Functional groups and elemental analyses of cuticular morphotypes of Cordaites principalis (Germer) Geinitz, Carboniferous Maritimes Basin, Canada

Zodrow, Erwin L; Mastalerz, Maria; Orem, William H; Šimunek, Zbynek; Bashforth, Arden Roy

Published in: International Journal of Coal Geology

Publication date: 2000

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Citation for published version (APA): Zodrow, E. L., Mastalerz, M., Orem, W. H., Šimunek, Z., & Bashforth, A. R. (2000). Functional groups and elemental analyses of cuticular morphotypes of Cordaites principalis (Germer) Geinitz, Carboniferous Maritimes Basin, Canada. International Journal of Coal Geology, 45(1), 1-19.

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Functional groups and elemental analyses of cuticular morphotypes of Cordaites principalis ž/Germar Geinitz, Carboniferous Maritimes Basin, Canada Erwin L. Zodrowa,) , Maria Mastalerzbc , William H. Orem , ZbynekÆÊ SimunekÆ d , Arden R. Bashforth e,1 a Department of Earth Sciences, UniÕersity College of Cape Breton, Sydney, NoÕa Scotia, Canada B1P 6L2 b Indiana Geological SurÕey, Indiana UniÕersity, 611 N. Walnut GroÕe, Bloomington, IN 47405-2208, USA c U.S. Geological SurÕey, MS 956, National Center, Reston, VA 22092, USA d Czech Geological SurÕey, KlaroÂÕ 3r131, 118 21 Praha 1, Czech Republic e Department of Earth Sciences, Memorial UniÕersity of Newfoundland, St. John's, Canada, A1B 3X5 Received 29 July 1999; accepted 19 June 2000

Abstract

Well-preserved cuticles were isolated from Cordaites principalis Ž.Germar Geinitz leaf compressions, i.e., foliage from extinct gymnosperm trees Coniferophyta: Order Cordaitales. The specimens were collected from the Sydney, Stellarton and Bay St. George subbasins of the once extensive Carboniferous Maritimes Basin of Atlantic Canada. Fourier transformation of infrared spectraŽ. FTIR and elemental analyses indicate that the ca. 300±306-million-year-old fossil cuticles share many of the functional groups observed in modern cuticles. The similarities of the functional groups in each of the three cuticular morphotypes studied support the inclusion into a single cordaite-leaf taxon, i.e., C. principalis Ž.Germar , confirming previous morphological investigations. Vitrinite reflectance measurements on coal seams in close proximity to the fossil-bearing sediments reveal that the Bay St. George sample site has the lowest thermal maturity, whereas the sites in Sydney and Stellarton are more mature. IR absorption and elemental analyses of the cordaite compressions corroborate this trend, which suggests that the coalified mesophyll in the leaves follows a maturation path similar to that of vitrinite. Comparison of functional groups of the cordaite cuticles with those from certain pteridosperms previously studied from the Sydney Subbasin shows that in the cordaite cuticles highly conjugated C±OŽ 1632 cmy1. bands dominate over carbonyl stretch that characterizes the pteridosperm cuticles. The differences demonstrate the potential of chemotaxonomy as a valuable tool to assist distinguishing between Carboniferous plant±fossil groups. Published by Elsevier Science B.V.

Keywords: Cordaites compression leaves; cuticles; Carboniferous; FTIR; elemental analyses

) Corresponding author. 503 Coxhead Road, Sydney, N.S., Canada B1R 1S1. E-mail addresses: [email protected]Ž. E.L. Zodrow , [email protected] Ž M. Mastalerz . , [email protected] Ž. W.H. Orem , [email protected]Ž. Z. SimunekÆ Ê , [email protected] Ž A.R. Bashforth . . 1 Presently at Anderson Exploration, 324 8th Ave. SW Calgary, Alberta, Canada T2P 2Z5.

0009-2541r00r$ - see front matter. Published by Elsevier Science B.V. PII: S0166-5162Ž. 00 00018-5 2 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

1. Introduction Ž.Fig. 1B and C . This circumstance provided the significant opportunity for a comprehensive study of Cordaitean fossil leaves Ž.Cordaites, Unger 1850 the cordaitean compressions in the basin. As a result, are known from early Carboniferous to early Per- five new cuticular morphotypes were established for mian deposits of the Euramerican palaeokingdom the Carboniferous leaf taxon Cordaites principalis Ž.Rothwell, 1988 , representing a lifespan of ca. 80 Ž.Germar Geinitz Ž Zodrow et al., 2000 . . million years. The cordaites trees from which the The impetus for the present study stems from the cordaitean leaves originated constituted a diverse recognition that future progress in phylogeny of Eu- group of extinct gymnospermous plants that had ramerican cordaiteans requires more adequate taxo- extremely variable growth habits and palaecological nomic parameters than are presently available. In this tolerances. Mire-dwelling cordaites trees included investigation, methods of Fourier transformation of mangrove-like forms up to 5 m tall with aerenchy- infrared spectraŽ. FTIR and elemental analyses are matous, stilt-like rootsŽ Cridland, 1964; Raymond, applied to three representatives of the five cordaitean 1988; Raymond and Phillips, 1983; Costanza, 1985. , morphotypes. The purpose is to assess the applicabil- and small, thicket-forming, understory shrubs ity of these techniques in classification, and to deter- Ž.Rothwell and Warner, 1984; Costanza 1985 . By mine which parameters could be of importance for comparison, cordaites trees growing on drier, well- future research in cordaitean chemotaxonomy. drained clastic substrates, such as floodplains, river levees, or extrabasinal lowlands were very tall, for- est-forming trees that towered tens of meters high ŽGrand'Eury, 1877; Mapes and Gastaldo, 1986; 2. Methods Rothwell, 1988; Rothwell and Mapes, 1988. . Cordaitean leaves, which can reach 1 m in length, Cuticles were prepared by macerating the com- are strap-like or linear in shape with longitudinal pressions from 7 h to 3 days in Schulze's oxidizing venation pattern that parallels the leaf marginŽ Fig. solution that consisted of 150 ml 70% nitric acid 1A. . The foliage is a common component of com- with 3±5 g dissolved potassium chlorate. After oxi- pression assemblages and has been exhaustively in- dation, samples were neutralized in a 4.5% ammo- vestigated since Grand'EuryŽ. 1877 . Based on com- nium hydroxide solution, and well rinsed in deminer- parative cuticle morphology, FlorinŽ. 1931, 1951 alized water. Through this process, 200 cuticular postulated that cordaites were ancestral to conifer mounts were prepared, and five new cuticular mor- trees, but the exact nature of the relationship between photypes of C. principalis Ž.Germar were erected the two taxa is equivocalŽ Meyen, 1984; Crane 1985; Ž.Zodrow et al., 2000 . Representative samples of Rothwell, 1986. . Alternatively, both taxa may have three of these cuticular morphotypes and their com- been derived from a common progenitorŽ Rothwell, pressions were investigated. Compression mounts 1977. , such as the progymnospermous Ar- were routinely examined under a light microscope to chaeopteris Ž.Beck, 1981 , or a pteridosperm Ž Roth- determine the presence of pyrite and other minerals, well, 1988. . and to observe variation in coalification patterns. Cordaitean compressions were first recorded from Specimens for FTIR were prepared using the the Carboniferous in New Brunswick and Nova Sco- potassium bromideŽ. KBr pellet technique. A very tia, Canada, by DawsonŽ. 1868, 1891 , and studied small amount of the cuticle or compressionŽ ap- systematically by BellŽ. 1940, 1944, 1962 . Since the proximately 2 wt.% of the mixture. was mixed with fossil-bearing strata in the Carboniferous Maritimes finely ground KBr to produce pellets. These were Basin covering parts of Nova Scotia, New Brunswick, analyzed on a Nicolet 20SXC spectrometer, equipped and NewfoundlandŽ. Fig. 2 generally have lower with a DTGS detector, at a resolution of 4 cmy1, thermal maturity, as a result of having experienced collecting 1024 scansrsample. The infrared signal limited tectonism and burialŽ Hacquebard and Ž.IR was recorded in the region between 400 and Cameron, 1989. , cordaitean cuticles are well pre- 4000 cmy1 wavenumber. Bands were identified by served and show delicate stomatalrepidermal details comparison with published assignmentsŽ Painter et E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 3

Fig. 1. Cordaites principalis Ž.Germar Geinitz, compressions and cuticles. Ž. A Fragments of leaf compressions with typically thick, primary veins parallel to the foliar margins. Bay St. George Subbasin, Newfoundland. B-24, cm scale.Ž. B Intact adaxial Ž. ad and abaxial Ž. ab cuticle, showing the typically elongate cells for morphotype 1, Bay St. George Subbasin, B-228. Scale bars60 mm.Ž. C Intact abaxial cuticle of morphotype 4, showing stomatal apparatusŽ. o . Sydney Subbasin, Nova Scotia, SY-211. Scale bars100 mm. Ž D . Mesophyllous matter on an inner surface of a cuticle from Bay St. George Subbasin. Scale bars10 mm. al., 1981; Wang and Griffith, 1985; Sobkowiak and Elemental analyses for C, H, N, O, and S in the Painter, 1992. . compressions and morphotypes were performed on 4 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

Fig. 2. Carboniferous Maritimes Basin of eastern, Canada, and study areas of the three subbasins.

dried samplesŽ. 608C on a Carlo Erba Elemental ous Maritimes BasinŽ. Fig. 2 . In the Sydney Sub- AnalyzerŽ. Lyons et al., 1995 . Mineral matter is basin, the compressions are entombed in grey, fis- defined as the difference between the summed weight sile, silty roof shale overlying the Lloyd Cove Seam. percent of an elemental analysis and 100%. The shale contains authigenic siderite bandsŽ details Standard X-ray diffraction methods were used to in Table 1. . In the Stellarton Subbasin, fossil leaves obtain the semiquantitative mineralogical data from occur in a fine-grained, 3-m-thick sandstone charac- rock matrices that entombed the studied compres- terized by ripple marks, and authigenic siderite. In sions. Additionally, petrography of thin sections pro- the Bay St. George Subbasin, the compressions are vided sedimentary and mineralogical data, and infor- entombed in muddy siltstone crevasse-splay deposits. mation concerning the relationship between textural This implies leaf transportation from the cordaites variation and compression preservation. trees growing within, or peripheral to, clastic swamps Ž.Bashforth, 1999 . Authigenic, lenticular masses Ž.maximum 7-mm length and 1.5-mm width of 3. Samples cuboidal pyrite are commonly found on the abaxial compression surfaces. The compressions originated from the Sydney With the exception of pyritic oxidation on abaxial Ž.Ž.Nova Scotia , Stellarton Nova Scotia , and Bay St. compression surfaces from the Bay St. George Sub- GeorgeŽ. Newfoundland subbasins of the Carbonifer- basin, no weathering effects were observed in any of E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 5 m, m m m m m 10 = m, phyllosilicates: m m m chlorite: maximum length 70 r m m m thick 5±300 m - 10 - b Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. Ž. illite 32% , kaolinite 23% Fine-grained, quartz: maximum diameter 80 illite 12% , plagioclase 9% diameter 300 illite 10% , chlorite 35% maximum diameter 80 Ž. r r r Quartz 47% , kaolinite 25% Fine-grained, angular quartz: maximum Quartz 17% , plagioclase 16% , Very fine-grained, subangular quartz: Mica Composition Texture r r r r 35 cm above an unnamed coal seam the Foord Seam siderite 5% , fine grains Cove Seam siderite 5% , bands 80 cm thick unit pyrite 4% , micron-sized maximum dimensions 110 associated coal seam a Early Westphalian D 13 m above mica Late Bolsovian basal 10 cm of mica Early Cantabrian top of the Lloyd quartz 22% , chlorite 16% , mica Semiquantitative X-ray mineralogic analysis; detection limit 1 to 3 wt.%. Approximate million of years before present. a b Stellarton 304 Sandstone Bay St. George 306 Siltstone Sydney 300 Silty shale Table 1 Geological characteristics of strata from whichSubBasin cordaitean compressions originated in the Carboniferous Maritimes Basin Age in Ma stage Rock type 6 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 Ž ells; 1: smallest guard wx wx very cutinized cuticle is visible very coalified cuticle is not visible as above aped polar cells Zodrow et veins . Ž the samples m thick vein per veins between m cm foliar cm two primary Ž. Ž. cm max. LengthŽ. Width Margin Thickness No. of primary, No. of Ž sclerotic . a SY-211 4B-178B-192 1B-206 19B-228 1B-c1 13-cm 1 2.5fragment 3B-1 15 2 parallel 8 18 4 15 40±50 1.5 6 5 ? 3 5 ? 20±21 3 nonparallel? ? as above ? 4 ? not measured range for not measured 32±34 as above 24±30 3 2 very thin, cutinized thin very and thin, `stringy' cutinized as very above thin, cutinized SL-9 2 15 4.5B-2 B-22 nonparallel 10±70 16±17 2 as above . Morphotype 4: single stomatal raw, nonstomatiferous bands are narrower than those in morphotype 1; 2: largest guard and largest lateral subsidiary c a cells, oblong lateral subsidiary cells, widest nonstomatiferous bands; 3: dimensions of guard cells between those of morphotypes 1 and 2, square-sh Table 2 Characteristics of the compression leaves, includingSubBasin morphotypes 1, 2, 3, and 4 Sample MorphotypeSydney Compressions SY-369 4 35 4 Vein Morphology nonparallel 40±50 20±24 Observations 4 clean surfaces StellartonBay St. George SL-7 B-24 2 1 18 13.5 2 3.5 parallel nonparallel 10±20 10±70 14±34 12±13 1±6 2 thinnest cuticles thickest cuticles al., 2000 . E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 7 the mineral assemblages that entombed the compres- The vein morphology of the studied cordaitean sion samples. An observation isŽ. Table 2 that thick- compression fossilsŽ. Table 2 fits the classical con- ness of the cuticlesŽ. visual estimates correlates posi- cept of C. principalis Ž.ŽGermar summary: Zodrow tively to thickness of the compressions. et al., 2000. .

Fig. 3. FTIR spectra of cuticular morphotype 4 from SydneyŽ. A , and of morphotype 2 from Stellarton subbasins Ž B, C . . 8 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

Table 3 IR absorbance ratios of cordaitean cuticles and compressions r r Subbasin Sample Morphotype CH 23CHŽ.Ž. 2800±3000 1600±1800 Cuticles Sydney SY-369 4 2.8 0.3 SY-211 4 2.8 0.3 Stellarton SL-7 2 3.1 0.6 SL-9 2 4.0 0.5 Bay St. George B-24 1 3.0 0.4 B-178 1 2.9 0.5 B-192 1 4.7 1.2 B-206 1 1.8 0.3 B-228 1 4.5 1.3 B-c1 3 ± ± B-1. one fragment 2 7.1 0.3 B-2. B-22. 5.7 0.4

r r Subbasin Sample Morphotype CH 23CHŽ. 700±900 2800±3000 Compressions Sydney SY-369 4 2.4 0.7 SY-211 4 2.7 0.9 Stellarton SL-7 2 2.6 0.7 SL-9 2 2.1 1.4 Bay St. George B-24 1 2.7 0.1 B-178 1 0.4 0.4 B-192 1 2.1 0.1 B-206 1 2.4 0.1 B-228 1 ± ± B-c1 3 1.8 0.2 B-1. very cutinized 2 4.4 0.0 B-2. very coalified 1.5 0.2 B-22. very coalified 2.3 0.2

±, Insufficient sample amount.

Table 4 Elemental, mineral-freeŽ. bracketed C, H, N, S, O, mineral matter, and atomic ratios HrC and OrC of the compressionsŽ. com and the cuticular morphotypesŽ. cut Subbasin Sample Morpho- %C %H %N type Com Cut Com Cut Com Cut Sydney SY-369 4 71.22Ž 75.63 . 51.18 Ž 63.27 . 5.40 Ž. 5.74 6.06 Ž. 7.50 2.02 Ž. 2.14 3.42 Ž. 4.23 SY-211 4 70.35Ž 73.04 . 49.47 Ž 60.37 . 5.13 Ž. 5.32 6.11 Ž. 7.45 2.50 Ž. 2.60 2.94 Ž. 3.59 Stellarton SL-7 2 61.24Ž 79.63 . 50.78 Ž 63.70 . 3.69 Ž. 4.80 5.69 Ž. 7.13 2.43 Ž. 3.16 3.47 Ž. 4.36 SL-9 2 73.78Ž 77.80 . 47.36 Ž 62.98 . 5.34 Ž. 5.63 5.37 Ž. 7.14 3.00 Ž. 3.17 2.77 Ž. 3.68 Bay St. B-24 1 52.05Ž 59.89 . 53.62 Ž 61.67 . 4.72 Ž. 5.44 7.11 Ž. 8.18 1.03 Ž. 1.19 4.64 Ž. 5.34 George B-178 1 45.44Ž 62.67 . 41.64 Ž 62.11 . 4.93 Ž. 6.80 5.53 Ž. 8.24 0.87 Ž. 1.19 2.10 Ž. 3.12 B-192 1 71.02Ž 75.39 . 39.07 Ž 60.15 . 6.04 Ž. 6.41 5.21 Ž. 8.03 1.64 Ž. 1.74 2.05 Ž. 3.15 B-206 1 53.50Ž 64.11 . 56.62 Ž 64.71 . 4.88 Ž. 5.85 7.20 Ž. 8.22 1.00 Ž. 1.19 3.16 Ž. 3.62 B-228 1 ± 43.50Ž 63.25 . ± 5.79 Ž. 8.42 ± 2.58 Ž. 3.75

±, Insufficient compression sample. aAssumed mineral matterswŽ.Ž100% y %CqHqNqSq0. .x bCorrection factors for nitration and oxidation due to maceration cannot be applied, as they are unknown for cordaites. E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 9

y1 r 4. Results cm. , and lower CH 23CH ratio in compressions Ž.Table 3 . In the out-of-plane region, compression 4.1. FTIR analysis SY-369Ž. Fig. 5A , two aromatic bands are distinct Ž750 and 813 cmy1 . , whereas the band at 857 cmy1 4.1.1. Sydney Subbasin, NoÕa Scotia is of very low intensity. The ratios of aromatic Two specimens, SY-369 and SY-211, represent- out-of-plane to aliphatic stretching bands for the ing cuticular morphotype 4, were analyzed. Both compressions from the Sydney SubbasinŽ 700± r y1 show similar characteristicsŽ. Fig. 3A . The CH2 and 900 2800±3000 cm.Ž are 0.7 and 0.9 Table 3: CH3 bands in the aliphatic stretching regionŽ 2800± SY-369 and SY-211. . y1 r 3000 cm. are distinct, with a CH 23CH ratio of 2.8Ž. Table 3 . The oxygenated groups are repre- 4.1.2. Stellarton Subbasin, NoÕa Scotia sented by a prominent band at 1632 cmy1 Ž C±O Two cuticular specimens, SL-7 and SL-9, repre- highly conjugated. and a shoulder at 1710 cmy1 senting morphotype 2Ž. Table 3 were analyzed Ž Fig. Ž.carbonyl stretch . The ratio of absorbance of the 3B and C. . They show that the functional-group

CH23 plus CH groups vs. oxygenated groups characteristics are generally similar to those in the Ž2800±3000 cmy1 .Žr 1600±1800 cmy1 . is approxi- Sydney Subbasin. The main difference between the mately 0.3. Aliphatic groups in the bending mode Sydney and Stellarton cuticles is a relatively higher around 1444 cmy1 are also distinct. The C±O groups absorbance of aliphatic stretching bands for the lat- in the 1030±1200 cmy1 range are of low ab- ter. This observation is confirmed by a higher sorbance. The bands at 891 and 803 cmy1 Ž SY-369: Ž.Ž.Ž2800±3000 r 1600±1800 ratio 0.5 and 0.6, Table r Fig. 3A. could be related to mineral, rather than to 3.Ž. . The CH 23CH ratios 3.1 and 4.0 are higher organic matter, also indicated by the 19.11% min- than for the Sydney cuticlesŽ. 2.8 . In addition, min- eral-matter content in this cuticleŽ. Table 4 . eral-matter peaks at around 900 cmy1 are not as Compressions from the Sydney Subbasin differ distinct as in the Sydney cuticles; in fact, a band at significantly from the corresponding cuticlesŽ com- 876 cmy1 of SL-9 is the only one detectedŽ Fig. 3B pare cuticle SY-369 in Fig. 3 to compression SY-369 and C. . in Fig. 4A. . The main differences are the presence of Compressions, exemplified by SL-9 in Fig. 4B, strong aromatic carbon band at 1608±1618 cmy1, from the Stellarton Subbasin reveal the presence of lack of oxygenated groups at approximately 1700 the same bands as in the compression from the cmy1 , distinct out-of-plane aromatic bandsŽ 700±900 Sydney SubbasinŽ. SY-369: Fig. 4A . A ratio of the

%S %O Mineralab Matter HrCOrC b Com Cut Com Cut Com Cut Com Cut Com Cut 1.79Ž. 1.90 0.19 Ž. 0.23 13.74 Ž 14.59 . 20.03 Ž 24.76 . 5.83 19.11 0.91 1.42 0.15 0.29 0.88Ž. 0.91 0.15 Ž. 0.18 17.46 Ž 18.13 . 23.28 Ž 28.41 . 3.68 18.06 0.87 1.48 0.19 0.35 0.23Ž. 0.30 0.13 Ž. 0.16 9.31 Ž 12.11 . 19.65 Ž 24.65 . 23.09 20.28 0.72 1.34 0.11 0.29 0.31Ž. 0.33 0.08 Ž. 0.11 12.40 Ž 13.08 . 19.62 Ž 26.09 . 5.17 24.80 0.87 1.36 0.13 0.31 12.34Ž. 14.2 0.15 Ž. 0.17 16.77 Ž 19.30 . 21.42 Ž 24.64 . 13.09 13.06 1.09 1.59 0.24 0.31 3.05Ž. 4.21 0.08 Ž. 0.12 18.22 Ž 25.13 . 17.70 Ž 26.40 . 27.49 32.96 1.30 1.59 0.30 0.32 1.43Ž. 1.52 0.01 Ž. 0.02 14.07 Ž 14.94 . 18.61 Ž 28.65 . 5.80 35.05 1.02 1.60 0.15 0.36 10.02Ž. 12.00 0.07 Ž. 0.08 14.05 Ž. 16.84 20.46 Ž. 23.38 16.55 12.50 1.19 1.52 0.20 0.27 ± 0.05Ž. 0.07 ± 16.85 Ž 24.50 . ± 31.23 ± 1.69 ± 0.29 10 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

Fig. 4. FTIR spectra of compressions associated with cuticular morphotype 4 from SydneyŽ. A , morphotype 2 from Stellarton Ž. B , and morphotype 1 Bay St. George subbasins.Ž. C, D .

absorbance of out-of-plane aromatic bands to the respectively. , suggesting variable aromaticity of these aliphatic groups in the stretching region gives vari- compressions. The out-of-plane aromatic region for able values: 0.7 and 1.4,Ž Table 3: SL-7 and SL-9, compression SL-9 reveals three aromatic bandsŽ 857, E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 11

Fig. 5. Out-of-plane aromatic region for the compressions associated with morphotype 4 from SydneyŽ. A , morphotype 2 from Stellarton Ž.B , and morphotype 1 from Bay St. George subbasins Ž C, D . . Band at 750 cmy1 represents orthosubstitutionŽ four neighboring C±H groups. , at 807±813 cmy1 tworthree neighboring C±H groups, while the band at 857±870 cmy1 represents penta-substituted aromatic rings containing isolated C±H groups.

807 and 748 cmy1 , Fig. 5B. , with the one at 807 4.1.3. Bay St. George Subbasin, Newfoundland cmy1 dominant, and the one at 857 cmy1 being the Six cuticular specimens representing morphotypes least importantŽ. aryl ring with isolated C±H groups . 1 and 2 were analyzed. Their spectra reveal signifi- 12 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

r cant variationsŽ. Fig. 6A±E . Cuticles B-192 and stretching bandsŽ. Fig. 6C and E , and high CH 23CH B-228 are characterized by very prominent aliphatic ratios Ž.)4, Table 3 . These two samples also have

Fig. 6. FTIR spectra of cuticular morphotype 1 from Bay St. George Subbasin. Note the prominent aliphatic stretching bands in the 2800±3000 cmy1 region and distinct oxygenated group bands at 1712 cmy1 in C and E, respectively. E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 13

r relatively highŽ.Ž. 2800±3000 1600±1800 ratios of pressed CH23 and CH bands, an almost undetectable 1.2 and 1.3Ž. Table 3 , a very prominent band at 1712 1712 cmy1 band, and a lower intensity of the 1030± y1 y1 y1 r cm , and an intense 1030±1200 cm region. Cuti- 1200 cm region. The CH 23CH ratio in this cles B-178 and B-206Ž. Fig. 6B and D have sup- group is below 2.9, and theŽ.Ž 2800±3000 r 1600±

Fig. 7. FTIR spectra collected from one 3-cm-long compression fragment associated with cuticular morphotype 2, Bay St. George Subbasin. Ž.A is highly cutinized, and Ž. B and Ž. C are highly coalified. 14 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

1800. ratio is not higher than 0.5. Based on the matter-free basis, for most samples, carbon is consis- functional-group distribution, the three cuticles B-24, tently higher, whereas H, N and O contents are lower B-178, and B-206Ž. Fig. 6 are similar to the cuticular for the compressions than for the cuticles. This characteristics from Stellarton and Sydney subbasins results in higher atomic HrC and OrC ratios for the in Fig. 3. cuticles. The higher sulfur content in compressions In addition to analyzing the individual cuticles results from pyrite adhering to abaxial surfacesŽ Ta- from Bay St. George, functional-group variations on ble 1. . The presence of sulfur in the cuticles is one 3-cm-long cordaitean-leaf fragment of highly unexpected, given the lengthy and intense oxidation variable coalificationrcutinization levels were stud- process that should have oxidized the pyrite. The ied. Although sample sizes from that fragment were very high concentrations of mineral matter in the small, resulting in IR spectra of poor quality, and not cuticlesŽ. 12.50% to 35.05% are also unexpected, as included in this paper, they nevertheless show con- optical and scanning-electron microscopic examina- r siderable variation in CH 23CH ratiosŽ. 5.7 and 7.1 , tions did not reveal significant amountsŽ Zodrow et and inŽ.Ž 2800±3000r1600±1800 ratios Table 3: 0.3 al., 2000. . However, detritus of silicate minerals are and 0.4. , along the length of a single leaf fragment. clearly visible during optical examination of the CompressionsŽ. B-24 and B-206 in Fig. 4C and D compressionsŽ. 3.68% to 27.49%, Table 4 . from Bay St. George Subbasin are very similar to On a mineral-matter-free basisŽ. Table 4 , the cu- one another, and similar to those from the Sydney ticular morphotypes from the three subbasins have and Stellarton subbasinsŽ. Fig. 4A and B . similar carbon content, averaging 62%. Compres- The main difference is that they tend to show sions, however, have variable carbon content, rang- lower aromaticity than specimens from the other two ing from highest 77.80% to 79.63% in the Stellarton subbasins. This is expressed mainly by lower inten- Subbasin, 73.04% to 75.63% in the Sydney, to the sity of aromatic out-of-plane region, and conse- lowest and most variable 59.89% to 75.39% in the quently lowerŽ.Ž.Ž 700±900 r 2800±3000 ratio Table Bay St. George Subbasin. Hydrogen content is higher 3. . Three aromatic bands are distinct in the out-of- in cuticles than in the compressions, and is generally plane region, and they occur in changing proportions highest for both cuticles and compressions in the between samples B-24 and B-206Ž. Fig. 5C and D . Bay St. George, and lowest in the Stellarton Sub- r The CH 23CH ratio is lower, compared to the cor- basin. Nitrogen content is higher in cuticles, and this responding cuticles, except in B-206Ž. Table 3 . difference is especially distinct in the Bay St. George Spectra of the 3-cm-long compression sample samples. As expected, sulfur is higher for the com- from Bay St. George Subbasin, B-1, B-22, and B-2, pressions, while cuticles have lower sulfur content in are shown in Fig. 7A±C. Spectrum B-1, representing all three subbasinsŽ. 0.02% to 0.23% . The compres- the highly cutinized area with visible cuticle, resem- sions from the Bay St. George Subbasin have high bles the cuticlesŽ intensely oxygenated groups at and variable sulfur contentŽ 1.52% to 14.2%, Tables 1645 and 1720 cmy1, and lack of aromatic out-of- 1 and 2. . Oxygen content is generally higher for the plane bands. . B-22 and B-2 that represent the highly cuticles than for compressions, and does not show coalified area of the compression fragment, without consistent differences among the samples from the visible cuticle, resemble the studied compressions by three subbasins. the presence of intense aromatic carbon band and aromatic out-of-plane bands, and absence of oxy- y1 genated groups in the 1600±1800 cm region. 5. Discussion

4.2. Elemental analysis 5.1. Comparison with modern cuticles

Table 4 presents elemental compositions of the The studied cordaitean cuticles share many func- cuticular morphotypes and compressions, and calcu- tional-group characteristics with those of modern lated amounts of mineral matter. On a mineral- cuticlesŽ. Holloway, 1982; Nip et al., 1989 . In both E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 15 modern and fossil cuticles, the most prominent bands are those related to the alkyl chainsŽ CH23 and CH groups in the 2800±3000 cmy1 range. , and to the oxygenated groups in the 1600±1800 cmy1 region. In modern cuticles, sugarsŽ polysaccharides, cellu- lose or hemicellulose.Ž , lipids cutin, waxes . , and lignin are significant componentsŽ Nip et al., 1986; Tagelaar et al., 1993; Kogel-KnabnerÈ et al., 1994. . In fossil cuticles, polysaccharides are absent, or occur only in trace amounts, cutin-derived material is pre- sent, but usually minor, lignin may be significant, whereas an important component is cutan. It is a resistant biopolymer composed of n-alkanes, n-alk-l- es and n-alpha-omega alkadienesŽ Nip et al., 1986; Tagelaar et al., 1993. . FTIR spectra show that cellu- lose is absent from most, if not all, of the cordaitean Fig. 8. Van Krevelen plotŽ. atomic HrC vs. CrO of cuticles and cuticles studied. In IR spectra, cellulose has a strong compressions from the Carboniferous Maritimes Basin: Ss y1 C±OH stretch at 1070 cm , and a strong C±O±C Sydney, TsStellarton, and BsBay St. George subbasinsŽ based stretch at 1030 cmy1 Ž Herqert, 1971; Blackwell, on Table 4. . Black ovals represents the areas of cuticle and of 1977.Ž , and only cuticles B-192 and B-228 Fig. 6: compression data from the pteridosperms of the Sydney Subbasin; Ž Bay St. George Subbasin. have increased absorbance areas for pure cutin and lignin are shown for reference Lyons et al., 1995. . in this region. If these bands are related to cellulose, this could suggest lower biodegradation for these two cuticles than for others from the subbasin. Alter- natively, the high mineral contentŽ 31.23% and 35.5%, Table 4. could account for increased ab- Macroneuropteris scheuchzeri, and Alethopteris les- sorbance in this region. However, the high mineral- quereuxii.. The plotting results show that atomic matter content in B-178Ž. 32.96%: Table 4 does not ratios OrC ratios of the cordaitean cuticles are close lead to increased absorbance in those spectral re- to those of the pteridosperm cuticles, but that the gions that suggests cellulose rather than mineral- HrC ratios of the cordaitean cuticles are consistently matter contribution. Some bands, such as at 1275 larger than those of the pteridosperm species studied cmy1, likely represent lignin, specifically guaiacyl by Lyons et al.Ž. 1995 . Fig. 8 clearly indicates a Ž.Durig et al., 1988 . The major bands of the spectra, substantial spread in HrC ratios, but a more uniform such as those in aliphatic stretching regionŽ 2800± pattern in OrC ratios in the cordaitean cuticles, 3000 cmy1 .Ž and oxygenated group region 1600± whereas the compressions show an OrC spread but 1800 cmy1 . , can, however, reflect both lignin and relatively uniform HrC pattern. This is interpreted cutan contributions, and FTIR cannot provide a dis- to be due to higher resistance of the cuticles to tinction between these two functional groups. oxidation than the compressions. Comparison of functional groups of the cordaitean cuticles to those of the pteridospermsŽ Lyons et al., 5.2. Comparison with selected pteridosperm cuticles 1995.Ž shows higher carbonyl stretch groups 1711 from Sydney Subbasin cmy1 . for the latter as the major discriminating criterion between the representatives of the two dif- Fig. 8 shows the distribution of atomic HrC and ferent DivisionsŽ Division Pteridospermophyta: Or- OrC ratios for the studied cordaitean compressions der Medullosales, and Division Coniferophyta: Order and their cuticular morphotypes, and for the cuticles Cordaitales, respectively, Taylor and Taylor, 1993. . and compressions of the pteridosperm species stud- In the cordaiteans studied, highly conjugated C±O ied from the Sydney Subbasin Ž Neuropteris oÕata, Ž1632 cmy1 . dominates over carbonyl stretch, which 16 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 is a potential avenue for further chemotaxonomic that can be related to differing maturation levels? research. The Lloyd Cove SeamŽ. Sydney Subbasin directly below the sampling site has a vitrinite reflectance

5.3. Variation in the biochemical makeup of the Ž.Rrandom of 0.65% Ž high volatile B bituminous rank . , cuticles and a 25-cm-thick coal seam 8 m above the Lloyd

Cove Seam has an Rrandom of 0.76%Ž high volatile An important question in evaluating FTIR data bituminous A rank. . In Stellarton, the Foord Seam from a point of view of classification potential is the shows an Rrandom of 0.92%Ž high volatile A bitumi- degree to which compressions and their cuticles were nous rank. , and in Bay St. George, the coal seam in biochemically altered during the 306-million-year the vicinity of the sample area has an Rrandom of history of fossil entombment. This will depend on 0.63%Ž. high volatile B bituminous rank . The last many factors, such as geochemical conditions during value is higher than previously determined by Hac- deposition of the cordaite leavesŽ Eh±pH, Garrels quebard and DonaldsonŽ. 1970 who recorded an R0 and Christ, 1965, p. 365. , history of sedimentary of 0.45%Ž. subbituminous B , and by Hyde et al. processes, and diagenetic effectsŽ Hacquebard and Ž.1991 who recorded an R0 of 0.56% Ž high volatile Cameron, 1989. . bituminous C. . Thus, as inferred from vitrinite re- Oxidation±reduction potentialŽ. Eh and pH dic- flectance values measured in this study, diagenetic tates the stability fields for minerals, and is a factor alteration of the cuticles and compressions should be in preservationrdegradation of compressions and cu- lowest in Bay St. George, increased in Sydney, and ticles. Based on the presence of authigenic pyrite in be highest in the Stellarton Subbasin. Table 3 shows the host rock at Bay St. George Subbasin, but its that the aromaticity factor for the compressions, absence from Sydney and Stellarton subbasins where which is expressed by ratio of absorbance of out-of- authigenic siderite is presentŽ. Table 1 , it is inferred plane aromatic H bands to the absorbance of aliphatic that the Bay St. George site was less oxic than the H bands in stretching mode, is indeed highestŽ al- other two subbasinal sites. Such differences could though variable. for the Stellarton, and lowest for the influence the preservation potential of cellulose and Bay St. George Subbasin. In addition, elemental lignin, and probably cause variation in cutinization analysis of the compressionsŽ. Table 4 shows the potential, as is clearly observed in the 3-cm-long highest carbon content in material from the Stellar- compression from Bay St. George Subbasin, but not ton Subbasin. All these observations corroborate vit- cause chemical modification of the resistant aliphatic rinite reflectance trends in the studied coal samples. macromolecule that dominates the composition of This suggests that mesophyll in the cordaitean-leaf cuticles. compressionsŽ. Fig. 1D follows a maturation path Major textural differences exist between the sam- similar to vitrinite, a result already known from pled lithologies in the SydneyŽ. Bay St. George and pteridosperm compressions studied by Lyons et al. r the Stellarton subbasins, where the former two show Ž.1995 . However, no trend in CH 23CH ratio, indi- maximum grain sizes of 70±110 mm and the latter cating the length of aliphatic chainsŽ Pradier et al., 300 mmŽ. Table 1 . However, our FTIR data do not 1992; Lin and Ritz, 1993. , is observed with increas- show great differences between the cuticles from ing thermal maturity. For the cuticles, aromatic H these two lithologies. This observation is consistent bands are not detected, and the aromaticity factor, as with data by Van Bergen et al.Ž. 1994 , relating defined above could not be calculated. A ratio of the preservation of seed coats to sedimentary texture, absorbance of the aliphatic stretching bands to the who concluded that tegmensŽ cutan-like macro- oxygenated groups in the 1600±1800 cmy1 region, r molecules. did not indicate chemical modification and CH 23CH ratio change erratically. There is also due to textural variability. However, the chemical more variation within the Bay St. George samples constituents lignin-cellulose in the seed coats were than there is among the three subbasins combined. better preserved in the coarse-grained sediments. At the maturation level corresponding to vitrinite Are there any characteristics in IR absorption of reflectance of 0.6% to 0.9%, the cuticles must be the studied cuticular morphotypes and compressions already dominantly composed of resistant cutan, and E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19 17 changes, such as degradation of polysaccharides, George Subbasin are not uniform in regard to func- lipids, and celluloserhemicellulose, likely took place tional groupsŽ. Fig. 6 . In the Sydney Subbasin, func- before this maturation level was reached. Cutan is a tional groups of morphotype 4 are similar to those of very aliphatic substanceŽ. Tagellar et al., 1993 , and morphotype 2 from the Stellarton Subbasin. FTIR confirms that aromatic hydrogen bands are absent in the cuticles. Elemental analysis supports the suggestion that 6. Conclusions the cuticles are chemically stable through maturation. On a mineral-matter-free basis, atomic C, N, and O Prior to the present investigation, an exhaustive contents do not differ in the three subbasins studied, study was done on cordaitean samples from the and hydrogen seems to be the only element showing Carboniferous Maritimes Basin to provide a proper a decrease from the Bay St. GeorgeŽ lowest matura- taxonomic framework for the interpretation of FTIR tion.Ž. to the Stellarton Subbasin highest maturation . and elemental analysesŽ. Zodrow et al., 2000 . The The lowest maturation level is consistent with atomic present approach suggests that the fossilized cuticles OrC ratios of the cuticlesŽ. Table 4 that are similar studied from the late Carboniferous Period, ca. 306 to those of modern cuticlesŽ compare: Lyons et al., to 300 million years, retained much of their original 1995, Van Krevelen plot of atomic HrC vs. OrC.. chemical makeup. Of particular interest for future This also suggests the absence of significant chemi- study are the samples from the Bay St. George cal effects from maceration. Subbasin, as they are the least taphonomically and Elemental changes related to maturation, such as chemically affected, implying that they are closest to increase in carbon content with increasing maturity, the biochemical makeup of the life cuticle in the are much more pronounced in the compression sam- cordaites leaves. In comparison, the pteridosperm ples. In the compressions, nitrogen content is the cuticles Ž M. scheuchzeri, N. oÕata, and A. les- highest in the Stellarton, and lowest at Bay St. quereuxii. from the Sydney Subbasin have experi- George Subbasin. Reasons for correlation of high enced much more chemical alteration. However, it is nitrogen to low sulfur content, and the very high evident that some biodegradation in the cuticles from sulfur content in compressions from Bay St. George the Bay St. George Subbasin took placeŽ e.g., losses Subbasin, may be related to an anoxic environment. of sugars, lignin, cellulose, lipids and others. . There- The cordaitean compressions show much higher fore, the comparative differences observed within the aromaticity than the cuticles extracted. The differ- group of the Bay St. George samples likely do not ence between the cuticle and the compressions re- reflect interspecific variation, but only varying de- flect differences in the parental material, as well as gree of maturation levels for the species, as exempli- much higher preservation potential of the cuticle. fied by cutinizationrcoalification variability in a The mesophyll of the leavesŽ precursor to compres- small 3-cm compression fragment. Therefore, the sion. underwent similar chemical changes to those in observed similarities of functional groups in the sam- vitrinite in the associated coals, as already observed ples of the three cuticular morphotypes studied from by Lyons et al.Ž. 1995 for the pteridosperms. the Carboniferous Maritimes Basin support conclu- sions, independently arrived at by morphological 5.3.1. Distribution of functional groups and correla- investigationsŽ. Zodrow et al., 2000 , that the com- tion to cuticular morphotypes 1, 2, and 4 pressions originated from a single cordaitean species, At Bay St. George Subbasin, cuticular morpho- i.e., the leaf taxon C. principalis Ž.Germar . How- types 1±3 were identifiedŽ. Zodrow et al., 2000 , but ever, for lack of FTIR spectral data from a taxonomi- sufficient amounts of sample material for FTIR anal- cally wider range of Euromerican cordaitean species, yses were available only for morphotypes 1 and 2 it is too early to say which of the functional-group Ž.Table 3 . The two morphotypes show no differences characteristics studied have the chemotaxonomic po- in functional groups found that could be consistently tential to promote a better understanding of the related to their different morphotypic character. Cuti- systematic position of cordaites in relation to other cles representing morphotype 1 from the Bay St. Carboniferous fossil±plant groups. 18 E.L. Zodrow et al.rInternational Journal of Coal Geology 45() 2000 1±19

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