The genesis and isotopic composition of carbonates associated with some Permian Australian coals

Chemical Geolop,y, 24 (19'79) 137- 150

137

~,.~ELsevierScientific Publishing Company, Amsterdam - Printed in The Netherlands

THE GENESIS AND ISOTOPIC COMPOSITION OF CARBONATES ASSOCIATED WITH SOME PERMIAN AUSTRALIAN COALS

K W. G O U L D andJ.W SMITH C S I R O Fuel Geoscietlce Unit, North Rydc, N S. W. 2113 (Australia) I Received Augusl, 19, 1977; rev=sedand accepted February 10, 1978)

ABSTRACT Gould, K.W. and Smith, J.W , 1979. The genes,s ~ld ,sotop,c composition o1' carbonates associated with some Permian1 Australian coals. Chem. Geol., 24' 137-150. S=derite and calc,te are the two forms ol'carbonate commonly associated with Permian Australian coals. The former occurs as disseminated spherulites and is a product or the early post. depositional environment.. Isotopic measurements show that. the CO= I',zed as siderite did not resuIt I'rom the direct, ox =daLton or photosynthetically derived materials, but rat.her from the anaerobic rermentation or these. The htgher concentrations or calcite are generally round towards the roofs of coal seams and are characterized by isotopic enrichments to ,','sC values or t 250/,~0 PDB. Isotopic exchange bel.ween CO= and CH 4 wiLhin the coal seam is postulated as the mechanism which leads to the formation of isoLop,caUy heavy CO~. At s,tes along the seam margins where the CO~ escapes, interaction with circulating metal ions or preexist.ing calcite results in the de position of "heavy." calc,te. With increas,ng alteration o1"coal by thermal metamorphism, the * JC content of calcites and I'Lnally siderites decreasesso that. it more nearly approaches that. or the associated coal

I N"I"ROD LICTIO N Prev,ous measurements (Fritz eL al., 1971 ) have shown the ':~C contents o f sider=tes occurring w=t,h carbonaceous shales t,o be unexpectedly high. An enrichment o f "lC in siderite relative to that in calcite o f 2 - 3 % o has been demonstrated (Galimov and GLrin, 1968) but such an isotopic I'ractionation cannot account for the high '3C values reported. Weber et aJ. (1.964) attempted to difl'erentiate between siderites of freshwater and marine origins on the basis of the higher ~JC contents o f the latter. C o n h r m a t i o n ol" this view, that the isotopic composit=on o f siderites rellects the e n v i r o n m e n t or" deposition, has not, been forthcoming. Rather, the consensus is that, the " h e a v y " COz necessary for the formation o1' siderite is produced sirnultaneously w i t h " l i g h t " CH, during the early anaerobic fermentation o f simple organic, compounds (Rosenfeld and Silverman, 1959; Oana and Deevey, 1960). This explanation satisfactorily accounts for not, only the ,sotopic composition o f the siderite, but, also =t,s u n d o u b t e d early origin.

138

On the basts of isotopic vartations through large sldenttc concretions anti the spread in measured 6"~C * values, tt has been suggested that later exchange processes bet,ween siderite and " l i g h t " b,ogenic bicarbonate may have reduced the "~C content, of the former (Curtis et a.l., 19"/2). Previously, Dei.nes (1968) has favoured a deep-seated origm in the lower crust, or upper mantle for rare heavy carbonat,e-C (~'>'~C +12 to ÷250/o.) en countered as calcite m a pendotite dike intruding coal and carbonaceous shale of Pennsylvanian age. Deuser (19'70) has reported the occurrence of Quaternary dolomites with p~l3C values ranging from -64 to +21°/0. in sub n~a.fi ne canyons. In studies of the diagenetic alteration of carbonaceous rocks, the occurrence of dmgenetic dolomltes wlth A'~C values ranging from - 2 5 to +21% o has been reported m marine Miocene shales (Murata et aJ., 196'7, 1969). No single, geologically acceptable reaction sat=sfactonly explains such a range of values and recourse was made to two reactions: (1 ) The oxidation of organic materials under a wlde variety of conditions to produce tsotopically "light" biogemc carbormtes {2) Isotopic exchange between CH,4 and carbonates to obtam "heavy" carbonates. The extensive role which the former reaction plays m natural processes is well documented and does not, require elaboration. However, the different mechanisms currently proposed and discussed here for the production of ~'~C. enriched siderites and, more particularly, calcites and dolomites, cannot be ac cepted unequivocally. The progressive ut.=lizationof organic materials to pro duce mcreasingly heavier CO,, ; isotopic exchange between CO,, and CH4 ; and the format,ran of both these gases during the bacterial fermentation of simple organ=c compounds, are pathways suggested to explain the wide range of~'~C values found. In th=s regard the part,lal direct bacterial reduction of CO2 to CH.~ seems not, to have been cormldered other than by Nissenbaum eL al. (19'72). Bot,h slderite and calcite c o m m o n l y occur tn coal seams. Siderite, when in the form of disseminated spherutites, ts generally thought, to be of early, precompachonal origin, whereas the calcite is a secondary mineral fillingcleats and partings in the seam (Kemezys and Taylor, 1964). The coexistence of these carbonates wit,hin a well-defined reducing system affords ml opportunity to obt,ain further data on: (I) the influence of environment on ~ C contents; (2) rates of tsot,opicexchange between carbonates of different generations and bicarbonates; and (3) sources of CO,, and mechanisms for its product, ton. EXPERIMENTAL In coaJ seams the highest concentrations of carbonates, especially calorie, are frequently found along root" margins. Consequently,where possible, samples were taken from several levels wLthin individual seams so that, verttcal variations might, be determined. "' ALl value, s o1' ~',' ~C and ,', '"C) are reported relaL,ve to Peedee Belemntte ( P D B )

139

Samples of coal were selected at various levels from the Castor, PoUux, Rider and Nipan seams &ore the Bowen Basin; Prom the Balgownie, Greta, Wongawilli, Bulli,Tongan'a and Fassil'ernseams from the Sydney Basin; and &ore the A/B seam in the Degulla area of the Galilee Basin. A sideriticshale Prom the Brolga No.l weU in the Cooper Basin was also sampled. Locations of samples within seams, together with analytical data, are given in the Appendix. Frequently, coals from the Bowen Basin show extensive thermal alteration owing to post.Permian intrusions of volcanic rock and to the ancient burning of coal seams {King and Jensen, 1966; King and Goscombe, 1968). A range of normal and apparently heat.aJtered coals was therefore included in the samples taken Prom this basin, so that isotopic changes in carbonates due to thermal effects might be observed. The heat-altered coals were &ore bores IV888, N895 and N896. These bores all penetrate a region or severe heat-alteration (Staines, 1972) and, in Pact,,the coal from N896 is visibly coked.

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In add=tion to these coals, a ser,es of single samples was collected at, widely spaced mtervals E'om normal uncorrelated seams along the eastern margm o1" the basin (bores N814, N824, NS2?, NS33 and NS45) to show the geographical extent of any isotopic features revealed. The locations of all bores and samples from the Bowen Basin are shown in Ftg.l. The coals and shale were coarsely crushed to 1 mm and calcite and sldent,e were handpicked under the microscope. X-ray diffraction analyses or the hand picked carbonates showed the separation of types by this method t,o he very satmfactory, as the carbonates in the fractior~ were essentially monomlnerallc. CO,, for isotopic analysis was liberated from calcite by reaction with 100% H~P(.'), at, 25"C (McCrea, 1950). Siderite reacts very slowly with H~'PO,4 and a du'ect comparison with calctte under these standard conditions ts difficult. Here, in an att~.mpt to overcome or reduce this problem, acid and carbonate were mltmlly mixed at 80"C and then allowed to react, for 72 h at 25~'C. Standard calcites treated in this way, rather than by the method of McCrea, as expected, showed no change in the I:~C contents of resulting CO,,. However, I~O contents were decreased by 1.2°/0.. Therefore, 180 contents of s.derites determined in this manner have been corrected by this amount. 'The ~:~C/~2'Cand 180/l~O isotop!s- ratios of the CO~ samples were measured relative to PDB using a Mtcromass I'') 602 mass spectrometer. The precision of measured motoptc rattos is l)t ~C :1: 0.2°/u.; ,~l~O ~_0.4u/,,j. A total of 142 coal samples was exammed. Twenty-foLir or these contaJned both calcite and slderH,e, 44 contained only calcite and 31 only siderite. The remainder were carbona Le-free RESULTS A N D DISCUSSI(-)N The total isot,opw data are presented grapillcally m F~.1.2 and m the form of frequency diagrams tn Fig.3. The isotopic composition of the siderite, although variable, shows much less variation in I~C content than the calcite, and h,q.,~a significantly smaller r=ige of ,')180values. Ofl,en siderite and calcite could not, both be handpicked from the sarne coal sample and thus a direct, cornpar=son of the total data IS not strictly justifiable. A more real.i~tc apprmsal of isotopic relationships between the carbonates ts afforded by Fig.4. Here in formation relating only to coexisting siderite and calcite is included. The ab senee of any regular tsot,optc relationship between the i~C values of these close. ly associated carbonates is m accordance with the view previously ~xpressed that. these two minerals represent different,, unrelated generations of carbonate. Evidently, exchange of C has been m m u m a l for this difference in I'~C contents to have been malnt,amed over geolo$cal time. O n t,he other hand, it,is not clear whether the broad slmdarity m the ,SIBO values of the carbonates (calcites -16.4 .f-5.2°/0., stderltes -I 6.3 "f-3.7%.) can be attributed to exchange wlth oxygen m groundwater at, the temperatures attained in bituminous coal seams (100"C), or whether the values reported here are representatlve of original =sot,oplc compositions. The former explanation appears more reasonable, but.

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does not satisfactorily account for the very smatl variations in '80 contents observed between well.preserved, hard sideritic spherulites and those which are crumbling and apparently partiagy oxndized, unless isotopic exchange of both snderit,e forms with groundwater ha,~ been vnrtuatly complete. Certainly the range of 'UO values found contrasts sharply with the values reported for dia. genetic carbonates from the Jurassic Kimmeridge Clay. These latter h'aO values are considered to reNect largely diagenetic temperatures and range from 0 t.o -6°/0., (Irwin et at., 1977). Another surprising feature, in view of the isotopic constancy of coal itself, is the variatnon within particular seams of both the "~C and '•O contents of associated carbonates. The suggestion is made that presumably the isotopic composition of these carbonates is largely controlled by local variations in fluid permeabiU ties. Previously it, has been widely accepted (Degens, 1969; Schwarcz, 1969) that only a few classes of compounds, including uncommon marine and saline

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carbonates, have b"~C values of ÷5%o PDB or more. On the basis of information referred to above (Murata eL al., 1967, 1969; Deines, 1968; F'ritz et el., 1971 ) and the preliminary, data listed here on carbonates associat,ed with coal seams, it, appears, m fact,, that, a very considerable reservoir of isotopK~aUy "heavy", and largely biologically-derived, carbonate ex ist,s m close proximity to reducing carbonaceous sediments. Prmzary carbonalc depostHon - 8zder, Lcs

At the surface of coal-forming swamps, where access to atmospheric 0., ts unrestricted, products enriched in ~"C resulting from the o×idatlon or micro bial utihzation of photosynthetical derived biogenic residues might, be expected. That, such processes did not always proceed {,o completion =s clearly ewdenced by the deposition of coal. HoweveL it, seems remarkable that, there is, as yet,, little or no evidence of isotopically "light" biogenic calcite or siderite in associaUon with coals. Presumably, although considerable corl. cent, rations of CO: might, have been generated, high acidit, les and O~ levels in surface waters prevented the formation of either carbonat,e; only where an. aerobic condthons were established was siderite deposlt, ed. Fact,ors possibly affecting the isotopic composition of the CO,, available for slderit,e format, ion under such condit, ions are: (1) the generation of heavy CO,~ together with light, CH,~ by anaerobic ferment, at, ion reactions, and (2) thedi.rect bacterial reduction of CO,, t,o CH4 by kinet, ically controlled reactmns which result in a =~C enrichment of the residual CO,,. The biological producUon of CH4 by these processes appears to be curt,aded by the presence of sulphate or sulphide (Claypool and Kaplan, 1974; Lrwm eL el., 197"/). However, in the largely freshwater environments in which most, coals are iniUally deposited, complete sulphate reduction and the removal of sulphldes as precipitates might be expected to be accomplished rapidly at, correspond ingly shallow depths. The bacterial fermentation of simple orga.nlc molecules has previously been suggesLed (Fritz et al., 19'71 ) as the mechanmm For siderite formaUon in other sit,uattons. The data presented here on siderite associat,ed with coals appear to support, t,hL,~ conclusion and iUust,rat.e the major role played in (.rarbonaceous sedtments by fermentation reacUons. The vanat, ion tn the motopic composi Lion of the siderite (4.2 + 3.2°/..) is of interest,, as this presumably reflects the t;yplcal early coal-forming environment. Although there are small, but possibly significaJlt, isotopic vanat, ions in siderites from different coal seams, no regular variations, part, icularly with re spect to depth, are observed within seams. Except, ions (,o this general finding are the ~=C enriched, extensively heaL-altered siderites (l~lg.2, samples a, b and c, and Fig.3) from the Pollux seam of the Bowen Basin (bore NS96). Evidently in the case of these siderites, isotopic exchange of Cbet, ween the carbonate and surrounding coked coal has been substantial.

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Scccmdary carbonate del~OStlttnt - Cah'ttes A similar general p~ct,ure to that, gwen above c a n n o t be p ~ n t e d for the cltstribuLion mid isotopic compostt, lon uf calclt,es. It, was e x p e c t e d that the ~J(.' c,.)nt,ent,s o f these would .also tie heavily influenced by the closely a,.,~socmt.ed a c c u m u l a t i o n s oF p h o t o s y n t h e t , wally-denved organw materml. This view was held, since t,hose o t h e r massive secondary o c c u n ' e n c e s (.)f caloit.e WtllCh exist, in a,.~soclat, lon with altered e t u d e oi is o,' w h wh h ave been d e p o s i t e d as blogen ical ly derived caprocks ( T h o d e eL aJ , 1954 ) are c o r r e s p o n d i n g l y enriched in t,he I,ghter isotope. In fact, as shown in Pigs.2 and 3, c~cfl,es with I'~C eont,ents up proxlmaUng those el' the assocmted coals (~'~C: - 2 3 . 9 tu - 2 6 . 0 o / . . ) are u m'om men. Moreover, if the calcites associated with tleat alt, ered coals from bores NS88, NS95 and N896 m the Bowen Ba,sm are e x c l u d e d from consideration on the basis o f their beiJlg atypical and probably substant, vally .altered by =sot.epic ex change with the s u r r o u n d i n g coals, then from t,he Appendix, it, is clear that, Ileavy calcit, es p r e d o m i n a t e both in frequency o f o c c u r r e n c e and concentral, ton, and that I,ght, calcites are generally u n c o m m o n and m low concentrat, ion. In view of. ( 1 ) the late st,age f o r m a t m n oF the r e m m m n g typwal d,agenet, w calcit,es at, seam t e m p e r a t u r e s presumably prohtblt, ing or severely limit,=ng biological act,~v=ty; and (2) the wider range in isot,opic c o m p o s i t i o n o f t,hese calcites relaUve to the siderites, a different, genesis for each c a r b o n a t e type is indicated. W~thm the coal seams e x a m i n e d , the situation is futt,her c o m p l w a t e d by tsot.opwally " h e a v y " calcites generally being found only m the roofs or towards I.he tops o f coal seams. This is not t,o say that .all cale~t,es so located are on riched In ~C, a,,; ts evident from the mfoiTnat,lon on b o r e h o l e 14 from the A / B seam o f the Galilee Basra. Tills seam m 16 m thick and was sampled m corn plet,e cross-section. T h e largest ,~,~*C value obt',uned was only -6°/0(~, and the average calcite value for the whole seam was - ! 4 2°/,.~ Since the orlglllal source, t_Drsources, o f the calot,e tn nuue of the seams can be known w~t,h any ce~a,amt,y and, since calcites w i t h / ' ~ C values e x c e e d i n g ÷5o/.o m'e utherwme c o m p a r a t i v e l y rare, ~t is presumed that those caJoLes strongly enriched in ~'~C are p r o d u c t s of sectmdary., strongly t'ractlonat, mg pro cesses. If th~s Is so, then, when t,he possible k n o w n excha.nge processes leading t,u substantial e n r i c h m e n t s tn ~C are reviewed, ~t, ~s evident, t h a t ' l l ) O n the m f o r m a t m n provided earlier, neither bacterial f e r m e n t a t i o n and the a c c o m p a n y i n g c o p r o d u c U o n o f CH.~ a.nd CO:, nor isotopw ex~'hange w~t.h existing s~der~te could produ~'e calcites wfl, h such high ~C c o n t e n t s (~r such varied mot,opw compos~Uons; 12) A kmetwally preferred reduction o f '"C enriched c a r b o n a t e species to CH,~, under e x t r e m e reducing conditions, and a c u r r e s p o n d m g increase ~n the ~*(? c o n t e n t o f the res~du'al c a r b o n a t e does n o t readily explaJn the isotopic distrlbuUon Claypool and Kaplan ( 1974 ) ca.It,dated that, at, 25"C, rectuct, ion of some 50% or the total avmlable C(): is required ~f the ,',~C value o f t.he

145

residual carbonate is to be increased from -20 to +200/oo PDB. At higher temperatures, a larger percentage conversion is required to produce thesame isotopic effect. Accordingly, reduction in this manner should be characterized by an reverse relationship between the 4' 1C value and carbonate concentration. No t,rend ,n this direction was seen in the samples examined, suggesting, on th,s evidence at, least, that reduction of CO,, per se plays only a minor role m calcite formation. (3) Since CH,~ is a major product of the maturation of bituminous coal, isotopic exchange and equilibration between pre-existing fossil carbonate and CH4, as prevtously suggest,ed by Murata et, al. (1967, 1969) to account for high concentrations of "~C in certain mar,ne shales, might also be of importance here. However, a significant, difference between the two systems is that, In one, the fossd, marine carbonat,e affords a C source isotopica.lly dist, iuct from the associated carbonac'eous shale, whilst, Ln the other, coal itself ,s almost, certain. ly the source of C for enclosing carbonates. Finally, a mechanism for heavy calcite formation is proposed which largely overcomes the problems ,nherent, m the sol,d-sLate exchange reactions between carbonate and CH.4 and also satisfactorily accounts for the distribution of the calcite. If it, is agreed that the coal is the most likely pr,mary source of carbonate-C, then isotopic exchange between CO~. and CH4 within the coal seam must, also be regarded as a possibil,t,y. It, is suggested that, heavy calcite ,s deposited along the upper seam marsns at, ~ose sites where escaping CO,, ennched m '~C owing to exchange w,th CH4, e,ther reacts with metal ions in solution or ex changes with preexisting carbonates. The former =s the alternat,ve presently favoured since, in a continuing, parallel study of younger coals, I,ttle calcite has yet been seen. This view is confirmed when the normal unaltered coals from the BHP 28 bore and from the Sirius Creek NoJ mine comprising the Castor, Pollux and R.ider seanls from the Bowen Basin are considered. The distribution and isotopic compomtmn of the calcite in these coals are shown In Table I. The coals examined have an age of some 230 Ma and give w)latile matter yields approximating 28% (dry ash-free basis). The temperature of coal,flcat,ion of these coals can be calculated from these data as approaching 80"C (Ka.rweil, 1955). However, since for much of the past, 100 Ma the overburden

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146

has been ~eagly reduced, t,emperatures prevadmg within the seam musl, also have been lower during t,his laLt,er period (M. Shibaoka, pets. commun., 1976). Calculation of t,emperagures at,tinned dunng the period of coalll'lcatlon when the overburden was great,est,, gwes a maximum temperature closer t,o 100"C, for a volatile matter yield t,o be reduced to 28~,. A rract, ionat, ton I'acLor o1' 1.055 has been calculated for I~C exchange bet, ween calcite and CH4 at 90"C, t,he mean or these t,wo coalil"ication l,empera. t,Lires (Bottinga, 1969). Consequently, il" an average measured b I ~C value or ap proxlmat,ely ÷ 15°/00 is ascribed to the heavy calcites occumng in the Bowen Basin coals (Table I), then a corresponding b l'~C value of about, -400/oo is requtred for the CH4 m isotopic equibbnum with the pa.rent CO,. Priednch and Ji.lngt,en (19"/2) have shown CH,4 desorb~d from coa.I of t,his rank (ret'lectmwe 1.25) i.o have a hl~C value of approxm'mi,ely -40o/.o PDB. Thus, a mechanism involving 'JC exchange between CH~ and CO,, mid the later deposit, ion or this a,~,calctte, is support, ed by the general tsot,optc distribution o1" C in the syst,em. The degree of I'~C em'ichment, and the occurrence and content, ration of calcites deposited along coal seam margins thus appear dependent, on : ( 1 ) isot,opic exchange between C species within the seam and t,he format, ion or heavy CO,,, and ell, her (2) Lhe avmlabillt,y, m close proxlmiL,y to the seam, of metal ions t,o react, wit, h and precipital,e the CO,, as carbonate, or (3) a con t,lnuing tsot,oplc ex~.~hange between early carbonate and later CO,. Fh'esumabiy, in the absence of these factors, concentrations o1" calcii, e ate insignif,cant,, or else calCll,e exhibits little enrichment, in I'~C. Clearly the l,emperal, ure requtred for isot,opic exchange bet, ween COz and CH4 and the accompanying deposition ot' heavy calcite may not be Leo high since, in those porl, lons of the seams which have been visibly heat,-alLered by magmat, ic intrusions, only isot,optcally very light, cal~:ites and stderltes occur. These presumably result from chemical mt,eraction or isoLopic exchange between carbonates and the bulk of Lhe 12C-ennched coal at, t,emperat,ures above those norma.[ly at,rained tn coal seams. Schidlowskl et at. (19'76) have called atgenl, iorl t,o a Precambriml sedimentary carbonate province in which b"3C values range rrom +2.6 to +13.6°/o,, and average +8.2 ± 2.60/00 PDB. The formal, ion of such heavy carbonal,es is regarded as "st, rong evidence of an exceptional depositional envh'onment," and evaporit, ic or sl,agnant, basin conditions are suggested. The heavy, ealcit,e sequence ~sociat, ed with the Bowen Basin coals has already been shown to ex tend over a distance el' 250 k.m and, as yet,, t,here is no reason to belteve this dis{,ribution of carbonat, e or mode of genesis t,o be uncommon. It, seems not improbable that, t,he further analyses of carbonat,es associated dizect, ly with mature organic restdues dating back t,o the Fh'eeambrian will reveal the exist,ence of more carbonate reservoirs unexpectedly and unusually enriched ul ' ~C

147

CONCLLISIONS

Disseminated sidertttc spherulites associated wtth Australian Permian coals are pr=mary products of the coaJ-form,ng envu~onment, and result from the Rxa tion of COz liberated during the early anaerobic fermentation of organic materials. There is no evidence to suggest that primary, isotopicalJy light, btogenie carbonates result, from the oxtdatton or photosynthetically derived materials. Calcstes are generally secondary in nature and occur largely as fillings bl cleavages along the upper margins of coal seams. It appears that, tsotopic exchange between CO,, and CH4 is frequently established within coal seams. At those sttes at whtch the '~C-enriched CO2 escapes from the seam, mteracUon w,th metal ions in solution or isotopic exchange with earlier carbonates results m the deposttion of heavy carbonates wtth b"~C values ranging up to +25o/,,. Calcites with h~'~C values of zero or less are comparatively rare in normal coals. The dtscovery, of these new reservoirs of ~C-ennched calcite suggests that some minor modificatton to the calculated average value of the terrestrial ~3C/'=C ratio is required. Although tsotoptc exchange between CH.4 and CO,,. appears to occur fre quently, the exchange between siderite and calctte appears to take place only m regions of extreme thermal alteration. ACK NOW LEDG EMENT

We are grateful to the marly companies who supplied the coal samples used m this study.

REFERENCES

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148

Fr,tz, P , B i n d u , P L,, FolLnsbee, F R and Ktouse, H R , 197] I s o t o p , c c o m p o s l t , o n o r d m genet,c siderites from Cretaceous sedu'nents in western Canada. J SedimenL Petrol , 41 282- 288

C'ahmov, R M and C,irin, Yu.P., 1968. Variation ,n the isotopic composition of carbon during the formation o1' carbonate concretions Geochem. Int., 5: 178-182. Irwin, H., Curt, is, C and Coleman, LI., 1977 Isotopic evidence for source of d,agenetm carbonates rormed during burial ol" organic rich sediments. Nature (London), 269 2(39-213 K a r w e , I , J , 195b D=eMetamorphoseder KohJenvom Standpunktder physikalischen Chemte. Disch. C,eol Ges. Z., 107. 1 3 2 - 1 3 9 Kemezys, M. and Taylor, C,.H., 1964 Occurrence and dmtr=bution o1' m,nerals in some AusLTalian coals. J. Inat Fuel, 37' 3H9-397 King, D. and C,oecombe, P.W., 1968. Coal geology or the Bowen Basra QId C,ov Mm J., Nov 1968, pp.492-499. K,ng, D and Jermen, A.R.., [966. Fused coal measures m the Bowen Basin QId. Coy. Mm J , (Nov. 1968), pp. 4 9 2 - 4 9 9 . McCrea, J.M., 1950 On the isotopic chemistry or carbonat,es and a paleotemperaturescale J Chem. Phys., 18 849-85'7. Murata, K.J., Friedman, 1.1. and Madsen, B M., 196'7. C,a.rbon 13.r,ch diagenet,c carbonates m Miocene Formation o1' Calil'ornia and Oregon. Science, 156: 1 4 8 4 - [ 4 8 5 . MuraLs, K J., Friedman, I I. and Madsen, B M , 1969. Isotopic compositio, or dragenetic carbonal,es ,n marine Miocene rormat=ons of Cal,rorn,a and Oregon [3 S. C,eol. Sure , Pror. Pap., 614 B. Nissenbaum, A , Presley, B.J. and Kaplan, I R.., 19'72. Early d,agenesm m a reduc,ng fjord, Saanich Inlet, British Columbm, 1 Chemical and isotoptc changes in major' components, of interstitial water C,eochim. Cosmochim. Acts, 36' 100'7-1027 Oana, S. and Deevey, E.S., 1960. Carbon 13 in lake waters and =is poss=ble bearing on paleolimnoloi,w.. Am J. Sci (Bradley Volume), 235A: 253-2'72 R.osenl'eld, W.P and Silverma,, S R , 1959. Carbon ,sotope rractionation =n bacterml productionol'methane Soence, 130 1 6 5 8 - 1 6 5 9 Scl-udlowskJ, M , Sichmsnn, R and Junge, C.E , 1976 Carbon mot,ape geochemistry or the Precambrtan bomagundi carbonate province, Rhodesia C,eochim Cosmochim Acts, 4(') 449--456 Schwartz, H P, 1969. taotopes m nature, 1 The stable motopes of carbon. In' K.H Wedepoid (Editor), Handbook ol" Geochemistry, II/1 Spr, nger, Berhn, pp6-B 1 - 6 B 15 Staines, H.R.E, 1972. Correlat,on ol'seams in the Rangal Coal Measures, Mackenz,e River Sttiua Creek, Blackwater CoalField. C,eol. Sure QId., Rep. No.70 Thode, H.C" , Wanless, R K and Wallouch, R , 1954. The origin of nat, re sulphur clepos=ts rrom motope I'ractionation st,udies. C,eochu'n. Cosmochim Acts, 5 2 8 6 - 2 9 8 . Weber, J N., WiUiams, F.G and Keith, M . L , 19R4 Paleoenvironrnenl.al signiJ'icance or carbon ,sotopic composit,on or siderite nodules ,n some shales or Pennsylvanian age J Sediment. Petrol, 34 8 1 4 - ~ 1 8

149

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