Petrographic classification of oil shales

International Journal of Coal Geology, 8 (1987) 203-231 203 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Petrographic Classification of Oil Shales

ADRIAN C. HUTTON

Department of Geology, University of Wollongong, PO Box 1144, Wollongong, N.S. W. 2500 (Australia)

(Received May 23, 1985; revised and accepted March 31, 1987)

ABSTRACT

Hutton, A.C., 1987. Petrographic classification of oil shales. Int. J. Coal. Geol., 8:203-231.

Oil shales are a diverse group of rocks that contain mineral matter and organic matter. The organic matter is derived from terrestrial, lacustrine and marine organisms. The maceral nomenclature system of the International Committee for Coal Petrology, used widely in coal petrography and petroleum source-rock studies, is suitable for describing the organic matter in oil shales provided the terminology for organic matter derived from algal precursors is divided into two sub- macerals - - telalginite and lamalginite. Macerals of the liptinite group, including alginite, are volumetrically important constituents of oil shales and are the major source of the shale oil that is formed during pyrolysis. Liptinite is easily characterized and quantified using fluorescence mode microscopy and thus the type and abundance of liptinite can be used as a basis for a petrographic classification of oil shales.

Oil shales are grouped, using the environment of deposition as the discriminatory criterion, into the three primary divisions of terrestrial, lacustrine and marine oil shales. Type and abundance of liptinite is then used to subdivide these three groups into cannel coal, torbanite, lamosite ( further subdivided into Rundle-type lamosite and Green River-type lamosite ), marinite, tasmanite and kuckersite.

INTRODUCTION

The probability of utilizing oil shales and discovering new deposits will be greatly increased as the geology of known deposits and an understanding of the included organic mat ter in the oil shales from these deposits, becomes bet- ter known. Little agreement as to either a definition of oil shale or the nature and origin of the included organic mat ter in these rocks has been agreed upon in the past. For example, Tissot and Welte (1978, p. 225) wrote "there is actually no geological or chemical definition of an oil shale. In fact any shallow rock yielding oil in commercial amounts on pyrolysis is considered to be an oil shale". This description is similar to those of Yen and Chilingar (1976) and Schlatter (cited in Prien, 1976). Tissot and Welte (1978, 1984 ) also reported that where a rock containing 2.5 weight percent (wt.%) kerogen is retorted, the total calorific value is used in heating the rock. Consequently, a lower limit of 5%

0166-5162/87/$03.50 © 1987 Elsevier Science Publishers B.V.

204

(presumably by weight) organic matter is commonly used in defining oil shales, although some United States literature uses 10 US gallons per short ton (Tis- sot and Welte, 1984; p. 255). Five weight percent is equivalent to approximately 5 volume percent (vol.%) given that the specific gravity of liptinite, the bulk of the organic matter in most oil shales, is just above 1 gram per cubic centimetre. For many Australian Tertiary oil shales, 5 vol.% organic matter is equivalent to a shale oil yield of approximately 25 1/tonne. Yields of less than 25 1/tonne are considered subeconomic for most proposed processing plants, even those envisaged for the Tertiary oil shales where the lower cutoff is ~en- erally given as 40 1/tonne.

In this paper, which deals with the petrography of oil shales rather than econo,nic issues, oil yield is not considered to be as important as the type and abundance of organic matter and thus any arbitrary lower cutoff figure for yield can be used. Indeed, in most Tertiary oil shale deposits, oil shale layers grade into barren claystone and the percentage of organic matter ranges from > 80% to < 1% by volume. However, for convenience, the term "oil shale" is applied to any rock containing 5 vol.%, or more, liptinite.

An upper limit is considered unnecessary because some oil shales are composed almost totally of liptinite. For example, Hutton (1982) reported one torbanite from Ermelo ( South Africa ) with 99% algal matter and Cane (1943) gave the yield of a torbanite from Marangaroo (New South Wales, Australia) as > 1000 I/tonne. This latter figure represents a conversion, of rock to shale oil, of > 99% by weight.

Most oil shales contain abundant liptinite with minor vitrinite and inertinite; some oil shales contain bitumen. The liptinite in oil shales is derived from numerous organisms once living in several different environments. The characterization of liptinite can be best achieved using organic petrographic techniques.

Any classification of rocks should be based primarily on easily recognizable properties of the key constituents, and for oil shales, these should be properties (such as type and abundance) of the organic matter. Until recently, petrographic properties of oil shales had not been well documented and classifications of oil shales had been based on criteria such as industrial use (Ozerov and Polozov, 1968), included mineral matter (Down and Himus, 1940; Jaffe, 1962), physical properties (Mott, 1951), chemical properties of the organic matter, commonly termed kerogen (Bitterli, 1963; Combaz, 1974; Tissot and Welte, 1978; Alpern, 1979), especially when referring to a Van Krevelen dia- gram, or combinations of two or three of these features.

The importance of the organic matter in oil shales should not be overlooked because it is the type and abundance of organic matter that not only determine the chemical and physical properties of the oil shale but the yield and chemistry of the shale oil as well.

Classification of oil shales has been seriously retarded in two main areas.

205

Until recently, transmitted-light microscopy and chemical examination have been the most commonly used methods of identifying organic matter and both have limited potential for discriminating between the different kinds of organic matter in rocks. In transmitted light, liptinite macerals, the dominant organic matter in most oil shales, show little optical contrast with clay and other fine- grained mineral matter, especially in samples of low rank. With the advent of blue/ultraviolet fluorescence-mode microscopy, the properties of liptinite macerals have been elucidated and detailed data on the type and quantity of these macerals can be provided. Several authors have listed or figured types of organic matter, and associated optical properties, in recent publications (Alpern et al., 1972; Combaz, 1974, 1980; Robert, 1979, 1981; Alpern, 1980).

Petrographic data can be related to the chemistry of oil shales and shale oils. Thus data pertaining to probable yield, seam thickness, environment of deposition and both vertical variation and lateral variation in deposits can also be obtained using fluorescence-mode microscopy.

Fluorescence-mode microscopy is rapid, involves minimal sample prepara- tion and is relatively inexpensive. It may be used for outcrop, core or cuttings samples and as little as a few grams of sample is all that is required for detailed characterization of a given sample.

The derivation of a useful classification of oil shales has been hindered by the lack of serviceable terminology and nomenclature for oil shales. Termi- nology has been, to say the least, both chaotic and parochial with an ad hoc duplication of names for oil shales which have similar organic constituents but which are found in different deposits (Table 1 ). In this paper, a limited number of new terms are introduced because several distinctive and important organic assemblages have not been described or named. Many previously used terms do not relate to important properties of the oil shales and are discarded.

The main advantages of the system proposed in this paper, compared with others previously used, are: (a) it uses, refines and extends terminology, namely maceral terminology of

the International Committee for Coal Petrology (ICCP), that is already in widespread use;

(b) nomenclature and classification are based on organic constituents; these are the same constituents that determine most of the properties, including the more important ones, of the oil shale and derived shale oil;

(c) the main elements of the classification are generally easily recognized; (d) the system is natural as well as systematic and therefore complements

studies in coal petrography and studies of petroleum source-rocks; and (e) the categories of oil shale defined have different characteristics, modes of

occurrence, specific oil yields and, on the basis of preliminary data, oil quality.

Aspects of the classification that need further study and/or refinement include:

206

(a) the system does not separate marine oil shales that contain mostly bituminite from those that contain mostly alginite with only minor bituminite;

(b) the classification neither uses nor accounts for the abundance of vitrinite- like organic matter, probably derived from algal precursors and possibly related to bituminite, that occurs in some marine oil shales;

(c) it places strongly fluorescing alginite, derived from acritarchs and dinoflagellates, in the lamalginite group although the fluorescence intensity is similar to that from tasmanitid telalginite in the same sample; and,

( d ) this classification does not consider the oil producing potential of the weakly fluorescing matrix, which contains both mineral and organic matter, that is found in oil shales such as that from the Green River Formation (USA) and many marine oil shales; available data suggest that the oil potential of the matrix, although volumetrically large, is probably not as significant as previously believed.

NOMENCLATURE

Many previous studies of oil shale and related rocks have been limited to single deposits or even individual aspects of a lithology or deposit. Conse- quently, little systematization in terminology has been attempted when referring either to types of oil shale or the included organic matter. Many terms have restricted or obscure usage (Table 1 ). Genetic or compositional features are largely ignored.

Organic matter in oil shales and related rocks is generally referred to by two terms - - bitumen (a soluble component) and kerogen or kerobitumen, the insoluble fraction (Saxby, 1976). Where "bitumen" is used for the soluble fraction of organic matter in oil shales, it is used in a chemical sense. Hunt (1979) also used it in a chemical sense when he defined bitumens as "native substances of variable colour, hardness and volatility, composed principally of the elements carbon and hydrogen and sometimes associated mineral matter, the non-mineral constituents being largely soluble in carbon disulphide" (p. 546). Thus asphalts, natural mineral waxes, asphaltites and petroleum are considered to be bitumens. The solubility of bitumen depends significantly on the temperature at which extraction is carried out and on both the polarity and chemical reactivity of the solvent (Saxby, 1976). The use of either the char- acter or abundance of recovered soluble bitumen in a petrographic classification of oil shales is not warranted.

In other geological contexts the definitions of bitumen are quite varied. For example, "bitumen is a generic term applied to natural inflammable substances of variable color, hardness and volatility. Bitumens are composed principally of a mixture of hydrocarbons substantially free from oxygenated bodies" (Gary et al., 1974, p. 77). This paper advocates the bitumen terminology used by Jacob (1975), who used a petrographic approach to the classification of

207

TABLE 1

Terms previously used for oil shale

General terms for oil .shale

Terms pertaining to

Torbanite Tasmanite Cannel coal

Bituminous shale Boghead coal Spore shale Spore coal Oil mineral Parrot coal White coal Resin coal Pelionite Torbane Hill mineral Cuticular coal Alum shale Boghead gas coal Candle coal Tripolite Kerosene shale Kennel coal Marahuito Algal shale Cannelite Albertite Bathvillite Parrot coal Stellarite Bituminite Curley coal Schistes bitumineux Brown cannel coal Bastard shale

Wollongongite Toula paper shale Boghead Boghead mineral Bituminite Cannel coal Gas coal Algal coal Oil mineral Methol brown shale Petroleum -oil-cannel-coal Olenikite

Several of the names are not now used in the same sense as they were initially; several are trans- lations of others. (Data from Came, 1903; Down and Himus, 1940; Mott, 1951; Jaffe, 1962.)

b i tumen. Jacob based his c lass i f icat ion on t h a t of A b r a h a m (1945). B i t u m e n compr ises a range of types of organic mat te r . T h e s e have readi ly recognizable opt ical charac ter i s t ics . B i t u m e n may be f luorescing or non-f luorescing; it can be in te rs t i t i a l to f r amework grains or occur as balls, pods and lenses in a var ie ty of l i thologies.

B i t u m e n occurs in only a l imi ted n u m b e r of oil shales and where it does occur, it is mos t ly a m ino r cons t i tuen t . I t is t he re fo re no t used as a discrimi- na t o ry p r o p e r t y in the classi f icat ion of oil shales.

C u m - B r o w n in t roduced the t e rm kerogen in 1912 (Cane , 1976) to deno te the insoluble organic m a t t e r in oil shale but , as discussed by Cane (1970), the specif ici ty of the t e r m has been lost and it is n o w a collective and of ten con- fusing t e r m for all or any organic m a t t e r in oil shale. F u r t h e r m o r e "k e ro g en " studies genera l ly re fer to bulk rock s tudies and any one or all o f the macera l groups m a y be c o m p o n e n t s of the "ke rogen" . T h u s kerogen is no t a sui table d i sc r imina to ry t e rm for use in a c lass i f ica t ion of oil shales.

L ip t in i t e - r i ch canne l coals have high shale oil yields and, u n d e r the defini-

208

tion of oil shale given in this paper, must be oil shales. Vitrinite, inertinite and liptinite macerals derived from terrestrial vascular plants are volumetrically minor components in all oil shales except cannel coals and canneloid shales. Terminology as defined by the I.C.C.P. (1963, 1971, 1975) and Stach et al. (1975, 1982), adequately encompasses these macerals where found in oil shales.

The maceral alginite was defined for algal matter derived from algae related to, or synonymous with, Botryococcus (such as Reinschia, Pila and Gloeocap- somorpha) and to a lesser extent, the algae Tasmanites and Cladiscothallus ( I.C.C.P., 1975). Most brown and bituminous coals commonly contain sparse or no algal matter whereas in most oil shales, organic matter derived from algae is dominant, and is derived from a number of precursors. Different precursors give rise to a number of forms of alginite, each of which has a range of properties (Tables 2 and 3 ). Thus the term alginite as defined for coals, if applied to oil shales, is inadequate and considerable revision is needed.

Hutton et al. (1980, p. 48) identified significant morphological differences between members of the alginite maceral and subdivided alginite into alginite A ("discrete colonial or unicellular algal bodies related to either Botryococcus or Pachysphaera:) and alginite B ("finely lamellar benthonic algal material which constitutes the bulk of the organic matter in many important oil shales").

The terms were subsequently used, as defined above, by Hutton (1980), Kantsler (1980), Cook et al. (1981) and Kalkreuth and Macauley (1984). Alginite B was redefined by Hutton (1981, 1982) to include phytoplankton such as dinoflagellates, acritarchs and the organic remains of diatoms.

In this paper, "telalginite" is used instead of alginite A and "lamalginite" is used instead of alginite B. Lamalginite and telalginite are defined as follows: (a) Telalginite is alginite, derived from large colonial or thick-walled unicel-

lular algae (Plate 1), with strong fluorescence at low rank and with distinctive external structure, and in many cases internal botanical structures, when viewed in sections perpendicular to bedding.

(b) Lamalginite is alginite, derived from small, unicellular or thin-walled, colonial planktonic or benthonic algae (Plate 1 ), with weak to moderate (rarely intense) fluorescence at low rank and a distinctive lamellar form with little recognizable structure in sections perpendicular to bedding.

"Tel" is derived from tela (Latin) meaning tissue. The use of telalginite is consistent with the use of the bituminous coal term telinite meaning cell walls of recognizable plant tissue in vitrinite (I.C.C.P., 1971) and the brown coal term textinite, derived from the Latin textum meaning tissue, network, or structure. "Lam" is derived from "lamellar" which is the characteristic shape of this alginite in sections perpendicular to bedding. Lamalginite occurs in oil shales formed in a variety of environments and although derived from a diverse group of precursors, the lamellar form is the common property of this alginite. Ginzberg and Letushova (1976) referred to colloalginite and thallomoalginite but neither of the prefixes "collo" and "thallomo" are used. "Collo" is derived

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211

from the Greek kolla meaning glue {I.C.C.P., 1971) and has connotations of an amorphous nature. Clearly lamalginite is not amorphous and therefore "collo" is not suitable. "Thallomo" is not used because the prefix tel was already in use.

The terms telalginite and lamalginite are compatible with other terms used by the I.C.C.P. and, if correctly used, convey significant information as to the properties of the macerals.

Properties of several forms of telalginite and lamalginite are summarized in Tables 2 and 3, respectively. Table 4 correlates liptinite terminology, relating to oil shales, used in this paper with that used elsewhere.

CLASSIFICATION OF OIL SHALES

Organic-rich rocks can be conveniently divided into the three categories of oil shales, bi tumen-impregnated rocks and humic coals {Fig. 1 ) although several other schemes have been used in the past. This division allows any of the presently used coal or bi tumen classifications to be included in a general classification of organic-rich rocks. Tar sands are not included as oil shales, not- withstanding the large volume of oil that is produced from these rocks. The organic matter in tar sands and bitumen-impregnated rocks is of secondary origin, that is, it is a mixture of alteration products derived from biodegrada- tion, metamorphism or maturat ion of organic matter. Thus the organic matter in tar sands is more akin to petroleum than to solid "kerogen". Existing sub- divisions of bitumen, as have been proposed by Abraham (1945), Bell and Hunt (1963), Hunt (1963) and Jacob (1975), would not be invalidated by the oil shale classification proposed here.

Because organic matter in oil shales is derived from a variety of organisms which include precursors of terrestrial, lacustrine and marine origin, it follows that a natural subdivision of oil shales should include these terms as a basis for a primary subdivision. Thus the three major types of oil shales are (Fig. 1): (a) Terrestrial Oil Shale - - oil shale composed of liptinite derived from terres-

trial organisms. { b ) Lacustrine Oil Shale - - oil shale composed of liptinite derived from dom-

inantly lacustrine (including brackish, saline or freshwater lacustrine) organisms; and

(c) Marine Oil Shale - - oil shale composed of liptinite derived from dominantly marine organisms.

The type and quantity of included liptinite is used to divide each of the primary oil shale types into secondary groups where necessary (Fig. 2 ).

Types of oil shale

Cannel coal. Cannel coal is a brown to black, homogeneous oil shale composed of liptinite derived from terrestrial vascular plants { Plates 1.1 and 2 ) and generally vitrinite and inertinite.

TA

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198

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C O A L

HUMIC TERRESTRIAL

OIL SHALE

LACUSTRINE MARINE

B I T U M E N - IMPREGNA1T=D T A R S A N D ROCK

A k NAPHTHENE- ASHPHALTENE-

RICH RICH

213

J J J J J V I T R A I N CANNEL LAMOSITE MARINITE GILSONITE ALBERTITE OIL

C L A R A I N COAL TORBANITE TASMAN|TE GRAHAI~TE WURTZILITE BITUMEN

DURAIN KUCKERSITE

FUSAIN

Fig. I. Classification of organic-rich rocks showing the primary division of oil shales into terrestrial, lacustrine and marine oil shales.

TENAESTmAL OIL SHALE

LJthotype CANNEL COAL TOAl~tNrrE

VASCULAR GREEN ALGAE Preeureoy Orsanisms PLANTE

Growth VARIOUS PLANK TONIC PLANKTONIC BENTHONIC Form COLONIAL COLONIAL ALGAE?

UNICELLULAR ALGAL OOZE

SPORINITE TELALGINITE LAMALGINITE LAMALGINITE Dominant Maeefal/ RIESINITE ConMBulmt CUTINITE

Known Angiosperms Pfla Podleatrum ? Precursors Gymnosperrne R e l n e e M a Gmmtodlelmn

Cleiato- apheeridium

RelAted Vaslaus Extent Botryo©occua Pediastrum Extant Blue- Orgeniems Vascular Plants breUnlI Green Algae

LACUGTEINE MARINIE OIL KHALE OIL SHALE

LAMOSITE MARINITE TASMANITE J %

RUNDLE GREEN RIVER TYPE TYPE

GREEN ALGAE ?BLUE-GREEN GREEN ALGAE GREEN ALGAE A L G A E ACRITARCH8

DmOFt.AGEL- LATE8

KUCKERSlTE

GREEN ALGAE

PLANKTONIC PLANKTONIC UNICELLULAR UNICELLULAR COLONIAL

LAMALGINITE TELALGINITE TELALGINIT1E BITUMINITE

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I d J m

Various Extent PechyaGhaora 8otryo©oceus Algae Acrltar¢ha pelegl¢a braunii

Dinollagellat ea

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- Trsee TelaigJnne Ggorlnito 8portnno Vitrinite 81tumlnlte fle0Jnite Bitumen Sporlnlte

TulelglnJte Yltrinlta Vltrlnlte InertilUta

Inortlnlta Lamallkdt e Eporlnlte Bitumen

Fig. 2. Secondary divisions of oil shales giving important properties of each oil shale.

Torbanite. Torbanite is a black to greenish-black oil shale in which the principal liptinite is telalginite derived from Botryococcus-related, lacustrine algae (Plates 1.2 and 3).

215

Lamosite. Lamosite is a pale brown to dark greyish-brown oil shale in which the principal liptinite is lamalginite derived from lacustrine algae and other phytoplankton ( Plates 1.3, 1.4, 1.5, 4 and 5).

Marinite. Marinite is a grey to dark greyish-black oil shale in which the principal liptinite is lamalginite derived from marine algae and other phytoplankton and/or bituminite derived from marine precursors (Plates 1.6 and 6).

Tasmanite. Tasmanite is a dark grey to black oil shale in which the principal liptinite is telalginite derived from marine tasmanitids ( Plates 1.7 and 7 ).

Kuckersite. Kuckersite is a brown oil shale in which the principal liptinite is telalginite derived from Gloeocapsomorpha prisca ( Plate 1.8 ).

Minor liptinite components occur in most oil shales but usually in such small quantities that it is not necessary to include them in the definitions.

Figure 3 summarizes the more important aspects of the respective oil shales and characteristics of the deposits.

PLATE 1 Oil shales (photographed in fluorescence mode; sections perpendicular to bedding unless stated) 1. Tertiary canne l coal, from Freshford (New Zealand), composed of suberinite (centre), with

abundant sporinite, liptodetrinite and nonfluorescing vitrinite (within suberinite and bottom right). Field width = 0.34 mm.

2. Permian torbani te , from Newnes (New South Wales, Australia), composed of telalginite derived from Reinschia in a nonfluorescing groundmass of desmocollinite, inertodetrinite, micrinite and mineral matter. Field width = 0.56 mm.

3. Tertiary lamosite, from Condor deposit ( Queensland, Australia), composed of abundant, dis - crete lamalginite derived from the colonial alga Pediastrum with sparse telalginite and pyrite (black grains) in a clay-sized groundmass. Field width = 0.28 ram.

4. Verylowgradelamosite, from the Rundle deposit (Queensland, Australia),containinglamal- ginite derived from the colonial alga Pediastrum. Field width = 0.28 mm; section oblique to bedding.

5. Tertiary lamosite, from the Green River Formation ( Colorado, U.S.A. ), containing abundant layered lamalginite, with variable fluorescence colours and intensities, with mineral-rich pods and interlaminae; also abundant pyrite. Field width = 0.22 mm.

6. Cretaceous mar in i te , from the Toolebuc Formation (Queensland, Australia), containing dis- persed lamalginite and nonfluorescing mineral grains in a groundmass of weakly fluorescing bituminite. Field width = 0.28 mm; sample was irradiated with UV-violet radiation for 30 minutes.

7. Permian tasmani te , from the Mersry River area (Tasmania, Australia), composed of abundant telalginite, derived from Tasmanites, with a groundmass of nonfluorescing mineral matter. Field width = 0.44 mm.

8. Ordovician kuckers i te , from Estonia, composed of telalginite derived from the alga Gloeo- capsomorpha. Field width-- 0.44 mm.

216

PLATE 2 Cannel coals (photographed in fluorescence mode ) 1. Hale River deposit ( Northern Territory, Australia);thiscannelcoaliscomposedofabundant

sporinite and less strongly fluorescing liptodetrinite and resinite; nonfluorescing components include vitrinite, rare inertinite and mineral matter; although not in this field, Botryococcus is a minor constituent. Field width = 0.18 mm; section parallel to bedding.

2. Nagoorin deposit (Queensland, Australia); a cannel coal from a brown coal unit that is interbedded with lamosite; it contains abundant resinite (large resinite bodies and small blebs) with cutinite (lower right) and minor liptodetrinite. Field width = 0.28 mm; section oblique to bedding.

MICROLITHOTYPES

Macerals rarely occur singly; they are usually associated with other macerals of the same or another maceral group. Maceral associations or microlithotypes may be either monomaceral, bimaceral or trimaceral, that is, predominantly composed of one, two or three macerals respectively. I.C.C.P. (1963, 1971, 1975) and Stach et al. (1975, 1982) recognized algite as the monomaceral microlith- otype comprising layers with > 95 vol.% alginite and at least 0.05 mm thick. Recognition of the macerals telalginite and lamalginite leads to the recognition of telalgite and lamalgite as microlithotypes comprising > 95 vol.% telalginite and lamalginite respectively. Both terms have limited use because these microlithotypes rarely occur. Of the two, telalgite occurs more commonly than lamalgite and has been observed in tasmanite and very rich torbanite samples such as those from Ermelo ( South Africa) and Newnes, Glen Davis and Temi (all in New South Wales, Australia). Lamalgite has been observed in thin layers of Green River oil shale but in most cases few layers are greater than 0.05-0.06 mm thick. Thus alginite microlithotypes are of minor occurrence in torbanites and are of very restricted occurrence in other oil shales.

Many torbanite samples are composed of subequal telalginite, vitrinite and inertinite (either vitrinite or inertinite may be the dominant non-algal con- st i tuent) . Liptinite-vitrinite-inertinite microlithotypes are termed vitriner- toliptites with presumably, if convention is followed, the alginite-rich assemblage in torbanite called vitrinerto-algite.

217

PLATE 3 Torbanites (photographed in fluorescence mode; sections perpendicular to bedding) 1. Alpha deposit (Queensland, Australia); this torbanite is composed of abundant telalginite

with well-preserved cell structure; many colonies contain pyrite infilling the central cavity and cell spaces as shown in this field. Field width = 0.56 ram.

2. Carnarvon Creek deposit {Queensland, Australia); this torbanite is a low-grade torbanite that contains well-preserved telalginite; the groundmass between colonies contains mostly vitrinite and inertinite with only minor mineral matter. Field width = 0.56 ram.

3. Temi deposit (New South Wales, Australia); telalginite is smaller than that in the Alpha and Carnarvon Creek torbanite and the cell structure is less well-preserved. Field width-- 0.34 ram.

4. Ermelo Deposit (South Africa); this torbanite contains very small telalginite that has a thin brown fluorescing margin; the telalginite also fluoresces quite strongly in reflected white light. Field width = 0.28 ram.

Carbominer i t e , the mine ra l - r i ch coal mic ro l i tho type , con ta ins 20-60% mineral mat te r ; if the dens i ty of the rock is g rea te r t h a n 2.0 g / cm 3, it is regarded as waste (S tach , 1975, I982) . L a m a l g i n i t e - d o m i n a t e d oil shales con ta in as l i t t le as 5 vol.% algini te wi th mos t 20-30 vol.%. I f c a rbomine r i t e is appl ied senso stricto, m a n y oil shales, such as lamosi te and mar in i te , should be grouped as ca rbomine r i t e wi th m a n y regarded as "was te" . T h u s the ca rbomine r i t e mic ro l i tho type requires revis ion i f it is to be appl ied to oil shales.

M a n y samples of Aus t ra l i an T e r t i a r y lamosi te are composed of in te r lami- na t ed a lgini te-r ich and v i t r in i t e - r i ch layers. Lamalg in i t e is no t found in the coaly layers. T h e a b u n d a n t v i t r in i te s igni f icant ly a l ters the shale oil compo-

218

PLATE 4 Lamosite (photographed in fluorescence mode; sections perpendicular to bedding unless stated) 1. Condor deposit ( Queensland, Australia) ; this lamosite contains lamalginite derived from the

dinoflagellate Septodinium; some of the lamalginite is partly infilled with nonfluorescing mineral matter; small black grains are pyrite. Field width = 0.18 mm.

2. Rundledeposit {Queensland, Aust ra l ia ) ; th is lamosi teconta insabundant lamalgin i teder ived from Pediastrum; Rundle samples also contain strongly fluorescing lamalginite (upper centre ) of unknown origin. Field width = 0.28 ram.

3. Orepukideposit {New Zealand); this lamosi te contains abundant lamalginite andtelalginite ( left of centre ) ; the field shows much more telalginite than is the norm; the telalginite is so strongly fluorescing that the lamalginite is underexposed. Field width = 0.30 mm.

4. Aleksinac deposit (Yugoslavia); the lamalginite is derived in part from Pediastrum and some of it is partly infilled with pyrite (left of centre). Field width = 0.24 mm.

5. Duaringadeposit {Queensland, Australia) ; in this sample the lamalginite is derived from large Pediastrum with long processes that give the appearance of a diffuse corona around each lamella. Field width = 0.28 mm.

6. Elko deposit ( Nevada, U.S.A. ) ; this lamosite contains abundant lamalginite and trace nonfluorescing vitrinite ( centre and upper left of centre) ; nonfluorescing mineral grains are abundant in this field. Field width = 0.28 mm.

219

PLATE 5 Green River-type larnosite Lamosite from Zaire containing abundant layered lamalginite, of a form similar to that which occurs in Green River oil shale, numerous authigenic mineral grains and bitumen (above centre ). Field width = 0.18 mm; section perpendicular to bedding.

sition and thus this lamosite subgroup is an important oil shale type. In this paper, the term "carbonaceous" is used to denote oil shales of this type. The minimum vitrinite content is taken as 5 vol.%.

DISCUSSION

Alginite

Coal macerals have a range of chemical compositions and physical properties ( Stach et al., 1975, 1982 ) but each is recognizable, microscopically, by such properties as reflectance, colour and relief. Thus maceral definitions are based on a range, albeit a narrow one, of properties. Just as other macerals have properties that vary within clearly defined limits, so also do telalginite and lamalginite.

Four algae, Gloeocapsomorpha prisca (Plate 1.8), Botryococcus braunii (Plate 2), Foerstia (Plate 8.1) and Tasmanites (Plates 7.1 and 7.2) are readily recognizable in sections perpendicular to bedding. Alginite derived from these algae is placed in telalginite. None has been allotted submaceral status although the optical properties of any one type are reasonably constant but significantly different to the optical properties of the other types of telalginite.

Fluorescence and reflected-light properties of the various alginite groups are responsive to factors such as maturat ion stage state of preservation and parent organisms. The state of preservation in telalginite ranges from poor to excel- lent (Plates 1 and 3). Alpha (Australia) torbanite and some Australian Ter- tiary lamosites, have telalginite that is infilled with and/or replaced by pyrite (Plate 3.1 ). (In the latter oil shales, telalginite is also infilled and/or replaced by carbonate and quartz. ) Fluorescence intensity from pyritized telalginite is

220

PLATE 6 Marinite (photographed in fluorescence mode; sections perpendicular to bedding unless stated} 1. Marinite from the Posidonia Shale (Germany) containing sparse lamalginite, > 0.08 mm long

and abundant lamalginite < 0.04 mm long; Other fluorescing components found elsewhere in the sample include bituminite, telalginite derived from tasmanitids and rare sporinite. Field width = 0.28 mm.

2. Marinite from the Huron Member of the Ohio Shale (Means Prospect, Kentucky, U.S.A.) composed of lamalginite and thicker-walled telalginite derived from tasmanitids. Field width = 0.34 mm.

3. Marinite from the Toolebuc Formation (Julia Creek, Queensland, Australia) composed of lamalginite; much of the smaller lamalginite is enclosed within weakly fluorescing bituminite although this does not show out in the photograph. Field width = 0.18 mm.

4. Marinite from the Doublehorn Shale (Texas, U.S.A.) containing abundant lamalginite and sparse telalginite derived from thick-walled tasmanitids; some of the lamalginite is infilled with nonfluorescing mineral matter (upper right). Field width=0.28 mm.

much reduced compared to the fluorescence intensity of non-pyritized telalginite. Pyritization of telalginite in Alpha samples is most common in weath- ered samples.

Where telalginite and lamalginite coexist, the fluorescence intensity of telalginite is generally much more intense than that of lamalginite (Plate 4.3). This is not the case in marinite where lamalginite, derived from dinoflagellates, has more intense fluorescence than the tasmanitid telalginite. Where two or more types of telalginite or two or more types of lamalginite occur in the same sample, the fluorescence intensities and colours of each type are usually

++ + ~ +++

. . . . 0

221

PLATE 7 Tasmanite [rom Alaska (photographed in fluorescence mode; sections perpendicular to bedding) 1. Tasmanite composed of densely packed telalginite with sparse mineral matter between some

of the algae; some algae appear to have a double wall. Field width = 0.34 ram. 2. Tasmanite, of lower grade than in the previous field, composed of strongly fluorescing telalgin-

ite that has been broken; almost all algae have been infilled with nonfluorescing mineral matter. Field width = 0.34 ram.

CANNEL TORBANI,TE LAMOSITE MARINITE TASMANITE KUCKERSITE

COAL A

RUNDLE GREEN RIVER TYPE TYPE

Precursor TERRESTRIAL PLANKTONIC PLANKTONIC BENTHONIC PLANKTONIC PLANKTONIC PLANTS ALGAE ALGAE ALGAE ALGAE ALGAE

Environment of

Oapoeition

Hand- Specimen

Age

Resources

Seam Thickness

(m)

Seam Geometry

Average Yield (L/tonne)

Maximum Yield (L/tonne)

Peat Swamb Lacustrine (in a Fresh to Stratified or Markte ShlllowMarlna Peat Swamp) Brackish Lake Saline Lake

Black to Black to Olive-Grey, Brown, Grey to Bark Dark Grey to Brown, Bri t t le GroenMB-Black, Brown to Dark Laminated Greyish Black. Black. Massive

Conchoidai Greyish-Brown, Massive to to Laminated Fracture Massive to Laminated

Laminated

Carbon)tarsus Carboniferous Carboniferous Tertiary Cambrian to Permian to Tertiary Permian Tert)ary Cretaceous Cretaceous Jurassic

Small Small Larpe Very L m Small

variable 0.2-2 30-75 15-130 1-10 1-2

variable lansoidel laterally laterally laterally lensoldsl persistent persistent persistent

60 -100 230-800 00-130 135 60-80 115-150

300 1 0 9 0 320 460 1SO? 290 t SSO a

(t - Tasmania, a - Alaska)

Fig. 3. Important properties of oil shales and characteristics of the deposits.

PLANKTONIC ALGAE

Shallow Marine

Brown, Massive

Ordovlclan

Large

1-3

lateral ly persistent

210-320

400?

222

r - - w

i

PLATE 8 (photographed in fluorescence mode ) 1. Telalginite, derived from Foerstia, in marinite from the Huron Member of the Ohio Shale

(Means Prospect, Kentucky, U.S.A. ) ; the alga has well-preserved cell structure and is up to 5 mm long. Field width = 0.34 mm; section perpendicular to bedding.

2. Telalginite, derived from Tasmanites, in Mersey River (Tasmania, Australia) tasmanite; Tas- manites is unicellular and is porate (although this does not show in the photograph). Field width = 0.28 mm; section parallel to bedding.

different. For example, in marinite from the Devonian Huron Member of the Ohio Shale ( Kentucky, U.S.A. ), telalginite derived from Foerstia ( Plate 8.1 ) has much weaker intensity than tha t for telalginite derived from tasmanitids ( Plates 6.2 and 6.4). In the same samples, lamalginite derived from acritarchs and dinoflagellates has more intense fluorescence than telalginite derived from Foerstia. Despite its intense fluorescence, the former lamalginite is placed in the lamalginite maceral because in sections perpendicular to bedding it has the distinctive lamellar form tha t is characteristic of lamalginite.

Australian Tertiary lamosites contain liptodetrinite ( < 0.01 mm in length) that has the same fluorescence and textural properties as lamalginite. It occurs in siltstone and claystone as diffuse fragments and is abundant in strew mounts. The fluorescence properties suggest that this organic matter is derived from alginite that has probably been degraded by mechanical, bacterial or other biological agents. Algodetrinite would be a suitable term for this organic matter but the definition of liptodetrinite ( Stach et al., 1975, 1982 ) precludes the use of this term.

Alginite and bi tumini te

Teichmfiller (1974a) defined bituminite as a liptinite maceral with properties midway between those of sporinite and vitrinite. It is distinguished above all by the fact that it is "amorphous". Previously, Teichmiiller (1950) had referred to bituminite as "amorphous bitumen" and Diessel ( Stach et al., 1975) had used the same term for bituminite in sapropelic coal from the Kathar ina Seam of the Ruhr area. Teichmiiller (1974a) listed the following properties of bituminite:

223

(a) slightly higher reflectance than cutinite or sporinite in low-rank hard coals but lower reflectance than vitrinite;

(b) less intense fluorescence than sporinite or cutinite with dark orange to brown colours;

(c) amorphous form; (d) occurs as striae of various sizes with asymmetrical boundaries in Carbon-

iferous hard brown coals; (e) occurs as a groundmass in bogheads and sapropelites; (f) is closely associated with vitrinite and micrinite; (g) may be transformed into micrinite in the flame to gas flame coal stage. Bituminite is soft, polishes with difficulty and transmits light freely ( Stach et al., 1975; 1982).

Teichmiiller (1974a) and Teichmiiller and Ottenjahn (1977 ) considered that bituminite was formed from organisms rich in fats and proteins. Bituminite in Posidonia Shale of West Germany was divided, by Teichmiiller and Ottenjahn, into three types - - Type I, Type II and Type III. Creany (1980) recognized Type I bituminite in the Boundary Creek Formation (Beaufort-Mackenzie Basin of Canada) as well as matrix bituminite ( referred to as a fourth type by Teichmiiller (1982), and one other unnamed form.

Teichmiiller (1974b) stated that alginite played a larger part in the formation of peat than can be assumed on the quantities of observed alginite. It was believed that during humification, the majority of these algae, in contrast to the alginite-forming algae, are not preserved morphologically. The algae and bacterial bodies were assimilated into the coal and do not retain their original form. Thus while the above implies that some alginite inherently lacks "preservation properties", the occurrence of well-preserved structure of alginite in torbanite, tasmanite, kuckersite and marinite illustrates that many algae have an innate ability to be preserved.

Given the respective properties of bituminite as described by Teichmiiller (1974a, 1982), bituminite and lamalginite are not equivalent macerals. The use of bituminite should be restricted to: (a) amorphous or poorly structured organic matter in coal, and other humic-

rich rocks such as cannel coal and some torbanite, where it occurs as a groundmass enclosing telalginite and humic macerals; and

(b) amorphous or poorly structured organic matter in marinite. The use of bituminite in both contexts is consistent with the descriptions

given by Teichmiiller (1982).

Types of oil shales

The petrographic classification used in this paper has been developed from those given in Hut ton (1980), Hut ton et al. (1980), Cook et al. (1981) and Hutton (1981). The terms for the different types ofoil shale have been derived

224

from one or more distinctive features of the organic mat ter in the oil shale with the exception of torbanite, tasmanite and kukersite which are used consis- tently and without ambiguity. Although the terms do not have genetic connotations they are well entrenched in the literature, are widely used terms at present and each is restricted to a specific oil shale type. The terms are useful in a petrographic classification and replacement of these terms is therefore not only unnecessary but would be extremely difficult, if not impossible.

Cannel coal is "microstratified, black and dull, sometimes with a rather greasy lustre. It is very homogeneous and compact and breaks with a conchoidal fracture" (Stach et al., 1975, p. 134). Cannel coal can be distinguished from "boghead coals" by the lack of alginite in the former. The composition of cannel coals is variable. For example, Stach et al. (1975) stated that cannel coal may contain dominantly sporinite or fine-grained vitrinite. However, it is also implied in that cannel coal may contain abundant sporinite, resinite or cutinite since the "composition of cannel coals is similar to that of clarite, durite and trimacerite" (p. 135 ). All cannel coals (such as those figured in Plate 2 ) with the exception of liptinite-poor, vitrinite-rich cannel coal, would produce significant volumes of shale oil during pyrolysis and can be classed as an oil shale. Liptinite-poor cannel coals should remain in the coal group ( Fig. 1 ).

"Sapropelic" coal, which includes both boghead and cannel coal is reported to form from subaquatic organic muds which accumulated under anaerobic conditions (Stach et al., 1975, 1982). Furthermore, essential consti tuents are biological and physical degradation products of contemporaneous peat swamps ( Moore, 1968). The latter conditions are probably necessary for the formation of cannel coal with abundant bituminite but are unlikely to be mandatory where resinite-rich coals, such as from Kutch (India) and suberinite-rich coal, such as from Freshford (New Zealand), were formed.

Alginite content of torbanite and alginite-bearing coal ranges from < 1 vol.% to 99 vol.% (Plate 3). Any cutoff value that separates torbanite from telalginite-bearing coals is thus arbitrary. However, for consistency of definitions, 5 vol.% telalginite is the arbitrary lower limit for torbanite. The terms boghead, boghead coal and kerosene shale have been used in the past but their use as oil shale terms is not advocated.

Petrographically, lamalginite can be divided into two types: - - th in-wal led alginite which occurs as discrete entities {<0.5 mm long)

enclosed in mineral mat ter in all but the very rich samples ( Plates 1.3, 1.4 and 4 ) ; and

- - layers composed of' numerous sheet-like algal remains ( Plates 1.5 and 5), some or all of which may have been biologically or physico-chemically degraded. The two types of lamalginite are referred to as "discrete lamalginite" and

"layered lamalginite", respectively, wherever specificity is required. Oil shales with either type of lamalginite were grouped together previously as lamosite

225

(Hutton, 1980, 1981; Hut ton et al., 1980). Oil shales characterized by abundant layered lamalginite [for example Green River lamosite (Plate 1.5 ) and lamosite from Zaire (Plate 5 ) ] generally have ifiterlaminated organic-rich and mineral-rich laminae whereas laminations are usually not as well-developed in lamosites with discrete lamalginite (for example Rundle oil shale). T h e precursors of some lamalginite have been identified to genus level ( Plate 9 ).

The two types of lamosite should also be separated because: (a) Green River-type was formed under more saline conditions than Rundle-

type; and (b) Green River-type is probably derived from blue-green algae ( Eugster and

Surdam, 1974), whereas Rundle-type is derived mostly from green algae. Combaz (1980) used the term laminite to denote laminated oil shales. This

usage of the term has a slightly different sense to that originally used by Lombard (1963) who used it to denote finely stratified flysch. Other authors subsequently applied laminite to fine-grained sediments in low-energy environments (Combaz, Compagnie Franqaise des Petroles; pers. commun., 1985). Combaz (1980) included oil shales from the Sahara and Paris Basin as well as the Irati and Green River oil shales in his use of laminite. Laminite is a term which is suitable to Green River oil shale and other oil shales with well-defined laminations and layered lamalginite. However, it has been pre-empted and further usage of this term in relation to oil shales is not warranted.

Marine oil shales are divided into three types - - kuckersite, tasmanite and marinite. The inclusion of kuckersite in the primary group of marine oil shales and the inclusion of torbanite in freshwater oil shales illustrates that classifications separate rocks which may have characteristics in common. Telalginite in both kuckersite and torbanite is derived from Botryococcus-related algae (Cane, 1977), yet the former is of marine origin (Zalessky, 1916; Duncan, 1976) and the latter is of lacustrine origin. The "shallow sea lagoons" of Zales- sky could encompass backwater or tidal flat lagoons which have a considerable input of freshwater runoff. Such an environment would be comparable to the Coorong area of South Australia where coorongite, believed by many to be a precursor of torbanite, forms.

Brown, massive Ordovician oil shale from the Galena Group, Illinois, contains abundant Botryococcus-telalginite some of which is poorly structured and some which has well-preserved structure. The latter have yellow to yellowish- orange fluorescence whereas the former have weaker orange fluorescence. Many of the properties of the Galena Group oil shale, both petrographically and in hand-specimen, are similar to corresponding properties of kuckersite. Burgess (1975) has interpreted the environment of deposition of the oil shale section of the Galena Group as brackish "adjacent to a truly marine one nearby". Marine fossils including brachiopods, bryozoans and trilobites are found in overlying limestone. The Galena Group oil shale is tentatively placed in the

226

PLATE 9 Algal precursors of lamalginite in Australian Lamosite (photographed in fluorescence mode ) 1. Pediastrum• a stellate• •acustrine c•l•nial algae that is typical•y flattened; Rundle dep•sit. Field

width = 0.09 mm. 2. Septodinium, a freshwater dinoflagellate; Condor deposit. Field width=O.OT mm. 3. Pediastrum; Duaringa deposit. Field width = 0.07 mm. 4. Pediastrum with long thin processes; Duaringa deposit. Field width=O.O8 mm. 5. Pediastrum, Duaringa deposit. Field width =0.14 mm. 6. Cleistosphaeridium, a freshwater acritarch; Stuart deposit. Field width = 0.06 mm.

torbani te group. However , the similarit ies in proper t ies between oil shale f rom the Galena Group and kuckers i te may indicate a similar e n v i r o n m e n t of deposition for both. Fu r the r s tudy is required to de te rmine if the chemical properties of kuckersi te and oil shale f rom the Galena Group are similar.

227

Tasmanite (Plates 1.7 and 7.1 and 7.2 ) is composed of abundant tasmanitid telalginite, with minor lamalginite and vitrinite. It is not possible to distin- guish between the genera Tasmanites and Leiosphaeridium in fluorescence mode. Oil shales in which either genus is dominant are classed as tasmanite.

Liptinite in marinites comprises telalginite derived from tasmanitids, lamalginite derived from marine algae, sporinite and bituminite. Minor constituents usually include vitrinite, inertinite and bitumen. Many marinites also contain abundant vitrinite-like organic matter, much of which may have been derived from algae. Reflectance values for this "vitrinite" range from 0.20% to 0.35%. "Vitrinite" is commonly associated with micrinite and, in many samples, has a weak brown fluorescence. Although an algal origin is inferred for this organic matter, further study is required to determine the origin of this organic matter and whether marinites containing this vitrinite-like organic matter should be placed in the same group as those without it.

Marine petroleum source-rocks have the same organic assemblage as marinites; lamalginite and/or bituminite are dominant in many. The petrographic classification advocated in this paper, can be extended to include petroleum source-rocks if required.

L A M A L G I N I T E

• Toarcian Shale (France)

• Posidonia Shale (Germany)

• Sunbury Shale (USA)

• New Albany Shale (USA)

• Antrim Shale (USA)

,~ Ooublehorn Shale (USA)

Chattanooga Shale (USA)

• Cleveland Member (USA)

4F

B I T U M I N I T E T E L A L G I N I T E

Fig. 4. Abundance of telalginite, lamalginite and bitumen in selected marinite samples.

228

"Mixed oil shale" has been used ibr oil shales of marine origin and which contain telalginite, lamalginite and humic matter ( Hutton, 1980, 1981; Hutton et al., 1980; Cook et al., 1981 ). The term "mixed oil shale" is only valid if the designated oil shale has a mixed assemblage of liptinite, that is, the oil shale contains two or more co-dominant liptinite macerals. For example, Fig. 4 shows the distribution of liptinite in selected marinite samples. Several samples have co-dominant lamalginite and bituminite; another sample has co-dominant bituminite and telalginite. Oil shale of the latter type is, strictly, both a marinite and a tasmanite; it should be classed as a mixed oil shale.

It is possible that conditions within any basin, in which oil shale was forming, changes with time. Thus two types of oil shale could form at different times. For example, if the salinity of a lake increased, Green River-type lamosite could form instead of Rundle-type lamosite. Sherwood et al. (1984) stated that lamosite from the Mae Sot deposit of Thailand had properties midway between those of the Rundle lamosite and those of Green River lamosite. Other samples from Mae Sot are typical of those from the Rundle deposit ( Hutton, 1982). Thus the samples described by Sherwood et al. and Hutton may well illustrate that conditions changed within the Mac Sot basin. Such occurrences where two types of oil shale form within the same basin, are probably not common.

CONCLUSIONS

Any classification is only useful if the constituents of the population can be accurately, and easily, identified and if the classification accommodates most members of a population without erecting a large and unworkable number of categories. A petrographic classification of oil shales does this.

Organic matter in oil shales and related sedimentary rocks is derived from a variety of precursors ranging from simple unicellular freshwater or marine algae and phytoplankton to large terrestrial vascular plants. The volumetrically important components of oil shales are generally liptinite, and in particular, alginite. Liptinite is easily recognized using normal coal petrographic techniques and it is therefore logical and useful to construct a petrographic classification of oil shales. The type and quantity of liptinite should be the dominant criteria for the hierarchical subdivision of oil shales.

The petrographic classification of oil shales suggested in this paper is based on terminology already in use for coal and petroleum source-rock studies. Two alginite macerals, telalginite and lamalginite, have been defined and this per- mits the characterization of seven types of oil shales - - cannel coal, torbanite, Rundle-type lamosite, Green River-type lamosite, marinite, tasmanite and kuckersite. The classification can be extended to include petroleum source- rocks because most of these are composed of macerals of the liptinite group.

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ACKNOWLEDGEMENTS

T h e major pa r t of this s tudy was carr ied out whilst the au tho r was the recip- ient of an Aus t ra l i an Pos tg r adua t e Research Scholarship . Dur ing this per iod discussions were held wi th Professor A.C. Cook and Mr N.R. Sherwood. South- ern Pacific Pe t ro l eum N L and Cent ra l Pacific Minera ls N L provided mos t of the samples of Aus t ra l i an Te r t i a ry oil shales. N u m e r o u s pe rsons suppl ied samples of overseas oil shales. The au tho r grateful ly acknowledges this help.

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Petrographic classification of oil shales