Early Miocene, Czech Republic)

Revision of Potamogeton fossils from the Most Basin and their palaeoecological significance (Early Miocene, Czech Republic) VASILIS TEODORIDIS Only 37 incomplete endocarps and fragments of Potamogeton wiesaensis Kirchheimer from the Nástup-Tušimice Mine and cores of KU 115 and MR 59, and one incomplete leaf assigned as Potamogeton praenatans Knoll from the Bílina Mine (horizon No. 1) are described from the Most Basin. These samples studied here stratigraphically belong to the Holešice, Libkovice and Lom members of the Most Formation. According to the analysis of Potamogeton autecology and the floristic composition of the horizon No. 1, the fossil taxa can be interpreted as elements of an aquatic and reed vegetation. • Key words: leaves, endocarps, Potamogeton, palaeoecology, Early Miocene, Most Basin. TEODORIDIS, V. 2007. Revision of Potamogeton fossils from the Most Basin and their palaeoecological significance (Early Miocene, Czech Republic). Bulletin of Geosciences 82(4), 409–418 (4 figures, 1 table). Czech Geological Sur- vey, Prague. ISSN 1214-1119. Manuscript received January 2, 2007; accepted in revised form April 11, 2007; issued December 31, 2007. • DOI 10.3140/bull.geosci.2007.04.409 Vasilis Teodoridis, Charles University in Prague, Faculty of Education, Department of Biology and Environmental Ed- ucation, M.D. Rettigové 4, 116 39 Prague 1, Czech Republic; [email protected] Occurrences of Potamogetonaceae are extremely rare in at base, leaf margins entire or serrate, rarely crimped, vena- the area of the Most Basin. This study focuses on a revision tion parallelodromous to acrodromous with 1–35 veins. and modern evaluation of leaf and carpological material Fruits of Potamogeton are best considered as a drupe previously collected by Č. Bůžek (from 1961 to 1962) and having a membranous exocarp, fleshy mesocarp and stony others and its implication for the palaeoecological signifi- endocarp. Potamogeton fruits are born laterally on a fruit- cance. E. Knobloch gave an overview about the Neogene ing spike usually in whorls of four, with from one to over and Early Quaternary Potamogeton fossils from Moravia 20 whorls per spike. Each fruit is sessile, attached at the and Slovakia including short comments on Czech speci- base of the ventral (adaxial) margin and contains a single, mens (Knobloch 1977, pp. 30, 31). pendulous, campylotropous ovule. The fruits are D-shaped The family Potamogetanaceae contains perennial or to subovate in lateral view, bisymmetrical and strongly bi- rarely annual floating-leaved or submersed glabrous herbs laterally flattened in the plane of symmetry. They are nar- growing in fresh or brackish waters, sometimes stranded by rowly ovate in transverse section (Collinson 1982, p. 84); receding water levels (Haynes et al. 1998). The systematics see Fig. 4F–H. The seed is equally lobed and curved of the Potamogetonaceae is contentious and usually two or around an internal process from the lateral and ventral three genera are determined; Potamogeton L., Groenlandia faces of the fruit wall. A rounded depression is present on J. Gay and Coleogeton (Rchb.) Les & R.R. Haynes (Les & the external faces of the fruit in the position of this process. Haynes 1996), the latter newly reassigned as Stuckenia A germination valve occupies the entire dorsal margin and Börner (Haynes & Hellquist 2000); see Les & Haynes extends around the base of the fruit. (1995), Haynes et al. (1998). The foliage of Potamogeton L. occurs as submersed or floating leaves in alternate to subopposite position. The floating leaves have a firmer tex- Geological settings ture, mostly petiolate, rarely subsessile, elliptic to ovate in outline, subulate to obtuse at apex and cuneate to rounded The Most Basin is located between the Doupovské hory or cordate at base, leaf margins entire, venation paral- Mts. and the České středohoří Mts. in northwestern Bohe- lelodromous to acrodromous with 1–51 veins. The sub- mia and genetically belongs to the tectonic system of the mersed leaves are sessile or petiolate, linear to orbicular in Eger Graben. The basin fill spans the time interval from the outline, subulate to obtuse at apex and cuneate to perfoliate Oligocene to late Early Miocene. These sediments belong 409 Bulletin of Geosciences Vol. 82, 4, 2007 levels; a coal horizon (depth 48–50 m) and a light brown clayey horizon with plant fragments (depth 49.8–50 m) (Jirotka 1976, Kvaček & Bůžek 1982). These horizons belong to the coal seam of the Lom Member (Figs 1, 2). The core KU 115 (Kundratice) has yielded only one endocarp from a coal-clayey horizon (depth 97.0–98.0 m) corresponding to the uppermost part of the Libkovice Member (Figs 1, 2). The endocarps from the Nástup-Tu- šimice Mine (7 specimens) are bound in a brown clayey horizon that contains also a rich fish fauna (Oberhelová 1983, p. 7) and belongs to the uppermost part of the Hole- šice Member (Kvaček 2006); Figs 1, 2. Similarly, the studied leaf material is bound to a sandy-clayey horizon (No. 1) from the Bílina Mine (Bůžek et al. 1992), corresponding to the lower part of the Libkovice Member (Figs 1, 2). Material and methods The fossil carpological material is compressed, carbonace- ous and three-dimensionally preserved and was obtained Figure 1. Geographical position of the studied localities and cores in the from the cores by washing. It is housed in the palaeontolo- area of the Most Basin. gical collection of the National Museum, Prague (NM – 37 specimens). The incomplete leaf (DB 1-55) is from horizon stratigraphically to the Střezov Formation and the Most No. 1 (Bílina Mine) and is housed in the palaeontological Formation (sensu Domácí 1977). The volcanic rocks of the collection of the Severočeské doly, a.s., Doly Bílina (DB). Střezov Formation consist of magmatic weathered lava The comparative fossil leaf material from the locality Le- flows related to volcanogenic deposits. These sediments žáky (Most Basin) originally assigned (erroneously) to Po- are also mixed with weathered residua of older rocks from tamogeton (Hurník in Hurník & Knobloch 1966) is housed wider surroundings, and had been transported within a ri- in the geological collection of the Regional Museum in ver system of the so-called “Hlavačov Gravel and Sand” Most (MM). Comparative extant material was obtained (Váně 1985, Rajchl & Uličný 2005). This river system pro- from the herbaria of the Charles University, Prague (PRC), bably persisted during depositing of the first Duchcov National Museum, Průhonice (PR) and W. Szafer Institute Member of the Most Formation (e.g., Teodoridis 2004), of Botany, Polish Academy of Sciences, Krakow (KRA). called previously and/or informally the Underlying Forma- The specimens were examined and detailed studies and ob- tion (sensu Elznic 1973). The overlying Holešice Member servations made using a binocular microscope and a 15 kV corresponds to a sedimentary setting of the Main Coal Jeol JSM – 6380 LV scattered electron microscope (SEM) Seam that has been interrupted by irregularly distributed used at the Institute of Geology and Palaeontology, Faculty sandy-clayey bodies of the Žatec Delta (e.g., Václ & Mal- of Science, Charles University in Prague. One specimen of kovský 1962, Rajchl & Uličný 2005) and the Bílina Delta Potamogeton wiesaensis Kirchheimer (G 8537) from the (e.g., Mach 2002). These delta bodies are situated in the SE Nástup-Tušimice Mine was studied for the structure of the part of the basin. The deposition of the Libkovice Member, testa. A mechanically isolated testa was washed in water i.e. the Overlying Formation sensu Elznic (1973), conti- and briefly macerated in Schulze solution, followed by rin- nued the sedimentary process in the Most Basin. These sing in weak potassium hydroxide solution (KOH), then sediments, mostly clay or claystone spread over the mire water, and embedded in glycerine directly on the micros- covering the previous “coal” layers. A coal-forming vege- cope glass, after a few minutes covered with a cover slide tation re-appears in the uppermost part of the Most Forma- and sealed with nail polish. tion and has delimited the range of the Lom Member sensu Currently accepted morphological terminology follows Domácí (1977), i.e. the Lom Formation of Elznic (1973). Stearn (2004) for leaves and Velichkevich & Lesiak (1996) More details about the geological situation can be found in for fossil endocarps. Symbols and abbreviations for distin- Malkovský et al. (1985), Mach (2002), Rajchl & Uličný guishing vegetation storeys in environmental reconstruc- (2005), Teodoridis & Kvaček (2006), etc. tion and climatic parameters are: E1 (herbs and vines), E2 The core MR 59 (Mariánské Radčice) offers the most (shrubs and lianas), E3 (trees under 25 m high) and E4 abundant material (29 specimens) from two fossiliferous (trees over 25 m high). 410 Vasilis Teodoridis Potamogeton fossils from the Most Basin Description Potamogetonaceae Dumortier Potamogeton L. Potamogeton wiesaensis Kirchheimer Figure 3A–P 1942 Potamogeton? n. sp., Kirchheimer, p. 443, fig. 18. 1957 Potamogeton wiesaensis Kirchheimer, p. 271, 354, pl. 13, fig. 61a–c. 1985 Potamogeton sp., Friis, p. 74, pl. 22, figs 15, 16 (Fas- terholt flora, Middle Miocene). 2003 Potamogeton wiesaensis Kirchheimer. – Czaja, p. 95, pl. 19, figs 6, 7. 2003 Potamogeton wiesaensis Kirchheimer. – Teodoridis, p. 25, pl. 7, figs 3, 4, 10, non 9, pl. 8, figs 8, 9 . Description. – Endocarps one-loculed with a strongly curved seed cavity, oval to rounded in outline (Fig. 3E, I), robust and thick-walled, often laterally compressed, 1.74–(2.61)–2.89 mm long and 1.25–(1.95)–2.3 mm broad, maximal thickness in transversal plane 1.02–(1.06)–1.12 mm; base rounded, basal wart rarely incomplete preserved (Fig. 3B), apex obtuse including indistinct fragmentary acute base of style (Fig. 3E, J), lateral sides markedly con- vex with distinct central depression, oval to rounded in outline (Fig. 3B), 0.44–(0.5)–0.63 mm long and Figure 2.

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