Geo.Cro.2-3-61-KB.pdf 113 � Bernhard Hubmann1, Lisa Verderber2 and Fritz Messner3 AB STRA CT The Lower to Middle Devonian (Emsian – Eifelian) calcareous green algal fl ora of the Graz Palaeozoic (Austria) contains halimedalean representatives of Pseudolitanaia, Pseudopalaeoporella, Zeapora, Maslovina and a new lan- ciculoid taxon. Occurrences within the Graz thrust complex are restricted to four localities in the Rannach Nappe and may be characterised as monogeneric mass occurrences. Consequently, they are interpreted as algal baffl estones originating from halimedalean meadows. Keywor ds: Devonian, green algae, mass occurrences, Graz Palaeozoic, Austria 1 Institute for Earth Sciences, Karl-Franzens-Universität Graz, Heinrichstr. 26, A-8010 Graz, Austria; (bernhard.hubmann@uni-graz.at) 2 BG/BRG Carneri, Carnerigasse 30-32, A-8010 Graz, Austria 3 Auenbruggergasse 8, A-8073 Feldkirchen bei Graz, Austria Devonian calcareous green algal fl ora of the Rannach Nappe (Graz Palaeozoic, Austria) Geologia Croatica 61/2–3 113–122 5 Figs. 2 Pls. Zagreb 2008 Geologia CroaticaGeologia Croatica � 1. INTRODUCTION 1.1. The Palaeozoic of Graz Weakly and/or unmetamorphosed Palaeozoic successions are irregularly distributed in Austria (Fig. 1). Generally two major regions of Palaeozoic developments can be distinguished which are separated by the Periadriatic Fault, the most prominent alpine fault system. These are the Eastern Alpine Variscan sequences; (i.e. the Greywacke Zone, the Gurktal Nappe, the Graz Palaeozoic and some isolated outcrops in south Styria and Burgenland) and the Southern Alpine sequences (i.e. the Carnic Alps and the Karawanken Mountains). The Palaeozoic Graz region extends over about 1250 km2 and is isolated from other low grade metamorphic (anchizonal to greenschist) facies, Palaeozoic occurrences by tectonic bo un- daries in the North, East and West as well as by younger over- lying strata in the South (Fig. 2). The Northwestern and Western parts of the Graz Palaeo- zoic are bordered by polycrystalline units (Austroalpine Crys- talline Zone), i.e. the Gleinalm, St. Radegund and the Raabalm. Further South, Palaeozoic successions are transgressively over- lain by Neogene sediments of the “Styrian Basin” whereas the Southwestern part is unconformly overlain by Upper Cre - taceous sediments of the Kainach Gosau (cf. Fig. 2). Facies developments are characteristic of the Palaeozoic Graz as well as “polyfacial” nappes but the original relation- ships of these to each other have not been clearly identifi ed. Investigations based on lithology, tectonic position and meta- morphic superimposition divide the Graz Palaeozoic into bas al, intermediate and upper nappe groups (FRITZ & NEUBAUER, 1990). These three nappe systems are identifi ed by specifi c characteristics and contain the following units:Fi gu re 1: Austria and its disconnected Palaeozoic units (shaded areas). Geologia Croatica Geologia Croatica 61/2–3 114 The Basal Nappe System (Upper Silurian to Middle De vonian) consists of the “Schöckl-Hochschlag-Nappe-Group” and was deformed under upper greenschist facies conditions (HUBMANN et al., 2006). Volcanoclastics dominate the Late Silurian to Early Devonian, while in the Middle Devonian time span carbonates prevail. The Intermediate Nappe System (Early Silurian to Upper Devonian) consists of the “Laufnitzdorf-Nappes” and “Kalk- schiefer Nappes” and contains pelagic limestones, shales, vol - canoclastics as well as siliciclastics. The Upper Nappe System (Upper Silurian to Upper Car - boniferous) consists of the “Rannach-Hochlantsch-Nappes”. Both nappes have similar facies development in common, es pecially from the Emsian to the Givetian. Successions of the Rannach Nappe are characterised by volcanoclastic rocks (Early to Middle Devonian; Reinerspitz Group), siliciclastics and fossil-rich carbonates (Early to Middle Devonian; Ran - nach Group, Lantsch Group) of near-shore environment fol - lowed by the pelagic Forstkogel Group (Late Givetian to Bashkirian) and the shallow marine Dult Group (HUBMANN et al., 2003). Palaeogeographic interpretations of the whole Palaeozoic succession have resulted in the assumption that the Rannach and Hochlantsch Nappes represent nearshore facies develop- ments, whereas the “Laufnitzdorf Facies” represents the area furthest away from the shore. Successions of the Schöckl Nap pe have an intermediate position in this scenario (HUB - MANN, 1993). The stratigraphic sequence indicates a sedi- mentary area changing from a passive continental margin with continental breakup (alkaline volcanism) to shelf and platform geometries during Silurian to Devonian time (FRITZ et al., 1992). During this time, constant subsidence resulted in in creasing carbonate production in the Upper Nappe System and during Pragian to Givetian time deposition changed from near-shore facies to open platform environments. When the carbonate platform drowned in the Frasnian, cephalopod lime- stones were deposited. 1.2. Review of stratigraphy and environmental architecture of the Rannach Nappe The main reasons why the Rannach Nappe offers the highest probability for algal discoveries are that it has the least meta- morphic overprint, and the sedimentary successions were de v- eloped nearest to the shore in moderate water depths. Due to basal volcanoclastics (Kehr and Kötschberg For - mations) and marly crinoid-rich sequences (Parmasegg Forma- tion), the peritidal Flösserkogel Formation is assumed to range from the Lower Pragian. The formation comprises different types of dolostones, silt- to sandstones and subordinate dolo- mitic limestones which are interpreted as deposition in a supra- to shallow subtidal, barrier-surrounded lagoon, or tidal fl ats (FENNINGER & HOLZER, 1978). Near Graz, the lower parts of the succession are interpreted as sand bars whereas the upper parts (which are separated by volcanic tuffs), contain meadows of the spaghetti-like stromatoporoid Amphipora. The presence of very rare conodonts indicates a (Lower?) Emsian age (cf. EBNER et al., 2000, 2001). Another formation belonging to the Rannach Group is the Plabutsch Formation. It overlies or rather interfi ngers with the Flösserkogel Formation and predominantly contains typical “reefbuilding organisms” (HUBMANN, 1993, 2003) which are present in all sections. Nevertheless, there is no outcrop evidence of a “true reef” rather than coral-stromatoporoid- carpets and lagoonal sediments which are the dominant fea - tures. Environmental investigations indicate deposition on a differentiated and slightly inclined carbonate platform (HUB - MANN, 1993). The following features support the assumption that sedimentary conditions were unfavourable for reef forma- tion: the rarity of in situ organisms, the intermittent but gener- ous supply of clayey sediments (marl-limestone intercalations) and plentiful supply of lime mud, a temporary infl ux of large amounts of continental phytoclasts, storm impacts (several tempestite sequences within the profi les) and especially their effects on biocoenosis (HUBMANN, 1995). This phase is terminated by a repetition of tidal fl at depos- its similar to the Flösserkogel Formation and obviously caused by a eustatic sea level fall. A transgression resulted in a se qu- ence with sharp biofacies contrasts between patch-reefs and monotonous mudstones of Givetian age (the Kollerkogel, Tyrnaueralm, and Zachenspitz Formations). During the uppermost Givetian to lower Frasnian, sedi- mentation of shallow platform carbonates was replaced by micritic cephalopod limestones (Steinberg Formation). This sedimentation continued up to the Bashkirian (Sanzenkogel Formation, Forstkogel Group). The sequence is terminated by shallow marine sediments, shales and limestones with birds- eye structures. 1.3. Algal horizons In two of the above mentioned formations, remains of algal thalli have been found, namely in the Lower Devonian (Pra - Fi gu re 2: Simplifi ed sketch of the Graz Palaeozoic. Shaded patches correspond with areas of the Rannach Nappe outcrops. Numbers of localities indicate the algal disocveries mentioned in the text. Geologia Croatica 115 Bernhard Hubmann et al.: Devonian calcareous green algal fl ora of the Rannach Nappe (Graz Palaeozoic, Austria) gian?-Emsian) Flösserkogel Formation and in the Middle De vo nian (Eifelian) Plabutsch Formation. All these algal fi nd- ings are monogeneric mass occurrences and therefore make up the majority of the rock. Consequently, they are interpreted as (par) autochthonous baffl estones. According to FENNINGER & HOLZER (1978), profi les of the Flösserkogel Formation contain “dasyclads” in the skel- etal grains of the tidal fl at-deposits (Pfaffenkogel). Although further investigations confi rm the occurrence of reworked Ortonella-remains and pieces of halimedaleans, algal thalli suitable for taxonomic determination have not been discov- ered. Well preserved, determinable algae have so far been detected only at the following four localities: 2. SAMPLING LOCATIONS Locality 1: (Coordinates: 47°08’25’’N/15°15’27’’E) At a suc - cession north of the Rein monastery (ca. 20 km North of Graz) an occurrence of little disarticulated lanciculoid algae was observed. This location is characterised by dark-grey to black, micritic to pelmicritic dolomites, (equivalent to Amphipora meadows), and can be assigned to a slightly subtidal deposi- tional environment. Rocks yield a high number of algal thalli, mainly consisting of 8–15 articuli. Moreover, the thalli at the surface of weathered rocks seem to be very well preserved. Anatomic details, however, are only visible using a darkfi eld condensator. Locality 2: (Coordinates: 47°03’40’’N/15°22’34’’E) The oldest known algal taxon of the Graz Palaeozoic, Zeapora, oc curs in the Plabutsch Formation (formerly “Barrandeikalk”). It is restricted to one single outcrop, the former illite mine on the Southern slope of the Kollerkogel at the border to the urban area of Graz. The black, graphitic horizon containing algal thalli is located only a few dm above the illite at the base of the Plabut- sch Formation. PENECKE (1894) described these fragile fossils as Zeapora gracilis, but assigned them mistakenly to the Bryo- zoans. FLÜGEL (1959) recognized their algal nature and HUB - MANN (2000) later revised and emended his description. Locality 3: (Coordinates: 47°05’25’’N/15°22’11’’E) The occurrence of Pseudopalaeoporella lummatonensis and Pseu- dolitanaia graecensis is also located near the city of Graz (at a small path on the Southern slope of the Frauenkogel). The upper parts of the Plabutsch Formation are characterised by alternating layers of clayey limestones, red mudstones and marls. In the clayey limestones of this alternating sequence, masses of Pseudopalaeoporella lummatonensis but only a subordinate number of Pseudolitanaia graecensis thalli occur. Fi gu re 3: Stratigraphic column of the Rannach Nappe: 1) Kehr Formation, Kötschberg Formation; 2) Parmasegg Formation; 3) Flösserkogel Formation, Bameder Formation; 4) Plabutsch Formation; 5) Kollerkogel Formation; 6) Steinberg Formation; 7) Sanzenkogel Formation; 8) Höchkogel Formation; 9) Hahngraben Formation. Geologia Croatica Geologia Croatica 61/2–3 116 PLATE I 1 Polished surface of algal limestone from locality 3 with an oblique section through Pseudolitanaia graecensis. 2 Thin-section of Pseudolitanaia graecensis, transverse section exhibiting dichotomous off sets of cortical fi laments that branch off coarse medullary fi laments. Locality 3. 3 Cross-section of Pseudolitanaia graecensis from the locality3. 4 Weathered surface of algal limestone of locality 3 built up exclusively by densely packed thalli of Pseudopalae- oporella lummatonensis. Note the minor degree of calcifi cation in the medullary region of algal bodies. 5 Oblique longitudinal section of Pseudopalaeoporella lummatonensis showing a well defi ned cortical zone and a poorly calcifi ed central axis from the locality 3. 6 Cross-section of Pseudopalaeoporella lummatonensis from the locality 3. 7 Surface of algal limestone from locality 2 (abandoned quarry at Kollerkogel) with densly packed thalli of Zeapora gracilis. 8 Photomicrograph of thin-section illuminated by darkfi eld condensor. Oblique longitudinal section of Zeapora gracilis. Note the large peripheral tubules fi lled with coarse-grained sparite. 9 Photomicrograph of thin-section illuminated by darkfi eld condensor. Cross-section of Zeapora gracilis. Cortical fi laments vary due to diff erent orientation of their clubbed shapes. All white scale bars represent 1 mm. Geologia Croatica 117 Bernhard Hubmann et al.: Devonian calcareous green algal fl ora of the Rannach Nappe (Graz Palaeozoic, Austria) Geologia Croatica Geologia Croatica 61/2–3 118 PLATE II 1 Weathered surface of an algal bearing limestone of locality 4 (road cut St. Pankrazen) exhibiting cross sections of Maslovina sp. 2 Longitudinal section of a fragment of Maslovina sp. Note arrangement of numerous, fi ne medullary fi laments. 3 Cross-section of Maslovina sp. showing a well-defi ned medullar zone. Note terminations of the cortical fi laments (amphora-shaped utricles). 4 Weathered surface of the undetermined lanciculoid alga of locality 1. 5 Photomicrograph of thin-section illuminated by darkfi eld condensator. Longitudinal section the lanciculoid alga. 6 Photomicrograph of thin-section illuminated by darkfi eld condensator. Cross section is exhibiting four coarse medullary fi laments. 7−9 Branching thalli of (7) Pseudolitanaia graecensis, (8) Zeapora gracilis, and (9) new lanciculoid alga. All white scale bars represent 1 mm. Geologia Croatica 119 Bernhard Hubmann et al.: Devonian calcareous green algal fl ora of the Rannach Nappe (Graz Palaeozoic, Austria) Geologia Croatica Geologia Croatica 61/2–3 120 The slight disarticulation of the thalli as well as their occur- rence in clayey limestones, indicate a hydrodynamically low depositional environment. Locality 4: (Coordinates: 47°08’01’’N/15°11’02’’E) The outcrop is situated along the road about 2 km South of St. Pankrazen (30 km NW of Graz). The lower parts of the Plabut- sch Formation contain a mass occurrence of Maslovina which has recently been the subject of taxonomic investigation (VER - DERBER, 2007). The respective horizon lays only a few dm above the basis of the shale horizon which corresponds in posi- tion to the illite horizon of the Kollerkogel. 3. RESULTS AND DISCUSSION The Graz taxa Genus Pseudolitanaia MAMET & PRÉAT, 1994 Pseudolitanaia graecensis (HUBMANN, 1990) (Fig. 4 B, Fig. 5 B; Pl. I, Figs. 1–3; Pl. II, Fig. 7) 1990 Litanaia graecensis – HUBMANN, p. 148–150, fi gs. 3–4, pl. 35, fi gs. 1–6 1994 “Litanaia” graecensis – HERRMANN & HUBMANN, p. 200, pl. 1, fi g. 5 1994 Pseudolitanaia graecensis – MAMET & PRÉAT, p. 148 The thallus is erect, cylindrical and continuous; its central part consists of 4 to 12, generally 8 irregular fi laments with appen- dices which develop towards a high number of cortical fi la- ments. These cortical fi laments are more or less oblique with a signifi cantly increasing diameter and a spatula-shape. They end up as fi ne fi laments of second order dichotomy and their termination resembles Pseudopalaeoporella. Average diam- eter of thalli is 2.8 mm, central fi laments vary between 0.25 and 0.33 mm, and cortical fi laments are approximately 0.88 mm thick. Genus Pseudopalaeoporella MAMET & PRÉAT, 1985 Pseudopalaeoporella lummatonensis (ELLIOTT, 1961) (Fig. 4 A, Fig. 5 A; Pl. I, Figs. 4–6) 1961 Palaeoporella lummatonensis – ELLIOTT, p. 251–254, pl. 9, fi gs. 1–5; pl. 10, fi gs. 1–4 1983 Palaeoporella lummatonensis – BASSOULLET et al., p. 553–554, pl. 13, fi gs. 1–2 1985 Palaeoporella lummatonensis – ROUX, p. 564 1985 Pseudopalaeoporella lummatonensis – MAMET & PRÉAT, p. 70–72, pl. 3, fi gs. 2–8 1987 Pseudopalaeoporella lummatonensis – MAMET & PRÉ AT, p. 441, fi g. 4 Fi gu re 4: Green algae of the Graz Palaeozoic: reconstructions of the outer morphology of (A) Pseudolitanaia graecensis, (B) Pseudopalaeoporella lummatonensis, (C) Zeapora gracilis, (D) Maslovina sp. and (E) the undetermined lanciculoid alga. Fi gu re 5: Organisational diff erences of (A) Pseudolitanaia graecensis, (B) Pseudopalaeoporella lummatonensis, (C) Zeapora gracilis, (D) Maslovina sp. and (E) the undetermined lanciculoid alga. Geologia Croatica 121 Bernhard Hubmann et al.: Devonian calcareous green algal fl ora of the Rannach Nappe (Graz Palaeozoic, Austria) 1987 Funiculus venosus n. gen. et n. sp. – SHUYSKY & SHIR- SHOVA, p. 100–101, fi gs. 1–4 1990 Pseudopalaeoporella lummatonensis – HUBMANN, p. 150–151, fi g. 5, pl. 35, fi gs. 1–6 1992 Pseudopalaeoporella sp. – BUGGISCH & FLÜGEL, p. 80, pl. 1, fi gs. 5–6; pl. 3, fi g. 2 1992 Pseudopalaeoporella lummatonensis – MAMET & PRÉAT, p. 55, pl. 3, fi gs. 1–11 1993 Pseudopalaeoporella lummatonensis – HUBMANN & FENNINGER, p. 648–649, fi g. 1 1993 Palaeoporella lummatonensis – VACHARD, p. 97–98, pl. 6, fi gs. 6, 18, 21–25 1994 Pseudopalaeoporella lummatonensis – HERRMANN & HUBMANN, p. 198–200, fi g. 4, pl. 1, fi gs. 2–4 1994 Pseudopalaeoporella lummatonensis – KOCH-FR ÜCHTL & GEE, p. 4–7, fi g. 3, pl. 1, fi gs. 1–6; pl. 2, fi gs. 7–15; pl. 3, fi gs. 16–23 When unbranched, thalli are cylindrical in form with a medullar zone and an extensive radial envelope. Their diameters vary between 0.8–1.8 mm (mean value about 1.4). The medullar zone (~ 0.65 mm in diameter) is composed of several central tubes (up to 20?) and makes up approximately half the entire thallus diameter in cross section. Central fi laments are arranged parallel to the thallus axis and are closely spaced. Cortical fi la- ments develop from central tubes in acute angles into numer- ous lateral tubes with a second and third order dichotomy. The fi laments are commonly swollen just below the points of br anch- ing and widen trumpet-like towards the thallus surface. Genus Zeapora PENECKE, 1894 Zeapora gracilis (PENECKE, 1894) (Fig. 4 C, Fig. 5 C; Pl. I, Figs. 7–9, Pl. II, Fig. 8) 1894 Zeapora gracilis – PENECKE, p. 610, pl. 10, fi g. 11 1959 Zeapora gracilis – FLÜGEL, p. 147–149, fi gs. 1–2 2000 Zeapora gracilis – HUBMANN, p. 31–37, fi gs. 3–5 The thalli clearly show numerous peripheral tubules arranged around a central axis fi lled with a bundle of medullar fi la- ments. The medullar zone, usually 0.39 to 0.40 mm in diam- eter, consists of 4–6 (up to 10 and more) slightly interwoven fi laments. Their diameters vary between 0.08–0.21 mm. The cortical zone is fi lled with massive carbonate deposits and perforated by roundly-elongated, densely packed fi laments. Cortical fi laments vary considerably in longitudinal and cross sections due to different orientation of their bowl-like shapes. In some specimens, they seem to be segmented. Genus Maslovina OBRHEL, 1968 Maslovina sp. The thallus is of a straight, cylindrical shape, occasionally un dulated. Thalli vary in length between 3.0–11.5 mm, diam- eters measure between 0.78–2.55 mm (median value 1.9 mm), and are internally organised into a generally poorly calcifi ed medullar area and a cortical zone. The medullar part (diameter averages 0.93 mm) consists of a high number (>40) of inter- woven fi laments (on average 0.04 mm wide) which give rise to fi ner, cortical fi laments (approximately 0.02 mm in diam- eter). They divide dichotomously at an acute angle and reach a third order dichotomy at the outermost cortical part. At this stage cortical fi laments develop towards densely packed am phora-shaped utricles which constitute the thallus surface. Reproductive organs are not observed. Maslovina sp. differs from the type species M. meyenii in having more numerous medullar tubes (> 40); these numer- ous tubes are also a characteristic feature of the Devonian spe - -cies M. australense (see MAMET & POHLER, 2002). The far greater thallus diameter and length is what distinguishes Maslovina sp. from the two other species. The most remark- able differentiating feature, however, is that Maslovina sp. has outermost cortical fi laments developing into a layer of tightly packed utricles which are, in contrast to M. meyenii, amphora- shaped. M. australense differs from the other two species in showing irregularly spaced, thin terminal fi laments forming an irregular epiderm (MAMET & POHLER, 2002; OBREHL, 1968). Undetermined lanciculoid alga (Fig. 4 E, Fig. 5 E; Pl. II, Figs. 4–6, 9) Regularly segmented algal bodies only minor disarticulation exhibiting. Thalli consist of up to 25 bowl-shaped elements (articuli, chalices) surrounding a straight or slightly bent stem (rachis). Occasionally thallus ramifi cations are observed. Thin-sections expose an internal assembly of four central fi laments pervading the whole thallus. They apparently do not vary considerably in diameter (approximately 0.15–0.20 mm), but may be slightly curved or undulating. From medullary fi la- ments a great number of cortical fi laments branch off radially, and perpendicular to the central axis decreasing their angles with growth. Each tapered segment contains two rows of corti- cal fi laments and increases its diameter towards the growth direction. These segments resemble the bell of a trumpet and are densely stacked one above the other. The outer morphology of the articuli of our lanciculoid alga resembles the genus Quasilancicula, but its chalices are more compressed. Its tentacle-shaped chalice edges, however, show similarities with Lepidolancicula. ACKNOWLEDGEMENT We acknowledge the valuable contributions made by the referees Bernard Mamet and Felix Schlagintweit. The study is a contribution to the project NAP0001 (IGCP 497). REFERENCES BASSOULLET, J.P., BERBIER, P., DELOFFRE, R., GENOT, P., PON- CET, J. & ROUX, A. (1983): Les Algues Udoteaces du Paléozoique au Cénozoique. – Bull. Centres Rech. Explor. – Prod. Elf Aquitaine, 7, 449–621. 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(2007): Devonian halimedacean green algae with spe- cial emphasis on a new species from the Graz Palaeozoic. – Unpub- lished Diploma Thesis, K.-F. – University Graz, 94 p. Manuscript received February 19, 2008 Revised manuscript accepted May 19, 2008