Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group (North Alpine Foreland Basin, Central Paratethys)

Transcription

1 Newsletters on Stratigraphy, Vol. 48/1 (2015), Stuttgart, January 2015 Article Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group (North Alpine Foreland Basin, Central Paratethys) Patrick Grunert 1,2 *, Gerald Auer 1, Mathias Harzhauser 3, and Werner E. Piller 1 With 5 figures, 1 plate, 3 tables and 1 appendix Abstract. Herein, we present a new stratigraphic model for the upper Oligocene to lower Miocene Puch - kirchen Group which comprises deep-marine deposits in the central North Alpine Foreland Basin. Stratigraphic constraints are inferred from the integration of new bio- (calcareous nannoplankton) and chemostratigraphic (δ 13 C bulk ) data from the drill-site Hochburg 1. The first occurrences of Helicosphaera carteri and H. ampliaperta are recorded in the section and indicate a stratigraphic range from nannoplankton zones NP25 to upper NN2/ CNO6 to CNM4. The correlation with the upper Chattian to lower Burdigalian is strongly supported by the δ 13 C bulk record that mirrors major trends in global reference records between ~ 24.2 Ma and ~ Ma. Seismic surveys suggest that at least 100 m of sediment have been eroded from the top of the Puchkirchen Group at Hochburg 1, and deposition extended even further into the Burdigalian. Within the Puchkirchen Group, the boundary between the Lower and Upper Puchkirchen formations occurs at ~ Ma. The new age model for Hochburg 1 significantly improves previous stratigraphic concepts of the Puchkirchen Group and resolves some long-lasting stratigraphic issues in the study area. The implications of the new correlation for analyses of sedimentary budget, subsidence rates, sequence stratigraphy and the regional stage concept challenge our understanding of the development of the North Alpine Foreland Basin as well as the Central Paratethys. Key words. Puchkirchen Group, Paratethys, calcareous nannoplankton, stable carbon isotopes, Chattian, Aquitanian 1. Introduction The Puchkirchen Group (often referred to as Puchkirchen Formation or Puchkirchen Series by other authors) comprises an up to 2500-m-thick upper Oli - go cene and lower Miocene sequence of intercalated deep-marine marls, sands and conglomerates that constitute prolific reservoir rocks for biogenic gas in the central North Alpine Foreland Basin (Malzer et al. 1993, Wagner 1998, Piller et al. 2004, Schulz et al. 2009, Schulz and van Berk 2009). The economic importance of the Puchkirchen Group and the access to core material and seismic imagery recovered in the course of hydrocarbon exploration have stimulated considerable scientific research efforts to improve reservoir prediction (Hinsch 2008). Originally attrib- Authors addresses: * Corresponding author; patrick.grunert@uni-graz.at 1 University of Graz, Institute for Earth Sciences (Geology and Paleontology), NAWI Graz, Heinrichstraße 26, A-8010 Graz, Austria. 2 Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ , United States of America. 3 Natural History Museum Vienna, Geological-Paleontological Department, Burgring 7, A-1014 Vienna, Austria Gebrüder Borntraeger, Stuttgart, Germany DOI: /nos/2014/ /2014/0056 $ 5.75

2 112 P. Grunert et al. Fig. 1. Study area and locations of 1) the herein studied drill-site Hochburg 1; 2) the stratotype of the Puchkirchen Group and boundary stratotype of the Egerian stage, Puchkirchen 1 (Küpper and Steininger 1975); and 3) the Traun section in Bavaria, the primary site of stratigraphic studies in this part of the basin (Hagn 1981, Martini 1981, Reiser 1987, Wenger 1987). Dark grey areas indicate the extension of Cenozoic sediments in the NAFB. uted to turbidite and mass flow deposition triggered by the advancing Alpine nappes (Malzer et al. 1993, Wagner 1996, 1998), recent studies have linked the Puchkirchen Group to submarine channel deposition (De Ruig 2003, De Ruig and Hubbard 2006, Hubbard et al. 2009, Bernhardt et al. 2012). The complex sedimentary architecture of the Puchkirchen Channel System, which was 3 5 km wide and 10s of kilometers long, has since become a prime example for submarine channel deposition in foreland basins. The Puch kir - chen Group has also played a pivotal role in the establishment of the regional stratigraphic framework of the Central Paratethys, specifically the definition of the regional Egerian stage (Papp 1968, Papp and Steininger 1975, Piller et al. 2007). Despite the scientific and economic significance of the Puchkirchen Group, reports on its stratigraphic correlation are ambiguous. There is a general agreement on a Chattian to Aquitanian age, but considerable debate revolves around the range of the Puchkirchen Group within each of the two stages (Rögl et al. 1998). While reports from drill-sites correlate the bulk of the Puchkirchen Group with the Chattian (Küpper 1966, Küpper and Steininger 1975, Hochuli 1978, Rögl et al. 1979, Rögl 1994, Rögl and Rupp 1996), data from surface outcrops indicate a younger age with considerable portions of the Puchkirchen Group in the Aquitanian (Müller 1970, Cicha et al. 1971, Hagn 1981, Martini 1981, Reiser 1987, Wenger 1987). Reworking, sub - marine erosion and imbrication have certainly contributed to these contradictions, but the published reports additionally suffer from a small number of investigated samples. In this study, we present new stratigraphic constraints for the Puchkirchen Group based on calcareous nannoplankton and stable carbon isotopes. The data come from a series of samples of drill-site Hoch - burg 1, a location largely unaffected by disruptive channel deposition and tectonic activity. We propose a substantially improved age model for the Puchkirchen Group that helps to resolve some of the long-standing stratigraphic issues and allows new perspectives on the development of the North Alpine Foreland Basin and in particular the Puchkirchen Channel System close to its source areas. 2. Geological setting & Regional geology The study area is located in the Puchkirchen Trough which extends from Bavaria to Upper Austria and Salzburg in the central North Alpine Foreland Basin (NAFB; in many studies referred to as Molasse Basin; Fig. 1). It parallels the Alpine thrust front with a westeast trending axis and contains a thick succession of Eocene to lower Miocene marine sediments of the Central Paratethys, which are overlain by lower Miocene to Holocene continental deposits (Malzer et al. 1993, Kuhlemann and Kempf 2002, Grunert et al. 2013). From late Eocene to early Miocene, the NAFB acted as one of the main sedimentary basins of the Central Paratethys and initially provided a major marine gateway between the Paratethys and the Mediterranean/Atlantic areas (Rögl 1998, Kuhlemann and Kempf 2002). This connection was interrupted during late Oligocene and marine sedimentation was sub - sequently confined to the eastern NAFB with the Puchkirchen Trough as the only deep-marine depo - center (Wagner 1998, Kuhlemann and Kempf 2002, Grunert et al. 2010, 2013). During this time, sediment distribution in the m deep trough was strongly controlled by an extensive sinuous basinaxial channel, which resulted in the deposition of the Puchkirchen Group and the basal Hall Formation (De Ruig and Hubbard 2006, Hubbard et al. 2009, Bern-

3 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 113 hardt et al. 2012, Grunert et al. 2013). Highly productive surface waters resulted in the development of an extensive oxygen minimum zone along the northern slope (Wagner 1998, Grunert et al. 2010, Rupp and Ćorić 2012). The trough was confined by vast shelf and slope areas in the north and west and a steep and tectonically active southern slope adjacent to the Alpine thrust front (Rögl et al. 1979, Reiser 1987, Wenger 1987, Wagner 1998, Zweigel 1998, Kuhlemann and Kempf 2002, De Ruig 2003, Grunert et al. 2010, 2013, Hinsch 2013). Major rivers entered the basin from the north, west and south and delivered large amounts of sediment, which partly fed the channel system (Kuhlemann and Kempf 2002, Hinsch 2008, Grunert et al. 2013). After the re-opening of the westward connection to the Mediterranean in the early Burdigalian, increasing rates of sedimentation and decreasing rates of subsidence led to the eventual infill of the Puchkirchen Trough and the final closure of the seaway by the middle Burdigalian (Zweigel 1998, Grunert et al. 2013). 2.1 The Puchkirchen Group The Puchkirchen Group consists of heavily intercalated marls, sands and conglomerates related to submarine channel deposition in the Puchkirchen Trough (Wagner 1998, Hinsch 2008, Hubbard et al. 2009). Deposits of the Puchkirchen Group extend over an area of 2400 km 2 and their thickness increases significantly from the north towards the Oligocene Miocene basin axis in the south where they may reach a thickness up to 2500 m (Aberer 1958, Wagner 1998, Zweigel 1998, Hinsch 2013). The Puchkirchen Group overlies con - cordantly the up to 450-m-thick hemipelagic marls, turbidites and mass-wasting deposits of the Zupfing Formation (Wagner 1998). At the top, the Puchkirchen Group is separated by a basin-wide unconformity from the lower and middle Burdigalian Hall Formation, which comprises heterogenic sediments related to the terminal phase of submarine channel, turbidites, prograding deltas, and deep-water deposition (Wagner 1998, Hinsch 2008, Grunert et al. 2013). To the north, the Puchkirchen Group passes into the finely laminated, organic-rich slope deposits of the Ebelsberg Formation, and the Linz Formation represents the coeval shallow water deposits of the northern shelf (Wagner 1996, 1998, Grunert et al. 2010, Rupp and Ćorić 2012). The southern portions of the Puchkirchen Group are heavily tilted and imbricated (Hagn 1981, Reiser 1987, Wenger 1987, Hinsch 2013). The Puchkirchen Group is subdivided into two units, the Upper and Lower Puchkirchen formations, which are primarily distinguished by characteristic species of agglutinated foraminifera: Psammosiphonella cylindrica and Reticulophragmium aff. amplectens characterize the Lower Puchkirchen Formation, Gaudryinopsis austriacus is indicative for the Upper Puchkirchen Formation (Rögl et al. 1998). Further informal subdivisions of both formations have been inferred from lithofacies, which are primarily applied in industrial studies. Three lithofacies types are distinguished in the Lower Puchkirchen Formation termed Liegende Tonmergel ( Lower calcareous shales ), Sand-Schotter-Gruppe ( Sand-gravel group ), and Hangende Tonmergel ( Upper calcareous shales, Küpper and Steininger 1975, De Ruig 2003). An informal subdivision into four alternating lithofacies types termed A4 A1 (bottom to top; A stands for Aquitanian) has been developed for the Upper Puchkirchen Formation (Aberer 1958). While the A4 and A2 horizons comprise sandy conglomerates, the A3 and A1 horizons consist of finer-grained deposits. A1 is in many cases characterized by fine lamination with good macrofossil preservation ( A1 Fischschiefer ). The complex sedimentary architecture of the Puch - kirchen Group results from a long-lived basin-axial channel belt, the Puchkirchen Channel System, which was fed by the Bavarian Shelf and the Alpine hinterland (Malzer et al. 1993, Wagner 1998, DeRuig 2003, DeRuig and Hubbard 2006, Hinsch 2008, Hubbard et al. 2009). The large amounts of sand delivered by tributary channels down to water depths of 1000 m constitute prime reservoirs for biogenic gas (Malzer et al. 1993). Stratigraphic correlation of the Puchkirchen Group is primarily based on biostratigraphic studies in the Austrian part of the Puchkirchen Trough from the 1960s and 1970s in the course of establishing a regional stratigraphic framework for the Central Paratethys. These studies have later been complemented by investigations in Bavaria in the 1980s. A review of available biostratigraphic data, summarized in Table 1 and Fig. 3, shows that a Chattian to Aquitanian age is commonly assumed, but there is considerable disagreement about the exact range within this time frame (Rögl et al. 1998). Stratigraphic correlation of the Puchkirchen Group has suffered from several obstacles including reworking, submarine erosion and tectonic deformation as well as low sampling resolution and different stratigraphic concepts. A detailed discussion of the reasons for the obvious discrepancies

4 114 P. Grunert et al. Table 1 Review of all available stratigraphic information on the Puchkirchen Group and under-/overlying lithostratigraphic units. Top and Base datums refer to Raffi et al. (2006), Wade et al. (2011) and Gradstein et al. (2012). Method Biostratigraphic Sites Lithostratigraphic unit Remarks Reference marker/zone Upper Austria Planktic FO & LO Paraglo- Puchkirchen 3 (core 1) undefined levels Base: Ma; Top: Ma; Hochuli (1978), Rögl foraminifera borotalia opima opima unknown in Zupfing Fm. Top: Ma; Pgr. opima nana et al. (1979), Rögl and continues into Puchkirchen Rupp (1996), Rögl et Group al. (1998) Calcarous NP24 Puchkirchen lower part of Zupfing Fm. index taxon Spheonlithus cipe- Sachsenhofer et al. nannoplankton Oberschauersberg roensis (FAD: Ma) absent; (2010) Eggerding inferred from Helicosphaera recta Planktic FO Globigerina unknown middle part of Zupfing Fm. Base: Ma Rögl (1994) foraminifera angulisuturalis Larger benthic FO Miogypsinoides Kirchham 1 ( m) Lower Puchkirchen Fm. Base: Ma?; Küpper (1966, 1975); foraminifera complanatus Eberstallzell 6 ( m) Top: Ma/22 Ma? Papp (1975); Cicha et Eberstallzell 7 ( m) al. (1998) Oberaustall 4 ( m) Planktic LO Globigerina Treubach-1 Upper Puchkirchen Fm. Top: 22.9 Ma; G. ciperoensis Rögl et al. (1979), foraminifera ciperoensis Geretsberg-1 rare in upper part Rögl (1994), Rögl Zupfing-1 and Rupp (1996) Calcarous upper NN2 NN3 Treubach-1 lower Hall Fm. presence of H. ampliaperta Rögl et al. (1979), nannoplankton Geretsberg-1 Grunert et al. (2013) Hochburg 1 Larger benthic FO Miogypsina Steyr an der Enns Hall Fm. Base: Ma?; imbricated Pap (1960), Papp foraminifera intermedia (1975), Cicha et al. (1998)

5 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 115 Bavaria Planktic LO Turborotalia Übersee Rupelian marls Top: Reiser et al. (1987) foraminifera ampliapertura (Ober-Rupel) Planktic FO Globigerinoides unknown Rupelian marls (Rupel Base: Ma; Rögl et al. (1998) Rögl et al. (1998) foraminifera primordius Tonmergelschichten) refer to Reiser (1987) but the description cannot be found there Planktic FO Globigerinoides Rainer Mühle/Prien section Lower Puchkirchen Fm. Base: Ma Cicha et al. (1971), foraminifera primordius Nonnenwald Mulde (Unter-Eger 1) Reiser (1987), p. 110 Ampfing 1 Calcareous upper NP24 NP25 unknown Lower Puchkirchen Fm. no references or details presented Rögl et al. (1998) nannoplankton (Unter-Eger) Calcareous NP25 Thalberg-Graben/Traun section upper part of Lower Puch- Base: Ma; Top: Ma Hagn (1981), Martini nannoplankton Rainer Mühle/Prien section kirchen Fm. (Unter-Eger) Sphenolithus ciperoensis Zone; (1981) Wildenwart/Prien section Zygorhablithus bijugatus present Calcareous NN1 Zillerleite/Traun section upper part of Upper Puch- Base: Ma; Top: Ma Hagn (1981), Martini nannoplankton kirchen Fm. (Ober Eger) Triquetrorhabdulus carinatus (1981) Zone; Helicosphaera cf. carteri present; Z. bijugatus absent Calcareous NN1 NN2 unknown Upper Puchkirchen Fm. no references or details presented Rögl et al. (1998) nannoplankton (Ober-Eger) Planktic FO Globoquadrina Teufelsgraben/Traun section base Upper Puchkirchen Base: 22.4 Ma; Gqu. dehiscens Wenger (1987) foraminifera dehiscens Fm. (Ober-Eger) continues to top of Puchkirchen Group Calcareous? NN1 NN2 Maierhof Ortenburg Sands Helicosphaera carteri present, Martini (1981) nannoplankton other index taxa missing

6 116 P. Grunert et al. between the Upper Austrian and Bavarian study area is given in section 5.3. In general, the Lower Puch kir - chen Formation has been correlated with calcareous nannoplankton zones upper NP24 NP25, planktonic foraminifera zones N2 N4 and shallow benthic zone SBZ 23 (Küpper 1966, Rögl et al. 1979, Hagn 1981, Reiser 1987, Rögl 1994). For the Upper Puchkirchen Formation, a correlation to nannoplankton zones NP25 to NN1 NN2 and planktonic foraminifera zone N3 N5 has been suggested (Rögl et al. 1979, Hagn 1981, Reiser 1987, Rögl 1994). Locally, the Puchkirchen Group is correlated with the lower and middle parts of the regional Egerian stage (Egerian a c sensu Papp and Steininger 1975, Rögl et al. 1998, Piller et al. 2007). However, some authors imply an extension into the lower Eggenburgian stage (Rögl and Rupp 1996, Wagner 1998, Rupp 2011). Regarding lithostratigraphic terminology, the present study follows the recommendation of Piller et al. (2004) in the stratigraphic chart of Austria and applies the term Puchkirchen Group ( Puchkirchen Gruppe ) with the subunits Lower and Upper Puchkirchen formations. This terminology differs from previous concepts. Papp (1968) introduced the name Puchkirchener Serie (Puchkirchen Series) for deposits, which have previously been described as Chatt (Chattian) and Aquitan (Aquitanian; Aberer 1958). In 1975, the Puchkirchener Serie was described in detail from sediment cores of the drill-site Puchkirchen 1 and selected as one of several faciostratotypes for the regional Egerian stage (Fig. 1; Küpper and Steiniger 1975). In the same study, the subdivision into an Untere Puchkirchener Serie and an Obere Puchkirchener Serie (lower and upper Puchkirchen Series) based on the content of benthic foraminifera was introduced (Küpper and Steininger 1975). This concept was perpetuated in subsequent publications (e. g., Rögl et al. 1979). Papp and Steininger (1975) summarized the Puchkirchen Series, the Linz Sands (now Linz Formation) and the Schieferton as Puchkirchener Schich - tengruppe (Puchkirchen Group). In many later publications, the term Puchkirchen Formation consisting of the Lower and Upper Puchkirchen Formations replaced Puchkirchener Serie (e. g., Rögl 1994, Wagner 1996, 1998, Rögl et al. 1998, De Ruig 2003, Hinsch 2008, 2013). While the aforementioned terminological concepts have been applied to the Austrian portions of the Puch - kirchen Group, a different terminology has been developed for its continuation into SE Germany. There, the Lower Puchkirchen Formation is commonly referred to as Unter-Eger which is subdivided into Unter- Eger I and Unter-Eger II (lower Egerian I and II, the subdivision implying the then assumed Oligocene/ Miocene boundary) while the term Ober-Eger (upper Egerian) is applied to the Upper Puchkirchen Formation (Hagn 1981, Reiser 1987, Wenger 1987, Rögl et al. 1998). More recent studies have adopted the terms Lower and Upper Puchkirchen Formations (Zweigel 1998), which are also considered in the stratigraphic chart of Germany (Doppler et al. 2005). 2.2 The Puchkirchen Group at drill-site Hochburg 1 The sample material of the present study originates from borehole Hochburg 1 located in the central part of the Puchkirchen Trough in Upper Austria (N ; E ; Grunert et al. 2013; Fig. 1). Drilled in 1983 by Rohöl-Aufsuchungs AG (RAG), a ~ 3400-m-thick succession of Jurassic to Holocene deposits has been penetrated. Within this succession, the m-thick Puchkirchen Formation ( m depth in drill-hole) superposes ~ 156-m-thick marls of the Zupfing Formation ( Tonmergelstufe, Rupel Tonmergel ). The subdivision into a Lower and Upper Puchkirchen Formation is based on geophysical well-log data, seismic correlation and benthic foraminiferal analysis (Rögl 1991; unpublished internal reports by RAG 1983; Fig. 2). The Lower Puchkirchen Formation ( m) consists of clay marls with varying contents of sand. Prominent sand layers are restricted to the interval between 1980 m and 2040 m. The foraminiferal index taxon Psammosiphonella cylindrica occurs regularly in this interval, Reticulophragmium aff. amplectens is present between m (Rögl 1991). The occurrences of early Oligocene planktonic foraminifera between m suggest a certain amount of reworking from the Zupfing Formation. A generally low rate of re-deposition is in agreement with seismic images that show that the submarine channel was located km to the south at this time (Hinsch 2008). The Upper Puchkirchen Formation ( m) shows a more diverse lithology and the informal A4 A1 horizons are distinguished in the internal reports. The lower part of the Upper Puchkirchen Formation (A4 and A3 horizons; m) consists of sandy clay marls with occasionally intercalated sand layers similar to the Lower Puchkirchen Formation. Horizon A2 ( m) is mainly composed of sands while sandy clay marls are rare. Finally, A1

7 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 117 ( m) comprises sandy clay marls with frequent intercalations of sands and conglomerates. Seismic images suggest that the lithological succession of the Upper Puchkirchen Formation is related to the northward migration of the channel belt over time. The base of the formation has been defined by the first occurrence of the index species Gaudryinopsis austriacus (Rögl 1991). On a few occasions ( m; m) reworking from the Lower Puch kir - chen Formation is indicated by occurrences of P. cylindrica and R. aff. amplectens. G. ciperoensis s. l. occurs frequently up to 1720 m and then becomes rare to absent. Bound by an erosional unconformity, the Upper Puchkirchen Formation is overlain by the ~ 750-mthick Hall Formation. Litho-, bio-, and chemofacies of this formation have been described in detail by Grunert et al. (2013; Fig. 2). In the present study, only the basal Hall Formation, which contains the terminal channel deposits, and part of the lower Hall Formation ( m) are addressed. The channel deposits of the basal Hall Formation ( m) comprise thick layers of sands and conglomerates that frequently contain reworked microfossils and sediment clasts of the Upper Puchkirchen Formation (Grunert et al. 2013). With the cessation of channel deposition in the Puchkirchen Trough, turbiditic sands become frequent in the lower Hall Formation 3. Material and methods As no sediment cores are available from the Puch - kirchen Group at Hochburg 1, all samples used in this study are drill cutting samples representing estimated 2 m of sediment thickness each. 18 samples, taken in intervals of m from the Lower and Upper Puchkirchen formations, have been analysed for their contents of calcareous nannoplankton. Smear slide preparation followed the standard methodology of Bown and Young (1998). The sediment was suspended in a mixture of distilled and tap water and fully disaggregated by ultrasonic treatment for c. 5 seconds. The suspension was then transferred to a coverslip and slowly dried on a heating plate at 60 C. The slides were permanently mounted using Euparal and studied using a light microscope (Zeiss Axioplan 2) under parallel and crossed nicols with a magnification of Coccoliths were identified on the species level if possible following the taxonomic concepts of Bown (1998) and Galovic and Young (2012), supplemented by the Nannotax 3 website (Young et al. 2014) and the handbook of calcareous nannofossils (Aubry 1984, 1988, 1989, 1990, 1999, 2013). Biostratigraphic zonation follows the concepts of Martini (1971, recalibrated in Gradstein et al. 2012) as well as Backman et al. (2012) and Agnini et al. (2014). The terms Base (B) and Top (T) are used when referring to biostratigraphic datums defined in the global stratigraphic framework (Backman et al. 2012, Gradstein et al. 2012, Agnini et al. 2014); the terms first occurrence (FO) and last occurrence (LO) refer strictly to the local occurrences of these bioevents at Hochburg sediment samples from the Lower and Upper Puchkirchen formations as well as the basal and lower Hall Formations ( m) have been selected for analysis of their stable carbon isotope signature (δ 13 C bulk ) and carbonate content. δ 18 O bulk has not been considered a suitable tool for stratigraphic correlation at Hochburg 1 for two reasons: 1) δ 18 O is considerably more prone to be diagenetically altered by porewater than δ 13 C (see section 5.2); 2) Observations under the light microscope have revealed the regular occurrence of gypsum crystals that might additionally bias the δ 18 O bulk -signal (Marshall 1992). δ 13 C bulk measurements have been performed at the Institute for Earth Sciences at the University of Graz, using an automatic Kiel II preparation line and a Finnigan MAT Delta Plus mass spectrometer. Samples were dried, homogenized with a mortar and reacted with 100% phosphoric acid at 70 C. Analytical precision, based on replicate analysis of international standards NBS-19 and NBS-18 and an internal laboratory standard is better than 0.04 for δ 13 C. Results are reported in conventional δ-notation relative to the Vienna Pee Dee Belemnite standard (VPDB) in units. In sediments with very low carbonate content, dissolved 12 C in pore waters might have compromised the δ 13 C bulk record (see Discussion section for details). In order to address such a diagenetic bias appropriately, carbonate content was calculated as calcite equivalent percentages (CaCO 3 = 8.34*TIC) for each sample (Grunert et al. 2013). Powdered samples have been analysed for total carbon (TC) and total organic carbon (TOC, following acidification of samples to remove carbonate) contents by using a Leco CS-300 device. Total inorganic carbon (TIC) has been calculated by subtraction of TOC from TC.

8 118 P. Grunert et al. Fig. 2. Lithology and stratigraphy of the studied interval at drill-site Hochburg 1. Subdivision into Zupfing Fm., Lower and Upper Puch kir chen Fms. and Hall Fm. is based on internal biostratigraphic reports and seismic interpretation by RAG and Grunert et al. (2013). First occurrences (FOs) of benthic foraminiferal index species for the lithostratigraphic units are indicated in grey (Rögl 1991, Grunert et al. 2013). FOs of nannoplankton marker species identified in the present study are indicated in black. The potential last occurrence (LO) of T. carinatus has been adopted from Grunert et al. (2013). FRO = first recorded occurrence, referring to index taxa present in the lowermost sample of the studied interval.

9 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 119 Plate 1. Representative calcareous nannofossils from the Hochburg 1 borehole. Scale bar 5 μm. a) Coccolithus pelagicus (Wallich, 1877) Schiller, 1930; crossed nicols; 1680 m. b) Reticulofenestra minuta Roth, 1970; crossed nicols; 1680 m. c) Reticulofenestra haqii Backman, 1978; crossed nicols; 1640 m; d) Small (6 μm) Helicosphaera ampliaperta Bramlette and Wilcoxon, 1967; crossed nicols; 1640 m. e) Large (10 μm) Helicosphaera ampliaperta Bramlette and Wilcoxon, 1967; crossed nicols; 1630 m. f) Helicosphaera scissura Miller, 1981; crossed nicols; 1630 m. g) Helicosphaera carteri (Wallich, 1877) Kamptner, 1954; crossed nicols; 1630 m. h) Helicosphaera carteri (Wallich, 1877) Kamptner, 1954; crossed nicols; 1940 m. i) Helicosphaera euphratis Haq, 1966; crossed nicols; 1790 m. j) Reticulofenestra stavensis (Levin & Joerger, 1967) Varol, 1989; crossed nicols; 2000 m. k) Reticulofenestra bisecta (Hay, Mohler and Wade, 1966) Roth, 1970; crossed nicols; 2000 m. l) Reticulofenestra umbilicus (Levin, 1965) Martini and Ritzkowski, 1968; crossed nicols; 2020 m. m) Toweius rotundus Perch-Nielsen in Perch-Nielsen et al., 1978; crossed nicols; 2020 m. n) Tribrachiatus orthostylus, Shamrai, 1963; 1640 m. o) Discoaster kuepperi Stradner, 1959b; parallel light; 1950 m. p) Watznaueria barnesiae (Black, 1959) Perch- Nielsen, 1968; crossed nicols; 1640 m.

10 120 P. Grunert et al. Table 2 Abundance of nannoplankton taxa at Hochburg 1. Abundance was semi-quantitatively inferred from the amount of specimens of nannoplankton taxa in the view field. F (few): single specimen in the slide or occasional specimens in some view fields. R (rare): regular encounters every two to five view fields. C (common): one or more specimens every view field with absences in some view fields. A (abundant): one or more specimens in every view field. NN/NP zone CNM/CNO zone depth in m autochthonous taxa Braarudosphaera bigelowii Calcidiscus leptoporus (small form) Coccolithus miopelagicus Coccolithus pelagicus Cyclicargolithus floridanus Helicosphaera ampliaperta Helicosphaera carteri Helicosphaera euphratis Helicosphaera scissura Helicosphaera sp. Pontosphaera multipora Reticulofenestra bisecta Reticulofenestra daviesii Reticulofenestra haqii Reticulofenestra minuta Reticulofenestra pseudoumbilicus Reticulofenestra stavensis Sphenolithus moriformis Triquetrorhabdulus carinatus Umbilicosphaera jafari Umbilicosphaera sp. Zygrhablithus bijugatus reworked Paleogene taxa Chiasmolithus modestus Cribrocentrum reticulatum Cruciplacolithus sp. Cyclicargolithus luminis Discoaster kuepperi Discoaster lodoensis? Discoaster sp. Lanternithus minutus Micrantholithus attenuatus Pontosphaera plana Reticulofenestra umbilicus Sphenolithus radians Sphenolithus spiniger Toweius rotundus Tribrachiatus orthostylus reworked Cretaceous taxa Arkhangelskiella cymbiformis Broinsonia parca parca Eiffellithus eximus Praediscosphaera sp. Prediscosphaera cretacea Quadrum gartneri Retecapsa ficula Watznaueria barnesiae 1612 C R F R F F R R R F F F R CNM F A R R F F F F C A R R F F F R 1640 F F R R F F F C R F F F F R F F F 1680 NN F F F F F 1720 F F C C F F F F F CNM F R A F R F F F C C F F F R 1790 F C C F F R C F F F F 1850 F C A R F R C A F R F F R F F F R NN1? 1912 F F C R F F F R C A F F F F F F F F F F F 1940 F C C R F R C R F F F R 1950 F R C R R R C F F F R 1970 F R F F C R C F F F R 1980 R F F C R C F R F R NP25/24 CNO5/ C C F A R C F F F R F F F F R 2020 R R F C R F C F F F F F F R 2070 F R C A F C R R F F F F F F F R 2090 R F F R F R F F F F F F F F F F

11 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group Results 4.1 Calcareous nannoplankton Results for the calcareous nannofossil assemblages are summarized in Table 2 and Fig. 2, the most important taxa are depicted in Plate 1. The assemblages comprise poorly to moderately well preserved coccolith specimens with frequent partial dissolution, etching and overgrowth. Total coccolith abundances are low except for a few samples. In general, samples with higher coccolith abundances also have higher amounts of well-preserved specimens. Assemblages of the lowermost samples are dominated by Reticulofenestra bisecta and R. minuta, with major contributions of Coccolithus pelagicus, Cyclicargolithus floridanus and Reticulofenestra stavensis. A significant change in assemblage composition occurs at 1940 m when C. pelagicus and R. minuta begin to dominate. The first occurrence (FO) of Helicosphaera carteri is also recorded at this depth. The FO of Helicosphaera scissura is observed at 1850 m. Helicosphaera ampliaperta first occurs at 1640 m, and it is recorded commonly from 1630 m together with H. scissura. All samples contain ~ 20 35% (estimate based on visual inspection) of reworked taxa of the Paleogene Fig. 3. Correlation of the Puchkirchen Group to the Central Paratethys stages and global bio- and chemostratigraphic tie points. Correlation of regional stages based on Rögl (1998), Piller et al. (2007) and Hilgen et al. (2012). Planktonic fora - minifera (PF) zonation follows Wade et al. (2011) and Gradstein et al. (2012); calcareous nannoplankton (CN) zonation follows Gradstein et al. (2012), Backmann et al. (2012) and Agnini (2014); larger benthic foraminifera zonation follows Cahuzac and Poignant (1997) and Gradstein et al. (2012). Global δ 13 C stack from Zachos et al. (2008). Numbers 1 and 2 in the Puchkirchen Group column refer to stratigraphic concepts of previous studies in Bavaria and Upper Austria and indicate the maximum range of the lithostratigraphic units. Number 3 refers to the herein discussed concept; note that the uppermost part of the Puchkirchen Group (indicated in grey) cannot be observed at Hochburg 1 and that the boundary between the Puchkirchen Group and the Hall Fm. is only tentative. See text for details.

12 122 P. Grunert et al. and Cretaceous. Prominent taxa reworked from the Cretaceous include Micula spp., Arkhangelskiella spp. and Watznaueria barnesiae. Reworked Paleogene taxa include Discoaster kuepperi, Reticulofenestra umbilicus, Tribrachiatus orthostylus, Sphenolithus radians, Sphenolithus spiniger, and Lanternithus minutus. Occurrences of these taxa throughout the section imply that nearly all long ranging autochthonous taxa (most prominently C. pelagicus, R. minuta and Cy. floridanus) might be at least partly contaminated by reworked specimens at Hochburg 1. Table 3 Contents of total inorganic carbon (TIC) and carbonate (CaCO 3 ) and carbon isotope values for the bulk sediment (δ 13 C bulk ) in the studied interval of Hochburg 1. A1 A4: horizons of the Upper Puchkirchen Formation (see section 2 for details). Sample IDs refer to depth in borehole (m). Unit Sample TIC Carbonate δ 13 C Unit Sample TIC Carbonate δ 13 C lower Hall Fm. A2 A1 basal Hall Fm A3 A4 Lower Puchkirchen Fm

13 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group Carbonate content Results for TIC and calculated CaCO 3 content are shown in detail in Table 3 and Fig. 4. CaCO 3 content of the Lower Puchkirchen Formation is rather homogenous with a mean value of 29% and minimal variability (σ = 2%). In contrast, the Upper Puchkirchen Formation shows a significantly higher variability in its values (A = 29%, σ = 12%) which results from a more diverse lithology. In its lower portion (A4 horizon), values show a minor increase compared to the Lower Puchkirchen Formation (A = 31%, σ = 6%). Variability in this interval shows a similar magnitude as in the Lower Puchkirchen Formation except for the minimum at 1770 m. Subsequently (A3 and A2 horizons), values become significantly more variable (A = 35%, σ = 13%), punctuated by two major positive peaks at 1680 m and 1620 m. The top of the Upper Puchkirchen Formation (A1 horizon) is marked by a severe drop in carbonate content (A = 15%, σ = 6%) with minimum values between 1600 m and 1570 m. In the basal Hall Formation, CaCO 3 content increases to values comparable to the lower part of the Upper Puchkirchen Formation (A = 32%, σ = 4%). In the lower Hall Formation, carbonate content and variability increase slightly (A = 34%, σ = 7%). 4.3 Bulk δ 13 C Results for δ 13 C bulk are shown in detail in Table 3 and Fig. 4. Lowest δ 13 C bulk values within the Puchkirchen Group occur at the base of the Lower Puchkirchen Formation ( m; A = 0.87 ; σ = 0.11 ). Following a pronounced increase of ~ 0.7, isotopic values increase steadily until 1850 m with some variability and distinct maxima at 1990 m, 1930 m, 1890 m and Fig. 4. Carbonate content (CaCO 3 ) and stable carbon isotopes (δ 13 C bulk ) across the studied interval at Hochburg 1. Vertical black bars indicate episodes of minor reworking (Rögl 1991; see section 5.2 in the text). Solid grey lines indicate lithostratigraphic boundaries, dashed grey lines indicate the first occurrences (FOs) of biostratigraphic index taxa in the section and the inferred calcareous nannoplankton zonation.

14 124 P. Grunert et al m (A = 0.09 ; σ = 0.24 ). At the top of the Lower Puchkirchen Formation ( m) δ 13 C bulk values drop by ~ 0.8 but recover quickly in the lower part of the Upper Puchkirchen Formation until they reach another maximum at 1780 m. After a major drop of ~ 1.2 values remain low with some variability until 1612 m (A = 0.39 ; σ = 0.26 ). An overall positive trend, only interrupted by a negative excursion at 1590 m, occurs in the uppermost part of the Upper Puchkirchen Formation (A = 0.05 ; σ = 0.46 ). The transition into the basal Hall Formation is characterized by an abrupt decrease of ~ 1.5 in δ 13 C bulk (A = 0.67 ; σ = 0.35 ). A further decrease with more stable values is observed in the lower Hall Formation (A = 0.95 ; σ = 0.13 ). 5. Discussion 5.1 Nannoplankton zonation Generally, poor to moderate preservation and the absence of several prominent biostratigraphic markers coupled with the common appearance of reworked taxa, make accurate biostratigraphic dating of the Puchkirchen Group challenging. Nevertheless, based on the first occurrences of a few index taxa three bio - stratigraphic intervals are distinguished in the section: 1) Frequent occurrences of Reticulofenestra bisecta and R. stavensis (the large 10 μm morphotype of R. bisecta) and the absence of typical Neogene species such as Helicosphaera carteri indicate a correlation of the interval between m with nannoplankton zones NP24 25/CNO5 6. The absence of zonal markers in this interval did not allow a clear assignment to zone NP24 or NP25/CNO5 or CNO6 for the lowermost interval ( m). Considering the position of the NP25/NN1 boundary between 1950 m and 1940 m a correlation with upper NP25/CNO6 can be inferred (see below). Rare but consistent occurrences of poorly preserved Reticulofenestra umbilicus in the lowermost interval ( m) are considered the result of reworking and not a separate bioevent (top NP22/CNO2) (Plate 1). This interpretation is further supported by the lack of planktonic foramini - fera indicative for the early Rupelian at Hochburg 1 (Rögl 1991) as well as the correlation of the underlying Zupfing Fm. with nannoplankton zone NP25 (Rögl et al. 1979, 1998). 2) The interval between m is assigned to nannoplankton zones NN1 lower NN2/CNM1 lower CNM4 based on the FOs of Helicosphaera carteri and H. ampliaperta (Plate 1). The Base of H. carteri is recorded at the top of NP25 at the Lemme-Carosio section, the type locality for the Oligocene/Miocene boundary (Aubry 1996). However, this species becomes common only in the lowermost Miocene (e. g., Backman et al. 2012) and consequently the Base of H. carteri is used in the Mediterranean/Paratethys area to approximate the Oligocene/Miocene boundary (Galović and Young 2012). Thus, we adopt the Base of H. carteri close to the NP25/NN1 boundary (top of CNO6 close to the CNO6/CNM1 boundary) to approximate the base of zone NN1 (CNM1). This interpretation is additionally supported by the mere disappearance of R. bisecta as well as R. stavensis at the same depth, two taxa with their topmost occurrence commonly recorded at the Oligocene/Miocene boundary (Fornaciari and Rio 1996, Bown 1998, Kameo and Bralower 2000, Raffi et al. 2006, Henderiks and Pagani 2008). Although any correlation based on bio - stratigraphic markers using the top occurrence of taxa should be treated with caution at Hochburg 1 given the high amount of reworked taxa, the coincidence of the assemblage change with the FO of H. carteri is remarkable and strengthens our interpretation. 3) The Base of Helicosphaera ampliaperta, recorded at Ma within NN2 and CNM4, is generally considered a reliable bioevent to approximate the Aquitanian/Burdigalian boundary as well as the Bur1 sea level lowstand (Fornaciari and Rio 1996, Raffi et al. 2006, Backman et al. 2012). Based on the FO of H. ampliaperta the interval from 1640 m to the top of the Puchkirchen Group at Hochburg 1 is correlated with the upper NN2 and middle to upper CNM4 zones. While the application of first occurrences excludes reworking of older sediments as a bias on the stratigraphic interpretation, contamination by allochthonous sediment from shallower parts of the drill-hole has to be considered as a potential problem. With respect to Hochburg 1 we argue that contamination is minimal for the studied samples based on the following three observations: First, internal reports show that benthic fora - minifera indicative for the superimposed Hall Formation (e. g., Elphidium ortenburgense, Lenticulina buergli; Grunert et al. 2013) have not been found in the samples of the Puchkirchen Group. Second, the new dataset reveals a very different geochemical signature of the Puchkirchen Group and the Hall Formation. Any contaminated sample should thus be recognizable by a distinctive negative δ 13 C bulk signature which is not the

15 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 125 case (Fig. 4). With respect to the A1 horizon, contamination would, in addition, not allow for the very low CaCO 3 values observed in this interval. Finally, trends in the size of H. ampliaperta at Hochburg 1 are consistent with previous reports (Holcová 2009, Backman et al. 2012): the first specimens of H. ampliaperta recorded at 1640 m at Hochburg 1 are generally small (~ 5 μm) and of low abundance. At 1630 m, H. ampliaperta significantly increases in abundance with specimens generally larger (7 10 μm). We argue that a contamination of the samples would have obscured this widely observed evolutionary trend. 5.2 Carbon isotope stratigraphy The herein proposed nannoplankton zonation is supported and refined by the δ 13 C bulk -data (Fig. 5). The comparison of the Hochburg 1 isotope record with the global δ 13 C stack of Zachos et al. (2008) and Vandenberghe et al. (2012; recalibrated from Cramer et al. 2009) reveals an excellent agreement of major trends. A prominent feature of the global stack traversing the Oligocene/Miocene boundary (and thus a primary target for correlation) is a prolonged phase of increased δ 13 C values which extends from NN1/top CNO6 to CNM1 into the lower part of NN2/CNM2 3 (~ Myrs) and is accentuated by four positive excursions (Figs. 3, 5). A comparable pattern of elevated δ 13 C bulk values punctuated by four positive peaks is recognizable at Hochburg 1 between 1940 m and 1770 m, an interval correlated herein to NN1 lower NN2/CNM1 CNM3 (Fig. 5). This plateau is preceded in the global stack by a gradual increase in δ 13 C in the later part of NP25/CNO6 which is interrupted by several brief minima, most prominently between 24 and 24.2 Myrs, at 23.7 Ma and between 23.3 and 23.4 Myrs. Similarly, three minima ( m; 2010 m; m) punctuating an overall positive trend are recognized at Hochburg 1 during the NP25 interval suggesting an approximate age of ~ 24.2 Ma for the base of the Puchkirchen Group. The rather homogenous lithology in the Lower Puch kir - chen Formation and the A3 4 horizons of the Upper Puchkirchen Formation allows for a simple test of the proposed correlation: we calculated a sedimentation rate of ~ 11.5 cm/ka (uncorrected for compaction) between the FOs of H. carteri and H. ampliaperta and applied it to the NP25 interval. The result suggests an age of ~ 24.4 Ma for the base of the Lower Puch kir - chen Formation which is very close to the estimate from the δ 13 C bulk record. δ 13 C values in the global stack fall abruptly from the plateau in the middle Aquitanian and stay at a lower level far into the Burdigalian. A sudden decrease in values followed by lower values is also recognized at Hochburg 1 which continues until the FO of H. ampliaperta. Above the FO of H. ampliaperta correlation with the global stack is complicated by a more diverse, often sandy to conglomeratic lithology. The overall positive trend in δ 13 C bulk values at the top of the Upper Puchkirchen Formation is not easy to correlate and the previously calculated sedimentation rates cannot be applied anymore. Two transitions towards positive values occur in the global stack between 20.4 and 20.2 Myrs and 19.9 and 19.8 Myrs. Based on the current data-set it is not possible to decide for one of these datums. A concern with any geochemical data is alteration of the original signal by diagenesis. Although δ 13 C of bulk sediment samples is considered comparably resistant, diagenetic alteration may occur due to the release of 1) 12 C to the pore water during breakdown of sedimentary organic matter, and 2) 12 C originally bound to clay particles (Marshall 1992). In most cases the quantity of 12 C introduced from these sources into the bulk carbonate is neglectable. However, at a low carbonate content the amount of diagenetic 12 C might bias the original signature towards more negative δ 13 C values. In the case of the Puchkirchen Group, a CaCO 3 content 20% only occurs in the uppermost part (A1 horizon). Diagenetic overprint by 12 C in this interval seems nonetheless unlikely, as statistical analysis shows no significant correlation between CaCO 3 and δ 13 C bulk (R 2 = 0.004). Only the extreme negative excursion at 1590 m might be associated with diagenesis. In general, there is no correlation for the Puchkirchen Group observed at Hochburg 1 (R 2 = 0.01; R 2 = 0.1 for Lower Puchkirchen Formation, R 2 = 0.02 for Upper Puchkirchen Formation). Reworking of older carbonate is another potential source for alteration of the original δ 13 C signal. Fora - minifera and calcareous nannoplankton are identified as the main components of the bulk carbonate by Rögl (1991) and our own data; pteropods, common in the lower part of the Upper Puchkirchen Formation, are primarily preserved as fillings of pyrite. Based on visual inspection, reworked coccoliths from the Cretaceous and the Paleogene contribute ~ 20 35% to the nannoplankton assemblages. However, there are no major differences or abrupt changes in the portion of reworked specimens between the samples or at major steps in the isotope record observed. As pointed out in

16 126 P. Grunert et al. Fig. 5. Correlation of the δ 13 C bulk -record of Hochburg 1 with global δ 13 C stack of Zachos et al. (2008). Encircled numbers indicate minima and maxima in the global stack that are used for correlation with the NAFB isotope record; grey numbers indicate tentative correlations. Dashed lines indicate the Base datums of Helicosphaera carteri and H. ampliaperta. Grey and black bars indicate the range of the base of the Puchkirchen Group as calculated from sedimentation rates (see text) and the range of the δ 13 C-maximum observed in both isotopic records. Global stack and nannoplankton zonation are calibrated to the GTS 2012 (Gradstein et al. 2012). section 2, reworked planktonic foraminiferal shells from the early Oligocene occur between 1920 m and 1970 m. Reworking from the Lower into the Upper Puchkirchen Formation is indicated from m and m by the occurrences of some reworked benthic foraminifera (Rögl 1991). Planktonic foraminifera, larger benthic foraminifera or coralline red algae indicative for the Cretaceous, Paleocene or Eocene are absent from the studied interval (Rögl 1991). Given the overall low number of coccoliths, we

17 Stratigraphic constraints for the upper Oligocene to lower Miocene Puchkirchen Group 127 thus consider only reworking of lower Oligocene carbonates as indicated by planktonic foraminifera as a potential bias on the δ 13 C data (Fig. 4). Sachsenhofer et al. (2010) report δ 13 C values of 2.5 and 0.1 for the Zupfing Formation from several boreholes in the NAFB, and a test sample from the Zupfing Formation at Hochburg 1 (2140 m) reveals a similarly depleted value of 1.2. Reworking of lower Oligocene carbonates might thus have contributed to a minor extent to the depletion of δ 13 C values between 1920 m and 1970 m. 5.3 A new stratigraphic concept for the Puchkirchen Group The herein presented bio- and chemostratigraphic evidence from Hochburg 1 allows for the inference of some basic stratigraphic constraints for the Puchkir - chen Group in general that significantly improve previous correlations. An age 24.5 Ma can be generally assumed for the base of Puchkirchen Group as the gradual and conformable transition from the Zupfing Formation into the Lower Puchkirchen Group is not only observed at Hochburg 1 but represents a general feature in the NAFB (Wagner 1998). Based on the carbon isotope record, the boundary between the Lower and Upper Puchkirchen Formations can be constrained to ~ Ma. The top of the Puchkirchen Group at Hochburg 1 has been significantly eroded by the Base Hall Channel (Grunert et al. 2013). Seismic images indicate that the Upper Puchkirchen Formation outside areas of channel deposition continues for another ~ 100 m. Applying the previously calculated sedimentation rates for the Lower Puchkirchen Formation at Hochburg 1 (which was located outside the channel at the time of deposition; see section 5.2), 100 m of sediments correspond to ~ 0.9 Myrs, thus indicating the upper boundary of the Puchkirchen Group between 19.5 and 18.9 Myrs. However, this is a preliminary estimate that should be investigated in detail at other, better suited drill-sites than Hochburg 1. The new stratigraphic concept with a range from upper Chattian to lower Burdigalian differs significantly from previous studies. As highlighted in section 2.1 and Table 1, there is considerable disagreement between reports from Bavaria and Upper Austria about the correlation of the Puchkirchen Group (Rögl et al. 1998). The published information from Austrian drillsites suggests a maximum range of the Puchkirchen Group from Ma to 22.9 Ma, a significantly older age compared to Hochburg 1. In contrast, stratigraphic data from Bavaria, mostly from the imbricated Traun section located ~ 36 km SW of Hochburg 1 (Fig. 1), indicate an age Ma for the base of the Puch - kirchen Group and an age significantly younger than Ma for its top (Table 1). Most importantly, the continuous occurrence of Globoquadrina dehiscens (Base: Ma; Wade et al. 2011, Gradstein et al. 2012) in an 875-m-thick succession of the Upper Puchkirchen Formation indicates a significant extension of the Puchkirchen Group into the lower Miocene. The review of previous studies suggests that the contradictory stratigraphic reports result from two main problems. First, unpublished internal reports by RAG show that explorational drilling is largely focused on the southern basin margin where re-deposition of older sediments through the channel system occurs frequently, and the Puchkirchen Group is often heavily imbricated (see also Hinsch 2008, 2013). Second, most studies are based on a small number of samples and lack precise or any information about localities as well as position and number of samples, making it almost impossible to integrate the different reports. In the present study, most of these issues are avoided as Hochburg 1 is located further to the north and the interpretation relies on continuous, well-documented sampling. In the light of the herein presented evidence, it is possible to integrate the previously reported biostratigraphic datums (which are not in conflict with the new age model; Table 1) and to conclude this long-lasting debate. Support for the discussed stratigraphic correlation comes from a preliminary survey of internal biostratigraphic reports on planktonic foraminifera from various RAG drill-sites in Upper Austria and Salzburg (mostly conducted by Fred Rögl). Faunas of the Puch - kirchen Group commonly contain species that extend well into the lower Miocene (e. g., G. ciperoensis, Tenuitella munda) and in contrast to published data and in agreement with the Bavarian study area Gqu. dehiscens has been reported from imbricates of the Upper Puchkirchen Formation in some instances (e. g., drill-site Geo 1). With respect to calcareous nannoplankton, internal reports (conducted by Stjepan Ćorić) show that H. ampliaperta has been found in the Upper Puchkirchen Formation before (e. g., at drillsite Nuss-W4) but considered as contamination from overlying sediments in the drilling-process. As outlined before, our new data challenge this view and strongly suggest an autochthonous occurrence (see section 5.1). The new concept also agrees with the available stratigraphic information for under- and overlying