Evolution of the Urgonian shallow-water carbonate platform on the Helvetic shelf during the late Early Cretaceous

Sedimentary Geology 387 (2019) 18–56

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Evolution of the Urgonian shallow-water carbonate platform on the Helvetic shelf during the late Early Cretaceous Lucie Bonvallet a,b, Annie Arnaud-Vanneau b, Hubert Arnaud b,†, Thierry Adatte a, Jorge E. Spangenberg c, Melody Stein d, Alexis Godet e, Karl B. Föllmi a,⁎ a

Institut des Sciences de la Terre, Géopolis, Université de Lausanne, Lausanne 1015, Switzerland Association Dolomieu, 8 Chemin des Grenouilles, La Tronche 38700, France Institut des Dynamiques de la Surface Terrestre, Université de Lausanne, Lausanne 1015, Switzerland d Institut de Physique du Globe de Strasbourg, Université Strasbourg, Strasbourg 67074, France e Department of Geological Sciences, University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, USA b c

a r t i c l e

i n f o

Article history: Received 25 January 2019 Received in revised form 11 April 2019 Accepted 14 April 2019 Available online 24 April 2019 Editor: J. Knight Keywords: Tethys Urgonian Barremian Aptian Isotopes Alps

⁎ Corresponding author. E-mail address: [email protected] (K.B. Föllmi). † Deceased.

https://doi.org/10.1016/j.sedgeo.2019.04.005 0037-0738/© 2019 Elsevier B.V. All rights reserved.

a b s t r a c t Urgonian platform carbonate (Cretaceous; Barremian, Aptian) forms an important lithostratigraphic unit in the Helvetic fold- and thrust unit of the northern Swiss Alps. Its widespread distribution and ubiquity allow for an integrated high-resolution study of macro- and microfacies, benthic foraminiferal biostratigraphy, sequence stratigraphy, and carbon-isotope and phosphorus records. The resulting data confirm the importance of environmental forcing and sea level change on the style of carbonate production and accumulation along the margin of the northern Tethys during the late Early Cretaceous. Stratal geometries, the succession of microfacies, the identification of major emersion surfaces, and biostratigraphy observed and analysed in twelve sections through the inner, middle, and outer platform, and in the panorama of the Churfirsten range, permit subdivision of the analysed succession into eight depositional sequences. The succession starts with a phase of sedimentary condensation (Altmann Member (Mb); late Hauterivian – late early Barremian; sequences H7, H8, and B1), followed by the deposition of hemipelagic sediments (Drusberg Mb; restricted to sequence B2 of the late early Barremian on the inner platform; and covering the late early Barremian to the middle late Barremian on the outer platform, and to the early Aptian on the outer shelf, thereby showing an important diachroneity of its upper boundary related to the inception and progradation of the Urgonian platform), and the development of predominantly lagoonal carbonate (Schrattenkalk Formation (Fm); early late Barremian – early Aptian; sequences B3, B4, B5, and A1). The Schrattenkalk Fm documents important progradation and aggradation of the carbonate platform, and the change from a ramp-like to flat-topped geometry. The oldest, allochthonous remains of the shallow-water carbonate platform were identified intercalated in and on top of the lower Barremian Drusberg Mb (sequence B2). Sequence boundary (SB) B3 resulted from an important regressive phase near the early-late Barremian boundary, which led to the emersion of the hemipelagic sediments of the Drusberg Mb in the inner part of the shelf and to the deposition of a lowstand systems tract at the base of the Lower Schrattenkalk Mb (late Barremian; sequences B3–5) in intermediate and distal domains. Deposition of in-situ platform carbonate started during the following transgressive phase in the middle late Barremian, which flooded the entire investigated area. The associated faunal assemblages and phosphorus contents indicate a concomitant increase in nutrient input, which led to a mixed photozoan-heterozoan platform association dominated by annelids and flat orbitolinids, and the formation of a condensed phosphate-rich bed on the outer shelf (Chopf Bed; middle late Barremian). The subsequent sea-level highstand allowed for the deposition of the first typical Urgonian carbonates rich in corals and rudists. This depositional sequence (B3) terminated by the important infilling of accommodation space combined with sea-level fall of at least 15 m. Later on, close to the Barremian-Aptian boundary, a further, major emersion phase (SB A1) was triggered by sea-level fall, estimated here as at least 16 m, which terminated this first phase in the deposition of rudist and coral-rich platform carbonates covering the middle late to latest Barremian (B3–B5). The overlying Rawil Mb (lowermost Aptian; transgressive systems tract A1) resulted from progressive deepening and document a phase of increasing eutrophication of the depositional environment, resulting in a mixed siliciclastic-carbonate platform build-up, characterized by sea-grass facies and the massive occurrence of Palorbitolina lenticularis. The overlying Upper Schrattenkalk Mb (lower Aptian; highstand systems tract A1) records recovery of the rudist-rich photozoan Urgonian platform. Its subsequent demise occurred well

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before the Selli oceanic anoxic episode (OAE 1a). It was initiated by emersion of the platform due to highamplitude sea-level fall (SB A2), followed by eutrophication during the subsequent transgressive phase. The carbon-isotope records show an increase towards more positive values during the Lower Schrattenkalk Mb and the base of the Rawil Mb, interrupted in most sections by an excursion to lower values near the Barremian– Aptian boundary. A shift to lower values occurred also in the uppermost part of the Rawil Mb, followed by variable trends in the Upper Schrattenkalk Mb. These long-term trends are well correlated with the basinal record (Angles, La Bédoule). Deviations in the correlations are related to the influence of facies and microfacies, primary mineralogy, emersion phases, and post-depositional alteration. © 2019 Elsevier B.V. All rights reserved.

1. Introduction During the late Early Cretaceous, photozoan shallow-water carbonates rich in rudists, corals, chaetetids, and stromatoporoids accumulated in tropical and subtropical seas to build up the largest and most widespread platforms of the entire Mesozoic (Ager, 1981; Michalik, 1994; Philip, 2003; Simo et al., 2003). Relicts of these so-called Urgonian platforms crop out around the world, such as from Spain to Pakistan on the northern Tethyan margin (Portugal, Rey, 1979; Spain, Vilas et al., 1995; Millán et al., 2011; Sardinia, Dieni et al., 1963; France, Masse, 1976; Masse and Fenerci-Masse, 2012; Arnaud et al., 2017; Frau et al., 2018; Alps, Bollinger, 1988; Schenk, 1992; Bonvallet, 2015; Slovenia, Croatia, Velic, 2007; Hungary, Peybernès, 1979; Serbia, Sudar et al., 2008; Romania, Bucur, 1997; Iran, Wilmsen et al., 2013; Pakistan, Pudsey et al., 1985), and from Morocco to the Middle East for the southern Tethyan margin (Morocco-Algeria-Tunisia, Canérot et al., 1986; Godet

et al., 2014; Italy, Chiochini et al., 2012; Graziano and Raspini, 2018; Israel, Bachmann and Hirsch, 2006; Turkey, Masse et al., 2009; Middle East, Van Buchem et al., 2010). They also appear in the Pacific Ocean (Indonesia, Hashimoto and Matsumaru, 1971; Hokaido, Matsumaru, 2005; Resolution Guyot, Arnaud et al., 1995; Arnaud-Vanneau and Sliter, 1995), and in South and Central America (Venezuela, Arnaud et al., 1994, 2000; Mexico, Omana-Pulido and Pantoja-Alor, 1998; Barragan-Manzo and Diaz-Otero, 2004). The installation and evolution of these platforms mirror the history of sea-level change and paleoclimatic and environmental conditions in general. Oceanic anoxia and eutrophication events interfered in particular with the evolution of Urgonian platforms. For example, the demise of the Urgonian platform along the northwestern margin of the Tethys was linked to the unfolding of the early Aptian Oceanic Anoxic Event 1a (OAE1a; Schlanger and Jenkyns, 1976; Föllmi et al., 2006, 2007; Tejada et al., 2009; Jenkyns, 2010; Huck et al., 2011). A further example

Fig. 1. Location of the Helvetic realm on a paleogeographic map of the western Tethys for the Aptian (from Godet et al., 2013; redrawn after Masse et al., 1993).

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Fig. 2. (A) Tectonic map of the Helvetic nappes, redrawn after the tectonic map of Switzerland 1:500′000 (Swiss Federal Office of Topography – Swisstopo, Berne). (B) Palinspastic reconstruction of the Helvetic nappes, redrawn after Kempf and Pfiffner (2004). Identical colors are used for the nappes on both panels.

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Fig. 3. Synthetic representation of the succession of upper Hauterivian to lower Aptian lithostratigraphic units in a proximal and distal setting, and their relation to the sequence stratigraphic scheme adopted here (ammonite biostratigraphy from Reboulet et al., 2018; sequence stratigraphy from Arnaud et al., 1998; synthetic logs modified after Bodin et al., 2006b).

is the change from Urgonian-type facies rich in rudists and corals to a mixed siliciclastic–carbonate depositional system near the BarremianAptian boundary in central Europe (“Lower Orbitolina Beds”), which was associated with climate perturbations and concomitant changes in terrigenous and nutrient input (Stein et al., 2012a, 2012b; Carević et al., 2013). Climate perturbations and regional to global oceanic anoxia were important in the late Early Cretaceous and were the likely consequence of episodes of increased volcanic activity, such as related to the formation of the Ontong-Java large igneous province (LIP; e.g., Kuroda et al., 2011), which started in the late Barremian. In spite of these proposed links between the evolution of the Urgonian platform and climate, environment, and sea level, many details are not yet known, such as the conditions allowing for the development of Urgonian platforms. This is often related to the difficulty to obtain precise time control, resulting in different and often conflicting age models (e.g., Clavel et al., 2013; Frau et al., 2018), in spite of recent advances in the use of carbon- and strontium-isotope records in the dating and correlation of shallowwater carbonates (Wissler et al., 2003; Millán et al., 2011; Godet et al., 2011; Huck et al., 2011; Huck and Heimhofer, 2015). In the area of the northern Tethyan platform presently preserved in the Swiss Helvetic Alps, the distal part of the Urgonian platform crops out in form of the Schrattenkalk Formation (Fm), offering access to a transect of over 80 km across the platform (Trümpy, 1969; Ferrazzini and Schüler, 1979). The “Helvetic” Urgonian represents an important platform segment, which is hitherto less well studied than its equivalents in the Jura Mountains and eastern France (e.g., Arnaud-Vanneau and Arnaud, 1990; Arnaud, 2005; Godet et al., 2010; Huck et al., 2011; Masse and Fenerci-Masse, 2012; Clavel et al., 2013), and in the eastern Alps (e.g., Bollinger, 1988), in spite of its presence as prominent cliffforming rocks in the northern Alps. Especially poorly known are the

ages of both the oldest shallow-water carbonates in the Urgonian succession, as well as the oldest typical Urgonian carbonate association including rudists, stromatoporoids, chaetetids and corals. Unclear is also the relationship between the presence of a phosphatic bed of middle late Barremian age (Chopf Bed; Bodin et al., 2006b) in the outer shelf and facies change within the Urgonian succession. Questions remain also with regards to the pause in Urgonian-type carbonate production close to the Barremian-Aptian boundary, documented by the Rawil Member (“Lower Orbitolina Beds”), which is build up by a partly heterozoan assemblage. Unclear is also the influence of sea-level change in the formation of the Urgonian succession and the impact of sea-level fall associated with phases of platform emersion in the overall evolution of the platform. A final question concerns the modalities of evolution of the Urgonian succession and its correspondence to general paleoceanographic trends shown by the pelagic carbon-isotope record, and the relationship between facies change on the platform with the occurrence of phosphate- and organic-rich deposits in basins. With these questions in mind, we examined, logged, and sampled in detail 12 representative sections of the Drusberg Fm, occurring below or distally substituting the Urgonian Schrattenkalk Fm, and the Schrattenkalk Fm itself (Bonvallet, 2015). Based on partly quantitative trends in facies and microfacies, and on the stratal geometries observed in the sections and in a panorama across the Churfirsten (eastern Switzerland), we propose a sequence-stratigraphic framework. We also analysed the whole-rock carbon-isotope and phosphorus records with the goal to elucidate the interactions of local and more regional changes in the carbon cycle and its effects on the platform and vice versa the influence carbonate production and platform biology on the carbon-isotope record. The overall aim of this study is thus to reconstruct the evolution of the Helvetic Urgonian platform during the Barremian and earliest Aptian in high detail and to relate it to paleoenvironmental

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Fig. 4. Chronostratigraphy of the inner platform (left) to outer shelf successions of latest Hauterivian to early Aptian age through the Helvetic realm. Sequence stratigraphic framework is based on Arnaud (2005) and ammonite biostratigraphy on Reboulet et al. (2018). Mb = Member; Fm = Formation; Sb = sequence boundary.

changes shaping shallow marine carbonate production during the late Early Cretaceous. It is important to note here that this study would not have been possible without the previous and partly pioneering contributions by

Kaufmann (1867), Heim (1910–1916), Oberholzer (1933), Heim and Baumberger (1933), Fichter (1934), Lienert (1965), Bollinger (1988), Schenk (1992), Funk et al. (1993), Wissler et al. (2003), Linder et al. (2006), and Stein et al. (2012a).

Fig. 5. Photos from a selection of investigated sections and cores; (A) base of the section at Valsloch. The Altmann Mb is covered by vegetation; (B) section at Alvier. On the right side is the locality Glännli (Briegel, 1972); (C) section of Kistenpass; (D) general overview of the section at L'Ecuelle; (E) section at Brienzer Rothorn (from Ribaux, 2012); (F) section at justistal; (g) overview of the lower part of the section at Harder; (H-J) core from Morschach: (H) Drusberg Mb, rich in bioturbation (arrows); (I) Rawil Mb, showing lag levels associated with tempestite deposits (arrow for an example); (J) Upper Schrattenkalk Mb, showing light grey carbonate rich in rudists (arrows); (K) near the base of the Drusberg Mb in the section at Harder. The lower part of the Drusberg Mb is composed of marl-carbonate alternations (base of photographed outcrop) intercalated with massive bioclastic carbonate beds, which show hummocks at their stratigraphic top (pointed at by the corresponding author); (L) section at Tierwis; (M) close-up of the Lower Schrattenkalk Mb of the section at Valsloch; (N) section at Lämmerenplatten; KF = Kieselkalk Fm; AM = Altmann Mb; DM = Drusberg Mb; SF = Schrattenkalk Fm; LSM = Lower Schrattenkalk Mb; RM = Rawil Mb; USM = Upper Schrattenkalk Mb; GF = Garschella Fm.

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2. Geological setting The Helvetic thrust-and-fold complex of the central European Alps was formed during the Alpine orogeny and represents the former northern passive margin of the Tethys (e.g., Heim, 1910–1916; Ramsay, 1981; Pfiffner, 1993) (Fig. 1). Trümpy (1969), Ferrazzini and Schüler (1979), and Kempf and Pfiffner (2004) developed palinspastic reconstructions of the Helvetic complex in order to place the tectonic nappes in their original paleogeographic position on the northern Tethyan shelf (Fig. 2). These reconstructions are used here to locate the sections in their original depositional context. The studied sections are located in the Swiss Alps and cover the Tierwis Fm (late Hauterivian to early Barremian on the platform and up to early Aptian on the outer shelf beyond the platform margin) and Schrattenkalk Fm (latest early Barremian or early late Barremian to early Aptian; Figs. 3–5). They were selected according to their position on the platform, allowing building up a data base representative for the Helvetic Urgonian platform (Table 1). The sections at Kistenpass, Tierwis, and L'Ecuelle represent the proximal, inner area of the platform. The intermediate part close to the platform margin is documented by the sections at Justistal, Harder, Morschach, and Valsloch. The transition to the distal, outer shelf beyond the platform margin is embodied by the sections at Brienzer Rothorn and Alvier. The location of the platform margin can be traced by the disappearance of the Schrattenkalk Fm and the presence of hemipelagic sediments of the Drusberg Mb replacing the Schrattenkalk Fm. This is the case in the southern part of the Wildhorn nappe (Prabé synclinal; Crêta Besse–Chamosaire–Bella Lui area; Badoux et al., 1959), the area south of the Lake of Thun, in the southeastern part of the Lungerersee area, the southern part of the Engelberg valley (Hantke, 1961), and in the eastern part of the Säntis nappe in the Alvier region and Vorarlberg (Briegel, 1972; Föllmi, 1986; Bollinger, 1988). The substitution of the Schrattenkalk Fm by the Drusberg Mb is also illustrated in the isopach maps of Zerlauth et al. (2014). The platform-outer shelf transition zone runs almost parallel to the Alps according to Heim (1910–1916). In this zone the lateral change between shallow-water platform and hemipelagic facies is accomplished in b10 km across strike (Heim, 1910–1916; Ziegler, 1967). The section at Rawil represents the type locality of the Rawil Mb (Schenk, 1992; Stein et al., 2012a). The section at Valsloch is chosen as a reference section for the Schrattenkalk Fm, since it presents the most complete and expanded section measured. It is located in the Churfirsten range, and is part of the panorama of its southern cliff. The panorama encompasses the range between Schären (Swiss coordinates: 736.004/223.075; international coordinates: N 44° 53.416/E -1° 50.322) to Nideri (744.344/223.305; N 44° 53.417/E -1° 50.329), and provides information on depositional geometries and lateral facies changes. 3. Methods 3.1. Field work and sample preparation The twelve sections mentioned above were described, documented and measured in detail for their lithology, facies, and sedimentology, and well over 2000 samples for microfacies and geochemical investigations were collected in intervals of 1 m or less. Higher sample densities were applied across facies boundaries and discontinuity surfaces. The samples were sawn in order to remove weathered surfaces and veins, and the micritic part of the rock samples was privileged for the chemical analyses, if present. Rock powders were obtained by using a mechanical agate mill. 3.2. Microfacies analysis A total of 1931 thin sections was studied, using conventional optical microscopy. An Olympus BX51 microscope (Olympus, Tokyo, Japan)

equipped with an Olympus Altra 20 camera and the Olympus Image Analysis© software was used for digital photomicrography. The microfacies classification of Arnaud-Vanneau and Arnaud (2005) (Fig. 6) established in the Urgonian limestone of the Chartreuse and Vercors areas was used for this study. This classification is based on present-day analogues with regards to the environmental position of organisms and certain carbonate components (ooids), in addition to the effects of light, salinity, currents, and trophic levels. It consists of 12 microfacies types, which are arranged on a proximal –to-distal platform transect, from the most external F0 characterized by a pelagic faunal association, to the shallowest F11, which represents an internal lagoonal facies close to emersion (Fig. 6). Three annex microfacies types (FT1, FT2, and FT3) are used to characterize the main transgressive phases during the deposition of the Rawil Mb, according to Arnaud-Vanneau and Arnaud (2005): FT1: reworking and lag; FT2: accumulation of Palorbitolina lenticularis, associated with detrital quartz, annelids, and Choffatella decipiens; and FT3: accumulation of Dasycladaceae. These microfacies types were regrouped into six microfacies associations (AF1 to AF6), according to comparable bathymetries, grain-size sorting and biotic content. AF1 represents hemipelagic facies (F0–2), AF2 outer-shelf facies (F3–4), AF3 platform-margin facies (F5–7), AF4 lagoonal facies (F8–10), and AF5 supratidal facies (F11). An additional microfacies association is identified, which is used to characterize the main transgressive phases (AF6). It consists of wackestone/packstone including reworked grains. For the section at Valsloch, a counting technique was performed on 77 thin sections (Bernaus, 1998; González-Lara, 2001; Hfaiedh et al., 2013; Raddadi et al., 2005). On a reference surface of 1.2 × 1.7 cm, all visible, entirely preserved or fragmented components (such as foraminifera, oncolites, algae, etc.) were counted on each selected thin section. The counted components are grouped in assemblages representing similar ecologic environments, which range from deeper, open-marine, to confined and estuarine depositional settings. This quantitative approach allowed us to refine the scale used for the distribution of microfacies assemblages relative to the qualitative approach used for the other sections, and as such, nine assemblages were determined (A1–A9) for the section at Valsloch (rather than the six associations (AF1–6) used for the microfacies analysis of all other sections). 3.3. Sequence stratigraphic analysis In this study, key surfaces were identified using field observations and sedimentological and paleoecological analyses of thin sections. Once identified, the surfaces and trends in facies and microfacies allowed us to adopt a sequence-stratigraphic scheme, which is correlatable with the one developed in the Vercors region of SE France by Arnaud and Arnaud-Vanneau (1989, 1991), Arnaud-Vanneau and Arnaud (1990), and Hunt and Tucker (1993), and which is based on the model developed by Vail et al. (1977) and subsequently described in numerous publications (e.g., Van Wagoner et al., 1988; Emery and Myers, 1996; Coe et al., 2003; Catuneanu et al., 2009). The sequence-stratigraphic model is chronostratigraphically calibrated in the Angles section of the Vocontian Trough, where the presence of ammonites allows for biostratigraphic time control, as shown in Fig. 4. The same sequence-stratigraphic approach was applied in previous studies for the Rawil Mb in the Helvetic Alps (Embry, 2005; Stein et al., 2012a). 3.4. Panorama of the Churfirsten range The panorama was photographed from the southern side of the lake of Walensee (between Quarten and Oberterzen; 738.349/218.339; N 44° 53.414/E -1° 50.325) in a high-resolution fashion by the stacking of 460 photos. The photos were taken by a Canon EOS 7D, a zoom lens Canon EF image stabilizer 70–200 mm, an automatic x2 tele-converter Kenko Teleplus MC 7 DG, and a robotic camera mount Gigapan Epic

Bodin et al., 2006a; Stein et al., 2012a Wissler et al., 2003; Stein et al., 2012a Briegel, 1972; Wissler et al., 2003

Schenk, 1992; Bodin et al., 2006a Ribaux, 2012 Schenk, 1992; Stein et al., 2012a

Ziegler, 1967; Schenk, 1992

2, 5C, 7, 9, S1 2, 5D, 7, 9, 19, 25, S2 2, 5N, 9, S3 2, 5F, 7, 9, 17, 25, S4 2, 9, S5 2, 5G, 5H, 7, 9, S6 2, 5E, 7, 9, S7 2, 9, 16, 20, 25, S8 2, 5H-J, 7, 9, 25, S9 2, 3, 5L, 7, 9, 23, 25, S10 2, 5A, 5M, 7, 9, 23, 25, S11 2, 3, 5B, 7, 9, 23, S12 N 44° 53.449/E -1° 50.308 N 44° 53.419/E -1° 50.355 N 44° 53.424/E -1° 50.304 N 44° 53.445/E -1° 50.313 N 44° 53.441/E -1° 50.315 N 44° 53.442/E -1° 50.315 N 44° 53.448/E -1° 50.326 N 44° 53.422/E -1° 50.295 N 44° 53.410/E -1° 50.365 N 44° 53.423/E -1° 50.327 N 44° 53.417/E -1° 50.327 N 44° 53.417/E -1° 50.333 722.715/185.749 579.336/124.832 613.081/140.041 628.427/176.557 631.347/169.493 631.250/170.991 645.955/182.008 601.157/137.186 690.299/205.511 742.970/234.730 742.224/224.041 749.644/222.586 Inner platform Inner platform Inner platform Inner platform Intermediate platform Intermediate platform Distal platform Intermediate platform Intermediate platform Inner platform Intermediate platform Distal platform Infrahelvetics Morcles nappe, normal limb Dolderhorn nappe Wildhorn nappe Wildhorn nappe Wildhorn nappe (overturned) Wildhorn nappe (overturned) Wildhorn nappe Drusberg nappe Säntis nappe Säntis nappe Säntis nappe

3.7. Bulk-rock mineralogy

East of Bifertenstock 2.5 km from Anzeindaz Close to the col. of Gemmi In Loubenegg Along road and railway Northern side of Interlaken North of Brienz Midway station of cablecar Golf course of Morschach Close to the Säntis summit Churfirsten range Eastern side of the Alvier

The total phosphorus content was measured on 1182 samples from the sections at L'Ecuelle, Tierwis, Interlaken, Kistenpass, Harder, Brienzer-Rothorn, and Valsloch, using the ascorbic acid molybdate blue method (Eaton et al., 1995) and following the procedure described in Bodin et al. (2006c). The phosphorus content was determined by a UV/Vis Perkin Elmer Lambda 25 spectrophotometer at the Institute of Earth Sciences of the University of Lausanne, and calibrated with internal standard solutions providing a precision better than 5%.

4. Results

Kistenpass L'Ecuelle Lämmerenplatten Justistal Interlaken Harder Brienzer Rothorn Rawil Morschach (drill hole) Tierwis Valsloch Alvier

Grisons Vaud Valais Berne Berne Berne Berne Berne Schwyz St. Gall St. Gall St. Gall

3.6. Phosphorus content

Position on platform

International coordinates

A total of 1958 samples was analysed for their stable carbon and oxygen isotope composition at the Institute of Earth Surface Dynamics of the University of Lausanne using the procedures described by Revesz et al. (2001). Analyses of aliquots of all samples were performed using a Thermo Fisher Scientific (formerly ThermoQuest/Finnigan, Bremen, Germany) GasBench II preparation device interfaced with a Thermo Fisher Scientific Delta Plus XL continuous flow isotoperatio mass spectrometer (IRMS). The CO2 extraction was performed at 90 °C. The carbon and oxygen-isotope ratios were reported in the delta (δ) notation as the per mil (‰) deviation relative to the Vienna– Pee Dee belemnite standard (VPDB). Analytical uncertainty (1 σ), monitored by replicate analyses of the international calcite standard NBS-19 and the laboratory standards Carrara Marble were not greater than ± 0.05‰ for δ13C and ±0.1‰ for δ18O. To assess the possible heterogeneity of the carbon and oxygen isotope composition within a hand specimen, a detailed micro-drilling subsampling (100 to 300 μg) was performed on eight selected samples. These samples contain facies-representative bioclasts, and calcite veinlets within the micritic matrix. A total of 54 subsamples was analysed for their C and O isotope composition and the results were compared to those of the corresponding whole-rock δ13C and δ18O values.

Tectonic unit

Swiss coordinates

3.5. Carbon and oxygen isotope analysis

Locality

Canton

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Pro. The software used to combine the photos is the Gigapan stitch software. The interpretation of this panorama is based on the visual observation of the evolution of marker beds and intervals through the panorama. Sequence stratigraphic interpretations and in particular the identification of sequence boundaries were controlled in the section at Valsloch, which is located in the eastern part of the Churfirsten range (Fig. 2).

Name

Table 1 List of the outcrop and drill-hole localities.

Figures

References

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The bulk-rock mineralogy was analysed on 68 samples from the section at Valsloch on a Scintag XRD 2000 diffractometer in the Institute of Earth Sciences at the University of Lausanne, based on procedures described by Kübler (1983) and Adatte et al. (1996). This method permits the semi-quantification of its mineralogy using external standards with an error of 5%.

4.1. Brief description of the investigated lithostratigraphic units In the following, we provide a brief description of all investigated lithostratigraphic units. They are interpreted more in detail with regards to their (micro-)facies and sequence stratigraphy in Section 5.2. The Altmann Member (Mb) is the basal member of the Tierwis Fm and consists of mostly strongly condensed, phosphate and glauconiterich deposits (Fichter, 1934; Funk, 1969, 1971; Wyssling, 1986; Bodin et al., 2006a; Föllmi et al., 2007; Godet et al., 2013) (Figs. 3, 4). In the more expanded sections (Säntis and Fluhbrig regions), a marly, crinoidrich carbonate including several phosphate and glauconite-enriched hardgrounds and condensed beds is present (Rick, 1985; Bodin et al., 2006a). The age of the Altmann Mb is based on ammonite biostratigraphy

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and includes the time span between the late Hauterivian to the late early Barremian (Balearites balearis to Kotetishvilia compressissima zones; Fichter, 1934; Rick, 1985; Wyssling, 1986; Bodin et al., 2006a) (Fig. 4). The Altmann Mb is mostly extremely thin (b1 m) or even absent (like in the Glarus and Mürtschen Nappes representing the proximal part of the shelf; Funk, 1971; Funk et al., 1993) (Figs. 7, 8A). The overlying Drusberg Mb is characterized by an alternation of hemipelagic marl and marly limestone beds, and in proximal sections by important oyster accumulations (e.g., Kistenpass; Figs. 3, 4). In the sections at Justistal and Harder, the Drusberg Mb includes important intervals of bioclastic carbonate. These intercalations represent approximately 20% of the total Drusberg Mb for the section at Harder (Fig. 5K). Where the Drusberg Mb is overlain by the Schrattenkalk Fm, the age of the Drusberg Mb is restricted to the latest early Barremian in proximal areas and confined to a single sequence (B2). It extends to the middle late Barremian (Moutoniceras moutonianum to Gerhardtia sartousiana zones; Bodin et al., 2006b, 2006c) in intermediate areas. In distal areas, the hemipelagic facies of the Drusberg Mb replaces the Schrattenkalk Fm entirely and as such it persists through the late Barremian and early Aptian (Heim and Baumberger, 1933; Föllmi, 1986; Bollinger, 1988). The maximum thickness of this member is observed in intermediate and external parts of the platform, and maximum accommodation occurred in the section at Alvier, where the thickness of the unit reaches 120 m. The sediment-accumulation rate is minimal for sections located on the inner platform (Tierwis and Kistenpass), where the thickness does not exceed 40 m. The Schrattenkalk Fm diachronically overlies the Drusberg Mb and is subdivided into a Lower and an Upper Schrattenkalk Member (Mb) by the Rawil Mb - an equivalent of the “Lower Orbitolina Beds” (Schenk, 1992; Stein et al., 2012a) (Figs. 3, 4). The Lower Schrattenkalk Mb consists generally of a thickly bedded or massive shallow-water platform carbonate reaching a maximal thickness of 100 m (Heim, 1910–1916; Schenk, 1992) (Figs. 5, 7, 8C–E). Stratigraphic microfacies, stratal geometries and the presence of important emersion surfaces enables three sequences to be distinguished (B3–B5). Its age encompasses the latest most early Barremian and the entire late Barremian in proximal areas, whereas towards more distal areas this unit starts later, such as in the middle late Barremian Gerhardtia sartousiana Zone at Tierwis (Bodin et al., 2006b) (Fig. 4). The Lower Schrattenkalk Mb is overlain by the Rawil Mb, which distinguishes itself from the under- and overlying Schrattenkalk Mbs by an increase in detrital material and the resulting presence of marl and sandy carbonate (Stein et al., 2012a) (Figs. 3–5, 7, 8F). The regional distribution of detritus is quite variable, and in certain regions, such as in Vorarlberg (western Austria), detrital levels are very low and the Rawil Mb cannot be distinguished as such (Heim and Baumberger, 1933; Bollinger, 1988). Three subunits are observed within the Rawil Mb, which are labelled A, B, and C (cf. Section 5.2). The sediment thickness is minimal in the inner part of the platform (22 m and 32 m for the sections of L'Ecuelle and Tierwis) and in the section at Justistal, where only the first 6.5 m are recorded. In intermediate and distal parts, this unit has a comparable thickness, comprised between 40 m and 50 m. The Rawil Mb represents the transgressive and earliest highstand systems tracts of sequence A1 and its age is restricted to the early Aptian Deshayesites oglanlensis and the early Deshayesites forbesi Zones (Stein et al., 2012a) (Fig. 4). The Upper Schrattenkalk Mb is composed of a thickly bedded or massive carbonate, which altogether represents a succession of thinning- and shallowing-upward parasequences (Figs. 3–5, 7, 8G). It has a comparable

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thickness in all investigated platform sections, with approximately 20 m at L'Ecuelle and 33 m at Rawil on the inner platform. The maximum thickness occurs at Alvier (about 50 m). The Upper Schrattenkalk Mb represents the remainder of the HST of sequence A1. Its age is restricted to the late Deshayesites forbesi Zone (Arnaud, 2005) (Fig. 4). In the sections at Valsloch, Morschach, and Rawil, the top of the Upper Schrattenkalk Mb is overlain by carbonates with a deeper water facies, rich in echinoderms and annelids. This unit is identified as representative of the overlying Grünten Mb, which is an equivalent of the “Upper Orbitolina Beds” (Wissler et al., 2003; Linder et al., 2006), and which represents the basal member of the Garschella Fm. In the section at L'Ecuelle, the top of the Schrattenkalk Fm is directly covered by the coarse-grained sandstones of the upper Aptian Brisi Mb (middle member of the Garschella Fm), and large extraclasts composed of Orbitolinarich carbonates of likely Grünten Mb origin are present in the infillings of karst pockets. At Tierwis, the Schrattenkalk Fm is covered by glauconitic deposits of the Albian Selun Mb (upper member of the Garschella Fm). At Justistal, the Upper Schrattenkalk Mb and the upper part of unit B and the entire unit C of the Rawil Mb were removed by erosion. The remainder of the Rawil Mb is directly overlain by Eocene sedimentary rocks. Detailed lithologs of each analysed section including the carbonisotope and phosphorus data and sequence-stratigraphic and microfacies interpretations are present in the Supplementary data set (Figs. S1–S12). 4.2. Carbon-isotope records 4.2.1. Individual subsamples The δ13C and δ18O values of the micro-drilled subsamples are presented in Table 2 and compared with the values obtained for whole-rock powder of the same samples. For most samples, the values obtained for the micro-drilled micrite and whole-rock powder differ b0.2‰ for δ13C and 0.3‰ for δ18O. In some samples (e.g., EC 166, MC 137, and KP 61), the different components in the subsamples (rudist, oncolite, oyster, recrystallized bioclasts, and cement) differ up to 4‰ for δ13C and 3.8‰ for δ18O (both in EC 166). 4.2.2. Whole-rock samples In the Altmann Mb, carbon-isotope values are comprised between +0.5‰ and 1.5‰. For the Drusberg Mb, a distinction between three groups of sections is made with regards to their δ13C records (Figs. 9, S1–S12). Those of Kistenpass, L'Ecuelle, and Morschach, which are all part of the proximal platform domain, show a plateau with a mean value of 1.1‰, 1.5‰, and 2.4‰, respectively. The sections at Tierwis and Justistal display an excursion to higher δ13C values followed by a decrease. The Valsloch, Harder, Alvier, and Brienzer Rothorn sections, which are representative of the distal platform, exhibit two well-developed trends towards more positive values with a maximum of +2.5‰ for Harder and around +2‰ for the sections at Valsloch, Alvier, and Brienzer Rothorn. For the basal part of the Lower Schrattenkalk Mb (sequence B3), the sections at Valsloch, Justistal, Harder, and Brienzer Rothorn show a plateau in δ13C values, with a mean value of 2.2‰, 1.8‰, 2.6‰, and 2.2‰, respectively. The δ13C curves from Morschach and Tierwis indicate also a plateau (mean value of 2.2‰ and 1.5‰, respectively), followed in the upper 10 m by a shift to higher values, which reaches a maximum of 3.8‰ and 2.5‰, respectively. The δ13C record of the section at L'Ecuelle displays an abrupt decrease to a plateau of negative values,

Fig. 6. Distribution of principal microfacies types along a rimmed platform (redrawn after Godet et al., 2010, and Arnaud-Vanneau and Arnaud, 2005) and examples of microfacies types F0 to F11 and FT. (A) F0, pelagic facies rich in radiolaria (Valsloch, VA 317); (B) F1, facies rich in sponge spicules (Morschach, MC 259); (C) F2, facies with irregular sea urchin (Morschach, MC 238); (D) F3, facies with circalittoral foraminifera (arrows) (Harder, HA46); (E) F3a, facies rich in colonial annelids (L'Ecuelle, EC 61); (F) F3b, accumulation of Eopalorbitolina transiens (Morschach, MC 206); (G) F4, facies with branched bryozoans (L'Ecuelle, EC 38); (H) F5, facies with rounded debris (Harder, HA 179); (I) F6, oolitic facies (Tierwis, TW 25); (J) F7, facies with corals (Morschach, MC 173); (K) F8, facies with canaliculate rudists (Morschach, MC 154); (L) F9, facies with rudists (Morschach, MC 163); (M) F10, oncolitic facies (Morschach, MC 165); (N) F11a, facies with keystone vugs (Valsloch, VA 26); (O) F11b, confined supratidal facies (Tierwis, TW 32); (P) FT, reworked facies (Valsloch, VA 255).

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Fig. 7. Sedimentological logs of a selection of representative sections and their microfacies distribution along a proximal to distal transect through the Helvetic platform. The grey line corresponds to the top of the Altmann Mb.

L. Bonvallet et al. / Sedimentary Geology 387 (2019) 18–56

with a minimum of −2.6‰, interrupted by an excursion to higher values (maximum of 1.6‰) 10 m below the top of this unit. The middle part of the Lower Schrattenkalk Mb (sequence B4) is characterized by a plateau for the sections at Tierwis (mean value 2.5‰), Morschach (mean value 3.5‰), Justistal (mean value of 2.2‰), and Harder (mean value of 2.7‰). For the section at L'Ecuelle, the δ13C record presents a shift to higher values (maximum of −0.8‰). The section at Valsloch shows saw-tooth variations in its δ13C record, followed by an excursion to lower values (minimum of 1‰), which is directly followed by a shift to higher values (maximum value of 3‰). The sections at Alvier and Brienzer Rothorn are characterized by a slight increase in the δ13C values (maxima of 3.2‰ and 3‰, respectively). The δ13C record of the upper part of the Lower Schrattenkalk Mb (sequence B5) represents a plateau in the sections at Morschach (mean value 3.3‰), Valsloch (mean value 3.3‰), Rawil (mean value 1.8‰), and Harder (mean value 2.5‰). A progressive shift to lower values is observed at L'Ecuelle (minimum value 1.5‰), Justistal (minimum value 1.6‰), and Alvier (minimum value 1‰). The sections at Tierwis and Brienzer Rothorn show a shift to higher values followed by a change to lower values in the last meters (maxima of 3.1‰ and 3.3‰, and minima of 0.1‰ and 0.6‰, respectively). The Rawil Mb is characterized by an excursion to higher δ13C values, followed by a shift to lower values in the sections at Tierwis, L'Ecuelle, Justistal, Rawil, and Brienzer Rothorn. In the sections at Valsloch and Morschach, the plateau reached in the previous unit is continued at the base and followed by a shift to lower values (mean values of −1.5‰ and −2.6‰, respectively). In contrast, the section at Harder presents a plateau followed by an excursion to higher values at the top of the Rawil Mb (maximum value 3‰). The δ13C record of the Upper Schrattenkalk Mb is highly fluctuating in the sections at Tierwis, L'Ecuelle, and Valsloch. In the sections at Morschach and Rawil, a plateau is reached (mean values of 3.5‰ and 2.4‰, respectively). In the section at Valsloch, the δ13C record exhibits a trend to higher values towards the Grünten Mb (maximum value of 3.7‰; Fig. 9).

4.3. Total phosphorus content The phosphorus (P) content was measured in the sections at L'Ecuelle, Interlaken, Harder, Brienzer Rothorn, Tierwis, and Valsloch (Figs. 9, S1– S12). For all sections, the P content shows an upward decreasing trend from the base of the Tierwis Fm to the Schrattenkalk Fm. The highest values are recorded in the Altmann Mb and the first few meters of the Drusberg Mb with values ranging between 500 ppm and 1000 ppm, and maximum values of 11,700 ppm reached in the upper Altmann Mb hardground at Tierwis. The Drusberg Mb is characterized by relatively high P contents: above 100 ppm for the sections at Tierwis, Valsloch, Harder, and Brienzer Rothorn, and above 50 ppm for L'Ecuelle (mean value 128 ppm). The base of the Lower Schrattenkalk Mb is marked by a decrease in P content in all sections, with a mean value of 78, 44, 91, 87, and 121 ppm for the sections at Tierwis, L'Ecuelle, Valsloch, Harder, and Brienzer Rothorn, respectively. An enrichment is observed in the lower part of the Lower Schrattenkalk Member showing the accumulation of Eopalorbitolina transiens, Choffatella, and annelids at L'Ecuelle and Valsloch. The middle and upper parts of the Lower Schrattenkalk Mb show a slight decrease in P values, with minimum values in the upper part of the member of 4, 12, 10, 33, and 81 ppm for the sections at Tierwis, L'Ecuelle, Valsloch, Harder, and Brienzer Rothorn, respectively. The overlying Rawil Mb is characterized by an increase in P content (Stein et al., 2012a). In the sections at Tierwis, L'Ecuelle, and Harder, this increase occurs directly above the boundary with the underlying Lower Schrattenkalk Mb. In Valsloch, the P content exhibits higher values in the upper part of the Rawil Mb and top interval. The values decrease in the Upper Schrattenkalk Member until the last meters, where the P content reaches higher values, likely due to infiltrations from the superjacent Garschella Fm (Fig. 9).

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5. Discussion and interpretations 5.1. Biostratigraphy Ammonites and benthic foraminifera (especially orbitolinids) were used to obtain a biostratigraphic framework for the successions studied. The sequences identified in the Helvetic Alps were also correlated with those from the Vercors, where the stratigraphic ranges of orbitolinids were calibrated (Arnaud-Vanneau, 1980; Arnaud-Vanneau and Arnaud, 1990; Arnaud et al., 1998; Arnaud, 2005). Ammonites constrain the basal Altmann Member to the interval between the latest Hauterivian to late early Barremian (Balearites balearis to the Kotetishvilia compressissima zones), if the definition of the upper boundary of the Altmann Member at Tierwis proposed in Section 5.2.1 is adopted (Fichter, 1934; Rick, 1985; Wyssling, 1986; Bodin et al., 2006a). In the hemipelagic deposits of the Drusberg Mb, the biostratigraphic markers are ammonites and circalittoral foraminifera (Lenticulina). In the bioclastic carbonate beds of the Drusberg Mb, the presence of Paleodictyoconus sp., Cribellopsis elongata, Falsurgonina sp., and Paracoskinolina sunnilandensis is observed. The lower part of the Lower Schrattenkalk Mb (sequence B3) is characterized by the presence of Praedictyorbitolina carthusiana, Paleodictyoconus actinostoma, Paleodictyoconus cuvillieri, Eopalorbitolina/Palorbitolina transiens, Orbitolinopsis debelmasi, Falsurgonina sp., Montseciella sp., and Paracoskinolina sunnilandensis, and the first occurrence of Paracoskinolina reicheli and Neotrocholina friburgensis (Figs. 10, 11). The middle part of the Lower Schrattenkalk Mb (sequence B4) is characterized by the presence of Neotrocholina friburgensis, Paleodictyoconus cuvillieri, Cribellopsis neoelongata, and Parakoskinolina maynci, like sequences B3 and B5 (Fig. 11). The upper part of the Lower Schrattenkalk Mb (sequence B5) is characterized by the last occurrence of Neotrocholina friburgensis, and by the presence of Palorbitolina lenticularis, Orbitolinopsis buccifer, Paracoskinolina maynci, and Paracoskinolina cf. hispanica (Figs. 10, 11). Close to the Barremian–Aptian boundary, a major change in the composition of the benthic foraminiferal associations is observed, which is in particular characterized by the disappearance of Neotrocholina friburgensis, Paracoskinolina hispanica, P. reicheli, Paleodictyoconus cuvillieri, and P. actinostoma (temporary disappearance of the latter in the basal interval of the Rawil Mb, unit A, which is essentially devoid of large benthic foraminifera), the high abundance of Palorbitolina lenticularis, Paracoskinolina maynci, Orbitolinopsis buccifer, O. kiliani, and O. cuvillieri; and the appearance of Paracoskinolina arcuata, Orbitolinopsis briacensis, and O. pygmaea (Arnaud-Vanneau, 1980; Raddadi, 2005). The base of the Upper Schrattenkalk Mb is characterized by the first occurrence of Orbitolinopsis briacensis, Orbitolinopsis pygmaea, and Paracoskinolina arcuata (Figs. 10, 11). In general, the benthic foraminiferal successions are well comparable between the Helvetic and Subalpine Chains sections. The biostratigraphic observations indicate an age from the Moutoniceras moutonianum to the Gerhardtia sartousiana zones for the onset of the Lower Schrattenkalk Mb, depending on the position on the platform. The age of the Rawil Mb corresponds to the Deshayesites oglanlensis zone and early Deshayesites forbesi zone. The Upper Schrattenkalk Mb as a whole belongs to the late Deshayesites forbesi zone (Fig. 4). Note that alternative and conflicting age models exist for equivalent units of the Urgonian in France and the French-Swiss Jura (e.g., Clavel et al., 2013; Frau et al., 2018). The ages proposed here for the Helvetic succession are the ones adopted by the Swiss commission of stratigraphy (www.strati.ch) and already earlier used by different authors (e.g., Bollinger, 1988; Funk et al., 1993; Wissler et al., 2003). 5.2. Facies evolution and sequence stratigraphy 5.2.1. Sequences H6, H7, and B1 (Altmann Member) Bodin et al. (2006a) attributed sequence B1 and the transgressive systems tract (TST) B2 to the Altmann Mb, whereas the highstand

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L. Bonvallet et al. / Sedimentary Geology 387 (2019) 18–56 Table 2 Comparison of carbon and oxygen-isotope analyses on micro-drilled subsamples and corresponding bulk-rock samples. Identifier

Type of compound

δ13C VPDB

δ18O VPDB

EC 166 BIS (1) EC 166 BIS (2) EC 166 BIS (3) EC 166 BIS (4) EC 166 BIS (5) EC 166 carb (W-R) EC 166 biot (W-R) KP 61 (1) KP 61 (2) KP 61 (3) KP 61 (4) KP 61 (W-R) LB 27 (1) LB 27 (2) LB 27 (3) LB 27 (4) LB 27 (5) LB 27 (W-R) MC 10 (1) MC 10 (2) MC 10 (3) MC 10 (4) MC 10 (5) MC 10 (6) MC 10 (W-R) MC 137 (1) MC 137 (2) MC 137 (3) MC 137 (4) MC 137 (5) MC 137 (6) MC 137 (W-R) TW-145 (1) TW-145 (2) TW-145 (3) TW 145 (W-R) VA 15 (1) VA 15 (2) VA 15 (3) VA 15 (4) VA 15 (5) VA 15 (6) VA 15 (W-R) VA 122 (1) VA 122 (2) VA 122 (3) VA 122 (4) VA 122 (5) VA 122 (6) VA 122 (W-R)

Rudist Micrite Vein Vein Bioturbation Bulk rock (micrite) Bulk rock (bioturbation) Oyster layer 1 Oyster layer 2 Oyster layer 3 Micrite Bulk rock Rudist 1 Rudist 2 Bioclaste Micrite Calcitic vein Bulk rock Rudist 1 Rudist 2 Echinoderm Bioclast Micrite 1 Micrite 2 Bulk rock Recrystallized bioclast 1 Recrystallized bioclast 2 Recrystallized bioclast 3 Orbitolinidae Micrite 1 Micrite 2 (dark) Bulk rock Orbitolinidae Micrite Calcitic vein Bulk-rock Recrystallized bioclast 1 Recrystallized bioclast 2 Bivalve Coral 1 Coral 2 Micrite Bulk rock Rudist (calcite) Rudist (recrystallized aragonite = calcite) Oncolite Micrite Dark micrite Calcitic vein Bulk rock

−1.5 −2.3 −1.8 −5.5 −3.8 −2.9 −3.9 2.9 1.4 1.5 1.4 1.5 1.8 1.5 1.6 2.0 1.6 1.7 3.1 3.9 3.9 3.3 3.8 3.7 3.5 2.3 3.6 1.9 3.3 3.2 4.4 3.0 2.0 2.0 2.1 1.9 2.4 2.3 2.6 3.5 3.4 3.6 3.4 1.9 2.4 2.7 2.6 2.7 2.9 2.6

−4.2 −4.9 −8.1 −5.3 −5.2 −5.0 −8.2 −3.9 −4.6 −4.7 −4.8 −4.9 −3.2 −3.0 −3.1 −3.0 −4.8 −3.4 −2.4 −3.4 −3.4 −3.7 −3.7 −3.4 −4.0 −2.6 −5.2 −2.5 −2.4 −2.1 −3.8 −2.5 −3.2 −3.6 −5.1 −3.5 −6.5 −6.1 −7.0 −3.6 −4.2 −3.7 −3.2 −3.3 −3.7 −3.8 −4.1 −3.6 −6.3 −4.6

systems tract (HST) B2 and the TST B3 belong to the Drusberg Mb (Figs. 4, 7). In this contribution, the boundary between the Altmann Mb and the Drusberg Mb in the reference section at Tierwis is placed on top of a siliceous and phosphatic hardground, which is below the original boundary described by Bodin et al. (2006a). This implies a readjustment of the sequence stratigraphic framework of Bodin et al. (2006a) such that the whole depositional sequence B2 belongs to the Drusberg Mb. With this amendment, the mostly strongly condensed Altmann Mb includes three sequences (H6, H7, and B1). 5.2.2. Sequence B2 (Drusberg Member) The Drusberg Mb is dominated by outer-shelf facies (F0 to F3) rich in sponge spicules, irregular echinoids, circalittoral foraminifera,

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calcispheres, and radiolaria (Figs. 4, 7, 8B). In the sections at Justistal and Harder, intervals are present, which are composed of bioclastic shallow-water facies (F4–F6, FT) including ooids, dasycladal algae, orbitolinids, and miliolids. These compounds were reworked and transported by storms, as is indicated by their intercalation in hemipelagic sediments (F1, F2), the presence of sharp and partly erosive boundaries, and hummocks (in the section at Harder; Fig. 5K). In proximal areas, the Drusberg Mb constitutes a single sequence (B2). Its transgressive systems tract (TST) is composed of sedimentary rocks with open-marine facies (F0–F2). In the Churfirsten area west of the section at Valsloch - on the western side of Zuestoll, the presence of a massive bioclastic carbonate body below sequence boundary (SB) B3 is observed, which is interpreted as part of the highstand systems tract (HST) of sequence B2 (cf., Section 5.3). Lithostratigraphically speaking, in this area, this unit needs to be considered as part of the base of the Schrattenkalk Fm, because of its carbonate composition and its presence directly underneath the carbonate of sequence B3. In proximal and intermediate parts of the inner platform (sections at Tierwis and L'Ecuelle, and the core of Morschach), the contact between the hemipelagic deposits of the Drusberg Mb and the shallow-water carbonate of the overlying Lower Schrattenkalk Mb represents an emersion surface, which is identified as SB B3. In the section at Tierwis, the top of the Drusberg Mb is represented by a 5 m-thick bed of marl, covered by an early cemented, fractured grainstone. These microfractures are filled by mud, which formed during emersion (Fig. 12C, D). In the section at L'Ecuelle, microfacies types F3 and F4 are present in the upper part of the Drusberg Mb and in the basal part of the Lower Schrattenkalk Mb. However, at 75 m from the base of the Drusberg Mb, we observed a paleosol with rootcasts associated with partial early dissolution and a vadose silt present in root molds (Fig. 12A, B), which we interpreted as SB B3. In the section at Morschach, the Drusberg Mb is interrupted and covered by a bioclastic limestone showing various extraclasts from different origins: oolitic wackestone, orbitolinid-rich or calcisphererich packstone (Fig. 12G, I, J). The grainstone is early cemented and partially dissolved (Fig. 12E, F). The shallow-water deposits are composed of a laminated tidal grainstone showing early cementation with meniscus cement (Fig. 12H). In more external parts of the Helvetic shelf, lag deposits showing a mix of different types of shallow-water grains in an outer-shelf matrix characterize the boundary between the Drusberg Mb and the Lower Schrattenkalk Mb. This is also the case west of Zuestoll, where a bioclastic carbonate at the base of the Lower Schrattenkalk Mb is attributed to this interval, due to its massive structure and the presence of reworked grains, which occur also in the same interval in the nearby section at Valsloch (Fig. 12K). In the section at Harder, the presence of nuclei surrounded by an iron-oxide coating in storm-deposited bioclastic sedimentary rocks suggests that the reworked material was partly derived from soils (Fig. 12L–N). In the sections at Alvier and Brienzer Rothorn, this level is correlated with the first occurrence of shallower facies (Ribaux, 2012). 5.2.3. Sequence B3 (lower part of the Lower Schrattenkalk Member) Lowstand systems tracts (LSTs) are usually not preserved on a shallow-water platform and are embodied in the hiatus of the SBs. An exception is found in the sections at Valsloch and Justistal, where the Lower Schrattenkalk Mb includes an LST (LST B3) at its base (Justistal), or near its base (Valsloch, on top of the bioclastic carbonate of HST B2). LST B3 consists of a bioclastic accumulation (F5–F7), which shows a characteristic progradation (Justistal, Valsloch). In the section at Alvier, LST B3 is characterized by the occurrence of outer-shelf facies F3 and F4.

Fig. 8. Spatial distribution of microfacies for the Altmann Mb to the Upper Schrattenkalk Mb. The size of each pie chart is related to the thickness of the unit. Each analysed site is plotted on the palinspastic map established by Trümpy (1969), Ferrazzini and Schüler (1979), and Kempf and Pfiffner (2004).

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Fig. 9. Carbon-isotope records and phosphorus contents in the studied sections arranged along a palinspastic transect. The carbon-isotope records are correlated with the hemipelagic reference section of Angles – Combes Lambert (Godet et al., 2006).

This unit is overlain by a lag deposit representing the transgressive surface (TS) B3. TST B3 is extremely thick and bioclastic in Valsloch. The trend in facies in this section is shallowing upward, as is indicated by the development of patch reefs. In the sections at Tierwis, L'Ecuelle, and Morschach, the Lower Schrattenkalk Mb starts with the late TST B3 and dominant components are small echinoderm fragments,

bryozoan clasts, and conic orbitolinids. In the sections at Justistal and Valsloch, the TST B3 and following deposits are dominated by oolite and bioclastic, partly reworked carbonate rich in green algae, miliolids, Neotrocholina, Sabaudia, and Palorbitolina transiens. The maximum flooding surface (MFS) B3 is characterized by the deepest, outer-platform bioclastic facies (F3, F4), with the important

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occurrence of colonial and isolated annelids (Fig. 13) and of Eopalorbitolina transiens. This fauna association reflects dysoxic and mesotrophic conditions (Martínez-Taberner et al., 1993; Fornós et al., 1997). In distal settings, the deepening of the environment is marked by reduced sedimentation rates, leading to the deposition of a condensed glauconitic and phosphatic interval, which is called the Chopf Bed (Gerhardtia sartousiana zone; Briegel, 1972; Bodin et al., 2006b). On the Helvetic shelf, lagoonal facies rich in rudists makes its first appearance in HST B3. This unit starts with bioclastic facies in the sections at Tierwis and Valsloch, followed by the installation of lagoonal facies, which arrives earlier on the inner platform at Tierwis than at Valsloch. The maximum in progradation documented in HST B3 is indicated by the presence of reworked bioclasts in the distal, outer-shelf section at Alvier. The top of sequence B3 (SB B4) is marked by an emersion surface and paleosol on the inner and intermediate platform. The sections at L'Ecuelle and Valsloch show a superficial karst, which penetrates down to ca. 15 m below the SB B4 (Fig. 14A, B). In the sections at Tierwis and Morschach, indications for dissolution are associated with paleosol features, such as root traces, deposition of green marl, and pedogenic cement (arranged in rosettes similar to Microcodium), illustrated in Fig. 14C, E–J. In the section at Tierwis, the last meters of sequence B3 exhibit meteoric amber cement (Fig. 14D). In the sections at Justistal and Harder, in the intermediate part of the platform, the top of this sequence is marked by intense dolomitization (Fig. 14L). At Justistal, dissolution features are present and bioturbations are filled by dolomitic cement. In distal parts, SB B4 is characterized by the maximum abundance of grains reworked from the platform. In Alvier, the SB B4 is placed above the bed showing a maximum of reworking of very shallow platform sediments. At Brienzer Rothorn, the SB B4 is placed based on variations in microfacies, and in particular in the ratio of circalittoral foraminifera versus spicules (Ribaux, 2012), which decreases below SB B4. The clay mineralogy shows a peak in the ratio of kaolinite versus smectite in this level (Ribaux, 2012). This key feature is also known from the Angles section in SE France (Godet et al., 2008) and is used for correlation here. 5.2.4. Sequence B4 (middle part of the Lower Schrattenkalk Member) In proximal areas, TST B4 starts with lagoonal facies rich in rudists (F8, F9). Upwards, with the occurrence of oolites and bioclastic deposits, its facies becomes gradually more distal. This trend lasts up to the maximum flooding surface (MFS). In the sections at L'Ecuelle and Morschach, the facies is extremely confined up to the MFS, including oncoids and Bacinella nodules (F10) intercalated in supratidal facies (F11). In the section at L'Ecuelle, the MFS is characterized by a yellowish interval marked by an increase in silt content. In the section at Morschach, the presence of deeper lagoonal facies (F8) including sparse glauconite grains characterizes the MFS. In the section at Tierwis, the MFS is marked by the presence of radiolaria and sponge spicules. In the intermediate area, in the sections at Valsloch, Justistal, and Harder, TST B4 consists mainly of bioclastic (F5) and outer-platform facies (F4), which is characterized by reduced thickness. The sections of the distal realm are composed of open-marine facies (F0–F3) and the MFS is marked by an increase in marly beds. In proximal parts HST B4 is characterized by an overall increase in confinement towards the top, which goes along with evidence for emersion, and which is associated with the deposition of supratidal facies and the development of early dissolution features. In intermediate parts of the platform, an evolution is observed in HST B4 starting with outer-platform facies (F3–F4) at the base and ending with a lagoonal (F8, F9) and supratidal environment at the top. The sections at Justistal and Harder are peculiar and show a dominance of oolitic parasequences at Justistal, and intense grain reworking at Harder, where outer-platform facies occurs. In distal areas, sections exhibit pelagic and hemipelagic facies corresponding to the Drusberg Mb with microfacies types F4 and F5 at the top of B4 at Alvier (Fig. 8D). Sequence B4 was less prograding than the previous one. In the distal part

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of the platform, the shallowest facies reaching the top of this sequence is outer-platform facies (F3–F4). 5.2.5. Sequence B5 (upper part of the Lower Schrattenkalk Member) Sequence B5 is characterized by the widespread development of lagoonal facies. In proximal domains, SB B5 is marked by early dissolution, and TST B5 starts with supratidal facies, consisting of beach deposits with keystone vugs and paleosols (root molds, green marl, and pedogenic cements). The TST evolves from a restricted to outer lagoonal facies (F10, F8). The MFS is characterized by the occurrence of Chondrodontes, stromatoporoids, and glauconite grains, which are markers of an open-marine environment. In intermediate parts of the shelf, SB B5 is marked by superficial karstification. TST B5 begins with supratidal facies including beach deposits. In the section at Morschach, the TST starts with several levels of Palorbitolina lenticularis accumulations, which are interpreted as beach deposits. TST B5 continues with outer lagoonal facies (F8), followed by outer-platform facies (F5–F7). This is also the case for the section at Justistal, where lagoonal facies appears for the first time. The MFS is marked by deeper facies. In the section at Rawil, it is characterized by outer-shelf facies, rich in chaetetids, planktonic echinoderms, small foraminifera, spicules, and calcispheres, and radiolaria (F1). In the sections at Valsloch and Morschach, the MFS is marked by detrital input and the presence of flat Palorbitolina. In the section at Justistal, the MFS shows the presence of Lithocodium nodules without Bacinella. In Harder, the SB B5 is marked by intense dolomitization. There, the following TST B5 is characterized by granular facies rich in reworked grains and ooids (F5–F6). The abundance of reworked grains in outer-shelf facies (F2–F4) indicates the MFS. In distal areas, the facies of TST B5 is characteristic of the outer shelf (F1–F3). In the section at Alvier, sparse bioclasts are present in the matrix and annelids are abundant. The MFS is indicated by a marly level. HST B5 is characterized by restricted lagoonal to supratidal facies (F9–F11) with reworked sediment accumulations (by storms?), beach facies including keystone vugs, or restricted facies (mudstone/wackestone rich in Istriloculina and bird's eyes in proximal and intermediate areas). Oncoids and Bacinella nodules are abundant, and karst features overprint the facies in the upper part of the HST. In the section at Harder, a bioclastic facies (F5–F6) forms the HST. In the section at Alvier, reworked rudist shells are recorded in the uppermost part of HST B5. The top of this unit is marked by a major emersion surface, associated with superficial karst, the presence of microcaves, early dissolution, vadose silt, and asymmetric cements, in particular in the sections at Valsloch, Rawil, and Tierwis. This surface includes the BarremianAptian boundary and coincides with the SB A1. In the section at L'Ecuelle, this surface is affected both by intense early dissolution of rudist shells, which are infilled by sandstone (Fig. 15A), as well as by the presence of a dense network of Thalassinoides partly infilled by a yellowish sandstone (Fig. 15B), and of dark sandy infiltrations composing a vertical fracture network. In the section at Tierwis, this SB is placed in the same position as previously proposed by Embry (2005) and Stein et al. (2012a), in the uppermost part of the massive limestone of the Lower Schrattenkalk Mb, where we observe a sudden stop in karstification and the presence of lag deposits and intense reworking above the SB. In the section at Rawil, the SB is marked by a thin layer of terra rossa deposits, and early dissolution and karstification affected the section up to at least 15 m below this surface (Fig. 16). In the sections at Valsloch and Justistal, SB A1 was not recognized in the field, but was identified based on microfacies analysis. In the Justistal section, the complex history of this limit is recorded in a single thin section (Fig. 17), which shows that the initial depositional environment consisted of muddy supratidal facies (F11). The subsequent emersive phase is marked by early dissolution of aragonitic elements such as dasycladales, and voids infilled by vadose silt. This event is followed by karstification and soil formation. Traces of karst associated with this emersion surface are recorded up to 16 m below this surface. In the core of Morschach, two alternative positions are possible for the

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attribution of the SB A1. The first is based on the δ13C record and its correlation with the Valsloch section. The second one is applied here and is based on microfacies analyses, and more precisely on the important occurrence of Palorbitolina lenticularis, green algae, and increased quartz content (Fig. S8). In this core, evidence of subaerial exposure occurs in numerous intervals and none was recognized as a major one. 5.2.6. Sequence A1, transgressive systems tract (Rawil Member) The Rawil Mb corresponds to the TST and the early highstand systems tract (HST) of the first sequence of the Aptian (sequence A1; Stein et al., 2012a) (Figs. 4, 7), as is documented by the progressive deepening of facies and the general increase in clay input resulting from important transgression (Stein et al., 2012a). In general, the first few meters of the Rawil Mb (unit A; Fig. 18) are organized in several cm to dm thick calcareous parasequences, showing features of subaerial exposure at their top. These suggest the rapid infilling of accommodation space. Lag and transgressive microfacies type FT1 is common, and is associated with levels rich in quartz and clay, in particular in the sections at Rawil, Tierwis, L'Ecuelle, and Justistal. This particular facies is

interpreted as typical of a lagoonal estuarine depositional environment (Embry, 2005). For example, in the section at Tierwis, the base of the Rawil Mb consists of calcareous sandstone and sandy carbonate, containing poorly sorted quartz grains, wood remains, and a marine fauna including miliolids (Embry, 2005; Stein et al., 2012a). Fragments of reworked Charophytes are preserved in the sections at Tierwis, Rawil, and Justistal. Palorbitolina lenticularis or Orbitolinopsis were not observed in the basal interval A, and they reappear in the overlying intervals B and C. For the section at L'Ecuelle, Palorbitolina is found in the sandy bioturbation infillings, which reach as deep as 10 cm into the emersion surface on top of the Lower Schrattenkalk Mb (Fig. 15D), and which are covered by a carbonate breccia contained in a laminated sandstone (Fig. 15C). It is likely that unit A is missing in this section, which suggests that the deposits associated with TST A1 did not extend to this proximal region. In the sections at Rawil and Morschach, the absence of unit A may reflect the effect of local paleotopographic highs. In the section at Valsloch, above a 2-m observational hiatus, the Rawil Mb is composed of a deeper-water facies (F3), which is followed by a more lagoonal facies including irregular urchins (Nucleopygus roberti), and by

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a layer rich in small ooids (b100 μm) and Lithocodium-Bacinella nodules. At Alvier, unit A is represented by open-marine facies (F1, F2). In general, unit A ends with an epikarstic surface. Unit B corresponds to the middle TST A1 and consists of symmetrical parasequences (also described as “cyclic parasequences” in Bernaus (1998) and Arnaud et al. (2000); or as “deep-water cycles” in Bernaus et al. (2003)) showing progressively outer-shelf facies in most sections through the gradual enrichment in sponge spicules and/or thin grainstone levels rich in small circalittoral foraminifera (e.g., Gaudryina), which goes along with the presence of Palorbitolina lenticularis and Orbitolinopsis (Fig. 18). These parasequences typically consist of a lag deposit at their base, containing reworked organisms from different habitats (FT1), followed by wackestone rich in green algae (FT3). The overlying deposits are associated with microfacies type FT2, and are rich in annelids, detrital quartz, and foraminifera attributed to sea-grass environments (e.g., Choffatella decipiens, Palorbitolina (Palorbitolina) lenticularis lenticularis; Arnaud-Vanneau, 1980). The parasequences continue with inner lagoonal deposits rich in oncoids (F9–10), and end with supratidal sediments, which are rich in corals, and include stromatoporoids and chaetetids in a muddy sediment, which may be associated with a hardground surface. Tempestite and beach deposits (F11) occur as well (Fig. 15G, H). In the section at L'Ecuelle, this interval is composed of parasequences and ends with a hardground on top of a bank rich in hermatypic corals, which is bioeroded and sealed by a reddish sandy matrix rich in orbitolinids and echinoids (Fig. 15E–F). Unit C includes the late TST, the MSF, and the early HST of sequence A1 (Fig. 18). It represents a second deepening phase, interpreted as the maximum flooding interval. Its sedimentary rocks display a microfacies characteristic of a sea-grass environment rich in dasycladal algae, including massive accumulations of Palorbitolina lenticularis and Choffatella, and showing an increase in quartz contents. This specific microfacies is mainly distributed on the proximal platform, becomes rare (b10%) in the intermediate sections at Morschach and Valsloch, and is missing on the outer platform (Alvier and Brienzer Rothorn). Unit C is characterized by the gradual appearance of an open-marine facies, within a thicker interval of approximately 20 m for the sections at Valsloch, Morschach, and Tierwis, and 10 m for the sections at Rawil and

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L'Ecuelle. In these latter sections, the most distal microfacies (F1–F3) is found within this interval, with deposits rich in sponge spicules, calcispheres, radiolaria, and deeper-water benthic foraminifera (e.g., Gaudryina). Echinoderms are also abundant in this interval and corals associated with lime mud are present in the section at Rawil. The drill core of Morschach shows an enigmatic occurrence of a series of emersive horizons intercalated with deposits attributed to microfacies type F3, rich in circalittoral foraminifera and small echinoderm fragments. In the section at Valsloch, two alternative intervals may represent the MFS; the first one occurs in the lower part of unit C, where the quantification of components and the presence of planktonic foraminifera indicate maximum deepening. The second possible interval is in the upper part of unit C, where the last appearance of open-marine facies (F3) was observed. Unit C ends with a marly limestone rich in Palorbitolina lenticularis (close to facies F3). This level is associated with one or several emersion levels, which define the boundary to the overlying, rudist-bearing Upper Schrattenkalk Mb. 5.2.7. Sequence A1, highstand systems tract (Upper Schrattenkalk Member) The Upper Schrattenkalk Mb embodies the HST of sequence A1 (Fig. 4). Overall, the member is characterized by shallowing-upward. Its facies distribution shows the development of an inner lagoonal environment (F8–F10) on the whole platform with supratidal areas representing at least 10% in the sections at Tierwis, Valsloch, Rawil, and L'Ecuelle (Fig. 8G). The two sections at Alvier and Harder display a different facies type. At Alvier, N20% of the Upper Schrattenkalk Mb is occupied by granular facies (F5) showing evidence for maximal progradation of the carbonate platform. At Harder, the Upper Schrattenkalk Mb starts with bioclastic and oolitic facies, and terminates with lagoonal facies (20%), which again is indicative of progradation of the carbonate platform. In the sections at Valsloch, Rawil, and Tierwis, its basal interval consists of oolitic microfacies (F6). In the sections at Morschach and l'Ecuelle, the Upper Schrattenkalk Mb directly starts with rudist-rich carbonates, which are attributed to a lagoonal environment (F8–F9). In the section at Rawil, a reddish erosive surface overlain by a nodular level extremely rich in quartz is observed; 15 m below the top of the Rawil section, the Upper Schrattenkalk Mb includes a level of

Fig. 10. Photomicrographs of large benthic foraminifera. (1) Neotrocholina friburgensis, oblique section (Tierwis, TW 4); (2) Palorbitolina-Eopalorbitolina transiens, axial section through the embryonic apparatus (Valsloch, VA 186); (3) Praedictyorbitolina carthusiana, oblique section (Morschach, MC 170); (4) Urgonina alpillensis?, oblique section (Justistal, LB 228); (5) Paleodictyoconus cf. actinostoma, axial section (Tierwis, TW 18); (6) and (8) Paracoskinolina cf. reicheli, oblique section (Justistal, LB 106 and LB 186). (7) Falsurgonina sp., oblique section (Justistal, LB 218); (9) Paleodictyoconus, transverse section (Tierwis section, sample TW23, HST B3); (10) Paleodictyoconus actinostoma, axial section through the embryonic apparatus (Tierwis section, sample TW 62, TST B4); (11) Cribellopsis elongata, transverse section (Justistal section, sample LB 230, HST B2); (12) Paleodictyoconus, sub-axial section (Valsloch section, sample VA 255, HST B2); (13) Paleodictyoconus actinostoma, axial section (Tierwis section, sample TW 82); (14) Paleodictyoconus cuvillieri, sub-axial section (Tierwis section, sample TW 47, TST B4); (15) Paleodictyoconus cuvillieri, transverse section (Tierwis section, sample TW 99, HST B4); (16) Paleodictyoconus actinostoma, transverse section (Tierwis section, sample TW 62, TST B4); (17) Praedictyorbitolina?, oblique section (Morschach section, sample MC 217, TST B3); (18) Montseciella, oblique section (Tierwis section, sample TW 46, TST B4); (19) Montseciella?, transverse section (Justistal section, sample LB 34, HST B5); (20) Paracoskinolina reicheli, sub-axial section (Tierwis section, sample TW40, TST B4); (21) Cribellopsis elongata, sub-axial section (Justistal section, sample LB 226, HST B2); (22) Praedyctiorbitolina, oblique section (Justistal section, sample LB 217, LST B3); (23) Palorbitolina/Eopalorbitolina transiens, axial section through the embryonic apparatus (Tierwis section, sample TW 82, HST B4); (24) Falsurgonina, transverse section (Morschach section, sample MC 110, HST B5); (25) Orbitolinopsis debelmasi, sub-axial section (Tierwis section, sample TW 23, HST B3); (26) Paracoskinolina sunnilandensis of large size, sub-axial section (Morschach section, sample MC 112, HST B5); (27) Cribellopsis neoelongata, transverse section showing a row of pores (Valsloch section, sample VA 70, TST A1); (28) Falsurgonina, transverse section (Morschach section, sample MC 150, TST B4); (29) Palorbitolina/Eopalorbitolina transiens, axial section through the embryonic apparatus (Tierwis section, sample TW 62, TST B4); (30) Neotrocholina friburgensis, sub-axial section (Tierwis section, sample TW 100, TST B5); (31) Falsurgonina, sub-axial section (Tierwis section, sample TW 57, TST B4); (32) Paracoskinolina reicheli, transverse section (Tierwis section, sample TW 46, TST B4); (33) Paracoskinolina reicheli, sub-axial section (Valsloch section, sample VA 178, TST B3); (34) Paracoskinolina sunnilandensis, subaxial section (Tierwis section, sample TW 46, TST B4); (35) Paracoskinolina reicheli, sub-axial section (Justistal section, sample LB 106, HST B3); (36) Neotrocholina friburgensis, axial section (Tierwis section, sample TW 82, HST B4); (37) Paracoskinolina maynci, transverse section (Valsloch section, sample VA 102, TST B5); (38) Cribellopsis neoelongata, axial section (Tierwis section, sample TW 89, HST B4); (39) Cribellopsis neoelongata, sub-axial section (Harder section, sample HA 247, TST B4); (40) Paracoskinolina cf hispanica, sub-axial section (Morschach section, sample MC 112, HST B5); (41) Paracoskinolina cf hispanica, sub-axial section (Harder section, sample HA 244, TST B4); (42) Paracoskinolina arcuata, transverse section (Tierwis section, sample TW 145, HST A1); (43) Orbitolinopsis pygmaea, sub-axial section (Valsloch section, sample VL 23, TST A1); (44) Palorbitolina lenticularis, axial section through the embryonic apparatus (Harder section, sample HA 378, HST A1); (45) Orbitolinopsis pygmaea, sub-axial section (Tierwis section, sample TW 129, HST A1); (46) Orbitolinopsis pygmaea, transverse section (Tierwis section, sample TW 129, HST A1); (47) Palorbitolina arenaceous, sub-axial section (Valsloch section, sample VA 63, TST A1); (48) Orbitolinopsis kiliani, transverse section (Valsloch section, sample VA 45, TST A1); (49) Palorbitolina lenticularis lenticularis, axial section through the embryonic apparatus (Morschach section, sample MC 43, mfs A1); (50) Paracoskinolina maynci, sub-axial section (Justistal section, sample LB 36, HST B5); (51) Paracoskinolina arcuata, sub-axial section (Tierwis section, sample TW 144, HST A1); (52) Palorbitolina lenticularis with annular chambers, transverse section (Valsloch section, sample VA 45, TST A1); (53) Paracoskinolina arcuata, sub-axial section (Tierwis section, sample TW 156, HST A1); (54) Orbitolinopsis cuvillieri, sub-axial section (Valsloch section, sample VL 19, TST A1); 55. Orbitolinopsis buccifer, sub-axial section (Morschach section, sample MC 95, HST B5); (56) Orbitolinopsis buccifer, sub-axial section (Morschach section, sample MC 15, HST A1); (57) Orbitolinopsis briacensis, sub-axial section (Valsloch section, sample VA 6, HST A1); (58) Orbitolinopsis cuvillieri, sub-axial section (Valsloch section, sample VA 70, TST A1); (59) Paracoskinolina arcuata, sub-axial section (Valsloch section, sample VL 26, TST A1); (60) Orbitolinopsis briacensis?, sub-axial section (Valsloch section, sample VA 23, TST A1); (61) Orbitolinopsis briacensis, sub-axial section (Tierwis section, sample TW 137, HST A1); (62) Paracoskinolina maynci, sub-axial section (Valsloch section, sample VA 14, HST A1); (63) Paracoskinolina maynci, sub-axial section (Morschach section, sample MC 99, HST B5); (64) Paracoskinolina maynci, sub-axial section (Tierwis section, sample TW 100, TST B5); (65) Orbitolinopsis cuvillieri, sub-axial section (Tierwis section, sample TW 130, HST A1); (66) Orbitolinopsis kiliani, sub-axial section (Morschach section, sample MC 15, HST A1); (67) Orbitolinopsis kiliani, sub-axial section (Tierwis section, sample TW 123, HST A1).

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Fig. 11. Stratigraphic distribution of Orbitolinids and Neotrocholina friburgensis in the Helvetic nappes (modified after Arnaud et al., 1998). The colored markers correspond to the sequences for which these species are characteristic: pink: sequence B2; green: sequence B3; yellow: sequence B4; blue: sequence B5; orange: sequence A1. Ammonite biostratigraphy from Reboulet et al. (2018). A selection of identified benthic foraminifera are illustrated in Fig. 10.

calcareous lithoclasts in a well-sorted sandy matrix. The matrix is composed of small angular quartz grains (around 50 μm) and includes small muscovite minerals and marine fossil debris (foraminifera, shells, green algae). Sigmoidally shaped pebbles present in this level contain a lagoonal facies rich in miliolids (F8 type). In the section at Tierwis, a succession of parasequences consists of rudist-rich carbonates followed by carbonates containing corals and stromatoporoids, which end with carbonates including nerineid accumulations. In the drill core of Morschach, an internal, confined microfacies containing oncoids (F10) and Bacinella nodules are dominant throughout the Upper Schrattenkalk Mb. The top surface of HST A1 is eroded and deeply karstified. The terminal karst shows its maximum thickness in the intermediate part of the platform. It reaches up to 26 m deep in the section at Harder, around 20 m deep in the sections at Valsloch, Morschach and L'Ecuelle (Fig. 19), and 15 m deep at Tierwis. The section at Rawil is affected by intense karstification in the form of a network of karstic caves, occluded by polyphase void filling to a depth of 90 m (Fig. 20). The oldest infills are sediments belonging to the Grünten Mb.

5.3. Interpretation of the panorama of the Churfirsten range The Churfirsten panorama represents the transition from the intermediate to the distal, south-eastward parts of the platform, in a section oblique to the direction of platform progradation. Several key observations made during the analysis of the geometries are summarized here. The indicated sequences and their respective systems tracts are part of the interpretation provided in Fig. 21–22 and S13–30. It should be noted here that a remarkably detailed geological interpretation of the panorama was already published by Heim (1910–1916). The progradation of the Schrattenkalk Fm above the Drusberg Mb is observed near the base of the panorama. The deposits below SB B3, identified in the section at Valsloch, are more calcareous on the western side, and change laterally to marl towards the eastern side (Fig. 8). The carbonate body belonging to the HST B2 shows eastward progradation, which extends to Schibenstoll. The SB B3 is associated with a jump in the progradation at the base of the calcareous cliff, between HST B2, which ends on the western side of the Schibenstoll, and the LST B3, which ends eastward, on the eastern side of Tristencholben (Figs. 21–22). The

Fig. 12. Photomicrographs illustrating the observed emersion features associated with sequence boundary SB3 between the Drusberg and Lower Schrattenkalk Mbs; (A) root molds in a wackestone of microfacies type F4; arrow shows an infilling with vadose silt (L'Ecuelle; EC 47); (B) early dissolution of cement (L'Ecuelle; EC 47); (C and D) paleofractures (Tierwis; TW 3); (E and F) truncation of grains by early dissolution (Morschach; MC 227); (G, I, and J) lithoclasts of various origin; (G: oolitic limestone; I: packstone with orbitolinidae; J: wackestone with spicules and calcispheres; all Morschach; MC 227); (H) meniscus cement (Morschach; MC 225); (K) lag deposit containing large ooids in a deeper-water matrix (Valsloch; VA 225); (L) root traces (Harder; HA 189); (M and N) Iron-coated grains reworked from a paleosol (Harder; HA 188).

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Fig. 13. Close-up on an annelid-rich interval associated with the TST of sequence B3 of the Lower Schrattenkalk Mb in the section at Valsloch.

LST B3 shows a maximum in eastward progradation along a distance of 2.5 km to Tristencholben (Figs. 21–22). We used the sections at Tierwis, Valsloch, and Alvier together with the interpretation of the panorama of the Churfirsten range to establish a chronostratigraphic transect through the intermediate and distal part of the platform (Fig. 23). 5.4. Carbon-isotope records 5.4.1. Validity of the carbon-isotope records Scatter plots of δ18O vs. δ13C values were used to assess the degree of alteration and diagenetic overprint on the isotope record of the studied samples (e.g., Choquette and James, 1987). For all studied localities, the covariance values are lower than 0.2 except for L'Ecuelle (0.62) and Interlaken (0.29; Fig. S31), suggesting that the primary carbonate carbon-isotope compositions were not too strongly affected by diagenetic modifications, except for those related to sequence boundaries and emersion horizons in general, and those of the sections at Kistenpass, Lämmerenplatten, and L'Ecuelle, which were affected by low-grade metamorphism (Frey et al., 1980; Burkhard, 1988), and show generally lowered δ13C values as a result (Fig. S31). The δ18O vs. δ13C scatter plots of selected samples on which microdrilling subsampling was performed (Fig. 24; Table 2) highlight variations between the different micro-drilled minerals and fossils, and the values obtained on powdered, whole-rock samples. Nevertheless, the values obtained for the micro-drilled micrite and whole-rock powders differ by not more than around 0.2‰ in most cases, which is in support of the reliability of the whole-rock δ13C record as an original signal. 5.4.2. Interpretation of the carbon-isotope records In the lower part of the sections (sequence B2), the δ13C values show two prominent excursions to higher values without any associated facies change (hemipelagic facies F0–F3). These two excursions are correlated with the excursions to higher values observed in the section at Angles (SE France; Godet et al., 2006), which occur in the upper lower Barremian (Kotetishvilia compressissima and Moutoniceras moutonianum zones; Fig. 9). The emersion phase associated with SB 3 in the proximal part of the platform is not reflected in the carbon isotope record. This may be best explained by the fact that the emerged substratum is composed of hemipelagic micritic facies, which was less altered during diagenesis because of compaction and the likely precipitation of marine cements, thereby reducing the porosity and hence rock-fluid ratios and the eventual presence of thermodynamically stable low magnesium calcite (Kroh and Nebelsick, 2010; Graziano and Raspini, 2018). In the Lower Schrattenkalk Mb, the δ13C record is highly influenced by the facies type present. The onset in deposition of lagoonal and associated sediments (F8–F10) is directly linked with excursions to higher

values. This is especially the case in the sections at Morschach and Valsloch, with amplitudes of +1.5‰ and +2‰, respectively. The same is also observed in the sections at Rawil, Justistal, and Tierwis, and to a lesser extent at L'Ecuelle. This trend is diachronous, depending of the position of the section relative to the platform. In proximal to inner intermediate sections it occurs in sequence B3 (HST B3; at Morschach, Tierwis, and L'Ecuelle), and higher up in intermediate sections (sequence B4 – HST B4 – at Valsloch; sequence B5 at Justistal). In proximal sections, the boundary between the Lower Schrattenkalk and the Rawil Mbs is characterized by minimal values (Fig. 25), which is likely related to the associated emersion phase. In contrast, the lower part of the Rawil Mb itself shows maximal values, which are associated with lagoonal facies. In distal sections, the boundary interval between the Lower Schrattenkalk Mb and the Rawil Mb is not marked by large shifts in δ13C, but the Rawil Mb shows an upwards trend towards lower values. This trend is also observed for the upper part of the Rawil Mb in proximal sections and may be related to the general, gradual shift towards a heterozoan association dominated by echinoderms. Up to three shorter-term excursions to lower values occur superimposed on this long-term trend, which mark the boundary of units A and B, near the boundary of units B and C (specifically in the sections at Tierwis and L'Ecuelle), and define or are close to the boundary between the Rawil and Upper Schrattenkalk Mbs, respectively (Fig. 25). The upper excursion to lower values is especially well defined in the more distal sections, where the basal interval of the Upper Schrattenkalk Mb coincides with the upper limb of the excursion. These excursions associate with emersion horizons. In proximal sections, the long-term trend to lower δ13C values continues well into the Upper Schrattenkalk Mb. In distal sections (Alvier and Brienzer Rothorn), the δ13C records seem less influenced by the compound-specific isotopic composition and post-depositional alteration. The exportation of aragonitic material from the shelf may, however, explain the higher values (maximum value +3.0‰) compared to the Vocontian record (Angles; Fig. 9). The overall trend in proximal sections correlates quite well with the δ13C records in the Angles and La Bédoule sections in SE France (Moullade et al., 1998; Renard et al., 2005; Wissler et al., 2003; Godet et al., 2006; Kuhnt et al., 2011; Stein et al., 2012b). Similar trends are also seen in the sections at Cluses (Huck et al., 2011, 2013), Balcon des Ecouges (Embry, 2005) and Gorges du Nant in the Vercors area (Bastide, 2014) (Fig. S32). These positive correlations confirm that changes in the global carbon cycle and its imprint on the δ13C record are also recorded on the Urgonian platform, as was already shown by Wissler et al. (2003), Embry (2005), Huck et al. (2011, 2013), and Stein et al. (2012a). Deviations from general trends in the δ13C record are related to the specificities of the Urgonian platform and its diagenetic history. In the following, we explore potential relationships between the trends and deviations therein and the mineralogical composition (aragonite versus calcite), primary porosity (e.g., in echinoderms), and the presence of emersion surfaces. In general, we observe high values in the often confined lagoons (see above), whereas the presence of oolitic and bioclastic facies (F5, F6) tends to lower δ13C values (e.g., TST B3 at Valsloch; sequences B2 to B4 at Justistal; sequences B3 to B5 at Harder). Excursions to higher δ13C values associated with the transition to lagoonal facies, and more general on and near carbonate platforms may be related to an increase in the accumulation and exportation of aragonitic components, as was proposed by Godet et al. (2006) and Föllmi et al. (2006, 2007), thereby following Swart and Eberli (2005). To estimate the initial content of aragonite in the deposits, a systematic quantification of components in thin sections was performed for the sections at Valsloch (Fig. S14) and Gorges du Nant in the Vercors area (Fig. S32). Components which were originally aragonitic include green algae (Scholle and Umer-Scholle, 2003; Flügel, 2004), which are partly preserved as fossil debris (e.g., dasycladales), and which may also have contributed

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Fig. 14. Photomicrographs illustrating the emersion phase associated with SB B4: (A) early dissolution cracks, filled in by micrite (Valsloch section; VA 139); (B) early dissolution, filled in by peloids (Valsloch section; VA 141); (C. and H) polyphased karst infilling (Tierwis section; TW 34); (D) amber meteoric cement (Tierwis section; TW 36); (E) pedogenic cement in rosette (Tierwis section; TW 35); (F and I) green marl associated with soil deposit (Tierwis and Morschach sections; TW 34 and MC 153); (G) dolomitic infilling of an early dissolution pocket (Tierwis section; TW 34); (J) root trace (Morschach section; MC 152); (K) epikarstic features (Morschach section; MC 152); (L) dolomite facies (Harder section; HA 251).

to the production of lagoonal micrite (Udoteacean algae; Lowenstam and Epstein, 1957; Neumann and Land, 1975; Milliman et al., 1993; Enríquez and Schubert, 2014). In our quantitative analysis, only the contribution of green algae in the form of preserved and recognizable fossils is considered. Aragonite is also important in rudists, where it is part of the inner shell and may represent an important proportion of the total exoskeleton, depending on the species (Steuber, 2002; Skelton and Gili, 2012) and in other mollusk groups such as gastropods, which are exclusively composed of aragonite (Bandel, 1990). A surprisingly good correspondence is seen between reconstructed aragonite contents and the δ13C record in the Gorges du Nant section, whereas the near absence of aragonite in the Valsloch section concurs with the trend to lower values in its δ13C record.

The intervals with the most negative values in the Valsloch section coincide with oolitic facies. Furthermore, the plateau of low values in the section at Valsloch corresponds to intervals highly enriched in echinoderms. This group is composed of high‑magnesium calcite, which is unstable under meteoric conditions (Kroh and Nebelsick, 2010). Echinoderms are also characterized by important porosity, with a range of 10–70% volume (Weber, 1969; Weber et al., 1969), which allows for the circulation of post-depositional fluids. These factors are likely involved in the generation of the observed trends towards lower values in this section. The facies-dependent isotope variations are shown in boxplots for each section in Fig. 26. For the sections at Valsloch, Morschach, and Rawil, the carbon isotope values are lower for the association of outershelf microfacies types (AF1–AF3) than of the AF4 (lagoonal facies). This

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Fig. 15. A Photos from the top of the Lower Schrattenkalk Mb and the overlying Rawil Mb at L'Ecuelle: (A) rudist shells showing early dissolution and infill by sandstone on the top surface of the Lower Schrattenkalk Mb (L'Ecuelle; EC 166); (B) network of Thalassinoides, infilled by yellowish sandstone on the top surface of the Lower Schrattenkalk Mb (L'Ecuelle; EC 166); (C) carbonate breccia contained in a laminated sandstone (L'Ecuelle; EC 172); (D) impregnations of dark sandstone at the base of the Rawil Mb (L'Ecuelle; EC 170); (E) hardground on top of unit B of the Rawil Mb, with bioeroded corals (orange lines) sealed by a reddish orbitolinid-rich sediment (L'Ecuelle; EC 197); (F) a bioeroded coral embedded in an orbitolinidrich carbonate (L'Ecuelle; EC 197); (G and H) accumulation of gastropods in a tempestite level terminating a cyclic parasequence of unit B in the Rawil Mb (Rawil, RW 37).

trend is less well expressed in the sections at Tierwis and Justistal, and is completely inversed in L'Ecuelle. Concerning the values of the AF5 (supratidal) and the AF6 (transgressive facies) associations, no clear trends are discerned, except for medians lower than those of the AF4, and a larger range of values, especially for the section at Tierwis. A further factor to be considered is the coincidence of excursions to lower values with the presence of evidence for emersion. This relation is observed both for the boundary interval between the Lower Schrattenkalk and Rawil Mbs in proximal sections, as well as for the excursions to lower values within the Rawil Mb (e.g., in the sections at

L'Ecuelle and Rawil) and near the base of the Upper Schrattenkalk Mb (e.g., in the sections at L'Ecuelle and Valsloch). It is clear, however, that not every emersion surface is associated with a δ13C excursion to lower values, and vice versa. 5.5. The evolution of the Helvetic shelf; tectonic processes and sea-level change In spite of its passive-margin configuration and the resulting tectonic stability (Trümpy, 1980), the northern Tethyan shelf underwent tectonic

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Fig. 16. Influence of sea-level fall associated with SB A1 on top of the Lower Schrattenkalk Mb in the section at Rawil. The stratigraphic log shows the levels of interest with numbers corresponding to the numbers of the photos and photomicrographs. At the sequence boundary (no. 1), evidence for emersion is given by terra rossa (T) deposits on the SB. The presence of karst (K) is indicated by caymanite (C) infilling, microbreccia, and vadose silt (levels 2 and 3, directly underneath SB A1). Level 4 shows the presence of lithoclasts with abundant (fresh-water) ostracods (FW-O) within a karst infill. Karst activity is recorded down to level 5, which corresponds to the maximum-flooding surface MFS B5. This interval contains a hemipelagic facies including calcispheres (Ca), radiolaria (R), and planktonic echinoderm (PE) remains, which shows small karstic fissures filled in with vadose silt. Photomicrographs are of sample RW 82 for (2) and (3), sample RW 89 for (4), and sample RW94 for (5).

readjustment during the Barremian-Aptian, which was related to rotation of the Iberian subcontinent, the continued opening of the Atlantic, and extension of the northern Tethyan Valais Basin (e.g., Arnaud, 1988; Olivet, 1996). As a consequence, subsidence rates were relatively high

in the Helvetic domain (Funk, 1985). Furthermore, pre-existing faults became reactivated during this time period, leading to tilting of block segments, as is observed on the platforms in Vercors, Gard, and southern Provence (Arnaud, 2005; Bastide, 2014). These tectonic rearrangements

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Fig. 17. Reconstructed history of the genesis of the sequence boundary on top of the Lower Schrattenkalk Mb (SB A1) within a single thin section from the section at Justistal (LB 16): (1) initial deposit composed of muddy supratidal facies (F11): top of the Lower Schrattenkalk Mb (HST B5); (2) sea-level fall associated with the SB A1: evidence of emersion marked by early dissolution of aragonitic organisms and void infilling by vadose silt; (3) pedogenesis and the formation of a paleosol; (4) superficial karst affecting sedimentary rocks in a depth of N16 m below this sample.

may have also created a complex topography on the Helvetic platform resulting in sudden changes in the thickness of stratigraphic sequences and their systems tracts. For instance, the sections at Morschach and Rawil include a succession of emersive levels overlain by deposits of deeper water facies. This may have been related to the presence of a paleotopographic high, where only the maximum transgression of each parasequence is recorded. Moreover, a complex karst system is present in the Rawil section, which is filled by caymanite-type deposits – i.e. void-filling, colored and banded dolomite precipitates - (Jones, 1992). This type of karstification affected the section N90 m deep (Fig. 20), and suggests recurrent subaerial exposure during and following deposition of the Schrattenkalk Fm. The absence of quartz in the karst infillings indicates that karstification occurred prior to deposition of the sand-rich Brisi

Mb of the Garschella Fm, as opposed to the section at L'Ecuelle, where fracture infills include sandstone of the Brisi Mb. Fig. 8 shows the spatial and temporal evolution of the Helvetic realm in a step-by-step, sequence-by-sequence fashion, from the latest Hauterivian to the early Aptian. Sequences H6 to B1 consist of the usually highly condensed Altmann Mb, which formed following the drowning of the heterozoan Kieselkalk platform (Bodin et al., 2006a). At Tierwis, a locally expanded section of around 30 m thickness is present, which is probably related to the presence of a normal fault (Bodin et al., 2006a). During the late early Barremian (essentially M. moutonianum zone), following this phase of widespread sedimentary condensation, a hemipelagic sedimentation regime was installed in the Helvetic realm. The maximum thickness of the resulting sequence B2 is observed

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Fig. 18. Synthetic log of the Rawil Mb and its equivalent in SE France – the Lower Orbitolina Beds -. The three units A–C are shown in light-, medium-, and dark green, respectively. Characteristic sedimentological and faunistic markers are listed for each unit (Arnaud-Vanneau, 1980; Raddadi, 2005).

at Alvier. A nearby listric paleofault may have locally enhanced subsidence (Trümpy, 1980). Intercalated tempestite calcarenites in the HST of sequence B2 (L'Ecuelle, Justistal, Harder, Valsloch, panorama of the Churfirsten) indicate the arrival of local platform carbonate factories, likely in a proximal position of the platform. This may have been the case in the region of the Lake of Thun, near Niedernhorn, where Schneeberger (1927) and Ziegler (1967) postulated the presence of a tectonically-induced shoal, which may have favored the early development of a carbonate platform in this area. Filling of accommodation space and seaward progradation of this shoal are illustrated by the decrease in thickness from sequences B3 to B5 at Justistal, whereas the same sequences become thicker at Harder. The infilling is also revealed by the installation of lagoonal facies in Justistal during deposition of sequence B5. Further platform shoals

may have developed during the late early Barremian, such as the one which produced the bioclastic deposits in sequence B2 at Valsloch and west of it, as observed in the panorama of the Churfirsten. SB B3 documents a phase of important sea-level fall, leading to emersion and soil formation on the inner part of the platform (Fig. 12). The emersion surface on top of hemipelagic facies of the Drusberg Mb illustrates a potentially important time lag. In intermediate domains, the presence of bioclastic beds containing reworked shallow-water grains suggests that shallow-water carbonate sedimentation occurred on the inner shelf. On the outer platform, hemipelagic deposition continued during this time. The transition between the inner platform and the external part of the shelf corresponds to ca. 40 km, as seen from the distance between the sections at Tierwis and Alvier. This suggests a peculiar paleotopography of the shelf, with a

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Fig. 19. Evidence of emersion on top of the Upper Schrattenkalk Mb (SB A2) in the section at L'Ecuelle. The photo with a red star illustrates the irregular contact between the Upper Schrattenkalk and the Brisi Mbs. The orange box shows the macroscopic aspects of the karstic pocket including blocks of the Grünten Mb. The blue stars indicate shallow-water carbonate facies of the Upper Schrattenkalk Mb. The green stars indicate the sandy facies of the Brisi Mb. The yellow stars indicate the heterozoan facies of the Grünten Mb, rich in flat orbitolinids. A: annelids; B: bryozoans; C: crinoids.

steeper slope dividing the platform from the outer shelf, which may have been triggered by synsedimentary faulting, as was proposed by Trümpy (1980) for the eastern part of Switzerland. He suggested the presence of a listric fault between the Säntis and Alvier sections, active until the early Barremian, leading to important variations in subsidence rates in different places of the Helvetic shelf during the Early Cretaceous in general. He related these observations to observed abrupt facies changes and assumed the presence of tilted blocks. Sequence B3 is characterized by a change in sedimentation pattern and the expansion of the shallow-water carbonate factory, which progressively covered the entire investigated area except for the two distal localities at Brienzer Rothorn and Alvier. The early late Barremian transgression flooded proximal, emerged areas, as is shown by the sections at L'Ecuelle, Tierwis, and Morschach. In a seaward direction, we note the presence of a LST composed of bioclastic deposits, which is especially well developed in the thick sections at Valsloch and Justistal. In the following, shallower sediments were deposited at the base of TST B3. Oolite accumulation preceded the arrival and establishment of corals and rudists in the inner and intermediate parts of the platform. During this period, the carbonate platform was characterized by a

maximum in progradation, as suggested by the presence of, reworked particles in the section at Alvier, which are attributed to sequence B3. Fig. 23 summarizes the temporal evolution of this platform along a proximal-to-distal transect, as preserved in the Säntis nappe. The period of low relative sea level documented in LST B3 is followed by a transgressive phase, which is associated with the landward development of onlaps and the deposition of shallow-water granular facies above the emersion surface. The highest accumulation rate is observed in the intermediate part of the platform. Deepening of the depositional environment through the whole shelf marked the maximum marine transgression phase. In inner and intermediate locations, the isolated and colonial annelids and flat orbitolinids present in this interval are characteristic of a mesotrophic environment. A phase of transgression during the early late Barremian is also indicated in the sea-level chart compiled by Haq (2014). The termination of sequence B3 is associated with a phase of sea level fall. The amplitude of the associated regression is estimated as large as at least 15 m. During deposition of the following sequence B4, the existing platform topography was filled in and leveled out. The areas characterized by important sediment accumulation during sequence B3 were covered

Fig. 20. Evidence of intense karstification related with SB A2 affecting an interval of up to 90 m below the top surface of the Upper Schrattenkalk Mb in the section at Rawil. The photomicrographs show different features of this major phase of emersion and karstification. Their numbers correspond to the numbers in the stratigraphic log. RW5: early dissolution of a nerineid gastropod, which is infilled by a vadose silt; RW7: karst with multiple infills; RW13: Early dissolution and infill by a vadose silt; RW14, RW24, and RW25: early fractures interrupted by karst infills; RW39, and RW44: root traces associated with soil formation; RW44: RW 59: Beachrock with pending cements; RW 64: karst with multiple infills; RW72: early dissolution of a nerineid gastropod, which is infilled by a vadose silt; RW 82: early dissolution of the aragonitic layer of a bivalve shell and karstic infill by caymanite; RW 82 (second photomicrograph) caymanite and polyphased karst infill.

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by thinner series composing sequence B4 (L'Ecuelle, Morschach, and Valsloch). Tierwis is an exception, because the series above sequence B3 is thicker. In the section at L'Ecuelle, the deposition of large oblique beds in the HST is likely due to synsedimentary slump folds. Justistal and Harder were probably located in a depression because of the abnormal thickness of B4, which is rich in oolitic accumulations possibly related to the presence of shoals. In the Alvier and Brienzer Rothorn sections on the outer shelf, sequence B4 still consists of hemipelagic deposits of the Drusberg Mb, which include reworked bioclastic grains (at Alvier). Sequences B5 and A1 indicates the presence of a subdued and uniform topography on the platform, as is suggested by the comparable thickness of all sections. The Rawil Mb (TST A1) is characterized by a generalized upward trend towards open-marine facies, illustrating deepening of the environment. All these observations and interpretations imply that the Helvetic realm evolved in two distinct phases: the first phase consisted of the recovery in sediment accumulation following a phase of drowning and sedimentary condensation (Altmann Mb). This phase witnessed the creation of topography during the deposition of sequences B2 and B3 and the shift from a platform ramp sensu Burchette and Wright (1992; cf., Bodin et al., 2006a) towards a flat-topped platform (“open platform”; Pomar et al., 2012), with the deposition of an aggradational bioclastic TST B3 (Pomar and Kendall, 2008) in the section at Valsloch. This is supported by the equivalent total thickness of the sequences and the similarity of facies distribution in the inner and intermediate parts of the platform. In the area of the platform slope, rapid facies changes suggest the presence of a distally steepened platform, as is, for example, indicated by the presence of calciturbidites in the upper part of the section at Brienzer Rothorn (Ribaux, 2012). The platform slope may have been accentuated by the activity of paleofaults and associated differential subsidence. The second phase comprises the further development of the Urgonian platform, during which its topography is leveled out (sequences B4, B5, and A1). The large amplitudes in sea-level change proposed by Haq (2014) for the early Aptian are intriguing. He suggested that in the time intervals corresponding to the formation of SB A1 and SB A2 were associated with major sea-level fall, with amplitudes of N75 m. This range of amplitudes cannot be confirmed on the Helvetic platform. In the section at Rawil, relative sea-level fall near the Barremian-Aptian boundary was at least 15 m, as indicated by the maximal depth of karstification and with that the base of the vadose zone. Sequence A1 ends also by a major emersion surface (SB A2), which is associated with karst on the whole platform. The comparable maximal depths of karst influence (between 15 and 26 m) through the inner and intermediate platform confirm the absence of major topography, and indicate an amplitude of sea-level fall of at least 30 m. The range of amplitudes identified here concurs well with those indentified in Russia and Oman for the late Early and early Late Cretaceous by Immenhauser (2005). According to Haq (2014), the regressions corresponding in time to SB A1 and SB A2 were followed by rapid transgressions. From our facies and microfacies analysis of Unit A at the base of the Rawil Mb, this cannot really be confirmed, as the change in facies is rather gradual. By contrast, sea-level rise following SB A2 was significant and a likely factor in the drowning of the Urgonian platform. The emersive surface is locally covered by a phosphatic hardground (Rohrbachstein Bed), which is overlain by heterozoan deposits of the Lower Grunten Mb (Linder et al., 2006; Föllmi and Gainon, 2008). 5.6. Phosphorus contents, platform facies, environmental and climate change The faunal and floral composition of sediments and records of detrital and phosphorus content are used here to infer trophic levels and their effects on the carbonate-producing ecosystems of the Helvetic platform.

Prior to the deposition of “Urgonian” facies, from the Valanginian onward, platform ecology was dominated by heterozoan assemblages, and its growth was repeatedly interrupted by extended phases of condensation, phosphogenesis, and platform demise (Kuhn, 1996; Föllmi et al., 2006, 2007; Godet et al., 2013). The Valangian-Barremian heterozoan assemblages are mainly composed of crinoids and bryozoans, and reflect an adaptation of the ecosystem to mesotrophic conditions and eventually also cooler waters (James and Clarke, 1997; Mutti and Hallock, 2003; Van de Schootbrugge et al., 2003). According to Kuhn (1996), Van de Schootbrugge et al. (2003), and Godet (2013), the condensation phases observed in the Helvetic realm were related to upwelling currents, which led to the repeated collapse of heterozoan carbonate-producing ecosystems. In addition, a general increase in phosphorus concentrations in the oceans during the Valanginian and Hauterivian may have favored the long-term presence of mesotrophic conditions on the Helvetic platform (Föllmi, 1995). The onset in the deposition of the condensed Altmann Mb is coarsely correlated with the Faraoni oceanic anoxic event recorded in different south and central European basins (Cecca et al., 1994; Bodin et al., 2006c). The Altmann Mb was deposited under mesotrophic to eutrophic conditions in a current-dominated depositional system, allowing condensation of the sediments and the formation of macroscopic phosphate deposits (Bodin et al., 2006a; Godet et al., 2013). On the central and western European continent, climate conditions during the late Hauterivian – early Barremian were postulated as warm and humid (Godet et al., 2008; cf. also O'Brien et al., 2017). The long-term negative gradient in phosphorus contents through the Drusberg Mb and Lower Schrattenkalk Mb suggests that nutrient levels were likely still enhanced during deposition of hemipelagic sediments of the Drusberg Mb (sequence B2), but decreased during shallowing and the appearance of the Urgonian platform. The Urgonian platform itself is characterized by the presence of a large lagoon, which was rimmed by oolitic shoals and small patch reefs. Its fauna is dominated by rudists, stromatoporoids, and corals, which represent a typical oligotrophic, photozoan association (Mutti and Hallock, 2003). The evolution of regional climate conditions during the Barremian is not as well defined as desired, and indications are present for warming (TEX86; O'Brien et al., 2017), more arid conditions (clay minerals, northwestern Europe; Ruffell et al., 2002), or more humid conditions (clay minerals, central Europe; Godet et al., 2008). The long-term decreasing trend in detrital and phosphorus contents, which lasted until the demise of the platform in the early Aptian, indicates that weathering rates lowered on the adjacent continents, enabling the installation and development of the Urgonian shallow-water carbonate platform. This long-term trend is punctuated by two shifts to higher phosphorus values, which occurred during the transgressions related with sequences B3 and A1. The resulting successions are associated with mixed photozoan – heterozoan assemblages. The first shift is associated with the MFS of sequence B3 (middle late Barremian) and was identified in corresponding successions in L'Ecuelle and Valsloch, where significant quantities of flat orbitolinids and colonial and isolated annelids are present. This assemblage is also known from the same sequence in the Vercors and Chartreuse area (Arnaud-Vanneau, 1980). Recent annelids prefer environments enriched in organic matter, which may be dysoxic (Martínez-Taberner et al., 1993; Fornós et al., 1997; Hfaiedh et al., 2013). The phosphatic and glauconitic Chopf Bed in the outer-shelf environment correlates in time to the MFS of B3 and embodies the macroscopic expression of the overall phosphorus enrichment during this transgressive time interval. The presence of the condensed phosphatic Chopf Bed and the ubiquity of annelids allow us to postulate that transgression related to sequence B3 led to higher trophic levels and a possible diminution in oxygen conditions on the carbonate platform. More specifically, deeper waters enriched in nutrients may have upwelled on the shelf and reached the platform, thereby affecting the carbonate factory. The transgression associated with TST B3 may have also induced the deposition of organic-rich sediments in the Lower Saxony Basin (Mutterlose et al., 2010), and may be related to a minor excursion

L. Bonvallet et al. / Sedimentary Geology 387 (2019) 18–56 Fig. 21. Overview of the panorama of the Churfirsten range including the section at Valsloch; Interpretation of the panorama in terms of sequence stratigraphy, lithology, and facies. The approximate distance between the summits of Schären and Tristencholben is 7 km. 47

48 L. Bonvallet et al. / Sedimentary Geology 387 (2019) 18–56 Fig. 22. (A) Central segment of the Churfirsten panorama including the section at Valsloch; (B and C) interpretation of the panorama in terms of sequence stratigraphy and lithology; (D and E) focus on the bioclastic carbonate body underneath the SB B3 (sequence B2). A jump in the degree of progradation between this body and the LST B3 is indicated by a black arrow. The approximate distance between the summits of Brisi and Tristencholben is 4 km.

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Fig. 23. Chronostratigraphic cross section based on the sections at Tierwis, Valsloch, and Alvier (all part of the Säntis Nappe). The section at Tierwis represents the internal part of the platform, Valsloch is located on the edge of the platform, and Alvier is in a distal, outer-shelf position. The length of the hiati shown in this transect are estimations, except for the one associated with SB B3 in the internal part, which length is based on bio- and sequence stratigraphy.

to higher values in the carbon-isotope record (Erba et al., 1999; Godet et al., 2006). The second shift to higher phosphorus values is associated with the Rawil Mb (e.g., sections at Tierwis and Valsloch), where the abundance of detrital material relative to the underlying and overlying members suggests that a mixed siliciclastic‑carbonate platform depositional system was installed. Based on clay mineral records and more particularly on the abundance of kaolinite, Stein et al. (2012a) proposed that a change towards warmer and more humid climate conditions triggered the increased input of nutrients and terrigenous materials (cf., O'Brien et al., 2017). The persistence of dasycladacean green algae, coral patch reefs, and rudists well into the lower part of the Rawil Mb suggests, however, that nutrient levels were not higher than mesotrophic (Mutti and Hallock, 2003). These organisms were joined by orbitolinids (Palorbitolina lenticularis), annelids, and the benthic foraminifer Choffatella, which were better adapted to mesotrophic conditions and became abundant and even dominant during deposition of the Rawil Mb. In its upper part, represented by the top of unit B and by unit C, light-independent fauna such as circalittoral foraminifera, echinoderms, and bryozoans became the most dominant groups, whereas corals, green algae, and rudists were greatly reduced. This progressive shift to a heterozoan association is explained by elevated nutrient levels and the effect of relative sea-level rise (Lees and Buller, 1972; Mutti and Hallock, 2003; Schlager, 2005). It shows that during this period the carbonateproducing ecosystem was able to adapt to changing paleoenvironmental conditions. The Rawil Mb is coeval with the deposition of laminated organic-rich deposits recorded in many basinal sections of the western Tethys and central Atlantic, such as at El Pui (Sanchez-Hernandez and Maurrasse, 2014) and Igaratza (Millán et al., 2009) in Spain, at Cassis-La Bédoule in southeastern France (Moullade et al., 1998; Stein et al., 2012b), and Cismon (Menegatti et al., 1998), Gorgo a Cerbara (Stein et al., 2011), and Capriolo (Föllmi et al., 2012) in Italy, and in the Lower Saxony Basin (Mutterlose et al., 2009). This interval was described as equivalent to the Taxy episode (Föllmi, 2012), and may have coincided with the onset of the Ontong Java LIP in the Pacific, according to Tejada et al. (2009).

The return of the Urgonian photozoan carbonate assemblage on the Helvetic platform took place during relative sea-level fall following the earliest Aptian transgression. The renewal of the oligotrophic fauna in the Upper Schrattenkalk Mb is likely due to a climate shift towards dryer conditions, which triggered a reduction in continental run-off (Stein et al., 2012a, 2012b). This is also indicated by the generally low values in phosphorus and detrital contents of the Upper Schrattenkalk Mb. The Upper Schrattenkalk platform shows maximum platform progradation, which coincided with the general development of Urgonian platforms around the Tethys, as is observed, e.g., in Italy (Amodio et al., 2013), central Iran (Wilmsen et al., 2013), Spain (Vilas et al., 1995), Oman (van Buchem et al., 2002), Serbia (Sudar et al., 2008), Hungary (Peybernès, 1979), Turkey (Masse et al., 2009), and Mexico (Barragan and Melinte, 2006; Skelton and Gili, 2012). In conclusion, the Urgonian platform developed during a prolonged phase of reduced detrital and nutrient input, which was preceded and followed by meso- to eutrophic phases associated with the oceanic anoxic Faraoni and Selli events in the latest Hauterivian and the middle early Aptian, respectively. Superimposed on this long-term trend were two further phases of enhanced nutrient input during the middle late Barremian and latest Barremian to earliest Aptian. In general, the late Barremian–early Aptian represents a period of optimal climate conditions for reef and carbonate platform growth, which allowed the development of large Urgonian-type platforms in tropical and subtropical environments not only in central Europe, but on a global scale. The Lower and the Upper Schrattenkalk Mbs are well comparable in terms of lithologies, facies, microfacies, and fossil associations (rudists, miliolids, etc.). The widespread twofold appearance of oligotrophic facies during the late Barremian and early Aptian is remarkable, especially if one considers the rather high density of anoxic episodes in nearby basins during this time interval (Föllmi et al., 2012). This underlines both the exceptional position of the Urgonian platform in the late Early Cretaceous, - in a time period which was otherwise characterized by meso- to eutrophic conditions, as well as the potential of the late Early Cretaceous environment to rapidly shift between oligo-, meso-,

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Fig. 24. δ18O - δ13C scatter plots of different micro-sampled carbonate components in eight selected samples. Numbers in parentheses behind each data point indicate the drilled microspots (cf., Table 2).

L. Bonvallet et al. / Sedimentary Geology 387 (2019) 18–56 Fig. 25. Correlation of the sequence stratigraphy and the carbon-isotope records from the Rawil Mb and its equivalents in southeastern and southern France with sections at Cluses, subalpine chains (after Wermeille, 1996; and Huck et al., 2013), Balcon des Ecouges, Bornes Massif (Raddadi, 2005; Embry, 2005), Gorges du Nant, Vercors massif (Raddadi, 2005; Bastide, 2014), and La Bédoule (Kuhnt et al., 1998, 2011; Stein et al., 2012b).

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Fig. 26. Box plots of carbon and oxygen-isotope values for all facies associations identified in the sections at Tierwis, Valsloch, Morschach, Justistal, Rawil, and L'Ecuelle.

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and eutrophic conditions as a consequence of increased volcanic activity, general climate change, and associated rapid sea-level change. The demise of the Urgonian Schrattenkalk platform near the boundary between the forbesi and deshayesi zones coincided with that of many other Urgonian platforms (Föllmi, 2008), such as the Apulian carbonate platform (Graziano, 2013) and the platform in the subalpine chains, eastern France (Huck et al., 2013). According to Huck et al. (2011), the time lag between the demise of the Urgonian platform and the onset of the Selli oceanic anoxic event is estimated at 300 kyr. This phase of important platform demise is associated with a change towards warmer and more humid conditions, associated with an increase in nutrient fluxes. 6. Conclusions The evolution of the Urgonian carbonate platform on the Helvetic shelf along the northern Tethyan margin was analysed for the time period between the latest Hauterivian and the early Aptian. The stratigraphic development in microfacies, biostratigraphy based on benthic foraminifera, δ13C records, phosphorus contents, and the identification of major emersion surfaces in twelve representative sections are used to propose a sequence-stratigraphic subdivision and a paleoenvironmental reconstruction. We observed the following important steps in the development of the Helvetic platform: ▪ The change from a sedimentary current-dominated, eutrophic regime, which started in the late Hauterivan and resulted in sedimentary condensation, and the formation of thin, glauconite and phosphate-rich deposits (Altmann Mb), to a phase of widespread hemipelagic sedimentation (Drusberg Mb) during the late early Barremian; ▪ The appearance of photozoan carbonate shoals, likely small and confined to local, tectonically induced highs during the late early Barremian; ▪ A regressive phase leading to emersion of the inner platform close to the boundary between the early and late Barremian; ▪ A transgression during the early late Barremian, allowing nutrientenriched deeper waters to upwell onto the platform and induce the appearance of a specialized ecosystem characterized by annelids and flat orbitolinids. A condensed phosphate- and glauconite-rich bed formed simultaneously on the outer shelf (Chopf Bed); ▪ The arrival of first typical Urgonian carbonates during the early late Barremian; ▪ The build up and out of an Urgonian platform (Lower Schrattenkalk Mb) during the late Barremian, whose morphology was progressively transformed from a platform ramp into a flat-topped and distally steepened platform, and whose evolution was interrupted by three periods of sea-level fall in the middle late Barremian, the latest Barremian and close to the Barremian-Aptian boundary; ▪ A prolonged transgressive phase near the onset of the Aptian, which was associated with increased detrital and nutrient input, and induced the progressive development of a mixed photozoanheterozoan carbonate-producing community (Rawil Mb); ▪ Recovery of the Urgonian platform (Upper Schrattenkalk Mb) during the early part of the early Aptian; and ▪ Emersion and demise of the Urgonian platform during the middle early Aptian, preceding the onset of the oceanic anoxic Selli episode.

In general, we observe that: ▪ The amplitudes of sea-level fall estimated by the depth of karst formation and as such of the vadose zone during the different emersion phases never exceed 30 m, which render them comparable to those measured in other tectonically stable regions (e.g., Immenhauser, 2005);

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▪ The overall long-term trends in the δ13C records are comparable along the NW Tethyan platform and correlate with those of the Vocontian Basin. Shorter-term deviations are related to the specificities of the mineralogy (aragonite versus calcite), the presence of ooids and echinoderms associated with diagenetic infill of pore space, and the presence of emersion surfaces; and ▪ The overall evolution of the Urgonian platform was not only related to sea-level change, but also paleoceanographic and paleoclimate conditions, which were responsible for low trophic levels and subdued detrital input.

Acknowledgements We are grateful to the Université de Lausanne and the Société Académique Vaudoise for their financial support. We also acknowledge the contribution of Laurent Nicod in the manufacturing of numerous thin sections. We furthermore thank the Tiefbauamt of Ct Schwyz and the CDS Ingenieure AG in Kriens for providing the Morschach core, which is stored at the Institute of Earth Sciences of the University of Lausanne. We also thank Hanspeter Funk (Baden) for providing a series of high-resolution airplane photos from the Churfirsten range. We highly appreciated the detailed and constructive reviews of Adrian Immenhauser, an anonymous reviewer, and the Editor-in-Chief Jasper Knight, which helped us to substantially improve the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.sedgeo.2019.04.005. References Adatte, T., Stinnesbeck, W., Keller, G., 1996. Lithostratigraphic and mineralogic correlations of near K/T boundary sediments in northeastern Mexico: implications for origin and nature of deposition. In: Ryder, G., Fastovsky, D., Gartner, S. (Eds.), The Cretaceous-Tertiary Event and Other Catastrophies in Earth history. Geological Society of America, Special Paper 207, Boulder, Colorado, pp. 211–266. Ager, D.V., 1981. The Nature of the Stratigraphical Record. John Wiley and Sons, New York. Amodio, S., Ferreri, V., D'Argenio, B., 2013. Cyclostratigraphic and chronostratigraphic correlations in the Barremian–Aptian shallow-marine carbonates of the centralsouthern Apennines (Italy). Cretaceous Research 44, 132–156. Arnaud, H., 1988. Subsidence in certain domains of southeastern France during the Ligurian Tethys opening and spreading stages. Bulletin de la Societe Geologique de France 8, 725–732. Arnaud, H., 2005. Sequence stratigraphy interpretation. In: Adatte, T., Arnaud-Vanneau, A., Arnaud, H., Blanc-Alétru, M.-C., Bodin, S., Carrio-Schaffhauser, E., Föllmi, K.B., Godet, A., Raddadi, M.C., Vermeulen, J. (Eds.), The Hauterivian-Lower Aptian sequence stratigraphy from Jura Platform to Vocontian Basin: a multidisciplinary approach. Géologie Alpine, Série Spéciale “Colloques et Excursions” 7, pp. 174–179. Arnaud, H., Arnaud-Vanneau, A., 1989. Séquence de dépôt et variations du niveau de la mer au Barrémien et à l'Aptien inférieur dans les massifs subalpins septentrionaux et le Jura (Sud-Est de la France). Bulletin de la Societe Geologique de France 5, 651–660. Arnaud, H., Arnaud-Vanneau, A., 1991. Les calcaires urgoniens des Massifs subalpins septentrionaux et du Jura (France): âge et discussion des données stratigraphiques. Géol. Alpine 67, 63–79. Arnaud, H., Arnaud-Vanneau, A., Blanc-Aletru, M.-C., Adatte, T., Argot, M., Delanoy, G., Thieuloy, J.-P., Vermeulen, J., Virgone, A., Virlouvet, B., Wermeille, S., 1998. Répartition Stratigraphique des Orbitolinidés de la Plate-forme Urgonienne Subalpine et Jurassienne (SE de la France). Géol. Alpine 74, 1–87. Arnaud, H., Arnaud-Vanneau, A., Bulot, L.G., Beck, C., MacSotay, O., Stephan, J.-F., Vivas, V., 2000. Le Crétacé inférieur du Venezuela oriental: stratigraphie séquentielle des carbonates sur la transversale Casanay-Maturin (Etats de Anzoátegui, Monagas et Sucre). Géol. Alpine 76, 3–81. Arnaud, H., Arnaud-Vanneau, A., Godet, A., Adatte, T., Massonnat, G., 2017. Barremian platform carbonates from the eastern Vercors Massif, France: organization of depositional geometries. Bulletin of the American Association of Petroleum Geologists 101, 485–493. Arnaud, H., Bulot, L., Arnaud-Vanneau, A., 1994. Stratigraphie Séquentielle de l'Aptien et de l'Albien sur la Transversal Pico Garcia–Casanay (Venezuela oriental). Rapport Aguasuelos Ingenieria, Caracas, Venezuela. Arnaud, H., Flood, P.G., Strasser, A., 1995. Resolution Guyot (Hole 866A, Mid-Pacific Mountains): Facies Evolution and Sequence Stratigraphy. In: Winterer, E.L., Firth, J.V., Sinton, J.M. (Eds.), Proceedings of the Ocean Drilling Project, Scientific Results, 143, College Station, TX, pp. 133–159.

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