International Journal of Coal Geology 45 Ž2000. 1–19 www.elsevier.nlrlocaterijcoalgeo
Functional groups and elemental analyses of cuticular morphotypes of Cordaites principalis žGermar/ Geinitz, Carboniferous Maritimes Basin, Canada d ˘ ˚ Erwin L. Zodrow a,) , Maria Mastalerz b, William H. Orem c , Zbynek , ˘ Simunek e,1 Arden R. Bashforth a b
Department of Earth Sciences, UniÕersity College of Cape Breton, Sydney, NoÕa Scotia, Canada B1P 6L2 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, KlaroÕ ´ 3 r 131, 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 ŽGermar. 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 spectra ŽFTIR. 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 ŽGermar., 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–O Ž1632 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
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Corresponding author. 503 Coxhead Road, Sydney, N.S., Canada B1R 1S1. E-mail addresses:
[email protected] ŽE.L. Zodrow.,
[email protected] ŽM. Mastalerz.,
[email protected] ŽW.H. Orem., ˘ ˚ .,
[email protected] ŽA.R. Bashforth..
[email protected] ŽZ. Simunek 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: S 0 1 6 6 - 5 1 6 2 Ž 0 0 . 0 0 0 1 8 - 5
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E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
1. Introduction Cordaitean fossil leaves Ž Cordaites, Unger 1850. are known from early Carboniferous to early Permian deposits of the Euramerican palaeokingdom ŽRothwell, 1988., representing a lifespan of ca. 80 million years. The cordaites trees from which the cordaitean leaves originated constituted a diverse group of extinct gymnospermous plants that had extremely variable growth habits and palaecological tolerances. Mire-dwelling cordaites trees included mangrove-like forms up to 5 m tall with aerenchymatous, stilt-like roots ŽCridland, 1964; Raymond, 1988; Raymond and Phillips, 1983; Costanza, 1985., and small, thicket-forming, understory shrubs ŽRothwell and Warner, 1984; Costanza 1985.. By comparison, cordaites trees growing on drier, welldrained clastic substrates, such as floodplains, river levees, or extrabasinal lowlands were very tall, forest-forming trees that towered tens of meters high ŽGrand’Eury, 1877; Mapes and Gastaldo, 1986; Rothwell, 1988; Rothwell and Mapes, 1988.. Cordaitean leaves, which can reach 1 m in length, are strap-like or linear in shape with longitudinal venation pattern that parallels the leaf margin ŽFig. 1A.. The foliage is a common component of compression assemblages and has been exhaustively investigated since Grand’Eury Ž1877.. Based on comparative cuticle morphology, Florin Ž1931, 1951. postulated that cordaites were ancestral to conifer trees, but the exact nature of the relationship between the two taxa is equivocal ŽMeyen, 1984; Crane 1985; Rothwell, 1986.. Alternatively, both taxa may have been derived from a common progenitor ŽRothwell, 1977., such as the progymnospermous Archaeopteris ŽBeck, 1981., or a pteridosperm ŽRothwell, 1988.. Cordaitean compressions were first recorded from the Carboniferous in New Brunswick and Nova Scotia, Canada, by Dawson Ž1868, 1891., and studied systematically by Bell Ž1940, 1944, 1962.. Since the fossil-bearing strata in the Carboniferous Maritimes Basin covering parts of Nova Scotia, New Brunswick, and Newfoundland ŽFig. 2. generally have lower thermal maturity, as a result of having experienced limited tectonism and burial ŽHacquebard and Cameron, 1989., cordaitean cuticles are well preserved and show delicate stomatalrepidermal details
ŽFig. 1B and C.. This circumstance provided the significant opportunity for a comprehensive study of the cordaitean compressions in the basin. As a result, five new cuticular morphotypes were established for the Carboniferous leaf taxon Cordaites principalis ŽGermar. Geinitz ŽZodrow et al., 2000.. The impetus for the present study stems from the recognition that future progress in phylogeny of Euramerican cordaiteans requires more adequate taxonomic parameters than are presently available. In this investigation, methods of Fourier transformation of infrared spectra ŽFTIR. and elemental analyses are applied to three representatives of the five cordaitean morphotypes. The purpose is to assess the applicability of these techniques in classification, and to determine which parameters could be of importance for future research in cordaitean chemotaxonomy.
2. Methods Cuticles were prepared by macerating the compressions from 7 h to 3 days in Schulze’s oxidizing solution that consisted of 150 ml 70% nitric acid with 3–5 g dissolved potassium chlorate. After oxidation, samples were neutralized in a 4.5% ammonium hydroxide solution, and well rinsed in demineralized water. Through this process, 200 cuticular mounts were prepared, and five new cuticular morphotypes of C. principalis ŽGermar. were erected ŽZodrow et al., 2000.. Representative samples of three of these cuticular morphotypes and their compressions were investigated. Compression mounts were routinely examined under a light microscope to determine the presence of pyrite and other minerals, and to observe variation in coalification patterns. Specimens for FTIR were prepared using the potassium bromide ŽKBr. pellet technique. A very small amount of the cuticle or compression Žapproximately 2 wt.% of the mixture. was mixed with finely ground KBr to produce pellets. These were analyzed on a Nicolet 20SXC spectrometer, equipped with a DTGS detector, at a resolution of 4 cmy1 , collecting 1024 scansrsample. The infrared signal ŽIR. was recorded in the region between 400 and 4000 cmy1 wavenumber. Bands were identified by comparison with published assignments ŽPainter et
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
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Fig. 1. Cordaites principalis ŽGermar. Geinitz, compressions and cuticles. ŽA. Fragments of leaf compressions with typically thick, primary veins parallel to the foliar margins. Bay St. George Subbasin, Newfoundland. B-24, cm scale. ŽB. Intact adaxial Žad. and abaxial Žab. cuticle, showing the typically elongate cells for morphotype 1, Bay St. George Subbasin, B-228. Scale bar s 60 mm. ŽC. Intact abaxial cuticle of morphotype 4, showing stomatal apparatus Žo.. Sydney Subbasin, Nova Scotia, SY-211. Scale bar s 100 mm. ŽD. Mesophyllous matter on an inner surface of a cuticle from Bay St. George Subbasin. Scale bar s 10 mm.
al., 1981; Wang and Griffith, 1985; Sobkowiak and Painter, 1992..
Elemental analyses for C, H, N, O, and S in the compressions and morphotypes were performed on
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E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
Fig. 2. Carboniferous Maritimes Basin of eastern, Canada, and study areas of the three subbasins.
dried samples Ž608C. on a Carlo Erba Elemental Analyzer ŽLyons et al., 1995.. Mineral matter is defined as the difference between the summed weight percent of an elemental analysis and 100%. Standard X-ray diffraction methods were used to obtain the semiquantitative mineralogical data from rock matrices that entombed the studied compressions. Additionally, petrography of thin sections provided sedimentary and mineralogical data, and information concerning the relationship between textural variation and compression preservation.
3. Samples The compressions originated from the Sydney ŽNova Scotia., Stellarton ŽNova Scotia., and Bay St. George ŽNewfoundland. subbasins of the Carbonifer-
ous Maritimes Basin ŽFig. 2.. In the Sydney Subbasin, the compressions are entombed in grey, fissile, silty roof shale overlying the Lloyd Cove Seam. The shale contains authigenic siderite bands Ždetails in Table 1.. In the Stellarton Subbasin, fossil leaves occur in a fine-grained, 3-m-thick sandstone characterized by ripple marks, and authigenic siderite. In the Bay St. George Subbasin, the compressions are entombed in muddy siltstone crevasse-splay deposits. This implies leaf transportation from the cordaites trees growing within, or peripheral to, clastic swamps ŽBashforth, 1999.. Authigenic, lenticular masses Žmaximum 7-mm length and 1.5-mm width. of cuboidal pyrite are commonly found on the abaxial compression surfaces. With the exception of pyritic oxidation on abaxial compression surfaces from the Bay St. George Subbasin, no weathering effects were observed in any of
SubBasin
Age in Maa stage
Rock typer associated coal seam
Compositionb
Texture
Sydney
300 Early Cantabrian 304 Early Westphalian D
Bay St. George
306 Late Bolsovian
Micarillite Ž32%., kaolinite Ž23%. quartz Ž22%., chlorite Ž16%., siderite Ž5%., bands-10 mm thick Quartz Ž47%., kaolinite Ž25%. micarillite Ž12%., plagioclase Ž9%. siderite Ž5%., fine grains- 5–300 mm Quartz Ž17%., plagioclase Ž16%., micarillite Ž10%., chlorite Ž35%. pyrite Ž4%., micron-sized
Fine-grained, quartz: maximum diameter 80 mm, micarchlorite: maximum length 70 mm
Stellarton
Silty shaler top of the Lloyd Cove Seam Sandstoner 13 m above the Foord Seam Siltstoner basal 10 cm of 80 cm thick unit 35 cm above an unnamed coal seam
a
Approximate million of years before present. Semiquantitative X-ray mineralogic analysis; detection limit 1 to 3 wt.%.
b
Fine-grained, angular quartz: maximum diameter 300 mm Very fine-grained, subangular quartz: maximum diameter 80 mm, phyllosilicates: maximum dimensions 110=10 mm
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
Table 1 Geological characteristics of strata from which cordaitean compressions originated in the Carboniferous Maritimes Basin
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Table 2 Characteristics of the compression leaves, including morphotypes 1, 2, 3, and 4
Sydney Stellarton Bay St. George
Sample
Compressions
Vein Morphology
Width max. Žcm.
Margin
Thickness Žmm.
No. of primary, thick vein per foliar Žcm.
No. of sclerotic veins between two primary veins
40–50 40–50 10–70 10–70 10–20
20–24 20–21 12–13 16–17 14–34 Žrange for the samples.
4 4 2 2 1–6
4 4 2 2 1 1
35 19 18 15 13.5 15
4 2.5 3.5 4.5 2 4
nonparallel parallel parallel nonparallel nonparallel ?
B-192 B-206 B-228 B-c1 3-cm fragment B-1
1 1 1 3 2
8 18 15 6 3
1.5 5 5 3 ?
? nonparallel? as above ? ?
B-22
Observations
Length Žcm.
SY-369 SY-211 SL-7 SL-9 B-24 B-178
B-2
a
Morphotypea
not measured not measured
32–34 24–30
3 2
clean surfaces as above wthickest cuticlesx as above wthinnest cuticlesx very thin, cutinized very thin, cutinized very thin, cutinized as above thin and ‘stringy’
very cutinized cuticle is visible very coalified cuticle is not visible as above
Morphotype 4: single stomatal raw, nonstomatiferous bands are narrower than those in morphotype 1; 2: largest guard and largest lateral subsidiary cells; 1: smallest guard cells, oblong lateral subsidiary cells, widest nonstomatiferous bands; 3: dimensions of guard cells between those of morphotypes 1 and 2, square-shaped polar cells ŽZodrow et al., 2000..
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
SubBasin
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
the mineral assemblages that entombed the compression samples. An observation is ŽTable 2. that thickness of the cuticles Žvisual estimates. correlates positively to thickness of the compressions.
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The vein morphology of the studied cordaitean compression fossils ŽTable 2. fits the classical concept of C. principalis ŽGermar. Žsummary: Zodrow et al., 2000..
Fig. 3. FTIR spectra of cuticular morphotype 4 from Sydney ŽA., and of morphotype 2 from Stellarton subbasins ŽB, C..
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
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Table 3 IR absorbance ratios of cordaitean cuticles and compressions Subbasin
Sample
Morphotype
CH 2 rCH 3
Ž2800–3000.rŽ1600–1800.
SY-369 SY-211 SL-7 SL-9 B-24 B-178 B-192 B-206 B-228 B-c1 B-1. one fragment B-2. B-22.
4 4 2 2 1 1 1 1 1 3 2
2.8 2.8 3.1 4.0 3.0 2.9 4.7 1.8 4.5 – 7.1
0.3 0.3 0.6 0.5 0.4 0.5 1.2 0.3 1.3 – 0.3
5.7
0.4
Sample
Morphotype
CH 2 rCH 3
Ž700–900r2800–3000.
SY-369 SY-211 SL-7 SL-9 B-24 B-178 B-192 B-206 B-228 B-c1 B-1. very cutinized B-2. very coalified B-22. very coalified
4 4 2 2 1 1 1 1 1 3 2
2.4 2.7 2.6 2.1 2.7 0.4 2.1 2.4 – 1.8 4.4 1.5 2.3
0.7 0.9 0.7 1.4 0.1 0.4 0.1 0.1 – 0.2 0.0 0.2 0.2
Cuticles Sydney Stellarton Bay St. George
Subbasin Compressions Sydney Stellarton Bay St. George
–, Insufficient sample amount. Table 4 Elemental, mineral-free Žbracketed. C, H, N, S, O, mineral matter, and atomic ratios HrC and OrC of the compressions Žcom. and the cuticular morphotypes Žcut. Subbasin Sydney Stellarton Bay St. George
Sample SY-369 SY-211 SL-7 SL-9 B-24 B-178 B-192 B-206 B-228
Morphotype
%C Com
Cut
%H Com
Cut
%N Com
Cut
4 4 2 2 1 1 1 1 1
71.22 Ž75.63. 70.35 Ž73.04. 61.24 Ž79.63. 73.78 Ž77.80. 52.05 Ž59.89. 45.44 Ž62.67. 71.02 Ž75.39. 53.50 Ž64.11. –
51.18 Ž63.27. 49.47 Ž60.37. 50.78 Ž63.70. 47.36 Ž62.98. 53.62 Ž61.67. 41.64 Ž62.11. 39.07 Ž60.15. 56.62 Ž64.71. 43.50 Ž63.25.
5.40 Ž5.74. 5.13 Ž5.32. 3.69 Ž4.80. 5.34 Ž5.63. 4.72 Ž5.44. 4.93 Ž6.80. 6.04 Ž6.41. 4.88 Ž5.85. –
6.06 Ž7.50. 6.11 Ž7.45. 5.69 Ž7.13. 5.37 Ž7.14. 7.11 Ž8.18. 5.53 Ž8.24. 5.21 Ž8.03. 7.20 Ž8.22. 5.79 Ž8.42.
2.02 Ž2.14. 2.50 Ž2.60. 2.43 Ž3.16. 3.00 Ž3.17. 1.03 Ž1.19. 0.87 Ž1.19. 1.64 Ž1.74. 1.00 Ž1.19. –
3.42 Ž4.23. 2.94 Ž3.59. 3.47 Ž4.36. 2.77 Ž3.68. 4.64 Ž5.34. 2.10 Ž3.12. 2.05 Ž3.15. 3.16 Ž3.62. 2.58 Ž3.75.
–, Insufficient compression sample. a Assumed mineral matters wŽ100%. y Ž% C q H q N q S q 0.x. b Correction factors for nitration and oxidation due to maceration cannot be applied, as they are unknown for cordaites.
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
4. Results 4.1. FTIR analysis 4.1.1. Sydney Subbasin, NoÕa Scotia Two specimens, SY-369 and SY-211, representing cuticular morphotype 4, were analyzed. Both show similar characteristics ŽFig. 3A.. The CH 2 and CH 3 bands in the aliphatic stretching region Ž2800– 3000 cmy1 . are distinct, with a CH 2rCH 3 ratio of 2.8 ŽTable 3.. The oxygenated groups are represented by a prominent band at 1632 cmy1 ŽC–O highly conjugated. and a shoulder at 1710 cmy1 Žcarbonyl stretch.. The ratio of absorbance of the CH 2 plus CH 3 groups vs. oxygenated groups Ž2800–3000 cmy1 .rŽ1600–1800 cmy1 . is approximately 0.3. Aliphatic groups in the bending mode around 1444 cmy1 are also distinct. The C–O groups in the 1030–1200 cmy1 range are of low absorbance. The bands at 891 and 803 cmy1 ŽSY-369: Fig. 3A. could be related to mineral, rather than to organic matter, also indicated by the 19.11% mineral-matter content in this cuticle ŽTable 4.. Compressions from the Sydney Subbasin differ significantly from the corresponding cuticles Žcompare cuticle SY-369 in Fig. 3 to compression SY-369 in Fig. 4A.. The main differences are the presence of strong aromatic carbon band at 1608–1618 cmy1 , lack of oxygenated groups at approximately 1700 cmy1 , distinct out-of-plane aromatic bands Ž700–900
%S
cmy1 ., and lower CH 2rCH 3 ratio in compressions ŽTable 3.. In the out-of-plane region, compression SY-369 ŽFig. 5A., two aromatic bands are distinct Ž750 and 813 cmy1 ., whereas the band at 857 cmy1 is of very low intensity. The ratios of aromatic out-of-plane to aliphatic stretching bands for the compressions from the Sydney Subbasin Ž700– 900r2800–3000 cmy1 . are 0.7 and 0.9 ŽTable 3: SY-369 and SY-211.. 4.1.2. Stellarton Subbasin, NoÕa Scotia Two cuticular specimens, SL-7 and SL-9, representing morphotype 2 ŽTable 3. were analyzed ŽFig. 3B and C.. They show that the functional-group characteristics are generally similar to those in the Sydney Subbasin. The main difference between the Sydney and Stellarton cuticles is a relatively higher absorbance of aliphatic stretching bands for the latter. This observation is confirmed by a higher Ž2800–3000.rŽ1600–1800. ratio Ž0.5 and 0.6, Table 3.. The CH 2rCH 3 ratios Ž3.1 and 4.0. are higher than for the Sydney cuticles Ž2.8.. In addition, mineral-matter peaks at around 900 cmy1 are not as distinct as in the Sydney cuticles; in fact, a band at 876 cmy1 of SL-9 is the only one detected ŽFig. 3B and C.. Compressions, exemplified by SL-9 in Fig. 4B, from the Stellarton Subbasin reveal the presence of the same bands as in the compression from the Sydney Subbasin ŽSY-369: Fig. 4A.. A ratio of the
Minerala Matter
%O
9
HrC b
OrC b
Com
Cut
Com
Cut
Com
Cut
Com
Cut
Com
Cut
1.79 Ž1.90. 0.88 Ž0.91. 0.23 Ž0.30. 0.31 Ž0.33. 12.34 Ž14.2. 3.05 Ž4.21. 1.43 Ž1.52. 10.02 Ž12.00. –
0.19 Ž0.23. 0.15 Ž0.18. 0.13 Ž0.16. 0.08 Ž0.11. 0.15 Ž0.17. 0.08 Ž0.12. 0.01 Ž0.02. 0.07 Ž0.08. 0.05 Ž0.07.
13.74 Ž14.59. 17.46 Ž18.13. 9.31Ž12.11. 12.40 Ž13.08. 16.77 Ž19.30. 18.22 Ž25.13. 14.07 Ž14.94. 14.05 Ž16.84. –
20.03 Ž24.76. 23.28 Ž28.41. 19.65 Ž24.65. 19.62 Ž26.09. 21.42 Ž24.64. 17.70 Ž26.40. 18.61 Ž28.65. 20.46 Ž23.38. 16.85 Ž24.50.
5.83 3.68 23.09 5.17 13.09 27.49 5.80 16.55 –
19.11 18.06 20.28 24.80 13.06 32.96 35.05 12.50 31.23
0.91 0.87 0.72 0.87 1.09 1.30 1.02 1.19 –
1.42 1.48 1.34 1.36 1.59 1.59 1.60 1.52 1.69
0.15 0.19 0.11 0.13 0.24 0.30 0.15 0.20 –
0.29 0.35 0.29 0.31 0.31 0.32 0.36 0.27 0.29
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E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
Fig. 4. FTIR spectra of compressions associated with cuticular morphotype 4 from Sydney ŽA., morphotype 2 from Stellarton ŽB., and morphotype 1 Bay St. George subbasins. ŽC, D..
absorbance of out-of-plane aromatic bands to the aliphatic groups in the stretching region gives variable values: 0.7 and 1.4, ŽTable 3: SL-7 and SL-9,
respectively., suggesting variable aromaticity of these compressions. The out-of-plane aromatic region for compression SL-9 reveals three aromatic bands Ž857,
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Fig. 5. Out-of-plane aromatic region for the compressions associated with morphotype 4 from Sydney ŽA., morphotype 2 from Stellarton ŽB., and morphotype 1 from Bay St. George subbasins ŽC, D.. Band at 750 cmy1 represents orthosubstitution Žfour 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 cmy1 dominant, and the one at 857 cmy1 being the least important Žaryl ring with isolated C–H groups..
4.1.3. Bay St. George Subbasin, Newfoundland Six cuticular specimens representing morphotypes 1 and 2 were analyzed. Their spectra reveal signifi-
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E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
cant variations ŽFig. 6A–E.. Cuticles B-192 and B-228 are characterized by very prominent aliphatic
stretching bands ŽFig. 6C and E., and high CH 2rCH 3 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.r International Journal of Coal Geology 45 (2000) 1–19
relatively high Ž2800–3000.rŽ1600–1800. ratios of 1.2 and 1.3 ŽTable 3., a very prominent band at 1712 cmy1 , and an intense 1030–1200 cmy1 region. Cuticles B-178 and B-206 ŽFig. 6B and D. have sup-
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pressed CH 2 and CH 3 bands, an almost undetectable 1712 cmy1 band, and a lower intensity of the 1030– 1200 cmy1 region. The CH 2rCH 3 ratio in this group is below 2.9, and the Ž2800–3000.rŽ1600–
Fig. 7. FTIR spectra collected from one 3-cm-long compression fragment associated with cuticular morphotype 2, Bay St. George Subbasin. ŽA. is highly cutinized, and ŽB. and ŽC. are highly coalified.
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E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
1800. ratio is not higher than 0.5. Based on the functional-group distribution, the three cuticles B-24, B-178, and B-206 ŽFig. 6. are similar to the cuticular characteristics from Stellarton and Sydney subbasins in Fig. 3. In addition to analyzing the individual cuticles from Bay St. George, functional-group variations on one 3-cm-long cordaitean-leaf fragment of highly variable coalificationrcutinization levels were studied. Although sample sizes from that fragment were small, resulting in IR spectra of poor quality, and not included in this paper, they nevertheless show considerable variation in CH 2rCH 3 ratios Ž5.7 and 7.1., and in Ž2800–3000r1600–1800. ratios ŽTable 3: 0.3 and 0.4., along the length of a single leaf fragment. Compressions ŽB-24 and B-206. in Fig. 4C and D from Bay St. George Subbasin are very similar to one another, and similar to those from the Sydney and Stellarton subbasins ŽFig. 4A and B.. The main difference is that they tend to show lower aromaticity than specimens from the other two subbasins. This is expressed mainly by lower intensity of aromatic out-of-plane region, and consequently lower Ž700–900.rŽ2800–3000. ratio ŽTable 3.. Three aromatic bands are distinct in the out-ofplane region, and they occur in changing proportions between samples B-24 and B-206 ŽFig. 5C and D.. The CH 2rCH 3 ratio is lower, compared to the corresponding cuticles, except in B-206 ŽTable 3.. Spectra of the 3-cm-long compression sample from Bay St. George Subbasin, B-1, B-22, and B-2, are shown in Fig. 7A–C. Spectrum B-1, representing the highly cutinized area with visible cuticle, resembles the cuticles Žintensely oxygenated groups at 1645 and 1720 cmy1 , and lack of aromatic out-ofplane bands.. B-22 and B-2 that represent the highly coalified area of the compression fragment, without visible cuticle, resemble the studied compressions by the presence of intense aromatic carbon band and aromatic out-of-plane bands, and absence of oxygenated groups in the 1600–1800 cmy1 region.
matter-free basis, for most samples, carbon is consistently higher, whereas H, N and O contents are lower for the compressions than for the cuticles. This results in higher atomic HrC and OrC ratios for the cuticles. The higher sulfur content in compressions results from pyrite adhering to abaxial surfaces ŽTable 1.. The presence of sulfur in the cuticles is unexpected, given the lengthy and intense oxidation process that should have oxidized the pyrite. The very high concentrations of mineral matter in the cuticles Ž12.50% to 35.05%. are also unexpected, as optical and scanning-electron microscopic examinations did not reveal significant amounts ŽZodrow et al., 2000.. However, detritus of silicate minerals are clearly visible during optical examination of the compressions Ž3.68% to 27.49%, Table 4.. On a mineral-matter-free basis ŽTable 4., the cuticular morphotypes from the three subbasins have similar carbon content, averaging 62%. Compressions, however, have variable carbon content, ranging from highest 77.80% to 79.63% in the Stellarton Subbasin, 73.04% to 75.63% in the Sydney, to the lowest and most variable 59.89% to 75.39% in the Bay St. George Subbasin. Hydrogen content is higher in cuticles than in the compressions, and is generally highest for both cuticles and compressions in the Bay St. George, and lowest in the Stellarton Subbasin. Nitrogen content is higher in cuticles, and this difference is especially distinct in the Bay St. George samples. As expected, sulfur is higher for the compressions, while cuticles have lower sulfur content in all three subbasins Ž0.02% to 0.23%.. The compressions from the Bay St. George Subbasin have high and variable sulfur content Ž1.52% to 14.2%, Tables 1 and 2.. Oxygen content is generally higher for the cuticles than for compressions, and does not show consistent differences among the samples from the three subbasins.
4.2. Elemental analysis
5.1. Comparison with modern cuticles
Table 4 presents elemental compositions of the cuticular morphotypes and compressions, and calculated amounts of mineral matter. On a mineral-
The studied cordaitean cuticles share many functional-group characteristics with those of modern cuticles ŽHolloway, 1982; Nip et al., 1989.. In both
5. Discussion
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
modern and fossil cuticles, the most prominent bands are those related to the alkyl chains ŽCH 2 and CH 3 groups in the 2800–3000 cmy1 range., and to the oxygenated groups in the 1600–1800 cmy1 region. In modern cuticles, sugars Žpolysaccharides, cellulose or hemicellulose., lipids Žcutin, waxes., and lignin are significant components ŽNip et al., 1986; Tagelaar et al., 1993; Kogel-Knabner et al., 1994.. In ¨ fossil cuticles, polysaccharides are absent, or occur only in trace amounts, cutin-derived material is present, but usually minor, lignin may be significant, whereas an important component is cutan. It is a resistant biopolymer composed of n-alkanes, n-alk-les and n-alpha-omega alkadienes ŽNip et al., 1986; Tagelaar et al., 1993.. FTIR spectra show that cellulose is absent from most, if not all, of the cordaitean cuticles studied. In IR spectra, cellulose has a strong C–OH stretch at 1070 cmy1 , and a strong C–O–C stretch at 1030 cmy1 ŽHerqert, 1971; Blackwell, 1977., and only cuticles B-192 and B-228 ŽFig. 6: Bay St. George Subbasin. have increased absorbance 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. Alternatively, the high mineral content Ž31.23% and 35.5%, Table 4. could account for increased absorbance in this region. However, the high mineralmatter content in B-178 Ž32.96%: Table 4. does not lead to increased absorbance in those spectral regions that suggests cellulose rather than mineralmatter contribution. Some bands, such as at 1275 cmy1 , likely represent lignin, specifically guaiacyl ŽDurig et al., 1988.. The major bands of the spectra, such as those in aliphatic stretching region Ž2800– 3000 cmy1 . and oxygenated group region Ž1600– 1800 cmy1 ., can, however, reflect both lignin and cutan contributions, and FTIR cannot provide a distinction between these two functional groups. 5.2. Comparison with selected pteridosperm cuticles from Sydney Subbasin Fig. 8 shows the distribution of atomic HrC and OrC ratios for the studied cordaitean compressions and their cuticular morphotypes, and for the cuticles and compressions of the pteridosperm species studied from the Sydney Subbasin Ž Neuropteris oÕata,
15
Fig. 8. Van Krevelen plot Žatomic HrC vs. CrO. of cuticles and compressions from the Carboniferous Maritimes Basin: Ss Sydney, T sStellarton, and Bs Bay St. George subbasins Žbased on Table 4.. Black ovals represents the areas of cuticle and of compression data from the pteridosperms of the Sydney Subbasin; areas for pure cutin and lignin are shown for reference ŽLyons et al., 1995..
Macroneuropteris scheuchzeri, and Alethopteris lesquereuxii .. The plotting results show that atomic ratios OrC ratios of the cordaitean cuticles are close to those of the pteridosperm cuticles, but that the HrC ratios of the cordaitean cuticles are consistently larger than those of the pteridosperm species studied by Lyons et al. Ž1995.. Fig. 8 clearly indicates a substantial spread in HrC ratios, but a more uniform pattern in OrC ratios in the cordaitean cuticles, whereas the compressions show an OrC spread but relatively uniform HrC pattern. This is interpreted to be due to higher resistance of the cuticles to oxidation than the compressions. Comparison of functional groups of the cordaitean cuticles to those of the pteridosperms ŽLyons et al., 1995. shows higher carbonyl stretch groups Ž1711 cmy1 . for the latter as the major discriminating criterion between the representatives of the two different Divisions ŽDivision Pteridospermophyta: Order Medullosales, and Division Coniferophyta: Order Cordaitales, respectively, Taylor and Taylor, 1993.. In the cordaiteans studied, highly conjugated C–O Ž1632 cmy1 . dominates over carbonyl stretch, which
16
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
is a potential avenue for further chemotaxonomic research. 5.3. Variation in the biochemical makeup of the cuticles An important question in evaluating FTIR data from a point of view of classification potential is the degree to which compressions and their cuticles were biochemically altered during the 306-million-year history of fossil entombment. This will depend on many factors, such as geochemical conditions during deposition of the cordaite leaves ŽEh–pH, Garrels and Christ, 1965, p. 365., history of sedimentary processes, and diagenetic effects ŽHacquebard and Cameron, 1989.. Oxidation–reduction potential ŽEh and pH. dictates the stability fields for minerals, and is a factor in preservationrdegradation of compressions and cuticles. Based on the presence of authigenic pyrite in the host rock at Bay St. George Subbasin, but its absence from Sydney and Stellarton subbasins where authigenic siderite is present ŽTable 1., it is inferred that the Bay St. George site was less oxic than the other two subbasinal sites. Such differences could influence the preservation potential of cellulose and lignin, and probably cause variation in cutinization potential, as is clearly observed in the 3-cm-long compression from Bay St. George Subbasin, but not cause chemical modification of the resistant aliphatic macromolecule that dominates the composition of cuticles. Major textural differences exist between the sampled lithologies in the Sydney ŽBay St. George. and the Stellarton subbasins, where the former two show maximum grain sizes of 70–110 mm and the latter 300 mm ŽTable 1.. However, our FTIR data do not show great differences between the cuticles from these two lithologies. This observation is consistent with data by Van Bergen et al. Ž1994., relating preservation of seed coats to sedimentary texture, who concluded that tegmens Žcutan-like macromolecules. did not indicate chemical modification due to textural variability. However, the chemical constituents lignin-cellulose in the seed coats were better preserved in the coarse-grained sediments. Are there any characteristics in IR absorption of the studied cuticular morphotypes and compressions
that can be related to differing maturation levels? The Lloyd Cove Seam ŽSydney Subbasin. directly below the sampling site has a vitrinite reflectance Ž R random . of 0.65% Žhigh volatile B bituminous rank., and a 25-cm-thick coal seam 8 m above the Lloyd Cove Seam has an R random of 0.76% Žhigh volatile bituminous A rank.. In Stellarton, the Foord Seam shows an R random of 0.92% Žhigh volatile A bituminous rank., and in Bay St. George, the coal seam in the vicinity of the sample area has an R random of 0.63% Žhigh volatile B bituminous rank.. The last value is higher than previously determined by Hacquebard and Donaldson Ž1970. who recorded an R 0 of 0.45% Žsubbituminous B., and by Hyde et al. Ž1991. who recorded an R 0 of 0.56% Žhigh volatile bituminous C.. Thus, as inferred from vitrinite reflectance values measured in this study, diagenetic alteration of the cuticles and compressions should be lowest in Bay St. George, increased in Sydney, and be highest in the Stellarton Subbasin. Table 3 shows that the aromaticity factor for the compressions, which is expressed by ratio of absorbance of out-ofplane aromatic H bands to the absorbance of aliphatic H bands in stretching mode, is indeed highest Žalthough variable. for the Stellarton, and lowest for the Bay St. George Subbasin. In addition, elemental analysis of the compressions ŽTable 4. shows the highest carbon content in material from the Stellarton Subbasin. All these observations corroborate vitrinite reflectance trends in the studied coal samples. This suggests that mesophyll in the cordaitean-leaf compressions ŽFig. 1D. follows a maturation path similar to vitrinite, a result already known from pteridosperm compressions studied by Lyons et al. Ž1995.. However, no trend in CH 2rCH 3 ratio, indicating the length of aliphatic chains ŽPradier et al., 1992; Lin and Ritz, 1993., is observed with increasing thermal maturity. For the cuticles, aromatic H bands are not detected, and the aromaticity factor, as defined above could not be calculated. A ratio of the absorbance of the aliphatic stretching bands to the oxygenated groups in the 1600–1800 cmy1 region, and CH 2rCH 3 ratio change erratically. There is also more variation within the Bay St. George samples than there is among the three subbasins combined. At the maturation level corresponding to vitrinite reflectance of 0.6% to 0.9%, the cuticles must be already dominantly composed of resistant cutan, and
E.L. Zodrow et al.r International Journal of Coal Geology 45 (2000) 1–19
changes, such as degradation of polysaccharides, lipids, and celluloserhemicellulose, likely took place before this maturation level was reached. Cutan is a very aliphatic substance ŽTagellar et al., 1993., and FTIR confirms that aromatic hydrogen bands are absent in the cuticles. Elemental analysis supports the suggestion that the cuticles are chemically stable through maturation. On a mineral-matter-free basis, atomic C, N, and O contents do not differ in the three subbasins studied, and hydrogen seems to be the only element showing a decrease from the Bay St. George Žlowest maturation. to the Stellarton Subbasin Žhighest maturation.. The lowest maturation level is consistent with atomic OrC ratios of the cuticles ŽTable 4. that are similar to those of modern cuticles Žcompare: Lyons et al., 1995, Van Krevelen plot of atomic HrC vs. OrC.. This also suggests the absence of significant chemical effects from maceration. Elemental changes related to maturation, such as increase in carbon content with increasing maturity, are much more pronounced in the compression samples. In the compressions, nitrogen content is the highest in the Stellarton, and lowest at Bay St. George Subbasin. Reasons for correlation of high nitrogen to low sulfur content, and the very high sulfur content in compressions from Bay St. George Subbasin, may be related to an anoxic environment. The cordaitean compressions show much higher aromaticity than the cuticles extracted. The difference between the cuticle and the compressions reflect differences in the parental material, as well as much higher preservation potential of the cuticle. The mesophyll of the leaves Žprecursor to compression. underwent similar chemical changes to those in vitrinite in the associated coals, as already observed by Lyons et al. Ž1995. for the pteridosperms. 5.3.1. Distribution of functional groups and correlation to cuticular morphotypes 1, 2, and 4 At Bay St. George Subbasin, cuticular morphotypes 1–3 were identified ŽZodrow et al., 2000., but sufficient amounts of sample material for FTIR analyses were available only for morphotypes 1 and 2 ŽTable 3.. The two morphotypes show no differences in functional groups found that could be consistently related to their different morphotypic character. Cuticles representing morphotype 1 from the Bay St.
17
George Subbasin are not uniform in regard to functional groups ŽFig. 6.. In the Sydney Subbasin, functional groups of morphotype 4 are similar to those of morphotype 2 from the Stellarton Subbasin.
6. Conclusions Prior to the present investigation, an exhaustive study was done on cordaitean samples from the Carboniferous Maritimes Basin to provide a proper taxonomic framework for the interpretation of FTIR and elemental analyses ŽZodrow et al., 2000.. The present approach suggests that the fossilized cuticles studied from the late Carboniferous Period, ca. 306 to 300 million years, retained much of their original chemical makeup. Of particular interest for future study are the samples from the Bay St. George Subbasin, as they are the least taphonomically and chemically affected, implying that they are closest to the biochemical makeup of the life cuticle in the cordaites leaves. In comparison, the pteridosperm cuticles Ž M. scheuchzeri, N. oÕata, and A. lesquereuxii . from the Sydney Subbasin have experienced much more chemical alteration. However, it is evident that some biodegradation in the cuticles from the Bay St. George Subbasin took place Že.g., losses of sugars, lignin, cellulose, lipids and others.. Therefore, the comparative differences observed within the group of the Bay St. George samples likely do not reflect interspecific variation, but only varying degree of maturation levels for the species, as exemplified by cutinizationrcoalification variability in a small 3-cm compression fragment. Therefore, the observed similarities of functional groups in the samples of the three cuticular morphotypes studied from the Carboniferous Maritimes Basin support conclusions, independently arrived at by morphological investigations ŽZodrow et al., 2000., that the compressions originated from a single cordaitean species, i.e., the leaf taxon C. principalis ŽGermar.. However, for lack of FTIR spectral data from a taxonomically wider range of Euromerican cordaitean species, it is too early to say which of the functional-group characteristics studied have the chemotaxonomic potential to promote a better understanding of the systematic position of cordaites in relation to other Carboniferous fossil–plant groups.
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Acknowledgements Funding from the Natural Science and Engineering Research Council of Canada ŽELZ. is highly appreciated. We also acknowledge the use of facilities in the Department of Earth Sciences at Memorial University of Newfoundland during the initial stages of this study. Critical assessments by the journal reviewers, B. Moesle and C. Eble, resulted in improvement of contents and style, for which we are grateful.
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