Introduction

The Reingraben Turnover is one of most conspicuous stratigraphic changes, which is mirrored in all facies belts of the entire NW Tethyan continental margin (Schlager and Schöllnberger 1974). This turnover is reflected in the biofacies and lithofacies as well as by evolutionary events. The development of widespread, prograding carbonate platforms was suddenly interrupted by siliciclastic input. Furthermore, several factors indicate an almost complete breakdown of reef ecosystems, combined with an abrupt decline of carbonate production (e.g., Riedel 1991; Rüffer and Zamparelli 1997; Flügel and Senowbari-Daryan 2000; Keim et al. 2001). Despite many investigations, the causes of the turnover remain poorly documented. In the present paper, global climatic changes combined with plate tectonics are supposed as the main driving force.

Many authors (e.g., Angermeier et al. 1963; Jerz 1966; Schuler 1968; Schulz 1970; Grottenthaler 1978) document marginal-marine facies at the northern alpine Raibl Event (= Reingraben Turnover in the Northern Alps), although these successions, deposited in high-energy conditions, most probably gained significant sedimentary gaps. Also, the basinal successions (Hallstatt facies) of the Eastern Alps had caught the attention of many authors (e.g., Plöchinger 1955, 1976, 1983, 1984, 1996; Mandl 1984, 1999; Gawlick 2000). Present descriptions have been kept also brief (e.g., Gawlick et al. 1999a), although the potential of complete basinal sequences (low-energetic setting) ought to be much higher than in the shallow-water facies.

Gawlick et al. (1999a) mentioned the Freygutweg section (within recent road cuttings), and the disused Jakobberg gallery which contain Reingraben (= Halobia) Shales and, therefore, represent the Reingraben Turnover mentioned above. As a pilot study in the context of FWF-Project P 16878 “The Carnian Turnover in the Western Tethyan Realm”, these sedimentary successions were examined from a multistratigraphical viewpoint with the goal to establish a high-resolution succession representative of the Hallstatt area.

Geography, palaeogeography and stratigraphy

Geography

Both sections are located near Bad Dürrnberg, about 2 km SSW of Hallein (Fig. 1). This area is flanked by the N-S striking Hoher Göll and Rossfeld mountain range near Salzburg, and by a glacially cut escarpment towards Berchtesgaden (Fig. 1).

Fig. 1
figure 1

a Geographic position of the sections and b the main geological and tectonical settings of the area (left column—modified after Braun 1998). c Simplified geological map of the fault-block region of Hallein-Berchtesgaden (right column—modified after Plöchinger 1955, Prey 1969, and Gawlick 2000)

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Palaeogeography

The Reingraben Turnover occurred during a rearrangement of tectonic plates: the Cimmerian Micro-Continent, positioned at the northern margin of the Tethyan realm, collided with the Eurasian plate as the supercontinent Pangaea disintegrated during the formation of the Neotethys and the future central Atlantic Ocean (Fig. 2a). Near the Ladinian-Carnian boundary, the northwestern part of the Tethys was split into separate oceanic basins (Stampfli and Borel 2002; see Fig. 2): the subducted Palaeo-Tethys in the south, and the Hallstatt-Meliata Ocean in the north. The investigated area is situated at the northwestern margin of the Hallstatt-Meliata Ocean (Fig. 2).

Fig. 2
figure 2

a Global palaeogeographic situation during Carnian and Norian times (modified after Stampfli and Borel 2002), and a generalised, ideal facies model (b) for the northwestern Tethyan margin (Carnian). Exaggerated relief

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After a phase of rapid Middle Triassic rifting, the Wetterstein shelf area shallowed due to a significant decrease in tectonic subsidence (Brandner 1984). This induced a change in carbonate platform geometries. In the earliest Carnian, a phase of Ladinian platform aggradation abruptly changed to a marked progradation.

During the Early to Late Carnian, several main facies areas developed on the shallow and hemipelagic epicontinental shelf of the NW Tethys. They include, from present NW to SE, the terrigenous Keuper facies belt of present Germany, and the laterally adjacent shelf facies of the so-called Bajuvaric and Tirolic tectonostratigraphic units of the Eastern Alps (Fig. 2b). The area of Bajuvaric and Tirolic units can be subdivided into different facies belts: a) a northern carbonate platform (Wetterstein Formation) interfingered towards the southeast with the, b) intraplatform-basinal Reifling Formation. Towards the southeast, within the Tirolikum, another up to 2000 m thick carbonate platform of the Wetterstein-Formation is marking the shelf margin area. The toe of the slope interfingers with Reifling Beds, and c) the Hallstatt facies belt. These regions can be subdivided in a proximal Hallstatt Grey facies and a more distal Red Hallstatt facies belt (“Salzberg facies”; see also Fig. 2b).

Due to tectonic shortening, lateral displacement, and subsequent erosion, the Meliaticum (see Fig. 2b), deposited on oceanic crust, is preserved only in local tectonic slivers (e.g., Mandl and Ondrejickova 1993).

Around the Julian 1/Julian 2 boundary, large rivers transported high amounts of siliciclastics in a bypass-system from the Baltic Craton towards Central Europe and, finally, towards the continental margin of the Hallstatt-Meliata Ocean (Tollmann 1976; Aigner and Bachmann 1992). The terrigenous material accumulated in basinal areas and, subsequently, also on the shelves. This interrupted the reefal development and resulted in a distinct lithological turnover (Reingraben Turnover). As shown herein, the shallow-water carbonate factory was shut off throughout the Tuvalian and resumed during the Early Norian.

Already in the Middle and Upper Triassic, salt diapirism, initiated by the Permian Haselgebirge, resulted in synsedimentary motions, documented by numerous sediment-filled fissures (Schlager 1969). The Jurassic transtensional Penninic ocean basin caused the separation of the Austroalpine facies belt, including the NCA, from the European hinterland. Coevally, compressional movements in the western Tethys and on Austroalpine shelves resulted in the development of a nappe stacking (Mandl 1999), which is well preserved in the Hallein-Berchtesgaden region. First, the Tirolic facies belt was overthrusted by the Juvavic (= Hallstatt) nappe (Fig. 1a). Increased transpressive motions during the latest Jurassic and Cretaceous led to an “out of sequence” thrusting of both units (Mandl 1999) producing a doubling of the nappe complex. The “lower” stack was in turn overthrusted by the Berchtesgaden nappe (Fig. 1a; southern Tirolic facies). The overlying (southern) blocks were eroded during the Cretaceous and the remaining relief was sealed by the Tertiary Gosau Group (Fig. 1a). For further discussion see, e.g., Decker et al. (1987), Frank (1987), Neubauer (1994), Schweigl and Neubauer (1997), Gawlick and Lein (1997, 2000), Gawlick et al. (1999b), Gawlick (2000), Gawlick and Diersche (2000), Frisch and Gawlick (2003).

Stratigraphy of the Hallstatt nappe

This unit is characterised by the interfingering of different but isochronous lithologies deposited in several subfacies belts. The primary spatial arrangement of both the proximal Grey facies and the distal Red facies (Fig. 2b) was profoundly overprinted by tectonic shearing and overprinting. The first reconstructing attempt of a standardised Hallstatt stratigraphic succession was published by Schlager (1969), revised by Mandl (1984), and finally specified by Mandl (1999) and Gawlick (2000); see Fig. 3. The primary position of the subfacies belts was up to the amounts of carbonate production on adjacent factories (Reijmer and Everaas 1991) as well as on underground movements. Already in the Upper Triassic, the submarine relief was composed of flat, elongated ridges (synsedimentary diapiric ridges; see Figs. 2b, 3) with calcareous successions and shallow basins inbetween with prevalent marly and clay-rich deposits.

Fig. 3
figure 3

Stratigraphic succession depending on palaeomorphological patterns (modified after Mandl 1984, 1999 and Gawlick 2000). The position of the sections might be placed on the upper edge between the top of the ridges and the basins (thin black arrows)

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Sections

Freygutweg section

First mentioned and investigated by Gawlick et al. (1999a), this section consists of condensed lowermost Carnian to Middle Lacian rocks. All beds dip uniformly SSE at 25°. The section is overturned. The basal part consists of a 5 m thick-bedded grey limestone sequence, covered by 2.75 m thick grey to violet-coloured Reingraben Shales. These units are overlain by about 2.3 m thick nodular red flaser limestones and 3 m thick medium-bedded light-coloured limestones (see Fig. 4). Unfortunately, the transition between the bedded grey limestones and the Reingraben Shales is completely overgrown and probably tectonically sheared: several excavation-attempts to a depth to circa 1 m reached no solid bedrock.

Fig. 4
figure 4

Comparison of two biostratigraphic zonations. Left columns according to Kozur (2003), the two right columns after Krystyn (1980, 1983) and referring to the Salzkammergut area

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Jakobberg gallery

The stratigraphic succession ranges from greyish-coloured bedded limestones of the Early Fassanian and Langobardian to the “Liasfleckenmergel” (basal Jurassic; Gawlick and Lein 1997, 2000; Gawlick et al. 1999a).

Medwenitsch (1949, 1958, 1962, 1963) mapped the galleries and notes dark Reingraben Shales intercalated between the overlying monotonous Norian-Rhaetian marl series and the underlying grey-bedded limestones. Gawlick and Lein (1997, 2000) revised the Jakobberg and Wolfdietrich galleries: the part of interest containing the Reingraben Turnover was described only briefly, without any detailed stratigraphic and information about the Carnian succession.

Based on bed by bed sampling, the present paper provides detailed biostratigraphic and microfacial information of the basinal Hallstatt facies for the first time. Bedded grey limestones are sharply overlain by thinly-bedded greenish marly limestones (Fig. 5a), subsequently followed by an 1.3 m thick succession of ochre-coloured limestones and marls (Fig. 5b), in turn overlain by about 1.1 m thick black Reingraben Shales. The boundary between bedded grey limestones and green marly limestones (Fig. 5a) as well as ochre coloured-limestones and Reingraben Shales (Fig. 5c), respectively, mark two distinctive lithological changes. Both “events” are conformable and were not caused by tectonic overprinting.

Fig. 5
figure 5

Upper part of the Freygutweg Section showing (a) the nodular red flaser limestones and (b) the Reingraben Shales

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Whereas the lower boundary of the Reingraben Shales is exposed, the upper boundary to overlying nodular red flaser limestones is walled by wood planking and/or sheared. All layers dip at 60° to SSE and in addition are displaced by normal faults dipping northward at 45° (Fig. 5c).

Biochronostratigraphy

The first chronostratigraphic charts for the Salzkammergut region, based on ammonites and conodonts were published by Krystyn (1970) and revised several times (Krystyn 1973, 1980, 1983). At present, global ammonite and conodont biochronology distinguish between several bioprovinces. The Tethyan bioprovince was compiled and constructed mainly by Gallet et al. (1994) and revised by Krystyn et al. (2002). This study focuses on the regional results of Krystyn (1980, 1983; see also Fig. 6).

Fig. 6
figure 6

a Sharp and undulating boundaries between the bedded grey limestones and the green marly limestone intercalation. b Ochre-coloured limestone succession, alternating with thinly bedded marly intercalations. c The sharp transition from ochre-coloured limestones to the black Reingraben Shales demonstrates the drastic change in environmental conditions connected with the “black shale-event”

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Fortunately, almost all the limestone beds contained enough conodonts to carry out biostratigraphic zonation and to determine the timeframe of the Reingraben Turnover. Further examinations (in the framework of the FWF-Project P 16878) on other globally distributed sections in different main facies belts will eventually call for a revision or a refinement of the present results (Figs. 7, 8).

Fig. 7
figure 7

Lithology, stable isotopes, conodont biostratigraphy and conodont zones (after Krystyn 1980 and 1983) of the Jakobberg gallery. a Isotopic sequence of the complete section, b detailed isotopic sequence of the uppermost 30 cm of the bedded grey limestones. Palaeotemperatures after O’Neil et al. (1969). Different species in the conodont box: (1) = Gladigondolella tethydis; (2) = Gladigondolella tethydis ME; (3) = Gondolella polygnathiformis

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Fig. 8
figure 8

Lithology, stable isotopes, conodont biostratigraphy, and reconstructed conodont zones (after Krystyn 1980 and 1983) of the Freygutweg section. Due to the lack of ammonites, the ammonite zones are construed after the conodont zones (the exact boundaries are, therefore, questionable). Palaeotemperatures after O’Neil et al. (1969). Different species in the conodont box: (1) = Enantiognathus petraeviritis; (2) = Hindeolella lautissima; (3) = Gondolella tadpole; (4) Gladigondolella tethydis; (5) Hindeolella pectiniformis; (6) Gondolella polygnathiformis; (7) Hindeolella sp.; (8) = Gondolella nodosa; (9) = Gondolella navicula; (10) = Ozarkodina sp.; (11) = Epigondolella triangularis; (12) = Epigondolella abneptis; (13) = Epigondolella spatulata; (14) = Epigondolella quadrata

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Excluding the bedded grey limestones, the lithological succession differs within both sections. The Reingraben Shales, which would allow for the correlation of both sections, exhibit stratigraphic gaps. The lower boundary, which is exposed in the Jakobberg gallery, might be tectonically sheared in the Freygutweg section; the upper boundary, exposed at the Freygutweg, is not preserved in the Jakobberg gallery. Intercalated thin-bedded calcareous beds in upper parts of the Reingraben Shales, which would enable further correlations, were not mentioned by former authors. Furthermore, the Reingraben Shales preferentially acted as a shear plane (e.g., Schweigl and Neubauer 1997) resulting in very rare outcrops of the shales in the Hallstatt Red facies. Due to this, a correlation of both sections should not be attempted using only lithological and facies criteria, but rather with biostratigraphic evidence (Figs. 7, 8).

The first occurrence of G. polygnathiformis Budurov and Stefanov (Fig. 9a) places the Ladinian-Carnian boundary at the base of both Salzkammergut sections (bedded grey limestones, literature data see Krystyn 1983, Orchard 1991, and Kozur 2003). Uppermost Langobardian (regoledanus ammonite zone) is evidenced by Gawlick et al. (1999a) in the lower part of the bedded grey limestones within the Jakobberg gallery. Uncertain is the presence of the G. mostleri conodont assemblage zone (abbreviated ‘A. Z.’) representing the lower aonoides ammonite zone or Julian 1/I (after Gallet et al. 1994) and of the G. tadpole Interval Zone (base of the upper aonoides ammonite zone or Julian 2/I1) in both sections. G. mostleri did not occur in the Freygutweg section and G. tadpole only very rarely (two specimens; Fig. 9f) in the middle part of the bedded grey limestones. The Gl. tethydis conodont assemblage zone (coexistence of Gl. tethydis Huckriede with G. polygnathiformis), representative for the upper aonoides ammonite zone and the austriacum ammonite zone (Julian 1/II to 2/II), includes the uppermost bedded grey limestones, the ochre-coloured limestones, and the Reingraben Shales. Because of the absence of G. auriformis and the abundance of G. tethydis (Figs. 9b–e, j) in the Salzkammergut sections we favor unlike to Krystyn (1983) the Gl. tethydis A. Z. As a result, the very depauperate fauna of G. polygnathiformis and Gl. tethydis allows only a general age assignment of Middle to Late Early Carnian (aonoides to austriacum ammonite zone resp. tethydis conodont zone). Stratigraphically important is the disappearance of Gl. tethydis on top of the shales. This proves the exclusive Lower Carnian age of the Reingraben terrigenous interval in the Hallstatt facies of Berchtesgaden and most probably elsewhere. Two lithological turnovers, a) the change of bedded grey limestones to ochre-coloured limestones and b), from ochre-coloured limestones to Reingraben Shales are embedded in this time interval. Halobia rugosa Gümbel, whose specimen were found by Medwenitsch (1949) in the Reingraben Shales of the Jakobberg gallery, has a first occurrence date at the beginning of the austriacum ammonite zone (Julian 2; see also Gruber (1976) and Krystyn in Gallet et al. (1994)). Following this, it is very likely to put the initial lithological change of the Reingraben Turnover exclusively within the uppermost aonoides ammonite zone and the austriacum ammonite zone (Julian 1/IIc to Julian 2).

Fig. 9
figure 9

Conodonts of the Freygutweg section (Lowermost Julian to uppermost Tuvalian); scale bar = 100 μm: a Gondolella polygnathiformis, Budurov and Stefanov; La 5; CAI = 1.0–1.5; b Gladigondolella tethydis, Huckriede; La 4; CAI 1.0–1.5; c Gladigondolella tethydis; La 2; CAI 1.0–1.5; d Enantiogratus petraeviritis, Huckriede; La 4; CAI 1.0–1.5; e Hibbardella lautissima, Huckriede; La 5; CAI 1.0–1.5; f Gondolella tadpole, Hayashi; La 2; CAI 1.0–1.5; g Gondolella polygnathiformis; J 16a; CAI 1.0; h Hindeolella pectiniformis, Huckriede; J 16a; CAI 1.0; i Hindeolella pectiniformis; J 16a; CAI 1.0; j Gladigondolella tethydis ME, Huckriede; J 16b; CAI = 1.0; k Gondolella polygnathiformis; T 01; CAI = 1.0; l Gondolella polygnathiformis; T 04; CAI = 1.0; l1) Gondolella polygnathiformis; detail from l; m Gondolella polygnathiformis; T 06; CAI = 1.0; n Gondolella polygnathiformis; T 12; CAI = 1.0; o Gondolella polygnathiformis; T 13; CAI = 1.0; o 1 Gondolella polygnathiformis; detail from o; p Gondolella nodosa, Hayashi; T 13, CAI = 1.0

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The lithological boundary between Reingraben Shales and the nodular red flaser limestones is covalent to the beginning of the G. polygnathiformis A. Z. (Figs. 9k–o; dilleri ammonite zone and lower subbullatus ammonite zone, Tuvalian 1 to 2/I) and is conterminous to a third lithological event (change from Reingraben Shales to nodular red flaser limestones). The first occurrence date of G. nodosa (Fig. 9p) in bed 13 defines the G. nodosa A. Z. (upper subbullatus ammonite zone and upper spinosus ammonite zone or Tuvalian 2/II to 3/II) at the very base of the bedded light-coloured limestones. The uppermost Carnian conodont assemblage zone identified by M. communisti (uppermost spinosus zone) is evidenced by Gawlick et al. (1999a).

The last occurrence of G. polygnathiformis in bed 16 and the first occurrence of G. navicula Huckriede (Figs. 10a, c) one bed above defines the Carnian-Norian boundary. Together with E. quadrata (Figs. 10h–i), E. spatulata (Fig. 10f), E. abneptis (Figs. 10b, e), and E. triangularis (Fig. 10d), these conodont specimen indicate a condensed and mixed fauna of the basal Norian (Lacian 1 to Lacian 3). Therefore, the Carnian/Norian boundary in the Salzkammergut is not equivalent with the lithological change from nodular red flaser limestones to bedded light-coloured limestones.

Fig. 10
figure 10

Conodonts of the Freygutweg section and Jakobberg gallery; scale bar = 100 μm: Conodonts of the Freygutweg section (Early and Middle Norian): a Gondolella navicula, Huckriede; L 06; CAI = 1.0; b Epigondolella abneptis s.l., Huckriede; L 06; CAI = 1.0; c Gondolella navicula; L 07; CAI = 1.0; d Epigondolella cf. triangularis, Budurov; L 07; CAI = 1.0; e Epigondolella abneptis, Huckriede; L 07; CAI = 1.0; f Epigondolella spatulata, Huckriede; L 08; CAI = 1.0; g Ozarkodina sp.; L 08; CAI = 1.0; h Epigondolella quadrata, Huckriede; L 07; CAI = 1.0; i Epigondolella quadrata; L 08; CAI = 1.0. Jakobberg gallery: Top of bedded grey limestones: j Gondolella polygnathiformis, Budurov and Stefanov; HB 7; CAI <1.0; k Gladigondolella tethydis, Huckriede; HB 7; CAI <1.0; l Didymodella alternata, Mosher; HB 7; CAI <1.0; m Gondolella polygnathiformis; HB 7; CAI <1.0; n Gladigondolella tethydis; HB 7, CAI <1.0

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Sedimentary facies

The description and interpretation of the lithofacies and microfacies are based on thin sections and faunal composition extracted from acid residues. Thin sections enabled microfacies analysis of the Carnian Turnover in the Hallstatt Red facies belt for the first time. Additionally, the faunal composition of every single bed gave further information about environmental conditions. The results are shown in Table 1 and Fig. 11.

Table 1 Facies interpretation spanning both sections. Shown are the main biogenic and abiogenic components as well as a brief interpretation. The units are classified after Dunham (1962). Abbreviation: SMF = “Standard Microfacies” and FZ = Facies Zone (after Flügel 2004)
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Fig. 11
figure 11

Simplified facies model of the Hallstatt Basin with controlling global and regional factors, interpreted from the different lithologies within the Reingraben Shales and the nodular red flaser limestones

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Description of the main lithologies (nomenclature according to Mandl 1999)

  1. 1.

    Bedded grey limestones: Greyish-coloured filament-wackestones containing algal crusts similar to “Tubiphytes” as reefal elements, peloids, and intraclasts, mixed with pelagic components (radiolarians and planktic crinoids). Further faunal components are conodonts and fish teeth (Figs. 12a, 13a–b).

    Fig. 12
    figure 12

    Thin sections of the Freygutweg succession: a Bedded grey limestones: similar to the Jakobberg gallery (Fig. 13a) containing a high percentage of allochthonous, reef-derived organisms: tiny, arcuate filaments of type 2 (black arrows), fragments of “Tubiphytes”-like algal relics (white arrows) and mud peloids (white triangles). All bioclasts occur without preferred orientation. b Biogenic “Reingraben” limestones: single calcareous intercalation, rich in filaments (mostly type 2), radiolarians, planktic crinoids, and foraminifers. The wackestone is intensely burrowed, large bioturbation tracks (e.g., worm or holothuroid-burrows) mostly show a blurred borderline to the surrounding matrix (accentuated with a dashed line). c Reingraben Shales/thinly laminated silty carbonate: nearly undisturbed lamination characterised by alternating limestone and clay-rich layers, pervaded and dissolved by horizontal stylolites. The direction of these stylolites changed in the more competent limestone layers (thin black arrows). d Lowermost nodular red flaser limestones: transition zone between the uppermost calcareous “Reingraben” interbeds and the nodular red flaser limestones. This zone (thickness circa 4 cm) is characterised by a breccia containing different, mostly angular components: disarticulated crinoid fragments (C), filament-bearing limestone intraclasts (Fi) and extraclasts similar to those occurring in bedded silty carbonate embedments (HS) underneath. Also notable are micritic envelopes (cortoids) formed by microborers (black triangles) in combination with micrite precipitation (white triangles). The angular lithoclasts are etched and rounded due to pressure solution. e Nodular red flaser limestones: the whole unit is characterised by etched “pseudoclasts” (Psk), formed by extensive pressure solution. These “pseudoclasts” bear filaments indicating a low rate of sedimentation and burrowing, the lack of orientation is caused by intensive bioturbation (“fan”). f Angled suture line of a horizontal stylolite enriched with reddish clay (nodular red flaser limestones). g Lithoclasts (LC) within a filament-bearing, altered intensively by micro-pressure solution. h Dorsal floating wing of a planktic crinoid (Osteocrinus sp.). i Geopetal texture showing a loosely packed peloidal internal filling, overgrown by spar. The round structure is a crinoid-fragment (white triangle). j Calcified radiolarians were most abundant in the upper parts of nodular red flaser limestones (white triangles). k The boundary between “pseudoclasts” and the surrounding biomicritices is often enriched with fragments of planktic crinoids (here; brachialia). l Burrows in a firmground filled with sediment rich in radiolarians and some filaments. m Example of several distinct hardgrounds representing phases of a reduced sedimentation within a single horizon (in this case: T 05, thickness circa 12 cm). Note: Scale bar all 1 mm

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    Fig. 13
    figure 13

    Thin sections from the Jakobberg gallery section: a The top of bedded grey limestones contains a high percentage of allochthonous reef-derived organisms: of major importance are “Tubiphytes”-like fragments (thin white arrow). b The very top of the bedded grey limestones is characterised by strongly reduced rate of sedimentation, strong bioturbation, firmgrounds, thrombolite crusts with authigene calcite particles and the coeval diminished occurrence of “Tubiphytes”-like fragments. Fi 1 = type 1 filament, Fi 2 = type 2 filament. c The green marly limestones show preferred orientation of densely packed filaments (type 2) defining the lower boundary of the Reingraben Turnover in the Hallstatt basin (Salzberg facies area). d Bedded dark grey limestones (pyrite-rich phacoidal wackestones): detrital calcites are very common and might be equated to reworked authigene calcites from the layers underneath. e–h Ochre-coloured limestones (thrombolite bindstones): The horizons are characterised by micro-alternations between detrital calcites and cloudy microbialite. The latter have encrusted and stabilised the calciclasts deposited beforehand. There are also synsedimentary shifts, sealed with crinoid- and calciclast-rich wackestones. i The boundary between the ochre-coloured limestones and black Reingraben Shales is very distinctive (also in thin sections) coinciding with a sudden increase of organic matter. j The basal “Reingraben” limestone intercalation has been intensively churned by bioturbation. The filaments (type 2) contoured the burrows (accentuated with dashed line). Note: Scale bar all 1 mm

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  2. 2.

    Green marly limestones: Greenish-coloured, pyrite bearing mud- to wackestones exclusively yielding filaments of type II (ostracod shales). Exposed only in the Jakobberg gallery (Figs. 13b–c).

  3. 3.

    Dark grey limestones: Dark grey-coloured pyrite flaser wackestones in the lower part and bioclastic mudstones in the upper part, respectively. Exposed only in the Jakobberg gallery (Fig. 13d).

  4. 4.

    Ochre-coloured limestones: Thinly alternating detritic flaser wackestones and thrombolite flaser bindstones. Characteristic are very thinly bedded interbeddings of thrombolite algal crusts and detrital, partly fixed clasts (calcite and quartz, see also Figs. 13e–f). In addition, the fauna is rather depleted, (common occurrence of filaments, rare foraminifers and crinoids, and very rare conodonts). “Tubiphytes”-like microbialites are absent. Exposed only in the Jakobberg gallery (Figs. 13e–h).

  5. 5.

    Reingraben Shales: They represent different lithologies ranging from unfossiliferous black shales in the lowermost part, intercalated burrowed biogenic wackestones in the lower and middle part, and unfossiliferous laminated mudstones as well as thin- to medium-bedded marls in the upper part (Figs. 12b–c, 13i–j). Faunal elements were found mostly in the burrowed calcareous intercalations. Notable is the occurrence of well-preserved Osteocrinus centrodorsalia within the middle part of the shales (Freygutweg section). Kristan-Tollmann (1970) recognized a global major appearance of osteocrinoids within the Ladinian to Carnian. All species, mentioned in this paper, were found in the Freygutweg section (Table 2).

    Table 2 Faunal composition of the Freygutweg section and the Jakobberg gallery. White circles: rare; grey circles: common; full black circles: abundant
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  6. 6.

    Nodular red flaser limestones: Consisting of primary filament, radiolarian and crinoid packstones enriched with fine red biomicrites, this very condensed unit obtained its nodular texture (“pseudoclasts”) through intensive horizontal and vertical pressure solution (Figs. 12e–m). The fauna consists mainly of filaments, radiolarians, crinoids, few gastropods, and rare complete ostracods. Whereas the frequency of filaments decreases towards the top, calcified radiolarians and crinoids increase. In the lower and middle parts, Tubiphytes-like algal crusts are completely absent. In the topmost part, they are sporadically present.

  7. 7.

    Bedded light-coloured limestones: The mud- and wackestones are rich in calcified radiolarians. Fewer faunal components are gastropods, juvenile ammonites, and filaments. The reoccurrence of Tubiphytes-like organisms indicate some reefal influence again.

Interpretation (see also Table 1)

The stratigraphic succession, represented by the sections, can be assigned to the flanks of synsedimentary ridges. This emanated from the stratigraphic model after Mandl (1984, 1999; see also Fig. 3) with regard to the varying palaeo-topography. Whereas the basins expose marl dominating sequences, the top of the ridges show an ongoing calcareous sedimentation. These two main lithologies interfingered towards the flanks.

The bedded grey limestones represent ancient periplatform-mud with reefal influence, deposited within a deeper, low-energy setting under normal environmental conditions. This is evidenced by epifaunal elements like gastropods and an intact endofauna (intensely burrowing and churning). Microbial algal crusts near the top of the bedded grey limestones point to an incipient change in environmental settings, turning to a minor supply of oxygen. The crusts enclose fine, probably authigenic calciclasts, which were generated due to a reducing micromilieu (Fig. 13b; see Reitner 1997). The very top of the bedded grey limestones exhibits an undulating and intensely burrowed surface, which can be interpreted as firmground and, therefore, represents a sedimentary gap (Fig. 13b). Densely packed, oriented filaments (Figs. 13b–c) within the overlying thin-bedded green marly limestones indicate very low accumulation rates under low-energy setting. No signs of bioturbation do affirm this observation. The complete absence of endofaunal elements proceed in the lower part of the dark grey limestones, whereas their upper part shows intensive burrowing again.

The main part of the ochre-coloured limestones consists of densely laminated bindstones which were deposited within dysaerobic settings (“biofilms”; see also Wilderer and Charaklis (1989), Reitner et al. (1995), and Reitner (1997)) in starved basins (Figs. 13e–g). The minor part consisting of bioclastic and lithoclastic packstone intercalations with synsedimentary structures retraces the above-mentioned diapiric movements (Fig. 13h).

The Reingraben Shales in both successions represent a restricted, almost anoxic setting under high terrigenous influx and very low carbonate supply. The distinct boundary occurring between ochre-coloured limestones and black Reingraben Shales (Figs. 5c, 13i) most likely was underlined by diagenetic conditions: most of the goethite contained within the ochre-coloured limestones is certainly not primary but was oxidised from pyrite due to oxygen-enriched pore water drainage. At the almost impermeable black shales, pore-water circulation stopped and so did oxidation of pyrite. Therefore, this lithological change in the Jakobberg gallery is interpreted as a combination of primary induced change in the depositional and ecological setting with subsequent diagenetic overprint. The anoxic Reingraben Shales are completely unfossiliferous and yield neither neritic nor planktic or epibenthic forms. The complete lack of bioturbation implies the absence of endobenthic life. The ancient microlamination, which probably existed beforehand, has now been overprinted by micro pressure solution.

The intercalated limestones in between the Reingraben Shales are interpreted as “event beds”, deposited during short recreation phases of the carbonate factory. We differ between bioclastic, burrowed, and “homogenised” interbeddings with allochthonous planktic components in the lower and middle parts (Figs. 12b, 13j) and thinly laminated, unfossiliferous intercalations in the upper part (Fig. 12c). Most likely, the intercalated limestones represent an acyclic succession of downslope calcareous suspension flows, which swept into the basins triggered by, e.g., regional storm events. In combination with a basin-spanning circulation period and, thus, oxygen-enrichment in the once starved basins, epi- and endobenthic life increased during short time intervals— the beds were burrowed intensely. The unfossiliferous interbeds were related to anoxic conditions. The absence of benthic life led to a preservation of the primary microlamination.

The frequency of unfossiliferous calcareous intercalations increases within the upper part of the Reingraben Shales before deposition of the nodular red flaser limestones. Thus, the depositional regime graded from clay to limestone-dominated sediments, first of all under anoxic conditions, then under aerobic bottom water.

The distinctive boundary between Reingraben Shales and nodular red flaser limestones can be explained by a drastic change in water circulation patterns. The boundary between the topmost laminated calcareous “Reingraben” interbedding and the basalmost red nodular flaser limestone bed exhibits a short stratigraphical gap represented by a thin-bedded breccia (thickness about 4 cm; see Fig. 12d). The well medium-bedded red limestones graduated to bedded light-coloured limestones which contain reefal components such as Tubiphytes, crinoids, and peloids again. This should not be interpreted as a basinward progradation of the adjacent shelves rather than a slightly recovered carbonate system and, therefore, an increased carbonate supply.

This overview of the lithology describes at least three abrupt and drastic changes in lithology and mineralogy, which were presumably due to the following superimposed controlling global as well as regional factors (in order of importance): (a) global, probably tethyan-wide variations in oceanic circulation and oxygen supply, (b) the varying regional topography of the oceanographic palaeo-relief and (c) differences in the ratio between carbonate supply and terrigenous influx. These are now discussed:

  1. (a)

    Due to the presence of pyrite in the Reingraben Shales, we can assume an Eh/pH-potential near the sediment–water interface. As a result, the increased iron input deriving from the weathering of terrigenous material, was reduced to pyrite. The red colour of the limestones, however, indicates oxidation of iron into hematite. According to this interpretation, the seafloor relief had evidently led to different levels of circulation: 1) low circulation and a reducing, anaerobic setting in the flat basins of the Hallstatt Grey facies and 2) moderate circulation and dysaerobic bottom water upon the top and flanks of the ridges within the Hallstatt Red facies. Due to the mobility of the submarine relief with time, the boundary between anaerobic and aerobic bottom water changed upon the flanks (red limestones). Only the deeper regions of the flat basins are assumed to have remained constantly anaerobic.

  2. (b)

    The topography was controlled by the mobile Permian Haselgebirge and had the form of elongated ridges and intervening shallow basins. Nodular red flaser limestones were deposited upon the ridges and their flanks, interfingering with black Reingraben Shales at the bottom of the flanks (Situation in the Julian 2; see Fig. 3).

  3. (c)

    The above-mentioned “event beds” within the Reingraben Shales affirm the thesis of Reijmer and Everaas (1991): they showed from a Rhaetian example in the Southern Alps, that the Carnian basins were profoundly conditioned by the development of the adjacent shelves. At times of short recreations, increased mud supply caused calcareous suspension flows into the basins intermitting the monotonous series of black shales (Fig. 14).

    Fig. 14
    figure 14

    Rock composition of the two sections, based on X-Ray fluorescence analysis

    Full size image

Water depth

The close relationship between shelf and adjacent basin requires diminished basinal water depth. Bathymetric reconstructions have been discussed controversially in the last decades (a compilation of several authors was published by Rieche (1971) as well as Wendt and Aigner (1985)). Later investigations (Reading 1986 and Schmidt 1990) favoured water depths of 70–100 m.

Isotopes

Oxygen and carbon ratios were measured in all calcareous and marly beds to interpret primary ecologic and secondary diagenetic overprints.

Due to the complete lack of brachiopods and belemnites for analysis, four whole-rock samples were extracted instead from every bed (weights between 0.05 and 0.37 mg) with a dental drill. Attention was paid to obtain mudstones without late cements derived from shell cavities and fissure fills. The average of the values (best three of four) represents the isotope ratio which is pictured in Figs. 7 and 8. Isotopic analyses were performed with a Thermo Quest Finnigan Delta Plus XL spectrometer. The results are expressed in δ‰ units and reported against the V-PDB standard. The reproducibility for the isotope determinations was ± 0.2 ‰ (1σ) for δ18O and ± 0.1 ‰ (1σ) for δ13C.

As for the δ13C values, the combined succession of both the Freygutweg section and the Jakobberg gallery show a slightly increasing trend within the bedded grey limestones (2.7–3.2 ‰), decreases slightly in the ochre-coloured limestones (2.0–3.0 ‰) and increases again towards the nodular red flaser limestones and bedded light-coloured limestones (max. 3.8 ‰). In contrast, the δ18O values decrease: Very “heavy” values prevail, ranging from 0.4 to −0.8 in the uppermost part of bedded grey limestones to about −1 to −1.5 (“lighter values”) in the nodular red flaser limestones and the bedded light-coloured limestones.

Marshall (1981) published very similar δ18O values from Jurassic and Triassic Tethyan limestones of several sections in Sicily and northern Italy. He points out that the “heavy” δ18O values in pelagic chalks and limestone nodules originated from early high-magnesium calcite cements rather than from an abnormal sea-water composition. Also, Bellanca et al. (1995) described similar “heavy” δ18O values from Carnian deep-water limestone and marls from the Sicani Mountains, Sicily. In their paper, Julian dark marls with interbedded calcilutites show almost negative δ13C values. These marls were assumed to have been deposited in a basin with “dominantly anoxic to dysaerobic bottom waters”. In contrast, the ochre-coloured limestones and black Reingraben Shales, described in this paper, which were also considered to be deposited within a locally restricted basin, show positive δ13C values and do not confirm this. As there is no signal in δ13C through the transition from the bedded grey limestones to the Reingraben Shales, it is assumed that there was no marked or substantial change in seawater chemistry during the Reingraben Turnover. Keim and Brandner (unpublished data) have gained similar results from starved basins in the Southern Alps.

X-ray data

In addition to biochronology and facies interpretation, all beds underwent X-ray fluorescence analysis to identify the main mineral composition. The samples were pulverised and measured by a Siemens D-500 X-Ray Diffractometer (standard operating procedure). The simplified “translation” into graphic data, as shown in Fig. 11, was computed using “Analysis Technique for Rock Material, RVS 11.062, edition 1987”. This is a semiquantitative method to calculate the main components of rock material such as calcium carbonate, dolomite, clay minerals, quartz, feldspar, micas, gypsum, and goethite. The absolute percentage matter of accessorial dispersed pyrite, observed in thin sections of the dark grey limestones and calcareous “Reingraben” interbeds, respectively, was below the detection limit.

Some remarks must be given regarding gypsum, goethite, and dolomite. After deposition, gypsum recrystallised in the gallery as a secondary precipitation of salt and is enriched in fine molds and minor joints. Goethite was oxidised by oxygen-rich drainage water. Dolomite sprouted as crystals near stylolites and minor joints.

Fig. 11 illustrates a sudden increase of terrigenous influx (mainly clay minerals) occurring with deposition of the Reingraben Shales. The short-term interferences in the content of calcium carbonate within the ochre-coloured limestones and Reingraben Shales have been caused by calcareous interbeds. The basal part of the nodular red flaser limestones reveal high carbonate contents, which decrease towards the top of this unit. The top of the red limestones and the bedded light-coloured limestones show a similar composition: as discussed in the section on biostratigraphy, the lithological boundary is not identical with the biostratigraphic boundary.

Discussion

The Reingraben Turnover is only one regional synonyme for a synchronous series of similar major sedimentary changes, traceable throughout the whole Tethyan realm (e.g., Martini et al. 2000; L. Krystyn pers. comm., Vienna) at the beginning of the Late Triassic. Despite having different names, all turnovers are comparable by their sudden influx of large amounts of siliciclastics and anoxic sediments, combined with local extinction events and a depleted fauna (e.g., Simms and Ruffel 1989; Krystyn 1991). The siliciclastic material covered the carbonate platforms and shelves unconformly and, according to most theories, should have caused an abrupt decline of almost all Tethyan carbonate factories. It is still disputed, and there is need of further investigations, whether the reefs were (a) aerially exposed, (b) had been drowned due to an increased subsidence rate, or (c) had been degenerated by a forced siliciclastic input combined with anoxia. These points are now discussed in detail:

  1. (a)

    There is evidence of aerial exposure due to the existence of palaeokarst features in shallow-water facies, probably caused by a dramatic regression (e.g., Bechstädt and Dohler-Hirner 1983; Mutti and Weissert 1995).

  2. (b)

    Continuous stratigraphic successions existing in the Wetterstein facies belt (e.g., Angermeier et al. 1963). Brandner (1984) explained the regional differences in lithology, namely continuous and discontinuous successions between Wetterstein Limestone and Raibl Beds and their equivalents, with regional tilting of tectonic blocks. However, exact evidence for reef drowning in the Carnian is still missing.

  3. (c)

    According to Hallock and Schlager (1986), extensional tectonic processes are too slow to drown a carbonate platform. They offer another explanation. The decline of the carbonate factory is generated by nutrient excess. In the Carnian period, this nutrient overflow might have been caused by increased terrigenous input. This resulted in increased bioproductivity, major water pulp, and, at least, minor productivity of the carbonate factory.

As shown in the section on biochronostratigraphy, the Hallstatt sequence should mirror the platform and shelf development temporally delayed in the basin: the terrigenous input covering the platforms (wherever exposed or drowned) caused a decline in the carbonate production during a regressional stage (e.g., Brandner 1984; Hallock and Schlager 1986; Mandl 1999). This is indicated by the diminished depositional rate on top of the bedded grey limestones (Fig. 13b). Subsequently, the siliciclastic material, mainly clay mixed with quartz, feldspar, micas, etc., was swept into the basins. Whereas intraplatform basins (Reifling Basin) were filled completely with clay and sand (Lunz Sandstones) with a thickness of more than 200 m, terrigenous deposits in the Hallstatt Basin amount only a few metres. In the Hallstatt Basin, the first terrigenous sign produced a distinct boundary indicated by the first appearance of green marly limestones (Jakobberg gallery). The subsequent clay-dominated sedimentation (Reingraben Shales) is evidence of a reducing, starved basin without water circulation. The fact that the occurrences of black shales are not persistently traceable may have—apart from secondary tectonical shearing—also sedimentary reasons: As discussed before, the submarine topography was characterised by synsedimentary ridges and several interjacent flat basins. These starved basins probably were connected to each other, but eventually became isolated causing coeval depositions of black shales, whereas on top of the ridges carbonate sedimentation was interrupted by condensed horizons. From the stable isotopic data we can assume that the general chemistry of ocean water perhaps was fairly uniform during the whole Carnian—a “global black shale event” ought to be marked by sharp and distinct shifts in δ13C values.

In the Upper Julian, an incipient transgression, combined with a slow recovery of the platforms led to the formation of condensed limestones with less clay and quartz (nodular red flaser limestones). The bedded light-coloured limestones indicate a return to “normal” sedimentary conditions: the shelves recovered completely during a transgressional pulse in the basal Norian (Mandl 1999).

Finally, two superimposed factors could have caused the sudden increase of terrigenous influx: (a) changed plate constellations and orogenic events, and (b) a, therefore, forced continental (monsoonal) climate, discussed as followed:

  1. (a)

    As is noted in the section on palaeogeography, the event happened in a time of general plate rearrangement. Within the NCA, the terrigenous event might be relatable to the Kimmerian orogeny of the eastern northern Tethys (Brandner 1984; Bechstädt and Schweizer 1991) as well as the flexural uplifting of the Fennoscandian High (Aigner and Bachmann 1992). The latter might have caused a decreased rate of subsidence and a flat shelf (prograding carbonate platforms, e.g., Brandner 1984; Bechstädt and Schweizer 1991; Mandl 1999) and large amounts of weathering products.

  2. (b)

    Due to the very large landmass of Pangea, climate conditions must have been very similar to those of present Asia. Therefore, Hay et al. (1994) and Mutti and Weissert (1995) postulated “megamonsoonal” climates for Pangea and the Tethyan realm. During the Middle and Late Carnian, increased rainfall and humid weathering conditions generated large amounts of fluvial sediments (Simms and Ruffel 1989). The “Schilfsandstein” and comparable deposits unconformly covered the Mid European realm by a thickness of 20 m (Aigner and Bachmann 1992) and were transported south-eastwards towards the Tethys. This fact is evidenced not only by the widespread siliciclastic coverings in Europe, but also by extinction events (Simms and Ruffel 1989).

Conclusions

The Reingraben Turnover was studied at two sections near Bad Dürrnberg, Austria, using a multistratigraphical approach. Based on biochronostratigraphy, the lithological change could be placed in the uppermost aonoides ammonite zone and the austriacum ammonite zone (Julian 1/IIc–2/II). This lithological change should not be understood as a rapid “event”, implying a very short time gap. The Turnover can rather be split into three “events” which reflected, temporally delayed with regards to the carbonate platform and shelf evolution, the basinal development: a) Increased terrigenous input weakened the carbonate factory on the shelves and led to stagnating basinal deposition rates, followed b) by the initiation of black shales. The abrupt turnover to sedimentation under aerobic setting is marked by the c) red nodular flaser limestones. Finally, d) the slow recovering of the adjacent shelf is reflected in carbonate sedimentation towards the basins.

Microfacies analysis affirmed the high dependency of the Hallstatt Basin on adjacent carbonate factories, combined with varying water circulation, oxygen supply, and local tectonics, such as syndepositional movements.

Stable isotopic datasets show no significant change in water chemistry during the whole Carnian emphasising that the black shale event was without global relevance.

Climate changes, for example, increased precipitation caused by megamonsoonal activity related to changes in plate assemblage, are presumed to have been the superimposed, global factors that trigger very similar, maybe comparable events throughout the Tethyan realm.