Introduction

Carbonate successions are unparalleled archives of global and local environmental, climate and accommodation changes responding through variations in depositional environments, vertical and lateral facies patterns and biota associations (Schlager 2003; Flügel 2004; Wright and Burgess 2005; Pomar and Hallock 2008). In Western Tethys, the Norian (Upper Triassic)–Jurassic sedimentary successions (Fig. 1) recorded changes in depositional regime and facies associations governed by sea-level oscillations, climate, biotic crisis and extensional tectonics (Flügel 2002; Krystyn et al. 2005; Gawlick et al. 2009; Kaufmann 2009; Berra et al. 2010). The end-Triassic mass extinction, one of the big five biotic crises, affected diverse marine and terrestrial groups and coincided with major changes in palynological assemblages (Sepkoski 1996; Hallam 2002; Hesselbo et al. 2002; Hillebrandt and Urlichs 2008; Ruhl et al. 2009; Clémence et al. 2010; McRoberts et al. 2012; Pálfy and Zajzon 2012; Richoz et al. 2012; Wignall and Atkinson 2020). This extinction was driven by environmental perturbations related to volcanic CO2 emissions of the CAMP basalts (Central Atlantic Magmatic Province; Marzoli et al. 2004). The study of Western Tethys Norian–Lower Jurassic successions in the Northern Calcareous Alps (NCA, Austroalpine, Austria; Figs. 1, 2) contributes to unravel the interplay of factors influencing carbonate sedimentary environments at a regional scale. In fact, from late Norian to early Jurassic, these depositional settings witnessed: (a) the demise of a long-lasting, hundreds of kilometres wide and over 1000 m thick, Norian early-dolomitized inner platform (Hauptdolomit) adjacent to hundreds of kilometres wide carbonate shelf (Dachstein Limestone and Reef); (b) a major late Norian–Rhaetian change in sediment supply with the input of fine siliciclastics, previously absent, alternating with carbonate strata (Hochalm and Eiberg members of the Kössen Formation), attributed to a change towards more humid climatic conditions (Berra et al. 2010); (c) the late Rhaetian development of intraplatform basins (Eiberg Basin; Golebiowski 1990; Kaufmann 2009; Mette et al. 2012; Krystyn et al. 2005; Restental Basin; Gawlick et al. 2009; Richoz et al. 2012; Hillebrandt et al. 2013), passing laterally to shallow-water carbonates (Oberrhätkalk/Upper Rhaetian Limestone; Schäfer 1979; Golebiowski 1990; Krystyn et al. 2005) with margins with coral patch reefs (Bernecker et al. 1999; Bernecker 2005; Kaufmann 2009) or distally steepened ramp with skeletal packstone/grainstone and mounds (Piller 1981; Stanton and Flügel 1989, 1995; Flügel 1981, 2002); (d) a sea-level fall followed by rapid rise and biotic turnover across the end-Triassic extinction event (McRoberts et al. 2012); (e) the late early Jurassic rifting leading to the opening of the Penninic Ocean (Bernoulli 1964; Eberli 1988; Gawlick et al. 2009).

Fig. 1
figure 1

A Palaeogeographic map during the fine siliciclastic input in the late Norian showing the climatic belts, with the arrows indicating the possible extent of the humid belt, characterised by an increase in rainfall precipitation (redrafted after Berra et al. 2010). B Reconstruction of the Western Tethys passive margin during the late Norian (redrafted after Haas et al. 1995 as modified in Mandl 2000). C N–S Norian to Rhaetian lithofacies cross section of the Northern Calcareous Alps (NCA) from the Hauptdolomit to the development of the Eiberg Basin (modified after Mandl 2000; Krystyn et al. 2005). The blue star and blue dashed line rectangle represent the approximate location of the studied stratigraphic succession

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Fig. 2
figure 2

A Geological map of the study area (redrafted after Schnabel et al. 2002). Insert in the upper left corner shows the map of Austria with the location of the study area in the eastern NCA. B Chronostratigraphic scheme of the NCA proposed by Gawlick et al. (2009) reporting the nomenclature of the lithostratigraphic units in the study area. The blue dashed line rectangle marks the stratigraphic succession in the study area comprised between the Eiberg and Restental Basins. In grey stratigraphic gaps in the sedimentary succession (redrafted after Gawlick et al. 2009). C Geological map redrafted after Kreuss (2014) showing the investigated area between Esslingalm and Stumpfmauer peak in the Königsberg syncline with the location of the measured stratigraphic logs (redrafted after the GEOFAST Geologische Bundesanstalt 1:50,000, 100 – Hieflau compiled by Kreuss 2014)

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The continuity of the Norian–Lower Jurassic succession cropping out in the NCA provides optimal conditions for the investigation of the sedimentary responses of shallow-water settings to some of the most significant environmental, climatic and tectonic changes affecting the Upper Triassic–Lower Jurassic stratigraphic record. Despite several studies performed on the Eiberg Basin in the western NCA (Hillebrandt et al. 2013), and on the Eiberg Basin southern margins (Upper Rhaetian Limestone; Stanton and Flügel 1989, 1995; Satterley et al. 1994; Bernecker et al. 1999; Tomašových 2006; Rizzi et al. 2020), shallow-water carbonate facies of the Kössen Fm. and Upper Rhaetian Limestone (time-equivalent to the Eiberg Basin), were not investigated in detail in the eastern NCA. To improve the knowledge on NCA stratigraphy and sedimentary evolution, the succession in the Stumpfmauer area (central eastern Austria; Fig. 2) was investigated for detailed facies characterisation and compared with other palaeogeographic domains of Western Tethys.

Geological setting of the NCA

The NCA (Fig. 2A) are a ~ 500 km long WSW–ENE-striking fold and thrust belt belonging to the Austroalpine domain (Tollmann 1976; Ratschbacher et al. 1989, 1991; Gawlick et al. 1999; Mandl 1999, 2000; Frisch et al. 2000; Frisch and Gawlick 2003; Schmid et al. 2004). The Triassic Austroalpine passive margin faced the Neo-Tethys to the E–SE (with ophiolite obduction in the Middle Jurassic; Gawlick et al. 2008). From the early–middle Jurassic, the Austroalpine became separated from Europe by the opening of the Penninic Ocean to the N–W (Gawlick and Missoni 2019). In the NCA, an Upper Permian to Eocene sedimentary succession is exposed, with the Triassic shallow-water carbonates representing the thickest deposits (Tollmann 1965, 1976, 1985; Mandl 2000; Krystyn et al. 2005). In this study, following Gawlick et al. (1999), the classical tectonic subdivision of the complex internal structure of the NCA in a lower Bavaric, intermediate Tyrolic and an upper Juvavic nappe group is used descriptively, without any structural significance of these units.

Upper Triassic–Lower Jurassic stratigraphy of the NCA

The Norian succession consists of thousands of square kilometres wide and more than 1000 m thick inner platform facies (Figs. 1B, C, 2B), pervasively early dolomitized, known as Hauptdolomit (Tollmann 1965, 1976, 1985; Fruth and Scherreicks 1982, 1984). This unit, with different lithostratigraphic names and some differences in the stratigraphic range, extends to the Western Carpathians, Transdanubian Range, Southern Alps, Dinarides and Southern Apennines (Iannace and Frisia 1994; Buckovic et al. 2001; Vlahović et al. 2005; Berra et al. 2010; Caggiati et al. 2018; Héja et al. 2018; Haas et al. 2022). Landward, the NCA Hauptdolomit interfingered with the Keuper shallow-marine hypersaline environments, with carbonate, siliciclastic and evaporite deposits. Basinward, the Hauptdolomit was adjacent to lagoonal subtidal–peritidal cyclic strata (Lofer cyclothems of the Dachstein Limestone; Fischer 1964; Enos and Samankassou 1998; Missoni et al. 2005), passing to the Dachstein Reef shelf margin (Fig. 1C). The Dachstein Reef (Flügel 2002; Bernecker 2005) faced the Hallstatt outer shelf of the Neo-Tethys Ocean (Matzner 1986; Kozur 1991; Gawlick et al. 1999; Gawlick and Böhm 2000; Köppen and Carter 2000). The Hauptdolomit is overlain by a well-bedded, 10–400 m thick, only partly dolomitized, carbonate unit, labelled as Plattenkalk (Steiner 1965a, b; Czurda and Nicklas 1970; Golebiowski 1989). Fruth and Scherreiks (1982, 1984) considered the Plattenkalk as part of the Hauptdolomit, representing its uppermost transitional calcareous portion.

Terrigenous input affected the carbonate shelf during the latest Norian–Rhaetian time with the deposition of the Kössen Fm., consisting of the Hochalm and the Eiberg members (Kuss 1983; Golebiowski 1989, 1990; Rizzi et al. 2020). The Hochalm Mb. represents an upper Norian–lower Rhaetian shallow-water succession, which was divided in four units by Golebiowski (1989). Units 1 and 2 (Lumachellen realm) consist of shallowing-upward cyclothems similar to those in the Hauptdolomit and Dachstein Limestone, at times capped by marlstone, indicative of an intertidal to open subtidal shelf. Unit 2 facies are similar to Unit 1 but indicative of more open marine conditions. The overlying Unit 3 is dominantly siliciclastic with marlstone and claystone alternating with metre-thick calcareous beds. Unit 3 documents a transgressive event at regional scale, corresponding to the maximum transgression of the Kössen Fm. onto the margin of the Dachstein Limestone shelf in the south, close to the Norian–Rhaetian boundary (Golebiowski 1989; Satterley 1996a, b). Unit 4 of the Hochalm Mb. is a massive, 10–20 m thick, laterally continuous unit rich in corals, labelled as Hauptlithodendronkalk (Suess and Mojsisovics 1868), Lithodendronkalk (Schlager and Schöllnberger 1974; Golebiowski 1989), or Korallenkalke (Kuss 1983) traceable for about 300 km across an E–W transect in the NCA (Golebiowski 1990). The overlying upper Rhaetian Eiberg Mb. represents deposition in an intraplatform basin of estimated water depth up to 150–300 m (Golebiowski 1990; Kaufmann 2009; Mette et al. 2012; Krystyn et al. 2005; Hillebrandt et al. 2013). The Eiberg Mb. is subdivided into 4 units, consisting of well-bedded bioclastic limestone rich in echinoderm debris passing upward to alternating calcareous mudstone and marlstone with Zoophycus burrows, documenting a deepening trend (Golebiowski 1989; Mette et al. 2012, 2016). The Eiberg Basin was lateral to shallow-marine carbonates (Oberrhätkalk/Upper Rhaetian Limestone; Figs. 1C, 2B) overlying the coral-rich Unit 4 of the Hochalm Mb. (Golebiowski 1990; Wegerer and Gawlick 1999; Bernecker 2005; Rizzi et al. 2020). The southern margin of the Eiberg Basin at the Steinplatte was interpreted as a distally steepened carbonate ramp formed by the deposition of autochthonous biogenic sediment (massive mound facies with bioclastic sand and shell coquinas) on an antecedent homoclinal ramp (Stanton and Flügel 1995; Flügel 2002), laterally adjacent to the Dachstein Limestone shelf (Kaufmann 2009).

The Triassic–Jurassic transition was affected by a sea-level fall followed by a long-term sea-level rise during the Hettangian (Kaufmann 2009; McRoberts et al. 2012), with the drowning of the Dachstein shelf (Gawlick et al. 2009; Gawlick and Missoni 2019). The early Jurassic extensional tectonics, leading to the opening of the Penninic Ocean, produced half-graben basins and structural highs (Bernoulli and Jenkyns 1974; Eberli 1988; Manatschal and Bernoulli 1999) with condensed successions accumulated on footwall highs (i.e. Kalksburg Fm., Adnet Fm., Hierlatz Limestone Mb., Allgäu Fm.) between the Hettangian and early Toarcian, followed by Middle–Upper Jurassic pelagic deposits (Ruhpolding Radiolarite Group; upper Bajocian–lower Tithonian; Eberli 1988; Böhm et al. 1995; Ebli 1997; Gawlick et al. 2009).

Stratigraphy of the study area

The study area between the Stumpfmauer and Esslingalm is part of the Königsberg syncline (Fig. 2; Mandl 2000; Schnabel et al. 2002; Strauss et al. 2020). Steiner (1965a, b, 1967) identified the following units above the Hauptdolomit, from base to top: (1) 100 m of partly dolomitized limestone beds, attributed to the Plattenkalk (uppermost Norian); (2) 30 m of marlstone alternating with highly fossiliferous limestone, labelled as Mergel- und fossilreiche Kössener Schichten (Kössen Beds, Rhaetian); (3) 60 m of well-bedded limestone with corals and marlstone (Kössener Schichten, Hauptlithodendronkalk, Mergellagen); (4) 2 m of crinoid-rich limestone (Krinoidenkalk marker bed, upper Rhaetian); (5) 30 m of oolitic limestone labelled by Steiner (1967) as Oberrhätkalk (heller, dickbankiger Oberrhät Oolithkalk, also reported as Pseudoolithkalk). According to Steiner (1967), in the study area, the Oberrhätkalk/Upper Rhaetian Limestone consists of micrite coated grains, aggregate grains, peloidal and ooidal grainstone facies. Nevertheless, the Upper Rhaetian Limestone in the southern margin of the Eiberg Basin includes coral and calcareous sponge reefs, reef mounds and bioclastic facies (Bernecker 2005; Krystyn et al. 2005; Kaufmann 2009). The Kreuss (2014) GEOFAST geological map (Fig. 2C) confirms the mapping proposed by Steiner (1967) and does not provide a nomenclature of the Lower Jurassic lithostratigraphic units.

Methods

The Norian–Lower Jurassic succession was investigated from the Esslingalm area to the Stumpfmauer peak in the Königsberg syncline (Figs. 2C, 3). Six stratigraphic logs (Figs. 4, 5) were measured: Log EA (103 m thick), Log EC (31 m thick), Log EG (54.7 m thick), Log EL (34.5 m thick), Log ED–EE (117.9 m thick) and Log EI (129.4 m thick). More than 330 thin sections were analysed through standard petrographic analysis. Staining with alizarin red and potassium ferricyanide (Dickson 1966) was performed to identify the presence of dolomite and ferroan calcite. Detailed information about sample location is reported in the Online Supplementary Information.

Fig. 3
figure 3

A Panoramic view of the studied succession at Tanzboden, SW of the Stumpfmauer peak (see Fig. 2C for location), with yellow dashed lines marking the boundaries between the distinguished sedimentary units. B Outcrop photo showing the boundary between Unit B marlstone/claystone and the overlying coral boundstone of Unit C in Log EC at 3.55 m. C Outcrop photo showing the boundary between Unit E and the overlying Unit F in Log EI at 57 m with different bedding attitude suggesting an angular unconformity. D Outcrop photo of the upper part of Log EI showing the boundary between Units F and G at 95.10 m in Log EI. Legend and key of the stratigraphic logs reported in Figs. 4 and 5

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Fig. 4
figure 4figure 4

Stratigraphic logs EA, EG, EC and EL measured in the Esslingalm area (see Fig. 2C for location) showing the superimposed lithofacies types grouped in the sedimentary units A, B, C, D and E. Legend for Figs. 4 and 5 is reported in a separate page

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Fig. 5
figure 5

Stratigraphic logs ED–EE and EI measured in the Esslingalm area (see Fig. 2C for location) showing the superimposed lithofacies types grouped in sedimentary units C, D, E, F and G. Legend for Figs. 4 and 5 is reported in a separate page

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Results

The logged succession (Figs. 3, 4, 5) consists of 32 lithofacies types, labelled from F1 to F32 (Table 1). Associations of these lithofacies compose seven vertically superimposed sedimentary units, labelled from base to top as Units A–G (Table 2), spanning the upper Norian to lower Jurassic. The investigated sedimentary succession overlies hundreds of metres of massive to decimetre-thick beds of replacive fabric-retentive to destructive dolomite (Hauptdolomit) and partially dolomitized (Plattenkalk) peritidal inner shelf carbonates (Fig. 2C).

Table 1 Descriptions of the lithofacies from F1 to F32 identified in the studied succession
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Table 2 Sedimentary units from A to G and lithofacies associations identified in the study area from upper Norian to lower Jurassic with the interpreted depositional environments
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Unit A

Unit A includes lithofacies from F1 to F10 and F20. Bioturbated calci-mudstone with rare peloids and skeletal fragments (F1; Fig. 6A) can occur replaced by dolomicrite to anhedral non-planar dolomicrosparite (F1D), at the base of log EA (Fig. 4). Skeletal wackestone to packstone (F2), sometimes dolomitized (F2D), contains bivalves, gastropods, brachiopods, aulotortid foraminifera and reworked lithoclasts (Fig. 6B). Wackestone to packstone beds with ostracods (F3) are associated with centimetre-thick claystone intervals (Fig. 6C). Peloidal calci-mudstone/wackestone to packstone with fenestrae (F4) and laminated stromatolite boundstone (F5) alternate and occur capped by erosional surfaces (Fig. 6D–F). Lithofacies F6 represents skeletal wackestone/packstone to floatstone/rudstone with brachiopods and bivalves (including decimetre-size megalodontids), gastropods and aulotortid foraminifera (Fig. 6G). The label F7 is used to address all the fine-grained siliciclastic deposits (claystone, marlstone, argillaceous mudstone) forming millimetre, decimetre to metre-scale beds (Fig. 3B). Skeletal peloidal packstone (F8) includes bivalves, gastropods, foraminifera (aulotortids, duostominids, textulariids, Triasina hantkeni), and dasyclad algae (Fig. 6H). Bioturbated packstone with moulds of ooids with peloids as nuclei characterises lithofacies F9 (Fig. 7A). Grainstone beds with isopachous rims of fibrous marine cement (F10) contain micrite coated grains, radial ooids, aggregate grains, intraclasts, foraminifera (Aulotortus sp., Triasina hantkeni) and peloids (Fig. 7B). Unit A includes also beds of packstone/rudstone with reworked bioclasts, lithoclasts and intraclasts of lithofacies F1, F2, F4 and F5, overlying erosional surfaces (F20; Fig. 6D).

Fig. 6
figure 6

Photomicrographs and outcrop photos of lithofacies F1–F8 from Unit A. A Burrowed calci-mudstone with rare peloids and skeletal fragments showing claystone input and undetermined recrystallized bioclastic debris (F1; sample EA0.02 at 0.02 m in Log EA). B Skeletal wackestone to packstone with biomoulds of aulotortid benthic foraminifera, bivalves and carbonate lithoclasts (F2; sample EA1.2 at 1.2 m in Log EA). C Marlstone/claystone interbedded with ostracod wackestone/packstone (F3; sample EA4.3 at 4.3 m in Log EA). D Erosional karstic surface at the top of F4 overlain by F1 calci-mudstone in log EA at 18.62 m. E Peloidal mudstone/wackestone with fenestrae (F4; sample EA19.9 at 19.9 m in Log EA). F Laminated stromatolite boundstone (F5; sample EA2.25 at 2.25 m in Log EA). G Skeletal packstone to floatstone/rudstone with bivalves (F6; sample EA29.6 at 29.6 m in Log EA). H Skeletal peloidal packstone with foraminifera and dasyclad algae (white arrow) (F8; sample EA27.35 at 27.25 m in Log EA)

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Fig. 7
figure 7

Photomicrographs of lithofacies F9–F10 from Unit A and F11–F12 from Unit B. A Packstone with moulds of superficial ooids with peloids as nuclei and burrows (F9; sample EA 11.2 at 11.2 m in Log EA). B Coated grain peloidal bioclastic grainstone with isopachous fibrous marine cement, bivalves, gastropods, radial ooids and intraclasts (F10; sample EA12.2 at 12.1 m in Log EA). C Nodular skeletal floatstone/rudstone with bivalves and echinoderms associated with claystone (F11; sample EA115.3 at 85.1 m in Log EA). D Boundstone to wackestone/floatstone with phaceloid corals associated with claystone forming solution seams due to compaction and pressure solution (F12; sample EA65.9 at 65.9 m in Log EA). E Corals are embedded in wackestone to packstone with bivalves, gastropods, brachiopods, rare ammonoids and siliceous sponges (F12; sample EA120.75 at 90.5 m in Log EA). F Phaceloid corals encrusted by serpulids surrounded by wackestone with brachiopod and bivalve fragments (F12; sample EC0.3 at 0.3 m in Log EC). G Coral colony in the lower part surrounded by wackestone with siliceous sponge (F12; sample K0.5 Tanzboden). H Skeletal wackestone to floatstone surrounding the corals with Bacinella-Lithocodium encrusting and infilling corals, calcareous sponge and bivalve bioclastic debris (F12; sample EC4.1 at 4.1 m in Log EC)

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Unit A (38–55 m thick) is organised in vertically stacked, metre-scale (2–10 m thick) lithofacies packages (Fig. 4) with basal F1, F2, F3, F6, F8 and top F4, F5, F9, F10 separated by erosional surfaces, few millimetres to centimetres thick claystone (F7) and lithoclastic beds (F20; Fig. 6D). The lower boundary of Unit A with the Plattenkalk is transitional and placed at the first metre-scale intercalation of claystone, associated with the gradual disappearance of dolomitized beds, whereas the upper boundary with Unit B is sharp and marked by the onset of the ~ 50 m thick claystone/marlstone succession (F7).

Unit B

Unit B (Figs. 3A, B, 4) consists of brown to black claystone and marlstone (F7) alternating with 0.5–1 m thick calcareous beds (F11, F12). Lithofacies F11 consists of nodular beds of bioturbated skeletal wackestone/floatstone to packstone/rudstone with common bivalves, brachiopods, gastropods and echinoderms (Fig. 7C). Phaceloid coral boundstone to floatstone (F12) forms decimetre to metre-thick beds. Retiophyllia and Thecosmilia-type corals are sometimes encrusted by Bacinella-Lithocodium or serpulids and occur in marly skeletal wackestone/packstone with crinoids, brachiopods, rare calcareous and siliceous sponges and ammonoids (Figs. 7D, H, 8A).

Fig. 8
figure 8

Photomicrographs of lithofacies F12–F13 from Unit B and Unit C and F14–F17 from Unit D. A Skeletal peloidal wackestone to packstone with calcareous sponges, brachiopods, bivalves and Lithocodium surrounding phaceloid corals (F12; sample EC3.8 at 3.8 m in Log EC). B Outcrop photo of a phaceloid coral colony (F13; Log EA at 94.0 m). C Corals are embedded in skeletal peloidal wackestone/packstone with brachiopods and are encrusted by Bacinella-Lithocodium (F13; sample EC6.8 at 6.8 m in Log EC). D Skeletal packstone with oncoids, crinoids and micrite coated Triasina hantkeni (F14; sample EA133 at 102.8 m in Log EA). E Coated grain grainstone with Triasina hantkeni, siliceous and calcareous sponges and coral fragments (F15; sample EL4.1 at 4.1 m in Log EL). F Coated grain grainstone with Triasina hantkeni, calcareous sponges and meniscus and pendant vadose meteoric cement indicative of subaerial exposure and meteoric diagenesis (F15; sample EL4.1 at 4.1 m in Log EL). G Bioturbated peloidal coated grain packstone (F16; sample ED21.8 at 32.80 m in Log ED–EE). H Peloidal packstone with micritic intraclasts (F17; sample ED9.8 at 20.80 m in Log ED–EE)

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Unit B is approximately 50 m thick but tectonic displacement prevents a reliable estimate of the thickness. The lower and upper boundaries are sharp (Fig. 3B).

Unit C

Unit C consists of metre-scale massive boundstone and floatstone with corals (F12, F13) associated with lithofacies F8, F11 and F20. Phaceloid corals form decimetre- to metre-scale colonies (Fig. 8B). Corallites are often encrusted by Bacinella-Lithocodium and surrounded by wackestone/packstone with bivalves, gastropods, brachiopods, calcareous and siliceous sponges (Fig. 8B, C); rare chert nodules are present.

Unit C (8–11 m thick) basal and top boundaries are sharp (Fig. 3B). Siliciclastic input is rare and occurs only at the base.

Unit D

Unit D consists of lithofacies F1, F2, from F6 to F20, and F22 organised in 2–5 m thick stacked lithofacies packages separated by metre-thick intervals of claystone/marlstone (F7; Fig. 5). Unit D distinctive lithofacies are: (a) packstone–wackestone to floatstone with oncoids and abundant aulotortid and Triasina hantkeni foraminifera (F14; Fig. 8D); (b) coated grain grainstone with cross-lamination, micrite coated Triasina hantkeni, molluscs and rare calcareous and siliceous sponges and corals with isopachous fibrous marine and meniscus and pendant cement (F15; Fig. 8E, F); and (c) bioturbated packstone with micrite coated grains, aggregate grains and peloids (F16; Fig. 8G). Rare packstone with peloids and micritic intraclasts (F17; Fig. 8H) forms decimetre-thick irregular beds. Bacinella-Lithocodium boundstone (F18) is characterised by clotted peloidal micrite, rare corals, siliceous and calcareous sponges and millimetre-wide, irregular-shaped voids filled by blocky sparite cement (Fig. 9A, B). Grainstone to rarely packstone with abundant aggregate grains contains micritized ooids and coated grains with micrite envelopes, bivalves, gastropods, Triasina hantkeni and Parafavreina (F19; Fig. 9C, D). Beds of packstone/rudstone with reworked intraclasts and lithoclasts overlie erosional surfaces (F20; Fig. 9E). Decimetre-thick beds of cross-laminated coated grain ooidal grainstone (F22) also occur.

Fig. 9
figure 9

Photomicrographs of lithofacies F18, F19, F20 from Unit D and F19 and F21 from Unit E. A Bacinella-Lithocodium boundstone with clotted peloidal micrite microbialites (F18; sample ED21.5 at 32.50 m in Log ED–EE). B Bacinella-Lithocodium boundstone with clotted peloidal micrite and rare calcareous sponges (F18; sample ED52.2 at 43.20 m in Log ED–EE). C Grainstone with aggregate grains, micritized ooids and micrite coated Aulotortus sinousus with early marine fibrous cement (F19 in Unit D; sample ED86.5 at 77.50 m in Log ED–EE). D Grainstone with aggregate grains, micrite coated grains and Parafavreina faecal pellets with marine isopachous rims of fibrous cement (F19 in Unit E; sample EI40.2 at 40.20 m in Log EI). E Lithoclastic intraclastic packstone/rudstone (F20) above an erosional surface overlying lithofacies F1 and F2 reworking Triasina hantkeni (F20; sample ED45 at 38.5 m in Log ED–EE). F Outcrop photo of lithoclastic crinoidal ooidal rudstone with centimetre-size lithoclasts (F21; sample EI0.1. at 0.10 m at the base of Log EI). G Photomicrograph of lithoclastic rudstone with lithoclasts of F22 ooidal grainstone to packstone affected by meteoric diagenesis with vadose meniscus and pendant cement and crinoids (F21; sample EI0.1 at 0.10 m in Log EI). H Rudstone/grainstone with lithoclasts, peloids, crinoids, silicified bioclasts, ooids and quartz grains (F21; sample EI1 at 1.0 m in Log EI)

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Unit D is 80–110 m thick with the lower boundary with Unit C marked by a sharp transition from massive coral boundstone (F13) to several metres-thick oncoidal skeletal packstone/floatstone (F14). The upper boundary with Unit E is characterised by an erosional surface at the top of Unit D, overlying both coated grain grainstone with Triasina hantkeni (F15, Log EL; Fig. 4) and boundstone to floatstone with phaceloid corals associated with claystone (F12, Log ED; Fig. 5) with irregular dissolution vugs, vadose pendant and meniscus cement and red iron oxide stained micritic crusts (Fig. 8F).

Unit E

Unit E constitutes a prominent ridge, forming the crest of the Stumpfmauer (Fig. 3A). This unit (57 m thick) is subdivided into a lower and upper part. The lower part (13 m thick) is characterised by packstone/grainstone to rudstone beds (up to 1 m thick) with centimetre-size rounded lithoclasts, partially silicified, radial ooids, micrite coated grains, peloids, abundant crinoids and bivalves (F21; Figs. 9F–H, 10A). Lithoclasts are mostly ooidal grainstone (F22) with isopachous fibrous marine cement followed by meniscus and pendant cement. The F21 basal bed is overlain by claystone (F7) and fine-grained bioturbated peloidal packstone with siliceous sponge spicules (F23; Fig. 10B, C). The upper part of Unit E (45 m thick) consists of grainstone with aggregate grains (F19) and cross-bedded peloidal coated grain ooidal grainstone with bivalves and sparse quartz grains (F22). F22 can be divided in F22A, F22B and F22C, based on the dominant grain types. F22A is a fine- and medium-grained grainstone dominated by peloids (Fig. 10D); F22B includes peloids, micrite coated grains and radial ooids (Fig. 10E, F). F22C is dominated by radial ooids with isopachous fibrous cement, quartz grains and bivalves (Fig. 10G). Lithofacies F19 and F22 occur both in Units D and E but in Unit E, they lack aulotortid foraminifera.

Fig. 10
figure 10

Photomicrographs of lithofacies F21, F22 and F23 from Unit E. A Grainstone to packstone with radial ooids, peloids, crinoids and quartz grains with vadose meniscus cement followed by blocky sparite (F21; sample EI0.1 at 0.10 m in Log EI). B Bioturbated peloidal packstone with bivalves and siliceous sponge spicules (F23; sample EI5.4 at 5.40 m in Log EI). C Peloidal packstone with siliceous sponge spicules (F23; sample EL11 at 11.15 m in Log EL). D Peloidal grainstone with micritized ooids (F22A; sample EI57 at 56.5 m in Log EI). E, F Mixed coated grain ooidal peloidal grainstone with disarticulated and isoriented bivalve shells (F22B; sample EI52.9 at 52.9 m in Log EI). G Ooidal grainstone with radial ooids, quartz grains, bivalve shells and isopachous rims of marine fibrous cement in crossed polarizers showing the presence of detrital quartz grains (F22C; sample EI21.6 at 18.0 m in Log EI). H Peloidal grainstone with cement-filled voids (intertidal fenestrae/keystone vugs), at the top of Unit E made of bedded peloidal ooidal grainstone with planar cross-lamination (F22A; sample EI57B at 57.0 m in Log EI)

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The boundary with the underlying Unit D shows an abrupt lithofacies change, coinciding with an erosional surface (F15 in Log EL in Fig. 4, F12 and F7 in log ED in Fig. 5). The upper boundary with Unit F is sharp and marked by a rapid lithofacies change between cross-bedded peloidal ooidal grainstone with millimetre-size fenestral voids below (F22A; Fig. 10H) and dark grey bivalve wackestone/packstone to rudstone/floatstone above (F24; Figs. 3C, 5).

Unit F

Unit F (39 m thick; Fig. 5) is subdivided into two parts based on lithofacies associations. The lower part (7 m thick) consists of dark grey bioturbated bivalve wackestone/packstone to rudstone/floatstone with rare dasyclad algae (F24; Fig. 11A, B) and ostracod wackestone/packstone (F25; Fig. 11C). The upper part (32 m thick) is characterised by peloidal grainstone to packstone (F26) with micrite coated grains, oncoids, bivalves, gastropods, Thaumatoporella parvovesiculifera, Cayeuxia, and benthic foraminifera (textularids, possible Siphovalvulina, lituolids, Evertyciclammina praevirguliana; Fig. 11D–G). F26 is alternating with metre-thick massive microbial boundstone (F27; Figs. 11H, 12A) or oncoidal packstone/rudstone (F28; Fig. 12B), with evidence of dissolution vugs, pendant and meniscus cement. F27 microbial boundstone consists of leiolitic and clotted peloidal micrite with Cayeuxia, Thaumatoporella parvovesiculifera and millimetre-size cavities filled by peloidal micrite, isopachous rims of marine fibrous cement and blocky sparite (Figs. 11H, 12A).

Fig. 11
figure 11

Photomicrographs of lithofacies F24, F25, F26 and F27 from Unit F. A, B Bioturbated skeletal packstone to floatstone dominated by bivalves with rare dasyclad algae (F24; sample EI58.5 at 58.5 m in Log EI). C Bioturbated packstone to wackestone with ostracods (F25; sample EI63.1 at 63.1 m in Log EI). D Peloidal grainstone to packstone with Thaumatoporella parvovesiculifera, micrite coated grains and lituolid benthic foraminifera (F26; sample EI68.7 at 71.3 m in Log EI). E Peloidal grainstone to packstone with possible lituolid foraminifer Evertyciclammina praevirguliana and vadose meteoric meniscus cement (F26; sample EI68.7 at 71.3 m in Log EI). F Lithofacies F26 at the top of Unit F showing lithoclasts of F24 bivalve wackestone/floatstone with borings, erosional features and meniscus cement related to reworking of a subaerially exposed substrate (F26; sample EI88.2 at 90.8 m in Log EI). G Peloidal grainstone to packstone with coated grains with vadose meniscus cement related to subaerial exposure followed by early marine isopachous fibrous cement (F26; sample EI86.7 at 89.3 m in Log EI). H Microbial boundstone with clotted peloidal and leiolitic micrite with Cayeuxia (F27; sample EI71 at 73.6 m in Log EI)

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Fig. 12
figure 12

Photomicrographs of lithofacies F27 and F28 from Unit F and outcrop photo and photomicrographs of lithofacies F29, F30, F31 and F32 from Unit G. A Microbial boundstone with primary micrite-sustained cavities filled by marine fibrous isopachous and burial blocky sparite cement (F27; sample EI83.2 at 85.8 m in Log EI). B Packstone to floatstone/rudstone with oncoids at the top pf Unit F (F28; sample EI91.7 at 94.2 m in Log EI). C Siliceous sponge spicule packstone with chert (F29; sample EI92.8 at 95.4 m in Log EI). D Coated grain peloidal grainstone to sandstone with detrital monocrystalline and polycrystalline quartz grains (F30; sample EI93 at 96.2 m in Log EI). E Bioturbated skeletal peloidal wackestone with bivalves, gastropods and Aeolisaccus (F31; sample EI101.2 at 103.8 m in Log EI). F Cross-laminated peloidal coated grain grainstone with bidirectional lamination, crinoids and chert nodules (F32; sample EI117 at 117.0 m in Log EI). G Outcrop photo of lithofacies F32 cross-laminated peloidal coated grain grainstone with crinoids and chert showing bidirectional cross-lamination. H Peloidal coated grain grainstone with crinoids and detrital quartz (F32; sample EI117 at 117.0 m in Log EI)

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Unit F overlies Unit E cross-bedded grainstone with fenestrae (F22A) with a sharp contact, possibly associated with an angular unconformity (Fig. 3C). The upper boundary with Unit G is also sharp and marked by F26 and F28 with centimetre-size black lithoclasts sharply overlain by the chert and sponge spicule packstone (F29; Fig. 12C) belonging to Unit G (Fig. 3D).

Unit G

Unit G is composed of lithofacies F29, F30, F31 and F32 with the dominance of F32 (Fig. 5). Red to dark grey, 20 cm thick siliceous sponge spicule packstone are sometimes completely silicified (F29; Fig. 12C) and overlain by packstone/grainstone with abundant detrital quartz grains to sandstone, echinoderm debris, micrite coated grains, angular lithoclasts and peloids (F30; Fig. 12D). Lithofacies F31 consists of massive to metre-scale beds of bioturbated skeletal wackestone with bivalves, gastropods, ostracods, peloids, benthic foraminifera (possible Siphovalvulina, Evertyciclammina praevirguliana), Thaumatoporella parvovesiculifera and Aeolisaccus (Fig. 12E). Lithofacies F32 is characterised by 10 to 40 cm thick cross-bedded and cross-laminated (bidirectional) peloidal, micrite coated grain grainstone with abundant crinoids, decimetre-size chert nodules, quartz grains and rare glaucony (Fig. 12F–H).

Unit G is 34 m thick; its lower boundary is represented by the first sponge spicule packstone with chert (F29; Fig. 3D). The upper boundary is marked by the sharp occurrence of red colour crinoidal rudstone to packstone (Fig. 2B, C).

Interpretation of sedimentary units and depositional models

The nearly 350 m thick sedimentary succession from Units A to G (Fig. 13) recorded the evolution of the depositional environments in a shallow carbonate shelf or low-angle ramp system (Figs. 14, 15), located north of the intraplatform Eiberg Basin, across the Triassic to Jurassic boundary. The stratigraphic succession from Unit A to G includes the Hochalm Mb. of the Kössen Fm., Upper Rhaetian Limestone, Schattwald Beds, shallow-water strata transitional to Lower Jurassic and the Hettangian–Sinemurian Kalksburg Fm. (Figs. 2, 13).

Fig. 13
figure 13

Correlation panel showing the relationships between the different stratigraphic units identified in the study area. The transition from Triassic to Jurassic is tentatively located in the lower part of Unit E  above the subaerial exposure at the top of Unit D and the transgressive lag with carbonate lithoclasts, detrital quartz and crinoids followed by F23 peloidal packstone with sponge spicules. For the log details refer to Figs. 4 and 5; for the location of the logs refer to Fig. 2

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Fig. 14
figure 14

Simplified diagram showing the depositional environments and lithofacies distribution during the vertical evolution of the succession from Unit A to D based on the stratigraphic logs measured and reported in Figs. 4 and 5

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Fig. 15
figure 15

Simplified diagram showing the depositional environments and lithofacies distribution during the vertical evolution of the succession from Unit E to G based on the stratigraphic logs measured and reported in Figs. 4 and 5

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Unit A peritidal cyclothems

Unit A is organised in metre-scale shallowing-upward cyclothems, showing in the lower part subtidal restricted (F1, F2, F3) to open marine (F6, F8), low-energy environments passing upward to intertidal and supratidal lithofacies (F4, F5) or high-energy shoal grainstone deposits (F9, F10; Fig. 14). Cyclothems are bounded by erosional surfaces with fine siliciclastic input (F7), overlain by transgressive lags reworking the lithoclasts of the underlying lithofacies (F20). Fragmented skeletal biota (bivalves, brachiopods, corals) testify for marine currents and/or storm events in subtidal open marine environments (F6).

Unit A asymmetric peritidal cyclothems are similar in terms of internal facies organisation to the cycles in the Dachstein Limestone (Lofer facies), described by Fischer (1964) as deepening upward cycles. The Dachstein Limestone Lofer cycles have been investigated by several authors concluding that these cyclothems are the result of the interplay of autocyclicity, tectonic activity, sea-level oscillations and climatic variations (Satterly and Brandner 1995; Satterley 1996a, b; Enos and Samankassou 1998; Samankassou and Enos 2019). Unit A cyclothems differ from those of the Dachstein Limestone for the presence of millimetre to decimetre-thick F7 claystone/marlstone layers, overlying the erosional cycle boundary (Fig. 6D). The predominance of cyclothems with capping intertidal-supratidal or high-energy shoal lithofacies suggests a progradational trend at the scale of the high-frequency accommodation oscillations, as also suggested by Satterley (1996a, b) in the basal part of the Dachstein Limestone. Nevertheless, the whole Unit A records an upward trend towards more open marine conditions, with the upward decrease in occurrence and thickness of the intertidal–supratidal F4 and F5 lithofacies and the increase in thickness of the subtidal open marine F6. The transitional lower boundary between the Plattenkalk and Unit A with the gradual decrease of dolomitized beds might reflect a climate change from arid to more humid conditions. This is supported by the siliciclastic input and the reduced efficiency of the early dolomitization processes, similarly to what is documented in the Southern Alps at the top of the Norian Dolomia Principale (Berra et al. 2010).

The occurrence of Triasina hantkeni in Unit A confirms at least a late Norian age because of its stratigraphic distribution as late Norian–Rhaetian (Zaninetti et al. 1992; Maurer et al. 2008). On the basis of lithofacies character and stratigraphic position, Unit A corresponds to Units 1 and 2 of the Hochalm Mb. of the Kössen Fm. by Golebiowski (1990). Units 1 and 2 accumulated in a shallow-marine, restricted peritidal setting evolving upward to open-shelf conditions, affected by episodic terrigenous input and storm events (Kuss 1983; Golebiowski 1990), as observed in Unit A. In the Hochalm section, Units 1 and 2 are approximately 100 m thick and late Norian in age (Golebiowski 1990).

Unit B claystone/marlstone with fossiliferous beds

Unit B represents the thickest claystone and marlstone (F7) succession alternating with metre-scale fossiliferous packstone/rudstone to boundstone (Figs. 13, 14). F7 records the siliciclastic input in a low-energy subtidal environment with high turbidity, below storm wave base. The fossiliferous beds F11, rich in bivalves and brachiopods, might represent low to moderate-energy conditions below the fair-weather wave base and oscillating around the storm wave base (cf. Tomašových 2004, 2006). The F12 beds with phaceloid corals, calcareous and siliceous sponges encrusted by Bacinella-Lithocodium must have accumulated in shallower photic conditions, above storm wave base.

Unit B records a significant fine-grained siliciclastic input on the carbonate shelf, which could be related to a global climate change (Kaufmann 2009) responsible for a shift of climate belts during a cooling interval (Berra et al. 2010). Unit B corresponds to Golebiowski (1990) Unit 3 of the Hochalm Mb. of the Kössen Fm. that was interpreted as accumulated within an open subtidal shelf with terrigenous input in water depth > 20 m. This unit reflects the maximum extension of the Kössen Fm. towards the Dachstein Limestone shelf (Golebiowski 1989; Satterley 1996b). In the reference section, Unit 3 is 30 m thick and latest Norian–early Rhaetian in age (Golebiowski 1990), whereas in Rizzi et al. (2020), it is reported as early Rhaetian.

Unit C coral boundstone to floatstone

Unit C records the rapid expansion of phaceloid coral boundstone across the shelf coinciding with a decrease in siliciclastic input with respect to Unit B (Figs. 13, 14). Unit C was deposited in a low-energy environment, as inferred from the abundance of micrite matrix surrounding the corals. The presence of corals, rare dasyclad algae and Bacinella-Lithocodium in F13 suggests photic depths.

Unit C corresponds to a marker bed that can be traced across the NCA (Hauptlithodendronkalk Steiner 1967; Schlager and Schöllnberger 1974; Kuss 1983; Satterley 1996b) and coincides with the lower Rhaetian Unit 4 of the Hochalm Mb. of the Kössen Fm. (Golebiowski 1990).

Unit D subtidal cyclothems with claystone

Unit D sharply overlies Unit C coral boundstone; it is the thickest unit characterised by regular occurrences of metre-scale F7 claystone/marlstone alternating with diverse carbonate lithofacies from F1 to F22 (Figs. 13, 14). Calci-mudstone and bioclastic wackestone (F1, F2) are indicative of restricted low-energy subtidal deposition. Bioturbated packstone with oncoids, micrite coated grains, peloids, benthic foraminifera and microbial boundstone (F14, F16, F17, F18) represent subtidal, low- to moderate-energy, open marine, photic depositional environments as suggested by the occurrence of dasyclad algae (F14) and Bacinella-Lithocodium (F18). High-energy shoals, above effective wave base, are represented by grainstone with micrite coated grains, aggregate grains, micritized and radial ooids (F15, F19, F22A, F22C). Unit D shallowing-upward cyclothems consist of basal metre-scale intervals of claystone/marlstone (F7) overlain by low to moderate-energy bioturbated subtidal, skeletal packstone to wackestone beds (F1, F2, F6, F11–F14, F16–F18) evolving to high-energy coated grain skeletal grainstone (F15, F19, F22A, F22C). Cyclothems are capped by sharp erosional surfaces on subtidal lithofacies with centimetre-scale irregular karstic dissolution vugs overlain by claystone/marlstone (F7) and transgressive deposits reworking eroded lithoclasts (F20) filling the karstic dissolution cavities (Fig. 9E). Unit D is indicative of subtidal settings, periodically affected by subaerial exposure and fine siliciclastic input, but lacking deposition in intertidal and supratidal environments as in Unit A. The absence of intertidal-supratidal lithofacies could be related to non-deposition or erosion. The occurrence of subaerial exposure surfaces at the top of subtidal lithofacies is indicative of sea-level falls, probably related to high-frequency eustatic oscillations controlled by climate or tectonics (Satterley 1996a, b).

In the Eiberg Basin, SW of the study area, the Kössen Fm. strata overlying the coral boundstone bed (Unit 4 of the Hochalm Mb. by Golebiowski 1990; Unit C in this study) correspond to deposition in an intraplatform basin (Eiberg Mb. of the Kössen Fm.; Golebiowski 1990). According to Golebiowski (1990, 1991), the shallow-marine successions resting upon Unit 4 coral boundstone, lateral to the Eiberg Basin, constitute the Oberrhätkalk/Upper Rhaetian Limestone. Hence, following Golebiowski (1990), Unit D in this study overlies Unit C coral boundstone and corresponds to the Upper Rhaetian Limestone, time-equivalent to the Eiberg Mb. and the Steinplatte complex facing the southern margin of the Eiberg Basin (Fig. 1C). Unit D lithofacies are similar to those described as Upper Rhaetian Limestone in the Bavarian Calcareous Alps, rich in Triasina hantkeni and with evidence of vadose meteoric cement (Schott 1983, 1984). In the geological maps by Schnabel et al. (2002) and Kreuss (2014), Unit D is mapped as Kössen Fm. and it is overlain by ooidal grainstone (Unit E in this study) mapped as Oberrhätkalk/Upper Rhaetian Limestone (Figs. 2, 13). Unit D upper boundary displays the evidence of vadose meteoric diagenesis due to subaerial exposure in different locations, at a present-day distance of 0.5 km (Figs. 4, 5, 13), that could be related to the regional sea-level fall associated with the onset of the end-Triassic extinction event (Satterley et al. 1994; Bernecker et al. 1999; Kaufmann 2009; McRoberts et al. 2012). This event was followed by the latest Rhaetian–Hettangian transgression passing to more open marine conditions (Delecat et al. 2011).

Unit E ooidal coated grain peloidal grainstone with basal transgressive lag

The basal part of Unit E with lithoclastic crinoidal ooidal packstone/grainstone to rudstone (F21) reworking clasts of ooidal grainstone affected by vadose meteoric diagenesis (e.g. meniscus, pendant cement, red matrix with iron oxide) represents a transgressive lag overlying an erosional surface at the top of Unit D, suggesting the reflooding of a subaerially exposed, shallow shelf and the presence of a stratigraphic gap between Unit D and E. The overlying claystone/marlstone (F7) and peloidal packstone with sponge spicules (F23) are indicative of low-energy, below storm wave base deposition. The upper part of Unit E consists of cross-bedded peloidal coated grain ooidal grainstone with bivalves, Parafavreina and quartz grains (F22) representing high-energy shoals, above wave base characterised by the first input of sand-grade quartz grains that will become abundant in the overlying Unit G.

The lower part of Unit E (F21, F7, F23) could be interpreted as the transgressive deposition, followed by the progradation of ooidal coated grain peloidal grainstone shoal (F22). The top of Unit E records a shallowing-upward trend to intertidal conditions, as documented by fenestrae in the uppermost peloidal grainstone (F22A; Fig. 10H), just below the contact with the bivalve packstone to rudstone (F24) of Unit F (Figs. 3C, 11A, B). In Unit E, benthic foraminifera as Aulotortus sp. and Triasina hantkeni, common in Unit D lithofacies F14 and F15 and indicative of Rhaetian age, were not identified.

In the Schnabel et al. (2002) and Kreuss (2014) geological maps (Fig. 2), Unit E is mapped as Oberrhätkalk/Upper Rhaetian Limestone, following the attribution by Steiner (1967). Strauss et al. (2020) instead mapped Unit E as Kössen Fm., not distinguishing the Kössen Fm. from the Upper Rhaetian Limestone. Unit E overlies an 80–110 m thick succession of subtidal cyclothems (Unit D) that, in this reconstruction, is attributed to the Upper Rhaetian Limestone. Unit E postdates a laterally extensive, subaerial exposure at the top of Unit D that could correspond to the end-Triassic sea-level fall associated with the extinction event (McRoberts et al. 2012; Hillebrandt et al. 2013) and does not contain any biostratigraphic marker indicative of Rhaetian age (i.e. Aulotortus sinuosus, Triasina hantkeni). Hence, Unit E may represent the Oberrhätkalk/Upper Rhaetian Limestone time-equivalent to the Steinplatte and Adnet platform margin as originally mapped by Steiner (1967) and maintained in recent geological maps (Schnabel et al. 2002; Kreuss 2014; Strauss et al. 2020) but, as presented in this study, it could most likely correspond to a younger shallow-water succession transitional to the lower Jurassic, post-dating the end-Triassic extinction and sea-level fall. This revised stratigraphy would result similar to what described in the western NCA, where the top of the Kössen Fm. is marked by subaerial exposure, overlain by the uppermost Rhaetian Schattwald Beds, followed by the Hettangian Löruns oolite (McRoberts et al. 1997; Felber et al. 2015).

Unit F bivalve-rich, microbialite and oncoidal lithofacies

The low-diversity, low-energy bivalve- and ostracod-rich lithofacies (F24–F25), overlain by microbialite and oncoidal peloidal lithofacies (F26–F28), suggest a stressed environment, scarce in skeletal biota, possibly related to the aftermath of the end-Triassic extinction. Unit F lithofacies represents shallow, low-energy restricted (F24, F25, F27, F28) to moderate-energy (F26) depositional settings within the photic zone. The presence of meniscus cement and reworked lithoclasts in F26 and F28 suggests events of subaerial exposures followed by transgressions. As for Unit E, Unit F is mapped as Upper Rhaetian Limestone in the Schnabel et al. (2002) and Kreuss (2014) geological maps. However, the presence of Aeolisaccus, lituolid foraminifera as Evertyciclammina praevirguliana, Thaumatoporella parvovesiculifera and putative Siphovalvulina supports an early Jurassic age. The stratigraphic data from this study suggest that Unit F may correspond to a shallow-water inner shelf succession, possibly time-equivalent to the lower Jurassic part of the Kendlbach Fm. in other areas of the NCA. Microbialites with siliceous sponges are described in the Hettangian strata overlying the southern margin and slope into the Eiberg Basin in the outcrops in Adnet and Steinplatte (Schöll Fm.; Delecat and Reitner 2005; Delecat et al. 2011).

Unit G cross-laminated coated grain peloidal grainstone with quartz and chert

Unit G starts with sponge spicule packstone with chert (F29), suggesting a deepening with respect to the underlying oncoidal lithofacies F28 of Unit F (with evidence of subaerial exposure at the top) and records a significant input of detrital quartz (F30). The coated grain peloidal grainstone with crinoids, quartz grains and chert (F32) represents a mixed carbonate–siliciclastic open marine shelf affected by bidirectional tidal currents. Cross-laminated coated grainstone beds (F32) are attributed to the Kalksburg Fm. (Hettangian–Sinemurian; Fig. 2B).

The deepening trend documented by Unit G may reflect the onset of the extensional tectonics associated with the opening of the Penninic Ocean, recorded in different Lower Jurassic successions of the NCA (Gawlick et al. 2009). Drowning of the shelf is marked by the overlying red crinoidal rudstone with ammonites and belemnites belonging to the Hierlatz Limestone Member of the Adnet Fm. and the Allgäu Fm. (Figs. 1 C, 15).

Discussion

The lithofacies characterisation and stratigraphic reconstruction of the Upper Triassic–Lower Jurassic succession in the Stumpfmauer study area provide detailed data for comparisons with coeval sedimentary successions in Western Tethys (Fig. 1) and for improving the understanding of the Tethyan depositional settings across the Triassic/Jurassic boundary.

Comparisons across Western Tethys

The investigated shallow-water Norian–Rhaetian to lower Jurassic lithofacies types and the superimposed sedimentary units display similarities with time-equivalent examples in the western NCA (McRoberts et al. 1997), Western Carpathians (Tomašovych 2004), Transdanubian Range (Vörös and Galácz 1998; Héja et al. 2018; Haas et al. 2022), Dinarides (Buckovic et al. 2001), Central Austroalpine (Furrer 1981; Berra and Cirilli 1997) and Southern Alps (Jadoul et al. 2004, 2005; Masetti et al. 2017).

Specifically, in the Western Carpathians, the Rhaetian Fatra Fm. consists of mixed carbonate–siliciclastic deposits with high lateral facies variability (Tomašovych 2004). Superimposed peritidal and shallow subtidal carbonate lithofacies and dark colour skeletal marlstone accumulated in inner-middle ramp to intraplatform basin settings under the influence of storm events (Tomašovych 2004). The Fatra Fm. lithofacies associations are similar to those recognised in the Hochalm Mb. of the Kössen Fm. and described in Units A, B, and C in this study. The abundance of calcareous sponges associated with corals in the Fatra Fm. suggests more stressed and ecologically unstable conditions with respect to the Hauptlithodendronkalk of the NCA (Unit C), likely due to the more landward and restricted palaeogeographic position with respect to the NCA (Tomašovych 2004). The absence of extensive coral patch reefs in the Western Carpathians may reflect water energy, salinity and turbidity unsuitable for corals (Tomašovych 2004).

A striking correspondence seems to exist between the study area and the Lombardy Basin in the Southern Alps (N Italy), where the peritidal early-dolomitized platform interior with fault-controlled intraplatform basins of the Dolomia Principale (Norian; Berra and Jadoul 1996; Berra et al. 2010) is followed by subtidal claystone (Riva di Solto Shales, upper Norian), shallowing-up into cyclic mixed carbonate–siliciclastic ramp (Zu Limestone, Rhaetian; Jadoul et al. 2004). The Riva di Solto Shales and Zu Limestone (together up to 1000 m thick) are time-equivalent to the NCA Kössen Fm. and Upper Rhaetian Limestone, with similar stratigraphic evolution and palaeoenvironmental affinities (Unit B, C, D), although the greater thickness reflects higher subsidence rate in the Lombardy Basin. The Zu Limestone was divided in three members, from base to top, Zu1, Zu2 and Zu3 (Masetti et al. 1989; Lakew 1990; Jadoul et al. 1994, 2004; Galli et al. 2005, 2007; Rigo et al. 2009). Zu1 Member is a cyclical succession of claystone, marlstone and micritic limestone with bivalves. Zu2 Member is a massive limestone unit, up to 25 m thick and laterally continuous for 160 km, consisting of coral patch reefs, bioturbated wackestone and ooidal packstone/grainstone, locally rich in megalodontid bivalves. Zu3 Member is composed of marlstone, marly and micritic limestone organised in asymmetric shallowing-upward cycles, with basal marlstone (10 m thick) passing to peloidal ooidal grainstone or packstone and bioturbated wackestone/packstone with Triasina hantkeni, corals, calcisponges, bryozoans, megalodontid bivalves and dasyclad algae (Lakew 1990; Jadoul et al. 1994; Galli et al. 2007). The top of Zu3 is affected by meteoric diagenesis due to subaerial exposure (Lakew 1990; Jadoul et al. 2005). The Rhaetian Zu2 and Zu3 members match with Unit C and D distinguished in this study, in terms of lithofacies types, benthic foraminifera association and cyclic patterns. The subaerial exposure identified at the top of Unit D can be correlated with the subaerial exposure at the top of Zu3. The Zu3 Member is overlain by the Malanotte Formation (from latest Rhaetian to early Hettangian; Bottini et al. 2016) consisting of bedded marly limestone, with sparse claystone beds with quartz grains and bioturbated bioclastic limestone with thin-shelled bivalves and sponge spicules passing to grainstone–packstone with micritised ooids (Galli et al. 2005, 2007). The Malanotte Fm. resembles the strata in the lower Unit E dominated by peloidal packstone with siliceous sponge spicules (F23). Biostratigraphic and magnetostratigraphic studies located the Triassic/Jurassic boundary in the lower part of the Malanotte Fm. (Galli et al. 2007; Muttoni et al. 2010; Bottini et al. 2016; Zaffani et al. 2018). The overlying Hettangian Albenza Fm. consists of cross-bedded ooidal grainstone passing upward to peloidal packstone and bio-intraclastic grainstone (Galli et al. 2005, 2007; Jadoul and Galli 2008). The Albenza Fm. lithofacies are similar to the upper Unit E dominated by coated grain ooidal grainstone (F22). In western Lombardy, Jadoul et al. (2005) described a shallow-water subtidal to intertidal succession (35 m thick, Alpe Perino Limestone; Hettangian–lower Sinemurian) overlying the Albenza Fm. ooidal grainstone on structural highs before the Sinemurian deepening and pelagic limestone deposition (Moltrasio Fm.). Jadoul et al. (2005) reported lower Jurassic shallow-water carbonates developed on structural highs in the western (Varese High) and eastern (Botticino High) Lombardy Basin with lithofacies types (Alpe Perino Limestone, Corna Fm.) that are similar to lithofacies F26, F27 and F28 (Unit F) from this study.

The similarities between the Lombardy Basin and the NCA were already highlighted by Galli et al. (2007) who linked the Zu Limestone, Malanotte Fm. and Albenza Fm. succession to the Vorarlberg region of the western NCA, where the Kössen Fm. is  overlain, above an erosional unconformity, by the marlstone and marly limestone of the Schattwald Beds and Lorüns oolite (McRoberts et al. 1997), as it is proposed for Unit E in this study.

The Triassic–Jurassic boundary in shallow-water carbonates from the eastern NCA

Integrating the results from this study with the regional reconstructions (Gawlick et al. 2009; Krystyn et al. 2005) and the comparison with other paleogeographic domains, a revised depositional reconstruction of the study area is proposed in Fig. 16. Unit D subtidal cyclothems with claystone, mapped as Kössen Fm. in the Kreuss (2014) geological map, is interpreted as time-equivalent to the Eiberg Mb. and the Upper Rhaetian Limestone at the southern margin of the Eiberg Basin. In fact, in the Steinplatte area the top of the Upper Rhaetian Limestone is affected by a subaerial exposure (Kaufmann 2009), similarly to the exposure at the top of Unit D. The overlying Unit E coated grain ooidal grainstone, mapped as Upper Rhaetian Limestone by Kreuss (2014), is interpreted as transitional to lower Jurassic, based on the lack of Rhaetian biostratigraphic markers as well as the lack of corals and diverse skeletal biota that characterise Units C and D before the end-Triassic extinction. This hypothesis is supported by the similarity of Unit E lithofacies (F19, F22) with aggregate grain and ooidal grainstone deposits dated to the Hettangian–Sinemurian described in the Lombardy Basin (Albenza Fm., Southern Alps, N Italy; Galli et al. 2005, 2007; Bottini et al. 2016), Trento Platform (Calcari Grigi Group, Southern Alps, NE Italy; Borsato et al. 1994; Preto et al. 2017; Masetti et al. 2017; Vulpius and Kiessling 2018; Julian Alps, Slovenia; Ciarapica and Passeri 1990), western Dinarides (Croatia; Buckovic et al. 2001), Transdanubian Range (Kardosrét Limestone, Hungary; Vörös and Galácz 1998), Western Carpathians (Tatra Mts., Hronicum domain, Poland; Rychliński et al. 2018) and Apennines (Central and Southern Italy, Calcare Massiccio; Ciarapica 2007), as well as in the western NCA (Löruns, Austria; McRoberts et al. 1997; Felber et al. 2015). The abundance of ooids in Unit E and of microbialites in Unit F might reflect the effect of the biotic crisis related to the end-Triassic extinction as observed elsewhere in the aftermath of extinction events (e.g. Permian–Triassic; Li et al. 2015; end-Triassic, United Arab Emirates; Ge et al. 2019). Unit G chert layers, the abundance of detrital quartz and the sedimentological features of lithofacies F32 correspond to the Kalksburg Fm. (Hettangian–Sinemurian; cf. Gawlick et al. 2009).

Fig. 16
figure 16

Modified depositional model cross section partially redrafted after Krystyn et al. (2005) as reported in Fig. 1C including stratigraphic and palaeogeographic information reported in Gawlick et al. (2009) and references therein. The blue dashed line rectangle marks the inferred location of the studied succession. The Plattenkalk has been added as a transitional unit (due to decreasing dolomitization) between the Hauptdolomit and the Hochalm Mb. of the Kössen Fm. The age of the Hochalm Mb. has been assumed late Norian–early Rhaetian as proposed by Golebiowski (1990) and supported by the observations in this study. The diagram includes also the stratigraphic position of the sedimentary units identified in the study area from Unit A to G. The marker bed represented by the lower Rhaetian coral limestone (Unit C coral boundstone corresponding to Unit 4 of the Hochalm Mb. of the Kössen Fm. according to Golebiowski 1990) separates the Hochalm from the Eiberg members. According to Golebiowski (1990) the shallow-water successions above Unit 4 coral limestone time-equivalent to the Eiberg Basin are labelled as Oberrhätkalk/Upper Rhaetian Limestone that corresponds to Unit D in this study. Unit D is capped by subaerial exposure as the Upper Rhaetian Limestone in the Eiberg Basin southern margin in correspondence of the end-Triassic extinction event. Strata belonging to Unit E, F and G are interpreted as post end-Triassic extinction and early Jurassic in age representing a shallow-water setting north of the Eiberg Basin during the early Jurassic. This is a revised interpretation because  this succession is reported as Upper Rhaetian Limestone in the published geological maps (Schnabel et al. 2002; Kreuss 2014)

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Controlling factors on the stratigraphy of Western Tethys

The similarities, in terms of lithofacies associations and stacking pattern, among coeval successions deposited in different palaeogeographic domains (i.e. eastern and western NCA, Central Austroalpine, Western Carpathians, Transdanubian Range, Dinarides, Southern Alps) reveal that the Norian to Jurassic stratigraphic evolution of Western Tethys was controlled by the interplay of environmental, climatic and tectonic regimes producing similar sedimentological responses at regional scales. These factors can be identified influencing the Western Tethys depositional settings: (a) climate change controlling the intensity of weathering triggering a major input of clay and the demise of the widespread early dolomitization, suggesting a transition towards humid conditions in the latest Norian–Rhaetian (Berra et al. 2010), (b) Rhaetian favourable conditions for the expansion of coral boundstone; (c) biocalcification crisis of the end-Triassic extinction event (McRoberts et al. 2012), (d) an end-Triassic sea-level fall followed by rapid rise (Hallam and Wignall 1999; Pálfy and Zajzon 2012), (e) early Jurassic recovery of carbonate production with ooidal grainstone and microbialites; (f) early Jurassic extensional tectonics with development of structural highs where shallow-water carbonates accumulated before the drowning represented by red crinoidal-rich and hemipelagic limestone (Bernoulli 1964; Eberli 1988; Jadoul et al. 2005; Gawlick et al. 2009; Gawlick and Missoni 2019).

This study performed in the eastern NCA on the upper Norian–Rhaetian to Jurassic mixed carbonate–siliciclastic sedimentary units and the comparison with coeval successions demonstrate that regional and global processes drove the stratigraphic evolution of Western Tethys, from the Austroalpine to the Southern Alps to Western Carpathians, as recorded by the strikingly similar lithofacies character and stratigraphic evolution.

Conclusions

The sedimentological investigation of the nearly 350 m thick, shallow-water Rhaetian–Lower Jurassic mixed carbonate–siliciclastic succession of the Stumpfmauer area in the eastern NCA allowed identifying 32 lithofacies, grouped in seven sedimentary units (from A to G), recording the stratigraphic evolution of shelf depositional environments, located north of the upper Rhaetian Eiberg Basin.

This shallow-water succession comprises: the Hochalm Mb. of the Kössen Fm. (Unit A peritidal cyclothems, Unit B claystone/marlstone with fossiliferous beds) and the regional coral limestone marker bed Hauptlithodendronkalk (Unit C coral boundstone to floatstone), the Upper Rhaetian Limestone time-equivalent to the Eiberg Mb. of the Kössen Fm. (Unit D subtidal cyclothems with claystone), shallow-water carbonate strata transitional to the Lower Jurassic up to the Kalksburg Fm. (Unit E ooidal coated grain peloidal grainstone with basal transgressive lag, Unit F bivalve-rich, microbialite and oncoidal lithofacies, Unit G cross-laminated coated grain peloidal grainstone with quartz and chert).

Differently from the published geological maps, in this study Units E and F are attributed to a lower Jurassic shallow-water depositional system post-dating a laterally extensive subaerial exposure surface at the top of Unit D, based on: (a) the sharp change in skeletal biota with the disappearance of corals and Rhaetian foraminifera (e.g. Triasina hantkeni) common in the underlying Unit D; (b) the onset of abundant detrital quartz, siliceous sponge spicules and chert, and (c) the similarities with Lower Jurassic ooidal grainstone lithofacies and stratigraphic evolution in the western NCA, Southern Alps, Western Carpathians, Transdanubian Range and Dinarides. Unit E ooidal grainstone and Unit F microbial boundstone are interpreted to reflect the biotic crisis in the aftermath of the end-Triassic extinction.

The evolution of the studied succession demonstrates the influence of climate, environmental changes and extensional tectonics (linked to the opening of the Penninic Ocean) on the western Tethys carbonate shelf, driving similar responses in different palaeogeographic domains: a shift towards humid conditions required to explain the latest Norian–early Rhaetian clay input (Units A and B), the Rhaetian expansion of phaceloid coral boundstone (Unit C), a major sea-level fall (top of Unit D) followed by transgression and change in skeletal biota marking the end-Triassic extinction and transition to early Jurassic (Unit E), the aftermath of the biotic crisis manifested by abundance of ooidal grainstone and microbialites (Units E and F), lower Jurassic shallow-water carbonate strata on structural highs (Units E, F and G) and gradual deepening upward due to extensional tectonics.