Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin

PALAEO-08134; No of Pages 18 Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2017) xxx–xxx

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Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin Martina Pippèrr ⁎, Bettina Reichenbacher Department of Earth and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-University, Richard-Wagner-Straße 10, D-80333 Munich, Germany

a r t i c l e

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Article history: Received 5 May 2016 Received in revised form 18 December 2016 Accepted 1 January 2017 Available online xxxx Keywords: Western Paratethys Ottnangian Karpatian Rzehakia facies Stratigraphy Palaeogeography

a b s t r a c t The North Alpine Foreland Basin (NAFB) experienced rapidly changing palaeoenvironmental conditions at the end of the Early Miocene (middle-to-late Burdigalian, Paratethys stages Ottnangian and Karpatian), with transformation of fully marine settings into brackish and eventually freshwater environments. These changes were related to global sea-level fluctuations, climate oscillations, and tectonic processes associated with the uplift of the Alps. This study presents a new and comprehensive data set, derived from 13 boreholes and 491 core samples from the Molasse Basin of southwest Germany, that provides a significantly better understanding of late Early Miocene palaeoenvironments in the NAFB. Based on lithostratigraphy, biostratigraphy, and palaeoecological interpretation of rich fauna and flora assemblages, we show that the upper Burdigalian sediments comprise a regressive lower segment (Grimmelfingen Formation and equivalents), as indicated by the occurrence of the bivalve Rzehakia, and a transgressive upper component (Kirchberg Formation and equivalents) characterized by the advent of new fish and mollusc assemblages. Furthermore, we present a new lithostratigraphic concept for the Kirchberg Formation, which forms an important part of the Upper Brackish Molasse (OBM). Based on biostratigraphic constraints and recently published magnetostratigraphic data, it appears that the regressive segment of the upper Burdigalian OBM sediments correlates with the end of the global third-order sea-level cycle Bur 3, while the transgressive component reflects the Karpatian transgression at the beginning of sea-level cycle Bur 4. This implies that the Karpatian transgression actually affected the Molasse Basin of southern Germany and Upper Austria, whereas previous studies had considered this part of the NAFB as terrestrial during that time span. The new results are depicted in three palaeogeographic maps for the NAFB at 18 Ma, 17.5–17.1 Ma and 17 Ma, respectively. © 2017 Elsevier B.V. All rights reserved.

1. Introduction The North Alpine Foreland Basin (NAFB, Fig. 1A), also referred to as Molasse Basin, formed in the Late Eocene/Early Oligocene and existed until the Late Miocene. It was part of the Western and Central Paratethys, which developed in the course of the Alpine orogeny through isolation from the northern Tethys (e.g. Rögl and Steininger, 1983; Rögl, 1999; Popov et al., 2004). However, the presence of numerous endemic species among the Oligo-Miocene fauna and flora of the Paratethys and NAFB renders stratigraphic correlation with the Tethys realm difficult (see Piller et al., 2007). As a result, regional chronostratigraphic stages have been introduced for the Oligocene and Miocene Series in the Central Paratethys realm, and are also widely used for the Molasse sediments of the NAFB (Fig. 2). The NAFB extends from the Rhône Basin in the west via Switzerland and southern Germany to Lower Austria in the east (Fig. 1A). The Swiss and SW German sectors of the NAFB correspond to the area of the Western Paratethys, while the SE German and Austrian portions represent the ⁎ Corresponding author. E-mail addresses: [email protected] (M. Pippèrr), [email protected] (B. Reichenbacher).

western zone of the Central Paratethys. The sedimentary fill of the NAFB Basin, which reaches thicknesses of over 5000 m in places, includes largely siliciclastic marine, brackish and terrestrial sediments and represents one of the most continuous Oligocene-Miocene archives in Europe (e.g. Schlunegger et al., 1997; Kuhlemann and Kempf, 2002; Abdul Aziz et al., 2010). In the Swiss and SW German segment of the NAFB, the sedimentary succession as a whole is divided into two transgressive-regressive megacycles, which are separated by an extensive unconformity (e.g. Lemcke, 1988; Bachmann and Müller, 1992). The first megacycle (Oligocene to lowermost Miocene) comprises the lithostratigraphic groups of the Lower Marine Molasse, Lower Brackish Molasse and Lower Freshwater Molasse, while the second megacycle (lower Miocene to upper Miocene) consists of the Upper Marine Molasse, Upper Brackish Molasse and Upper Freshwater Molasse (e.g. Doppler et al., 2005). An especially interesting time span in the geological history of the NAFB is the late Early Miocene (middle to late Burdigalian, Central Paratethys stages Ottnangian and Karpatian) because this interval saw significant changes in palaeoenvironmental conditions in the region (e.g. Lemcke, 1988; Kuhlemann and Kempf, 2002). Lower Ottnangian sediments are usually fully marine, middle Ottnangian successions are dominated by restricted marine conditions, upper Ottnangian sediments

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Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 1. (A) Schematic map of the North Alpine Molasse Basin. (B) Locations of the boreholes Glött (succession with OMM – OBM/Kirchberg Fm – OSM), Günzburg, Offingen, Gundremmingen, Lauingen, Holzheim, Dillingen, Buttenwiesen, Pfaffenhofen T1 and T3, Druisheim, Hamlar 1, and Gempfing (successions with USM or Jurassic limestone – OBM/Grimmelfingen and Kirchberg Fms. – OSM). In addition, we refer to the boreholes Burgau, Lutzingen, Hamlar 2 (Pippèrr et al., 2016; successions with OMM and without OBM) and the outcrops near Illerkirchberg, the type locality of the Kirchberg Fm (Reichenbacher, 1989). OMM = Upper Marine Molasse, OBM = Upper Brackish Molasse, OSM = Upper Freshwater Molasse.

are characterized by a brackish facies, and the Karpatian deposits are generally thought to reflect the presence of freshwater environments (e.g. Wenger, 1987; Doppler et al., 2005; Piller et al., 2007; Rupp et al., 2008; Pippèrr, 2011). Abundant shells of the bivalve Rzehakia (formerly Oncophora) often characterize the brackish deposits; this conspicuous Rzehakia facies can be traced across the entire Paratethys and is considered to denote the final regressive phase of the Ottnangian Paratethys sea (e.g. Čtyroký, 1968; Čtyroký et al., 1973a; Steininger et al., 1976; Harzhauser and Piller, 2007). However, whether the emergence of this noticeable Rzehakia facies was related to global sea-level fluctuations, climate oscillations or the Alpine orogeny has not yet been resolved.

The objective of this study is to present comprehensive new data based on 13 boreholes and 491 core samples from the SW German sector of the NAFB (= SW German Molasse Basin), which significantly enhance our understanding of the middle and late Burdigalian (Ottnangian– Karpatian) palaeoenvironments in the NAFB and western Paratethys, respectively. We show that what has previously been identified as the Rzehakia facies in the SW German Molasse Basin actually comprises a regressive plus a transgressive sedimentary unit. Based on biostratigraphic constraints and recently published magnetostratigraphic data (Reichenbacher et al., 2013; Sant et al., submitted), we conclude that the transgressive sediments represent the Karpatian transgression at the beginning of the global third-order sea-level cycle Bur 4. This implies

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 2. Global and regional stratigraphy of the Early Miocene (after Piller et al., 2007) and lithostratigraphic units in the South German Molasse Basin (Doppler et al., 2005; Reichenbacher et al., 2013).

that, although sedimentation took place in a tectonically active foreland basin, global sea-level change was the main factor that controlled the deposition of marine vs. non-marine sediments in the late Burdigalian. 2. Geological setting 2.1. The Molasse Basin The sediments and fossil assemblages studied here are derived from the SW German sector of the Molasse Basin (NAFB), which was part of the Western Paratethys. During the Oligocene and Miocene Epochs that witnessed the uplift of the Alpine-Carpathian, Dinarid and Balkan mountains, the Paratethys extended from the Rhone Basin in France to Central Asia (Popov et al., 2004). The rise of these mountain ranges ultimately isolated the Paratethys realm from the northern part of the Tethys, but temporary connections subsequently existed with the Mediterranean Tethys, the Indo-Pacific and the Atlantic (Rögl and Steininger, 1983; Rögl, 1999; Popov et al., 2004). This study deals with the Lower Miocene Paratethys stages Ottnangian and Karpatian (Fig. 2). The biostratigraphy of the marine sediments of Ottnangian and Karpatian age is based largely on molluscs and benthic foraminifers (e.g. Papp et al., 1973; Wenger, 1987; Cicha et al., 1998; Piller et al., 2007). Data for the brackish and freshwater sediments are provided by molluscs, small-mammal teeth, fish otoliths and charophytes (e.g. Reichenbacher, 1993, 1999; Böhme, 2003, 2010; Reichenbacher et al., 2004, 2005; Kälin and Kempf, 2009; Abdul Aziz et al., 2010; Jost et al., 2015). In the S German segment of the Molasse Basin, the sedimentary succession as a whole is divided into two transgressive-regressive megacycles. The second megacycle (Miocene) includes the Upper Marine Molasse (OMM; Eggenburgian – middle Ottnangian), the Upper Brackish Molasse (OBM; upper Ottnangian – Karpatian) and the Upper Freshwater Molasse (OSM; Karpatian – Pannonian) deposits (Doppler et al., 2005; Reichenbacher et al., 2013). The sediments show considerable regional variation in facies, both from West to East and from South to North. As a result, the terms “western Molasse” (SW German sector of the Molasse Basin) and “eastern Molasse” (SE German sector of the Molasse Basin) are informally used for the facies in the areas of the South German Molasse Basin to the west and east of Munich, respectively (Doppler et al., 2005; Pippèrr, 2011). 2.2. The Upper Marine Molasse (OMM) At the beginning of the Ottnangian, a new, basin-wide transgression flooded the NAFB, and the Paratethys was connected to the western

Mediterranean Tethys by a narrow seaway (e.g. Allen et al., 1985; Kuhlemann and Kempf, 2002; Pippèrr et al., 2016). The marine sediments of this transgressive phase are represented by the Ottnangian part of the Upper Marine Molasse (in German Obere Meeresmolasse, OMM). Note that we use here the German abbreviation OMM to avoid confusion with the older sediments of the Lower Marine Molasse (Untere Meeresmolasse in German, traditionally abbreviated as UMM). The OMM sediments show a considerable variety of litho- and biofacies, and both informal and formal lithostratigraphic names have been introduced for the individual local units (see Doppler et al., 2005; Heckeberg et al., 2010; Pippèrr, 2011; Pippèrr et al., 2016). The sediments studied here come from sites in the SW German sector of the Molasse Basin, where the OMM comprises the lower Ottnangian “OMMBasisschichten” (coarse-grained glauconitic sands with gravels) and the Kalkofen Formation (sandy-to-marly sediments), as well as the middle Ottnangian Baltringen and Steinhöfe Formations (coarse- to fine-grained glauconitic sands) (Heckeberg et al., 2010). These lithostratigraphic units and their microfossil assemblages have recently been described in detail in Pippèrr et al. (2016) (boreholes Burgau and Hamlar 2; see Fig. 1). Furthermore, a lower to middle Ottnangian marginal-marine facies can be differentiated (Pippèrr et al., 2016: borehole Lutzingen and some outcrops). 2.3. The Upper Brackish Molasse (OBM) In the late Ottnangian the S German and Austrian sectors of the Molasse Basin were affected by a regression. In the German segment, the late Ottnangian to early Karpatian time span saw the development of brackish to limnic and also terrestrial successions, which are collectively referred to as the Upper Brackish Molasse (= “Süßbrackwassermolasse”, meaning ‘Fresh-to-Brackish Molasse’ in older work), and are indicative for variable and complex palaeogeographical settings. The Upper Brackish Molasse (OBM) represents a group in terms of lithostratigraphy and comprises: (1) the fluviatile to estuarine Grimmelfingen Formation, the most probably terrestrial Albstein, and the brackish Kirchberg Formation of the western S German Molasse Basin; (2) the lacustrine to slightly brackish Bunte Mergelserie and the brackish Sand-Kalkmergelserie in the central S German Molasse Basin; and (3) the brackish Oncophora-Beds of the eastern S German Molasse Basin (see also palaeogeographic maps in Section 7). In the study area, the late Ottnangian regression initiated the incision of the so-called Graupensandrinne, an erosive channel that formed near the northern margin of the Molasse Basin (Moos, 1926; Kiderlen, 1931; Reichenbacher et al., 1998). On the topographically elevated region to the south of the Graupensandrinne (“Albsteinschwelle” sensu Lemcke et

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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al., 1953) developed calcareous, mostly terrestrial deposits (=Albstein). The “Graupensand River” eroded the underlying OMM and deposited the Grimmelfingen Formation, which comprises largely carbonate-poor to -free, fine-to coarse-grained, partially gravelly sands (Graupensande), grading upwards into the fine-grained sediments of the GraupensandDeckschichten (e.g. Doppler et al., 2005; Reichenbacher et al., 2013). Kiderlen (1931), Lemcke (1988) and others interpreted the sedimentary structures of the Grimmelfingen Fm as fluvial, but Luterbacher et al. (1992) and Asprion and Aigner (2000) later found evidence for an estuarine environment, while Tipper et al. (2003) have more recently argued that the Graupensand Channel resulted from submarine erosion and that the Grimmelfingen Fm is consequently marine. The fossil-rich marls of the Kirchberg Fm overlie the Grimmelfingen Fm and probably record a short-term transgression of the Swiss Molasse Sea (Kiderlen, 1931; Lemcke, 1988; Reichenbacher et al., 1998). The lithostratigraphic concept of the Kirchberg Fm, the type locality of which is Illerkirchberg (Fig. 1), is based on Kranz (1904), and has been refined by Schlickum (1963) and Reichenbacher (1989). Based on their fossil contents, the deposits can be divided into the lower and upper Kirchberg Fm (see also Section 5). Various interpretations of the stratigraphic relationships between the Kirchberg Fm (Western Paratethys) and the Oncophora-Beds (Central Paratethys, Lower Bavaria and Austria) have been proposed. For Reichenbacher (1993), Zöbelein (1994) and others, the two are essentially contemporaneous. Schlickum (1971) and Lemcke (1988) assume that the Kirchberg Fm is slightly younger, whereas Doppler (1989) supposes that the Kirchberg Fm slightly predates the Oncophora-Beds. 3. Materials and methods The samples studied here were assembled from cores recovered from 13 boreholes (Fig. 1) that were drilled under the auspices of the Bavarian Environmental Agency (Landesamt für Umwelt, LfU) between 2010 and 2014. The cores are logged as LfU-FB Offingen 1, LfU-FB Burgau 1, LfU-FB Glött 1, LfU-FB Gundremmingen 1, LfU-FB Holzheim 1, LfU-FB Dillingen 1, LfU-FB Lutzingen 1, LfU-FB Buttenwiesen 1, LfUFB Druisheim 1, LfU-FB Hamlar 1 and LfU-FB Hamlar 2; as well as Günzburg Brunnen 3 neu, Vogelhölzl N Lauingen, Pfaffenhofen, kommun. WV, GWM T 1 and Pfaffenhofen, kommun. WV, GWM T 3, and WWA Donauwörth, Gempfing W4. All cores are stored in the Bavarian Environmental Agency's archive in Hof (Germany). To study their microfossil content, 492 samples were taken from the cores (Table 1). The samples were processed by soaking in dilute hydrogen peroxide for several hours. Then the samples were washed under running water through 63 μm, 200 μm and 400 μm mesh sieves. Down to a grain size of 400 μm, microfossils were picked completely; smaller grain-sizes were picked from representative splits of the samples. Microfossils were identified to species level (as far as possible), sorted and counted (see Appendices 1–2: benthic foraminifers; Appendix 3: bivalves, gastropods, fish otoliths, ostracods, charophytes, fruiting and seeds). Identification of foraminiferal genera and species follows Wenger (1987), Cicha et al. (1998) and Rupp and Haunold-Jenke (2003), while the palaeoecological interpretations follow Murray (1991, 2006) and Sen Gupta (1999). The identification of fish otoliths follows Reichenbacher (1993) and Gierl and Reichenbacher (2015). The taxonomic classification of the ostracods primarily follows Straub (1952) and Witt (2000), and that of charophytes follows Berger (1992). The gastropods from the boreholes are described in detail in Salvador et al. (2016). 4. Results Based on micropalaeontological analyses and the study of lithofacies, two different successions are recognizable in our core samples. The sediments from Glött can be assigned to (1) the Upper Marine Molasse, (2) Albstein, (3) the Upper Brackish Molasse (Kirchberg Fm), and (4) the

Table 1 Numbers of samples from the different boreholes: Lower Freshwater Molasse (USM), Upper Marine Molasse (OMM), Upper Brackish Molasse (OBM) and Upper Freshwater Molasse (OSM). Borehole

OSM

OBM (K. Fm)

OBM (Gr. Fm)

OMM

USM

Glött Günzburg Offingen Gundremmingen Lauingen Holzheim Dillingen Buttenwiesen Pfaffenhofen T1 Pfaffenhofen T3 Druisheim Hamlar 1 Gempfing Samples in total

7 0 13 7 0 11 11 8 3 5 3 5 16 89

3 26 12 5 23 14 7 17 17 13 24 39 9 209

Albstein 1 18 8 13 8 11 1 18 7 1 30 11 10 136

19 Hiatus Hiatus Hiatus Hiatus Hiatus Hiatus Hiatus Not drilled Not drilled Hiatus Hiatus Hiatus 19

Not drilled 2 8 8 Hiatus 0 16 1 Not drilled Not drilled 1 2 Hiatus 38

Upper Freshwater Molasse (Fig. 3). The deposits from the sites Günzburg, Offingen, Gundremmingen, Lauingen, Holzheim, Dillingen, Buttenwiesen, Pfaffenhofen T1 and T3, Druisheim, Hamlar 1 and Gempfing can be subdivided as follows: (1) Lower Freshwater Molasse or Jurassic limestone, (2) Upper Brackish Molasse (Grimmelfingen Fm and Kirchberg Fm), and (3) Upper Freshwater Molasse (Figs. 3 and 4). Given the geographic locations of Glött and the remaining drilling sites (see Fig. 1B), it is obvious that the sediments that make up the Grimmelfingen Fm were deposited in a relatively restricted area along the northern border of the Molasse Basin. In this zone, the sands of the Grimmelfingen Fm overlie Jurassic limestone or sediments of the Lower Freshwater Molasse, and OMM sediments are absent. The sites to the South (Burgau: Pippèrr et al., 2016, and Glött: this study) and North (Lutzingen and Hamlar 2: Pippèrr et al., 2016) include marine OMM sediments, but the Grimmelfingen Fm is absent (Fig. 1). This pattern confirms the Graupensand Channel model: Within the Channel, OMM sediments were completely eroded away. 4.1. Upper Marine Molasse and Albstein In the set of cores studied here, OMM and the Albstein facies are found only in Glött (Fig. 3). There, the OMM is at least 12 m thick and can be divided into two segments based on lithofacies and fossil content, above all foraminiferal assemblages. The lowermost OMM deposits, which are unbedded and consist of grey or greenish-grey sandy marls and calcareous fine sands with relatively few glauconite, can be assigned to the Kalkofen Fm (97.37–99 m). Above follow sediments of the Baltringen Fm (87–97.37 m), which consist mainly of unbedded, green-to-grey and glauconite-rich coarse-to-fine sands that exhibit a fining upwards trend. In its lowermost part, the Baltringen Fm (“Baltringer Horizont”) includes medium- to coarse-grained sands, with some fine gravel and fossil remains (fragments of molluscs and balanids, teeth of sharks and rays), whereas silty fine sands occur in the uppermost part. The transition from the OMM to the Albstein facies (sensu Lemcke et al., 1953) is indistinct, as the sandy lithofacies of the OMM gradually changes into a silty calcareous facies. The Albstein deposits reach a thickness of 1.87 m and consist of silts with calcareous concretions and limestone layers. The most abundant microfossils in the OMM samples are benthic foraminifers. In particular, the deposits that make up the Kalkofen Fm (5 samples) contain rich (124 to 450 tests, Appendix 1), relatively diverse (12 to 33 species) and well-preserved assemblages that are dominated by hyaline taxa (mainly Elphidium spp., Elphidiella spp., Nonion commune, Hanzawaia boueana, Ammonia beccarii group). Agglutinated species (Spiroplectammina pectinata, Siphotextularia concava, Textularia sp.) are very rare, and miliolid forms are almost absent (1 test: Sigmoilinita sp.). Planktonic foraminifera (Globigerina praebulloides, G.

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 3. Profiles and fossil content of the samples recovered from the boreholes in the western section of the study area (Glött, Günzburg, Offingen, Gundremmingen, Lauingen, Holzheim, and Dillingen). Lower Freshwater Molasse (USM), Upper Marine Molasse (OMM), Upper Brackish Molasse (OBM) and Upper Freshwater Molasse (OSM).

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 4. Profiles and fossil content of the samples obtained from boreholes in the eastern section of the study area (Buttenwiesen, Pfaffenhofen T1 and T3, Druisheim, Hamlar 1, and Gempfing). Lower Freshwater Molasse (USM), Upper Brackish Molasse (OBM) and Upper Freshwater Molasse (OSM).

ottnangiensis, G. dubia; Globigerinoides trilobus) and marine ostracods (Hemicyprideis dacia elegantior, Cytherella vulgata, Pterygocythereis sp., Costa cf. polytrema, Olimfalunia ex gr. plicatula, Olimfalunia minor, Olimfalunia glabra, Loxoconcha linearis, L. eggeriana) also occur in the Kalkofen Fm. In contrast, the sands of the Baltringen Fm (14 samples)

contain few benthic foraminifera (0 to 49 tests, Appendix 1) and planktonic foraminifera and ostracods are absent or rare. Moreover, the benthic foraminiferal assemblages exhibit little diversity (0 to 14 species), with Ammonia and Elphidium (e.g. E. glabratum, E. subtypicum) being the most abundant genera. Macro- and microfossils are largely absent

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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in the Albstein deposits, but one sample yielded three teeth assigned to sparid fishes and a ray. The Albstein sediments also include calcareous remains of fossil roots. 4.2. Upper Brackish Molasse: Grimmelfingen Formation The sediments of the Grimmelfingen Fm (Graupensande and Graupensand-Deckschichten) discordantly overlie the Jurassic limestone or Lower Freshwater Molasse (USM), and reach a thickness of between 0.45 m (Dillingen) and 50 m (Druisheim) (Figs. 3 and 4). The deposits are largely comprised of carbonate-poor to -free, coarse- to fine-grained, sometimes gravelly sands. In most cases, the mica-rich sands contain few, if any, small-sized glauconite grains (probably reworked). Only at some levels in the cores from Günzburg (~ 50– 54 m) and Dillingen (~59–59.5 m) glauconite occurs more abundant. In most cores, the uppermost part of the Grimmelfingen Fm consists of fine-grained deposits (Graupensand-Deckschichten, GD in Figs. 3 and 4) including mainly carbonate-poor to -free, in some places also carbonate-rich, silty to fine-sandy sediments. In Offingen, as well as in Pfaffenhofen T1 and T3, the Graupensand-Deckschichten include calcareous layers and concretions (with rhizoconcretions present in Pfaffenhofen T1) similar to those seen in the Albstein facies. Macro- and microfossils are for the most part absent in the Grimmelfingen Fm, only few beds contain fossils (Figs. 3 and 4). Shells of bivalves characteristic of brackish habitats (Rzehakia partschi, Mytilopsis and cardiids) and/or fish teeth (shark, ray) occur in the basal layers (Offingen, Gundremmingen, Buttenwiesen, Druisheim) and in the lower part (Günzburg) of the Grimmelfingen Fm. The latter yielded also a small number of brackish gastropods (Nematurella bavarica) and fish otoliths (Gobius). A strikingly different lithofacies and a comparatively rich fossil assemblage occur in the middle levels of the Grimmelfingen Fm of Buttenwiesen. There, coaly sediments with plant remains and silty-tosandy deposits with an autochthonous freshwater fauna appear (4 samples; gastropods: Gyraulus, Planorbarius, Theodoxus, Bithynia, Stagnicola, Ferrissia; teeth of cyprinid fishes) in addition to numerous charophytes (mainly Stephanochara group praeberdotensis, determinations by Barbara Bassler, LMU Munich). Brackish gastropods (N. bavarica) are rare in this section. The fine-grained sediments of the Graupensand-Deckschichten present sparse occurrences of charophytes, freshwater gastropods (Bithynia, Gyraulus, Planorbarius, Stagnicola) and fish teeth (cyprinids and others). However, in Druisheim, several layers of the GraupensandDeckschichten include bivalve shells (Rzehakia) or numerous gastropod remains assigned to the genus Viviparus. A single small-mammal (rodent) tooth (Megacricetodon) was found in a sample from Offingen (determination by J. Prieto, Munich and D. Kälin, Wabern). 4.3. Upper Brackish Molasse: Kirchberg Formation The Kirchberg Fm overlies the Grimmelfingen Fm in all boreholes (n = 12) in which the Grimmelfingen Fm is represented. At Glött, the Kirchberg Fm occurs above Albstein deposits. The boundary between the Grimmelfingen Fm and the Kirchberg Fm that is drawn in this study is based on a distinct increase in carbonate and fossil contents (see Section 5). Furthermore, in several boreholes (Glött, Günzburg, Lauingen, Holzheim, Buttenwiesen, Pfaffenhofen T3), the basal layer of the Kirchberg Fm contains marly-to-sandy deposits with numerous bioclasts. The Kirchberg Fm is generally characterized by clay-rich to silty marls, in places accompanied by marly limestones and calcareous, fine-grained sands. The thickness varies between 0.63 m (Glött) and 12.85 m (Lauingen). Macro- and microfossils (bivalves, gastropods, fish otoliths, fish teeth, ostracods and charophytes) are usually abundant in the Kirchberg Fm (Figs. 3 and 4; Appendix 3). Only the section recovered from the Gundremmingen borehole was comparatively poor in fossils (shell fragments, bones and fish teeth). Generally, fossils are well-preserved, sometimes with their original coloration, but corroded or diagenetically

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altered fossils can appear in places. The lower and upper Kirchberg Fm can be clearly distinguished in 10 of the 13 boreholes based on the fossil assemblages that characterize each subdivision (see below). In the remaining three boreholes (Glött, Offingen, Dillingen) only the upper Kirchberg Fm is represented. The lower Kirchberg Fm predominantly includes marine-euryhaline and brackish taxa, whereas limnic species are less frequent. Shells of brackish bivalves (Limnopagetia, Limnopappia, Cerastoderma socialis, Mytilopsis clavaeformis, M. amygdaloides) are usually abundant in the most basal layers. Gastropod assemblages comprising mainly Nematurella, Ctyrokya, Hydrobia and Melanopsis, fish otoliths of marineeuryhaline groups such as herrings (Clupeonella humilis, C. cornuta), glass perches (Dapalis formosus, D. curvirostris, Ambassis sp.) and gobies (mainly Eleogobius gaudanti), as well as certain ostracod species (e.g. Caspiolla kirchbergensis, Candona suevica), occur throughout the lower Kirchberg Fm. Foraminifers occur only in a layer of glauconitic sands in Hamlar 1 (6 samples with 1–338 individuals, Appendix 2), where they are found together with brackish gastropods (Nematurella bavarica) and freshwater ostracods (Heterocypris straubi). The moderately to well-preserved benthic foraminiferal assemblage is extremely dominated by Ammonia and Elphidium glabratum. Both taxa are known to have had a high tolerance to fluctuations in salinity (e.g. Murray, 2006; Sen Gupta, 1999). The upper Kirchberg Fm contains large numbers of freshwater gastropods (e.g. Gyraulus, Planorbarius, Bithynia, Stagnicola), while brackish gastropods become rare (Nematurella bavarica and Hydrobia semiconvexa) and brackish bivalves are absent. Shells and opercula of Bithynia may cooccur with ostracods (e.g. Mediocypris candonaeformis) or charophytes (e.g. Chara molassica, Chara notata, Nitellopsis spp., Appendix 3). Further elements that characterize the upper Kirchberg Fm are otoliths of euryhaline fishes (e.g. Paralebias weileri, Hemitrichas martini, Gobius spp.) and freshwater fishes (e.g. Aphanolebias konradi, Cyprinidae), while otoliths of the above-mentioned marine-euryhaline fishes are lacking or very rare. In Gempfing, the uppermost sample of the Kirchberg Fm also includes a few (23), possibly reworked, benthic foraminifera (Bolivina dilatata, Bulimina elongata, Elphidium matzenense, Protelphidium roemeri, Nonion commune, Ammonia). In Pfaffenhofen T 1, the uppermost sample within the upper Kirchberg Fm contains a single tooth of (?)Megacricetodon aff. collongensis (determination by J. Prieto, Munich). 5. New lithostratigraphic definition of the Kirchberg Formation The type section of the (usually up to 15 m thick) Kirchberg Formation is exposed at Illerkirchberg near Ulm (Figs. 1 and 5). The litho- and biofacies, as well as the litho- and biostratigraphy of this locality are described in detail in Reichenbacher (1989). However, in its previous definition, the lower boundary of the Kirchberg Fm remained vague, and opinions differ with respect to how this lithostratigraphic unit should be differentiated from adjacent units (see Doppler, 1989; Zöbelein, 1994). 5.1. Lower boundary (Grimmelfingen Fm/Kirchberg Fm) Based on the results of this study, the Kirchberg Fm can be defined as a predominantly fossil-rich, marly facies with a characteristic and diverse macro- and microfauna (Section 4.3; Appendix 3). Below this fossiliferous marl facies lie either extremely fossil-poor sediments or sands with abundant shells of the snail Viviparus suevicus. Depending on the occurrence of Viviparus, these sediments have been termed fluviatile sands and Suevicus Beds in Kiderlen (1931) and river sands and Viviparen-horizon in Kranz (1904), Schlickum (1963) and Reichenbacher (1989) (see Fig. 5). Kiderlen (1931) considered the fluviatile sands and also the sands with Viviparus to belong to the Grimmelfingen Fm. In contrast, Kranz (1904), Reichenbacher (1989) and subsequent authors (e.g. Reichenbacher et al., 2013) regarded these sands as representing the lowermost bed of the Kirchberg Fm.

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 5. Lithostratigraphy, assemblage zones and lithofacies of the Kirchberg Formation at the type section Illerkirchberg (according to Reichenbacher et al., 2013, modified). Assemblage zones 1– 8 refer to the biostratigraphic zonation described in Reichenbacher (1989), which is based on typical assemblages of fish otoliths, bivalves, gastropods, ostracods and charophytes. According to the results of this study, assemblage zone 1 (Viviparen-Zone and equivalents) correlates with the Grimmelfingen Fm (in Reichenbacher, 1989: Kirchberg Formation).

Here we assign both the fluviatile sands and the Viviparus sands to the Grimmelfingen Fm (see Fig. 5) for the following reasons: The litho- and biofacies of these sands are similar to those of the sediments of the Grimmelfingen Fm (see Section 4.2). In Druisheim, the fine-grained sands and sandy silts below the fossil-rich marls (Kirchberg Fm) are largely carbonate-poor and contain only few shell fragments, while the subjacent sandy-to-silty facies includes either abundant Viviparus or some Rzehakia shells, while other fossils are rare (Fig. 4). In the type section (Fig. 5), the ‘river sands’ and the sands with Viviparus contain a few brackish bivalves (Rzehakia partschi, Mytilopsis and cardiids), which we have also found in the lower part of the Grimmelfingen Formation (boreholes Günzburg and Offingen, see Fig. 3). Other fossils are sparse and include a few ostracod shells (Mediocypris) and fish otoliths (Clupeonella) (Reichenbacher, 1989: Table 3). Consequently, the new base of the Kirchberg Fm is drawn to coincide with the first occurrence of fossiliferous marly sediments with a rich and often well-preserved macrofauna, mainly composed of marine-euryhaline bivalves (e.g. Cerastoderma sociale) as well as brackish bivalves and gastropods (Mytilopsis amygdaloides, M. clavaeformis, Ctyrokya conoidea, Nematurella bavarica). The microfossil assemblages of these basal layers are also quite characteristic, with numerous shells of the ostracod Caspiolla kirchbergensis and abundant teeth of primary marine fishes (Sparidae). In previous work, the basal layers of the Kirchberg Fm have been termed

“Cardien-Schichten” and “Congerien-Schichten” (Kranz, 1904), “Congerien- and Cardienhorizont” (Schlickum, 1963), “Horizont 2a” and “Horizont 2b” or “Spariden-Horizont” and “Congerien-Horizont” (Reichenbacher, 1989), and “Spariden-Zone” and “Mytilopsis-Zone” in Reichenbacher et al. (2013). Here we follow the terminology of Reichenbacher et al. (2013) (see Fig. 5). It should, however, be noted that the Spariden-Zone and their equivalents (Cardien-Schichten, Horizont 2a) are represented only at some localities, and when they are present they underlie the Mytilopsis-Zone and its equivalents (Horizont 2b).

5.2. Upper boundary (Kirchberg Fm/OSM) The sands and silts of the OSM overlie the Kirchberg Fm. In all cores studied here, the boundary between the two units is indistinct. Here, it is drawn where the fossil content (macro- and microfossils) noticeably declines and sandy sediments or brown coal beds occur. In the samples from Offingen, Buttenwiesen and Gempfing fossil-rich horizons occur in places also in the lower OSM sediments (Figs. 3 and 4). However, typical brackish-water fossils (e.g. Dapalis otoliths) are absent from these sections. As a result, the OBM/OSM transition must be considered as a change in litho- and biofacies, and not as a chronostratigraphic boundary.

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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6. Stratigraphy 6.1. Upper Marine Molasse and Albstein Of all the cores studied here, only that from the borehole Glött included sediments of the Upper Marine Molasse (OMM) and Albstein. The OMM sediments of Glött contain planktonic and benthic foraminifers. Characteristic Burdigalian planktonic foraminifera in the Central and Western Paratethys include Globigerina ottnangiensis and G. dubia (Cicha et al., 1998). These species are present in the Kalkofen Fm of Glött, clearly indicating a Burdigalian age for this formation. Benthic foraminiferal assemblages signal clear differences between Eggenburgian and Ottnangian OMM deposits (e.g. Knipscheer, 1952; Hagn, 1953, 1959, 1961; Wenger, 1987; Pippèrr and Reichenbacher, 2009, 2010; Pippèrr, 2011). Typical index species are absent in Glött. Nevertheless, the occurrence of Pappina primiformis and the abundance of Elphidium glabratum clearly point to an Ottnangian age, because P. primiformis is restricted to Ottnangian OMM strata in the S German Molasse Basin and frequent occurrences of E. glabratum have been considered to be characteristic for the Ottnangian in the German as well as in the Austrian Molasse Basin (see Wenger, 1987; Rupp and Haunold-Jenke, 2003; Pippèrr and Reichenbacher, 2009, 2010; Pippèrr, 2011). Moreover, the marine succession of Glött can be subdivided into two sedimentation cycles, which is consistent with previous data from other sites and boreholes in the SW German Molasse Basin (e.g. Lemcke et al., 1953; Pippèrr et al., 2016). The sedimentation cycle corresponding to the lower Ottnangian is in Glött represented by the Kalkofen Fm, while that of the middle Ottnangian encompasses the Baltringen Fm. Differentiation between the sedimentation cycles is based on an abrupt change of sediments and benthic foraminiferal assemblages (Appendix 1). Notably, the Steinhöfe Fm (uppermost OMM, above Baltringen Fm) is absent in Glött, while this formation is present in the borehole Burgau to the southwest (Fig. 1) (Pippèrr et al., 2016; see here Fig. 1). The more complete OMM succession seen in Burgau may indicate that the regression of the OMM Sea began in the distal (northern) Molasse Basin and proceeded towards the SW. 6.2. Upper Brackish Molasse 6.2.1. Grimmelfingen Formation Since lower to middle Ottnangian OMM sediments are found to the north and south of the Graupensand Channel (boreholes Glött, Burgau, Lutzingen, Hamlar 2; Fig. 1), the sediments of the Grimmelfingen Fm can be interpreted as a channel-fill cut in the OMM. Accordingly, the Grimmelfingen Fm should be younger than the OMM deposits. The co-occurrence of Rzehakia, Mytilopsis and cardiids in the Grimmelfingen Fm suggests a predominantly upper Ottnangian age, while the appearance of Megacricetodon indicates that the uppermost Grimmelfingen Fm may reach to the lower Kapatian (see below). In the Molasse Basin of Lower Bavaria and Austria and in the Western Carpathian Foreland Basin (Central Paratethys realm), the late Ottnangian is characterized by the occurrence of a regressive brackish facies with an endemic bivalve fauna, the so-called Rzehakia fauna, which is characterized by the presence of the bivalve Rzehakia (formerly Oncophora) as well as Mytilopsis and Limnopagetia (Čtyroký et al., 1973a; Mandic and Ćorić, 2007; Piller et al., 2007). In Lower Austria north of the Danube, and in the Western Carpathian Foreland Basin, the Oncophora-Beds are transgressively overlain by marine deposits of Karpatian age, characterized by the appearance of new elements in the marine fauna (Čtyroký et al., 1973a; Ćorić and Rögl, 2004; Mandic and Ćorić, 2007; Piller et al., 2007). Therefore, Rzehakia has long been regarded as an index fossil for the upper Ottnangian in this region of the Central Paratethys (see Čtyroký et al., 1973a, 1973b). Outside this region, Rzehakia occurs in the southern Slovakian-Northern Hungarian Basin (Pannonian Basin), also in marine sediments of lower Karpatian age (Čtyroký et al., 1973a; Mandic and Ćorić, 2007).

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Fossil mammals in the basal layer of the Grimmelfingen Fm are indicative for the mammal unit MN 4a (Heizmann, 1984; Reichenbacher et al., 1998; Sach and Heizmann, 2001). The uppermost part of the Grimmelfingen Fm (GD in Offingen, Fig. 3) has yielded a rodent tooth assigned to the genus Megacricetodon, and members of this genus first appear in mammal unit MN 4b (Heissig, 1997; Prieto, 2007; Kälin and Kempf, 2009) (see Fig. 6A). While the exact duration of MN 4a is not known, a correlation with the middle to late Ottnangian seems plausible according to Berger et al. (2005), Pippèrr et al. (2007), Kälin and Kempf (2009) and Reichenbacher et al. (2013). On the other hand, correlation of MN 4b with the early Karpatian is well supported, being constrained by a combination of bio-, litho- and magnetostratigraphic data (Kälin and Kempf, 2009; Reichenbacher et al., 2013) (see Fig. 6A). Taking all the evidence together, the biostratigraphic evidence provided by the bivalve and small mammal assemblages is coherent, and the Grimmelfingen Fm can therefore be correlated with the late Ottnangian to early Karpatian (uppermost part of the GD). 6.2.2. Kirchberg Formation As in the type locality of the Kirchberg Fm (Illerkirchberg), the fossilrich marls in the cores investigated here include characteristic mollusc and fish faunas (e.g. Cerastoderma sociale, Nematurella bavarica, Dapalis formosus, D. curvirostris, Eleogobius gaudanti, Morone cf. moravica). In the context of our new definition of the base of the Kirchberg Fm, it is important to mention that Rzehakia does not occur in the Kirchberg Formation, neither in our set of cores nor at the type locality. All previous reports of the occurrence of Rzehakia in the Kirchberg Fm referred to the lowermost sand layer (Zone 1 in Reichenbacher, 1989), which is now assigned to the Grimmelfingen Formation (Fig. 5 and Section 5). The sediments of the Kirchberg Fm (Pfaffenhofen T1) contain a small-mammal tooth that was identified as Megacricetodon aff. collongensis. As species identification on the basis of a single tooth is generally difficult, this identification should be viewed with some caution. It does, however, fit well with previous reports of this species from the Kirchberg Fm and the lowermost OSM deposits (Reichenbacher et al., 1998, 2004, 2013; see here Fig. 6). As M. aff. collongensis is an index species for the mammal unit MN 4b in the NAFB, which can be correlated with the early Karpatian (see above), its occurrence indicates a Karpatian age for the Kirchberg Fm. Benthic foraminifers occur in abundance in a sandy layer within the Kirchberg Fm in Hamlar 1. A few individuals are also present in Gempfing. The assemblages are similar to Ottnangian OMM faunas in the S German Molasse Basin (e.g. Elphidium glabratum, E. rugulosum). However, in the Central Paratethys the majority of these species also occur in Karpatian strata (see Cicha et al., 1998, 2003). In Hamlar 1, the age of the sands is constrained by the presence of Pappina breviformis (Appendix 2), which first appears in the middle Ottnangian and is common in Karpatian strata of the Central Paratethys (e.g. Cicha et al., 2003). In the S German Molasse Basin, this species is extremely rare in middle Ottnangian OMM deposits (Pippèrr, 2011). A single Protelphidium roemeri test was found in the Glött core. According to Cicha et al. (1998), this species is restricted to Eggenburgian and Ottnangian strata. However, the foraminifera of Glött are probably reworked. 6.2.3. Magnetostratigraphy Magnetostratigraphic data for the cores from Druisheim, Hamlar 1 and Gempfing are provided in Reichenbacher et al. (2013). Moreover, new magnetostratigraphic data are available for Glött, Offingen, Gundremmingen, Lauingen, Holzheim, Dillingen, Buttenwiesen (Sant et al., submitted). The data reveal that the Grimmelfingen Fm has a reverse (lower part) – normal – reverse (uppermost part) polarity pattern. The lower Kirchberg Fm is consistently reverse and the upper Kirchberg Fm has reverse to normal polarity (Fig. 6). The magnetostratigraphic and biostratigraphic data taken together provide strong support for a correlation of the greater part of the Grimmelfingen Fm with the late Ottnangian (abundant Rzehakia in several layers, fossil

Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002

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Fig. 6. (A) Stratigraphic overview of the late Early Miocene and early Middle Miocene in the study region (from Reichenbacher et al., 2013; modified after Sant et al., submitted; this report). (B) Lithostratigraphic units in the South German Molasse Basin (compiled from Lemcke, 1988; Reichenbacher, 1993; Pippèrr et al., 2007; Reichenbacher et al., 2013; this study).

mammals of MN 4a in the basal deposits; see above). The finding of a small rodent tooth (Megacricetodon) indicative for MN 4b (and thus for the Karpatian) does not conflict with this interpretation, because this fossil was recovered in the uppermost layers of the Grimmelfingen Fm (see above). Furthermore, the Kirchberg Fm can be correlated with the Karpatian (Reichenbacher et al., 2013; this study). 7. Discussion 7.1. Stratigraphic correlations and palaeogeography The Kirchberg Fm (Western Paratethys) can be correlated with the Karpatian, and is therefore younger than previously suggested by most authors. Furthermore, we conclude that deposition of the brackish Kirchberg Formation occurred as a result of the Karpatian transgression (see Section 7.2). This implies that a revised age model is needed for the entire OBM, and probably also for the underlying OMM sediments. Based on our new data and a reassessment of published data (Lemcke et al., 1953; Lemcke, 1988; Reichenbacher, 1993; Doppler et al., 2000; Pippèrr et al., 2007; Reichenbacher et al., 2013; Pippèrr, 2011), we propose a new chronology for the OBM units in the S German sector of the Molasse Basin (see Fig. 6B). Lemcke (1988: pp. 43 and 133) had already suggested that the OBM strata in the S German Molasse Basin can be subdivided into a regressive OBM I (late Ottnangian) and a transgressive OBM II (?Karpatian). A review of previous data together with our new data fully supports this picture. 7.1.1. Sand-Kalkmergelserie (northern Central German Molasse Basin) The OBM in the northern central part of the S German Molasse Basin is represented by the 40–60 m thick Sand-Kalkmergelserie (Figs. 6B and 7), which is known from several boreholes (Lemcke et al., 1953; Doppler et al., 2000). Its lower portion largely comprises fine sandy, partially carbonate-free sediments with mica and some glauconite. This succession is termed the “sandy segment” of the Sand-Kalkmergelserie (Fig. 6B) and records a regressive phase, during which the marine OMM facies was gradually transformed into a brackish facies (gradual change

of litho- and biofacies; see Lemcke et al., 1953; Doppler et al., 2000: borehole Stockhausen). Fossils are relatively infrequent and include a few small-sized foraminifers, Bithynia opercula and fish teeth (Lemcke et al., 1953), while Rzehakia, Mytilopsis, cardiids and Melanopsis occur in the borehole Stockhausen (Doppler et al., 2000; our unpublished data). Based on the occurrence of Rzehakia (the most common fossil in Stockhausen) and the overall similarity of their fossil contents, the sandy segment of the Sand-Kalkmergelserie is regarded here as being contemporaneous with the Grimmelfingen Fm (Fig. 6B). Lithofacies and fossil content change in the upper part of the SandKalkmergelserie. This portion is referred to as the “marly segment” (Fig. 6B) because the sediments are now predominantly marly. The microfossil assemblages are very similar to those from the Kirchberg Fm, with several shared species among the fish and mollusc fauna (see Reichenbacher, 1993: Table 12). These faunal assemblages, as well as the presence of marine-euryhaline fish species that are characteristic for the lower Kirchberg Fm (Dapalis formosus, D. curvirostris, Eleogobius gaudanti), provide strong support for a correlation with the Kirchberg Fm – and thus reflect the Karpatian transgression. 7.1.2. Bunte Mergelserie (western Central German Molasse Basin) Southwest of the depositional area of the Sand-Kalkmergelserie (approximately between the rivers Iller and Lech) a mixed facies developed (Lemcke et al., 1953). Lemcke et al. (1953) reported 1- to 4.5-m thick “Albstein-like” sediments above thin layers of sands or directly above OMM sediments. These authors interpreted both the Albstein-like sediments and the thin sand layers as stratigraphic equivalents of the sandy segment of the Sand-Kalkmergelserie. Above follow fluviatile to lacustrine or slightly brackish deposits referred to as the lower Bunte Mergelserie (3–52 m) and upper Bunte Mergelserie (5–41 m). A prominent change in the heavy mineral spectrum differentiates these two units. The lower Bunte Mergelserie exhibits a GSA (garnet-stauroliteapatite) spectrum, whereas a GE (garnet-epidote) spectrum characterizes the upper Bunte Mergelserie (Lemcke et al., 1953). The clear shift in the heavy mineral spectra is indicative of a fundamental reorganisation of the drainage systems in the Molasse Basin of S

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Germany and Lower Austria (Lemcke et al., 1953; Lemcke, 1988; Reichenbacher, 1993; Kuhlemann and Kempf, 2002). Based on the observation that fossils typical of the lower Kirchberg Fm (teeth of Sparidae, Mytilopsis amygdaloides) occur in the upper Bunte Mergelserie, but not below it (Reichenbacher, 1993: Table 11), it can be assumed that this reorganisation is coincident with the transgressive event that resulted in the deposition of the marine-to-brackish Kirchberg Fm. 7.1.3. Aschaholz Formation (southern Central German Molasse Basin) The sediments of the Aschaholz Fm (~45 m thick) are known from outcrops in Upper Bavaria (Figs. 6 and 7). Like the Sand-Kalkmergelserie, the Aschaholz Fm can be subdivided into a lower, regressive segment consisting of clayey-silty sediments and an upper, transgressive segment characterized by fossil-rich marls (Pippèrr et al., 2007). The latter contains diverse fossil assemblages (charophytes, ostracods, gastropods, bivalves: Mytilopsis, fish otoliths), of which several species are also represented in the Kirchberg Fm, while others are known from the Oncophora-Beds in Lower Bavaria (see Pippèrr et al., 2007: Table 3). 7.1.4. Oncophora-Beds (East German and Upper Austrian Molasse Basin) The Molasse Basin of SE Germany (Lower Bavaria) and Upper Austria documents the transition from the marine OMM sediments to the brackish Oncophora Beds that is typical for the Central Paratethys realm (e.g. Čtyroký et al., 1973a). It is marked by a change in lithofacies, but the decrease in salinity seems to occur gradually (e.g. Schneider et al., 2011). The OncophoraBeds can reach a thickness of up to 70 m (Rupp et al., 2008) and a lithostratigraphic subdivision was established by Schlickum and Strauch (1968). Accordingly, the lower Oncophora-Beds include the “Mehlsande”, “Schillhorizont” and “Glimmersande” and the upper Oncophora-Beds comprise the “Aussüßungshorizont”, “Schillsande” and “Lakustrische Schichten” (= “Süßwasserschichten”). The lower Oncophora-Beds are predominantly sandy; Rzehakia guembeli is the most abundant faunal constituent and is sometimes found together with Limnopagetia bavarica, Mytilopsis rottensis and several gastropods (Schlickum, 1971; Schneider et al., 2011). This faunal composition – and in particular the abundance of Rzehakia – provides evidence for a late Ottnangian age (see Section 6.2). The upper Oncophora-Beds are less sandy than the lower Oncophora-Beds and mainly comprise silts and marls. Mytilopsis rottensis and Limnopagetia are the most abundant taxa, while Rzehakia is absent or occurs sparsely; several species of gastropods are also present (Schlickum and Strauch, 1968; Reichenbacher, 1993). In addition, the upper Oncophora-Beds include fish otoliths, and their faunal composition is comparable to that of the fish fauna of the Kirchberg Fm, although there are some differences (Reichenbacher, 1993). Furthermore, an increase in salinity has been reported for the Schillsande (Schlickum and Strauch, 1968). Accordingly, Lemcke (1988) was probably correct in assuming that the uppermost sections of the Oncophora-Beds (Schillsande and Lakustrische Schichten) are contemporaneous with the Kirchberg Formation. Nevertheless, to obtain an unambiguous correlation, detailed magnetostratigraphic data for the Oncophora-Beds in Lower Bavaria will be required. 7.2. Palaeoenvironmental developments 7.2.1. Upper Marine Molasse and regressive Upper Brackish Molasse The litho- and biofacies of the boreholes (including Burgau, Hamlar 2 and Lutzingen: Pippèrr et al., 2016) provide evidence for a single transgressive-regressive Ottnangian sequence, which is in accordance with data from the Central Paratethys. There, the Ottnangian corresponds to a single, third-order sea-level cycle (Kováč et al., 2004; Piller et al., 2007; see here Fig. 2). The OMM sediments (Kalkofen Fm and equivalents) that document the early Ottnangian sea-level highstand (Fig. 7A) contain rich and diverse foraminiferal assemblages, which are indicative of marginal marine to neritic environments with normal marine salinity (Pippèrr, 2011; Grunert et al., 2012; Pippèrr et al., 2016; this study). In the middle Ottnangian Baltringen Fm, a decline in marine life is discernible (see Section 4.1 and Appendix 1) and this is consistent

11

with the results of other studies (e.g. Pippèrr, 2011). The foraminiferal assemblages indicate a decrease in water depth and a reduced water exchange to the open ocean. In the S German and Austrian Molasse Basin, the regression resulted in the deposition of brackish, limnic, and terrestrial sediments (regressive OBM sensu Lemcke, 1988) and the incision of the Graupensand Channel (Fig. 7B). In the western part of the S German Molasse Basin the OMM deposits south of the Graupensand Channel (boreholes Glött and Burgau) gradually change into the silty-calcareous Albstein facies (silts with calcareous concretions and limestone layers). The genesis of this facies has been much discussed in the past, with various authors (e.g. Geyer and Gwinner, 1991) interpreting the Albstein as a pedogenic caliche (calcrete) horizon, whereas Zöbelein (1985) suggested that calcareous algae formed these carbonates in a shallow freshwater lake. However, limnic fossils are absent in the Albstein samples from the sites studied here, whereas a sample from Glött yielded three teeth of marine fishes (probably remnants of the OMM) and remains of fossil roots. Therefore, the Albstein carbonates may actually have formed in a terrestrial environment as palaeosol. To the north of the Albstein facies, the sediments of the Grimmelfingen Fm discordantly overlie the Jurassic limestones or Lower Freshwater Molasse. The origin of this facies has also been discussed previously. The majority of authors interpreted the sediments of the Grimmelfingen Fm as fluviatile to estuarine (e.g. Kiderlen, 1931; Reichenbacher et al., 1998; Luterbacher et al., 1992), while Tipper et al. (2003) argued that the Graupensand Channel resulted from submarine erosion and that the Grimmelfingen Fm is therefore marine. However, based on the results of the present study, a marine environment can be excluded for the Grimmelfingen Fm because it comprises largely carbonate-free sediments, whereas OMM deposits are generally carbonate-rich. In addition, for the most part glauconite grains occur sparsely (reworked grains) and marine microfossils (e.g. foraminifers) are absent in the sands of the Grimmelfingen Fm. Moreover, freshwater fossils (e.g. Viviparus) appear in the middle and upper parts of the Grimmelfingen Fm, and brackish molluscs (Rzehakia, Mytilopsis, cardiids, and Nematurella) are found in the middle to lower sections (see Section 4.2). Consequently, the sediments of the Grimmelfingen Fm were most probably deposited in a fluviatile to estuarine environment. According to Kiderlen (1931) and Reichenbacher et al. (1998), the Graupensand River was a south-westward directed fluvial system which discharged into the Swiss Molasse Sea (Fig. 7B). Kiderlen (1931) noted that the marine influence is greatest in the SW and rapidly decreases towards the NE. The results of this study confirm this observation, since only the deposits of the Grimmelfingen Fm from Günzburg (located in the SW, see Fig. 1) contain a comparatively rich brackish fossil assemblage as well as deposits of glauconitic sands. The Grimmelfingen Fm varies widely in thickness between our cores (0.45 to 50 m) and comprises predominantly coarse- to fine-grained, partially fine gravelly sands. Moreover, coaly sediments and silty-to-sandy deposits with a rich lacustrine fauna are present in Buttenwiesen. However, sands with coarse gravels and gravelly layers are absent. According to Kiderlen (1931), this facies occurs only locally (as channel bars, in which the coarse facies is particularly developed) and is frequently present in the outcrops near Grimmelfingen (near Ulm, see Fig. 1). All in all, a small-scale differentiated fluviatile environment with varying flow energy, stagnant water zones and floodplains can be assumed. Probably the river system originated from the Palaeo-Main (Doppler and Schwerd, 1996) and received input from smaller streams to the South and North (e.g. Palaeo-Brenz, -Egau; Kiderlen, 1931). The fine-grained deposits in the topmost sections of the Grimmelfingen Fm (in our cores and as also described by Kiderlen, 1931) very probably indicate the gradual siltingup of the Graupensand River. Local calcareous layers and concretions similar to those of the Albstein facies occur in the cores from Offingen and Pfaffenhofen (T1 and T3). The abundant calcareous rhizoconcretions in two samples from Pfaffenhofen (within the Graupensand-Deckschichten) indicate pedogenic processes.

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7.2.2. Transgressive Upper Brackish Molasse The fossil-rich marls of the Karpatian Kirchberg Fm transgressively overlie the Grimmelfingen Fm, and most probably represent a shortterm transgression of the Swiss Molasse Sea (Kiderlen, 1931; Lemcke, 1988; Reichenbacher et al., 1998; Reichenbacher et al., 2013; see Fig. 7C). Furthermore, transgressive brackish deposits (transgressive OBM sensu Lemcke, 1988) with rich faunas also occur above Albstein deposits (Lemcke et al., 1953; this study: borehole Glött) and are also known from other areas of the S German Molasse Basin (Kirchberg Basin, marly segments of the Sand-Kalkmergelserie and Aschaholz Fm; see Section 7.1 and Fig. 7). The brackish transgression was possibly associated with a global rise in sea level. The Karpatian of the Central Paratethys (easternmost Austrian Molasse Basin, Vienna Basin, Carpathian Foreland Basin, see Fig. 1) has been linked with a new transgression from the Mediterranean Sea via the Slovenian Trans-Tethyan Trench Corridor that can be recognized based on new elements in the marine fauna (Kováč et al., 2004; Harzhauser and Piller, 2007). According to Piller et al. (2007), the Karpatian transgression can be correlated with the sea-level rise at the beginning of the global third-order sea-level cycle Bur 4 (see Fig. 2). The fossil assemblages of the lower Kirchberg Fm are indicative of a shallow brackish environment with largely mesohaline salinity, whereas the assemblages of the upper Kirchberg Fm suggest brackish-tofreshwater conditions. The transition to the OSM deposits is very indistinct, with the faunal changes indicating a gradual freshening of the brackish environment. In the lower Kirchberg Fm, benthic foraminifers (predominantly marine-euryhaline taxa) associated with brackish fossils occur in a glauconitic sand layer in Hamlar 1 (Fig. 4), which point to brackish-marine conditions. This layer is notably absent in the other cores. Doppler (1989) described similar deposits from a borehole near Günzburg-Reisenburg, i.e. sands with glauconite and foraminifers, but their assignment to the Kirchberg Fm is somewhat uncertain. Taken as a whole, it can be assumed that the depositional environment of the Kirchberg Fm was more differentiated than previously thought, and was apparently influenced by fluviatile inputs and strong currents. Based on co-occurrences of well-preserved and reworked brackish microfossils (e.g. fish otoliths) in some samples, it seems very likely that brief discontinuities in sediment supply, as well as erosional events, locally interrupted the build-up of the Kirchberg Fm at different times (see also Reichenbacher et al., 2013). Such hiatuses would explain why the thickness of the Kirchberg Fm is less than might be expected, given the relatively long time span over which it developed. 7.3. Comparisons During the late Ottnangian, the area of the Central Paratethys (easternmost Austrian Molasse Basin, Vienna Basin, Carpathian Foreland Basin, and Pannonian Basin Systems) was influenced by a regression, and this regressive phase can be correlated with the fall in global sea level during the Early Miocene sea-level cycle TB 2.1 of Haq et al. (1988) and Bur 3 of Hardenbol et al. (1998) (e.g. Kováč et al., 2003; Piller et al., 2007; Harzhauser and Piller, 2007). This is in good agreement with the situation in the Western Paratethys (study area), where the late Ottnangian brackish-to-freshwater sediments reflect the onset of its isolation from the Mediterranean Sea in the west and the Central Paratethys to the east of the Amstetten Swell (Fig. 7). Nevertheless, the taxonomic composition of the Rzehakia fauna in the S German Molasse Basin and the Central Paratethys region to the east of the Amstetten Swell suggests the occurrence of faunal exchanges via transitory interregional connections (Mandic and Ćorić, 2007). The Karpatian has been linked with a new marine transgression from the Mediterranean Sea into the Vienna Basin, the western Carpathian Foreland Basin, and the Pannonian Basin Systems (see Section 7.2.2).

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The lowermost Karpatian sea-level lowstand deposits (primarily terrestrial, alluvial, fluviatile and deltaic deposits) are rapidly replaced by overlying marine, neritic to shallow bathyal sediments (Kováč et al., 2003). This Karpatian transgression is associated with the late Early Miocene sea-level rise during global sea-level cycle TB 2.2 of Haq et al. (1988) and Bur 4 of Hardenbol et al. (1998) (Kováč et al., 2003, 2004; Harzhauser and Piller, 2007; Piller et al., 2007). Our new data indicate for the first time that the Karpatian transgression (Bur 4, see Fig. 2) also influenced the Western Paratethys. However, in contrast to the fully marine environments of the Central Paratethys region to the east of the Amstetten Swell, the Karpatian in the S German Molasse Basin is characterized by restricted marine and brackish deposits (see Section 7.2.2 and Fig. 7). Finally, the environments of the Upper Freshwater Molasse were established in the late Karpatian due to uplift of the NAFB and the Amstetten Swell (e.g. Lemcke, 1988; Kuhlemann and Kempf, 2002) (Fig. 6), whereas marine conditions persisted in the Central Paratethys to the east of the Amstetten Swell (Kováč et al., 2003, 2004). 8. Summary and conclusions 1. The results of this study confirm the existence of the proposed Graupensand Channel, within which OMM sediments were completely eroded away. The sediments of the OBM/Grimmelfingen Fm (with brackish or freshwater faunas) were deposited in a fluviatile to estuarine environment; a marine environment (as proposed by Tipper et al., 2003) can be excluded. Accordingly, the sediments of the Grimmelfingen Fm are younger than the OMM deposits. 2. The fossil-rich marls of the OBM/Kirchberg Fm transgressively overlie the Grimmelfingen Fm, and transgressive brackish deposits are also known from other areas of the S German Molasse Basin. This short-term brackish transgression was possibly associated with the global sea-level rise at the beginning of the third-order sea-level cycle Bur 4. This would be consistent with previous magnetostratigraphic data indicating that the Kirchberg Fm is Karpatian in age. 3. Thus, the OBM in the western and central parts of the S German Molasse Basin (Western Paratethys) can be subdivided into a regressive phase (Grimmelfingen Fm and equivalents) and a transgressive phase (Kirchberg Fm and equivalents). The regressive phase can be assigned to the upper Ottnangian, whereas the transgressive stage is Karpatian in age. Our new data thus support the previous suggestion made by Lemcke (1988), which, however, has largely be ignored in subsequent studies. 4. A new lithostratigraphic concept of the Kirchberg Fm is presented. Accordingly, the Kirchberg Fm is characterized by a predominantly fossil-rich marly facies. 5. Rzehakia occurs in the Grimmelfingen Fm, but is absent from the Kirchberg Fm as defined here. The gastropod and bivalve assemblages of the brackish Kirchberg Fm are similar to, but not entirely congruent with those of the Oncophora-Beds in the Central Paratethys because endemic species occur in each sub-basin (Lower Bavaria: e.g. Schlickum, 1971; Reichenbacher, 1993; Austria: Mandic and Ćorić, 2007; Czech Republic: Čtyroký, 1972). 6. New palaeogeographic maps are presented for the study area and the adjacent regions. However, to obtain more precise correlations between the brackish sediments of the Western and the Central Paratethys, new biostratigraphic and magnetostratigraphic data will be needed from the brackish Oncophora-Beds in the Central Paratethys. Acknowledgements This study was financially supported by the European Fund for Regional Development (EFRE) and the Bavarian Environment Agency (LfU). Special thanks go to Gerhard Doppler and Dietmar Jung (both

Fig. 7. (A) Facies and environments in the Molasse Basin during the early Ottnangian. Map: Kuhlemann and Kempf (2002); modified after Pippèrr et al. (2016). (B, C) Facies and environments of the Molasse Basin during the late Ottnangian (B) and early Karpatian (C). Map: Kuhlemann and Kempf (2002); modified after Lemcke et al. (1953), Lemcke (1988), Doppler and Schwerd (1996), Berger et al. (2005), Mandic and Ćorić (2007), Kowalke and Reichenbacher (2005, Fig. 1) and this report.

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LfU) for providing lithological logs of the boreholes and for critical discussion of the geological context. Sincere thanks go to Steffen Stark (LfU) for his logistical support in the core archive of the LfU, to Jerome Prieto (LMU Munich) and Daniel Kälin (Wabern) for identifying the small-mammal

teeth and to Barbara Bassler (LMU Munich) for charophyte identification. For constructive comments we are grateful to Madelaine Böhme (Universität Tübingen, Germany), an anonymous reviewer and the editor of PPP Thierry Correge (Université Bordeaux, France).

Appendix 1 Table 2 Benthic foraminifera from the Upper Marine Molasse of the borehole Glött, as well as the numbers of benthic and planktonic Foraminifera per sample. Bulimina spp. = B. elongata D' ORB., B. schischkinskaye SAMOILOVA; Cibicidoides sp. = C. lopjanicus (MYATLYUK), C. tenellus (REUSS), Cibicidoides cf. ungerianus (d' Orb.), Cibicidoides sp. indet.

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Appendix 2 Table 3 Benthic foraminifera from the Upper Brackish Molasse of the borehole Hamlar 1.

Appendix 3 Table 4 Brackish and limnic fossils of the Upper Brackish Molasse (OBM) deposits (Grimmelfingen Formation and Kirchberg Formation) and the Upper Freshwater Molasse (OSM). Gastropods: the taxa found in the core samples from the boreholes are described in detail in Salvador et al. (2016). Fish otoliths: identification largely follows Reichenbacher (1993) and Gierl and Reichenbacher (2015). Ostracods: identification largely follows Straub (1952) and Witt (2000). Charophytes (determinations by Barbara Bassler, LMU Munich): taxa after Berger (1992). X = present in two or more boreholes. OSM

OBM/Kirchberg Fm

Bivalves Rzehakia partschi (GÜMBEL) Cerastoderma sociale (KRAUSS) Limnopagetia/Limnopappia spp. Cardiidae indet. Mytilopsis amygdaloides (DUNKER) Mytilopsis clavaeformis (KRAUSS) Mytilopsis sp. indet. (fragments) “Unio” (fragments)

X

Lower section Lower section X Lower section Lower section X X

Gastropods Theodoxus cyrtocelis (KRAUSS)

X

X

OBM/Grimmelfingen Fm X Günzburg X

Offingen (basis layer)

X (continued on next page)

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Table 4 (continued) OSM Theodoxus obtusangula (KRAUSS) Melanopsis impressa KRAUSS Tinnyea lauraea (MATHÉRON) Bithynia glabra (VON ZIETEN) Ctyrokya conoidea (KRAUSS) Hydrobia semiconvexa SANDBERGER Nematurella bavarica (SANDBERGER) Viviparus cf. suevicus WENZ Stagnicola armaniacensis (NOULET) Stagnicola praebouiletti SCHLICKUM Lymnaea dilatata (NOULET) Ferrissia cf. wittmanni (SCHLICKUM) Gyraulus albertanus (CLESSIN) Gyraulus applanatus (THOMAE) Planorbarius mantelli (DUNKER) Fish otoliths Clupeonella cornuta (REICHENBACHER) Clupeonella humilis (H. V. MEYER) Paralebias weileri (SALIS) Aphaniolebias konradi (REICHENBACHER) Hemitrichas martinii (REICHENBACHER) Hemitrichas schwarzhansi (REICHENBACHER) Atherinidarum brzobohatyi (MARTINI) Channa elliptica (SALIS) Ambassis sp. Dapalis crassirostris (RZEHAK) Dapalis curvirostris (RZEHAK) Dapalis formosus (H. V. MEYER) Morone cf. moravica WEILER Mugil applanatus (RZEHAK) Gobius doppleri REICHENBACHER Gobius gregori REICHENBACHER Gobius helvetiae SALIS Eleogobius brevis (AGASSIZ) Eleogobius gaudanti GIERL & REICHENBACHER Gobius sp. indet. Cyprinidae (lapilli) Ostracods Darwinula cylindrica STRAUB Darwinula stevensoni (BRADY & ROBERTSON) Paralimnocythere rostrata (STRAUB) Candona suevica STRAUB Candona sp. indet. Caspiolla kirchbergensis (STRAUB) Pseudocandona praecox (STRAUB) Cyclocypris sp. Ilyocypris gibba (RAMDOHR) Mediocypris candonaeformis (STRAUB) Eucypris spp. Heterocypris straubi WITT Cypridopsis sp.

X Reworked Reworked X X X X X

Offingen X X

Reworked (Buttenw.) Reworked (Buttenw.)

Offingen Offingen Offingen X X X

Gempfing

X X X Buttenwiesen Offingen X X Offingen

Charophytes Nitellopsis (Tectochara) “ginsburgisantes“ Nitellopsis (Tectochara) ginsburgi RIVELINE Nitellopsis (Tectochara) groupe meriani Nitellopsis sp. Chara notata GRAMBAST & PAUL Chara venusta REICHENBACHER & SCHWARZ Chara groupe minutissima Chara spp. Chara molassica STRAUB Chara microcera GRAMBAST & PAUL Hornichara lagenalis (STRAUB) Sphaerochara groupe hirmeri Stephanochara groupe praeberdotensis Stephanochara groupe ungeri Lychnothamnus sp.

Dillingen

Fruiting and seeds Stratiotes sp. Potamogeton sp.

Pfaffenhofen T3 Pfaffenhofen T1 and T3

Offingen + Dillingen 1 (Holzheim) 1 (Hamlar) Offingen Dillingen Dillingen Gempfing

X

OBM/Kirchberg Fm

OBM/Grimmelfingen Fm

X X X X X X X

X

X X X X X X X

Lower section Lower section X X X X X X X X X X X 1 (Buttenwiesen) X X X X X X X

X X X X X X X X X X X X X

X X X X X Buttenwiesen X X Druisheim Buttenwiesen X X X X

X Druisheim X X X X X X X

Lauingen: 1cf. Günzburg

Druisheim cf. (Buttenwiesen)

? (Günzburg)

Buttenwiesen Buttenwiesen Buttenwiesen

X Offingen

X

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Please cite this article as: Pippèrr, M., Reichenbacher, B., Late Early Miocene palaeoenvironmental changes in the North Alpine Foreland Basin, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.01.002