside from the plant kingdom, Fungi, including fungal forms within Chromista (Oomycetes) and Protozoa (slime molds), are, along with bacteria, among the most important organisms in the passage from peat to lignite to subbituminous coals.
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Fig. 1. Fungal hyphae. Photo 919 38; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm.
defined in 2001 (International Committee for Coal and Organic Petrology, 2001) with separation of sclerotinite into funginite and secretinite. Close scrutiny of published descriptions and figures is therefore necessary when examining the literature on fossil fungi. There is a misconception, owing to the lack of abundant funginite in Pennsylvanian coals, that it is absent in the Pennsylvanian coal. Schopf (1952) noted that fungi were rare in the Pennsylvanian coals he had examined. Stach (1935, 1957), Duparque and Delattre (1953b), Stach and Pickhardt (1957) ,Beneš (1959, 1969), Taylor and Osborn (1996), and Taylor and Taylor (1997) observed the presence of Paleozoic fungi. Robinson (1990) noted their rarity, while Beneš (1959) noted how
Fig. 3. Macrinite with structured fusinite, semifusinite, and secretinite (?) at base of particle. Macrinite with included inertodetrinite (fine, bright particles) and funginite between cutinite “leaves.” Photo 05 21; Maastrictian Onyema coalfield, Nigeria, hvCb. Scale bar = 100 μm.
common they are. As noted above, caution must be taken when citing fungal occurrences described by pre-2001 authors as many of the fungal forms identified by Stach (1935, 1957), Duparque and Delattre (1953b), Beneš (1959), and others are now known to be secretinite. That said, all of the latter authors illustrate at least some macerals that meet the modern description of funginite. Macrinite, as will be discussed below, can also have a distinct origin, being the consequence of the degradation of woody, and other, plant parts.
Fig. 2. A/ Fungal hyphae. Photo 903 12; Powder River Basin, Paleocene, subbituminous/hvCb. Scale bar = 100 microns. B/ Funginite. Photo 903 13; Powder River Basin, Paleocene, subbituminous/hvCb. Scale bar = 100 μm. C/ Funginite (center). Photo 917 78; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. D/ Funginite within macrinite, funginite adjacent to macrinite, and funginite in a detrital maceral zone. Photo 11 11; Maastrictian Okaba-Odagbo coalfield, Nigeria, hvCb. Scale bar = 100 μm.
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Fig. 4. Funginite in liptinite (resinite or liptodetrinite). Photo 06 comp; Maastrictian Onyema coalfield, Nigeria, hvCb. Scale bar = 100 μm.
Macrinite has been frequently misidentified. Most often, both before and after the International Committee for Coal and Organic Petrology (2001) clarification of inertinite nomenclature, macrinite has been confused with secretinite, which, as stated, both here and elsewhere (Lyons et al., 1986; Hower et al., 2008a,b), has a different biological origin. The misidentifications of macrinite notwithstanding, there are varieties of inertinite macerals that defy conventional classification. In our experience, the inertinites found in the “ragged edge” (brecciated marginal marine) sections of the Herrin coalbed in western Kentucky do not yield to an easy classification (Hower et al., 1987; deWet et al., 1997; Hower and Williams, 2001; O'Keefe et al., 2008). Bright macerals, in distinct contrast to the ambient high volatile bituminous rank vitrinite of the region, preserve woody textures more reminiscent of a woody peat than of fusinite/semifusinite or of macrinite at different extremes of the inertinite spectrum. As an example of the problems in the assignment of macrinite in the inertinite spectrum, Winston's (1993) investigation of inertinite macerals was flawed in many respects. Repeating an interpretation that had been passed through the literature of the time, he discussed degradofusinite strictly as a variety of fusinite. The degradofusinite in his usage, something common to the prevailing usage in the literature, would more properly be termed macrinite under the 1994 ICCP nomenclature (International Committee for Coal and Organic Petrology, 2001). The diagenetic pathways of fusinite and macrinite can be quite distinct. Both, in general, originated from wood, although macrinite can contain fragments of other maceral types, but divergent pathways of alteration and preservation led to distinct macerals. Winston's (1993, p. 213) description of “fungi preserved as vitrinite” is problematical. Clearly, this is impossible as vitrinite is a product of vascular plants and fungi are a distinct kingdom of life. For the same reason, fungi cannot be preserved as fusinite, although they can attain the same, or higher, reflectance as fusinite, contrary to the statement on page 217 of his publication. Relationships between funginite, or fungal sclerotinite in the older nomenclature, and degraded maceral assemblages were discussed by Duparque and Delattre (1953a,b) and Stach (1956), among others. Stach (1956) drew a parallel between fungal degradation and varying water levels in the paleoswamps. He associated the development of “massive micrinite,” macrinite in modern nomenclature, with fungal activity. In Tertiary Chulotka Peninsula (Russia) brown coals, Lapo and Malán (1981) noted an association of funginite and macrinite. Cross and Phillips (1990) mentioned the role of fungus in degradation of plant material, but did not elaborate further, building their discussion on the contributions of vascular plants to coal development. Sweeney et al. (2009) noted an association between fungal degradation and subsequent mineralization of wood. Eble et al. (1994) noted that microbial degradation is a pathway to inertinite development,
drawing a clear distinction between fire and microbial degradation, but ultimately did not distinguish between the distinct macerals resulting from the dichotomous origins. Belkin et al. (2009) described the occurrence of funginite in vitrinite in several Cenozoic coals from Sumatra, Kalimantan, and Sulawesi. No alteration of vitrinite was noted in their investigations, in contrast to high volatile A bituminous Oligocene Romanian coals where vitrinite in the vicinity of funginite was slightly degraded and had a higher reflectance (Belkin et al., 2008). Beneš and Kraussová (1964, 1965) and Beneš (1959, 1969) noted that the amount of funginite in a coal is related to the petrology, with clarodurite and durite richest in funginite. The “fungidurites” of Beneš (1960) represent aerobic disintegration, with the distribution of inertinite indicative of specific conditions in the formation of coal. Most of the illustrated “funginite”2 in the latter contribution, however, would now be identified as secretinite. More of the illustrations accompanying Beneš and Kraussová (1964, 1965) are legitimate funginite, redeeming their interpretation in contrast to Beneš (1959, 1960). Teichmüller (1958) observed fungi more frequently in her sapropelic “Reid-Moor Kohle” facies than in less-degraded facies. Straka (1960) made similar observations in studies of Madagascar peats. Schwab (1962) also examined the link between fungi and coal facies. In Czechoslovakian coals, Beneš and Kraussová (1965) found the sapropelic and detrital horizons to have the most funginite, with brighter lithotypes being funginite-poor. Moore and Hilbert (1992), Esterle and Ferm (1994), and Moore et al. (1996) described fungal oxidation of southeast Asian peats. In particular, Moore et al. (1996) note mycorrhizal hyphae associated with roots in the peat. In investigations of humic soils, Waksman (1944) found that fungal spores and mycelium were abundant, along with bacteria and actinomycetes, surrounding disintegrating roots. In studies of modern Everglades' peat, Wallace and Dickinson (1978) describe distinct differences in fungal populations with respect to different flora. The relationships are complex, with differences between the Rhizophora, Juncus, and Cladium peats dependent upon the distinct ecological niches of the flora. The largest fungal population was found in the highly decomposed Cladium peat. Aside from the vegetation variables, within modern peats there is a seasonal variation in fungal activity, peaking in October in northern hemisphere temperate climates and varying with moisture, pH, N2, P, and K (Pavlenko, 1965; Latter et al., 1967). Fell (1977) noted an optimal temperature for fungal activity in a study of Rhizophora mangle leaf-fall degradation. Certain types of plants may provide some protection, such as through enzymes or tannins, against microbial degradation (Exarchos
2
Beneš (1960) appears to have been the originator of the term funginite.
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Fig. 5. A/ Macrinite, with possible included funginite (lower right, within body labeled as macrinite) and shreds of the surrounding sporinite (within thinning left edge of body labeled macrinite), internal to megasporinite. Photo 922 33; Queensland, Australia, Late Triassic, hvCb. Scale bar = 100 μm. B/ Macrinite adjacent to cutinite. Photo 919 33; Queensland, Australia, Late Triassic, hvCb. Scale bar = 100 μm. C/ Macrinite with included inertodetrinite and liptinite. Oxidized resinite adjacent to macrinite. Photo 925 32; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. D/ Macrinite with included cutinite and other detrital liptinites and inertodetrinite. Photo 917 80; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. E/ Macrinite with included liptodetrinite and inertodetrinite. Photo 934 33; Wyoming. Paleocene, subbituminous. Scale bar = 100 μm. F/ Sporinite (center) with included funginite. Photo 934 42; Wyoming. Paleocene, subbituminous. Scale bar = 100 μm.
and Given, 1977; Given et al., 1983; Given, 1984). Through the production of antibiotics, fungi are capable of altering their environment (Waksman, 1944; Holding and Franklin, 1965; Wallace and Dickinson, 1978; among others). While bacteria are still of great importance in the ecosystem, fungi form an increasing proportion of the “microflora”3 with a fall of pH and rise in organic matter (Latter et al., 1967). A number of studies, including those by Waksman and Stevens (1929), Waksman (1944), Visser (1964), Latter et al. (1967), Baker (1970), Given et al. (1983), and 3
Microflora is author's word; it is now recognized that fungi are not part of the “flora”.
Wűst et al. (2001) have noted the sharp decrease with depth of aerobic bacterial and fungal activity in modern peats. Schopf (1952) also called upon this as a mechanism in the formation of coals. Waksman and Stevens (1929) found that all of the latter activity died out by 75–90-cm depth, with an increase in the activity of anaerobic bacteria at greater depths. Visser (1964) found up to 280 × 106 bacteria/g and 580 × 103 fungi/g in surface low moor peat. Latter et al. (1967) noted up to 3.5 × 109 bacteria/cm3 and up to 600 m of fungal mycelium/cm3 in a mixed moor peat and Read and Boyd (1986) found up to 2 km of fungal mycelium/cm3 in a forest soil.
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2. Procedure All coals were prepared as epoxy-bound particulate pellets, prepared to a 0.5-μm final polish, and examined using oil-immersion reflected-light optics at a final magnification of 500×. With the exception of the Nigerian coals, the coals were all part of commercial petrographic investigations contracted to the CAER. As such, specific locations are confidential. Permission to use the photographs and generalized locations and ages was granted by the contractor. The Cretaceous Nigerian Onyema and Okaba-Odagbo coalfield samples, part of the U.S. Geological Survey's World Coal Quality Inventory, were graciously supplied by Susan Tewalt and Harvey Belkin (both U.S., Geological Survey). Because of the confidentiality agreements surrounding the coal samples in this investigation, the complete maceral analysis of the individual samples cannot be released. In all cases, however, when discussing macrinite or funginite, we are discussing macerals occurring in trace to minor quantities. Macrinite never exceeds 3.8% (mineralincluded basis) and funginite is less abundant.
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uncertain affinity, possibly either resinite or liptodetrinite, contains abundant funginite in a Nigerian Maastrictian Onyema coal (Fig. 4). Macrinite conforming to the shape of the surrounding megaspore (Fig. 5A) suggests that the macrinite was formed/emplaced as soft, pliable material. Other macerals may be present within the macrinite: cellular structure, possibly funginite, is visible along the lower right edge of the inertinite and darker material, possibly part of the megaspore, is visible to the left. Fig. 5B illustrates macrinite adjacent to cutinite, with resinite also visible in the image. The discrete macrinite bodies seen in Fig. 5C are slightly rounded, suggesting transport. Also included within
3. Discussion There are multiple complex paths from the living plants, animals, fungus, bacteria, algae, and other components of the mire to the material we see preserved as coal. Just within the narrow focus of this work, we recognize that woody components of the plant can be humified/gelified as vitrinite, charred to produce fusinite and semifusinite, or rotted to form macrinite. The latter can be further charred, attaining a fusinite/ semifusinite reflectance. Provenance begets the maceral, but provenance has a diffuse time line. Vitrinite, fusinite/semifusinite, and macrinite are all products of physical and/or biogeochemical alteration. The further transition of macrinite to a higher reflectance is an additional phase of alteration. While an indication of the conditions in the mire at the time of alteration, charring of macrinite does not change the previous steps in its development. Reflectance alone does not determine the maceral. The interrelationships between macerals can be complex and of varying degrees of causality. As noted above, fungal matter is often surrounded by vitrinitic macerals of anomalously high reflectance for the sample. The cause of this increased reflectance may be due to enzymes secreted by the fungi as they decompose woody remains, or it may be due to fluid migration along a weak horizon during coalification, or some other cause entirely. Proximity does not necessarily imply a genetic association. Funginite, in its various forms, is a central part of our discussion. Fungal hyphae can be found within huminite/vitrinite macerals, as illustrated in Fig. 1 and in Fig. 2A. Such occurrences can potentially be overlooked in a maceral analysis, in places because the occurrence is subtle, resulting in an undercount of the funginite. The fungal spore on the right in Fig. 2B is the more classic form of funginite. In this case, at least two smaller fuginite bodies can be seen in the attrinite/densinite horizon below and to the left of the larger funginite. A similar association between funginite and detrital vitrinite (vitrodetrinite) was noted in high volatile bituminous Oligocene coals from Romania (Belkin et al., 2008). A large funginite spore from the same series of coals is associated with a thin rind of vitrodetrinite on Fig. 2C. The Nigerian Maastrictian Okaba–Odagbo coal sample presents another complex assemblage (Fig. 2D). In this view, we find funginite within macrinite, funginite adjacent to macrinite, and funginite in a detrital maceral zone. Close associations of inertinite macerals with liptinites are of interest, particularly with respect to the observations of the combustion origin of fusinite and semifusinite. The Nigerian Maastrictian Onyema coal sample contains complex examples of macrinite (Fig. 3). The macrinite body at the base of the particle contains fusinite, semifusinite, funginite, and, arguably, gray secretinite. The macrinite between the cutinite layers contains bright inertodetrinite and funginite. If the macrinite developed in situ in proximity to the cutinite, it poses an argument against a combustion origin for the macrinite. A liptinite of
Fig. 6. A/ Transition between macrinite and semifusinite. The maceral does not have the distinct structure characteristic of semifusinite, but does have some remnant hints of cell walls. Photo 923 11; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. B/ Fungal damage to fusinite precursor. Photo 924 07; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. C/ Possible fungal damage to fusinite precursor, with remnant fusinite structure less distinct than typical fusinite. Photo 925 37; New Mexico, Cretaceous, hvBb. Scale bar = 25 μm.
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Fig. 8. A/ Fusinite, semifusinite (?), inertodetrinite, secretinite (?), and distinct fungal sclerotia in macrinite. Photo 08 11; Maastrictian Okaba–Odagbo coalfield, Nigeria, subbituminous. Scale bar = 25 μm. B/ Funginite in macrinite. Photo 917 81; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. C/ Funginite in macrinite, with liptodetrinite and inertodetrinite inclusions. Photo 934 44; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. D/ Funginite in macrinite. Photo 934 38; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. E/ Funginite in macrinite, with included inertodetrinite. Photo 934 50; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. F/ Funginite in macrinite, with included inertodetrinite. Photo 917 29; Wyoming, Cretaceous, hvCb. Scale bar = 25 μm.
the assemblage of particles is a rounded, slightly oxidized resinite. The macrinites have included inertodetrinite, a feature that will be further illustrated below. The macrinite in Fig. 5D suggests a soft/fluid emplacement mechanism. The cutinite and liptodetrinite within the macrinite is brighter than would be expected for high volatile C
bituminous coals, indicating slight oxidation of the liptinites. Similarly, the liptodetrinite within Fig. 5E macrinite is brighter than would be expected for subbituminous coals, suggesting mild oxidation. While not an example of macrinite, Fig. 5F illustrates funginite within a spore. In this case, the fungal damage to the spore was confined to the interior.
Fig. 7. A/ Macrinite (bottom half of image). Photo 883 12; Montana, Paleocene, subbituminous. Scale bar = 100 μm. B/ Macrinite (left to right across diagonal), similar to maceral illustrated by Schopf (1947, figure 21) for Tertiary Coos Bay, Oregon, coals. Photo 919 36; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. C/ Macrinite (center), with other inertinite macerals. Photo 919 xxx 01; Queensland, Australia, Late Triassic; hvCb. Scale bar = 25 μm. D/ Macrinite, with included inertodetrinite, showing areas of varying degradation. Photo 917 23; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. E/ Macrinite with included inertodetrininite. Photo 925 29; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. F/ Varying macrinite textures. Photo 925 38; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. G/ Macrinite bands. Photo 931 19; Republic of South Africa, Permian, hvBb. Scale bar = 100 μm. H/ Macrinite. Inertodetrinite inclusion in macrinite/corpogelinite/secretinite. Photo 934 23; Wyoming, Paleocene, subbituminous. Scale bar = 100 μm.
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The distinction between macrinite and fusinite and semifusinite is not always as clear as would be desired. The transition between macerals has certainly led to some of the confusion in the literature. Ideally, the current ICCP nomenclature (International Committee for Coal and Organic Petrology, 2001) should establish clear lines between the inertinite macerals. Fig. 6A, however, illustrates a maceral, or series of macerals, without the distinct features of semifusinite, but also without the amorphous features of macrinite. Possible fungal damage to fusinite-precursor material is seen in Fig. 6B, with Fig. 6C showing a less distinct illustration of the same phenomena. As noted above, macrinite can include inclusions of inertinite and liptinite. Macrinite is generally recognized by its mottled appearance (Fig. 7A). Certain macrinites have a smoother surface in cross section (Fig. 7B). The latter maceral, identified as macrinite in this study, bears a resemblance to a maceral, identified as a fungal mycellium, illustrated by Schopf (1947) in his study of the Coos Bay, Oregon, coals. The cross section of the macrinite in Fig. 7C is finely textured, with a sub-micron mottling, a distinct difference from the previous two examples. An origin from charring of resin cannot be excluded. In that case, perhaps it should be considered as a variety of secretinite. Fig. 7D illustrates a macrinite body with varying degrees of degradation. In particular, within an area in the lower left of the macrinite, oxidized liptodetrinite is evident. Fig. 7E, along with Fig. 7D, shows macrinite with inclusions of inertodetrinite. In contrast, the macrinite on Fig. 7F is relatively featureless. The bright maceral to the right in Fig. 7F is problematical. In outline, it resembles cutinite, and charring of cutinite cannot be ruled out, while in brightness and texture, it is a funginite- or macrinite-like inertinite. Fungal replacement of liptinite is possible, with fungal replacement of a Pennsylvanian megaspore as an example (Hower et al., 2008a,b). Macrinite bands, showing varying levels of preservation of the included material, are shown on Fig. 7G. Fig. 7H is of interest not so much for the macrinite as for the inertodetrinite (?) inclusion in the corpogelinite/macrinite/secretinite body. The association of funginite with macrinite is not always evident. While the association of fungus and degraded plant tissues would lead to the hypothesis that fungus (and other microorganisms and insects) is responsible for detrital and gelified macerals, the lack of recognizable fungal remains may not mean that they were not contributors to the maceral assemblage. In previous pictures, we have not emphasized the association of funginite and macrinite, although subtle aspects of the association can be seen in Figs. 3, 5A, 7A and D. Fig. 8A illustrates an association between funginite and macrinite in a Cretaceous coal from Nigeria. The Maastrictian Okaba–Odagbo macrinite assemblage contains fusinite, semifusinite, inertodetrinite, and fungal sclerotia. Funginite is more abundant in a Cretaceous coal from Wyoming (Fig. 8B). Fungal sclerotia are evident in the Fig. 8C macrinite. Liptodetrinite and inertodetrinite inclusions are also part of the latter macrinite body. Funginite is present in more subtle forms in Fig. 8D–F. 4. Conclusions Throughout our studies of the petrology of coal and of the origin of macerals, we must always seek to enter studies with an open mind. Discoveries by our mid-20th-century predecessors may provide guidance, but we need to openly assess the validity of such discussions in light of modern nomenclature and more recent discoveries concerning the interrelationships between plants and other microorganisms. We should always let the macerals be the guide, but temper this with the full complement of the available petrographic and biological knowledge available. Macrinite is usually an uncommon maceral in coals, thus, its origin is not the subject of as much discussion as the vitrinite-group macerals or the more common inertinite-group macerals: fusinite and semifusinite. Traditional interpretations in the coal petrology literature have indicated a degradational origin for macrinite. Fungal spores, hyphae, and mycelia, all as the maceral funginite, are often, but not always, found
in association with macrinite. Funginite is also found in association with degraded vitrinites. The latter two occurrences may, indeed, be part of a continuum from subtly degraded vitrinites to the more completely degraded macrinite. Overall, the inertinite-group macerals are a complex assemblage of forms exhibiting different paths to the forms we see in coals. The origins are multiple; for example, funginite is not from the same kingdom as the, generally, wood-derived origins of fusinite, semifusinite, or the woody precursors of macrinite. As seen in the figures, macrinite can encompass other macerals, including the remnants of liptinites and fragments of fusinite-derived inertodetrinite, in addition to funginite. Fundamentally, macrinite has its origins in the same material as fusinite; the difference in the end product being the consequence of the path of fungal or microbial degradation. Acknowledgements We thank Tristana Duvalliet for her generous assistance in the translation of French manuscripts. We wish to acknowledge discussions with Andrew Scott and Aureal Cross, both helpful in focusing our attention on the important details of this work. Ian Glasspool and Anne Raymond provided constructive critiques of the work and we were guided by editor Ralf Littke in making revisions of the original submission. References Baker, J.H., 1970. Quantitative study of yeasts and bacteria in a Signy Island peat. British Antarctic Survey Bulletin 23, 51–55. Belkin, H.E., Tewalt, S.J., Hower, J.C., Stucker, J.D., Tatu, C.A., Buta, G., 2008. Geochemistry and petrography of Oligocene bituminous coals from the Jiu Valley, Petrosani basin (southern Carpathian Mountains), Romania. The Society for Organic Petrology, 25th Annual Meeting, Oviedo, Asturias, Spain, p. 81. Program and Abstracts. Belkin, H.E., Tewalt, S.J., Hower, J.C., Stucker, J.D., O'Keefe, J.M.K., 2009. 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Palaeogeography, Palaeoclimatology, Palaeoecology 106, 287–305. Esterle, J.S., Ferm, J.C., 1994. Spatial variability in modern tropical peat deposits from Sarawak, Malaysia and Sumatra, Indonesia: Analogues for coal. International Journal of Coal Geology 26, 1–41. Exarchos, C., Given, P.H., 1977. Cell wall polymers of higher plants in peat formation: the role of microorganisms. In: Given, P.H., Cohen, A.D. (Eds.), Interdisciplinary Studies of Peat and Coal Origins. Geological Society of America Microform Publication 7, p. 123. http://www.caer.uky.edu/publications/gsapub7/Exarchos.pdf. Fell, J.W., 1977. Microbial activities in the decay of Rhizophora mangle leaves. In: Given, P.H., Cohen, A.D. (Eds.), Interdisciplinary studies of peat and coal origins. Geological Society of America Microform Publication 7, p. 123. http://www.caer.uky.edu/ publications/gsapub7/Fell.pdf. Given, P.H., 1984. An essay on the organic geochemistry of coal. In: Gorbaty, M.L., Larsen, J.W., Wender, I. 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Schwab, G., 1962. Uber Pilzreste aus dem Unterfloz von Mallis (Mecklenberg). Monatsberichte der Deutschen Akademie der Wissenschaften zu Berlin 4, 3–4. Scott, A.C., 1989. Observations on the nature and origin of fusain. International Journal of Coal Geology 12, 443–475. Scott, A.C., 2000. The pre-quaternary history of fire. Palaeogeography, Palaeoclimatology, Palaeoecology 164, 281–329. Scott, A.C., 2002. Coal petrology and the origin of coal macerals: a way ahead? International Journal of Coal Geology 50, 119–134. Scott, A.C., Cripps, J.A., Collinson, M.E., Nichols, G.J., 2000. The taphonomy of charcoal following a recent heathland fire and some implications for the interpretation of fossil charcoal deposits. Palaeogeography, Palaeoclimatology, Palaeoecology 164, 1–31. Scott, A.C., Glasspool, I.J., 2005. Charcoal reflectance as a proxy for the emplacement temperature of pyroclastic flow deposits. Geology 33 (7), 589–592. Scott, A.C., Glasspool, I.J., 2006. The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration. Proceedings of the National Academy of Sciences of the United States of America 103, 10861–10865. Scott, A.C., Glasspool, I.J., 2007. Observations and experiments on the origin and formation of inertinite group macerals. International Journal of Coal Geology 70, 53–66. Scott, A.C., Jones, T.P., 1994. The nature and influence of fire in Carboniferous ecosystems. Palaeogeography, Palaeoclimatology, Palaeoecology 106, 91–112. Stach, E., 1935. Lehrbuch der Kolhenpetrographie. Borntraeger, Berlin. Stach, E., 1956. La sclérotinite et son importance pour l'origine de la durite. Annales des Mines de Belgique, pp. 73–89. Stach, E., Pickhardt, W., 1957. Pilzreste (Sklerotinit) in paläozoischen Steinkohlen. Paläontologische Zeitschrift 31, 139–162. Straka, H., 1960. Uber Moore und Torf auf Madagaskar und den Maskarenen. Erdkunde 2, 14. Sweeney, I.J., Chin, K., Hower, J.C., Budd, D.A., Wolfe, D.G., 2009. Fossil wood from the middle Cretaceous Moreno Hill formation: unique expressions of wood mineralization and implications for the processes of wood preservation. International Journal of Coal Geology 79, 1–17. Taylor, T.N., Osborn, J.M., 1996. The importance of fungi in shaping the ecosystem. Review of Paleobotany and Palynology 90, 249–262. Taylor, T.N., Taylor, E.L., 1997. The distribution and interactions of some Paleozoic fungi. Review of Paleobotany and Palynology 95, 83–94. Teichmüller, M., 1958. Rekonstruktion verscheider Moortypen des Hauptflozes der Niederrheinischen Braunkolhle. Fortsch. Geol. Rheinlnd. und Westf. 2 xx-yy. Teichmüller, M., 1974. Űber neue Macerale Liptinit— Gruppe und die Entstehung von Micrinit. Fortsch. Geol. Rheinlnd. und Westf. 24, 37–64. Visser, S.A., 1964. The presence of micro-organisms in various strata of deep tropical peat deposits. Life Sciences 3, 1061–1065. Waksman, S.A., 1944. Three decades with soil fungi. Soil Science 58, 89–115. Waksman, S.A., Stevens, K.R., 1929. Contribution to the chemical composition of peat: V. The role of microorganisms in peat formation and decomposition. Soil Science 28, 315–340. Wallace, B., Dickinson, C.H., 1978. Peat microfungi in three habitats in the Florida Everglades. Mycologia 70, 1151–1163. Winston, R.B., 1993. Reassessment of the evidence for primary fusinite and degradofusinite. Organic Geochemistry 20, 209–221. Wűst, R.A.J., Hawke, M.I., Bustin, R.M., 2001. Comparing maceral ratios from tropical peatlands with assumptions from coal studies: do classic coal petrographic interpretation methods have to be discarded? International Journal of Coal Geology 48, 115–132.
Contents lists available at ScienceDirect
International Journal of Coal Geology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j c o a l g e o
Notes on the origin of inertinite macerals in coals: Observations on the importance of fungi in the origin of macrinite James C. Hower a,⁎, Jennifer M.K. O'Keefe b, Michael A. Watt c, Timothy J. Pratt d, Cortland F. Eble e, J.D. Stucker f, Allison R. Richardson f, Irena J. Kostova g a
University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, Kentucky 40511, United States Department of Physical Sciences, Morehead State University, Morehead, Kentucky 40351, United States Weatherford Laboratories, Arvada, Colorado 80007, United States d Formerly: Ticora Geosciences, Arvada, Colorado 80007, United States e Kentucky Geological Survey, Lexington, Kentucky 40506, United States f Department of Earth & Environmental Sciences, University of Kentucky, Lexington, KY 40506, United States g Sofia University “St. Kliment Ohridski”, Department of Geology and Paleontology, 15, Tzar Osvoboditel Blvd., 1000 Sofia, Bulgaria b c
a r t i c l e
i n f o
Article history: Received 10 March 2009 Received in revised form 4 August 2009 Accepted 6 August 2009 Available online 20 August 2009 Keywords: Fungus Funginite Macrinite Degradation Rot
a b s t r a c t Macrinite is a, generally, rare inertinite maceral, often incorporating remnants and fragments of other macerals, including vitrinite, liptinite, and other inertinite. The associated inertinites include multiple forms of funginite. Funginite is also commonly found in association with vitrinite of slightly elevated reflectance and with degraded varieties of vitrinite. Together with the highly degraded macrinite, the latter two associations are here inferred to be part of a continuum of fungal and microbial degradation of peat. In any case, the origin of some macrinite is potentially distinct from that of inertinite generated by fire. © 2009 Elsevier B.V. All rights reserved.
1. Introduction A number of taphonomic processes have been proposed to account for the generation of inertinite-group macerals. In recent years, an emphasis has been placed on fire as a mechanism for the generation of most macerals of the inertinite group, macrinite and funginite included (Scott, 1989, 2000, 2002; Winston, 1993; Scott and Jones, 1994; Guo and Bustin 1998; Petersen, 1998; Bustin and Guo, 1999; Scott et al., 2000; Scott and Glasspool, 2005, 2006, 2007; McParland et al., 2007). In general, we do not dispute this mechanism and recognize that macrinite can be charred and originate from the same starting material as fusinite. We emphasize that fire does not fully address the origin of some nonfusinite/non-semifusinite inertinites and we seek to expand the dialogue on the origin of these macerals, in part by revisiting older voices on the subject and also through the introduction of new examples. Most micrinite, not discussed further in this paper, is clearly of a different origin than fusinite and semifusinite, and are generally thought to be the product of cracking of hydrocarbons in the coal, perhaps at the onset of the oil window (Teichmüller, 1974). Very fine
⁎ Corresponding author. E-mail address: [email protected] (J.C. Hower). 0166-5162/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2009.08.006
inertodetrinite might be confused with micrinite, however, leading to a broader definition of the maceral (International Committee for Coal and Organic Petrology, 2001). Secretinite, formally established as a maceral in the 1994 International Committee for Coal and Organic Petrology (ICCP) nomenclature (International Committee for Coal and Organic Petrology, 2001), is considered to be charred resins. Perhaps, in light of its pathway as an inertinite, it can be considered to be part of the fusinite/semifusinite track of inertinite formation. Funginite, long recognized in coal (Jeffrey and Chrysler, 1906; although Jeffrey, 1924, later dismissed the importance of fungi in coal development), and recognized as a discrete maceral since the Third Congress of Carboniferous Stratigraphy and Geology (Heerlen, Limbourg, The Netherlands, 25–30 June1951) (Beneš, 1959), refers to the fossil spores, sclerotia, and hyphae of fungal bodies. Funginite, while it can be charred, is clearly different from other inertinite macerals, first as being the product of a non-plant organism1 and second in not universally attaining high reflectance. Funginite as a maceral was
1 In general discussions of coal, we would argue that it is generally overlooked that coal is a product of all five (or six, depending upon who is counting) kingdoms of life. In terms of shaping the humic coals as we see them, aside from the plant kingdom, Fungi, including fungal forms within Chromista (Oomycetes) and Protozoa (slime molds), are, along with bacteria, among the most important organisms in the passage from peat to lignite to subbituminous coals.
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Fig. 1. Fungal hyphae. Photo 919 38; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm.
defined in 2001 (International Committee for Coal and Organic Petrology, 2001) with separation of sclerotinite into funginite and secretinite. Close scrutiny of published descriptions and figures is therefore necessary when examining the literature on fossil fungi. There is a misconception, owing to the lack of abundant funginite in Pennsylvanian coals, that it is absent in the Pennsylvanian coal. Schopf (1952) noted that fungi were rare in the Pennsylvanian coals he had examined. Stach (1935, 1957), Duparque and Delattre (1953b), Stach and Pickhardt (1957) ,Beneš (1959, 1969), Taylor and Osborn (1996), and Taylor and Taylor (1997) observed the presence of Paleozoic fungi. Robinson (1990) noted their rarity, while Beneš (1959) noted how
Fig. 3. Macrinite with structured fusinite, semifusinite, and secretinite (?) at base of particle. Macrinite with included inertodetrinite (fine, bright particles) and funginite between cutinite “leaves.” Photo 05 21; Maastrictian Onyema coalfield, Nigeria, hvCb. Scale bar = 100 μm.
common they are. As noted above, caution must be taken when citing fungal occurrences described by pre-2001 authors as many of the fungal forms identified by Stach (1935, 1957), Duparque and Delattre (1953b), Beneš (1959), and others are now known to be secretinite. That said, all of the latter authors illustrate at least some macerals that meet the modern description of funginite. Macrinite, as will be discussed below, can also have a distinct origin, being the consequence of the degradation of woody, and other, plant parts.
Fig. 2. A/ Fungal hyphae. Photo 903 12; Powder River Basin, Paleocene, subbituminous/hvCb. Scale bar = 100 microns. B/ Funginite. Photo 903 13; Powder River Basin, Paleocene, subbituminous/hvCb. Scale bar = 100 μm. C/ Funginite (center). Photo 917 78; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. D/ Funginite within macrinite, funginite adjacent to macrinite, and funginite in a detrital maceral zone. Photo 11 11; Maastrictian Okaba-Odagbo coalfield, Nigeria, hvCb. Scale bar = 100 μm.
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Fig. 4. Funginite in liptinite (resinite or liptodetrinite). Photo 06 comp; Maastrictian Onyema coalfield, Nigeria, hvCb. Scale bar = 100 μm.
Macrinite has been frequently misidentified. Most often, both before and after the International Committee for Coal and Organic Petrology (2001) clarification of inertinite nomenclature, macrinite has been confused with secretinite, which, as stated, both here and elsewhere (Lyons et al., 1986; Hower et al., 2008a,b), has a different biological origin. The misidentifications of macrinite notwithstanding, there are varieties of inertinite macerals that defy conventional classification. In our experience, the inertinites found in the “ragged edge” (brecciated marginal marine) sections of the Herrin coalbed in western Kentucky do not yield to an easy classification (Hower et al., 1987; deWet et al., 1997; Hower and Williams, 2001; O'Keefe et al., 2008). Bright macerals, in distinct contrast to the ambient high volatile bituminous rank vitrinite of the region, preserve woody textures more reminiscent of a woody peat than of fusinite/semifusinite or of macrinite at different extremes of the inertinite spectrum. As an example of the problems in the assignment of macrinite in the inertinite spectrum, Winston's (1993) investigation of inertinite macerals was flawed in many respects. Repeating an interpretation that had been passed through the literature of the time, he discussed degradofusinite strictly as a variety of fusinite. The degradofusinite in his usage, something common to the prevailing usage in the literature, would more properly be termed macrinite under the 1994 ICCP nomenclature (International Committee for Coal and Organic Petrology, 2001). The diagenetic pathways of fusinite and macrinite can be quite distinct. Both, in general, originated from wood, although macrinite can contain fragments of other maceral types, but divergent pathways of alteration and preservation led to distinct macerals. Winston's (1993, p. 213) description of “fungi preserved as vitrinite” is problematical. Clearly, this is impossible as vitrinite is a product of vascular plants and fungi are a distinct kingdom of life. For the same reason, fungi cannot be preserved as fusinite, although they can attain the same, or higher, reflectance as fusinite, contrary to the statement on page 217 of his publication. Relationships between funginite, or fungal sclerotinite in the older nomenclature, and degraded maceral assemblages were discussed by Duparque and Delattre (1953a,b) and Stach (1956), among others. Stach (1956) drew a parallel between fungal degradation and varying water levels in the paleoswamps. He associated the development of “massive micrinite,” macrinite in modern nomenclature, with fungal activity. In Tertiary Chulotka Peninsula (Russia) brown coals, Lapo and Malán (1981) noted an association of funginite and macrinite. Cross and Phillips (1990) mentioned the role of fungus in degradation of plant material, but did not elaborate further, building their discussion on the contributions of vascular plants to coal development. Sweeney et al. (2009) noted an association between fungal degradation and subsequent mineralization of wood. Eble et al. (1994) noted that microbial degradation is a pathway to inertinite development,
drawing a clear distinction between fire and microbial degradation, but ultimately did not distinguish between the distinct macerals resulting from the dichotomous origins. Belkin et al. (2009) described the occurrence of funginite in vitrinite in several Cenozoic coals from Sumatra, Kalimantan, and Sulawesi. No alteration of vitrinite was noted in their investigations, in contrast to high volatile A bituminous Oligocene Romanian coals where vitrinite in the vicinity of funginite was slightly degraded and had a higher reflectance (Belkin et al., 2008). Beneš and Kraussová (1964, 1965) and Beneš (1959, 1969) noted that the amount of funginite in a coal is related to the petrology, with clarodurite and durite richest in funginite. The “fungidurites” of Beneš (1960) represent aerobic disintegration, with the distribution of inertinite indicative of specific conditions in the formation of coal. Most of the illustrated “funginite”2 in the latter contribution, however, would now be identified as secretinite. More of the illustrations accompanying Beneš and Kraussová (1964, 1965) are legitimate funginite, redeeming their interpretation in contrast to Beneš (1959, 1960). Teichmüller (1958) observed fungi more frequently in her sapropelic “Reid-Moor Kohle” facies than in less-degraded facies. Straka (1960) made similar observations in studies of Madagascar peats. Schwab (1962) also examined the link between fungi and coal facies. In Czechoslovakian coals, Beneš and Kraussová (1965) found the sapropelic and detrital horizons to have the most funginite, with brighter lithotypes being funginite-poor. Moore and Hilbert (1992), Esterle and Ferm (1994), and Moore et al. (1996) described fungal oxidation of southeast Asian peats. In particular, Moore et al. (1996) note mycorrhizal hyphae associated with roots in the peat. In investigations of humic soils, Waksman (1944) found that fungal spores and mycelium were abundant, along with bacteria and actinomycetes, surrounding disintegrating roots. In studies of modern Everglades' peat, Wallace and Dickinson (1978) describe distinct differences in fungal populations with respect to different flora. The relationships are complex, with differences between the Rhizophora, Juncus, and Cladium peats dependent upon the distinct ecological niches of the flora. The largest fungal population was found in the highly decomposed Cladium peat. Aside from the vegetation variables, within modern peats there is a seasonal variation in fungal activity, peaking in October in northern hemisphere temperate climates and varying with moisture, pH, N2, P, and K (Pavlenko, 1965; Latter et al., 1967). Fell (1977) noted an optimal temperature for fungal activity in a study of Rhizophora mangle leaf-fall degradation. Certain types of plants may provide some protection, such as through enzymes or tannins, against microbial degradation (Exarchos
2
Beneš (1960) appears to have been the originator of the term funginite.
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Fig. 5. A/ Macrinite, with possible included funginite (lower right, within body labeled as macrinite) and shreds of the surrounding sporinite (within thinning left edge of body labeled macrinite), internal to megasporinite. Photo 922 33; Queensland, Australia, Late Triassic, hvCb. Scale bar = 100 μm. B/ Macrinite adjacent to cutinite. Photo 919 33; Queensland, Australia, Late Triassic, hvCb. Scale bar = 100 μm. C/ Macrinite with included inertodetrinite and liptinite. Oxidized resinite adjacent to macrinite. Photo 925 32; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. D/ Macrinite with included cutinite and other detrital liptinites and inertodetrinite. Photo 917 80; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. E/ Macrinite with included liptodetrinite and inertodetrinite. Photo 934 33; Wyoming. Paleocene, subbituminous. Scale bar = 100 μm. F/ Sporinite (center) with included funginite. Photo 934 42; Wyoming. Paleocene, subbituminous. Scale bar = 100 μm.
and Given, 1977; Given et al., 1983; Given, 1984). Through the production of antibiotics, fungi are capable of altering their environment (Waksman, 1944; Holding and Franklin, 1965; Wallace and Dickinson, 1978; among others). While bacteria are still of great importance in the ecosystem, fungi form an increasing proportion of the “microflora”3 with a fall of pH and rise in organic matter (Latter et al., 1967). A number of studies, including those by Waksman and Stevens (1929), Waksman (1944), Visser (1964), Latter et al. (1967), Baker (1970), Given et al. (1983), and 3
Microflora is author's word; it is now recognized that fungi are not part of the “flora”.
Wűst et al. (2001) have noted the sharp decrease with depth of aerobic bacterial and fungal activity in modern peats. Schopf (1952) also called upon this as a mechanism in the formation of coals. Waksman and Stevens (1929) found that all of the latter activity died out by 75–90-cm depth, with an increase in the activity of anaerobic bacteria at greater depths. Visser (1964) found up to 280 × 106 bacteria/g and 580 × 103 fungi/g in surface low moor peat. Latter et al. (1967) noted up to 3.5 × 109 bacteria/cm3 and up to 600 m of fungal mycelium/cm3 in a mixed moor peat and Read and Boyd (1986) found up to 2 km of fungal mycelium/cm3 in a forest soil.
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2. Procedure All coals were prepared as epoxy-bound particulate pellets, prepared to a 0.5-μm final polish, and examined using oil-immersion reflected-light optics at a final magnification of 500×. With the exception of the Nigerian coals, the coals were all part of commercial petrographic investigations contracted to the CAER. As such, specific locations are confidential. Permission to use the photographs and generalized locations and ages was granted by the contractor. The Cretaceous Nigerian Onyema and Okaba-Odagbo coalfield samples, part of the U.S. Geological Survey's World Coal Quality Inventory, were graciously supplied by Susan Tewalt and Harvey Belkin (both U.S., Geological Survey). Because of the confidentiality agreements surrounding the coal samples in this investigation, the complete maceral analysis of the individual samples cannot be released. In all cases, however, when discussing macrinite or funginite, we are discussing macerals occurring in trace to minor quantities. Macrinite never exceeds 3.8% (mineralincluded basis) and funginite is less abundant.
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uncertain affinity, possibly either resinite or liptodetrinite, contains abundant funginite in a Nigerian Maastrictian Onyema coal (Fig. 4). Macrinite conforming to the shape of the surrounding megaspore (Fig. 5A) suggests that the macrinite was formed/emplaced as soft, pliable material. Other macerals may be present within the macrinite: cellular structure, possibly funginite, is visible along the lower right edge of the inertinite and darker material, possibly part of the megaspore, is visible to the left. Fig. 5B illustrates macrinite adjacent to cutinite, with resinite also visible in the image. The discrete macrinite bodies seen in Fig. 5C are slightly rounded, suggesting transport. Also included within
3. Discussion There are multiple complex paths from the living plants, animals, fungus, bacteria, algae, and other components of the mire to the material we see preserved as coal. Just within the narrow focus of this work, we recognize that woody components of the plant can be humified/gelified as vitrinite, charred to produce fusinite and semifusinite, or rotted to form macrinite. The latter can be further charred, attaining a fusinite/ semifusinite reflectance. Provenance begets the maceral, but provenance has a diffuse time line. Vitrinite, fusinite/semifusinite, and macrinite are all products of physical and/or biogeochemical alteration. The further transition of macrinite to a higher reflectance is an additional phase of alteration. While an indication of the conditions in the mire at the time of alteration, charring of macrinite does not change the previous steps in its development. Reflectance alone does not determine the maceral. The interrelationships between macerals can be complex and of varying degrees of causality. As noted above, fungal matter is often surrounded by vitrinitic macerals of anomalously high reflectance for the sample. The cause of this increased reflectance may be due to enzymes secreted by the fungi as they decompose woody remains, or it may be due to fluid migration along a weak horizon during coalification, or some other cause entirely. Proximity does not necessarily imply a genetic association. Funginite, in its various forms, is a central part of our discussion. Fungal hyphae can be found within huminite/vitrinite macerals, as illustrated in Fig. 1 and in Fig. 2A. Such occurrences can potentially be overlooked in a maceral analysis, in places because the occurrence is subtle, resulting in an undercount of the funginite. The fungal spore on the right in Fig. 2B is the more classic form of funginite. In this case, at least two smaller fuginite bodies can be seen in the attrinite/densinite horizon below and to the left of the larger funginite. A similar association between funginite and detrital vitrinite (vitrodetrinite) was noted in high volatile bituminous Oligocene coals from Romania (Belkin et al., 2008). A large funginite spore from the same series of coals is associated with a thin rind of vitrodetrinite on Fig. 2C. The Nigerian Maastrictian Okaba–Odagbo coal sample presents another complex assemblage (Fig. 2D). In this view, we find funginite within macrinite, funginite adjacent to macrinite, and funginite in a detrital maceral zone. Close associations of inertinite macerals with liptinites are of interest, particularly with respect to the observations of the combustion origin of fusinite and semifusinite. The Nigerian Maastrictian Onyema coal sample contains complex examples of macrinite (Fig. 3). The macrinite body at the base of the particle contains fusinite, semifusinite, funginite, and, arguably, gray secretinite. The macrinite between the cutinite layers contains bright inertodetrinite and funginite. If the macrinite developed in situ in proximity to the cutinite, it poses an argument against a combustion origin for the macrinite. A liptinite of
Fig. 6. A/ Transition between macrinite and semifusinite. The maceral does not have the distinct structure characteristic of semifusinite, but does have some remnant hints of cell walls. Photo 923 11; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. B/ Fungal damage to fusinite precursor. Photo 924 07; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. C/ Possible fungal damage to fusinite precursor, with remnant fusinite structure less distinct than typical fusinite. Photo 925 37; New Mexico, Cretaceous, hvBb. Scale bar = 25 μm.
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Fig. 8. A/ Fusinite, semifusinite (?), inertodetrinite, secretinite (?), and distinct fungal sclerotia in macrinite. Photo 08 11; Maastrictian Okaba–Odagbo coalfield, Nigeria, subbituminous. Scale bar = 25 μm. B/ Funginite in macrinite. Photo 917 81; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. C/ Funginite in macrinite, with liptodetrinite and inertodetrinite inclusions. Photo 934 44; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. D/ Funginite in macrinite. Photo 934 38; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. E/ Funginite in macrinite, with included inertodetrinite. Photo 934 50; Wyoming, Paleocene, subbituminous. Scale bar = 25 μm. F/ Funginite in macrinite, with included inertodetrinite. Photo 917 29; Wyoming, Cretaceous, hvCb. Scale bar = 25 μm.
the assemblage of particles is a rounded, slightly oxidized resinite. The macrinites have included inertodetrinite, a feature that will be further illustrated below. The macrinite in Fig. 5D suggests a soft/fluid emplacement mechanism. The cutinite and liptodetrinite within the macrinite is brighter than would be expected for high volatile C
bituminous coals, indicating slight oxidation of the liptinites. Similarly, the liptodetrinite within Fig. 5E macrinite is brighter than would be expected for subbituminous coals, suggesting mild oxidation. While not an example of macrinite, Fig. 5F illustrates funginite within a spore. In this case, the fungal damage to the spore was confined to the interior.
Fig. 7. A/ Macrinite (bottom half of image). Photo 883 12; Montana, Paleocene, subbituminous. Scale bar = 100 μm. B/ Macrinite (left to right across diagonal), similar to maceral illustrated by Schopf (1947, figure 21) for Tertiary Coos Bay, Oregon, coals. Photo 919 36; Queensland, Australia, Late Triassic; hvCb. Scale bar = 100 μm. C/ Macrinite (center), with other inertinite macerals. Photo 919 xxx 01; Queensland, Australia, Late Triassic; hvCb. Scale bar = 25 μm. D/ Macrinite, with included inertodetrinite, showing areas of varying degradation. Photo 917 23; Wyoming, Cretaceous, hvCb. Scale bar = 100 μm. E/ Macrinite with included inertodetrininite. Photo 925 29; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. F/ Varying macrinite textures. Photo 925 38; New Mexico, Cretaceous, hvBb. Scale bar = 100 μm. G/ Macrinite bands. Photo 931 19; Republic of South Africa, Permian, hvBb. Scale bar = 100 μm. H/ Macrinite. Inertodetrinite inclusion in macrinite/corpogelinite/secretinite. Photo 934 23; Wyoming, Paleocene, subbituminous. Scale bar = 100 μm.
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The distinction between macrinite and fusinite and semifusinite is not always as clear as would be desired. The transition between macerals has certainly led to some of the confusion in the literature. Ideally, the current ICCP nomenclature (International Committee for Coal and Organic Petrology, 2001) should establish clear lines between the inertinite macerals. Fig. 6A, however, illustrates a maceral, or series of macerals, without the distinct features of semifusinite, but also without the amorphous features of macrinite. Possible fungal damage to fusinite-precursor material is seen in Fig. 6B, with Fig. 6C showing a less distinct illustration of the same phenomena. As noted above, macrinite can include inclusions of inertinite and liptinite. Macrinite is generally recognized by its mottled appearance (Fig. 7A). Certain macrinites have a smoother surface in cross section (Fig. 7B). The latter maceral, identified as macrinite in this study, bears a resemblance to a maceral, identified as a fungal mycellium, illustrated by Schopf (1947) in his study of the Coos Bay, Oregon, coals. The cross section of the macrinite in Fig. 7C is finely textured, with a sub-micron mottling, a distinct difference from the previous two examples. An origin from charring of resin cannot be excluded. In that case, perhaps it should be considered as a variety of secretinite. Fig. 7D illustrates a macrinite body with varying degrees of degradation. In particular, within an area in the lower left of the macrinite, oxidized liptodetrinite is evident. Fig. 7E, along with Fig. 7D, shows macrinite with inclusions of inertodetrinite. In contrast, the macrinite on Fig. 7F is relatively featureless. The bright maceral to the right in Fig. 7F is problematical. In outline, it resembles cutinite, and charring of cutinite cannot be ruled out, while in brightness and texture, it is a funginite- or macrinite-like inertinite. Fungal replacement of liptinite is possible, with fungal replacement of a Pennsylvanian megaspore as an example (Hower et al., 2008a,b). Macrinite bands, showing varying levels of preservation of the included material, are shown on Fig. 7G. Fig. 7H is of interest not so much for the macrinite as for the inertodetrinite (?) inclusion in the corpogelinite/macrinite/secretinite body. The association of funginite with macrinite is not always evident. While the association of fungus and degraded plant tissues would lead to the hypothesis that fungus (and other microorganisms and insects) is responsible for detrital and gelified macerals, the lack of recognizable fungal remains may not mean that they were not contributors to the maceral assemblage. In previous pictures, we have not emphasized the association of funginite and macrinite, although subtle aspects of the association can be seen in Figs. 3, 5A, 7A and D. Fig. 8A illustrates an association between funginite and macrinite in a Cretaceous coal from Nigeria. The Maastrictian Okaba–Odagbo macrinite assemblage contains fusinite, semifusinite, inertodetrinite, and fungal sclerotia. Funginite is more abundant in a Cretaceous coal from Wyoming (Fig. 8B). Fungal sclerotia are evident in the Fig. 8C macrinite. Liptodetrinite and inertodetrinite inclusions are also part of the latter macrinite body. Funginite is present in more subtle forms in Fig. 8D–F. 4. Conclusions Throughout our studies of the petrology of coal and of the origin of macerals, we must always seek to enter studies with an open mind. Discoveries by our mid-20th-century predecessors may provide guidance, but we need to openly assess the validity of such discussions in light of modern nomenclature and more recent discoveries concerning the interrelationships between plants and other microorganisms. We should always let the macerals be the guide, but temper this with the full complement of the available petrographic and biological knowledge available. Macrinite is usually an uncommon maceral in coals, thus, its origin is not the subject of as much discussion as the vitrinite-group macerals or the more common inertinite-group macerals: fusinite and semifusinite. Traditional interpretations in the coal petrology literature have indicated a degradational origin for macrinite. Fungal spores, hyphae, and mycelia, all as the maceral funginite, are often, but not always, found
in association with macrinite. Funginite is also found in association with degraded vitrinites. The latter two occurrences may, indeed, be part of a continuum from subtly degraded vitrinites to the more completely degraded macrinite. Overall, the inertinite-group macerals are a complex assemblage of forms exhibiting different paths to the forms we see in coals. The origins are multiple; for example, funginite is not from the same kingdom as the, generally, wood-derived origins of fusinite, semifusinite, or the woody precursors of macrinite. As seen in the figures, macrinite can encompass other macerals, including the remnants of liptinites and fragments of fusinite-derived inertodetrinite, in addition to funginite. Fundamentally, macrinite has its origins in the same material as fusinite; the difference in the end product being the consequence of the path of fungal or microbial degradation. 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