(American Journal of Botany. 2000;87:752-753.)
© 2000 Botanical Society of
America, Inc.
Petrofilaments in palynological preparations
Alan Graham3,2,
Gordon D. Wood4,
William C. Elsik5 and
Robert C. Speed6
2 Department of Biological Sciences, Kent State University, Kent, Ohio 44242 USA;
4 23222 Willow Pond Place, Houston, Texas 77494 USA;
5 The MycoStrat Connection, P. O. Box 549, Snook, Texas 77878-0549 USA;
6 Department of Geological Sciences, Northwestern University, Evanston, Illinois 60608-2150 USA
Received for publication July 13, 1999.
Accepted for publication February 4, 2000.
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ABSTRACT
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Microscopic structures (petrofilaments) may develop during palynological laboratory processing procedures that are superficially similar to secondary wall thickenings and elaters. These filaments form from angular bodies that resemble fungal spores and resin bodies. The angular bodies are a type of hydrocarbon called asphaltene and extrude the filaments when compounds in the bodies react with solvents in the mounting medium. They may be misinterpreted as fossils and so are illustrated here for the first time in the published literature.
Key Words: artifact • microfossils • palynology • petrofilaments
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INTRODUCTION
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Plant microfossil assemblages frequently contain entities of uncertain biological affinity or include organic particles that can be misinterpreted as fossils. One example of the latter is profusely represented in Tertiary sediments collected from Barbados, West Indies. The samples contain dark angular to subrounded particles mostly between 20 and 25 µm in diameter (Fig. 1). Protruding from many of them are dark filaments ~3 µm in diameter. The filaments are smooth, solid, variable in length, and include shapes that are straight, curved, crosier-formed, and coiled (Figs. 2–4).
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Figs. 1–4. Dark, opaque to translucent hydrocarbon (asphaltene) bodies and petrofilaments from the Tertiary of Barbados, West Indies. 1. Low magnification (100x) of hydrocarbon bodies with extruded petrofilaments. 2–4. Variously curved to coiled petrofilaments (400x magnification)
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The specimens resemble germinating fungal spores and, when the filaments are shorter, lignified plant cells with outgrowths. When broken from the source, the filament fragments may superficially resemble segments of secondary wall thickenings or elaters. The former are relevant to the early occurrence of land vascular plants, and the latter to the origin of the Sphenopsida. The extruded material can also occur in other shapes that mimic fungal spores (Elsik, 1996
; erroneously indexed as petroliferous "droplets" in that volume) and, according to Groth (1980), they also look like resin bodies. They are none of these, however. Although they are familiar to palynologists, organic geochemists, and petrologists working in the petroleum industry, outside these applied laboratories their true nature is unknown.
The angular to subrounded bodies are actually a form of organically sourced hydrocarbon classified as asphaltenes. They may originate as amorphous kerogen and occur in rocks as secondary pore fillings (organic debris; Groth, 1980
). Upon palynological processing the angular boides often extrude filaments that resemble biological structures such as fungal hyphae, lignified plant cell walls, or elaters. The filaments are formed during the slide mounting process following maceration/acid treatment (HCL, HF) of a sample (Wood, Gabriel, and Lawson, 1996
). The organic residue in this study was mixed with Clearcol (Marblehead Testing Labs) and mounted on a coverslip. After drying on a hot plate the coverslip was affixed to a glass coverslide using Elvacite (DuPont diaphane), a plastic derivative that dries to a permanent mount. It is during this stage of the mounting process that the petrolic filaments are produced. The substrate body (bitumen) reacts with the solvents in the Elvacite, and this triggers the formation of the filament types illustrated here (Figs. 1–4). Filaments are always extruded downwards into the Elvacite (away from the coverslip).
There is little information available on these structures (abstracts by Groth, 1980, 1981
; Padilla et al., 1998
), especially in the biological literature. Their nature and origin are reported to help avoid misinterpretations, and illustrations of them are published here for the first time.
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FOOTNOTES
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1 
3 Author for correspondence.
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LITERATURE CITED
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Elsik, W. C. 1996 Fungi. In J. Jansonius and D. C. McGregor [eds.], Palynology: principles and applications. American Association of Stratigraphic Palynologists Foundation 1: 293–305.
Groth, P. K. H. 1980 Filament-producing hydrocarbons in palynology preparations. American Association of Petroleum Geologists 64: 715.
———. 1981 Implications of some solid hydrocarbons in palynologic preparations. Palynology 5: 216.
Padilla, H., S. E. Palmer-Koleman, G. D. Wood, and A. M. Alemán. 1998 The volcanic arc sequence of the Permo-Carboniferous Pular Formation, northern Chile: geology, geochemistry and palynofacies. Latin American Congress on Organic Geochemistry (Margarita Island, Venezuela): 32–34.
Wood, G. D., A. M. Gabriel, and J. C. Lawson. 1996 Palynological techniques—processing and microscopy. In J. Jansonius and D. C. McGregor [eds.], Palynology: principles and applications. American Association of Stratigraphic Palynologists Foundation 1: 29–50.
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