Sedimentary and Faunal Evidence for the Late Devonian Kellwasser and Annulata Events in the Balkan Terrane (Bulgaria)

Home , Geology of Bulgaria, Platyclymenia

GEOLOGICA BALCANICA, 44. 1–3, Sofia, Dec. 2015, p. 17–24.

Sedimentary and faunal evidence for the Late Devonian Kellwasser and Annulata events in the Balkan Terrane (Bulgaria)

Iliana Boncheva1, Valeri Sachanski1, 2, Ralph Thomas Becker3

1 Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 24, 1113 Sofia, Bulgaria; e-mail: [email protected] 2 University of Mining and Geology, Department of Geology and Geo-Information, Sofia, Bulgaria; e-mail: [email protected] 3 Westphälische Wilhelms-Universität, Institut für Geologie und Paläontologie, Corrensstr. 24, D-48149 Münster, Germany; e-mail: [email protected] (Accepted in revised form October 2015)

Abstract. The global Upper Kellwasser (Frasnian–Famennian boundary interval) and Annulata Events (base of upper Famennian, Upper Devonian IV-A) are recorded for the first time in deep marine sedimentary successions of western Bulgaria. Within the upper Parchar Formation of the Lyubash-Golo Bardo Unit, a distinctive black shale unit yielded frequent, partly still articulated bivalves (Guerichia) and a Platyclymenia-fauna, including the name-giving Pl. annulata, although smooth platyclymeniids are more common. This interval reflects within a thick Eovariscan flysch succession an episode of starved sedimentation, increased organic productivity, oxygen deficiency, and bloom of opportunistic specialists. The event biofacies agrees with a basinal setting far away from land and its nutrient input. The Upper Kellwasser interval is recognized within the thick flysch sequence of the Katina Formation in the Svoge Unit. It is characterized by an interruption of carbonate deposition, as it is typical for other basinal settings, for example, of the Rhenish and Thuringian basins of Germany.

Boncheva, I., Sachanski, V., Becker, R.T. 2015. Sedimentary and faunal evidence for the Late Devonian Kellwasser and Annulata events in the Balkan Terrane (Bulgaria). Geologica Balcanica 44(1–3), 17–24. Key words: Kellwasser and Annulata events, Balkan Terrane, Bulgaria

Introduction edge of their spatial distribution and, possibly, of their nature and origin. Late Devonian global events include a sequence of sud- This study concerns Bulgarian flysch successions, den biotic changes and various kinds of drastic environ- where sedimentary and faunal indications of two impor- mental perturbations. There were fast transgressions and tant Late Devonian global events, the Upper Kellwasser regressions (eustatic sea-level pulses) as well as cata- Event at the Frasnian–Famennian boundary and the ba- strophic sedimentary events, well documented by inter- sal upper Famennian Annulata Event, can be observed. vals of anoxic marine sediments with elevated organic There is a very high amount of publications on the Upper content, and changes in the geological record of stable Kellwasser Event, with a last general review by Racki isotopes and rare elements. The sequence of global black (2005) and a summary of comparable European strata and shale events of variable intensity, which were connected facies trends by Gereke, Schindler (2012). The global dis- with small-scale to mass extinctions, eustatic fluctua- tribution and characteristics of the Annulata Events have tions, have been summarized by Walliser (1984, 1996), previously been summarized by Becker (1992a, b), Becker House (1985, 2002), and Becker (1993). Their explana- et al. (2004), and Hartenfels (2011). Regionally, Spassov tion requires a profound knowledge of the distribution of (1960) published for the first time finds of the bivalve event beds in time and space, their palaeoecology, and Posidonomya cf. venusta (now the genus Guerichia) and a comparison between events of different magnitude. the presence of undeterminable goniatites in black shales Therefore, the recognition of some of the well-known of the Parchar Formation. Our new data enable to identify specific events in the Balkan region adds to the knowl- this black shale unit as Annulata Event beds.

17 Geological setting conditions in the middle part and a regression towards the end of the Devonian. The Devonian flysch accumulation in western Bulgaria marks the final stage of the regional Palaeozoic marine Lyubash-Golo Bardo Unit basin development, related to compression and the onset of Variscan orogeny. It is characterized by turbiditic The 1400 m thick Late Devonian flysch sediments of this siliciclastic successions, with carbonate lenses as mem- unit (Fig. 2) are subdivided into three formations: Parchar, bers within the sequence, and such conodont-bearing Tumba, and Propalnitsa (Yanev, Spassov, 1985). layers provided age data. They indicate flysch depo- The Parchar Formation represents an irregular alter- sition from within the Early Devonian (Emsian) until nation of black, grey to rusty grey or greenish-grey argil- the Early Carboniferous (Tournaisian). This interval lites, silstones and sandstones. Locally there are interbed- is unconformably overlain by Late Carboniferous and ded granular and pebbly conglomerates. The thickness Permian molasses. varies between 250 to 770 m. Intercalations of less than Devonian outcrops of flysch sediments are related 1 m thick, dark grey nodular or black, massive, apha- in Bulgaria to three tectonic units – the Lyubash-Golo nitic limestones occur predominantly in the lower part Bardo Unit, Morava Unit, and the Svoge Unit (Boncheva of the section. Single intercalations of lydites are also et al., 2010; Fig. 1). The most complete Late Devonian observed. The limestones yielded late Emsian to earliest sections of the Lyubash-Golo Bardo and Svoge units Famennian conodonts. Sachanski, Boncheva (2002) and are situated in the western part of the Srednogorie tec- Boncheva et al. (2010) documented the following zones tonic zone. and stages: late Emsian–early Eifelian (serotinus to par- titus zones), top Eifelian–Givetian (ensensis and varcus zones), middle–late Frasnian (hassi and rhenana zones), early Famennian (Lower triangularis Zone). A miospore association from the terrigenous matrix at the base of the rhythmic alternation confirms a late Emsian–early Eifelian age for the onset of turbiditic deposition. The Kellwasser event falls in a level right below the Frasnian– Famenian stage boundary and triangularis Zone. In the upper part of the Parchar Formation, ca. 615 m above its base, there is a distinctive black shale unit, which yielded frequent bivalves (Guerichia venusta, Figs 3.7-9) in association with clymeniids (involute, Figs 3.1-2, and evolute, Fig. 3.4, morphotypes of Platyclymenia cf. subnautilina, Pl. annulata, Figs 3.5-6, and Protactoclymenia sp., Fig. 3.3). It clearly represents one or both of the Annulata Black Shales, first recognized in the Rhenish Massif of Germany (Schmidt, 1924; detailed data in Becker, 1992b; Korn, 2004; and Hartenfels, 2011). It indi- Fig. 1. Location of Lyubash-Golo Bardo and Svoge units in the simplified tectonic sketch of Bulgaria (after Dabovski, cates a sudden eutrophication of the basin, with increased Zagorchev, 2009). organic productivity (accumulation of high amounts of organic matter), and oxygen deficiency at least near the sea-floor and possibly with fluctuating intensity (Racka et al., 2010). Guerichia was an opportunistic bivalve, which was specialized to low-oxygen (exaerobic) con- The Lyubash-Golo Bardo Unit is a fault-bounded ditions. Still articulated (bivalved) specimens that were structure. The Devonian consists regionally of black not attached to any algae (Figs 3.7 and 3.9) confirm their graptolitic shales (Gradishte Formation, Lochkovian), a benthic mode of life. They occur widely in the Annulata lydite series at the base of the Parchar Formation, and Event beds of Germany, Poland, Czech Republic, and a subsequent rhythmic succession of shales, siltstones, Morocco, and also in other Famennian black shale units, and sandstones. Accumulation of turbiditic sediments such as those of the global Dasberg and Hangenberg started during the Emsian–Eifelian, prior to the two other Crises (e.g., Rzehak, 1910; Bless et al., 1988; Racka et regions with Devonian sedimentation, and lasted into the al., 2010; Hartenfels, 2011). The Annulata Event falls in Early Carboniferous. This succession is unconformably the top part of the Upper trachytera Zone and, in the am- overlain by Permian continental clastic rocks. monoid zonation, at the base of Upper Devonian IV-A In the Svoge Unit turbiditic accumulation occurred (Pl. annulata Zone). It has been proposed to define since the Givetian, characterized by siliciclastics and the base of a future, formal upper Famennian substage cherty rocks at the beginning (Katina Formation). A typi- (Hartenfels et al., 2009). cal basinal trough development during the Late Devonian The ammonoid assemblage from the upper Parchar led to the accumulation of a thick flysch succession of Formation resembles in its composition the black, conglomerates, sandstones, shales, and siltstones. Based main Annulata Shales of Germany and Poland, on sedimentological investigations by Yanev (1985), where smooth platyclymeniids are by far dominant. there was regionally a tendency towards deeper water In slightly better oxygenated settings, indicated by

18 Fig. 2. Lithological columns and stratigraphical position of Kellwasser and Annulata events in the studied sections (after Boncheva, Yanev, 1993; Yanev, Spassov, 1985).

19 green shales or marls, other ammonoids, especially Becker et al., 2004; Hartenfels, 2011; Hartenfels, Prionoceras and Erfoudites, are more common, and Becker, 2013). In other regions, basinal Annulata these are associated by different benthos, such as shales may be dominated by cyrtoclymeniids (Kowala, small orthids and/or small gastropods (Becker, 1992a; Holy Cross Mountains, Hartenfels, 2011) or yielded

20 a rather unusual juvenile Gundolficeras-Erfoudites- Svoge Unit Platyclymenia-Protactoclymenia assemblage (southern Maider, Morocco, Webster et al., 2005). Con The succession consists of three Devonian formations temporaneous black Annulata Limestones of Germany (Fig. 2), the Ogradishte Formation (black shales), Romcha (Korn, 2002) and southern Morocco (Korn et al., 2000; Formation (greenish-grey shales; Angelov et al., 2010), Hartenfels, 2011) are also characterized by higher am- and Katina Formation (Tenchov, 1965). monoid diversity, although platyclymeniids are rather The Romcha Formation consists of predominant dominant. In summary, the new Bulgarian assem- greenish and grey-greenish, crudely bedded argillites blage is characteristic for a rather deep and strongly plus subordinate silty argillites in the lower part. A char- oxygen-deficient setting, which was hostile to benthos acteristic lithologic feature is the presence of lenticular apart from Guerichia and to various ammonoid groups nodules and „dark spots”. The lower boundary is a gradu- named above. al transition from the rocks of the Ogradishte Formation. The Tumba Formation crops out only in the range The formation is overlain with a short lithologic grada- of the Lyubash-Golo Bardo Unit as a thin strip. It over- tion by the Katina Formation. On the basis of chitino- lies with lithologic transition the Parchar Formation zoans (Lakova in Yanev et al., 2005) and its stratigraphic and grades into the subsequent Propalnitsa Formation. position below the Katina Formation, it has been assumed The thickness does not exceed 250 m. It is charac- that the unit covers parts of the Emsian (Early Devonian) terized by alternating lydites and shales, with minor and parts of the Middle Devonian (Angelov et al., 2010). sandstones and siltstones with land plant fragments. The unit thickness is 300–350 m. Fine-grained, dark grey to black argillites with in- The grey-green argillites are built of a microflake distinct lamination predominate and pass locally into groundmass containing small amounts of quartz and siltstones. Very typical is the presence of lydites with mica silt. Under the microscope lamination is observed poorly preserved radiolarians, locally in the form of as dark-coloured layers enriched in organic matter. The banded alternations. The age of the formation is ten- silty argillites build a 60–70 m thick package at the base of tatively assumed based on its position between the the sequence. These rocks display an indistinct laminated Parchar and Propalnitsa Formations. The radiolarian structure, which disappears upwards in the section. microfauna does not indicate any precise age; it only A characteristic lithologic feature of the Romcha refer the rocks to the Late Devonian. Formation is the presence of lenticular nodules and dis- The Propalnitsa Formation is built up of irregu- crete, thin (1–5 сm), discontinuous but normally bedded larly alternating siltstones, sandstones, and conglom- sandy-clayey layers. They are predominant in the upper erates. This lithological composition is similar to the levels of the sections and are distinguished as intervals Parchar Formation. Various sandstones and granular of 50–70 сm thickness (locally 10–15 сm). Beds with to pebbly conglomerates predominate. The unit thick- thicknesses of 10–20 сm, extending laterally for several ness ranges between 250 and 500 m. It is covered meters, are rarely encountered, too. They are strongly with angular discordance by Late Permian red-beds. deformed and crumpled by dense ripples (interpreted as Biostratigraphic data are based on land plants, such as cone-in-cone structure) on their surfaces. In the case of Cyclostigma hercynium, C. ursinum, C. kiltorkense, good preservation, such “cones” have a height of 1–8 сm Sphenophyllum subtenerrimum, Bowmanites tumbana, and a width of 3–4 сm at their base. Archaeopteris cf. halliana (Remy, Spassov, 1959; The Katina Formation starts with a ca. 380 m thick Yanev, Spassov, 1985), and Sphenophyllostachys tum- pre-flysch series of thick bedded, greenish lydites, grey bana (Tenchov, Yanev, 1987). These are assigned to the shales, and siliceous shales, which grade upwards into late Famennian–Early Carboniferous but Archaeopteris grey-greenish shales. Thin layers of fine-grained sand- is not known from the Carboniferous. stones with laterally variable thickness are interca-

← Fig. 3. Devonian ammonoids and bivalves from the Parchar Formation. Scale bar 5 mm. The specimens are stored in the Laboratory of Geocollections, Geological Institute, Bulgarian Academy of Sciences. 1 – Platyclymenia cf. subnautilina, involute morphotype; specimen Sp142b. 2 – Platyclymenia cf. subnautilina, involute morphotype; specimen SR.5.2.31. 3 – Protactoclymenia sp.; specimen Sp142a. 4 – Platyclymenia cf. subnautilina, evolute morphotype; specimen SR.5.2.31. 5 – Platyclymenia annulata; coarsely ribbed specimen Sp10-2. 6 –Platyclymenia cf. annulata; weakly ribbed specimen Sp10-1. 7 – Guerichia sp.; specimen Sp-135b 8 – Guerichia sp.; specimen Sp10-3. 9 – Guerichia sp.; specimen Sp10-4a.

21 lated. The pre-flysch succession does not contain fos- lack macrofauna, which indicates high organic produc- sils and is tentatively assigned to the Middle Devonian. tivity and anoxic (oxygen-deprived) conditions, at least Conformably, a flysch succession follows, up to 1000 m of bottom waters. Regional anoxia were probably caused thick, consisting of sandstones and shales. It belongs to the by the bacterial degradation of Corg, which consumes the Late Devonian–Visean (?), based on macroflora and on diluted sea-water oxygen. So far there are no geochemi- conodonts from single carbonate layers. Its upper bound- cal investigations, as they have been conducted in other ary is an erosional surface covered by terrigenous sedi- European F-F successions (e.g., Pujol 2005), which could ments of the Late Carboniferous, Permian, and Triassic. give more precise insights into oxygen levels, changes In the lower part of the flysch section a 15–20 cm of detrital input, or nutrient availability. But the region- thick lydite package is observed. The succession above ally strong tectonic overprint is rather unfavourable for consists of deep-water argillaceous sediments and tur- such studies. The decrease of carbonate deposition in the biditic sandstones. The latter are very fine or grainy and Upper Kellwasser interval is typical for basinal settings, consist of variable amounts of quartz and rock fragments for example in the “Cypridinenschiefer” facies of the with 10% cement. Siltstones are grey to dark grey, fine- Rhenish Slate Mountains (Piecha, 1993; Gereke, 2007) grained, finely stratified, and clayey to slightly sandy. or of Thuringia (e.g., Bartzsch et al., 1999, 2001). The monomineralic terrigenous grains make up 80–85% of the rock. Shales are dark to black, with a microband- ed texture. They contain fine dispersed organic matter, Remarks on the ammonoid fauna iron hydroxides, siliciceous material, and insignificant amounts of fine terrigenous detritus. There are rare sider- Becker (1992) and more recently Zong et al. (2014) ite concretions up to 5–15 cm in diameter. Lydites and commented on the partly difficult taxonomy of smooth silicified shales are dense and brittle, light grey, dark platyclymeniids, especially when squashed. The Platy grey or black, and consist of micro- to crypto-grained clymenia subnautilina Group includes Pl. ruedemanni as quartz and a variable amount (0–50%) of clay miner- a subjective synonym, but also the poorly known, more als. They form layers of 1–2 cm to 10–15 cm thickness. evolute Pl. quringi. Korn (2002) documented the consid- Some layers are interbedded by lenses of organic matter. erable intraspecific variability of umbilical width (uw) in The structure of the flysch succession is rhythmic, with a supposed subnautilina population from Kattensiepen in 0.5 –1.5 m thickness of individual rhythmes. Typical tur- the Rhenish Massif. This suggests that only very evolute bidite sedimentary structures are present, such as parallel forms, with uw/diameter > 0.5 should be assigned to and transversal lamination and convolute bedding. Pl. qurinigi. Within the forms with uw/dm varying be- Boncheva, Yanev (1993) provided evidence for the tween 0.40 to 0.48, the conch thickness or ratio between topmost Frasnian linguiformis Zone and the earliest whorl width (ww) and whorl height (wh) seems to be Famennian Lower triangularis Zone from the Katina more significant to separate species or subspecies. Since Formation. Based on subsequent progress in conodont this feature is not preserved in the Bulgarian material, it taxonomy and stratigraphy across the F/F boundary is identified as Pl. cf. subnautilina. However, there are (e.g., Schülke, 1995; Girard et al., 2005; Klapper, 2007a; clearly two different morphotypes with uw/dm ratios be- 2007b; Ovnatanova, Kononova, 2008), conodont identifi- tween 0.40 and 0.42 (Figs 3.1-2) and near 0.48 (Fig. 3.4). cations can be updated. The Frasnian samples 1006-1008 The latter resembles the Polish Pl. glabra, which Korn yielded a broken Ancyrognathus sp., Palmatolepis lyai- (2002) kept as a different species. olensis (originally identified as Pa. hassi), a more slen- A coarsely ribbed platyclymeniid (Fig. 3.5) can be der, rather smooth and subrhombic but incomplete form identified as Pl. annulata. The ribbing persists longer (originally identified as Pa. ederi), Pa. eureka (originally than in typical Pl. anulata richteri but the poor preserva- identified as Pa. subrecta), a specimen that is somewhat tion prevents a subspecies assignment. A second speci- transitional between Pa. anzhelae and Pa. bogartensis men (Fig. 3.6) shows more subdued ribbing and is identi- (= Pa. rotunda), and an incomplete specimen, which fied as Pl. cf. annulata. was previously identified as Pa. cf. linguiformis. This The single Protactoclymenia falls in the rather widely suggests the Upper rhenana to linguiformis zones umbilicate (uw/dm near 0.35) and ribbed species group (MN 13a-b zones of Girard et al., 2005). Records from around Pr. pseudarietina, Pr. tenuicostata, and Pr. enke- the basal Famennian (samples 970, 982, 988) include bergensis. Without knowledge of the cross-section and Pa. triangularis s.l. (sensu Klapper, 2007 = Pa. praeter- of ornament details, a species identification is not pos- ita Schülke, 1995, with relatively short side lobe; but not sible. All three ammonoid taxa are widely known from sensu the holotype, triangularis s. str., a more elongate the Pl. annulata Zone (UD IV-A). form with posteriorly directed side lobe), Pa. delicatula, Pa. clarkei, and an icriodid with very irregular, partly bulbose nodes, which was regarded as a rather extreme Conclusions variant of I. deformatus. Both sampled carbonate layers are separated by The global Upper Kellwasser Event can be recognized black shales, which fall in the interval of the Frasnian- within the Katina Formation of the Svoge Unit based Famennian boundary or of the black Upper Kellwasser on black shales intercalated between topmost Frasnian level of the Rhenish (German) type region (e.g., (linguiformis Zone) and basal Famennian (Lower tri- Buggisch, 1972; Schindler, 1990; Gereke 2007; Gereke, angularis Zone) limestones. Lithology and the lack of Schindler, 2012). Locally, the organic-rich sediments macrofauna suggest an anoxic, basinal setting.

22 The global Annulata Event is clearly marked within triggered by palaeoceanographic changes, not by land- the Parchar Formation of the Lyubash-Golo Bardo Unit derived influences. by a black shale, which yielded abundant guerichiids and The new Bulgarian Annulata Event record closes a typical Platyclymenia fauna of Upper Devonian IV-A. within the Prototethys the gap between previously known The faunal composition agrees with the anoxic, deeper European (Czech Republic, Poland) and Asian (Iranian) pelagic event biofacies of the Rhenish Massif (Germany) occurrences. and Holy Cross Mountains (Poland). This may reflect plate tectonic connections. Acknowledgements The development of both the Upper Kellwasser and Annulata events in rather thick flysch basins suggest epi- This paper is a contribution to IGCP 596 Project Climate sodes of condensation/sediment starvation and eutrophi- Change and Biodiversity Patterns in the Mid-Paleozoic cation far away from land. Both events were probably (Early Devonian to Late Carboniferous).

References

Angelov, V., Sachanski, V., Tanatsiev, S. 2010. Ogradishte and land). Kölner Forum für Geologie und Paläontologie 17, Romcha formations – new lithostratiphic units for the upper 1–228. Silurian and Devonian sediments in the Svoge tectonic unit. Gereke, M., Schindler, E. 2012. „Time-Specific Facies“ and Review of the Bulgarian Geological Society 71 (1–3), 5–15 biological crises – The Kellwasser Event interval near the (in Bulgarian). Frasnian/Famennian boundary (Late Devonian). Palaeo Bartzsch, K., Blumenstengel, H., Weyer, D. 1999. Stratigraphie geography, Palaeoclimatology, Palaeoecology 367/368, des Oberdevons im Thüringischen Schiefergebirge, Teil 1. 19–29. Schwarzburg-Antiklinorium. Beiträge zur Geologie von Girard, C., Klapper, G., Feist, R. 2005. Subdivision of the ter- Thüringen, N.F. 6, 159–189. minal Frasnian linguiformis conodont Zone, revision of Bartzsch, K., Blumenstengel, H., Weyer, D. 2001. Stratigraphie the correlative interval of Montagne Noire Zone 13, and des Oberdevons im Thüringischen Schiefergebirge, Teil 2: discussion of stratigraphically significant associated trilo- Berga-Antiklinorium. Beiträge zur Geologie von Thüringen, bites. In: Over, D.J., Morrow, J.R., Wignall, P.B. (Eds.), N.F. 78, 303–327. Understanding Late Devonian and Permian-Triassic Biotic Becker, R.T. 1992a. Regional developments of the glo- and Climatic Events: Towards an integrated Approach, bal hypoxic Annulata Event (Middle Famennian). Fifth Developments in Palaeontology & Stratigraphy. Elsevier, International Conference on Global Bioevents, Göttingen, Amsterdam, 20, 181–198. February 16-19, 1992, Abstract Volume, 13–14. Hartenfels, S. 2011. Die globalen Annulata-Events und die Becker, R.T. 1992b. Zur Kenntnis von Hemberg-Stufe und Dasberg-Krise (Famennium, Oberdevon) in Europa und Annulata-Schiefer im Nordsauerland (Oberdevon, Rhei Nord-Afrika – hochauflösende Conodonten-Stratigraphie, nisches Schiefergebirge, GK 4611 Hohenlimburg). Berliner Karbonat-Mikrofazies, Paläoökologie und Paläodiversität. geowissenschaftliche Abhandlungen E3, 3–41. Münstersche Forschungen zur Geologie und Paläontologie Becker, R.T. 1993. Anoxia, eustatic changes, and Upper 105, 17–527. Devonian to lowermost Carboniferous global ammonoid Hartenfels, S., Becker, R.T. 2013. El Gara South – new data diversity. Systematics Association, Special Volume 47, on Famennian ammonoid and conodont faunas and the 115–163. Annulata Events in the Rheris Basin (northern Tafilalt, Becker, R.T., Asshouri, A.R., Yazdi, M. 2004. The Upper Morocco). In: El Hassani, A., Becker, R.T., Taghiri, A. Devonian Annulata Event in the Shotori Range (eastern (Eds.), International Field Symposium “The Devonian and Iran). Neues Jahrbuch für Geologie und Paläontologie, Lower Carboniferous of northern Gondwana”, Abstract Abhandlungen 231, 119–143. Book, Documents de l´Institut Scientifique, Rabat, 26, Bless, M.J.M., Simakov, K.V., Streel, M. 1988. Advantages 48–51. and disadvantages of a conodont-based or event-strati- Hartenfels, S., Becker, R. T. and Tragelehn, H. 2009. Marker graphic Devonian–Carboniferous Boundary. Courier conodonts around the global Annulata Events and the defi- Forschungsinstitut Senckenberg 100, 3–14. nition of an Upper Famennian substage. SDS Newsletter 24, Boncheva, I., Lakova, I., Sachanski, V., Koenigshof, P. 2010. 40–48. Devonian stratigraphy, correlations and basin develop- House, M.R. 1985. Correlation of Mid-Palaeozoic ammonoid ment in the Balkan Terrane, western Bulgaria. Gondwana evolutionary events with global sedimentary perturbations. Research 17, 573–583. Nature 313 (5997), 17–22. Boncheva, I., Yanev, S. 1993. New data on the Paleozoic fly- House, M.R. 2002. Strenght, timing, setting and cause of mid-Pal- sch of the Sofiyska Stara Planina Mountain. Geologica aeozoic extinctions. Palaeogeography, Palaeoclimatology, Balcanica 23 (5), 15–22. Palaeoecology 181, 5–25. Buggisch, W. 1972. Zur Geologie und Geochemie der Kell Klapper, G. 2007a. Frasnian (Upper Devonian) conodont suc- wasserkalke und ihrer begleitenden Sedimente (Unteres cession at Horse Spring and correlative sections, Canning Oberdevon). Abhandlungen des Hessischen Landesamtes Basin, Western Australia. Journal of Paleontology 81 (3), für Bodenforschung 62, 1–68. 513–537. Gereke, M. 2007. Die oberdevonische Kellwasser-Krise in Klapper, G. 2007b. Conodont taxonomy sand the recogni- der Beckenfazies von Rhenohercynikum und Saxothurin tion of the Frasnian–Famennian (Upper Devonian) Stage gicum (spätes Frasnium/frühestes Famennium, Deutsch Boundary. Stratigraphy 4 (1), 67–76.

23 Korn, D. 2002. Die Ammonoideen-Fauna der Platyclymenia Schindler, E. 1990. Die Kellwasser-Krise (hohe Frasne- annulata-Zone von Kattensiepen (Oberdevon, Rheini Stufe, Ober-Devon). Göttinger Arbeiten zur Geologie und sches Schiefergebirge). Senckenbergiana lethaea 82 (2), Paläontologie 46, 1–115. 557–608. Schmidt, H. 1924. Zwei Cephalopodenfaunen an der Devon- Korn, D. 2004. The mid-Famennian ammonoid succession in Carbongrenze im Sauerland. Jahrbuch der Preußischen the Rhenish Mountains: the “annulata Event” reconsidered. geologischen Landesanstalt 44, 98-171. Geological Quarterly 48 (3), 245–252. Schülke, I. 1995. Evolutive Prozesse bie Palmatolepis in- Korn, D., Klug, C., Reisdorf, A. 2000. Middle Famennian der trüben Famenne –Stufe (Conodonta Ober-Devon): ammonoid stratigraphy in the Amessoui Syncline (Late Göttingen Arbeiten zur Geologie und Paläontologie, 67, Devonian, eastern Anti-Atlas, Morocco). In: Tahiri, A., 1-108. El Hassani, A. (Eds.), Proceedings of the Subcommission Spassov, Ch. 1960. Stratigraphie der Paleozoischen Sedimenten on Devonian Stratigraphy (SDS) – IGCP 421 Morocco zwischen Tran und Temelkovo (S.W. Bulgarien). Meeting, Travaux de l´Institut Scientifique, Série Géologie Proceedings on the Geology of Bulgaria, Series Stratigraphy & Géographie Physique 20, 69–77. and Tectonics 1, 93–102. Ovnatanova, N. S., Kononova, L. I. 2008. Frasnian Conodonts Tenchov, Y. 1965. Upper Devonian in the core of the Svoge from the Eastern Russian Platform. Paleontological Journal anticline. Review of the Bulgarian Geological Society 26 42 (10), 997–1166. (1), 109–112. Piecha, M. 1993. Stratigraphie, Fazies und Sedimentpetrographies Tenchov, Y., Yanev, S. 1987. The Paleozoic sediments in der rgythmisch und zyklisch abgelagerten, tiefober- Bulgaria. Guide Book, Problem Commission IX, Project devonischen Becken sedimente in Rechtsrheinischen 5.1 (Sofia, October 1987), Bulgarian Academy of Sciences, Schiefergebirge (Adorf – Bänderschiefer). Courier 1–86. Forschungsinstitut Senckenberg, 163, 1–151. Walliser, O.H. 1984. Geologic processes and global events. Pujol, F. 2005. Chemostratigraphy of some key European Terra Cognita 4, 17–20. Frasnian-Famennian boundary sections (Germany, Poland, Walliser, O.H. 1996. Global Events in the Devonian and France). Karlsruher Mineralogische und Geochemische Carboniferous. In: Walliser, O.H. (Ed.), Global Events and Hefte 30, 1–131. Event Stratigraphy in the Phanerozoic, Springer, Berlin, Racka, M., Marynowski, L., Filipiak, P., Sobstel, M., 225–250. Pisarzowska, A., Bond, D.P.G. 2010. Anoxic Annulata Webster, G.D., Becker, R.T., Maples, C.G. 2005. Biostratigraphy, Events in the Late Famennian of the Holy Ceross paleoecology, and taxonomy of Devonian (Emsian and Mountains (Southern Poland): Geochemical and palaeon- Famennian) crinoids from southeastern Morocco. Journal tological record. Palaeogeography, Palaeoclimatology, of Paleontology 79 (6), 1052–1071. Palaeoecology 297(3–4), 549–575. Yanev, S., Spassov, Ch. 1985. Lithostratigraphy of the Devonian Racki, G. 2005. Toward understanding Late Devonian glo- flysch between Tran and Temelkovo. Paleontology, bal events: few answers, many questions. In: Over, D.J., Stratigraphy and Lithology, 21, 82–86 Morrow, J.R., Wignall, P.B. (Eds.), Understanding Late Yanev, S. 1985. Devonian flysch in the Chernogorie (Southwest Devonian and Permian-Triassic Biotic and Climatic Bulgaria). Paleontology, Stratigraphy and Lithology, 21, Events: Towards an integrated Approach, Developments in 76–87. Palaeontology & Stratigraphy. Elsevier, Amsterdam, 20, Yanev, S., Lakova, I., Boncheva, I., Sachanski, V. 2005. The 5–36 Moesian and Balkan Terranes in Bulgaria: Palaeozoic ba- Remy, W., Spassov, Ch. 1959. Der paläontologische Nachweis sin development, plaeogeography and tectonic evolution. von Oberdevon in Bulgarien. Monatsbücher der Deutschen Geologica Belgica 8 (4), 185–192. Akademie der Wissenschaften zu Berlin 1 (6), 380–387. Zong, P., Becker, R.T., Ma, X. 2014. Upper Devonian Rzehak, A. 1910. Der Brünner Clymenienkalk. Zeitschrift des (Famennian) and Lower Carboniferous (Tournaisian) Mährischen Landesmuseums 10, 149–222. ammonoids from western Junggar, Xinjiang, northwest- Sachanski, V., Boncheva, I. 2002. Geological events and proc- ern China-stratigraphy, taxonomy and palaeobiogeog- ess dating by the rate of sedimentation in the area of Cherna raphy. Palaeobiology and Palaeoenvironments 95 (2), Gora Height. Geologica Balcanica 32 (2–4), 127–129. 159–202.