IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Preservation chemistry of coalified ovules (Trigonocarpus grandis), seed-fern, Cantabrian, Canada.
Autor/es:
ZODROW, E L; D`ANGELO, J A; HELLEUR, R
Lugar:
Albuquerque, New Mexico
Reunión:
Congreso; The Carboniferous-Permian Transition Conference, Albuquerque, New Mexico, USA; 2013
Institución organizadora:
New Mexico Museum of Natural History
Resumen:
Arnold (1938; 1948a, b) had the leading edge on studying North American coalified ovules of Carboniferous age, including Trigonocarpus Brongniart. We continue with such studies on coalified Trigonocarpus grandis (Lesquereux) Cleal et al. 2010 from the Sydney Coalfield, Canada (Fig. 1), investigating what structural aspects are preserved and why in terms of biochemistry. To this effect, we intensively used Nomarski phase-contrast microscopy (invented in the mid 1950’s), and spectrochemistry: Fourier transform infrared (FTIR) spectroscopy and pyrolysis gas chromatography with mass spectrometry (Py-GC/MS, cf. Zodrow et al., 2012). The latter two methods are powerful tools for solving problems in palaeophtychemistry, palaeochemotaxonomy/systematics, diagenesis of organic matter, and molecular taphonomy. A general problem, unlike with sectioned petrified seeds (Hoskins and Cross, 1946; Taylor, 1965), is keeping track of the original sequence of the structural components when preparing slides from the macerated coalified ovules, which we successfully did. Ovule 2-336 (Fig. 2A), ca. 1500 microns thick, separated into three distinct parts for reasons not understood (Fig. 2B). After further maceration (four days) each could be teased apart for a total of at least 15 structure/tissue layers (E.L. Zodrow, J.A. D’Angelo, and R. Helleur, unpubl., 2012). These layers are identified as 3 megaspore membranes with granulose exine surfaces, e.g., Fig. 2C; 2 nucellar cuticles, e.g., Fig. 2D; 7 integumentary epidermises, cuticles, e.g., Fig. 2E; and 3 structured, diaphanous layers or what we call tecta, e.g., Fig. 2F. Each megaspore membrane is covered with a coarse nucellar cuticle, which is individually covered with tecta, as are the integumentary epidermises, though only tectal fragments have been recovered because they are very difficult to see in water. In proposing a coalified model, two preservation biases are recognized. One is in respect to the three megaspore membranes which should be four for double-layered membranes of trigonocarpalean seeds (Darrah, 1968; Pettitt, 1966); the other is that integumentary epidermises cannot be odd numbered. This assumes correlation with ad- and abaxial surfaces, in reference to an imaginary medial plane axis (cf. Truernit and Haseloff, 2008, fig. 2). The model, assuming the telomic concept (Herr, 1995), can then conveniently be described in terms of inner and outer integuments and double-layered nucellus with granulose exine. What remains unresolved is the question of stomata on the outer abaxial epidermis. We found that preservation of the nucellus and epidermis correlates with the “oily” (aliphatic) contents, as revealed by the spectrochemistry used, and infer that this applies as well to the tectum and nucellar cuticle. Variation in the local Eh-pH paleoenvironment (Krumbein and Garrels, 1952) probably limited preservation of the “oily” tissues to a certain degree during early diagenesis (Berner, 1980). In general, we believe that the limit of what can be expected in terms of preservation from coalified ovules world-wide has been reached with the Sydney ovules. Important implications include that continued separation of Pachytesta from Trigonocarpus is deemed untenable, that “oily” chemistry has potential for the systematics of medullosalean ovules, ultimately for biostratigraphy, and that the large number of dispersed ovules is probably a Carboniferous kerogen source (Arnold, 1938). REFERENCES Arnold, C.A., 1938, Paleozoic seeds: Botanical Review, v. 5, p. 205-234. Arnold, C.A., 1948a, Paleozoic seeds II: Botanical Review, v. 14, p. 450472. Arnold, C.A., 1948b, Some cutinized seed membranes from the coal-bearing rocks of Michigan: Bulletin of the Torrey Botanical Club, v. 75, p. 131Berner, R.A., 1980, Early diagenesis: A theoretical approach: Princeton, N.J., Princeton University Press, 241 p. Cleal, C.J., Zodrow, E.L. and Mastalerz, M., 2010, An association of Alethopteris foliage, Trigonocarpus ovules and Bernaultia-like pollen organs from the Middle Pennsylvanian of Nova Scotia, Canada: Palaeontographica B, v. 283, p. 73-97. Darrah, E.L., 1968, The microstructure of some Pennsylvanian seeds and megaspores studied by maceration: Micropaleontology, v. 14, p. 87104. Herr, J.M., Jr., 1995, The origin of the ovule: American Journal of Botany, v. 82, p. 547-564.Hoskins, J.H. and Cross, A.T., 1946, Studies in the Trigonocarpales. Pt I. Pachytesta vera, a new species from the Des Moines Series of Iowa: American Midland Naturalist, v. 36, p. 207-250. Krumbein, W.C. and Garrels, R.M., 1952, Origin and classification of chemical sediments in terms of pH and oxidation-reduction potentials: Journal of Geology, v. 52, p. 1-33. Pettitt, J.M., 1966, A new interpretation of the structure of the megaspore membrane in some gymnospermous ovules: Journal of the Linnaean Society of London, v. 59, p. 253-263. Taylor, T.N., 1965, Paleozoic seed studies: A monograph of the American species of Pachytesta: Palaeontographica B, v. 117, p. 1-46. Truernit, E. and Haseloff, J., 2008, Arabidopsis thaliana outer ovule integument. morphogenesis: Ectopic expression of KNAT1 reveals a compensation mechanism: BMC Plant Biology, v. 8, p. 35, DOI: 10.1186/ 1471-2229-8-35. Zodrow, E.L., D’Angelo, J.A., Helleur, R. and Šimunek, Z., 2012, Functional groups and common pyrolysates products of Odontopteris cantabrica (index fossil for the Cantabrian Substage, Carboniferous): International Journal of Coal Geology, v. 100, p. 40-50.
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