Silurian sequence stratigraphy of the Carnic Alps, Austria

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Silurian sequence stratigraphy of the Carnic Alps, Austria

Carlton E. Brett a, Annalisa Ferretti b, Kathleen Histon b,⁎, Hans Peter Schönlaub c

a Department of Geology, University of Cincinnati, Cincinnati, 45221-0013, USAb Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, 41100 Modena, Italyc Austrian Academy of Science, Centre for Geosciences, Vienna, Austria

a b s t r a c ta r t i c l e i n f o

Article history:Received 14 June 2008Received in revised form 21 March 2009Accepted 1 April 2009

Keywords:Sequence stratigraphyEustasyBasin dynamicsSilurianCarnic AlpsAppalachian Foreland Basin

Sequence stratigraphy provides an alternative approach to correlation that may also serve as a predictiveframework for the interpretation of sea-level and sedimentological change. The main aim of this study is toapply sequence stratigraphic concepts to the biostratigraphically well constrained shallow to moderatelydeep shelf carbonates and basinal graptolitic shale facies of the Silurian successions in the Carnic Alps ofAustria in order to correlate the sequence packages and sea-level changes established there with thoseidentified in other areas of North America and Europe. Documenting local sea-level curves is essential fordetermining global eustasy. The sea-level curve for the Silurian of the Carnic Alps has been elaboratedwithin a refined stratigraphic framework for the Silurian based on conodont and graptolite biozonation[Melchin, M.J., Cooper, R.A., Sadler, P.M., 2004. The Silurian Period. In: Gradstein, F.M., Ogg, J.G., Smith, A.G.(Eds), A Geologic Time Scale. Cambridge University Press, Cambridge, pp. 188–201.]. In particular, the minorand frequent sea-level changes within the Silurian of the Carnic Alps are of special interest as thesestratigraphic intervals are poorly preserved and not well studied in other Silurian localities. Theinterpretation of the field and microfacies analysis indicates major sequence boundaries in the Llandovery(3), Wenlock (3), Ludlow (3) and Přídolí–Lochkovian (2) which may be correlated with coevaldisconformities in the Appalachian Foreland Basin of eastern North America and/or in the Welsh Basin ofthe British Isles. The following times appear to represent relative sea-level highstand maxima in the Silurianof the Carnic Alps, as indicated by dark, graptolitic shales in deep shelf to basinal carbonate-dominatedsections: a) early Aeronian, approximately the Coronograptus cyphus graptolite Zone/Demirastritestriangulatus graptolite Zone), b) the early Telychian (Oktavites spiralis graptolite Zone; Pterospathodus celloniconodont Superzone), c) late Telychian (lower Pterospathodus a. amorphognathoides conodont Zone); d)early to middle Sheinwoodian (Kockelella ranuliformis to Ozarkodina sagitta rhenana conodont Zones; Mo-nograptus riccartonensis graptolite Zones); e) mid-Wenlock ((?upper Kockelella walliseri conodont Zone;Cyrtograptus rigidus graptolite Zone); f) mid Homerian (Ozarkodina bohemica conodont Zone; Gothograptusnassa graptolite Zone); g) near the Wenlock–Ludlow boundary (Neodiversograptus nilssoni graptolite Zone);h) Polygnathoides siluricus conodont Zone; i) near the Ludlow–Přídolí boundary (upper Ozarkodina snajdriInterval Zone); j) lower Přídolí (Monograptus parultimus graptolite Zone) and k) at the Silurian–Devonianboundary (earliest Lochkovian: Icriodus woschmidti woschmidti conodont Zone. Of these, the earlier (at leastb–e) are well represented in the Appalachian Basin, as in Avalonian sections in Great Britain and in Baltica.Johnson [Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events.GFF 128, 115–121.] documented eight major highstands in global sea-level during the Silurian. The temporalresolution obtained in the Carnic Alps for local sea-level changes allows for refinement of the Telychian toPřídolí sea-level curve, as the stratigraphic successions are chronologically well-defined using both conodontand graptolite biostratigraphy and K-bentonite levels. Nearly all inferred deepenings in the Carnic Alpssection, with the exception of that in the Polygnathoides siluricus conodont Zone, approximately matchhighstands recorded on the Silurian sea-level curves of Johnson [Johnson, M.E., 1996. Stable cratonicsequences and a standard for Silurian eustasy. In: Witzke, B.J., Ludvigson, G.A., Day, J. (Eds.), Paleozoicsequence stratigraphy – Views from the North American Craton. Geol. Soc. Am. Spec. Pap. vol. 306, Boulder,pp. 203–212., Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes andevents. GFF 128, 115–121.]; however, the two Telychian highstands are not distinguished but rather arecombined as highstand 4 on the Johnson curve, although they are recognized by Loydell [Loydell, D.K., 1998.Early Silurian sea-level changes. Geol. Mag. 135 (4), 447–471.], and the upper Kockelella walliseri conodont

Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 1–28

⁎ Corresponding author.E-mail address: [email protected] (K. Histon).

0031-0182/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.palaeo.2009.04.004

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Zone deepening is not explicitly numbered by Johnson. These similarities suggest pervasive and probablyeustatic events that are manifested in the Apulia Terrane [Cocks, L.R.M., Torsvik, T.H., 2002. Earth geographyfrom 500 to 400 million years ago: a faunal and palaeomagnetic review. J. Geol. Soc. Lond. 159 (6), 631–644.],Laurentia and Avalonia during these time intervals.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

The correlation of depositional sequences and their internal cyclesacross sedimentary basins has proven to be an indispensablecomponent in stratigraphic correlation, paleoenvironmental recon-struction, taphonomy, paleoecology, and evolutionary studies (Vail etal., 1977; Van Wagoner et al., 1988; Wilgus et al., 1988; Ricketts, 1989;Brett et al., 1990; Vail et al., 1991; Emery and Myers, 1996; Brett et al.,1998; Catuneanu, 2002; Coe and Church, 2003).

Johnson (2006) identified eight large-scale highstands in sea-levelduring the Silurian, some of which may be linked to interglacialepisodes; the cause of others, however, especially for later Silurianevents remains unknown. Brett et al. (1990, 1998) highlighted theutility of detailed correlation of thin stratal packages within the LowerSilurian of eastern North America. Only with the increased strati-graphic resolution provided by new physical and biostratigraphiccorrelation of sequences and subsequences may it be possible todetect subtle but significant tectonic perturbations. Brett et al. (1990)noted that this type of study should be applied to foreland basin andepicratonic sea deposits in order to provide a new empirical databasewith which to test deductive models of eustasy and basin dynamics.This study seeks to identify Silurian depositional sequences in theCarnic Alps, to use these to develop a relative sea-level curve for thisinterval, and to compare this with patterns observed in Laurentia,Avalonia and Baltica. Continued stratigraphic investigations of thissort are needed in order to produce a consistent global sequencestratigraphic framework (Witzke et al., 1996). It is emphasized thatonly by interregional and intercontinental comparisons of numerouslocal relative sea-level curves placed within a refined chronostrati-graphic framework is it possible to gain an accurate picture of eustasyduring the Silurian.

In the present study we apply sequence stratigraphic concepts tothe well-dated mixed carbonate-siliciclastic sequences and graptoliticshales of the Silurian fromvarious sections in the Carnic Alps (Fig.1) inorder to correlate the sequences and sea-level changes theredetermined with those established in other areas of Europe andNorth America. This paper has several objectives, as outlined below:

1) To recognize and correlate sequence stratigraphic packages acrossthe Silurian depositional basin of the Carnic Alps section of theApulia Terrane (Cocks and Torsvik, 2002). Improved temporalstratigraphic resolution is required in order to provide a sounddatabase for testing eustatic vs. tectonic effects. Therefore, it isessential that precise data related to the timing of trangressive/regressive regimes are obtained from the biostratigraphically well-defined successions preserved there.

2) To recognize environmental and water depth changes from thesuccession of shelly benthic fossil assemblages, which have beendescribed from the sections to be investigated. The data availablemay be used as a control for elaborating the sea-level andsubsidence curves and testing some of the sequence stratigraphicconcepts being applied to the Silurian successions.

3) To develop a detailed sea-level curve for the Silurian of the CarnicAlps using concepts of sequence stratigraphy. Interregional andintercontinental comparisons of numerous local relative sea-levelcurves placed within a refined chronostratigraphic framework areessential for obtaining a more accurate picture of eustasy.

4) To determinewhether the pattern of sea-level change in the CarnicAlps succession is controlled by local tectonism or eustaticchanges. Detailed tracing of depositional sequences within the

Carnic Alps region may permit recognition of localized episodes ofuplift and subsidence. Correlation with global sea-level curvesderived from stable areas may also reveal anomalies produced bylocal tectonic effects.

5) To improve understanding of the paleoenvironmental and climaticsetting of the Carnic Alps. The Carnic Alps is a key area forunravelling the paleogeographic scenario of terranes derived fromthe northern margin of Gondwana during the Ordovician toSilurian interval.

6) To compare in detail the sea-level changes and stratigraphicsequences determined for the Carnic Alps in this study with thosepreviously inferred for the Appalachian Basin of Laurentia (Brett etal., 1990,1998; Brett and Ray, 2006) and do a brief comparisonwithreference to those currently being studied in the Welsh Basin ofAvalonia (Ray et al., in press) and Baltica (Calner et al., 2004;Jeppsson et al., 2005; Brett and Mclaughlin, unpublished data).

2. Previous work and methodology

This study is based upon and adds to the biostratigraphic andsedimentological studies of Walliser (1964), Schönlaub (1979, 1980,1997), and unpublished biostratigraphic data by the authors. Investi-gation of the dominant faunal groups has been carried out as part of aglobal multidisciplinary study of the Silurian of the Carnic Alps:conodonts (see above) and Ferretti and Schönlaub (2001), graptolites(Jaeger, 1975; Loydell, 2003), bivalves (Kříž, 1979, 1999, 2006),acritarchs (Priewalder, 1987), chitinozoa (Priewalder, 1997) andnautiloids (Histon and Schönlaub, 1999; Histon, 1999a,b, 2002a,b).Some of these fossils provide relative depth and other paleoecologicindicators for the studied sections and have also been used in the pastfor elaborating sea-level curves for the area (Histon and Schönlaub,1999; Kříž et al., 2003). Recent work by Ferretti (2005) and Ferrettiet al. (1999) on microfacies and biosedimentology, and taphonomicstudy of Silurian cephalopod limestones (Ferretti and Histon, 1997;Histon and Schönlaub, 1999; Histon et al., 1999; Ferretti and Histon, inpress) also aided in the determination of regressive and transgressivesystems tracts of the sections in question. The present investigation ofSilurian sequences complements ongoing sequence stratigraphicstudy on the Devonian of the Carnic Alps (Brett et al., 2001).

Preliminary field studies by Brett and Schönlaub of the Llandov-ery–lower Ludlow of the Cellon and Oberbuchach sections (Schönlauband Histon, 2000, Fig. 5; Brett et al., 2007) demonstrated that asequence stratigraphic approach was feasible in the Carnic Alps andshowed that correlation with coeval sequences in eastern NorthAmerica (Brett et al., 1990, 1995, 1998; Brett and Ray, 2006) in theAppalachian Foreland Basin and those being studied for the BritishIsles (Johnson et al., 1998; Ray and Thomas, 2007) might be possible.The main aspects of the fieldwork involved updating and revising theexisting detailed stratigraphic profiles from Schönlaub (1979, 1980,1997). Sections were logged in detail and measured precisely on acentimeter scale. In some cases additional samples were obtained forconodont biostratigraphy and thin section analysis was done to verifylithology and microfacies.

Particular emphasis was given to the identification and tracing ofthrough-going time-markers, such as K-bentonites (Histon et al.,2007), distinctive marker intervals, such as black shale beds andironstone horizons (Ferretti, 2005), and faunal epiboles (Ferretti andHiston, in press). This facilitated the detailed correlation of sequencesdeveloped in quite different facies on separate thrust sheets. A precise

2 C.E. Brett et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 1–28

https://www.researchgate.net/publication/229911429_Carbonate_depositional_environments_sequence_stratigraphy_and_exceptional_skeletal_preservation_in_the_Much_Wenlock_Limestone_Formation_(Silurian)_of_Dudley_England?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==

https://www.researchgate.net/publication/237737727_Earth_geography_from_500_to_400_million_years_ago_a_faunal_and_paleomagnetic_review._J_Geol_Soc_Lond?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==

https://www.researchgate.net/publication/233044184_Relationship_of_Silurian_sea_level_fluctuations_to_oceanic_episodes_and_events._GFF?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==


correlation of the classic Silurian sections originally documented bySchönlaub (1979, 1980, 1997) permitted identification of a transectfrom shallow to deeper deposits and establishment of the persistenceof depositional sequences. Sequence stratigraphic study in the CarnicAlps involved identification and elaboration of regressive andtransgressive systems tracts, highstand, lowstand, etc. Petrographicand paleontologic data from previous studies of these sections wereincorporated for elaborating a sea-level curve and in identifying sharpfacies offsets of relevance to sequence stratigraphy.

Relative water depths were interpreted from sedimentologic andpaleontologic evidence using the approach of benthic assemblages (BA)as outlined by Boucot (1975) and calibrated to approximate water

depths by Brett et al. (1993). The shallowest facies seem to be those oftheWenlock at the Lower Seewarte Base Section: comprisingwinnowedcrinoidal grainstones with possible pentamerid brachiopods; this isevidence for BA 3. The winnowed grainstones approach average stormwavebase but are still below fair weather wave base. A few of the moremassive limestones occur only in the upper Ludlow and Přídolí anddisplay a variety of features, such as possible stromatolites and ooids atthe Silurian/Devonian boundary at the Cellon section, platyceratidgastropods, hardgrounds and grainstones that all suggest a shallowshelf, BA 3 to 4 environment; though technically those terms wereoriginally defined on the basis of distinctive brachiopod communitiesthat are not present. Nearly all of these settings represent below normal

Fig. 1. Location of the Carnic Alps (Austria). (A) Location of the main occurrences of fossiliferous Paleozoic rocks in the Eastern and Southern Alps: the Carnic Alps; the KaravankeMountains; the Gurktal Nappe; the Graz Paleozoic (Rannach Nappe); theWestern and Eastern Graywacke Zone. The Periadriatic Line separates the Southern and the Eastern Alps. (B)Location of the studied Silurian sections in the Carnic Alps (Austria). The Austrian–Italian border runs E–W.10 km south of the village of Kötschach–Mauthen. Numbered stars showthe locality positions: (1) Cellon section, (2) Lower Seewarte Base section (3) Rauchkofelbodentörl section (4) Oberbuchach section (5) Rauchkofel Süd section, (6) Valentintörlsection (7) Rauchkofel Boden section (8) Seekopf Base section.

3C.E. Brett et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 1–28

https://www.researchgate.net/publication/230032355_Absolute_depth_of_Silurian_benthic_assemblages?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==


wavebase and generally above storm wavebase; certain units (forinstance the Cardiola Formation) show small-scale hummocky crossstratification and graded beds indicative of deposition from combinedstorm current/wave processes and thus a BA 3 to 4 setting. Cephalopod-and bivalve-rich nodular carbonate facies show evidence of low-energydepositionwithminimal transport, suchas slight fragmentationof shellsand bryozoans, and the presence of partially articulated crinoid columns(Kříž, 1999). Slight current alignment and telescoping of nautiloidsindicate minor currents (Histon and Schönlaub, 1999; Histon, 2002b;Ferretti and Histon, in press).The Rauchkofel Boden section containseyeless trilobites (Santel, 2001) suggesting a dysphotic to aphoticsetting, probably lower BA 4 or 5, although again, the typical indicatorbrachiopods are lacking. Green to black, graptolite-rich shales areassigned to BA 6 following Boucot (1975) and Boucot and Lawson(1999); these are considered to represent a basinal dysphotic to aphoticzonewell belowstormwave base. Colors reflect reducing conditions andthe presence of organic matter and lamination in many of these faciessuggest dysoxic to anoxic benthic conditions lacking burrowers.

In interpreting the Silurian sequences the key large-scale disconti-nuities and systems tracts were first established, including thesequence boundary (SB), transgressive surface (TS) and surface ofmaximum starvation (SMS) (Vail et al., 1977; Van Wagoner et al.,1988). Most sequences are subdivided by amaximum flooding surface(MFS) into a lower, shallow water but retrogradational (upwarddeepening) transgressive systems tract (TST) and an upper, deeperwater, aggradational to slightly progradational highstand systems tract(HST) (Brett et al., 1990). In many cases, a prominent contact betweenretrogradational carbonates and overlying shales, the so-called surfaceof maximum starvation (SMS; Vail et al., 1977; Sarg, 1988; Vail et al.,1991; McLaughlin and Brett, 2007) may divide the TST into early andlate portions. This discontinuity, typically more obvious than themaximum flooding surface, is thought to represent a period ofmaximum rates of sea-level rise. It is marked by a sharp corrosionsurface with iron mineralization, phosphatic nodules, and otherindications of sediment starvation and condensation.

3. Geological setting

3.1. Tectonic and paleogeographic setting

The paleogeography and relationship of the Paleozoic proto-Alpsand coeval neighboring areas, such as the Prague Basin (Barrandian,Bohemia), Sardinia, southern France and above all Spain and NorthAfrica is still controversial. The Carnic Alps extend in a W–E directionfor over 140 km continuing into the Western Karavanke Mountainswhere the Lower Paleozoic strata are distributed on either side of thePeriadriatic Line (Gailtal Fault), which separates the Southern and theEastern Alps. These rocks have been subdivided into a northern and asouthern domain, respectively (Fig. 1). The Carnic Alps of southernAustria represent one of the very few places in the world in which analmost continuous fossiliferous sequence of Paleozoic age has beenpreserved ranging from Late Ordovician to Permian in age. They arerepresented by shallow to deep-water fossiliferous marine sediments,which suggest a long-term displacement of the Apulia Terrane from amoderately cold climate of approximately 50° southern latitude in theLate Ordovician to the equatorial belt by the Permian (Schönlaub,1992). The reconstructed distribution of the various litho- andbiofacies of the Carnic Alps indicates a SW–NE directed polarityfrom shallow water carbonate platform environments to deeper shelfand finally deep-sea settings (Kreutzer, 1992). The latter must beassumed in the northern part of the Southern Alps, which, however, ismissing due to tectonic deformation along the Gailtal Fault as part ofthe Periadriatic Line separating the Southern from the Eastern Alps.

To the north a crystalline area is found consisting of metamorphicrocks also of Early Paleozoic age, but with a quite diverse lithologycompared to the Southern Alps. This fragment therefore belongs to a

different terrane to which the classic Lower Paleozoic deposits foundin Middle Carinthia and part of Steiermark (“Gurktal Nappe”), theGraz Paleozoic and probably the Graywacke Zone also pertain.Intraplate volcanism due to rifting throughout the Early Palaeozoicis characteristic for the area (Schönlaub and Histon, 2000).

Any reconstruction of the width of the intervening area and thenature of the rocks separating various Alpine terranes remains amatter of discussion. In a wider context these areas represent peri-Gondwanide terranes and arcs similar to Avalonia, Armorica–Iberia,Perunica and others (“Hun”-composite terrane after Stampfli, 1996;“Armorican Terrane Assemblage (ATA)” after Tait et al., 1999; Schätz etal., 2002), which originally formed the northern margin of Gondwana.Its break-up in the Early Ordovician was followed by rapid northwarddrift of continental fragments until they successively collided andaccreted with the northern continents of Laurentia and Baltica,respectively, starting in the Devonian and ending in the LateCarboniferous Variscan Orogeny (Schönlaub, 1998).

A relatively complete, although thin, Silurian succession of shallowto deep-water, fossiliferous marine sediments is preserved in the CarnicAlps sections, whose constituent units are biostratigraphically wellconstrained and hence, can be correlated with each other. The strata arewell exposed, and the emplacement of the heterogenic structural units iswell enough understood (Schönlaub and Kreutzer, 1994; Schönlaub,1997) to enable the correlation of stratigraphic sequences. A combinationof data sets derived from shallow to deeper shelf and basinal environ-ments should provide significant advancements in our understandingof Silurian sea-level history and subsidence rates and Paleozoic dynamicsof carbonate and siliciclastic sedimentation and add new informationtowards the determination of the paleogeographic position of the CarnicAlps during this interval by correlation with other areas where similarstudies have been carried out (Štorch, 2006; Ray and Thomas, 2007).

Recognizing the influence of the inferred sea-level changes duringthe Silurian Period may provide some hints into the well-knownrelationships between eustasy and changes in ocean basin volumedominated by slow variations in seafloor spreading rates or ocean ridgelengths (see Hays and Pitman, 1973; Pitmann, 1978; Kominz, 1984;Larson, 1991; Seyfried and Leinfelder, 1992; Garzanti, 1993; Miller et al.,2005; Fulthorpe et al., 2008). This may particularly apply to the peri-Gondwanide terranes, which broke off from the northern margin ofGondwana in the early Ordovician to drift rapidly northward until theyfinally collided and accreted with Laurentia and Baltica, respectively, inthe Devonian and Carboniferous. This long-lasting drift was interruptedby rifting and subduction related volcanism (Histon et al., 2007) whichmight have caused third order eustatic changes during that time.Variations in subsidence and sediment supplymay also account for suchchanges but in the present study seem to be negligible due to thereduced thickness of Silurian sediment pile.

3.2. Biostratigraphy

The Silurian and other Paleozoic sequences of the Carnic Alps are,in general, well-dated. Biostratigraphically important fossil groupsinclude primarily graptolites (Jaeger, 1975; Loydell, 2003) andconodonts (Walliser, 1964; Schönlaub, 1980; Ferretti and Schönlaub,2001). Trilobites (Feist in Schönlaub et al., 1992; Feist, 1999; Santel,2001), bivalves (Kříž, 1979, 1999, 2006), chitinozoans (Priewalder,1997), and acritarchs (Priewalder, 1987) are of equal importance forcorrelation, while the brachiopod (Havlíček et al., 1987) andcephalopod faunas (Gnoli and Histon, 1998; Histon and Schönlaub,1999; Histon, 1999a,b, 2002a,b) are useful also for taphonomic,paleoecologic and paleogeographic considerations.

3.3. General geologic history

Two major facies associations are displayed in the Late Ordovician ofthe central CarnicAlps:massive cystoid-rich limestones (“WolayerKalk”),


https://www.researchgate.net/publication/229911429_Carbonate_depositional_environments_sequence_stratigraphy_and_exceptional_skeletal_preservation_in_the_Much_Wenlock_Limestone_Formation_(Silurian)_of_Dudley_England?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==

https://www.researchgate.net/publication/230019566_Facies_development_depositional_settings_and_sequence_stratigraphy_across_the_Ordovician-Silurian_boundary_A_new_perspective_from_the_Barrandian_area_of_the_Czech_Republic?el=1_x_8&enrichId=rgreq-b3dd973e-167a-43ec-8cf1-88d38a2ac4df&enrichSource=Y292ZXJQYWdlOzIyMjg5Njc5MjtBUzoxNDIwNTc5NzY4OTc1NDFAMTQxMDg4MDY2OTk0NA==


quartz arenites and graywackes representing the shallowwater environ-ments and shales and bedded wackestones representing more basinalsettings (“Uggwa Kalk”). Minor diamictites and disconformities in theHirnantian Stage may record periglacial deposits. In most shallow waterareas the latest Ordovician and the earliest Silurian are missing(Schönlaub, 1988; Ferretti and Schönlaub, 2001; Ferretti, 2005; Ferrettiand Histon, in press). In deeper water settings this contact is nearlyconformable with the Hirnantian Plöcken Formation, belonging to theGlyptograptus persculptus graptolite Zone, succeeded by Silurian grapto-litic shales of the Parakidograptus acuminatus graptolite Zone (Nölblin-graben section, Bischofalm Facies: Jaeger and Schönlaub, 1980; Havlíčeket al., 1987; Schönlaub and Sheehan, 2003 and unpublished biostrati-graphic data by H.P.S.).

In the Carnic Alps the Silurian transgression started at the verybase of the Llandovery, i.e. in the Parakidograptus acuminatusgraptolite Zone although the index graptolite from the base of theSilurian, Akidograptus ascensus, has yet not been found. Its forerunner,however, from the latest Ordovician, Glyptograptus persculptus wasreported from thewestern Karavanke Alps (Jaeger et al., 1975) but wasalso recently found in the Carnic Alps (Štorch, pers. comm.). However,owing to the onlap of Silurian strata onto the latest Ordoviciandisconformity, a varying succession of Silurian shelf sediments islocally missing at some sections, which corresponds to severalconodont zones of Llandovery to Ludlow age in both the Carnic andKarawanken Alps. At some places even uppermost Přídolí strata mayrest disconformably upon Upper Ordovician limestones. In the basinalgraptolitic facies, however, a more or less continuous sedimentationacross the Ordovician/Silurian boundary has been documented. Ingeneral the available data for the Carnic and Karawanken Alps suggesta relatively complete, but strongly condensed late Llandovery toPřídolí succession in carbonate-dominated facies and a morecontinuous record in the graptolite-bearing sequences, somethingthat is not possible to demonstrate in other areas of the Eastern andSouthern Alps due to poor preservation and lack of fossils, as well asmetamorphic overprints.

Silurian strata are subdivided into four major lithofacies (Schön-laub, 1979, 1980) reflecting different depths of deposition andhydraulic conditions from high energy, shallow (BA 3) and mid-shelf to low-energy deeper shelf (BA 4–5) settings. The generalpattern is suggestive of a steadily subsiding basin and an overalltransgressional regime from the Llandovery to the Ludlow. Uniformlimestone and shale sedimentation suggest that more stable condi-tions were developed during the Ludlow to Přídolí (Schönlaub, 1997).Silurian deposits range from shallow water bioclastic limestones

dominated by pelagic faunas to nautiloid-rich limestones (Wolayerand Plöcken Facies), interbedded shales and wackestones (FindenigFacies) to green, gray and black graptolite-bearing shales and cherts(Bischofalm Facies). The thickness of the entire Silurian successiongenerally does not exceed 60 m, with the thickest sections in themixed shale and carbonate successions of the Findenig Facies; somesections are substantially thinner due to local onlap and condensation.

4. Key stratigraphic successions in the Carnic Alps

A series of distinctive paleogeographic/paleoenvironmental set-tings are represented on each of the different nappes or thrust sheetsof the Carnic Alps (Schönlaub, 1980, 1992; Brett et al., 2007). Becauseof the crustal shortening involved, these disparate facies arejuxtaposed in close succession (Kellerwand Nappe: Lower SeewarteBase section, Cellon Nappe: Cellon Section, Rauchkofel complex:Rauchkofel Boden, Valentintörl, Seekopf Base, Rauchkofelbodentörl,Rauchkofel Süd sections).

In the Carnic Alps the classic sections (Fig. 1) of Silurian stratainclude: (1) Cellon (Plöcken Facies), (2) Lower Seewarte Base (WolayerFacies), (3) Rauchkofelbodentörl (Plöcken Facies), (4) Oberbuchach(Findenig Facies), (5) Rauchkofel Süd (Plöcken Facies), (6) Valentintörl(transitional between Wolayer and Plöcken Facies), (7) RauchkofelBoden (Wolayer Facies), (8) Seekopf Base (Wolayer Facies), (9) Grapto-lithengraben (Bischofalm Facies), (10) Nölbling Graben (BischofalmFacies) and (11) Feistritz Graben (Findenig Facies). As noted, mostintervals are stratigraphically well-dated by conodonts and/or grapto-lites and are ideal for this study as they represent relatively completemoderately shallow to more basinal sequences ranging from the LateOrdovician to the Early Devonian. In these conditions, the possibility ofbeing able to delineate well-dated sequence stratigraphic packages andboundaries aswell as a precise sea-level curve is therefore quite high. Inthe present study, the wholly graptolitic shales (sections 9–11 above)were excluded because of the difficulty of recognizing sequences withinthem; only sections 1–8 will be considered in detail. In the followingsections eachof thesedistinctive facies groupingswill be considered andthe representative stratigraphy summarized briefly from proximal tomore distal facies.

4.1. Lower Seewarte Base section (Kellerwand Nappe, Wolayer Facies)

South of Valentintörl the Kellerwand Nappe shows a relatively thinsuccession of 40 to 50 m dominated by carbonates (Fig. 2). The lowestformal division of the Silurian, here as elsewhere in the proximal

Fig. 2. Lower Seewarte Base and Valentintörl sections overview. The Ordovician Wolayer Limestone forms a prominent base to the sequence at both of the above sections. Thedivisions of the Kok Formation can be easily identified at the former section, exposed at the base of Mount Seewarte, especially the thick band of the upper limestones. The recessedCardiola Formation and contact with the Alticola Limestone are quite evident. The Valentintörl, belonging to a different thrust sheet, forms a spectacular feature, here seen from anorthwest viewpoint. The Silurian succession is quite thin in comparison to the underlying Ordovician limestones. Altitude approximately 2100 m. Ord.–Ordovician, Sil.–Silurian,Dev.–Devonian, K–Kok Formation, C–Cardiola Formation, A–Alticola Limestone.



facies of the Carnic Alps, is assigned to a single lithological package,the Kok Formation (Figs. 3 and 4). This is a heterolithic unit thatprobably should be further subdivided. The lower portion of the KokFormation consists of a few meters of shale and thin ferruginouslimestones, which we informally term the “lower shales andferruginous limestone member”. This unit is of late Llandovery toearliest Wenlock age based on the occurrence of conodonts indicatingthe Pterospathodus celloni and Pterospathodus a. amorphognathoidesconodont zones.

The remainder of the Kok Formation is represented by skeletallimestones (informally named as “Kok limestones”), here provision-ally subdivided into lower and upper units by a distinctive brownishweathering interval of slightly argillaceous crinoidal limestones.At the Cellon section and elsewhere the Kok carbonates can befurther divided into three parts (see below) based upon twodistinctive shale intervals. However, the lower shale horizon (ofearly to middle Wenlock age) appears to be absent at the LowerSeewarte Base section.

Fig. 3. Lithostratigraphic column of the Lower Seewarte Base section. Kok Formation. Lettered units B–G are marker beds that appear to be correlative through several sections.Individual bed thickness is given on the left of the column in cm; description of lithology is given on the right of the column. The upper part of the section continues on the right-handside column. The Telychian part of the section is given in detail in Fig. 4 (part of section as indicated by 3 m point on left-hand side of column). Ord.–Ordovician, Lst–Limestone, Mn–manganese, Fe–Iron, Fm.–Formation, Pt.–Pterospathodus, A.–Ancoradella, dashed arrow line indicates tentative extension of biozone.



4.1.1. Lower shales and ferruginous limestonesAt the base of the succession is a complex interval that overlies an

erosion surface on massive carbonate grainstones of the WolayerLimestone (Late Ordovician; Amorphognathus ordovicicus conodontZone); this interval shows a series of traceable marker beds (letteredA–H in Figs. 3 and4). The contact between theOrdovician carbonate andthe overlying shales is irregular and evidently unconformable. LowestSilurianbedsare a thin successionof dark gray shales andgray to reddishsiliceous mudstones, typically 20 to 30 cm thick (Figs. 3 and 4; units Aand B), with few if any diagnostic fossils and therefore of uncertain age.However, a thin K-bentonite near the base of the shale appears tocorrelate with one found at the Cellon and Oberbuchach sections instrata of Telychian age (Histon et al., 2007). As in other related sections,

these shales/mudstones are overlain by a 70 cm complex interval(Figs. 3 and 4; unit C) of iron andmanganese-rich carbonate beds (Tietz,1976). Portions of this bed have a reddish-brown color and take on thecharacter of a true ironstone, the latter showing exceptional preserva-tion at the Lower Seewarte Base section; stromatolite-like manganifer-ous crusts also occur in the bed. Other portions of the bed are merely apinkish gray, slightly ferruginous limestone. Few macrofossils arepresent. However, samples of the bed have yielded the diagnosticconodont Pterospathodus celloni, indicative of the P. celloni Superzone(early Telychian, Llandovery) and of the Pterospathodus a. amorphog-nathoides zonal Group in the uppermost layers.

In turn, this distinctive mineralized carbonate bed is abruptlyoverlain by about 50 cm of dark gray to reddish ferruginous shales

Fig. 4. Details of the Telychian to earliest Sheinwoodian part of the Kok Formation at Lower Seewarte Base section. Lettered units A–G are marker beds that appear to be correlativethrough several sections. Section thickness is given in meters on the left of the column; description of lithology is given on the right of the column. The upper part of the sectioncontinues on the right-hand side column. Dashed arrow line indicates tentative extension of biozone. Abbreviations as in Fig. 3.



with thin nodular limestones (Figs. 3 and 4; units D–F). Conodontsampling by Schönlaub (1980) revealed the presence of Pterospatho-dus a. amorphognathoides indicative of the Pterospathodus a. amor-phognathoides conodont Zonal Group (Jeppsson, 1997) of latestTelychian or earliest Wenlock age. Unit D shales are bioturbated,contain a few nautiloid cephalopod conchs and are overlain bynodular skeletal grainstones and mudstones, approximately 25 cmthick, that also belong to the Pterospathodus a. amorphognathoidesconodont Zone. These, in turn, are followed by a second interval ofmedium dark to olive gray shale approximately 20 cm thick (Fig. 4;unit F).

4.1.2. Kok limestonesA sharp contact with overlying crinoidal grainstone marks an

important erosional sequence boundary. The lowest 27–30 cmgrainstone bed (unit G) apparently also belongs to the Pt. a.amorphognathoides Zonal Group though higher beds are poorlyconstrained. This basal grainstone is overlain by shales and argillac-eous grainstones of unit H, recording another, probably early Wenlockhighstand. The overlying beds (including basal unit I) of the lower KokFormation comprise 6–6.3 m of undifferentiated, massive crinoidaland brachiopod-rich grainstones (Fig. 3). Abundant, small, as yetunidentified, pentamerid? brachiopods towards the top of thisinterval suggest a shallowwater BA 3 (benthic assemblage 3) position.A 1.5 m thick distinct interval of brownish gray silty to argillaceouscrinoidal wacke- and packstones separates this lower crinoidalgrainstone interval from a higher grainstone interval of the upperKok Formation and appears to record a period of relatively deeperwater conditions (Fig. 3, refer to column on right; intervals 95 cm and60 cm). The upper package of skeletal grainstones comprises 3.5 m ofcrinoidal grainstones. The basal 70 cm interval has abundant, small, asyet unidentified, pentamerid? brachiopods both at the base and topand contains Kirkidium-type large pentamerid brachiopods typical ofBA 3 (Brett et al., 1993) within the unit (Fig. 3). Although thebiostratigraphy of the Kok Formation beds is still somewhat uncertain,the grainstone interval below the brownish crinoidal packstonesdocument the Ozarkodina sagitta sagitta conodont Zone.

The Kockelella ranuliformis–Ozarkodina sagitta rhenana conodontZones (as modified by Jeppsson, 1997), which are well represented inmore distal facies of other thrust sheets, such as at the Oberbuchachsection, are not recognized or are extremely condensed in this section.The upper portion of the Kok Formation, overlying the brown,argillaceous crinoid grainstone package, appears to belong to theAncoradella ploeckensis conodont Zone indicating an early Ludlow age.

4.1.3. Cardiola FormationThe upper portion of the Kok Formation is abruptly overlain by an

interval of dark gray to black shales with limestone intercalationsbelonging to the Cardiola Formation (Fig. 5). This unit is approxi-mately 3.3 m thick and comprises alternating black shales and thin,planar to hummocky-laminated fine-grained calcareous grainstonesand calcisiltites. The Cardiola Formation (Fig. 5), in addition toyielding a distinctive Cardiola-dominated molluscan fauna, hasproduced conodonts of the Polygnathoides siluricus Zone. This is inline with the dating of the Cardiola Formation elsewhere, asLudfordian (middle Ludlow).

4.1.4. Alticola LimestoneThe Cardiola Formation is highly distinctive and abruptly overlain

by massive beds of the Alticola Limestone, which, here as elsewhere,appear to be represented by a massive cephalopod-bearing, gray topinkish wacke- and packstone lithofacies that can be assignedtentatively (diagnostic conodonts being rare) to the Ozarkodinasnajdri conodont Zone. Higher beds are not exposed in this sectiondue to cover by debris from the Seewarte cliff (Fig. 2). Further to thewest, however, the Silurian/Devonian boundary beds are exposed in a

small outcrop at the base of Mount Seewarte (Suttner, 2007).Although dolomitized, this part resembles the general lithology ofthat unit at other localities.

4.2. Cellon section (Cellon Nappe, Plöcken Facies)

Deeper shelf facies are exposed in the Cellon avalanche gully nearPlöcken Pass, approximately 1 km from the Austria–Italy border,adjacent to Highway 110 (Fig. 6). This classic reference section, thestratotype for Silurian rocks in the Southern Alps, displays an excellentand nearly complete late Llandovery to Přídolí succession (Fig. 7)biostratigraphically well-defined by conodonts (Walliser, 1964 anddetailed log therein), chitinozoans (Priewalder, 1997 and detailed logtherein), and graptolites (Jaeger, 1975). In general, the previous sea-level curves proposed for the Silurian of the Carnic Alps area havereferred to the succession at this section (Histon and Schönlaub, 1999;Kříž et al., 2003) and the data, based mainly on depth indicationsderived from the faunas preserved there, support the findings of the

Fig. 5. Details of Cardiola Formation at Lower Seewarte Base section. Individual bedthickness is given on the left of the column in cm; description of lithology is given on theright of the column. The first limestone bed (150 cm in thickness) forms the contactbetween the Kok Formation and the Cardiola Formation. The upper contact with theoverlying Alticola Limestone is marked by a layer of large nautiloids parallel to bedding,sometimes up to 1 m in length.



present study. K-bentonite levels have also been described from theUpper Ordovician and from the Pterospathodus celloni conodontSuperzone and Cyrtograptus rigidus graptolite Zone in the Siluriansuccession which have been used for correlation with the othersections studied (Histon et al., 2007). Lower Silurian beds areunfortunately highly condensed or absent, and, indeed, the firstdatable portion of the succession lies in the middle Llandovery Series(latest Aeronian to Telychian Stages).

Again, the basal interval (beds 9–20 of Walliser, 1964), ranging inage from late Llandovery to middle Ludlow, is all assigned to the KokFormation. As before, it was convenient to subdivide this heterolithicsuccession into the lower shales and ferruginous limestones, and thelower, middle and upper Kok limestones; the latter calcareous unitsare separated from one another by thin shaly successions which arehighly condensed and/or truncated with respect to those in moredistal successions (see discussion of the Oberbuchach section, below).

4.2.1. Lower shales and ferruginous limestonesAs at the Lower Seewarte Base section the Cellon section

commences with dark gray, ferruginous and, unfortunately, highlyweathered shales and silty limestones that rest with marked wavyunconformity on siliciclastic siltstones and mudstones of the latestOrdovician Plöcken Formation, from which a Hirnantian conodontfauna has been documented recently (Fig. 7; Ferretti and Schönlaub,2001). This is a major hiatus representing at least six graptolite zones(Schönlaub, 1993). The basal Silurian beds, just above the O/Sboundary, bed 9 of Walliser (1964), have yielded chitinozoansdiagnostic of the upper Aeronian–lower Telychian Eisenackitinadolioliformis Biozone (Priewalder, 1997). Moreover, by physicalcorrelation into the sections at Rauchkofelbodentörl and Oberbu-chach, these basal shales are probably of early Telychian age. A thin K-bentonite near the base of the shale appears to correlate with onefound at the Lower Seewarte Base (Fig. 4) and Oberbuchach (Fig. 18)sections in strata of Telychian age (Histon et al., 2007). The first stratawell-dated by conodonts occur approximately 80 cm above the base ofthe Silurian and again comprise 40 cm of highly ferruginous andmanganese-stained, pinkish to red colored carbonates (Beds 10–10Cof Walliser, 1964). These beds yield crinoid ossicles and occasional

nautiloids in a matrix of iron-rich silty carbonate and are burrowedwith possible firmground surfaces. These beds, nearly identical to thelower ferruginous limestones (unit C) at the Lower Seewarte Basesection, have also yielded the diagnostic conodont Pterospathoduscelloni. Indeed, this is the stratotype section of the P. celloni conodont

Fig. 7. Lithostratigraphic column of the Cellon section. Section thickness is given inmeters on the left of the column; description of lithology is given on the right of thecolumn. Bed numbers after Walliser (1964). Ord.–Ordovician, Tely.–Telychian, Dev.–Devonian, Fm.–Formation, lst.–Limestone.

Fig. 6. Cellon section overview. The stratotype section for the Silurian of the Eastern andSouthern Alps is exposed in an avalanche gully to the southeast of Mount Cellon(2238 m) at an altitude of approximately 1500 m. The whole section ranges from lateOrdovician to early Carboniferous in age. The Silurian part of the section is 43 m in total.



Zone (Walliser, 1964), although that interval now assigned to theP. celloni conodont Superzone, has been substantially revised in recentstudies in the Baltic area (Männik, 2007) and much of what wasformerly considered to be lower P. celloni conodont Zone is nowassigned to the underlying Pterospathodus eopennatus Superzone.From this point upward the very detailed study by Walliser (1964 anddetailed log therein) has led to the development of a series ofstandardized numbered units, which will be used in the discussion.

The mineralized ironstone bed is overlain by about 55 cm of rusty-weathering ferruginous carbonate and dark shale (Beds 10D–10G ofWalliser, 1964). A pyritic/limonitic weathered bed, positionedapproximately 20 cm above the ironstone within the above package,of sooty brown mudstones and some thin nodular limestonesapproximately 20 cm thick (Beds 10 G–base 11 of Walliser, 1964),may correlate well with unit E in the Lower Seewarte Base section.This bed separates the lower dark shales from an upper black, pyriticshale package about 30 cm thick (Bed 11 of Walliser, 1964), a patternconsistent throughout the Carnic Alps in the Plöcken to FindenigFacies. The upper dark shale, has yielded graptolites of the Mono-graptus priodon level (Jaeger, 1975), which corroborates an earlyPterospathodus a. amorphognathoides Zonal Group assignment basedon conodonts collected from some of the thin limestones.

4.2.2. Kok limestonesA pinkish nodular wackestone with minor shaly partings, contain-

ing nautiloids and minor crinoid debris, which become more massiveupwards, 55–60 cm thick (Beds 11C–11F of Walliser, 1964) sharplyoverlies the upper dark shales at an apparent sequence boundary. Thisunit appears to lie near the top of the Pterospathodus a. amorphog-nathoides conodont Zone and therefore within the lower part of theWenlock (early Sheinwoodian). A more compact gray to reddishwacke-to packstone, 25–23 cm thick (Beds 12–12A of Walliser, 1964)with an apparent trilobite and brachiopod fauna, overlies the lowerlimestone bundle and appears to represent themore condensed upperpart of it. Immediately overlying limestone bed 12A at the Cellonsection is an interval of about 47 cm dominated by argillaceouslimestones and shales, poorly exposed in a trench (Bed 12B ofWalliser, 1964). Careful excavation of this zone indicates that itactually comprises three units, a lower dark gray shale, a middlebundle of black, somewhat fossiliferous packstones with adultbivalves being the dominant element of the fauna and with abundantgastropods, crinoid debris, adult and juvenile nautiloids and brachio-pods also noted in this accumulated horizon (Kříž, 1979, 1999; Ferrettiand Histon, in press), and an upper gray shale, which has yieldedgraptolites (Jaeger, 1975) diagnostic of the Cyrtograptus rigidusgraptolite Zone (probably equivalent to the upper Ozarkodina sagittarhenana conodont Zone). Detailed fieldwork has shown that this shalepasses upward into a series of four thin "gray" platy packstonelimestones (Beds 12C–D of Walliser, 1964) topped by a coarsecalcisiltite level with abundant pyritic material.

There is a distinct change to thicker carbonate development withfour levels of lenticular micritic gray limestone developed (Bed 12E ofWalliser, 1964). An abundant nautiloid fauna was noted in the lowerpart of this packstone/micrite series while crinoid debris andbrachiopod and bivalve faunas are more prevalent towards the top.

A sharp erosion surface with slight relief at the top of bed 12E(Walliser, 1964) and a stylolitic level indicates a break in sedimenta-tion at this point of the section. Recent study of carbon isotopestratigraphy at Cellon indicates a significant unconformity within theWenlock portion of the section (Wenzel, 1997) at the sharp basalcontact of bed 13 (Walliser, 1964). A major portion of the Ozarkodinasagitta rhenana and lower Kockelella walliseri conodont Zones intervalmay be missing at this unconformity.

In turn, these beds are sharply overlain by the massive middle Koklimestones, which comprise nodular towavy-bedded gray and pinkishgray limestones with dark red silt-filled burrows and ferruginous

stylolitic crusts. This part of the Kok Formation is a cephalopod-richlimestone with abundant nautiloid conchs of varying sizes. Some ofthese are telescoped within one another (Histon, 2002b). A few thinintervals within this mass of middle Kok limestones have diminutivebrachiopods and laminae of crinoidal debris (Histon and Schönlaub,1999; Ferretti and Histon, in press). The middle Kok limestone isdivisible into at least three portions. The upper 2m are separated fromthe lower by a slightly recessive shaly interval (base Bed 14 ofWalliser,1964). This parting may be of significance with regard to correlationinto more distal sections. The upper surface of the middle Koklimestone division (Bed 15A of Walliser, 1964) is sharply overlain by aone-centimeter yellowish weathering clay, which may represent abentonitic shale. This is then followed by approximately 0.5 m ofmedium dark gray to black shale with thin limestone carrying Kock-elella crassa Zone conodonts near the top. In turn, this indicates thepresence of the Wenlock–Ludlow series boundary within this darkgray shale band. Arguably, this shale zone may correlate with themuddy to silty, brown crinoidal packstone seen in the proximalsection at the Lower Seewarte Base section, which also appears to beclose to the Wenlock–Ludlow boundary (Fig. 7).

The shale is sharply overlain by more pink to reddish, wavy-beddedmassive wackestones of the upper division of the Kok Formation, hereapproximately 5m thick. Again this division has within it several small-scale cycles with abundant orthoconic nautiloids and a horizon ofmanganese enrichment near the middle of the unit. Reddish silt-filledburrows are typical of this interval, except near the top, where thelimestone becomes grayer in a final 20 cm zone and yields abundantdiminutive brachiopods and juvenile nautiloids, thatmaybe transitionaltoward the overlying Cardiola Formation.

4.2.3. Cardiola FormationThe Cardiola Formation (Beds 21–24 of Walliser, 1964) is extremely

distinctive in the Cellon section as it consists of about 3.5 m of jet-black,rusty-weathering shales with interbedded hummocky-laminated, finecalcarenite and calcisiltite beds (Fig. 8). Kříž (1979, 1999) described indetail the abundant bivalve faunas including the spectacular Cardiolaaccumulations on bed surfaces for which the formation was originallynamed (Geyer, 1894; Schönlaub, 1985). Other fossils include nautiloids,brachiopods, trilobites, chitinozoans, graptolites of the Diplograptusbohemicus level as well as conodonts of the Polygnathoides siluricusconodontZone. Pickett (2007)describeda single specimenof the colonialrugose coral Spongophyllum from a level 55 cm above the base of theCardiola Formation. He argued that it might have been transportedalthough it is difficult to understand amechanism for transport of suchanobject. Large silt-filled burrows characteristic of theKokunit are absent inthese laminated limestones. The upper surfaces of some limestones showfirmground burrowing suggesting intermittent intervals of oxygenationof the seafloor (HistonandSchönlaub,1999; Ferretti andHiston, inpress),but these are characteristically overlain by black, pyritic and laminatedshales, conducive to the preservation of graptolites.

4.2.4. Alticola and Megaerella LimestonesAgain, the beds of the Cardiola Formation are sharply overlain by

massive carbonates of the Alticola Limestone, which is slightly lessthan 20 m thick at this location and consists of several divisions. Thelower portion is light gray limestone with thin dolomitic silt-filledburrows and at the base scattered large cephalopod conchs. A one-meter interval approximately 2.75 m, at the base, shows a pinkishcoloration and is notable for the presence of coated grains andpossible small oncolites, as well as some crinoid and brachiopoddebris. A more massive middle division overlies this distinctivepinkish cephalopod-rich zone. This interval, forms a nearly verticalledge within the Cellon section avalanche gully and is, thereforedifficult to access, but appears to be gray wackestone, again featuringdolomitic, silt-filled burrows. A thin pale purplish bioclastic packstonewith coated grains (Bed 28 of Walliser, 1964) was identified at the top



of this section. This bed and overlying small rugose coral-bearingstrata are apparently in the upper Ozarkodina snajdri Interval Zone.

A highly distinctive upper division of the Alticola Limestone beginsapproximately 7 m below the top of the formation, near the Ludlow–

Přídolí boundary (Jaeger, 1975). Thin black shales intervene betweenledges of light gray laminated calcisiltites, some of which showburrowed firmground tops. This interval lies within the Monograptus

parultimus graptolite Zone. The alternating shale and limestonesuccession persists with minor modification to the top of the unitwherein massive ledges of the Megaerella Limestone sharply overliethe highest shaly carbonates.

The Megaerella Limestone of Přídolí age, comprises 8 m of massivewacke- to packstones with some skeletal grainstones in the upperthird. A general shallowing upwards trend through this interval is

Fig. 8. Detail of Cardiola Formation at Cellon Section; section thickness is given in meters on the left of the column; description of lithology is given on the right of the column. Bednumbers after Walliser (1964).



suggested by the occurrence of packstones and grainstones withabundant brachiopods near the top of the Megaerella Limestone; thetopmost bed (bed 47B) shows well-preserved fenestrate bryozoans.This unit shows a sharp contact with black shales and alternatingcalcisiltites, which bear fragmentary loboliths of the crinoid Scypho-crinites (Histon and Schönlaub, 1999). Conodonts from limestonesslightly above the black shale boundary indicate the Icriodus w.woschmidti conodont Zone and hence the earliest portion of theDevonian (Lochkovian Stage). Furthermore, some 1.5 m above thelithologic change the index graptolite for the base of the Devonian,Monograptus uniformis, was recorded by Jaeger (1975).

Thus, evidence from the classic Cellon section suggests a series ofshale-prone highstands, each dominated by dark, organic-rich andlaminated shale (Pasava and Schönlaub, 1999) facies, with a slight,upward shallowing trend. These are overlain by nodular to massivecarbonates with tightly-stacked cephalopod-rich beds that suggestcondensed offshore facies. The small proportion of dark siliciclasticmuds within these carbonate bases suggests relative sedimentstarvation during their deposition.

4.3. Rauchkofel Boden, Seekopf Base and Valentintörl sections

A series of thin, condensed Silurian sections occur on three relatedthrust sheets of the Rauchkofel structural complex. These areincomplete successions that commence with only minor, sporadicLlandovery occurrences and more definite, but thin Wenlocksediments. In order, the Rauchkofel Boden (Figs. 9 and 10), SeekopfBase (Figs.11 and 12) and Valentintörl (Figs. 2 and 13) sections appearto show progressively lesser representation of the basal units. In thecase of the Seekopf Base section onlap of higher Silurian units isobservable along a single outcrop (Fig. 11).

4.3.1. Kok limestonesThe taphonomy and sedimentology of the Kok Formation in these

sections have been studied in detail by Ferretti et al. (1999), Histonet al. (1999), Ferretti (2005), Ferretti and Histon (in press). Llandoverydeposits are represented, if at all, only as hematitic to manganese-richcrusts and oolitic grainstone infillings of corroded pits on the upper

surface of the OrdovicianWolayer Limestone. These thin sediment fillshave yielded conodonts of the Pterospathodus a. amorphognathoidesZonal Group (Ferretti, 2005). The overlying beds of Wenlock age arerepresented by massive to slightly nodular, pink to red, cephalopod-rich wackestones and packstones, with cephalopod conchs embeddedin a micritic matrix, rich in fragmentary trilobites, echinoderms,disarticulated bivalve shells, ostracodes, brachiopods and gastropods.

The Kok Formation is represented on the Rauchkofel Boden sheetonly by the equivalents of the middle and upper limestone division ofthe Cellon section with the basal beds yielding conodonts of the Ozar-kodina sagitta sagitta Zone (Fig. 10). A one-meter thick, massiveencrinitic limestone is present towards themiddle part of the formation(units 323/314 in Fig.10). Aminor nest of shaly partings (units 324/314in Fig. 10) consisting of thin layers of bioclastic limestone and ooliticgrainstones separated by thinly laminated iron-rich layers or crusts,mayrepresent the Wenlock–Ludlow boundary shales seen prominently atthe Cellon section. Unit 314 has yielded conodonts of the Kockelellacrassa conodont Zone. Juvenile nautiloids, associated with equidimen-sional articulated brachiopods and gastropods, are visible in pinkishhorizons towards the top of the formation (top 324–315), a faunalepibole which may be traced in many of the Carnic Alps sections.

On the Valentintörl thrust sheet the section commences with theLudlow age upper limestone division of the Kok Formation (Kockelellacrassa conodont Zone), which rests on a prominent unconformitysurface with solution hollows filled with microconglomeratic sedi-ment (Fig. 13). The 4.3 m red iron and manganese-rich calcareoussequence consists of mainly wackestone–packstone facies, withabundant trilobite fragments and an associated fauna that includesechinoderm ossicles, rare small ostracodes, bryozoans, brachiopods,cephalopods and gastropods. Laminated wackestones with echino-derms representing fine skeletal debris associated with cephalopodsare also present. The Cardiola Formation appears to be faulted out andthe Alticola Limestone has not been studied at this section.

The Seekopf Base section also exposes incomplete Silurian andDevonian sequences overlying the cystoid-bearingWolayer Limestone(Figs. 11 and 12). Reddish patches of silty carbonate, up to 20 cm indiameter, are locally preserved at the top of the Ordovician and weredated by conodonts as early Ludlow Kockelella crassa conodont Zone(Schönlaub, 1980). Their internal fabric consists of planar to wavy,sometimes discontinuous, fine micrometric laminae that may evolveinto small-scale dome-like structures. Owing to the irregular lamina-tion and microfabric, a microbial origin of these “stromatolite-like”structures was proposed (Ferretti, 2005). A recent resampling hasrevealed levels with a similar lamination, intercalated with echino-derm debris, of Wenlock age with conodonts indicative of the Ozar-kodina sagitta rhenana Zone (Ferretti and Histon, in press). The Ludlowis represented by typical light gray to pinkish wackestones topackstones, that may be dominated by echinoderm debris or trilobitesor by a mixture of both. In addition, peculiar pelmatozoan holdfastsmay be present in association with fine skeletal debris. Spectaculartrilobite-rich packstones, with minor brachiopods, are exposed in themiddle part of the Seekopf Base section (Fig. 12). Crinoidalwackestones appear to persist in the Seekopf Base section even intothe Polygnathoides siluricus Conodont Zone.

4.3.2. Cardiola FormationThe Cardiola Formation, varying from 10 to 20 cm in thickness, is

still recognizable at the Rauchkofel Boden section (Fig. 10). Itscharacteristic bituminous shale facies with lenses of dark micriticlimestone (about 10 cm thick), exposed in a trench excavated duringWorld War I (Fig. 9), corresponds to the Polygnathoides siluricusconodont Zone of the stratotype at the Cellon section. The fauna isdominated by unidirectionally oriented cephalopods embedded in amatrix of sorted aligned bioclasts, frequently coated by micriticenvelopes (Ferretti et al., 1999). Numerous bivalves of the CardiolaCommunity are reported from here (Kříž, 1979, 1999).

Fig. 9. Rauchkofel Boden Section overview. The classic section of the Wolayer Facies isexposed to the south of Mount Seewarte and Kellerwand (seen in the background2774m). The section is at an altitude of 2175 m. The limestone–limestone contact of theOrdovician Wolayer Limestone and middle division (herein) of the Kok Formation isseen to the left. The shaly Cardiola Formation was excavated during World War I as atrench used for observation of the Austrian/Italian border (see also Fig. 11). Theprominent sequence boundary with the overlying Alticola Limestone is thus wellexposed. The upper part of the Alticola Limestone forms a steep cliff to the right so theSilurian/Devonian boundary is not shown here. O–Ordovician, W–Wenlock, C–CardiolaFormation, Fm.–Formation, Lst.–Limestone.



4.3.3. Alticola LimestoneLower beds of the Alticola Limestone (n. 326–331 in Fig. 10: Upper

Ludlow–Přídolí) at the Rauchkofel Boden section comprise gray-pink

cephalopod wackestone to packstone with a diverse fauna dominatedby nautiloids, solitary corals and trilobites (Ferretti et al., 1999; Picket,2007; Ferretti and Histon, in press). Towards the top, the formation

Fig. 10. Lithostratigraphic column of the Rauchkofel Boden section. Section thickness is given in meters on the left of the column; description of lithology is given on the right of thecolumn. Ordovic.–Ordovician, T = Telychian. Wen = Wenlock, Devon.–Devonian, Lst.–Limestone, Pt.–Pterospathodus, Oz.–Ozarkodina, K.–Kockelella, Po.–Polygnathoides.



grades to darker gray, platy beds, with a greater micrite content andmicritized grains. The Silurian/Devonian boundary is drawn at thebase of gray and blackish platy crinoidal limestones containingabundant lobolith holdfasts of Scyphocrinites; this bed yieldedcommon conodonts Ozarkodina remscheidensis eosteinhornensis and,more frequently, Ozarkodina remscheidensis remscheidensis.

The basal part of the overlying lowermost Lochkov sequenceseems to be extremely condensed if compared to that of the Cellonsection. This interval is represented by thin-bedded, blackish lime-stone beds with shaly intercalations as at the Cellon section and isdated by the index conodont for the base of the Devonian, Icrioduswoschmidti woschmidti.

4.4. Rauchkofelbodentörl and Rauchkofel Süd sections

Only the lower beds of the Kok Formationwere examined in detailat these sections (Figs. 14 and 15). Overall, the facies and bedsuccessions rather closely resemble those of the Cellon and LowerSeewarte Base sections. Indeed, nearly every bed seen in thosesections is also present here (Figs. 15 and 16). The ferruginous

limestone bed (Bed 10 of the Cellon section; unit C of the LowerSeewarte Base section) is particularly well developed at Rauchkofel-bodentörl (Units 16–12 after Jaeger and Schönlaub, 1970) as is thesuccession of ferruginous limestones, mudstones and dark graptoliticshales, which overlie this bed (Jaeger and Schönlaub, 1970; Loydell,2003). Overall, these sections show more shale than does the CellonSection. In particular, at the Rauchkofel Süd section there is asubstantial thickness of black, very pyritic, rusty-weathering shale,

Fig. 11. Seekopf Base Section overview. The section lies along the Austrian–Italianborder at the base of Mount Seekopf (2554 m) at an altitude of approximately 2000 m.The Silurian succession (position shown by white line) overlies the Ordovician WolayerLimestone, with contact strata that overlap the latter ranging in age from Wenlock toLudlow.

Fig. 12. Lithostratigraphic column of the Seekopf Base section. Section thickness is given in meters on the left of the column; description of lithology is given on the right of thecolumn. Ord = Ordovician. Wen = Wenlock.

Fig. 13. Lithostratigraphic column of the Valentintörl section. Kockelella crassa conodontZone. Section thickness is given in meters on the left of the column; description oflithology is given on the right of the column.



overlying Ordovician pebble-bearing mudstones (periglacial (?)facies) of the Plöcken Formation and underlying the ferruginouslimestone beds of the Pterospathodus celloni conodont Superzone; thisrusty shale may correlate to the lower Telychian shales and K-bentonite at the Cellon and Oberbuchach sections. Loydell (2003)reported the occurrence of abundant graptolites, including Mono-graptus priodon, Monoclimacis woodae, Oktavites spiralis, and severalother species, indicative of a position low in the O. spiralis graptoliteZone (equivalent to the upper part of the P. celloni Superzone) 1.3 mabove the base of the Rauchkofelbodentörl section (Fig. 15, unit D).

The middle and upper Kok limestone divisions are represented byreddish, nautiloid-rich nodular wackestones at the Rauchkofelboden-törl section (Fig. 16). In this sense, they closely resemble the morecondensed versions of the Kok Formation at the Rauchkofel Boden andValentintörl sections. However, they are more complete as theycommence with earliest Wenlock limestones while this portion of thesection is highly condensed or absent at the latter localities. The basictri-partite division of the lower Kok limestones seen at the Cellonsection is apparent here (Figs. 15 and 16; shales above unit 2), withabout 0.5m of shaly strata (again poorly exposed) of mid-Wenlock age(Jaeger and Schönlaub, 1970) and correlative with beds 12B–C at theCellon section separating the lower compact cephalopod limestonefrom the upper, richer beds of later Wenlock (Homerian) age. Theupper contact is difficult to access at these localities.

The lower shalesportionof the section appears slightlyexpandedwithrespect to the Cellon section and the overall aspect of the facies, whilesimilar is slightly more distal than at that locality. Thus, these sectionsappear to forman intermediate between the Plöcken Facies and themuchthicker shalier Findenig Facies exposed at the Oberbuchach section.

4.5. Oberbuchach section (Findenig Facies)

The Findenig Facies is well displayed in a cut along a logging roadnear Oberbuchach described by Jaeger and Schönlaub (1980) as the“Oberbuchach 1 section” (Fig. 17). This section is approximately 45 mthick and overlies an as yet undescribed Upper Ordovician mudstone–limestone succession with the occurrence of the index graptoliteGlyptograptus cf. persculptus near the top (Fig. 18). The Siluriansuccession, assigned to the Nölbling Formation, consists dominantly ofdark, organic-rich and pyritic shales, but with nodular cephalopod-bearing limestones at several horizons in the Wenlock and especiallyin the Ludlow portions of the section. The succession is considerablyexpanded compared to those at the Lower Seewarte Base, Cellon or

Rauchkofelbodentörl sections (Fig. 16), particularly in the lower tomid-Wenlock portions. Conversely, based upon present biostratigra-phy, the lower Ludlow here may be considerably condensed or largelyremoved by erosion.

4.5.1. Nölbling Formation: Lower shales and ferruginous limestonesThe Silurian succession at the Oberbuchach section commences

with about 3 m of black, graptolitic shales, thin tabular black chertbands (lydites) and pyritic sandstones; these shales, at least in part,are dated as Aeronian, approximately the Coronograptus cyphusgraptolite Zone/Demirastrites triangulatus graptolite Zone (Jaeger andSchönlaub, 1980). The dark shales are sharply and perhaps uncon-formably, overlain by a 4 m thick, carbonaceous, quartz-richsandstone. This interval appears to record a regressive or lowstanddeposit; although it is not precisely dated, it is abruptly overlain bydark shales with a K-bentonite that may match with the lowest K-bentonite at the Cellon section (Histon et al., 2007). The overlyingheavily mineralized ochre-weathering ferruginous limestone (Unit 88of Jaeger and Schönlaub, 1980) is well-dated as belonging to thePterospathodus celloni conodont Superzone and appears to representthe same lower ironstone bed seen at all other sections (Walliser's bed10 at Cellon and unit C of the Seewarte section). Again, it is interpretedas a highly condensed interval recording sediment starvation duringtransgression.

The overlying 2 m shaly succession bears close similarities to thelower Pterospathodus a. amorphognathoides conodont Zone interval atthe Cellon section (Beds 10 (in part) and base bed 11 of Walliser,1964); indeed it can be correlated nearly bed for bed with that section(Fig. 19). As with that section it actually comprises two dark shalesseparated by a middle bundle of thin reddish weathering ferruginouslimestones.

4.5.2. Nölbling Formation: Lower Kok limestone-equivalentThe upper dark gray shale is abruptly overlain by a cream colored

limestone (Unit 90) that has been placed in the upper Pterospathodusa. amorphognathoides Zonal Group and the graptolite Monograptuspriodon was collected from a thin black shale interval immediatelyabove (Sampling levels 26–27, earliest Wenlock; Jaeger and Schön-laub, 1980). The overlying 4 m bundle of gray limestones shows rarenautiloids and brachiopod shell and crinoid fragments. It almostcertainly correlates with the lower limestone interval at the Cellonsection (Bed 12 of Walliser, 1964) and to the lower crinoidalgrainstones (Unit G) at the Lower Seewarte Base section (Figs. 16and 19). This facies clearly reflects a shallower environment than dothe underlying shales and was probably deposited during initialtransgression following a lowstand; this earliestWenlock event is verywidely recognizable globally (Johnson et al., 1998; Johnson, 2006).This thick limestone is abruptly overlain by black, sooty shale(sampling level 27 of Jaeger and Schönlaub, 1980) yielding graptolitesof the early Wenlock Monograptus riccartonensis Zone; the abruptcontact probably represents a maximum flooding surface or max-imum starvation surface.

4.5.3. Nölbling Formation: Lower Kok shale-equivalentAs noted, the lower Wenlock (Sheinwoodian) portion of this

section is greatly expanded compared to the Cellon avalanche gullysuccession. The Monograptus riccartonensis graptolite Zone (approxi-mately equivalent to the Kockelella ranuliformis–lower Ozarkodinasagitta rhenana conodont Zones) is represented by ∼3 m of dark,graptolitic shale and thin silty limestone (Sampling level 27, unit 91,levels 27–28, unit 92 of Jaeger and Schönlaub, 1980) that recordsa strong deepening in the early-mid Sheinwoodian; this intervalis represented by less than 0.5 m of dark shale and limestone (Beds12B–C of Walliser, 1964) at the Cellon section. Few fossils are presentother than graptolites, but the latter place these shales firmly withinthe lower–middleWenlock. Documentation of amajor positive isotope

Fig. 14. Rauchkofel süd Section overview. The section lies to the southeast of MountRauchkofel (2436 m), is not easily accessed and to date has been poorly studied. TheOrdovican succession belongs to the Plöcken Formation, seen to the left of the whiteline, overlain by shale dominated strata of the lower Kok Formation.





excursion (Ireviken Event) in the Oberbuchach succession (Wenzel,1997) also corroborates this age assignment. There are two minorcycles within this shale interval; each begins with very black, rusty“alum” shales and passes upward into dark gray laminated limestonesand minor cherts. Graptolites of the Monograptus antennularisgraptolite Zone occur within this interval between beds 91 and 92.

4.5.4. Nölbling Formation: Middle Kok limestone/shale-equivalentA bundle of limestones with interbedded shales occurs at the top of

this interval (Unit 92); this interval is thought to represent approxi-mately the level of the upper Ozarkodina sagitta rhenana to lowerKockelella walliseri conodont Zones on the basis of carbon isotopestratigraphy (Wenzel, 1997). The latter limestone interval, absent atthe Cellon section, represents a shallowing episode.

A second major interval of rusty dark shale and lydites (below unit93) overlying the lower Kockelella walliseri conodont Zone limestonebundle at Oberbuchach has yielded graptolites of the Cyrtograptusrigidus Zone in sampling levels 28–30 of Jaeger and Schönlaub (1980).This would equate to the upper K. walliseri conodont Zone andapparently is also absent at the Cellon section.

4.5.5. Nölbling Formation: Middle Kok limestone – equivalentThe upper Wenlock (Homerian: units 94–96, sampling level 31 of

Jaeger and Schönlaub, 1980) comprises two unequal nodular lime-stones separated by black, alum shales. The lower is thicker (Units 94and 95, ∼2.5 m) and consists of massive nodular, dark brownish graylimestone with moderately abundant nautiloids and crinoid ossicles.Black shale intercalations within the lower massive limestone haveyielded graptolites of the Gothograptus nassa Zone (Level 31). Thisinterval also displays a positive carbon isotopic excursion and mayrepresent the Mulde excursion recognized in Gotland and elsewhere(Calner et al., 2006).

The upper limestone (Unit 96, ∼50 cm thick) is mainly blacklaminated carbonate, but has a distinct crinoidal grainstone near itstop. Minor dark phosphatic material occurs at the sharp contact of thisgrainstone with the overlying black shale–lydite succession.

4.5.6. Nölbling Formation: Upper shaleThe Homerian limestones are overlain by about 9 m of dark gray

shale and lydite, which is poorly dated and controversial in age. Asingle sample (Level 32 of Jaeger and Schönlaub, 1980) has yieldedMonograptus dubius and Monograptus vulgaris indicating that thisshale may be of latest Wenlock age and probably corresponds to theprominent black shale within the Kok limestones (Bed 15B ofWalliser,1964) at the Cellon section. However, a shale sample less than 50 cmhigher reportedly yielded M. dubius and Monograptus bohemicus(Sampling level 33 of Jaeger and Schönlaub, 1980), suggestingassignment to the Saetograptus leintwardensis and Neocucculograptuskozlowskii graptolite Zone. If this is correct it would suggest that themain mass of the upper (Ludlow age) Kok limestone division (Beds16to 20 of Walliser, 1964) present at the Cellon section is reduced to justa few centimeters of dark, cherty laminated limestone at theOberbuchach section. Moreover, it would seem to imply that theundifferentiated upper 5 to 6 m of shale and laminated limestone inthis interval is equivalent to the Cardiola Formation at the Cellonsection and elsewhere. This interval is poorly exposed and difficult toaccess at the Oberbuchach section. Exposed beds look nearly identicalto the lower 3 m of the interval that is placed in the upper Wenlock.The upper beds show none of the features of the Cardiola Formation,distinctive in all other outcrops. No evidence of a major unconformitywas observed with careful excavation of the 0.5 meter section be-

tween samples 32 and 33 (at 40 m in the measured section of Jaegerand Schönlaub, 1980). The section appears conformable and assign-ment of the upper shales to the Ludlow is based upon a singlegraptolite sample. We suspect that the entire shale interval between40 and 46 m in the Oberbuchach section is of latest Wenlock to earlyLudlow (Eltonian) age and represents the Wenlock–Ludlow boundary(Eltonian) transgression. At present this situation remains unresolved.

4.5.7. Alticola Limestone – equivalentThe upper 8 m of section exposed at the Oberbuchach section

consists of light pinkish gray, medium bedded to massive cephalopodlimestone (Fig. 18). This interval has not been biostratigraphicallydated but has been considered to be the lateral equivalent of theAlticola Limestone. Unfortunately, the Silurian section is coveredabove this end of the outcrop so further test of this hypothesis is notpossible at this time. Upper Přídolí and basal Lochkovian beds areexposed on an upper large roadcut (Oberbuchach II section of Jaegerand Schönlaub, 1980). However, this exposure may belong to adifferent thrust sheet. The black shales and thin laminated calcisiltitesnear this boundary resemble the interval at the Cellon section andelsewhere.

5. Regional paleogeography and environmental gradients

The most proximal facies in the Silurian are represented by thegrainstone-rich carbonates exposed in the Kellerwande Nappe at theLower Seewarte Base section. This is a section of moderate thickness(some 40 m, although the top part is covered by debris), highlydominated by limestones with reduction of shales by depositionalpinching and/or erosive cut-out. Slightly more distal facies arerepresented in the Cellon section, the stratotype for the Silurian inthe Southern Alps. At the Cellon avalanche gully, a succession ofnodular, cephalopod-rich limestones and minor shales is present inthe Wenlock to lower Ludlow portion, whereas the upper Ludlow isrecorded in massive carbonate wackestone to grainstone facies withdark gray to black shales. Slightly more distal facies are recorded in theRauchkofelbodentörl and Rauchkofel Süd sections of the LakeWolayerregion, wherein the Lower Silurian portion of the section showssubstantial expansion in a dark gray to black shale succession. Deepershelf to basinal (Findenig) facies are represented by the Oberbuchachroadcut section. Here, the succession is dominated by dark gray toblack graptolitic shales. However, shallowing intervals within thesuccession (lowstand to early transgressive facies) are recorded inmassive to nodular, dark gray to somewhat pinkish limestones. Thesecarbonate beds make up less than 25% of the succession at theOberbuchach section in contrast to more proximal successions at theCellon or Rauchkofelbodentörl sections, in which carbonates dom-inate. Finally, the most distal basinal facies are represented in nearlypure greenish gray to black shale and bedded chert (lydite) of theBischofalm nappes exposed between the lower Bischofalm and LakeZollner, which were not examined in detail in the present study.

Somewhat uncertain in placement are the extremely thin,condensed sections seen in the Rauchkofel Boden, Valentintörl andSeekopf Base sections of the Lake Wolayer district. Although thesevery thin successions supposedly occur in the same structuralcomplex (Rauchkofel nappe complex) as do the Rauchokofelbodentörland Rauchkofel Süd sections, discussed above, they differ considerablyfrom the latter. As noted, these are highly condensed, with sporadiclate Llandovery occurrences and more frequent late Wenlock to earlyLudlow sediments at the base and thin cephalopod-rich limestonesrecording the Ludlow to Přídolí succession. Onlap of a strongly

Fig.15. Tentative correlation of the lower Kok Formation between the Lower Seewarte Base, Rauchkofelbodentörl and Rauchkofel Süd sections. Section thickness is given inmeters onthe left of the column for the Lower Seewarte Base section. Individual bed thickness is given on the left of the column in cm for some beds for Rauchkofel Süd andRauchkofelbodentörl sections. Lettered units A–E refer to marker beds that appear to be correlative with those at the Seewarte section. Bed numbers Rauchkofelbodentörl sectionfrom Jaeger and Schönlaub (1970). SB = Sequence boundary, MFS = Maximum flooding surface, Ordov. = Ordovician.





corroded surface is evident, especially in the Seekopf Base sectionwhere beds of varying Silurian or even Devonian age may restunconformably on the corroded surface of the Ordovician WolayerLimestone. As noted, the sections of Valentintörl and RauchkofelBoden are somewhat more complete with representation of upperWenlock to lower Ludlow strata at the bases. This suggests anonlapping relationship from Rauchkofel Boden to the Seekopf Basesection. But many questions remain. Does the disconformity representsubaerial exposure or submarine dissolution? We favor the latterinterpretation, as where we do see sediment fillings in pits or in theonlapping formations, they do not appear to represent shallow waterfacies, but are essentially similar in biofacies to the equivalent strataon other slices, such as at the Cellon section, and suggest that theserepresent slices through parts of a submarine high. It is unclearwhether these sections originally fit between the more proximalfacies, such as those represented at the Lower Seewarte Base sectionand the distal shaly facies, such as those seen in the Oberbuchachsection, or, whether they instead represent an outboard set of faciesthat originally lay beyond the shale-rich basinal successions ofOberbuchach. If the latter is the case, then these may represent atype of condensed submarine swell or seamount facies. However,their position in thrusts between the evidently shallow water LowerSeewarte Base section and the Rauchkofelbodentörl and Cellonsections may indicate that they are transitional between the WolayerFacies and deeper Cellon section (Plöcken Facies). Also, the faunas ofthese sections suggest that they represent facies shallower than thoseat the Cellon section. If so, their thinness and condensationmay reflectdevelopment of a bypass slope, which was initially steepenedpreventing sediment accumulation, though no evidence of slumpinghas been observed. Resolution of this issue may hinge not only onfurther mapping but detailed examination of the solution pits andtheir thin fillings (Ferretti, 2005; Ferretti and Histon, in press).

In any case, it is very important to note that despite onlappingrelationships and condensation the remaining strata in these thinsuccessions still show major and even minor marker intervals. Forexample, the Cardiola Formation is still present as a dark shalysuccession with thinly developed carbonate lenses. This evidencestrongly suggests a eustatic control on the basic cycles with a tectonicoverprint controlling the thickness of sections.

6. Comparison of sequence stratigraphy of the Carnic Alps, EasternLaurentia, Avalonia and Baltica

A brief comparison of the Carnic Alps sections with coeval Siluriansuccessions in the Appalachian basin of eastern Laurentia, Avalonia(Welsh Basin) and Baltica (Oslo region, Norway and Gotland)highlights both important similarities and some differences (seealso Brett et al., 2007). In general the relative sea-level patterns aresimilar, in some cases strikingly so, at a fine scale (Figs. 19 and 20).

The early Llandovery is very poorly recorded and highly condensedin proximal Carnic Alps sections. However, the later Llandovery toearly Ludlow highstand dark, ferruginousmudrocks noted in thewell-dated Carnic Alps sections (Cellon and Oberbuchach) have closelyanalogous counterparts in the central Appalachian basin and else-where (Fig. 19). This is also true of several of the condensed crinoidalto cephalopod-rich limestone beds that appear to record shallow,lowstand to transgressive facies. Of particular interest is the compar-ability of the middle Telychian to Wenlock (Pterospathodus celloni–Ozarkodina sagitta sagitta conodont Zones) succession in the CarnicAlps and those of the Appalachian Basin of Laurentia, the WelshBorderlands (UK) of Avalonia, and the Oslo graben region and Gotlandin Baltica.

6.1. Kok Formation–Nölbling Formation: Lower shales and ferruginoussequence

Sequence 1: At Oberbuchach the lowest strata immediately abovethe Ordovician/Silurian unconformity are dark shales and pyriticsandstones that yield graptolites of the Llandovery: upper Rhuddanianto lower Aeronian, approximately the Coronograptus cyphus–Demir-astrites triangulatus graptolite Zones. Deeper facies, represented byblack shales and thin-bedded cherts, overlie this basal sandy zone at aflooding surface. This deepening may correspond approximately toJohnson's (2006) highstand 1, represented by the Reynales Limestoneand Bear Creek Shale in the Appalachian Basin. However, at presentthis sequence is poorly characterized in the Carnic Alps. It is overlainwith substantial sequence bounding unconformity by sandy shales ofthe next sequence; a considerable interval, representing severalgraptolite zones may be missing at this contact.

Fig. 17. Oberbuchach Section overview. The section is exposed along a logging road at an altitude of approximately 1150 m and has a north facing aspect. The Ordovician succession(undescribed) continues along the track on the right for about 50 m. The divisions of the basal Llandovery sandstone/shale succession may be easily distinguished. Ord.–Ordovician,Lland.–Llandovery.

Fig. 16. Correlation of the lower Kok Formation and Cardiola Formation between the Cellon, Rauchkofelbodentörl and Lower Seewarte Base sections. Section thickness is given inmeters on the left of the column. Lettered units A–E refer to marker beds that appear to be correlative with those at the Seewarte section. Bed numbers in the Rauchkofelbodentörlsection from Jaeger and Schönlaub (1970). SB = Sequence boundary, MFS = Maximum flooding surface, Ord. = Ordovician, Tely. = Telychian, Dev. = Devonian.



At Oberbuchach a sandstone package appears to record a fallingstage or lowstand interval. Schönlaub (1997; his Fig. 5) shows thispackage as equivalent to the Lituigraptus convolutus to Monograptuscrispus zones but there seems to be little fossil evidence for this andthis interval would then encompass the time equivalents of twohighstands, 2 and 3 of Johnson (2006). Based upon Pterospathoduscelloni Superzone conodonts in the overlying ferruginous beds wesuggest that instead this shallowing upward succession may recordthe strong mid Telychian (Pterospathodus eopennatus to Pterospatho-dus angulatus conodont Zones; Männik, 2007) regression recognizedby Johnson (2006) and represented in the Appalachian basin by anunconformity overlain by reworked quartz conglomerate (OneidaFormation in New York State and probably by the Centre member ofthe Rose Hill Formation in Pennsylvania (Brett and Goodman,1996). Adistinct shallowing is also recorded in Baltica during theMonoclimaciscrispus–Monoclimacis greistoniensis graptolite Zones in the VikFormation by a strong shift in biofacies in sections at Ringerike andOslo areas of Norway (Baarli, 1990a,b). This interval may berepresented in the subsurface of Gotland by a reddish shale interval(Jeppsson et al., 2005). We further suggest that this strong regressionmay have removed any preexisting Silurian strata at more proximalCarnic Alps sections such as Cellon, resulting in a composite uncon-formity on Ordovician rocks.

Sequence 2A: A widespread condensed interval in the Pteros-pathodus celloni conodont Superzone is found throughout all theCarnic Alps sections. Thin, ferruginous limestones and dark graygraptolite-bearing shale with a thin K-bentonite occur at the base ofthe Kok Formation at Lower Seewarte Base and Cellon sections, andabove the previously mentioned sandstone bundle at the Oberbu-chach section (Histon et al., 2007). At Rauchkofelbodentörl Loydell(2003) recognized graptolites of the late Telychian Oktavites spiralisZone from probably correlative dark shale above a thin ironstone∼1.3 m above the base of the Kok Formation. This successioncorresponds to the lower part of highstand 4 of Johnson (2006),Loydell (1998), likewise argues for a strong sea-level highstand atabout the Oktavites spiralis graptolite Zone. The highstand wouldrepresent the Wolcott Furnace–Sauquoit Shale of central New York(Sequence S-III of Brett et al., 1990, 1998).

Dark shales of Oktavites spiralis age, are sharply overlain by awidespread manganiferous iron-rich limestone or mudstone, yieldingPterospathodus celloni Superzone conodonts.

Sequence 2B: The dark gray siliciclastics are sharply overlain bystrongly mineralized strata, which have yielded conodonts of thePterospathodus celloni Superzone (Walliser's upper bed 10–11 atCellon; units C on Figs. 15, 16). The basal contact of this bed records awidespread late Telychian lowstand. This interval, enriched insyngenetic iron and manganese minerals, represents a condensedinterval associated with sediment starvation and authigenic miner-alization during initial transgression. A comparable condensedferruginous interval the classic “Clinton” iron ore” (such as theWestmoreland oolitic ironstone of central New York), has beencorrelated throughout the Appalachian basin region fromNew York toAlabama (Brett et al., 1998). The prominent sequence boundingerosion surface at the base of this condensed bed was used todistinguish sequences S-III and S-IV throughout eastern NorthAmerica (Brett et al., 1990, 1998; McLaughlin et al., 2008).

The manganiferous condensed bed in the Carnic Alps is sharplyoverlain by dark gray shales and ferruginous carbonates, bearinggraptolites and conodonts diagnostic of the Pterospathodus a.amorphognathoides Zonal Group. At all localities examined, this Pter-ospathodus amorphognathoides interval shows a distinctive tri-partite

Fig. 18. Lithostratigraphic column of the Oberbuchach Section. Section thickness isgiven in meters on the left of the column; description of lithology is given on the right ofthe column.



division, with lower dark shales, middle nodular hematitic limestonesand upper dark shales that pass upward into shaly wackestones.Likewise, the coeval sequence S-IV interval in the Appalachian Basin

shows a comparable tri-partite aspect with lower black and olive togreen shales of the Williamson Formation, separated from upper grayshales and nodular carbonates or siltstones of the Rockway Formation

Fig. 19. Correlation and sequence interpretation of Llandovery–Lower Ludlow succession, Carnic Alps showing probable correlative intervals in Laurentia (New York), Avalonia(Welsh Borderland, UK), and Baltica (Gotland, Sweden) on right columns; in gotland column Halla-Kl. = Halla–Klinteburg formations. Bold dashed tie lines indicate approximatepositions of theWenlock and Ludlow Series boundaries. Abbreviations: Ord. = Ordovician, Tely. = Telychian, Wenl. =Wenlock, SB = Sequence boundary, PS = Parasequence, SS =Subsequence, FS= Flooding surface; SMS: surface ormaximum starvation; MFS=Maximum flooding surface, HST=highstand systems tract, RST=Regressive systems tract, TST=transgressive systems tract, EHST= early highstand systems tract, LHST= late highstand systems tract, CI = Condensed Interval, LST= lowstand systems tract, SSB = subsequenceboundary, M.Wenlock = Much Wenlock.





by a ferruginous/phosphatic condensed bed. In Gotland, this pattern isalso manifest in the lower and upper Visby succession withintervening Phaulactis condensed bed (Jeppsson, 1997; Calner,2008). This is the later part of Johnson's (2006) late Telychianhighstand, 4b herein; a second peak of sea-level highstand during themid-late Telychian was also identified by Loydell (1998). A compar-able strong deepening is recognized elsewhere in the uppermostLlandovery to early Wenlock: the Purple Shales of the WelshBorderland (Loydell, 2008), the dark uppermost Vik and Skinner-buchta Formations in the Oslo, Norway area (Baarli, 1990a,b; Baarliet al., 2003) and in the lower Visby Shale in Gotland (Jeppsson et al.,2006).

6.2. Lower Kok limestones – shale (lower Wenlock) sequence

Sequence 3A: Return to nodular to compact reddish cephalopod-rich carbonates (for instance upper bed 11–12A of the Cellon section)within the uppermost portion of the Pterospathodus a. amorphog-nathoides Zonal Group, and probably into the Pterospathodus p.procerus to lower Kockelella ranuliformis conodont Zones (lowerSheinwoodian), also is a local manifestation of an apparently wide-spread (global) shallowing and initial transgressive event. The sharpbase of bed 11C (Cellon section) of the lower Kok limestones divisionrepresents a sequence boundary and bed 11C through12A constitutesa transgressive systems tract. The upper contact is a sharplydemarcated surface of maximum starvation; it is overlain by verydark gray shales; the influx of these siliciclastics is thought to havebeen associated with an early Wenlock (mid-Sheinwoodian) high-stand. This interval is expanded in the Oberbuchach section, wherethe shale is ∼3 m thick and is overlain by an interval of tabular tonodular carbonates.

This interval is closely paralleled in the upper Clinton Group strata(sequence S-V) in the Appalachian Basin (Brett et al., 1990).Trangressive crinoidal grainstones and calcareous sandstones (Iron-dequoit-Keefer) of earliest Wenlock (early Sheinwoodian) age are theanalog of beds 11C–12A (Cellon section); a sharp flooding surface atthe top of this interval signals the change into deeper water mudrocksof the Rochester Shale (Cramer et al., 2006a,b), which also shows twodivisions separated by a middle limestone bundle, as does the Mo-nograptus riccartonensis graptolite Zone shale at Oberbuchach.

A similar pattern of transgressive crinoidal grainstones sharplyoverlain by dark shales has been also observed in the Buildwas–Coalbrookdale succession of Great Britain (Ray and Thomas, 2007)and in the upper Visby–lower Korpklint Member crinoid-richcarbonates, and overlying reefs and inter-reef shales (IrevikenMember) of the Hogklint Formation in Gotland (Riding and Watts,1991). This early Sheinwoodian transgression is clearly shown belowhighstand 5 on Johnson's (2006) sea-level curve hence, a similardetailed pattern occurs on four paleocontinents through the latestTelychian to early Sheinwoodian.

Sequence 3B: The bundle of limestones at about 18–20 m in theOberbuchach section (Fig. 18, unit 92), is thought to correspond to thelowstand/initial transgression in the mid-Sheinwoodian. The sharpchange from underlying Monograptus riccartonensis–Monograptusantennularis graptolite Zone shales may record a major sequenceboundary recognized in eastern North America between the Clintonand Lockport Groups (sequence S-V/VI boundary of Brett et al., 1990,1998), and it suggests a eustatic lowstand approximately within theupper Ozarkodina sagitta rhenana to lower Kockelella wallisericonodont zones. This strong shallowing, however, was only shown

as a minor deflection in the middle of highstand 5 on the curve ofJohnson (2006).

The lower Lockport Group, the Gasport and Goat Island Formations,in New York and Ontario is subdivided into two fourth order sequences,with a shaly biothermal Pekin Member of the Gasport representing thefourth order highstand and lower Goat Island dolostone the overlyinglowstand to transgressive systems tract. This two-fold subdivision mayalso be recorded at the Oberbuchach sectionwhere the mid-Sheinwoo-dian age limestone, bed 92, is separated by a thin shale interval from anunnumbered upper limestone. Termination of the Ireviken isotopicexcursion just above this latter level at Oberbuchach further corrobo-rates this correlation (Wenzel, 1997; Cramer et al., 2006b).The Irevikenexcursion is known to extend into the Gasport and lower Goat Islandformations in New York (Cramer et al., 2006b).

At present, the position of this sequence in the classic Welshborderlands section is uncertain. In Gotland, however, a very similarsuccession is present in the Tofta Formation (=HallshukMember andKoparsvik Formation of Riding andWatts, 1991) succession of reefy toperitidal carbonates that sharply overlie shaly or reefal upper HögklintFormation. Although these beds are correlative with the lowerLockport Group (Gasport-lower Goat Island formations) in theAppalachian Basin (sequence S-VI) on the basis of sequencestratigraphy and carbon isotope stratigraphy (B. Cramer personalcommunication) they are presently assigned to the Ozarkodina sagittarhenana conodont Zone, rather than to the lower Kockelella wallisericonodont Zone.

Dark, graptolitic shales between 20 and 30 m, yielding graptolitesof the Crytograptus rigidus Zone at Oberbuchach, seems to reflect amid to late Sheinwoodian highstand that is as yet not welldocumented elsewhere. This presumably represents the minor,unnamed deepening associated with the Hellvi Secundo episode inthe upper part of highstand 5 by Johnson (2006). In North America arelatively strong post-Ireviken excursion deepening interval isrecorded in argillaceous, cherty dolostones and shales of the upperGoat Island Formation of New York and the Lilly Shales of Ohio (Brettand Ray, 2006). The approximately coeval Vinemount Member andEramosa Formation of Ontario (Brett et al., 1995) comprises dark,bituminous dolostones and dark gray shales. These beds have yieldedfossil lagerstätten (Von Bitter et al., 2007); the extraordinarypreservation of biotas may record the incursion of dysoxic waterinto shelf environments. The shaly Vinemount Member and overlyingEramosa dolostones are interpreted as the highstand to falling stagesystems tracts of Sequence VIB in the Appalachian Basin (Brett et al.,1990, 1998). In Gotland, this highstand may be recorded in the thickshaly middle portion of the Slite Group, recognized by Jeppsson et al.(2005) as a highstand, but at present the details of this large coveredinterval are too poorly known to afford detailed comparisons.

6.3. Middle Kok Sequence

Sequence 4A: A major sequence boundary in the Carnic Alps isrepresented in the sharp base of the middle Kok limestone (bed 13 ofthe Cellon section) and at the time of the Ozarkodina sagitta sagittaconodont Zone (early Homerian). A widespread shallowing isrecognized at this time and erosion appears to have removed muchof the Sheinwoodian strata at this unconformity in all proximalsections of the Carnic Alps including the Lower Seewarte Base andCellon sections. An entire sequence, including substantial dark shale,represented at the Oberbuchach section has apparently been removedby this erosion surface in upramp sections. This is indicated not only

Fig. 20. Time-scale and graptolite/conodont biostratigraphy for the Early Silurian–earliest Devonian (Aeronian to Lochkovian) showing inferred relative sea-level curves. Time scaleadapted from Melchin et al. (2004); Sheinwoodian–Homerian boundary is placed at top of the error bar on date given by Melchin et al. (2004) because the large number ofpronounced cycles in Sheinwoodian suggests that the longer duration is warranted. North American curve based on data of Johnson (2006) adapted to time scale proportions ofMelchin et al. and from data of Brett et al. (1990, 1998) and McLaughlin et al. (2008). Numbers to left of curve indicate approximate positions of highstands identified by Johnson(2006). Carnic Alps curve based on studies of Histon and Schönlaub (1999), Kříž et al. (2003), Ferretti and Histon (in press) and new data, herein. Numbers on this curve indicate thehighstands of depositional sequences identified herein. Gotland curve based on sequence stratigraphy of Jeppsson et al. (2005) and unpublished data of P. McLaughlin and C. Brett.



by missing conodont/graptolite zones but also by truncation of theIreviken isotope excursion at the Cellon section (Wenzel, 1997). Theoverlying middle Kok limestone beds, condensed nodular, reddish,cephalopod limestone facies, represent lowstand to transgressivecarbonate development during the early Homerian.

This sequence also has its counterpart in equivalent age strata ofeastern Laurentia and Avalonia. The abrupt lower contact of the upperLockport Group (sequence S-VII) represents the same sequenceboundary and massive fossiliferous carbonates of the basal GuelphFormation are thought to be equivalent to the middle Kok limestones.Locally, in Ohio the erosion surface at the base of equivalent PeeblesDolostone has removed part or all of sequence S-VI (McLaughlin et al.,2008).

The strongly developed double carbonate package at the Oberbu-chach section (approximately equivalent to beds 14 and 15 at theCellon section) may be equivalent to the Homerian Much WenlockLimestone in the type Wenlock Edge area of the Welsh borderlandsand possibly to the lower Guelph Formation in eastern North America(Brett and Ray, 2001; Ray et al., in press). The intervening argillaceousinterval at the Oberbuchach section yielded graptolites of the Gotho-graptus nassa graptolite Zone (upper Wenlock; Homerian). This shalemay represent the short-lived deepening (Highstand 5A of Johnson,2006) associated with theMulde Event in Gotland and recorded in theshaly Halla Formation (Calner et al., 2006) as well as the middle shalyzone of the Much Wenlock Formation. Wenzel (1997) documentedrelatively high values of ∂13C for this interval at the Oberbuchachsection that may reflect the Mulde excursion. In the North Americanmid-continent area this highstand may be represented by thewidespread Waldron Shale (Cramer et al., 2006a,b).

Sequence 4B: Upper Homerian cephalopod limestones overlyingthe Gothograptus nassa graptolite Zone age shale may reflect thelowstand-early transgressive systems track represented by theLouisville carbonates in central North America (Cramer et al.,2006b; McLaughlin et al., 2008) and presumably coeval KlintbergFormation in Gotland (Calner and Jeppsson, 2003; Calner et al.,2004). In all areas this limestone shows a sharp contact withunderlying argillaceous facies and abrupt transition into overlyingshale. A sharp shift into dark, organic-rich shales in the latestKockelella crassa conodont Zone and coeval earliest Neodiversograp-tus nilssoni graptolite Zone represents a major deepening anddeposition of mostly euxinic sulphidic calcareous graptolitic blackshales (Pasava and Schönlaub, 1999) at or near the Wenlock–Ludlowboundary. In the Cellon section area the highstand appears to spanthis series boundary. This interval, Johnson's highstand 6, is wellrepresented in Avalonia by the abrupt deepening into the Elton bedsof the basal Ludlow in the type area and by the Hemse Marl inGotland (Jeppsson et al., 2005). Its position is not presently estab-lished in the Appalachian Basin.

6.4. Upper Kok–Cardiola shale sequence

Sequence 5: The sharp erosional base of the upper Kok limestones(beds 15–16 of the Cellon Section) represents another sequenceboundary. The nodular carbonates of the upper division of the KokFormation are again developed in the condensed cephalopod lime-stone facies associated with the lowstand to transgressive systemstract following one of the major shallowing intervals of the late ormedial Silurian, occurring during the early Ludlow. Massive carbo-nates in the Ancoradella ploekensis to lower Polygnathoides siluricusconodont Zones may record a shallowing/initial transgressionassociated with the upper Hemse Group in Gotland (Calner andJeppsson, 2003; Calner et al., 2004; Jeppsson et al., 2005).

A spectacular change is recorded in the Cardiola Formation of Po-lygnathoides siluricus conodont Zone age. The preservation ofhummocky cross-laminae and other primary sedimentary structuresin this facies contrasts with the heavily bioturbated facies of the

underlying Kok Formation. These dramatic changes in fabric of theCardiola Formation may be a function of suppression of bioturbationdue to widespread anoxic or dysoxic conditions. The CardiolaFormation represents an interval of relative eustatic highstand andan associated rise of pycnocline and incursion of low oxygen and/ornutrient-rich waters onto the moderate depth (above storm wave-base) shelf. This hypoxic interval within the upper part of the Polyg-nathoides siluricus conodont Zone extending into the overlying basalOzarkodina snajdri Interval Zone, is associated with the global LauEvent, an episode of abrupt extinction of graptolites, conodonts,pentamerid brachiopods, and other organisms (Calner, 2008).Schönlaub (1986) named a “Cardiola event” in the Carnic Alps,associated with changes in bivalves and faunal reorganization, andsuggested its equivalency to the Lau Event. In Gotland the Lau Event isrecognized within dark shales in the Botvide Member of the NärFormation and overlying oncolitic limestones of the Eke Formation(Jeppsson et al., 2005; Calner, 2008).

It should be noted that the Cardiola Formation highstand does notappear to coincide with the reported global highstand 7 of Johnson(2006), which is shown somewhat higher, in the Neocucculograptuskozlowskii graptolite Zone/Ozarkodina snajdri conodont Interval Zone,rather than in the Polygnathoides siluricus conodont Zone. It is possiblethat this strong transgression was diachronous (as suggested by Kříž,1999) or related to local subsidence. However, the occurrence ofrather similar dysoxic Cardiola facies, not only in the Carnic Alps, butalso in Bohemia and SW Sardinia, at approximately the same time(Polygnathoides siluricus conodont Zone), suggests that the effect waswidespread, interbasinal, and probably of eustatic origin.

Unfortunately, tectonic overprinting associated with the Caledo-nian and Salinic orogenies prevent comparison of successions inAvalonia and Laurentia. Red non-marine molasse sediments (earlyphase of “Old Red” facies) occupy the equivalent position in theWelshBasin. In the Appalachian foreland of North America dark shalycarbonate facies of the upper Wenlock to lower Ludlow McKenzieMember pass upward through transitional greenish shales into aredbed succession up to 300 m thick (Bloomsburg–Vernon clasticwedge). The latter are succeeded by the Salina Group, a succession ofshales, dolostones and evaporites that record the development ofrestricted hypersaline basins. Although the specific interval of theLudlow represented by these unusual black shale-prone facies ispoorly constrained there is at least circumstantial evidence of a majorclimatic/water mass shift during the Ludlow in both Baltica and theCarnic Alps area of the Apulia Terrane. Perhaps an interval of warmingfavored sluggish circulation and/or increased productivity and causedthe pycnocline to rise into shallow water environments in disparateareas.

6.5. Alticola Limestone–Megaerella Limestone

Sequence 6: A relatively strong shallowing is suggested by thesharp basal contact, a probable sequence boundary, of the AlticolaLimestone on the black shale of the Cardiola Formation. The presenceof oncolites or coated grains in the pink wackestone unit somewhatabove the base of the Alticola Formation may record maximumshallowing. A general upward deepening trend is recorded culminat-ing in fine-grained limestone beds presumably belonging to the lowerOzarkodina snajdri Interval Zone in the middle Alticola Limestone(Schönlaub, 1997; Histon et al., 1999).

An overlying bioclastic interval with coated grains, abundantnautiloids and small corals records a brief shallowing in the lateLudlow (upper Ozarkodina snajdri to lower Ozarkodina crispa zones).Johnson (2006) shows a comparable short-lived shallowing on theglobal curve. This shallowing may correspond to the regressiveBurgsvik Sandstone and immediately overlying shallow, reefalHamra Formation (also upper O. snajdri to lower O. crispa conodont



Zones), some of the highest units exposed in Gotland, although thesemay be slightly older (Jeppsson et al., 2005).

Sequence 7: Overlying interbedded platy limestones and dark grayshales with graptolites of the Monograptus parultimus graptolite Zonenear the top of the Alticola Limestone record a highstand interval inthe earliest Přídoli, associated again with dark, laminated facies(Histon et al., 1999; Brett et al., 2007; Ferretti and Histon, in press).This probably represents Johnson's (2006) highstand 8 in part,although Johnson shows this as a broad interval commencing in theM. parultimus graptolite Zone but peaking in the higher Monograptustransgrediens graptolite Zone. The overlying Megaerella Limestonerecords anoxic Přídolian shallowing in the final regression of theSilurian. Johnson (2006) shows continuous shallowing in the latestpart of the Silurian.

Sequence 8: Pack- and grainstone beds at the top of the MegaerellaLimestone, with brachiopod and bryozoan faunas record lowstand toinitial transgression. These shallow, neritic facies are followed by astrong pulse of deepening and of black shales and calcisiltites in thebasal Devonian (Lochkovian: Icriodus woschmidti woschmidti con-odont Zone/Monograptus uniformis graptolite Zone) RauchkofelFormation. The calcisiltites are considered to be largely allodapiccarbonates that interfingered with basinal dysoxic to anoxic blackmuds (For more details of the latter see Suttner, 2007). Comparablefacies successions, with black shales and calciturbidites, containingnear their top the distinctive crinoid Scyphocrinites, occur within theupper Ludlow to Přídolí in Morocco, the Prague Basin, and Sardinia;i.e., in north Gondwana and peri-Gondwana terranes.

A terminal Silurian to earliest Devonian transgression, probablyassociated with a latest Silurian–earliest Devonian eustatic transgres-sion, produced a return to normal salinity in the Appalachian Basinand deposition of the Cobleskill-Akron, Rondout and Keyser Forma-tions with diverse open marine faunas. The crinoid Scyphocrinites isabundant within the Keyser and coeval Manlius limestones in theAppalachian Basin, providing a tie to the epibole of this form seen inthe peri-Gondwana region. However, the rest of the fauna has little incommon between the Appalachian Basin and the Carnic Alps part ofthe Apulia Terrane.

7. Conclusions

A series of some 11 major depositional sequences can be identifiedin the Silurian strata in disparate facies exposed on several thrustsheets of the Carnic Alps: Llandovery (3), Wenlock (3), Ludlow (3)and Přídolí-Lochkovian (2). Detailed correlations of sequence bound-aries, flooding surfaces, and the delimited systems tracts indicate astrong allocyclic influence on development of these cycles.

In general, a proximal to distal shelf facies cross section isidentified in the Kellerwand Nappe (Lower Seewarte Base section),in the Rauchkofel Complex (Rauchkofel Boden, Valentintörl, SeekopfBase, Rauchkofelbodentörl, Rauchkofel Süd sections), Cellon Nappe(Cellon section), and Oberbuchach (Oberbuchach section) thrustsheets. These sheets were stacked in approximate proximal to distalorder from south to north. However, sequence correlations also showdistinct differences in subsidence along the shelf to basin gradient. Inparticular, the Rauchkofel Complex of thrust slices (Seekopf Base,Valentintörl, and Rauchkofel Boden) shows a series of thin successionswith variable, but generally poor representation of lower Siluriansediments. The presence of infills of late Telychian phosphaticsediments into an irregular corrosion surface, suggests long-termsediment bypass and/or starvation of this segment of the seafloor,whichmay thus be interpreted as parts of a bypassed slope or uplifted,isolated seamounts, as suggested previously.

The relative sea-level curve for the Llandovery–early Ludlow forthe Carnic Alps sections (Figs. 19 and 20) and the magnitude ofvariations in sea-level compare quite favorably with those inferred byJohnson (1996, 2006) for global sea-level changes during the Silurian.

Recent studies by Schönlaub and Sheehan (2003) and Berry (2003) onthe Late Ordovician glacio-eustatic interval have also shown that theCarnic Alps successions may be correlated with those of theOrdovician/Silurian boundary interval of Nevada.

Detailed comparison of the sequence boundaries and relative sea-level changes determined for the Carnic Alps, with those of NorthAmerica, Baltica (Norway, Gotland) and Britain shows strong simila-rities of pattern in the late Llandovery to early Ludlow (Fig. 19).Organic-rich, laminated intervals suggest continuous changes fromnormal marine conditions with aerobic bottom waters to anoxicinhospitable bottom conditions and these are noted at several levelsthroughout the Silurian into the Early Devonian. These events appearto correspond to eustatic highstands represented in other parts of theworld and possibly are linked with widespread hypoxia.

The following times appear to represent relative sea-level high-stand maxima in the Silurian of the Carnic Alps, as indicated by dark,graptolitic shales in deep shelf to basinal carbonate-dominatedsections.

(1) Llandovery: early Aeronian, probably post- Coronograptuscyphus graptolite Zone/Demirastrites triangulatus graptoliteZone (highstand of Sequence 1; Johnson's highstand 1.

(2) Llandovery: early Telychian, Pterospathodus celloni conodontZone/Oktavites spiralis graptolite Zone (highstand of Sequence2A, herein; early part of Johnson's highstand 4; herein termed 4a)

(3) Llandovery: late Telychian, lower Pterospathodus a. amorphog-nathoides conodont Zone (highstand of Sequence 2B; later partof Johnson's global highstand 4; herein termed 4b; includesIreviken Event interval; Jeppsson, 1997; see Calner, 2008)

(4) Wenlock: early Sheinwoodian, Kockelella ranuliformis to Ozar-kodina sagitta rhenana conodont Zones; Monograptus riccarto-nensis Zone (highstand of Sequence 3A; Johnson's highstand 5;includes Ireviken carbon isotopic excursion)

(5) Wenlock, mid-Sheinwoodian, Cyrtograptus rigidus graptolite Zone;probably upper Kockelella walliseri conodont Zone (highstandof Sequence 3B; unnamed upper part of Johnson's highstand 5)

(6) Wenlock: mid Homerian, lower Ozarkodina bohemica conodontZone;Gothograptus nassa graptolite Zone (highstand of sequence4A; Johnson's highstand 5a; probable Mulde Event interval)

(7) Ludlow: Gorstian, near Wenlock–Ludlow boundary, Neodiver-sograptus nilssoni graptolite Zone (highstand of Sequence 4B;Johnson's highstand 6)

(8) Ludlow, early Ludfordian, Polygnathoides siluricus conodontZone (highstand of Sequence 5; offset from Johnson's high-stand 7; includes probable Lau Event interval)

(9) Ludlow: late Ludfordian, upper Ozarkodina snajdri conodontZone(highstand of Sequence 6; Johnson's highstand 7?)

(10) Early Přídolí, Monograptus parultimus graptolite Zone (high-stand of Sequence 7; Johnson's highstand 8)

(11) Silurian–Devonian boundary (highstand of Sequence 8; earliestLochkovian: Icriodus woschmidti woschmidti conodont Zone/Mo-nograptus uniformis graptolite Zone; includes Klonk event interval)

However, it should be noted that the following key differencesoccur between the relative sea-level curve for the Carnic Alps versusthe original curve of Johnson (2006):

(1) early Llandovery black shales are absent in the Appalachian basin.(2) two peaks of sea-level highstand occur in the mid-late

Telychian, rather than a simple peak of highstand 4. However,these two peaks are recognizable in North America and hereintermed 4a and 4b.

(3) an early Sheinwoodian highstand in the upper Kockelella wallisericonodont Zone was not designated as a separate interval byJohnson, but also appears to be present in North America.

(4) the eustatic highstand Cardiola Formation (Polygnathoidessiluricus conodont Zone–Carnic Alps, Bohemia, Sardinia) is



not coincident with Johnson's global highstand (6) (which isshown in the Neocucculograptus kozlowskii graptolite Zone/Ozarkodina snajdri conodont Zone)

These comparisons suggest that most of the sequences identifiedin the Carnic Alps reflect global eustatic changes. However, develop-ment of comparable facies in coeval sequences (e.g., ironstones in thelate Telychian sequences of North America, Britain and the CarnicAlps) is more intriguing and may indicate proximity between theApulia Terrane and Laurentia, Baltica and Avalonia during this timeinterval as the environmental conditions affecting the northernGondwana derived terranes to the east and Laurentia to the westwere evidently quite similar.

Acknowledgments

Financial support for this investigation was provided by theAustrian Science Foundation (FWF) under project P15777-N06:Silurian Sequence Stratigraphy in the Carnic Alps.

Silurian research by C. B. is presently supported by NSF Grant EAR0518511 (to W. Huff and C.E. Brett). K.H. acknowledges financialsupport from the Geological Survey of Austria (2007). A.F. and K.H.acknowledge funds from project “Inerazioni Clima-Oceano nelSiluriano: processi, progressi e prospettive futuro” (2008–09; Fonda-zione Cassa di Risparmio di Modena and Università degli Studi diModena e Reggio Emilia).

Special thanks to Tim Phillips (UC, Cincinnati) and MonikaBrüggemann (GBA, Vienna) for graphics. The constructive commentsby the reviewers M.E. Johnson, M. Calner and F. Surlyk greatlyimproved the original manuscript. This paper also benefited frominsightful discussions with B. Cramer (Ohio State University) and P.I.McLaughlin (Wisconsin Geological Survey). Cramer reviewed Figs. 19and 20 and suggested numerous corrections on the biostratigraphictime scales. Grateful thanks to Lennart Jeppsson and Gudveig Baarlifor showing C.B. and K.H. the Gotland and Oslo Silurian sections.

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Silurian sequence stratigraphy of the Carnic Alps, Austria