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Org. Geochem. Vol. 18, No. 6, pp. 791-803, 1992 0146-6380/92 $5.00+0.00 Printed in Great Britain. All rights reserved Copyright © 1992 Pergamon Press Ltd
Organic geochemistry of geographically unrelated tasmanites*
F. R. AQUINO N~TO, I J. TRIGOIS, 2 D. A. AZEVEDO, ~ R. RODRIGUES 2 and B. R. T. SIMO~Srr 3 J Instituto de Qulmica da UFRJ, Ilha do Fundfio, CT, Bloco A, Sala 607, 21945, Rio de Janeiro, Brazil, 2Cenpes/Divex/Segeq/PETROBRAS, Ilha do Fund.~o, Quadra 7, 21910, Rio de Janeiro, Brazil and 3petroleum Research Group, College of Oceanography, Oregon State University, Corvallis, OR 97331,
U.S.A.
(Received 13 January 1992; accepted in revised form 19 June 1992)
Abstract--The biomarker analysis of three tasmanite rock samples from Tasmania, Alaska and Brazil showed an unusually high tricyclic terpane concentration relative to hopanes and steranes. A possible product-precursor relationship is advanced, associating Tasmanaceae algae with these tricyclic terpanes. These results support the search of possible precursor molecules in present day organisms which may be taxonomically related to these algae.
Key words--tricyclic terpanes, biomarkers, algae
INTRODUCTION
Sediments containing tasmanites-type microorganisms are very common in the geological record. Usually these organisms occur dispersed with other organic remains which complicates the study of their compos- ition. Certain modern organisms have been postulated as descendants of these unicellular fossil organisms, thought to be algae by some authors (Burlingame et al., 1969; Tappan, 1980 and references therein). Wall (1962) proposed a possible close affinity between Tasmanian tasmanites and present day Pachysphaera pelagica Ostenfeld (1899) and other species of Pachysphaera. Wall (1962) suggested that tasmanites could be classified in the class Chlorophyceae. Combaz (1966, 1967) reached similar conclusions while analyzing Saharan samples. Simoneit and Burlingame (1973) suggested that these organisms could be spores of green algae, and Sargeant (1989) also suggested that these unicellular organisms could be green algae (i.e. zoosporongia of Prasinophycean algae). A detailed classification of Brazilian Tasman- aceae has been put forward by Sommer and Bockel (1967).
Massive concentrations of these organisms in geo- logical sediments are rare, the best known example being the Tasmanian tasmanite (for a comprehensive review of tasmanites see Cane, 1974 and Muir and Sargeant, 1971). Other occurrences, such as the Alaskan (Tourtelot et al., 1967) and Saharan (Combaz, 1966) tasmanites, have also been reported. Recently, we have found some tasmanite.rich sediments in the Amazonia area of Brazil.
The molecular composition of these materials has been studied by several authors. Hydrocarbon analysis
*Presented at the 14th International Meeting on Organic Geochemistry, Paris, France, 18-22 September 1989.
showed a normal alkane distribution in Alaskan samples and a peculiar distribution for Tasmanian samples, with an abundance of a Ci9 alkyi-substituted tricyclic alkane (Cane, 1974). Carboxylic acid analysis from extracts and kerogen oxidations showed the presence of normal acids as well as keto, aromatic, mono and dicarboxylic acids, including tricyclic carb- oxylic acids (Burlingame et aL, 1969; Simoneit and Burlingame, 1973). The aromatic acids were related to phenanthrenes. Pyrolysis and hydrogenation of Tasmanian tasmanite alginite yielded alkyl-substituted cyclohexanes and a series of tricyclic and tetracyclic alkanes with unknown structures (Philp et al., 1981). A probable triterpane-like A,B-ring structure was proposed for the tricyclic series based on mass spectrometric data.
We have found that Tasmanian tasmanite hydro- carbons consist mainly of several C~9 and C20 tricyclic terpanes (Grimalt et al., 1988; Simoneit et aL, 1990) together with structures related to the now ubiquitous, extended tricyclic triterpane series (Aquino Neto et al., 1982, 1983; Heissler et al., 1984; Chicarelli et al., 1988). The aromatic fraction is composed primarily of ring-C aromatic tricyclic terpanes (Azevedo et al., 1992; Simoneit et al., 1990).
The purpose of the present work is to verify whether this unique lipid composition is a characteristic of these fossil organisms, irrespective of geological occurrence. If this is shown to be the case, then, for the first time, a direct connection between tricyclic terpanes and a precursor organism will have been established.
EXPERIMENTAL
After washing with dichloromethane, the samples were powdered in an agate mortar and extracted at least four times with dichloromethane/methanol (9: I)
791
792 F.R. AQUINO NF.TO et al.
in an ultrasonic bath. The solvent was removed from the extracts by rotary evaporation and the resulting bitumens were fractionated with hexane on silica gel 60 TLC plates (20 x 20 era, 0.25 ram). Visualization under u.v. light (254nm) allowed the isolation of saturated hydrocarbons, aromatic hydrocarbons, and resins plus asphaltenes. The saturate fractions of the Alaskan and Brazilian samples were further fractionated by urea adduction. The hydrocarbon fractions were analyzed by high resolution gas chromatography (HRGC) on a SE-54 capillary column (35 m x 0.30 mm, d r - 0.35 #m) using hydro- gen as carrier and temperature programming from 50 to 280°C at 3°C/rain. The same chromatographic conditions were used for HRGC-mass spectrometry (MS) analysis on a Hewlett-Packard-5987A quadru- pole instrument, using linear scanning (50-500 dalton, 1.87 s/decade) and electron impact ionization (70 eV). Multiple ion detection (MID) analyses were also performed when the concentration of key compound families was low. The biomarkers were identified by comparison of the mass spectra and GC retention index with those of standards and previously published data (Anders and Robinson, 1971; Aquino Neto et al., 1982, 1983; Moldowan et al., 1983; Rodrigues et al., 1987; Zumberge, 1983).
Stable carbon isotope analyses were carried out on demineralized whole rock and bitumens, using a continuous oxygen flow combustion line. The evolved CO2 was analyzed with a Finnigan Delta E mass spectrometer and the results expressed in 613C (%0) values relative to PDB standard.
For vitrinite reflectance, Ro, measurements the crushed rock was prepared as a scatter mount in a polyethylene mold. A cold setting methyl methaerylate ("Metset") resin and hardener were mixed (50:1), poured into the molds, and allowed to set (about 1 h). After sample polishing Ro values were measured in a Zeiss Standard Universal reflected light microscope
fitted with a photomultiplier. The illumination was provided by a stabilized 12 V high-intensity tungsten filament lamp, filtered to ensure incidence of mono- chromatic green light (546 nm). The oil objective lens used (magnification 40) had a reflective index of 1.518 (n) at 23°C. The polished blocks used for vitrinite reflectance measurements were also used for the observation of the fluorescence of the macerals under ultraviolet light.
Kerogen isolation was carried out by breaking the rock into 3-5 mm particles and washing under ultrasonic agitation for about 1 min with methanol to remove the excess soluble organic matter. Carbonates were removed with HCI (20%) and demineralization was performed with HF (40%). The neutral, washed residue was ultrasonicated with 2ml of ZnBr2 solution (2.0 g/era 3) and centrifuged for 10min at 1700 rpm. After washing, the supernatant kerogen concentrate was dried in a vacuum oven at 30°C.
GEOGRAPHICAL DISTRIBUTION OF THE SAMPLES STUDIED
The samples were purposely selected from widely different geographical and age settings.
The Tasmanian tasmanite (Upper Permian) sample was collected by T. C. Hoering and B. R. T. Simoneit in an abandoned shale mine on the Mersey River, 3 miles south of Latrobe, Tasmania, Australia (latitude 41°17'S, longitude 146°28'E and elevation ~35m).
The Alaskan tasmanite (Triassic) sample was obtained at 68°37"30"N and 158°22'30"W (U.S. Geological Survey field number 65 ADL 8) by H. A. Tourtelot.
The Brazilian tasmanite (Upper Devonian) core samples are from the Amazon Basin, from strata situated between 1072 and 1075.5m of a well designated 2-UM-1-AM (2°20'47"S, 58°42'57"W).
Table 1. General features and analytical results for the tasmanite samples
Sample location
Feature Tasmania Alaska Brazil
Geological age Permian Late Jurassic/ Devonian Early Cretaceous
Range of tasmanites sizes (#m) 472-690 290-523 290-559 Tasmanttes individuals/ram of sediment* approx. 25 approx. 80 approx. 10 Estimated maturation level (R, , % ) t 0.3-0.4 0.5-0.6 0.5-0.6 % Alginite of amorphous organic matter ~ 80 ~ 100 ~ 25 Other recognizable organic remains none none 10-20%
acritarchs Total organic carbon (%) 20.16 28.69 9.73 Extract yield (g/g TOC) 138 - - - - Bitumen fractions (%)
Saturate 19.8 2.6 - - Aromatic 15.2 12.8 - - N, S and O compounds 49.4 28.2 - - Asphaltenes 15.6 56.4 - -
6 ~3C of demineralized whole rock (Y~, vs PDB) - 13.86 - 14.41 - 30.74 (%,, vs PDB) 613C of the organic extract (%., vs PDB) - 11.37 - 2 7 . 2 0 - 2 8 . 8 0 (gh, vs PDB)
*Measured perpendicularly to the depositional plane, see Plate I. 1"In the absence of vitrinite and spores, only organic matter coloration and algal fluorescence colors were
used to infer the maturation levels.
793
Organic geochemistry of geographically unrelated tasmanites 795
RESULTS AND DISCUSSION
Description of the samples
Table 1 shows some typical data for the tasmanites analyzed. Microscopic observation of the samples shows the dense packing of the cells in the Alaskan and Tasmanian samples, while the individual cells are more isolated in the Brazilian sample (Plate 1). During kerogen preparations, the
aggregation of the cells resulted in their extensive breakage, yielding mostly fragments in the samples from Alaska and Tasmania. On the other hand, well-preserved whole cells were obtained in the kerogen concentrate from the Brazilian tasmanite. The tasmanites present in the Brazilian tasmanite can also be assigned as tasmanites punctatus. Other recognizable organisms in this sample are acritarchs (Table 1).
A
• Normal alkanes
Pregnane
+ Alkyl-cyclohexanes
o Isoprenoids
co Alkyl-methyl-cyclohexanes
• Tricyclic terpanes
B
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Fig. 1. HRGC traces of the hydrocarbons from Tasmanian tasmanite. A--Saturate fraction; B---aromatic fraction (for peak identification see Appendix and for conditions see experimental).
796 F.R. AQUINO NETO et al.
B i o m a r k e r s
The molecular composition of the saturates and aromatic fractions can be discerned in the GC and GC-MS data shown in Figs 1-6. The numbers and symbols referring to peaks in the gas chromatograms and mass fragmentograms are related to the com- pound structures given in the Appendix. Several series of compounds are present, but they do not occur in every sample in the same relative amounts (cf. Table 2).
Normal alkanes, alkylcyclohexanes, alkylphen- anthrenes and tricyclic terpanes are the only series
present in all three tasmanites. What is rather unusual is the high abundance of the tricyclic terpanes over hopanes and steranes in the three samples. In effect, the Tasmanian sample is constituted of only tricyclics (Fig. 4). The Alaskan sample has a tricyclic to hopane ratio of l : l and the Brazilian sample about 3:1 (Figs 5 and 6).
The presence of simple biomarker distributions in geological samples is usually associated with immature sediments. In more mature samples, hydrocarbon generation usually dilutes this initial biologically related fingerprint, shifting the pattern to a more typical petroleum-like distribution.
A 5,
87
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B
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~ Pregnane, methyl-pregnane
+ Alkyl-cyclohexanes
Isoprenoids.
CO Alkyl-methyl-cyclohexanes D
m m 40 m + & 71
I ~ I I I I 30 50 60 70 80
t R (rain)
17
Alkyl-phenanthrenes
o Alkyl-chrysenes
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Fig. 2. HRGC traces for the hydrocarbons from Alaskan tasmanite. A--Saturate fraction; B---aromatic fraction (for peak identification see Appendix and for conditions see Experimental).
$1
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Organic geochemistry of geographically unrelated tasmanites
Table 2. Relative molecular composition of the saturate and aromatic fractions of the three tasmanites studied, based on the total ion current traces
(TIC) or m/z 191 and 217 mass fragmentograms
Relative occurrence based on the TIC
Compound classes Tasmania Alaska Brazil
Tricyclic terpanes* + + + + + + + + + Hopanes* - - + + + Tr. Steranes C27--Cff[" Tr. Tr. Tr. Alkylcyclohexanes + + + + + + Methylalkylcyclohexanes + - - + + Normal alkanes + + + + + + + + Acyclic isoprenoids - - + + + + + + + Ring-C monoarom, tricyclics + + + + - - - - Alkylbcnzenes
C~-alkylbenzenes + + - - + + + C2-alkylbenzenes + + - - __ C3-alkylbenzenes - - __ +
Alkyltetralins + + - - + + Alkylnaphthalenes + + + + + Alkylphenanthrenes + + + + + + + + + + Alkyldibenzothiophenes - - - - + + Alkylchrysenes - - + + + + Alkylpyrenes - - - - Tr. Perylene - - + - -
Tr. = traces. * = Based on m/z 191. ~" = Based on m/z 217.
799
In the case of T a s m a n i a n tasmani te , the co- occurrence of a b u n d a n t tasmanites and a b u n d a n t tricyclic terpanes suggests a precursor (o rgan i sm) - p roduc t (b iomarker ) re la t ionship (see also Simonei t et al., 1986, 1990, 1992). The o ther two samples are more mature , showing a complex pa t t e rn even after removal o f the n-a lkanes by urea adduct ion. How- ever, the unusual ly h igh tricyclic to hopane rat io and the essential absence o f steranes, reinforces the pro- posed tasmanites-tricyclics connect ion. The unusua l a b u n d a n c e o f alkylcyclohexanes and alkylbenzenes in these sediments suggests tha t these c o m p o u n d s could also be character is t ic p roduc ts of these organisms. The es t imated vitr ini te reflectance values given in Table 1 for the T a s m a n i a n tasmani te reinforce the evidence tha t this sample is more immatu re t han the o ther two. The isotopic values for the T a s m a n i a n tasmani te (Table 1) are no t close to those for typical recent mar ine algae and they deviate significantly f rom the n o r m of Permian mar ine organic mat ter . This may indicate biosynthesis of these tasmanites unde r b loom condi t ions (Simonei t et al., 1992). The
t3C da ta for the A laskan and Brazil ian samples are more negative, and are thus similar to those normal ly found in b i tumen f rom ma tu re mar ine shales with algal affinities (Degens, 1969).
CONCLUSIONS
• Tricyclic terpanes are the p r imary b iomarkers in T a s m a n i a n tasmani te .
• A laskan and Brazi l ian tasmani tes also have relatively high amoun t s o f tricyclic terpanes.
• A re la t ionship between tasmanites and tricyclic terpanes is p roposed and appears to correlate with the compos i t iona l descr ipt ions of the macerals in these sediments.
• A search for tricyclic te rpane precursors should be pursued in present day microorganisms related to tasmanites.
Acknowledgements--We thank FINEP and CNPq for financial support, PETROBRAS for permission to publish this work, and M. A. McCaffrey, R. N. Leif and T. Aboul-Kassim for their comments which greatly improved the manuscript.
REFERENCES
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Aquino Neto F. R., Restle A., Connan J., Albrecht P. and Ourisson G. (1982) Novel tricyclic terpanes (C,9, C20) in sediments and petroleums. Tetrahedron Lett. 23, 2027-2030.
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Azevedo D. A., Aquino Neto F. R., Simoneit B. R. T. and Pinto A. C. (1992) Novel series of tricyclic aro- matic terpanes characterized in Tasmanian tasmanite. Org. Geochem. 18, 9-16.
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Cane R. F. (1974) A bibliography of tasmanite with an introduction and annotations. Pap. Proc. R. Soc. Tasmania 108, 211-225.
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Combaz A. (1967) Leiosphaeridaceae Eisenack 1954 et Protoleiosphaeridae Timofeev 1859--leurs aff~tc~es, leur r61e s&limentologique et g6ologique. Rev. Palaeobot. Palynol. 1, 309-321.
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Heissler D., Ocampo R., Albrecht P., Riehl J. J. and Ourisson G. (1984) Identification of longchaln tricyclic terpane hydrocarbons (C21-C30) in geological samples. J. Chem. Soc. Chem. Commun. 8, 496-498.
Moldowan J. M., Seifert W. K. and Gallegos E. J. (1983) Identification of an extended series of tricyclic terpanes in petroleum. Geochim. Cosmochim. Acta 47, 1531-1534.
Muir M. D. and Sargeant W. A. (1971) An annotated bibliography of the tasmanaceae and related forms. Microfossiles Organiques du Pal~ozoique. Les acritarches, Vol. 3, pp. 52-117. Editions du Centre National de la Recherche Scientifique, Paris.
Ostenfeld C. H. (1899) In lagttagelser over Overfladevandets, Temperatur, Saltholdighed og Plankton paa islandske og gronlandske Skibsrouter i 1898 (Edited by Knudson M. and Ostenfeld C. H.). Bianco Lunos, Copenhagen.
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Rodrigues R., Trindade L. A. F., Cardoso J. and Aquino Neto F. R. (1987) Biomarker stratigraphy of the Lower Cretaceous of Espirito Santo Basin, Brazil. Org. Geochem. 13, 707-714.
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Sommer F. W. and Bockel N. M. (1967) Brazilian Palaeozoic Algomycetes and Tasmanaceae. Palaeontology 10, 640-646.
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Wall D. (1962) Evidence from recent plankton regarding the biological affinities of tasmanites (Newton, 1875) and Leiosphaeridia (Eisenack, 1958). Geol. Mag. 99, 353-362.
Zumberge J. E. (1983) Tricyclic diterpane distributions in the correlation of Paleozoic crude oils from the Williston Basin. In Advances in Organic Geochemistry 1981 (Edited by Bjoroy M. et al.), pp. 738-745. Wiley, Chichester.
Appendix opposite
Organic geochemistry of geographically unrelated tasmanites
A P P E N D I X
Structures of Biomarkers Identified
1. C18H26 2. CtgH2s 3. C20H30
5. C23H36 6. C24H3s
4. C22H34
7. C27H ~
11. C~oHso
/ ~ 13. C33H ~
801
Continued overleaf
802 F.R. AQUINO NEro et al.
15. C14Hlo 16. C15H12 17. C16H14 18. C17H16
19. C18Hls 20. C18H12 21. C19H14 22. C2oH16
23. C23H34 24. C18H22 25. C12H8S 26. Cl3Hio S
27. C14H12S
31. C14It2o
28. ChilI6
32. C13H14 33. C15HIs
42. C20H36 43. C21H38 44. C23H42
29. C13H18 30. C12H12
40. C20H36 41. C19H34
45. C~tt~
Organic geochemistry of geographically unrelated tasmanites 803
46. C25H46
49. C22H38 50. C24H42
~ R 57. CIaH38 R = C3H 7 5S. C19H40 C4H9 59. C20I"I42 CsHI1
47. C~t4a 48. C21H36
51. C13H28 R = H 52. C14H30 CH 3 53. C15H32 C2H5 54. C16H34 C3H 7 55. Cv/H36 C4H 9 56. C18H38 CsHll
61. C17H34 CH 3 62. C18H36 C2H 5
~ R
64. C17H~ CH 3 65. ClsH~ C2H5 66. Cl~'13s C3H7 6% c~4o c4~ 68. C21H42 CsHII 69. C22H44 C6H13 70. C23H46 CTHI5 71. C24H4a CsHt7
