Bed 1 (exposed approx. 15 m): dark grey, micaceous, silty, calcareous claystones in the uppermost part (cf. Wohlwend et al. 2019).

• Schmidberg Member [“Unit 1” sensuWohlwend et al. 2019 (“Sissach Member”) and “Unit 1-3k” sensuWohlwend et al. 2019 (“condensed temporal equivalent of the Hirnichopf Member”)].

Bed 2 (0.26 m): Echinodermal biosparite. The echinoderm debris identified is mainly skeletal elements of crinoids. Bivalves, including Oxytoma inaequivalvis (Sowerby, 1819) occur. The upper part of the bed is dark brown to greenish in colour and micritic.

Bed 3a (0.2 m): Rust-brown marl with numerous small, brown to rust-red, weathered components, containing iron ooids alongside chamosite ooids.

Bed 3b (0.05 m): Iron oolitic marl with intraclasts. Similar to bed 3a, but contains significantly larger intraclasts. With occasional ammonites.

Bed 4a (0.1 m): Dark grey micrite with biodetritus and iron ooids, often with rust-red intraclasts and burrows. Also undetermined bivalves.

Bed 4b (0.15–0.2 m): Grey-brown, somewhat clayey limestone with biodetritus and iron ooids. Bed 4b often contains ammonites. Bivalves are common.

Ammonites: Staufenia sehndensis (Hoffmann, 1913).

Bed 5 (1.2 m): Monotonous clay marl with limestone concretions at the base. The only fossils from bed 5 are two belemnite rostra of the genus Brevibelus.

Bed 6a (0.12–0.16 m): Micrite with iron ooids and scarce echinoderm remains.

Ammonites: Ludwigia sp.

Bed 6b (0.2–0.25 m): Weathered light brown, when fresh dark grey to greenish grey biodetritus and iron ooid-bearing limestone. The iron ooids are mostly arranged in clusters. Intraclasts encrusted with limonite, up to fist-sized, are also common. In addition to numerous ammonites, various bivalves occur such as Idonearca sp., Plagiostoma sp., Chlamys textoria (Schlotheim, 1820), Coelastarte sp., and Gryphaea (Bilobissa) sublobata (Deshayes, 1830). Of the approximately 80 Ludwigia, Brasilia and Ludwigella specimens recovered from bed 6a, we list only the more common and typical morphospecies in the following list:

Ammonites: Staufenia staufensis (Oppel, 1856), Brasilia platychora (Buckman, 1899), B. crinialis (Buckman, 1899), B. effricata Buckman, 1902, B. bradfordensis (Buckman, 1881), B. aff. baylii (Buckman, 1887), B. floccosa (Buckman, 1899), Ludwigia gradata Buckman, 1903, L. reflua (Buckman, 1899) [by matrix], Ludwigella cf. rudis (Buckman, 1899), Lu. rudis (Buckman, 1899) [by matrix], Accardia noszkyi (Géczy, 1966), Abbasites aff. abbas Buckman, 1921.

Bed 6cuu (0.08 m): Biodetritus-bearing, micritic limestone bed of varying thickness. Where it does not fill the entire stratigraphic interval, it is overlain by dark grey marl with echinoid spines and Caenocidaris clavata Hostettler et al., 2023.

Bed 6cu (0.22 m): Iron-oolitic limestone with burrows. Ammonites (18 Graphoceratidae) locally somewhat more common, alongside bivalves.

Ammonites: Brasilia platychora (Buckman, 1899), B. decipiens (Buckman, 1888), Ludwigia gradata (Buckman, 1903), Ludwigella cf. rudis (Buckman, 1899), Ceccaites megacanthum (Brasil, 1895) sensu Géczy, 1966.

Bed 6cm (0.1 m): micritic limestone with iron ooids. The ammonites (16 graphoceratids) mostly have a maximum diameter of approx. 7 cm. They show a strikingly narrow and high whorl-section and are mostly juvenile.

Ammonites: Brasilia effricata Buckman, 1902, B. aff. similis (Buckman, 1889), B. floccosa (Buckman, 1899, B. tutcheri (Buckman, 1904), Ludwigella rudis (Buckman, 1899).

Bed 6co (i) (0.22–0.26 m): Micrite with iron ooids and nodules, ammonites are common (approx. 80 graphoceratids).

Ammonites: Brasilia platychora (Buckman, 1899), B. aff. elmii (Géczy, 1967), B. austera (Buckman, 1923), B. maggsi (Buckman, 1899), B. platys (Buckman, 1925), B. aff. crinialis (Buckman, 1899), Ludwigia gradata (Buckman, 1903), Ludwigella rudis (Buckman, 1899), Lu. cf. rudis (Buckman, 1899), Pseudaptetoceras klimakomphalum (Vacek, 1886) [by matrix], Ceccaites aff. dorni (Rulleau, 2009), Abbasites aff. abbas Buckman, 1921.

Bed 6co (ii) (very locally developed in the top of layer 6co): Mudstone with iron ooids and nodules, the ammonites are overgrown with microbiol crusts and serpulids (Plate 11: fig. 1). A specimen of the terebratulid Gigantothyris cf. gigantea Seifert, 1963, comes from the same bed.

Ammonites: Brasilia decipiens (Buckman, 1888).

Bed 7a (0.03–0.06 m): Rust-red, iron-oolitic marl. Primary spines and a corona fragment of Caenocidaris clavata morphotype globosaHostettler et al. 2023 were found in this layer, as well as primary spine fragments of Polycidaris sp.

Bed 7b (0.04–0.08 m): Mudstone with dense iron ooids.

Ammonites from beds 7a and 7b: Graphoceras stigmosum Buckman, 1902, G. fallax (Buckman, 1888), G. aff. fallax (Buckman, 1888), G. limitatum Buckman, 1902, G. decorum Buckman, 1902, G. stigmosum Buckman, 1902, G. spp., Hyperlioceras cf. rudidiscites Buckman, 1902, Euaptetoceras amplectens (Buckman, 1889), Eudmetoceras eudmetum Buckman, 1920, Eud. masticonnensis Elmi, 1963.

Bed 8 (0.06 m): Iron-oolitic marl.

Ammonites: Graphoceras cf. concavum (Sowerby, 1815), G. sp., Euhoploceras marginatum (Buckman, 1892)

Bed 9 (0.12 m): Mudstone with iron ooids.

Ammonites: Hyperlioceras cf. rudidiscites Buckman, 1902, H. spp., Graphoceras formosum (Buckman, 1888), G. spp., Ludwigella arcitenens Buckman, 1904, Euaptetoceras euaptetum Buckman, 1922, Euap. amplectens (Buckman, 1889), Eudmetoceras eudmetum, Eud. masticonnensis, Haplopleuroceras mundum Buckman, 1892 [loose from beds 7–9].

Comments on beds 7–9: Sections in the western part of the clay pit (section West in Fig. 1) showed that the beds 7–9 wedge out laterally, but at the same time increase in thickness (up to 0.8 m) at other locations outside the clay pit (Wohlwend et al. 2019: 122).

• Frickberg-Member [unit 4T and unit 4K sensuWohlwend et al. 2019 (“Waldenburg to lower part of Brüggli members“)].

Bed 10u (0.3 m): Clay marl with few iron ooids.

Bed 10m (0.5 m): Clay marl with few iron ooids.

Bed 10o (0.12 m): Clay marl, micritic concretion layer at the base.

Ammonites from beds 10u, 10m and 10o: Hyperlioceras acuticarinatum (Dorn, 1935), H. sp., Graphoceras stigmosum Buckman, 1902, Euhoploceras marginatum (Buckman, 1892), E. sp.

Bed 11 (0.12–0.15 m): Fresh grey, weathered rust-brown, biodetrital limestone with small iron-ooids and burrows. At the base, a layer with Gryphaea (Bilobissa) sublobata (Deshayes, 1832). The ammonites within the bed possess their shells. The bottom part of the bed contains numerous fossils including columnalia of Cyclocrinus rugosus (d’Orbigny, 1841), Holcobelus blainvillei (Voltz, 1830), Parvamussium pumilum (Lamarck, 1819), Oxytoma inaequivalvis (Sowerby, 1819), Plicatula sp., unidentified rhynchonellids, and branched bryozoans.

Ammonites: Hyperlioceras liodiscites Buckman, 1902, H. deflexum Buckman, 1904, H. cf. deflexum Buckman, 1904, Euhoploceras cf. polyacanthum (Waagen, 1867), E. modestum (Buckman, 1892), E. marginatum (Buckman, 1892).

Bed 12 (0.18 m): Biodetrius-rich, brown, iron-oolitic marl with small iron ooids. Very poor in fossils.

Ammonites: Hyperlioceras discitiforme Buckman, 1902, H. liodiscites Buckman, 1902, H. subsectum (Buckman, 1905), H. cf. subsectum (Buckman, 1905), H. sp.

Bed 13 (0.08 m): Marly mudstone with iron ooids.

Bed 14 (approx. 0.12 m): Mudstone with few iron ooids.

Section II (Böttstein-Buechhalde, Fig. 2, section middle column) is located approximately 60 m east of section I. The section recorded by Wohlwend et al. (2019, fig. 39) is located between these two sections. Although the individual beds in section II are similar to those in section I, they differ considerably in detail, suggesting deposition conditions above the wave base in shallow water:

The beds 6a–9 are approximately 1.5 times thicker than in section I. In the lower part, there are two iron oolitic clay marl horizons, which are absent in section I.

In particular, beds 6ax and 6cuu are two new layers that are very rich in fossils and better developed than in section I. Bed 6ax is a brown, iron oolitic and clayey bed that is very rich in fossils. Numerous echinoid spines and some corona fragments were found therein, as well as belemnites, a few small ammonite shells, bryozoans, brachiopods, and calcareous sponges (see Hostettler et al. 2023).

Ammonites:

Bed 3b: Leioceras goetzendorfense (Dorn, 1935).

Bed 4b: Staufenia sehndensis (Hoffmann, 1913), Ludwigia obtusiformis (Buckman, 1899).

Bed 6b: Ludwigia gradata Buckman, 1903 [by matrix], L. cf. reflua (Buckman, 1899), Abbasites aff. abbas Buckman, 1921.

Bed 8: Shahrudites sp. [from the base].

Bed 9: Graphoceras decorum Buckman, 1902, G. arcitenens (Buckman, 1904).

The iron-oolitic clay marl package of beds 10u–10o shows approximately the same thickness as in section I. However, the nodule layer lies deeper here and is divided into three parts. The uppermost iron-oolitic bed is located in bed 14 in both sections.

Ammonites:

Bed 11: Hyperlioceras liodiscites Buckman, 1902, H. deflexum Buckman, 1904.

Bed 16 (base): H. acuticarinatum (Dorn, 1935).

The bed sequence is shown in Fig. 2, section middle column.

Ammonites [loose from beds 17–20]: Emileites sp., Witchellia sp., Sonninia cf. nenningensis Oechsle, 1958.

Section III (Fig. 2, section left column) differs from section I mainly in that bed 5 is significantly thinner. This bed is also iron-oolitic and, in addition to a few ammonites, it yielded a rich accompanying fauna comparable to that of layer 6ax in section II. However, the fossils in bed 5 of section III are smaller than those in bed 6ax of section II. Bed 5 can be divided into three sections (5a, 5b and 5c). Ammonites were found exclusively in bed 5c. Beds 6ax and 6cuu in section III are not only comparatively thick, but also very rich in fossils. Bed 6c ends at its top with a well-developed hardground.

Ammonites

Bed 5: Brasilia baylii (Buckman, 1887), Ludwigia aff. murchisonae (Sowerby, 1827).

Bed 6a: Brasilia ex gr. platychora (Buckman, 1899).

A comparison of all sections under investigation with the previously published section by Wohlwend et al. (2019) shows that the strongly iron-rich basal section of the Schmidberg clay pit near Böttstein is almost identical to the corresponding section in the Riniken borehole (see Fig. 4). This correlation of the basal section of the Passwang Formation confirms the regional occurrence of this specific facies in the eastern Aargau Jura. At the same time, however, section West also shows how quick the iron-oolitic facies can change into a sandy/calcareous-dominated facies. The latter corresponds more to the typical lithology found at the type locality of the Sissach Member (Burkhalter 1996) in the Grütsch section near Thürnen, southeast of Sissach. A sequence dominated by sandy limestones can also be observed on the eastern side of the Aare River at Acheberg and then along the Surb River from Döttingen to Tegerfelden (Wohlwend et al. 2019).

• Genus Leioceras Hyatt, 1867.

Bed 3b (Opalinum Zone, Bifidatum Subzone): Two ammonites fall within the variation of L. goetzendorfense (Dorn, 1935) (= L. ‘comptum’ auct.) (Plate 1: fig. 2). The third, extremely coarse-ribbed and unusually large ammonite (half a whorl is missing) belongs to L. uncinatum (Buckman, 1899) (Plate 1: fig. 1).

• Genera Ludwigia Bayle, 1878 and Brasilia Buckman, 1898.

Bed 4: (Murchisonae Zone, Obtusiformis Subzone): In contrast to the incomplete holotype, a large L. obtusiformis (Buckman, 1899) shows that the shell of this species can become smooth on the body-chamber (Plate 2: fig. 1). Another more incomplete specimen of this species (Plate 2: fig. 2) even loses most of its sculpture at the end of the phragmocone. Wohlwend et al. (2019, plate 11, fig. 2) have illustrated L. cf. depilata (Buckman, 1925) from this bed.

Bed 5 (Bradfordensis Zone, Bradfordensis Subzone): Brasilia baylii (Buckman, 1887) (Plate 3: figs 2–4) is the most common species. In addition, a single L. aff. murchisonae (Sowerby, 1827) (Plate 3: fig. 1) was found. Maubeuge (1955) named a Ludwigia with somewhat coarser ribs – although this could also be a microconch – after the site where it was found, Beznau, as Ludwigia betznauensis Maubeuge, 1955.

Beds 6a and 6b (Bradfordensis Zone, condensed Bradfordensis and Gigantea subzones): Relatively common large, smooth-shelled Brasilia of the B. platychora (Buckman, 1899) group (Plate 5: fig. 1, 4: fig. 1). B. effricata Buckman, 1902, B. bradfordensis (Buckman, 1881) (Plate 4: fig. 3) and B. aff. baylii (Buckman, 1887) (Plate 4: fig. 5), have a taller whorl section, are weakly ribbed and are smaller at maturity. The small-sized B. floccosa (Buckman, 1899) (Plate 6: fig. 3) and B. crinialis (Buckman, 1899) (Plate 4: fig. 2) have an even narrower whorl section. The species L. gradata (Buckman, 1903) (Plate 4: fig. 4) and L. reflua (Buckman, 1899) still belong to the genus Ludwigia. In addition, the microconchiate Ludwigella rudis (Buckman, 1899) (Plate 5: fig. 2) occurs.

Beds 6cu to 6co (ii) (Bradfordensis Zone, Gigantea Subzone): As in beds 6a and 6b, large Brasilia with a medium wide umbilicus and smooth shells of the Brasilia platychora (Buckman, 1899) group (Plates 7: fig. 1, 10: fig. 2) and B. effricata Buckman, 1902 (Plate 8: fig. 3) are characteristic. Similar ammonites with a smaller umbilicus belong to B. decipiens (Buckman, 1888) (Plates 7: fig. 4, 11: fig. 1) and B. platys (Buckman, 1925). The species B. aff. similis (Buckman, 1889) (Plate 8: fig. 7), B. aff. elmii (Géczy, 1967), B. tutcheri (Buckman, 1904) (Plate 8: fig. 1), B. floccosa (Buckman, 1899) (Plate 8: fig. 2), B. austera (Buckman, 1923) (Plate 10: fig. 3), B. maggsi (Buckman, 1899) and B. crinialis (Buckman, 1899) (Plate 10: fig. 4) possess a smaller whorl-section. In addition, there are ammonites with a relatively broad, more subquadratic whorl-section, which we still assign to Ludwigia (L. reflua (Buckman, 1899) and L. gradata (Buckman, 1903) (Plate 7: fig. 3). The corresponding microconchs can be identified as Ludwigella rudis (Buckman, 1899) (Plate 8: fig. 6a, b) and Lu. cf. rudis (Buckman, 1899) (Plate 8: fig. 4), respectively.

• Genera Graphoceras Buckman, 1898 and Hyperlioceras Buckman, 1889.

At Böttstein, graphoceratids occur in the amplectens Biohorizon (Concavum Zone, Formosum Subzone; bed 7) and in the early Discites Zone. G. fallax (Buckman, 1888) (Plate 13: fig. 2) and G. aff. fallax (Buckman, 1888) are characterised by their coarse ribbing and wide umbilicus. G. formosum (Buckman, 1888) (Plate 14: fig. 1), on the other hand, has a slightly denser ribbing. Two ammonites with a fairly narrow umbilicus belong to the densely ribbed G. decorum Buckman, 1902 (Plates 13: fig. 4, 14: fig. 2). G. limitatum Buckman, 1902 differs from the similar morphospecies G. stigmosum Buckman, 1902 (Plates 13: fig. 3, 16: fig. 3) in its finer ribbing. A poorly preserved specimen belongs to G. cf. concavum (Sowerby, 1815). Furthermore, a specimen of the presumed microconchiate species Ludwigella arcitenens Buckman, 1904 was found (Plate 14: fig. 3).

Hyperlioceras occurs at Böttstein in the amplectens Biohorizon of the Concavum Zone and in the Discites Zone. As the youngest branch of the phyletic lineage of Graphoceratidae, they are primarily characterised by their distinct and striking keel. Buckman (1887–1907) also created an impenetrable taxonomic jungle for these forms by establishing numerous genera and species. The identification of our Hyperlioceras material is further complicated by the fact that the specimens are mostly more or less compressed, making it difficult to reconstruct the original whorl-sections and the sculptures. The species H. desori (Moesch, 1867), often cited from Switzerland, type species Ammonites desori Moesch, 1867 [from Frickberg near Frick, N Switzerland], is a junior homonym of Ammonites [= Hoplites or Busnardoites] desori Pictet & Campiche, 1860, and therefore invalid. Few specimens belong to the very flat, oxyconic species H. acuticarinatum (Dorn, 1935) (Plates 16: fig. 2, 18: fig. 4), which is characterised by its highly acute-angled whorl-section and barely offset shoulders. There exist single examples of H. discitiforme Buckman, 1902 (Plate 18: fig. 3) and H. deflexum Buckman, 1904 (Plate 17: fig. 1). The flat discoidal species H. liodiscites Buckman, 1902 (Plates 17: fig. 2, 18: fig. 1) was found at Böttstein exclusively in the Discites Zone. H. cf. rudidiscites Buckman, 1902 (Plates 13: fig. 1, 14: fig. 5) has a high-oval whorl-section, whereas H. subsectum (Buckman, 1905) and H. cf. subsectum (Buckman, 1905) (Plate 18: fig. 2) have a high triangular whorl-section with an overhanging umbilical edge and a concave umbilical band. An extremely large Hyperlioceras sp. (Plate 14: fig. 4) is labelled with bed ‘9’. We assume that this labelling was a mistake and that this specimen originates from higher beds for two reasons: firstly, specimens of the genus Hyperlioceras with this morphology (extremely large, final diameter probably around 30 cm, high-oval whorl-section with barely pronounced shoulders) are only known from the younger Discites Zone in southern England. Secondly, although this ammonite has an iron-oolitic matrix, it is grey rather than reddish to brownish like the matrix of the other specimens from this level. The specimen differs from all nominal species of the genus in its exceptionally flat umbilical edge and an exceptionally wide umbilicus. We therefore keep its species affiliation open for the time being.

• Genus Staufenia Pompeckj, 1906.

The genus Staufenia is represented by S. sehndensis (Hoffmann, 1913) (Plate 1: figs 3, 4) from the Obtusiformis Subzone (Murchisonae Zone) and some rather large specimens (Plate 6: fig. 2) of S. staufensis (Oppel, 1856) (Plate 6: fig. 1) from bed 6b (Bradfordensis Zone, condensed Bradfordensis/Gigantea subzones). The specimens from the Obtusiformis Subzone resemble ammonites from Chideock Hill (Dorset) and Gosheim (Southwestern Germany) identified as S. sehndensis by Chandler et al. (2023) and Dietze et al. (2025), respectively. The species S. staufensis (Oppel, 1856) has been described in detail by Hoffmann (1913), Rieber (1963) and Dietze et al. (2017).

The systematics of ammonites of the family Hammatoceratidae are controversially discussed in the literature (see, for example, Rulleau 2009; Kovács 2009; Howarth 2013).

We were able to recover representatives of this family at Böttstein from beds of the Bradfordensis Zone: a single specimen of Pseudaptetoceras klimakomphalum (Vacek, 1886) (Plate 9: fig. 4) clearly shows the characteristic flexuous ribbing of this species. The species Accardia noszkyi (Géczy, 1966) (Plate 5: fig. 3) was found relatively frequently. We assign a single example with shorter, more distinctive primary ribs and slightly curved ribs to Ceccaites megacanthum (Brasil) sensu Géczy (1966, plate 17, fig. 2) (Plate 7: fig. 2). Ceccaites aff. dorni (Rulleau, 2009) (Plate 8: fig. 5) fits well with C. dorni (Rulleau, 2009) [HT: Hammatoceras sieboldi Opp. in Dorn 1935, plate 1, fig. 2], except for the slightly stronger flexuous ribbing and the stronger spinose inner whorls.

The Concavum Zone at Böttstein contains representatives of the genera Eudmetoceras Buckman, 1920, Euaptetoceras Buckman, 1922 and the microconchiate genus ?Shahrudites Seyed-Emami, 2006. The species Euaptetoceras amplectens (Buckman, 1889) (Plates 12: figs 1, 3, 15: figs 1, 4) is extremely common in beds 7–9. In view of its rounded venter, we assign the species amplectens to the genus Euaptetoceras (type species: Euap. euaptetum Buckman, 1922) and not to the closely related genus Pseudaptetoceras Géczy, 1966 (type species: Harpoceras klimakomphalum Vacek, 1886). The rare species Euap. euaptetum Buckman, 1922 (Plate 15: fig. 5) differs from Euap. amplectens (Buckman, 1889) in its significantly larger umbilical width. Somewhat rarer, but still relatively common, are hammato­ceratids from the more evolute group of Eudmetoceras eudmetum Buckman, 1920 (Plates 12: fig. 4, 15: fig. 2). Coarsely ribbed inner whorls with shovel-like nodes at the dividing point of the ribs are attributed to the closely related species Eud. masticonnensis Elmi, 1963 (Plates 12: fig. 2a, b, 15: fig. 3). We tentatively assign two microconchiate Hammatoceratidae from the Concavum Zone to the genus Shahrudites Seyed-Emami, 2006. The two nominal species of this genus, Sh. asseretoi Seyed-Emami, 2006 and Sh. stoecklini Seyed-Emami, 2006, differ from ?Shahrudites sp. (Plate 13: figs 5, 6) in that their inner whorls are nodose, unlike our examples. Chandler (2022, figs 3h1–4) has illustrated an ammonite from the older ‘Scissum Zone’ [= Bifidatum Subzone, Opalinum Subzone] of Mapperton, which is very similar to our specimens, as Sh. asseretoi.

Remarkably, we have no records of Hammatoceratidae from the Discites Zone.

Dietze et al. (2013, figs 3a, b, 4f–k) described one ammonite each of the species Abbasites aff. abbas Buckman, 1921 and A. gardincola (de Gregorio, 1886) from layer 6 at Böttstein. A recently found specimen (Plate 10: fig. 1a–c) from layer 6co can also be identified as A. aff. abbas.

An ammonite of the species Haplopleuroceras mundum Buckman, 1892 (Plate 13: fig. 7) from the Formosum Subzone (Concavum Zone, Aalenian) represents the rare record of the genus Haplopleuroceras in the Swiss Jura. An ammonite belonging to Ha. subspinatum (Buckman, 1881) comes from the Moutier area (Dietze and Hostettler 2023, fig. 4A, B). Yin and Chandler (2016) have illustrated numerous Haplopleuroceras spp. from southern England and Tibet and demonstrated that this genus occurs typically at the Concavum/Discites zonal transition.

Sandoval and Chandler (2000) revised the early sonniniids [genus Euhoploceras Buckman, 1913] of the Upper Aalenian and the lowermost Bajocian based on extensive collections from SW England and S Spain. They selected three macroconchiate morphospecies within the variation spectrum of the early representatives of the sonniniids and assigned the remaining species of Buckman (cf. Buckman 1887–1907, who had listed a total of 69 species) to either E. acanthodes (Buckman, 1889), E. marginatum (Buckman, 1892) or E. modestum (Buckman, 1892) We follow principally this approach here. Recently, however, Chandler (2020) has departed from this concept and, when describing the rich sonniniid fauna from the lowermost Bajocian of Mapperton (Beaminster, Dorset), has reverted to Buckman’s numerous morpho­species, but assigned these each to one of the Sonninia [Euhoploceras] acanthodes, S. [E.]. marginata and S. [E.] modesta ‘morpho-groups’.

A small fragment of E. marginatum (Buckman, 1892) (Plate 13: fig. 8) originates from the Concavum Zone (amplectens Biohorizon). Further specimens of E. marginatum (Plates 16: fig. 4, 17: fig. 4) originate from the Discites Zone, as do all other specimens of sonniniids from Böttstein. The species E. modestum (Buckman, 1892) is barely sculptured and therefore easily recognisable. A very large and well-preserved specimen (Plate 17: fig. 3) is similar to E. polyacanthum with its coarse ribbing and long-lasting nodules, but differs from this species in its radial ribbing, which is why we refer to it as E. aff. polyacanthum (Waagen, 1867).

The single record of Sonninia cf. nenningensis Oechsle, 1958 (Plate 18: fig. 8) comes from the Trigonalis Subzone of the Laeviuscula Zone.

Two ex-situ found Witchellia sp. (Plate 18: fig. 6) and Witchellia jugifera (Waagen, 1867) (Plate 18: fig. 7) represent this subfamily.

Obtusiformis Subzone

We place bed 4 in the Obtusiformis Subzone of the Murchi­sonae Zone, which is proposed here for the first time for the Swiss Jura, in view of the highly comparable Staufenia ammonites from S England (Chandler et al. 2023) and from the W Swabian Alb in SW Germany (Dietze et al. 2025). In view of the limited number of ammonites found, we refrain from assigning bed 4 to the pustulifera or sehndensis biohorizons within the Murchisonae Zone (Hostettler and Koppka 2013; Wohlwend et al. 2019; Chandler et al. 2023; Dietze et al. 2025).

Bradfordensis Subzone

Bed 5 with Brasilia baylii and Ludwigia aff. murchisonae is to be placed in the Bradfordensis Subzone (Chandler 1997; Contini et al. 1997).

Condensed Bradfordensis / Gigantea subzones

Bed 6b contains with Staufenia staufensis and the “Artengruppe” [species-group] of Brasilia bradfordensis, typical ammonites of the younger Bradfordensis Subzone (Rieber 1963; Chandler 1997; Contini et al. 1997; Dietze et al. 2017). However, in terms of relative abundance, these two species occur significantly less frequently in bed 6b at Böttstein than in the beds of the Bradfordensis Subzone of SW Germany (Rieber 1963; Dietze et al. 2017). In contrast, bed 6b at Böttstein contains numerous ammonites that are more typical of the Gigantea Subzone (cf. Chandler 1997), such as B. platychora, B. effricata, B. decipiens, B. aff. similis, B. tutcheri, B. floccosa, B. maggsi, B. aff. crinialis, only some of which are reported from isolated occurrences in SW Germany (Rieber 1963; Dietze et al. 2017 [with only one ammonite identified as B. planata from the species group B. platychora - B. effricata, no evidence of small, extremely slender Brasilia species such as B. crinialis, B. tutcheri, etc.]). We therefore assume that bed 6b at Böttstein contains a condensed ammonite fauna from the Bradfordensis and Gigantea subzones of the Bradfordensis Zone.

This observation is consistent with the interpretation of the palynological data (Wohlwend et al. 2019).

Only two ammonites (Ludwigia sp. and Brasilia ex gr. platychora) were found in bed 6a, which also suggests a Bradfordensis/Gigantea subzone condensation in this bed.

Gigantea Subzone

We place beds 6cu, 6cm and 6co in the Gigantea Subzone for the following reasons: the genus Staufenia, which extends in SW Germany to the uppermost Bradfordensis Subzone but not to the Gigantea Subzone (Dietze et al. 2014, 2017, 2022a), has disappeared. Ammonites of the Brasilia bradfordensis group occur; in contrast to the occurrence of the staufensis Biohorizon of SW Germany (Rieber 1963; Dietze et al. 2017), the ammonite assemblage of beds 6cu to 6co as a whole is more similar to that of the southern German geisingensis and falcifera biohorizons (Gigantea Subzone). In this stratigraphical interval, as in the oldest biohorizon (Brasilia gigantea Biohorizon) of the Gigantea Subzone in S England (Chandler 1997), ammonites of the species grouped around B. platychora - B. effricata clearly dominate, alongside small, slender Brasilia around the species B. tutcheri and B. crinialis. In addition, the youngest biohorizon (Brasilia bradfordensis, similis Biohorizon) of the Bradfordensis Subzone in southern England (Chandler 1997) is dominated by ammonites of the B. bradfordensis - B. baylii group, which are sculptured on the flanks, in contrast to the ammonites from beds 6cu to 6co. However, the large ammonites of the species grouped around B. gigantea are absent at Böttstein. B. decipiens even occurs rarely in bed 6co, which indicates that beds 6cu to 6co are slightly condensed, but only within the timespan of the Gigantea Subzone. In one of the sporadic, small-sized lenses at the very top of bed 6 (bed 6co (ii)), only Brasilia decipiens has been found so far. Such large, flat, discoidal, unsculptured ammonites with a narrow umbilicus are characteristic for the (younger) Gigantea Subzone (Chandler 1997; Dietze et al. 2014).

The Concavum Subzone has not yet been documented at Böttstein.

Formosum Subzone

• amplectens Biohorizon

Beds 7–9 are characterised by the abundance of Euaptetoceras amplectens, Eudmetoceras ex gr. eudmetum-masticonnensis and graphoceratids. The genera Euhoploceras and Hyperlioceras are only accessory faunal elements. Strata with such ammonite associations are placed in the latest Aalenian (amplectens Biohorizon of the Formosum Subzone (Concavum Zone)) (Contini et al. 1997; Wohlwend et al. 2019). We also assign the beds 7–9 to the amplectens Biohorizon and thus still in the Aalenian.

Obtusiformis Subzone

N Switzerland: The numerous brief descriptions presented by Lieb from the 1950s are unhelpful for establishing a correlation, since his ammonite zonation cannot be interpreted with certainty. Bed 4 at Böttstein is biostratigraphically intermediate between Fauna 5 (faunal horizon sinon – opalinoides) and Fauna 6 (faunal horizon discoidea) sensuChrist (1999). Burkhalter (1996) documented a sehndensis horizon at Moretchopf in the central Swiss Jura. In the eastern Tabular and Folded Jura, Wohlwend et al. (2019) reported a sehndensis horizon in the Cheisacher section. An excellently preserved and very rich ammonite fauna of the sehndensis horizon was found near Cornol (Sous les Roches) (Hostettler and Koppka 2013). Whether these stratigraphic intervals designated as the sehndensis horizon correspond to bed 4 at Böttstein or are slightly younger cannot be decided with certainty at present.

In SW Germany, the strata relevant for correlation with bed 4 of Böttstein have now been placed in the pustuli­fera Biohorizon of the Obtusiformis Subzone (Dietze et al. 2025). In view of the few ammonites from bed 4, it must currently remain open whether this bed corresponds exactly to the pustulifera Biohorizon.

Bradfordensis and Gigantea subzones

N Switzerland: The numerous descriptions and ammonite determinations by Lieb from the 1950s cannot be interpreted with certainty, which is why they are not taken into account herein. Christ (1995, 2001) has identified a Gigantea Subzone for the Swiss Jura above the Staufensis Subzone and below the Concavum Subzone. On the other hand, the same author (Christ 1999) introduced a Bradfordensis Subzone above the Staufensis Subzone and retained a ‘(?-Gigantea)’ subzone above the former only with reservations. His fauna 11 (‘gigantea - similis’) could correspond to beds 6cu to 6co at Böttstein. However, this cannot be verified, since his ammonites were not illustrated. Interpretable information is only provided by Wohlwend et al. (2019). According to that, strata of the Bradfordensis Subzone occur in the Unterer Hauenstein, Wasserflue and Frickberg outcrops.

In the Swabian Alb (SW Germany), the beds of the Bradfordensis and Gigantea subzones are easily separable from one another (Rieber 1963; Dietze et al. 2014, 2017, 2022a, 2022b). Locally, however, both subzones may be condensed in the upper part of the Staufensis Bed near Achdorf (Wutach area). An exact correlation of beds 6cu to 6co with the biohorizons of the Swabian Alb (cf. Dietze et al. 2022a) is not possible. In any case, the ammonites of this stratigraphic interval at Böttstein roughly correspond to the geisingensis and falcifera biohorizons. The lenticular bed 6co (ii) can be roughly correlated with the decipiformis Biohorizon of Geisingen (Dietze et al. 2014).

Strata and ammonites of the amplectens horizon are repeatedly reported in the literature on N Switzerland at various locations from Cornol in the canton Jura in the west (Lieb 1953; Hostettler and Koppka 2013) to the Aare valley (Böttstein; this study). Lieb (1951) wrote that the ‘Concava zone’, including Eudmetoceras amplectens, Euaptetoceras infernense and Euap. euaptetum, occurs throughout the northern Swiss Jura mountains. In his description of the Aargau Table Jura west of the Aare River, Lieb (1954) distinguished an ‘Eutmetoceras zone’ [recte], which can only be distinguished from the Concava zone in Sespen. A little later, Lieb (1957) renamed this the ‘Eudmetoceras-Discites zone’ with evidence from Ghei (Wegenstetten), Sespen and Lägern. In contrast to the strata that characterize the top of the uppermost Concavum zone, this zone contained not only Eudmetoceras and Graphoceras, but also Hyperlioceras, although no Sonninia were found. Maubeuge (1955) described museum's material from the amplectens horizon of N Switzerland. Ammonites of the amplectens horizon have been recorded in numerous local and institutional collections from outcrops in the Moutier area (Cantons Bern and Jura). The stratigraphic situation at Moutier was recently described by Dietze and Hostettler (2023). The formosum/limitatum horizon of Christ (1999) rarely yields Euaptetoceras amplectens and Eudmetoceras eudmetum and lacks Hyperlioceras, and is therefore likely to be slightly older than the amplectens Biohorizon. Wohlwend et al. (2019) also described outcrops with layers of the amplectens Biohorizon in the eastern Folded and Tabular Jura. In addition, an Euaptetoceras amplectens was described from the borehole Schlattingen-1 in the western part of the canton Thurgau (Wohlwend et al. 2024).

In the Wutach area (SW Germany), there occurs a biohorizon within the basal Discites Zone containing numerous ammonites of the genus Euaptetoceras (Bayer 1969a; Dietze et al. 2026). It differs from the amplectens Biohorizon by the dominance of ammonites of the genus Hyperlioceras, whereas in the amplectens Biohorizon the genus Graphoceras dominates. Further investigations are needed to clarify, whether the beds containing Euaptetoceras at Ringsheim (Gassmann and Mattes 1984; Bosch 2006) and Lörrach-Stetten (Hoffmann 1966) in the Upper Rhine Graben, at Geisingen (Dietze et al. 2014) and at Metzingen in the central Swabian Alb (Bayer 1969a) should be assigned to the Aalenian or already to the Bajocian. Super-regionally, the amplectens Biohorizon, which was first used for strata in southern Alaska (Hall and Westermann 1980), offers an almost worldwide correlation potential for the Aalenian/Bajocian boundary (cf. the evidence in Hoffmann 1966; Westermann 1992 and Contini et al. 1997).

A detailed correlation of beds 10–16 with other sites in Switzerland is impossible, since previous publications did not specify the exact level at which the ammonites were found. However, the Discites Zone has been frequently reported throughout N Switzerland, from the canton Jura to the Aare River (cf. Burkhalter 1996; Wohlwend et al. 2019; Wohlwend et al. 2024).

In SW Germany, the Discites Zone is very well documented from Ringsheim in the Upper Rhine Graben (Gassmann and Mattes 1984; Bosch 2006), but stratigraphic studies at the level of biohorizons are still lacking. Bayer (1969b) has studied in detail the interval of the Discites Zone near Achdorf in the Wutach area. Bed 10 probably corresponds to either layer I or layer II of the Sowerbyi-Oolith near Achdorf. Beds 11 and 12 at Böttstein correlate roughly with layers III and IV of the Sowerbyi-Oolith there. The published data from the Swabian Alb (Quenstedt 1887; Rieber 1963) and from Franconia (Dorn 1935) are insufficient for a correlation below the zonal level.

In view of the scarce and ex-situ examples from Böttstein, we refrain from any correlation with outcrops in neighbouring areas.