Int loum Earth Sciences (1999) 88:60-75 J. Peckmann . V. Thiel . W. Michaelis' P. Clari C. Gaillard' L. Martire . J. Reitner © Springer-Verlag 1999 Cold seep deposits of Beauvoisin (Oxfordian; southeastern France) and Marmorito (Miocene; northern Italy): microbially induced authigenic carbonates Received: 13 October 1998 / Accepted: 5 February 1999 Abstract The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are found to be asso- ciated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito ("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 813Ccarbonate values, respectively. Highly positive values (+ 15%0) reflect the use of 13C-enriched CO2 produced by methanogenesis. Low 813C values of the Marmorito carbonates (-30%0) indicate the oxidation of seepage- derived hydrocarbons. Likewise, the 813C content of specific tail-to-tail linked isoprenoids, biomarkers for archaea, was found to be strikingly depleted in these sampies (as low as -115%0). The isotopic signatures corroborate that archaea were involved in the cycling of seepage-derived organic carbon at the ancient locali- ties. Another Miocene limestone ("Marmorito li me- stone") shows a strong imprint of methanotrophic bacteria as indicated by 813C va lues of carbonate as low J. Peckmann (IEI) . J . Reitner Institut und Museum für Geologie und Paläontologie, Georg-August-Universität. Goldschmidtstrasse 3, D-37077 Göttingen, Germany e-mail: jpeckma@gwdg.de. Fax: + 49-551-397918 V. Thiel, W. Michaelis Institut für Biogeochemie und Meereschemie, Universität Hamburg, Bundesstrasse 55, D-20146 Hamburg, Germany P. Clari, L. Martire Dipartimento di Scienze della Terra, via Accademia delle Scienze 5, 1-10123 Torino, Italy C. Gaillard UFR des Sciences de la Terre, UMR 5565 Centre de Paleontologie stratigraphique et Paleoecologie, Universite Claude Bemard, Lyon 1, 27-43 Boulevard du 11 Novembre, F-69622 Villeurbanne Cedex, France as -40%0 and biomarker evidence. Epifluorescence microscopy and field-emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation. In addition to lucinid bivalves previously reported from both locali- ties, we infer that sponges from Beauvoisin and tube worms from Marmorito depended on chemosynthesis as weil. Low 813C values of nodules related to sponge taphonomy (-27%0) indicate that sponges might have been Iinked to an enhanced hydrocarbon oxidation. Tube worm fossils from Marmorito closely resemble chemosynthetic pogonophoran tube worms from Recent cold seeps and are embedded in isotopically light carbonate (813C -300/00). Key words Carbonates . Cold seeps . Methane . Petroleum . Archaea . Bacteria . Sponges . Tube worms . Epifluorescence . Biomarkers . Jurassic . Tertiary . France . Italy Introduction Recent and ancient cold seep carbonates Seep carbonates are well-known products of the micro- bial oxidation of methane and other reduced gases seeping out from the sea f1oor. Since the past decade they have been documente'd from Recent and ancient seeps and vents situated in 'different geological settings. It has been suggested that sylphate reduction coupled with anaerobic oxidation of methane resulting in an increase in alkalinity is the driving reaction for the precipitation of carbonate at these sites (Ritger et al. 1987; Jörgensen 1989; Suess and Whiticar 1989). This hypothesis is supported by the abundance of pyrite in carbonates. Mg-calcite, aragonite and dolomite are the common authigenic minerals at cold seeps (Roberts et al. 1993). In addition to micritic matrices, different types of carbonate-cements have been reported, such as Reitz E (1992) Silurische Mikrosporen aus einem Biotit-Glim- merschiefer bei Rittsteig, Nördlicher Bayerischer Wald. N Jahrb Geol Paläontol Mh: 351-358 Reitz E , Höll R (1988) Jungproterozoische Mikrofossilien aus der Habachformation in den mittleren Hohen Tauern und dem nordostbayerischen Grundgebirge. Jahrb Geol BA 131 :329-340 Röhr C (1990) Die Genese der Leptinite und Paragneise zwischen Nordrach und Gengenbach im mittleren Schwarz- wald. Frankfurter Geowiss Arb Serie C 11: 1-159 Sutherland SJE (1994) Ludlow chitinozoans from the type area and adjacent regions. Palaeontograph Soc Monogr Lond 148:1-104 Tait JA, Bachtadse V, Franke W, Soffel HC (1997) Geodynamic evolution of the European Variscan fold belt: palaeomagnetic and geological constraints. Geol Rundsch 86 :585- 598 Todt W (1976) Zirkon-U/Pb-Alter des Malsburg-Granits vom Südschwarzwald. N Jahrb Mineral Mh: 532-544 Todt WA, Büsch W (1981) U-Pb investigations on zircons from pre-Variscan gneisses. 1. A study from the Schwarzwald, West Germany. Geochim Cosmochim Acta 45: 1789-1801 Torsvik TH, Smethurst MA, Meert JG, Voo RVd, McKerrow WS, Brasier MD, Sturt BA, Walderhaug HJ (1996) Conti- nental break-up and collision in the Neoproterozoic and Paleozoic: a tale of Baltica and Laurentia. Earth Sei Rev 40 :229-258 Traverse A (1988) Paleopalynology. Unwin Hyman, Boston, pp 1-600 59 Vogler WS (1995) Who can survive high-pressure metamor- phism? Bochumer Geol Geotech Arb 44:250-254 Wada H, Tomita T, Matsuura K, Iuchi K, Ho M, Morikiyo T (1994) Graphitization of carbonaceous matter during meta- morphism with reference to carbonate and pelitic rocks of contact and regional metamorphisms, Japan. Contrib Mineral Petrol 118 : 217-228 Wang G-F (1989) Carbonaceous material in the Ryoke meta- morphic rocks, Kinki district, Japan. Lithos 22 :305-316 Wendt 11, Kröner A, Fiala J, Todt W (1993) Evidence from zircon dating for existence of approximately 2.1 Ga old crystalline basement in southern Bohemia, Czech Republic. Geol Rundsch 82 :42-50 Wickert F, Altherr R , Deutsch M (1990) Polyphase Variscan tectonics and metamorphism along a segment of the Saxothu- ringian-Moldanubian boundary: the Baden-Baden Zone, northern Schwarzwald (F.R.G} Geol Rundsch 79 :627-647 Wimmenauer W (1988) Precambrian in the horst mountains of the Rhine graben area. In: Zoubek V (ed) Precambrian in younger fold belts. European Variscides, the Carpathians and Balkans. Wiley, Chichester, pp 381-408 Wopenka B, Pasteris JD (1993) Structural characterization of kerogens to granulite-facies graphite: applicability of Raman microprobe spectroscopy. Am Mineral 78: 533-557 Zulauf G, Dörr W, Fiala J, Vejnar Z (1997) Late Cadomian crustal tilting and Cambrian transtension in the Tepla-Barran- dian unit (Bohemian Massif, Central European Variseides). Geol Rundsch 86 :571-584 61 Table 1. Compilation of types of cold seep carbonates analysed in this study and their characteristics Cold seep carbonate Frequent fossils Carbonate species Stable isotopes Biomarkers Beauvoisin Lower Oxfordian carbonates Middle and Upper Oxfordian carbonates Marmorito Lucina lirnestone Tube-worm limestone Botryoidal aragonite Marmorito limes tone Lucinid bivalves Sponges Gastropods Cephalopods Crustaceans Foraminifera Ostracods See Lower Oxfordian carbonates, sea urchin Lucinid bivalves Foraminifera Tube worms Foraminifera None None Mg-calcite Calcite Dolomite Aragonite Calcite Calcite Calcite Aragonite Dolomite Calcite botryoidal aragonite or calcite, splayed calcite and yellow calcite (Beauchamp and Savard 1992). It has been presumed that botryoids are of bacterial origin (Roberts et al. 1993). Negative 813C values of seep carbonates are related to the microbial oxidation of thermogenic (-50%0 PDB) and biogenic (-60 to -110%0 PDB) methane (Whiticar et al. 1986; Hovland et al. 1987). The lowest 813C values measured for carbonates from Recent cold vents are -53.9%0 PDB (Roberts et al. 1993), -56.10/00 PDB (Hovland 1987) and -66.7%0 PDB (Ritger et al. 1987). The macro-fauna associated with cold vents is domi- nated by mussels, clam bivalves and tube worms (Paull et al. 1984; Kennicutt et al. 1985; Suess et al. 1985; Juniper and Sibuet 1987; Rosman et al. 1987; Hashi- moto et al. 1989; Callender et al. 1990). These inverte- brates harbour chemolithotrophic or methanotrophic bacteria wh ich supply their hosts with energy and nutrients by oxidizing reduced sulfur species or methane (Jannasch 1984). The interpretations of fossil seep sites are based on features similar to their modern counterparts, i.e. nega- tive 813Ccarbonate values and the localized occurrence of particular macroinvertebrate taxa ("fossil seep-search strategy"; Campbell et al. 1993). Here we report on two well-known examples of fossil seep carbonates. Special emphasis is placed on microbially induced precipitation and on the relevance of taphonomic processes sucQ as the bacterial degradation of soft tissues on the creation of bacterioform fabrics. Carbonate phases exhibiting enhanced concentrations of organic compounds were detected by epifluorescence microscopy. Furthermore, we applied organic geochemical techniques to trace molecular fingerprints of fossil chemosynthetic micro- biota associated with the formation of these ancient rocks. Beauvoisin 013e: - 26.5 to + 13.0%0 0180 : -7.1 to +2.9%0 oI3e: -13.6 to + 15.1 '1100 0180: -1.2 to +0.7%0 0 l3e: -35.5 to -0.1 '1100 d 180 : +0.1 to +4.9'1100 (Clari et al. 1994) 013e: -32.9 to -26.6%0 0180: -0.4 to + 0.1 %0 013C: -34.8 to -27.0%0 0180 : +0.3 to +2.7%0 oI3e: -40.2 to -17.3%0 0180: +4.8 to +4.9%0 n-alkanes n-alkanes PME Squalane Not analysed Crocetane PME Not analysed Methyl-sterols Methyl-hopanols Beauvoisin is located in southeastern France near Buis- les-Baronnies (Dröme; Fig. 1). Cold seep carbonates are exposed within the thick succession of J urassic black shales of the "Terres Noires" Formation in Lower Oxfordian to Upper Oxfordian strata (Gaillard et al. 1985). The fossiliferous carbonates have been characterized as pseudobioherms since they exhibit a bioherm-like shape but neither include reef-building organisms nor form a significant sea-floorrelief. The pseudobioherms are situated along major faults that were probably active during the deposition of the "Terres Noires" Formation (Gaillard et al. 1985). 7" Fig. 1 Location of the Beauvoisin and Marmorito outcrops 62 Faulting occurred in an extensional tectonic regime along the continental margins due to the opening of the Tethyan Ocean during the late Jurassic (Gaillard et al. 1992). The pseudobioherms have a high carbonate content compared with the surrounding hemipelagites (85 vs 35% CaC03 ) and grew within the sediment near to the sediment-water interface. Lower Oxfordian pseudobioherms are exposed in the dark, well-stratified marls of the upper part of the "Terres Noires" Formation (Fig.2). They are large conical or lenticular carbonate buildups 1-10 m in height. Pseudobioherms contain a rich endofauna. Dominant organisms are endobenthic, large-sized bivalves (Iucinids) which locally form very dense clus- ters similar to recent examples (cf. Sibuet and Olu 1998). Their palaeoecology has been studied and their communities have been found to be similar to those of recent hydrothermal vents and cold seeps (Rolin et al. 1990; Gaillard et al. 1992). Middle and U pper Oxfordian pseudobioherms occur Fig.2 Two Lower Oxfordian pseudobioherms (fore- and back- ground) embedded in dark marlstones of the Terres Noires Formation. The pseudobioherm in the background is approxi- mately 10 m in height and 15 m in width , Beauvoisin in the first limestone/marl alternations just above the "Terres Noires" Formation. Most of them are exposed in the basal " Argovian sequence" which corresponds to the Transversarium zone. The pseudobioherms form sm all lenses or columns of 1-2 m in height and width (Fig.3). They laterally pass into beds wh ich can be distinguished throughout the whole southeastern France basin (Gaillard et al. 1992). A genetic relation between these pseudobioherms and synsedimentary tectonics has been demonstrated by Gaillard and Rolin (1988). Marmorito Cold seep deposits occur near the village of Marmorito in the Monferrato hills , east of Torino in northern Italy (Fig. 1). The seep carbonates are embedded in the Miocene strata of the western Monferrato hills, most of which consist of coarse- to fine-grained siliciclastic sedi- ments deposited in a slope to inner shelf environment (Clari et al. 1988). The sequence of the Tertiary Pied- mont Basin is considered to be posttectonic, as the Fig.3 Middle Oxfordian pseudobioherm, Beauvoisin weak superimposed Tortonian to early Pliocene lateral thrusting of the Monferrato hills vanishes towards the Collina di Torino structure in the west (Ricci Lucchi and Vai 1994). Marmorito is one of the first examples for wh ich a relationship of ancient methane venting, fossil chemosynthetic bivalve communities, and methane-related carbonate precipitation has been demonstrated (Clari et al. 1988, 1994). The interpreta- tion was based on the isotopic composition of carbon- ates (813C values as low as -35%0) and on the presence of bivalve assemblages similar to those of modern seeps. Clari et al. (1988) reported two different types of methane-related carbonates, the Lucina limestone and the Marmorito limestone. The Lucina limestone is a light-brown marly limes- tone, packed with bivalve (lucinid) molds. Its minera- logy is calcitic. The micro-crystalline, extremely hard Marmorito limestone appears to be barren of fossils and exhibits either a calcitic or dolomitic mineralogy. A typical feature of the Marmorito limestone is a chaotic fabric due to an intense brecciation. Methods Standard petrographic microscopy was performed on thin sections (150 x 100, 100 x 75 and 48 x 28 mm). For petrographical staining a mixture of potassium ferri- cyanide and alizarin red, dissolved in 0.1% HCI, was used. Aragonite was stained with Feigl's solution (Feigl 1958). Titan-Yellow staining allowed the estimation of the Mg content of calcite (Choquette and Truse1l1978) by comparison with stained calcites of known Mg content. Mg measurements were performed with atomic absorption spectrometry on a Philips PU 9200X (Philips, Best, The Netherlands). Fluorescence micros- copy was carried out on a Zeiss Axiolab (larnp: HBO 50; filters: BP 365 FT 395 LP 397 and BP 450-490 FT 510 LP 520). A Leo 1530 Gemini was used for field- emission scanning electron microscopy on uncoated sampies that were etched with 1 % HCl for 1 min. Sampies for oxygen and carbon stable isotopic analyses were taken from the surfaces of polished blocks using a handheld microdrill. Carbon dioxide for analyses was obtained by reacting the sampie with 100% orthopos- phoric acid in vacuo at 25°C, and was analysed in a Finnigan MAT 251. The 813C and 8180 results are reported relative to the PDB standard (SD<0.04%) and appropriate correction factors were applied (Craig 1957). A correction factor for 8180 values of -0.57%0 (Kim and O'Neil 1997) was added to the aragonite sampies and a correction factor of -0.80/00 (Sharma and Clayton 1965) was added to the 8180 values of dolomite sampies. X-ray diffraction (XRD) was carried out on unoriented slurries using a diffractometer with Cu Ka radiation (Philips PW 1800, Philips, Best, The Netherlands). For biomarker analyses the carbonates were carefully cleaned (diluted HCI, acetone) and decalcified (diluted HCI). The residues were washed to 63 a pH of >5, and dried. After saponification (6% KOH in CH30H), the supernatant was decanted and the residue further extracted three times with CH2Chi CH30H (3: 1 v:v, ultrasonication 3 x 20 min). Subse- quently, the combined supernatants were extracted with CH2Ch vs water (pH2). The organic substances of the CH2Ch phase were fractionated by column chroma- tography (Merck silica gel 60). Hydrocarbons were eluted with n-hexane, and an alcohollester fraction with CH2Ch. Prior to further analyses, alcohols were converted to acetates by treatment with pyridine/acetic acid anhydride (1: 1; v:v). All analyses were run on a Carlo Erba Fractovap 4160 gas chromatograph (GC) using a 30 m fused silica capillary column (DB5, 0.32 mm i.d., 0.25-!-Lm film thickness), on-column injec- tion and a flame ionization detector. Compound iden- tifications were based on coupled gas chromatographyl mass spectrometry (GC-MS). The GC-MS system used was a Finnigan MAT CH7 A mass spectrometer inter- faced to a Carlo Erba 4160 gas chromatograph, equipped with aSO-rn fused silica capillary column (DB5HT, 0.3 mm i.d., 0.25 !-Lm film thickness) and on- column injection. Helium was used as carrier gas. Compound-specific isotopic signatures were analysed by GC-combustion-isotope ratio mass spectrometry (GC-C-IRMS) and were performed on a Finnigan MAT 252 mass spectrometer controlled by Isodat soft- ware. Isotope ratios are reported as 8-values [813C (%0), relative to the PDB standard]. The measurements were calibrated against internal standards of known isotopic composition (s = < 1 %0). Results Seep biota Beauvoisin Mollusks are the most frequent macro-fossils in Lower Oxfordian carbonates (see Table 1). They are domi- nated by large lucinid bivalves which are confined to pseudobioherms where they may form dense clusters (Fig. 4a). The largest specimens reach 18 cm in length. When preserved, the outer layer of the shell provides positive 813C values as high as + 5%0. These values are probably related to the symbiotic community with chemosynthetic bacteria (Rolin et al. 1990; Gaillard et al. 1992). Other mollusks include various gastropods and cephalopods (mainly amrnonites) which probably thrived on the rich food supply provided by bivalves and bacteria. Crustacean exoskeletons, fragments and coprolites, as weIl as fish teeth, reflect the presence of additional predators or scavengers. The crustacean coprolites belong to the form-genus Favreina (Brönni- mann 1955), wh ich is attributed to the anomuran super- families Thalassinoidea and Galatheoidea (Brönni- mann 1972). Probable deposit feeders, such as holothu- roids (sclerites), and suspension feeders, such as 64 Fig.4a-d Lower Oxfordian carbonates and associated biota, Beauvoisin. a Massive limestone with lucinid bivalves. b Polished slab showing the typical nodular fabric of the seep carbonates. The seale bar corresponds to 1.5 cm. c Sponge nodule (sn) lined by an outer rim of pyrite and within the micro-crystalline matrix (m). The seale bar corresponds to 1 mm. d Sponge nodule with hexactinellid spicules and the typical clotted, bacterioform fabric. The seale bar corresponds to 100 fLm crinoids (ossicIes), are found in minor abundance. These biota are common in bathyal environments of the Jurassie sea floor and are not restricted to vents. Among the microfauna benthic foraminifers (Spirillin- idae, Nodosariidae, Textulariidae, Ophthalmidium) and ostracods predominate. Planktonic foraminifers (Globi- gerinidae) , radiolarians and dinoflagellates are present but less numerous. Sponges are also frequent within Lower Oxfordian carbonates. Lyssaeid hexactinellids are most common and are accompanied by " lithistid" demosponges, unidentified demosponges and lychniscid hexactinel- lids. Some fossilized sponge bodies were found , but nodular aggregates containing spicules are much more common. These nodules are darker than the micritic matrix, in which they are embedded. They contain framboidal pyrite and are often lined by an outer rim of pyrite (Fig. 4c). Internally the nodules exhibit a c10tted fabric (Fig. 4d). Abundance of fossils is low in Middle and Upper Oxfordian limestones. Apart from that the fauna is very similar to the Lower Oxfordian carbonates. A remarkable feature of some pseudobioherms is the local mass occurrence of a small irregular sea-urchin Tithonia (Gaillard et a1. 1992). Marmorito In contrast to the Marmorito limestone, the Lucina limestone contains a diverse fauna (see Table 1). The limestone is named after large, articulated c1ams found in this rock. Due to the preservation as molds , a taxon- omie evaluation is not possible. Associated with the molds are peloids of two size c1asses. The diameter of the larger ones is approximately 1400 X 1000 fLm but may reach 3000 fLm. The smaller-sized peloids are approximately 140 X 110 fLm in diameter. The microfa- eies of the Lucina limestone is dominated by planktonic foraminifers. Foraminifers may be so frequent that the rock can be termed a foraminiferal packstone. In rocks where they are most abundant c1ams recede. Planktonic foraminifers belong to the order Rotalüda with the genera Globigerina and Orbulina predominating. Benthic foraminifers and fragments of echi noids are also common. A block of limestone with the remains of tube worms was found among blocks of the Lucina lime- Fig.S Polished slab of the tube-worm limestone. The white arrows point to worm tubes and the black arrow points to a Plano!ites-type burrow, Marmorito. The scale bar corresponds to 1 cm stone (Fig. 5). Tubes are arranged in dense clusters, predominantly in life position. The skeletons of tube worms were dissolved and resulting porosity is partly filled by calcitic cements. The interior of the tubes is filled with sediment and the diameter of molds varies from 700 to 1000 f.Lm. The clusters are enclosed in a micritic, brownish-yellow sediment. The microfacies of the limestone with tube worms is similar to the Lucina limestone, but planktonic foraminifers are less frequent. Planolites-type burrows up to 5 mm in dia- meter cross the sediment (Fig. 5). The cylindrical burrows filled with micrite are curved and do not branch. Seep carbonates Beauvoisin The Oxfordian seep carbonates are formed of micritic nodules. Nodules are densely packed in the centres and become scattered towards the margins, thus indicating a radial growth direction. Concretions formed around body fossils, such as ammonites and bivalves, are common. Other concretions are related to sponge taphonomy and burrowing (Fig. 4b). All kinds of nodules in the pseudobioherms are surrounded by fossiliferous micrites. Nodules and fossiliferous micrites consist of mainly non-ferroan , Mg-rich calcite. An intense red colour observed after Titan-Yellow staining is caused by a content of approximately 5 mole% MgC03. The limestones are locally recrystallized, forming a pseudospar with calcite crystals up to 25 f.Lm in diameter. Bitumen is frequent and enriched in joints. Pyrite is rare in the fossiliferous matrix micrites but is common in the nodules related to sponge taphonomy. Framboids are arranged in clusters which range from 40 to 250 f.Lm in diameter. 65 Joints caused by brecciation are filled by several generations of carbonate cements. The first generation is an iron-rich calcite of 20- to 300-f.Lm-sized sub- to euhedral crystals. It may be followed by bladed , high- Mg-calcite or aragonite, but never by both phases in one section. The most remarkable cements are botryoidal aragonites up to 550 f.Lm in radius which form the final cement generation. The botryoids origi- nate on iron-rich calcite and grow into the free joint space (Fig. 6). Most botryoids are preserved in their original aragonitic mineralogy. Only a small portion become calcitized or micritized with the micritization directed from the centre to the periphery. Dolomite makes up a significant portion of the rock volume. It occurs as partly ferruginous , euhedral rhomb-shaped crystals of approximately 100-140 f.Lm in size, embedded in a micritic matrix. Dolomitization is very selective, affecting preferentially the inter-nodular micrites. The Lower Oxfordian carbonates exhibit an intense fluorescence. The brightest fluorescence (yellow to white) is observed on the edges of micro-cavities and veins (Fig. 7). The micrites of the nodules exhibit a moderate brownish fluorescence wh ich corresponds to the amount of framboidal pyrite. In neomorphic zones two phenomena are observed: (a) nodules appear when excited by ultraviolet light; and (b) pseudospars occa- sionally show a laminated fabric (Fig. 8). The Middle and Upper Oxfordian limestones are made of homogeneous micrite. Framboidal pyrite is less common than in Lower and Middle Oxfordian carbonates. Calcitic cement is restricted to the interior of tubular cavities. Marmorito Lucina limes tone and tube worm limes tone. The molds of lucinid bivalves are enclosed in a packstone- or Fig. 6 Botryoidal aragonite ongmating on iron-rich calcite (XPL). Lower Oxfordian carbonate, Beauvoisin. The scale bar corresponds to 250 fLm 66 Fig.7 Epifluorescence micrograph of a former micro-cavity which is now filled by calcite spar. Note the intense fluorescence on the edge of the cavity. Lower Oxfordian carbonate, Beau- voisin . The seale bar corresponds to 250 /-lm Fig.8 Epifluorescence micrograph of a neomorphic zone which shows a laminated fabric due to excitation. Lower Oxfordian carbonate, Beauvoisin. The seale bar corresponds to 200/-lm wackestone matrix. The matrix, pellets, recrystallized shells and vein cements consist of low-Mg-calcite. Recrystallized shells are preferentially formed of a medium-grained granular cement but also contain elotted and laminated micritic crusts. These micritic crusts commonly be ar rhomb-shaped crystals of a brown, inelusion-rich calcite, indicating that the primary mineralogy of these micrites was dolomitic. Pyrite is extremely rare. The petrography of the tube- worm limestone is similar to the Lucina limestone. Botryoidal aragonite. One block found of botryoidal aragonite is composed almost entirely of botryoidal aragonite. The botryoids have a radius of up to 3.5 cm. They are only partly calcitized and are predominately preserved in their primary aragonitic mineralogy. Calci- tization is directed from the periphery to the centre. Fibrous aragonite crystals originate from a dark-brown nuelear mass exhibiting no fluorescence (Fig. 9) . Occa- Fig.9 The central portion of a botryoidal aragonite with aragonite fibres originating from a dark-brown nuclear mass, Marmorito. The seale bar corresponds to 500 /-lm sionally, the growth of crystals was interrupted and the fibres were covered by a concentric layer of dark- brown material, similar to the nuelear masses (Fig. lOa), but showing an intense fluorescence (Fig. lOb). Emerging from these layers the growth of a next generation of aragonite fibres continues. Marmorito limes tone. All Marmorito limestones analysed in this study revealed a dolomitic composition of the matrix. Due to an intense in situ brecciation, calcitic fracture fillings crosscut the micro-crystalline dolomite. The surfaces of the sediment elasts are over- grown by coatings with a eloudy appearance. The thick- ness of the overgrowth varies from 10 to 1000 J-Lm. They are also formed of dolomite and exhibit a globular fabric. Occasionally, the overgrowths form filamentous structures (Fig. 11a) which are then surrounded by the calcitic cements. The organic-rich overgrowth and espe- cially the surfaces of the filamenteous structures exhibit an intense white (BP 365) or yellow (BP 450-490) fluo- rescence (Fig. 11b). Most intense fluorescence halos are observed as particular globules (Fig. l1c, d) . Occasion- ally, some remains of these coatings are completely enelosed in the micro-crystalline dolomite (Fig. 11e, f), indicating that these organic-rich residues were enelosed during ongoing aggregation . The FE-SEM analyses show that the overgrowths consist of three types of precipitate habits, which are crusts composed of hemispheres, rod-shaped crystal aggregates with rounded, brush-like terminations, and dumbbells (Fig. 12). Stable isotopes and organic geochemistry Beauvoisin The ßl3C values of Lower Oxfordian carbonates vary widely between -26.5 and + 13.0%0 PDB (Fig. 13). The Fig.lOa,b Botryoida l aragonite, Marmori to. a Deta il from a botryoidal aragon ite with a concentr ic layer of dark-brown mate- rial, Marmorito. T he seale bar corresponds to 250 I-lm . b Same section as a. The conce ntric layer shows an in tense f1 uorescence, epifl uorescence micrograp h nodules related to sponge taphonomy exhibi t the most negative values (-26.5 to - 22.8%0), whereas the direct adj acent in ternodular micrites range from - 24.0 to + 13.0%0. 0180 values of early diagenetic carbonates range from - 0.5 to + 2.9%0 PDB. The stable isotope va lues of botryoidal aragonite exhibit a depletion in 13C (- 14.8 to - 12.0%0) and in 180 (- 7.1 to -6.6%0) . Carbonate concretions embedded in the marlstones distant from the pseudobiohe rms yielded 013C values of -19.0 and - 17.7%0 and show a marine signatu re fo r oxygen (0180: - 0.7 and + 0.4%0 PDB). The marlstones surrounding both cold seep carbonates and carbonate concretions are enriched in J3C ( + 0.8 and + 1.1 %0) and slightly depleted in 180 (- 1.3 and - 0.8%0). Va riations in stable isotope va lues are less extreme in Middle and U pper Oxfordian carbonates, but still significant. A previous study revealed oJ3C-values ranging from -13.6 to + 15.1 %0 and 0180 values ranging from -1.2 to + 0.7%0 (G aillard et al. 1992). The Middle Oxfordian carbo nates analysed in this study yielded 01 3C va lues that range from - 13.7 to -10.1%0 and 0180 va lues that range fro m -0.1 to + 0.2%0. Gas chromatograms (CI S + ) of the total hydro- carbon fractions obtained from two Beauvoisin sam pies (Lower Oxford ian, Middle Oxfordian) are shown in Fig. 14. In both sampIes the main components are n- alkanes with chain lengths fro m 12 to 33 carbon atoms and a broad concentration maximum around n-heptad- ecane (n-C17). With increasing chain lengths, n-a lkane concentrations rapidly decrease. T he observed, modal patterns are ubiqui tously fo und in ancient sediments and crude oils. In foss il mate rials, they are of limited biomarker significance, since they may be generated from the thermal maturation of sedimentary organic matter rather than from a particular biological source input. A more disti nctive fea ture of the Middle Oxfor- 67 di an carbonates is the occurrence of several acyclic isoprenoid hydrocarbons ranging up to C3S • Two prom- inent members were identified as 2,6,l0,15,l9-pentame- thylicosane (PME); according to IUPAC nomenclature, a Cw alkane is ca lied icosane; hence, "PMI" would be the correct acronym]. However, the compound has commonly been referred to as 2,6,l0,15,l9-pentamethy- le icosane (PME) heretofore. For reasons of com- patibility , we also use this abbreviation.], and a C30 homologue 2,6,l0,15,19,23-hexamethyltetracosane (squalane). In biogeochemistry and o il exploration geochemistry, PME and other acyclic isoprenoids with carbon ske letons in the range of C20 to C40 belong to the most wide ly used class of biomarkers for archaea , in particular methanogens (Brassell et al. 1981; Hahn 1982; Volkman et al. 1986; Wakeham 1990). The prom- inent abundance of PME thus reveals an indication for a pronounced activity of metharchaea associated with the fo rmation of the U pper Oxfordian carbonates. The isotopic signatures of PME as weil as squalane differ sharply from those observed fo r the n-alkane series. The latter show isotopic compositions normally found fo r marine lipids and petroleum hydroca rbons (around 01 3C = -30%0 PDB), whereas both isoprenoids are significantly depleted in 13C (01 3C = -75.7 and -67.5%0). The isotopic signatures of the n-alkanes indicate that they are not essentially autochthonous compounds, but at least partly o rigin ate from external, e .g. planktonic or detrital, sources. Even Iikely they represent petro- leum consti tuents derived fro m ancient seepage fl uids. O n the other hand, our data suggest that the biosyn- thesis of the isoprenoids occured in situ and involved the utilization of isotopica lly depleted, seepage-derived carbon. ' Marmorito The OJ3 C va lues of the investiga ted Marmorito limes- tone range fro m -40.2 to -17.3%0 (Fig. 13). The micro- crystalline matrix (-40.2 to -38.9%0) yielded lower OJ3C va lues than the ve in-filling ca lcitic cement (- 28.5 to - 17.3%0) . The 0180 values range from + 4.8 to +4.9%0 68 Fig.113-f Organic-rich remains within Marmorito carbonates. 3 Micro-crystalline dolomite (dark) crosscut by ca lcitic fracture fill - ings. Note the filamentous structures originat ing on the dolomite elast. Marmorito limestone. The scale bar corresponds to 500 fLm . b Detail from 3. The surfaces of the fi laments ex hibit an intense fluo rescence, epifluorescence micrograph. c Matrix dolomite (dark) overgrown by a cloudy coating adjacent to the ca lcitic spar (bright). Marmorito limestone. The scale bar corresponds to 200 fLm. d Same section as c. Most intense fluorescence halos a re particular globules. e Ca lcitic spar (feft), dolomitic coa ting and dolomitic matrix (right). Marmorito limestone. The scale bar corresponds to 250 fLm. f Same section as e. The coating em its an intense fluorescence. Some remains of the phase that coa ts the dolomite elast are embedded in the matrix in the dolomitie matrix and trom + 1.4 to + 2.1 %0 in the eements. The mierite of the tube-worm limestone is signifieantly 13C depleted (8 L3C: -32.9 to -26.6%0; 8 180: - 0.4 to +0.1%0). The botryoidal aragonite exhibits 8 L3 C values ranging from - 34.8 to - 27.0%0 and a 8 180 va lues ranging trom + 0.3 to + 2.7%0. Biomarker analyses were performed on the Marmo- rito limestone and on the tube-worm limestone. Agas ehromatogram of the total hydroearbon fraetion obtained trom the tube-worm limestone is shown in Fig. 15. The main eompound is PME, aecompanied by its C20 homologue eroeetane, an unusual eompound whieh has only onee been previously reported trom Fig.12a-d FE- SEM images (EHT 0.8 kV) of th e overgrowths on the elasts 01' the in situ brecciated Marmorito limestone. a The dolomitic micro-crystalline matrix (Da!), rod-shaped crystal aggrega tes 01' the overgrowth, and the calcitic cement (Ce) . The letters b, e, and d mark the details shown in b-d. The seole bar corresponds to 100 fLm. b Crusts composed of hemispheres. The seole bar corresponds to 30 fLm. c Rod-shaped crystal aggregates (eentre) between the dolomitic matrix (Da /) and the etched calcitic cement (Ce). The seole bar corresponds to 20 fLm . d Centre of a rod-shaped crystal aggrega te that contains a dumb- bell-shaped crysta l aggregate. The upper portion of the dumbbell is broken apart. The seole bar corresponds tol 0 fLm ancient sampies (McCarthy 1967; see Thiel et al. 1999 for further details). Both compounds are extremely depleted in 13C. Their Ol3C va lues of - 112 and - 115%0 diffe r by approximately 80%0 from those of the normal alkanes present in the same sampie. These features paralle l the observations from the M iddle Oxfordian Beauvoisin sam pie in an intriguing manner. They support the suggestion that certain archaea played a significant role in the biogeochemical cycling of carbon at these sites. A different situation exists for the Marmorito limes- tone which shows only minor amounts of isoprenoid hydrocarbons. [nstead , sterols and hopanols carrying an extra methyl group at C-4 and C-3, respectively , provide significant molecular markers in the alcohol 69 fraction (Fig. 16). These compounds are not commonly observed among sedimentary lipids. Likely biological precursors were identified in recent methanotrophic bacteria , e.g. Methylococcus capsulatus, wh ich produces 3-methylhopanepolyols (Neunlist and Ro hmer 1985; Summons e t al. 1994) as we il as " primitive" sterols showing single or double methylation at C-4 (Bouvier e t al. 1976). The presence of these or related compounds in the Marmorito limestone indicates a depositional environment, which at least temporarily permitted the growth of aerobic methanotrophs. Discussion Ancient chemosynthesis Lucinid bivalves a re the most prominent biota asso- ciated with the Oxfordian and Miocene cold seep carbonates. It has been presumed that they depended on chemosynthesis like their counterparts from the modern sea floor (Gaillard et a l. 1992; Clari et al. 1994). Sponges have been reported from some ancient seep deposits (Goedert and Squires 1990; Rigby and Goedert 1996). The "sponge nodules" of Beauvoisin which exhibit a c1otted , bacterioform fabric and contain 70 o botryoidal aragonite, Marmorito o l:::. o • ~ • • • ... tube worm limes tone calcitic vein, Marmorito limestone dolomitic matrix, Marmorito limestone nodule micrite, Lower Oxfordian matrix micrite, Lower Oxfordian botryoidal aragonite, Beauvoisin carbonate concretion, Beauvoisin Middle Oxfordian carbonates marlstone, Lower Oxfordian -7 -5 -3 •• • 15 5 3 5 -15 • I::. • I::. -25 'I 0 -dl CD I::. I::. 0 0 -35 0 -45 Fig, 13 Plot of the isotopic values of the carbonate phases fram Beauvoisin and Marmorito analysed in this study. Open symbols Marmorito; jilled symbols Beauvoisin frequent spicules are considered to be a product of bacterial soft-tissue degradation. In particular, the activity of sulphate-reducing bacteria is indicated by the dispersely distributed framboidal pyrite within the nodules and by an outer rim of pyrite on the nodules. The enrichment of 12C in the sponge nodules compared with the surrounding sediments may indicate that living sponges might have been linked to an enhanced hydro- carbon oxidation. Vacelet and Boury-Esnault (1995) reported on sponge-associated bacteria from cold methane seeps off Barbados, which display the morphological characteristics of methanotrophs. An uptake of carbon derived from microbial oxidation of hydrocarbons should result in 13C depletion of the sponge biom ass. Accordingly, the low 13Ccarbonate values of the sponge-nodules may result from the incor- po ration of CO2 derived from bacterial sponge tissue degradation. Most ancient seep carbonates contain remains of bivalves, but fossilized tube worms are rarely docu- mented. Tube worms were recognized from another locality in the Miocene-age "calcari a Lucina" (Terzi et al. 1994). The authors report on "unidentified vesti- mentiferan-like tubular fossils ". The tubes sampled during this study are too sm all in diameter to be attri- buted to vestimentifera, but resemble the sm aller pogonophora in dimensions and shape. Pogonophora from modern cold seeps depend on methane as they harbour methanotrophic bacteria, which supply their hosts with nutrients and energy (Southward et al. 1981; Schmaljohann and Flügel 1987). The tube worms of Marmorito are embedded in a micritic carbonate that exhibits 813C values of approximately -30%0, thus indi- cating the seepage of methane through the sedimentary environment of the tube-worm colony. The presence of archaea-derived biomarkers in the tube warm limes- tone does not prove a contemporaneous coexistence of these micro-organisms . with the oxygen-dependent invertebrates. More likely, these compounds originate from a subsurface population of the obligately anae- robic archaea, consistent with the view that methane- derived carbonates preferentially precipitate within the sediment (cf. Ritger et al. 1987; Gaillard et al. 1992). Organic residues and their implications on the composition of the seepage fluids Teichmüller and Ottenjann (1977) noticed that epifluorescence microscopy is a useful tool for detecting the relative distribution of organic residues enclosed in sedimentary rocks. In the hydrocarbon frac- tions of the Beauvoisin seep carbonates n-alkanes predominate. A connection between the content in aliphatic structures and the intense fluorescence of these rocks has to be taken into account. Bertrand et al. (1985) reported that fluorescence is favoured when chromophores (aromatic organic matter) are relatively iso la ted from each other within a dominantly aliphatic matrix. High concentrations of aromatic .organic matter may result in interactions that inhibit fluorescence. This is due to an effect termed "concentration quenching" when chromophores absorb both the exciting and emitted wavelengths. In coal petrology it is weil known that liptinites, which contain relatively large amounts of aliphatic constituents, exhibit the most intense fluores- cence (Stach et al. 1982; Tissot and Weite 1984). In the Oxfordian seep carbonates most intense fluo- rescence is observed on the edges of micro-cavities and veins where penetrating fluids might have been trapped. The n-alkanes enclosed in the Oxfardian carbonates were genera ted from thermal maturation of sedimentary organic matter. However, it is not evident whether the organic compounds were trapped after carbonate formation or seeped out of the sea floar syndepositionally. Notably, the carbon stable isotope composition of the Beauvoisin carbonates resembles that of carbonates from modern petroleum seeps (cf. Roberts and Aharon 1994). Methane was a major component of the fluids of the Miocene Marmorito seep. This is revealed by 813Ccarbonate values as low as -400/00 and chemofossils of methanotrophic bacteria. Fig. 14 Gas chromatogram (C15 + ) of the hydrocarbon fractions obtained from the Upper Jurassic sampies. Numbers in italies denote Ö!3C values (vs PDB) measured by GC-C-IRMS. Dots n-alkanes, n-12 = n-dodecane, n-17 = n- heptadecane. PME =2,6,10,15,19-pentame- thylicosane; Pr pristane; Ph phytane. PME and squalane are regarded as biomarkers for methanogenic archaea Qi a:: • Microbial activity and carbonate precipitation • • • • The Middle Oxfordian pseudobioherms contain biomarkers of archaea indicating a pronounced activity of methanogens associated with the carbonate forma- tion. Methanogens were found to produce heavy COz (öl3C: + 240/00) resulting in 13C-enriched carbonates precipitated in the methanic zone (Boehme et al. 1996). Indeed, Oxfordian carbonates exhibit Ö13C values as high as + 15.10/00. In contrast, those Middle Oxfordian carbonates which contained the markers of archaea yielded Öl3C values that range from -13.7 to -10.1 %0, thus indicating hydrocarbon oxidation rather than methane formation. The wide range in the carbon isotopic composition of the Lower Oxfordian carbon- ates implies that both methane formation and methane or hydrocarbon oxidation occurred in the same deposits and influenced carbonate formation. The low 71 n-17 • • Beauvoisin Lower Oxtordian • • • • • Pr • Ph • l.~ MUL.I& lU 1 I .! • .......... ~ -33,8 n -17 • -29,8 Pr • • Ph -30, 1 • Retention time Beauvoisin Middle Oxfordian ~ Range 01 hopanoids and acyclic isoprenoids / -67,5 ~ Squalane Retention time Öl3C values found for archaea-derived biomarkers from Marmorito may be assigned to an aerobic methane oxidation performed by a microbial consortium in which distinctive archaea participated (Thiel et al. , in press; cf. Hinrichs et al. 1999). However, it should be stressed that a severe 13e depletion mayaiso result from fractionation effects during uptake of other substrates such as acetate or methylamine (e.g. t Summons et al. 1998). The concIusion of a direct intro- duction of hydrocarbon carbon into cellular biomass by methanogenic archaea should thus be drawn with caution. Marmorito may thus be considered as an ancient counterpart of a known phenomenon which has frequently been reported from Recent sediments (Zehnder and Brock 1980; Hoehler et al. 1994; Harder 1997). In recent sediments anaerobic methane oxida- tion typically occurs at the base of the sulphate reduc- ti on zone and is ascribed to a consortium of sulphate 72 Fig. 15 Gas chromatogram (CIS + ) of the total hydro- carbon fraction obtained from the Marmorito tube-worm limestone. Numbers in italies denote O\3C values (vs PDB) measured by GC-C-IRMS. PME =2,6,10,15,19-pentame- thylicosane. PME and croce- tane are regarded as biomarkers for archaea - 115.6%0 Crocetane -112.2%0 ~ PME -38.4%0 n-Nonacosane Marmorito Tube worm limestone Total hydrocarbons -44.2%0 reducers and archaea. Thus, we consider archaea to account not only for the 13C enrichment in some phases of the Oxfordian carbonates, but also for the 13C deple- tion in other phases of the Oxfordian carbonates and in the Miocene tube-worm limestone. In addition to archaea, methanotropic bacteria are linked to the carbonate formation at cold seeps. The former presence of these organisms is crucial for the low Ö13C values of the Marmorito limestone (-400/00), since chemofossils of methanotrophs are most promi- nent in the samp\e studied. The biomarker data are corroborated by microscopic analyses. Abundant organic-rich overgrowths on dolomitic elasts indicate that bacterial biofilms were elosely associated with the Retention time formation of the Marmorito limestone. Epifluorescence microscopy revealed that residues of these biofilms were incorporated into the micro-crystalline dolomite while carbonate aggregation extended towards the periphery. The resulting "in situ lithification" may explain the extraordinary preservation of the organic remains produced by these particular bacteria. Additional evidence of bacterial activity associated with the Marmorito limes tone is given by the FE-SEM analyses. Typical features observed are crusts composed of hemispheres, rod-shaped crystal aggre- gates, and dumbbells. Intriguingly, these precipitate habits were induced by bacteria in laboratory experi- ments (Buczynski and Chafetz 1991). Dolomite sphe- Fig. 16 Partial gas chromato- gram of the alcohol fraction obtained from the Marmorito limestone (acetate deriva- tives). 4-Methylcholesterol and 3-methyl-bishomohopanol are regarded as biomarkers for aerobic methanotrophs ~ Marmorito limestone .~ Alcohols .~ &! Internal standard Bishomohopanol 4-Methylcholesterol Range 01 sterols and hopanols . ,(.Y~OH CH~ 3-Methyl- bishomohopanol I Retention time roids with dumbbell-shaped cores have previously been reported from the Marmorito limes tone by Cavagna et al. (in press). Micro-crystalline carbonates ~nd botryoidal aragonite Cold seep carbonates apparently show an excellent preservation potential with respect to metastable mineral phases and organic compounds. Examples for such metastable mineral phases are Mg-calcite from Beauvoisin or the botryoidal aragonites from both localities studied. A high preservation potential may arise from the rapid calcification, and the protective sealing by less permeable pelagic or hemipelagic sediments such as claystones or marlstones. Savard et al. (1996) suggest that the preservation of aragonite within Cretaceous seep deposits is related to the engulfment of sm all acicular aragonite bundles in stable calcite. To the best of our knowledge, the Beauvoisin samples represent the oldest known seep carbonates which contain botryoids preserved in their primary mineralogy. However, the time of aragonite precipitation is yet unclear, as the botryoids (a) originate on iron-rich calcite, (b) are not overgrown by later phases and (c) exhibit 8180 values of -7%0, in contrast to the less depleted early diagenetic carbonates ( + 2.8 to -0.50/00). Roberts et al. (1993) reported that botryoidal aragonites from the Gulf of Mexico arise from nuelear masses of dark-brown substances and suggested that this material represents the remains of bacteria elumps. The Marmorito botryoids exhibit similar nuelear masses. The concentric layers within the botryoids are formed of similar matter and exhibit an intense fluores- cence indicating an organic-rich composition. Organic nuelei like these supposed bacterial elumps may be able to trigger botryoidal aragonite formation. However, it is unlikely that they are essential for this process because not all botryoids from cold seeps display these features. It is also stressed that botryoidal aragonite is not confined to seep environments but is found in a variety of environments, e.g. reefs (James and Ginsburg 1979); therefore, methane-related bacterial activity is not crucial for its genesis. It has been presumed that dolomite precipitation may occur at methane seeps due to the depletion of sulphate by bacterial sulphate reduction coupled with methane oxidation (Ritger et al. 1987). Sulphate is known as a very effective inhibitor of dolomite crystal- lization (Baker and Kastner 1981). The sampie of the micro-crystalline Marmorito limestone exhibits no indi- cation of dolomitization within the parts that are now formed of dolomite. The transition between dolomite and calcitic veins is always sharp and the phase boundary between the different mineralogies generally coincides with sedimentary fabrics. These properties may be interpreted in terms of a primary precipitation of dolomite at the ancient seep. 73 The 8180 values of the dolomitic Marmorito limes- tone of approximately + 50/00 have to be decreased by 3-40/00 because of the different oxygen isotope fraction- ation during crystallization of calcite and dolomite (O'Neil and Epstein 1966; Fritz and Smith 1970; Tan and Hudson 1971; Land 1980). After this subtraction all 8180 values of the early diagenetic carbonate phases from Beauvoisin and Marmorito are elose to 00/00, thus indicating a carbonate precipitated from waters of fairly low temperature. This implies a classification of the ancient settings as "cold seep" rather than "hot vent" environments. Conclusion The following conelusions were reached as a result of this study: 1. The relation of the Oxfordian carbonates from Beauvoisin and the Miocene carbonates from Marmorito to hydrocarbon seepage was confirmed. 2. Distinctive molecular signatures of archaea were observed in both Oxfordian and Miocene seep carbonates. Stable carbon isotope and biomarker analyses elucidate that both, archaeal methanogen- esis and archaeal anaerobic methane oxidation, influenced the sedimentary environment and trig- ge red carbonate precipitation. 3. Methanotrophic bacteria (aerobic methanotrophs) played a crucial role in the formation of the micro- crystalline Marmorito limestone. Extremely negative 813C values (-400/00) and the presence of particular biomarkers corroborate the importance of methano- trophs for carbon cyeling. Organic-rich overgrowths on the resultant limestone elasts are formed of bacterial-induced precipiates and are interpreted as former biofilms and sites of carbonate aggregation. 4. In addition to lucinid bivalves, newly reported sponges (Beauvoisin) and tube worms resembling pogonophorans (Marmorito) are interpreted as ancient chemosynthetic taxa. 5. The Miocene seepage fluids (Marmorito) were dominated by methane. Oxfordian seepage fluids (Beauvoisin) were probably influenced by petro- leum constituents, as indicated by the Ccarbonate isotopic composition and the hydrocarbon pattern. 6. Specific carbonate phases from the ancient cold seep deposits are micro,-crystalline high-Mg-calcite (Beauvoisin), dolomite (Marmorito) and botryoidal aragonite (both sites). I Acknowledgements P. Albrecht, J. Hoefs, K. Simon and P. Wehrung are acknowledged for stable isotope measurements. We thank H . Becker and F. Brun for the preparation of thin sections and M. Hundertmark for photos of polished slabs. Our study was supported by the "Deutsche Forschungsgemeinschaft" (Mi-157f 10-5,6; Th-713f1). This paper is a contribution to SFB 468 "Wech- selwirkungen an geologischen Grenzflächen" (publication no. 14) at the University of Göttingen. We are grateful for the comments provided by G. Bohrmann (Kiel) and W. 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